Soil mechanics laboratory manual
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  • 1. SOIL MECHANICSLABORATORY MANUAL
  • 2. 14/06/2005 Soil mechanics laboratory manual 2IntroductionMost of the test procedures collected in this manual were specially prepared for the geotechnicallaboratory of DGM in Thimphu, BhutanThe test procedures are based on BS standards and some ASTM standards. However, in various casesthe test procedure was adapted to the type of equipment available in the laboratory. This means thatoften a realistic compromise had to be found between strict requirements and practical possibilities.Warning: Whenever tests have to be performed following a prescribed standard, always consultthat standard before testing.Version February 2004W. VerwaalReferencesHead, K.H. (1982): Manual of Soil Laboratory Testing. Vol. 1, Pentech Press, London, Plymouth.Head, K.H. (1982): Manual of Soil Laboratory Testing. Vol. 2, Pentech press. London, Plymouth.Bowels J.E. (1978): Engineering properties of soils and their measure mends, second edition. McGraw- Hill books company.Whitlow, R. (1983): Basic soil mechanics, Construction Press, London and New York.Annual Book of ASTM Standards, volume 04.08 : Soil and Rock (I) Published by ASTM in 2000BS 5930:1999 British Standard InstitutionBS 1377:1990 British Standard Institution, part 1-8Some Internet pages.. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 3. 14/06/2005 Soil mechanics laboratory manual 3CONTENTS1.1 CLASSIFICATION OF SOIL BS 5930:1999 SECTION 6 ........................................................................ 42.1 SIMPLE DRY SIEVING BS 1377: PART 2:1990. .................................................................................. 102.2 WET SIEVING - FINE SOILS BS1377: PART 2:1990. ......................................................................... 142.3 HYDROMETER TEST BS 1377: PART 2:1990 ..................................................................................... 18THE ATTERBERG LIMITS ............................................................................................................................ 233.1 LIQUID LIMIT WITH CASAGRANDE CUP. BS 1377: PART 2:1990 AND ASTM, 1995. D4318 ... 243.2 LIQUID LIMIT USING THE CONE PENETROMETER BS 1377: PART 2:1990 .............................. 273.3 PLASTIC LIMIT BS 1377: PART 2:1990................................................................................................ 304.1 DENSITY BS 1377: PART 2:1990 ............................................................................................................ 324.2 NATURAL MOISTURE CONTENT BS 1377:PART 2,1990 ................................................................ 345.1 PARTICLE DENSITY BS 1377: PART 2 1990 ....................................................................................... 355.1 VANE TEST BS 1377: PART 7 1990........................................................................................................ 385.2 TRIAXIAL TEST BS 1377: PART 8 1990 ............................................................................................... 405.3 DIRECT SHEAR TEST BS 1377: PART 7 1990 ..................................................................................... 466.1 CONSOLIDATION TEST BS 1377: PART 5: 1990................................................................................ 517.1 PROCTOR TEST BS 1377: PART 4: 1990.............................................................................................. 567.2 CALIFORNIAN BEARING RATIO TEST BS 1377: PART 4:1990..................................................... 61PERMEABILITY TESTS.................................................................................................................................. 668.1 CONSTANT HEAD TEST BS 1377: PART 5: 1990 ............................................................................... 678.2 FALLING HEAD PERMEABILITY TESTS. ........................................................................................... 739.1 POCKET PENETROMETER, HEAVY DUTY PENETROMETER ..................................................... 759.2 HAND VANE TESTER PILCON ............................................................................................................... 76 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 4. 14/06/2005 Soil mechanics laboratory manual 41.1 Laboratory classification of soil BS 5930:1999 section 6IntroductionIt is necessary to provide a classification of types of soil for the purpose of describing the variousmaterials encountered in site exploration. The system needs to be comprehensive, while still beingreasonable, systematic and concise.There are many different classification systems. The system we will use is the British soil classificationwith some adding’s from the ISO 14688.ProcedureThis classification can be separated in different parts.First there is a preliminary classification to determine whether the soil was laid down by naturalprocesses No MADE GROUND Yes NATURAL SOILNext: Does the natural soil comprise organic materials, have it organic odour? Yes ORGANIC SOIL.Next: Is the soil of low density? Yes VOLCANIC SOILNext: Remove all cobbles and boulders (>63mm). Do they weight more than the rest of the soil? Yes: are most particles >200mm? Yes BOULDERS No COBBELS No: Does the soil stick together when wet: No: are most particles >2mm Yes GRAVEL No SAND Yes: Does soil: Display low plasticity, Dilatancy, silky touch, Disintegrate in water and Dry quickly Yes SILT No CLAYClassification in practiceThe primary classification of natural soil can be done by a wet sieving procedure on a 63 µm sieve ifmore then 35% of the material is passing you are dealing with a fine grained soil if less than 35 % of thesample is passing you are dealing with a course grained soil.During the second part of the classification you have to determine the complete grading curve forcoarse-grained soil and the Atterberg limits for fine-grained soils, (determined on the part smaller than425µm).The 35% boundary between fine and course is approximate. Due to engineering behaviour it’ssometimes necessary to determine de plasticity of soil with a fine-course boundary below 35% fines.Classification of fine grained soils (soils that stick together when wet)Since the plasticity of fine-grained soils has an important effect on such engineering properties asstrength and compressibility, plastic consistency is used as a basis for their classification. Theconsistency of a soil is its physical state characteristic at given moisture content. Four consistency statesmay be defined for cohesive soils: solid, semi-plastic solid, plastic and liquid. The change in volume ofa saturated cohesive soil is approximately proportional to a change in moisture content; the generalrelationship is shown in fig. 1.1.2 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 5. 14/06/2005 Soil mechanics laboratory manual 5Fig 1.1.2 Consistency relationships.The transition from one state to the next in fact is gradual; however, it is convenient to define arbitrarylimits corresponding to a change over moisture content:LL = the liquid limit: the moisture content at which the soil ceases to be liquid and becomes plastic.PL = the plastic limit: the moisture content at which the soil ceases to be plastic and becomes a semi-plasticSL = the shrinkage limit: the moisture content at which drying-shrinkage at constant stress ceases.The two most important of these are the liquid and plastic limits, which represent respectively the upperand lower bounds of the plastic state; the range of the plastic state is given by their difference, and istermed the plasticity index (PI).PI = LL-PLThis value is reported to the nearest whole number. If it is not possible to perform the plastic limit test,the soil is reported as nonplastic (NP). This also applies if the plastic limit is equal to or greater than theliquid limit. Which can occur in some soils with high mica content.The relationship between the plasticity index and the liquid limit is used in the British SoilClassification System to establish the subgroups of fine-grained soil; fig. 1.1.3 shows the plasticitychart used for this purpose. The A-line provides an arbitrary division between silts and clays, andvertical divisions (of percentage liquid limit) define five degrees of plasticity:C = clay M = Silt for organic soil add O to symbolFig 1.1.3 Plasticity chart for classification of fine soils. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 6. 14/06/2005 Soil mechanics laboratory manual 6Low plasticity: LL <35%Intermediate plasticity: LL = 35% - 50%High plasticity: LL = 50% - 70%Very high plasticity: LL = 70% - 90%Extremely high plasticity: LL> 90%A given soil may be located in its correct sub-group zone by plotting a point, having co-ordinates givenby the soils plasticity index and liquid limit.The sub-group symbols are given in Table 1.1.4Fine-grained soils F = FINES L = low plasticity (undifferentiated) I = intermediate plasticity M = SILT H = high plasticity C = CLAY V = very high plasticity E = extremely high plasticityOrganic soils Pt = peat O = organicTable 1.1.4 sub-group symbols in British Soil Classification system.The liquid limit is determined with the cone penetrometer method (part 3.2 of this handbook).or withthe Cassagrande cup (part 3.1 of this handbook). The plastic limit is determined with the "rolling"method (part 3.3 of this handbook).Classification of coarse grained soilsFor the classification of coarse-grained soils it is necessary to make a particle-size analysis.Figure 1.1.5 shows the British Standard range of particle sizes.Determining the weight percentages falling within bands of size represented carries out the particle sizeanalysis of a soil by these divisions and sub-divisions. It can be done by dry sieving (part 2.1 of thishandbook), or by wet sieving (part 2.2 of this handbook).Fine grained Coarse grainedClay Silt Sand Gravel StoneColloids Fine Medium Coarse Fine Medium Coarse Fine Medium Coarse Cobbles Boulder 1 6 20 200 600 6 20 200 2 60 2 60 µm mmFig 1.1.5 British Standard range of particle sizes Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 7. 14/06/2005 Soil mechanics laboratory manual 7The grading curve is a graphical representation of the particle-size distribution and is therefore useful initself as a means of describing the soil. From the grading curve we can provide a descriptive term forthe type of soil (SOIL NAME).BOULDERS-COBBELS Main name Estimated boulder or cobble content of very course fractionOver 50% of material is very BOULDERS Over 50% is of boulder sizecourse (>60mm) (> 200mm) COBBLES Over 50% is of cobble size (200 mm to 60 mm)Mixtures of boulders or cobbles and finer materialTerm CompositionBOULDERS (or COBBLES) with a little finer material up to 5% finer materialBOULDERS (or COBBLES) with some finer material 5% to 20% finer materialBOULDERS (or COBBLES) with much finer material 20% to 50% finer materialFINER MATERIAL with many boulders (or cobbles) 50% to 20% boulders (or cobbles)FINER MATERIAL with some boulders (or cobbles) 20% to 5% boulders (or cobbles)FINER MATERIAL with occasional boulders (or cobbles) up to 5% boulders (or cobbles)The description of the finer material (FINER MATERIAL) is made accordance the standardSAND and GRAVELTerm Principal soil type Approximate proportion of secondary constitutionSlightly sandy or gravelly SAND up to 5%Sandy or gravely Or 5% to 20%Very sandy or gravelly GRAVEL over 20% SAND and GRAVEL about equal proportionsMixtures of sand and/or gravel with silt or clayTerm Principal soil Approximate proportion of secondary constitution type Coarse soil Coarse and/or fine soilSlightly clayey or silty and/or SAND >5%sandy or gravelly And/orClayey or silty and/or sandy 5% to 20%Aor gravelly GRAVELVery clayey or silty and/or >20% Asandy or gravellyVery sandy or gravelly >65%BSandy and/or gravelly 35% to 65%Slightly sandy and/or gravelly <35%A or described as fine soil depending on assessed engineering behaviour.B or described as coarse soil depending on assessed engineering behaviour Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 8. 14/06/2005 Soil mechanics laboratory manual 8A further quantitative analysis of grading curves may be carried out using certain geometric valuesknown as grading characteristics. First of all, three points are located on the grading curve to give thefollowing characteristic sizes (fig. 1.1.7):Fig 1.1.7 Grading characteristic.D1 0 = maximum size of the smallest 10% of the sampleD30 = maximum size of the smallest 30% of the sampleD60 = maximum size of the smallest 60% of the sampleFrom these characteristic sizes, the following grading characteristics are defined:Effective size, d10 D 60Uniformity coefficient, Cu = D10 (D 30 )2Coefficient of gradation (curvature) Cc = D60 * D10Cu < 3 indicate a uniform soil.Cu > 5 indicate a well-graded soil.Most well graded soils will have grading curves that are mainly flat or slightly concave, giving valuesof Cc between 0.5 and 2.0.Cc <0.1 indicate a possible gap-graded soil. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 9. 14/06/2005 Soil mechanics laboratory manual 9Fig 1.1.6 typical particle size distribution curvesBS description systemA recommended protocol for describing a soil deposit uses nine characteristics; these should be writtenin the following order:compactnesse.g. loose, dense, slightly cementedbedding structuree.g. homogeneous or stratified; dip, orientationdiscontinuitiesspacing of beds, joints, fissuresweathered statedegree of weatheringcolourmain body colour, mottlinggrading or consistencye.g. well-graded, poorly-graded; soft, firm, hardSOIL NAMEe.g. GRAVEL, SAND, SILT, CLAY; (upper case letters) plus silty-, gravelly-, with-fines, etc. asappropriatesoil class(BSCS) designation (for roads & airfields) e.g. SW = well-graded sandgeological stratigraphic name(when known) e.g. London clayNot all characteristics are necessarily applicable in every case.Example:(i) Loose homogeneous reddish-yellow poorly-graded medium SAND (SP), Flood plain alluvium(ii) Dense fissured unweathered greyish-blue firm CLAY. Oxford clay. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 10. 14/06/2005 Soil mechanics laboratory manual 102.1 Simple dry sieving BS 1377: Part 2:1990.Scope of the testDry sieving is the simplest of all methods of particle size analysis. According to the British Standarddry sieving may be carried out only on materials for which this procedure gives the same results as thewet sieving procedure. This means that it is applicable only to clean granular materials, which usuallyimplies clean sandy or gravely soils that is, soils containing negligible amounts of particles of silt orclay size. If in doubt about the validity of the dry-sieving method, the wet-sieving procedure should befollowed instead.If particles of medium gravel size or larger are present in significant amounts, the initial size of thesample required may be such that riffling is necessary at some stage to reduce the sample to amanageable size for fine sieving. The procedure is then referred to as "composite sieving".Sample preparationThe specimen to be used for the test is obtained from the original sample by riffling, or by subdivisionusing the cone-and-quarter method. The appropriate minimum quantity of material depends upon themaximum size of particles present, and is indicated in Table 2.2-1- The specimen is placed on a tray and is allowed to dry, preferably overnight, in an oven maintained at 105-110 °C.- After drying to constant weight, the whole specimen is allowed to cool, and is weighted to an accuracy within 0.1% or less of its total mass (M1). Maximum size of material Minimum mass of sample present in substantial proportion to be taken for sieving retained on BS sieve (mm) Pass 2 mm or smaller 100g 6.3 200g 10 500g 14 1kg 20 2kg 28 6kg 37.5 15kg 50 35kg 63 50kg 75 70kg 100 150kg 150 500kg 200 1000kgTable 2.1-1 Minimum quantities for particle size test. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 11. 14/06/2005 Soil mechanics laboratory manual 11Execution of the testSelection of sieves.The complete range of sieves specified by the British Standard is given in Table 2.1-2 It is notnecessary to use all sieves for every test, but the sieves used should adequately cover the range ofaperture sizes for each particular soil. For classification purposes we can use a short set.The sieves to be used are selected to suit the size of sample and type of material.Sieve frames must not be out of true, and should fit snugly one inside the other, to prevent escape ofdust. Sieves are nested together with the largest aperture sieve at the top, and a receiving pan under thesmallest aperture sieve at the bottom. Aperture size Standard Short full set set set Suitable sieve diametersConstruction A B C 450mm 300mm 200mmPerforated 75 mm + +Steel plated 63 + + +(Square holes) 50 + 37.5 + + + 28 + + 20 + + + + 14 + 10 + + 6.3 + + + 5 +Woven wire 3.35 + + + 2 + + (+) + + 1.18 + + 600 µm + + (+) + + 425 + 300 + + 212 + + 150 + + 63 + + (+) + +Lid and receiver + + + 19 sieves 13 sieves 7 sievesTable 2.1-2 metric sievesTest procedure- The dried soil sample is placed in the topmost sieve and is shaken long enough that all particles smaller than each aperture size can pass through. This can be achieved most conveniently by using a mechanical sieve shaker.- The whole nest of sieves with receiving pan is placed in the shaker, the dried soil is placed in the top sieve, which is then fitted with the lid, and the sieves are securely fastened down in the machine.- Agitation in the shaker should be for a minimum period of 10 min. Some shakers have a built-in timing device which can be pre-set to switch off the motor automatically after the desired period.- The maximum mass of sample, which can be sieved in one cycle, is depending on the used sieves and the particle size of the sample. See table 2.1-3.- Weighing, The material retained on each sieve is transferred to a weighed container. Any particles lodged in the apertures of the sieve should be carefully removed with a sieve brush, the sieve being first placed upside-down on a tray or a clean sheet of paper. These particles are added to those retained on the sieve. Weighing of each size fraction should be to an accuracy of at least 0.1% of the total initial test sample mass. The masses retained (Ms1, Ms2, etc.) are recorded against the sieve Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 12. 14/06/2005 Soil mechanics laboratory manual 12 aperture size on the particle size test work sheet. The mass (Mp) passing the 63µmm sieve is also measured and recorded. Maximum mass 450mm 300 mm 200 mmSieve diameter sieves diameter sieves diameter sievesAperture (kg) (kg) (g)50 mm 10 4.537.5 8 3.528 6 2.520 4 2.014 3 1.510 2 1.0 6.3 1.5 0.75 5 1.0 0.5 3.35 300 2 200 1.18 100600µm 75425 75300 50212 50150 40 63 25Table 2.1-3 maximum mass to be retained on each test sieve at the completion of sieving.CalculationsThe mass retained on the first sieve is denoted as Ms1.The mass passing the first sieve = M1- Ms1. The percentage passing the first sieve is given by M1 − Ms1 P1 = ∗ 100 % M1The mass passing the second sieve = M1 – Ms1 – Ms2. The percentage passing the second sieve is givenby M 1 − (Ms1 + Ms 2 ) P2 = ∗ 100 % M1And so on.The percentage passing any subsequent sieve can be written as M1 − ∑ M P= ∗ 100 % M1Where ∑M denotes the sum of the masses retained on all sieves down to and including the one inquestion: ∑M = Ms1+Ms2+Ms3+ etc.The calculated mass passing the last sieve should be equal, or very nearly equal, to the mass collected inthe receiving pan. If this is denoted by Mp, the percentage of fines, Pp passing the last sieve is Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 13. 14/06/2005 Soil mechanics laboratory manual 13 Mp Pp = * 100 % M1ReportingIn addition to the particle size curve and the usual sample identification data, the sheet should includethe visual description of the sample. This should be the description of the sample before testing, andmodified as necessary as a result of the additional information revealed by the test result. Any materialremoved before sieving, such as vegetation or an isolated cobble, should be reported.Tabulated data showing the percentage each sieve are sometimes required instead of, or in addition to,the grading curve.The method of test is reported as dry sieving in accordance with BS 1377:1975, Test 7(B). Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 14. 14/06/2005 Soil mechanics laboratory manual 142.2 Wet sieving - fine soils BS1377: Part 2:1990.Scope of the testIf a soil contains silt or clay, or both, even in small quantities, it is necessary to carry out a wet sievingprocedure in order to measure the proportion of fine material present. Even when dry, fine particles ofsilt and clay can adhere to sand-size particles and cannot be separated by dry sieving, even if prolonged.Washing is the only practicable means of ensuring complete separation of fines for a reliableassessment of their percentage. If clay is present, or if there is evidence of particles sticking together,the material should be immersed in a dispersant solution before washing. The dried representativesample is spread out on a tray and covered with water containing 2g/litre of sodiumhexametaphosphate. The soil is allowed to stand for at least an hour, and is stirred frequently. Thisdisperses the clay fraction, so that clay and silt will not adhere to larger particles.The procedure is described in detail below for non-cohesive soils containing little or no gravel.Sample Preparation- The specimen to be used for the test is obtained from the original sample by rifling, or by subdivision using the cone-and-quarter method. The appropriate minimum quantity of material depends upon the maximum size of particles present, and is indicated in Table 2.2.1 Page.- The specimen is placed on a tray and is allowed to dry, preferably overnight, in an oven maintained at 105-110 °C After drying to constant weight, the whole specimen is allowed to cool, and is weighted to an accuracy within 0.1% or less of its total mass (M1).Execution of the test- Selection of sieves.The complete range of sieves specified by the British Standard is given in Table 2.2.2It is not necessary to use all sieves for every test, but the sieves used should adequately cover the rangeof aperture sizes for each particular soil. For classification purposes we can use a short set. Maximum size of material Minimum mass of sample present in substantial proportion to be taken for sieving retained on BS sieve (mm) Pass 2 mm or smaller 100g 6.3 200g 10 500g 14 1kg 20 2kg 28 6kg 37.5 15kg 50 35kg 63 50kg 75 70kg 100 150kg 150 500kg 200 1000kgTable 2.2-1 Minimum quantities for particle size test. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 15. 14/06/2005 Soil mechanics laboratory manual 15 Aperture size Standard Short full set set set Suitable sieve diametersConstruction A B C 450mm 300mm 200mmPerforated 75 mm + +Steel plated 63 + + +(square holes) 50 + 37.5 + + + 28 + + 20 + + + + 14 + 10 + + 6.3 + + + 5 +Woven wire 3.35 + + + 2 + + (+) + + 1.18 + + 600 µm + + (+) + + 425 + 300 + + 212 + + 150 + + 63 + + (+) + +lid and receiver + + + + + 19 sieves 13 sieves 7 sievesTable 2.2-2 metrics sieves- Sieving coarse materialThe sample is sieved on a large-diameter 20 mm sieve, with a portion being taken at a time, so as not tooverload the sieve (see Table 2.2-3 ). Particles retained are brushed to remove finer material which maybe adhering to them, but individual particles must not be broken down. The material retained on the 20mm sieve, after drying, if necessary, is then sieved on appropriate larger aperture sieves and the amountretained on each is weighed.The fraction passing the 20 mm sieve, including "brushings" from larger particles, is then oven driedand weighed (M2). If M2 is much more then 2 kg the sample is subdivided to give a convenient mass M3for the remainder of the sieving operation.- Wash.The 2 mm sieve is nested in the 63mm sieve, but the lid and receiver are not used. An additionalintermediate sieve may be included to protect the 2mm and 63mm sieve from overloading if the soilcontains a high proportion of coarse or medium sand.The soil is placed a little at a time on the 2 mm sieve, and washed over a sink with a jet or spray ofclean water. The silt and clay passing the 63 mm sieve is allowed to run to waste. When the material onthe 2 mm sieve has been washed free of fines, washing on the 63mm sieve is continued until thewastewater is seen to run clear.During this operation the sieve must not be allowed to become overloaded with soil or to overflow withwater. The mass of soil retained on the 63mm should not exceed 150 g at any one time. Table 2.2-3gives the recommended maximum quantities that may be retained on each sieve. If this is likely to beexceeded, the material should be sieved in two or more portions.Warning: The sink used for this operation should be fitted with a silt trap. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 16. 14/06/2005 Soil mechanics laboratory manual 16 Maximum mass 450mm 300 mm 200 mm diameter diameter diameterSieve sieves sieves sievesAperture (kg) (kg) (g)50 mm 10 4.537.5 8 3.528 6 2.520 4 2.014 3 1.510 2 1.0 6.3 1.5 0.75 5 1.0 0.5 3.35 300 2 200 1.18 100600µm 75425 75300 50212 50150 40 63 25Table 2.2-3 maximum mass to be retained on each test sieve at the completion of sieving.- Drying The whole of the material retained on each sieve is allowed to drain, and is carefully transferred to trays or evaporating dishes. These are placed in an oven to dry at 105-110 °C, preferably overnight.- Weighing After cooling, the whole of the dried material is put together and weighed to an accuracy of 0.1% (M4).- Sieving The dry soil is passed through a nest of the complete range of sieves to cover the sizes of particles present, down to the 6.3 mm sieve. This operation may be carried out by hand or preferably on a sieve shaker, exactly as in the dry sieving procedure. Weigh the amount retained on each sieve to 0.1 % of its total mass. If the fraction passing the 6.3 mm sieve is small, i.e. not more than 150 g, the sample may be sieved by dry sieving on the appropriate sieves down to and including the 63 µm test sieve. Weigh the amounts retained on each sieve, and any fines passing the 63 µm test sieve (Mf), to 0.1 % of its total mass. If the fraction passing the 6.3 mm sieve is large i.e. substantially greater than 150 g, it should be accurately weighed (M5 ) and then subdivided to give a sample of 100-150 g. Weigh this fraction (M6 ) and then sieve on the appropriate sieves down to and including the 63 µm test sieve. Weigh the amounts retained on each sieve, and any fines passing the 63 µm test sieve, (Me) If riffling is not necessary, (M6 ) is the same as (M5 ).- Weighing The portion retained on each sieve is weighed, each to an accuracy of 0.1%. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 17. 14/06/2005 Soil mechanics laboratory manual 17Calculations- Calculation for the particles larger than 20mm in size, calculate the proportion by mass of material retained on each of the coarse series of sieves as a percentage of M1For example: ⎧ M (28mm) ⎫ Percentage retained on 28 mm sieve = ⎨ ⎬100 ⎩ M1 ⎭- Calculate the corrected mass of material retained on each of the sieves between 20 mm and 6.3 mm M2 by multiplying by , then calculate this mass as a percentage of M1 M3For example: ⎛ M 2 ⎞⎛ 100 ⎞ Percentage retained on 10 mm sieve = M(10 mm) ⎜ ⎜ ⎟⎜ ⎟⎜ ⎟ ⎟ ⎝ M 3 ⎠⎝ M1 ⎠- Calculate the corrected mass of material retained on each of the sieves finer than the 6.3 mm sieve ⎛ M5 ⎞⎛ M 2 ⎞ by multiplying by ⎜ ⎜ ⎟⎜ ⎟⎜ M ⎟ , then calculate this mass as a percentage of M1 ⎟ ⎝ M6 ⎠⎝ 3 ⎠For example: ⎛ M 5 ⎞⎛ M 2 ⎞⎛ 100 ⎞ Percentage retained on 300 µm sieve = M(300 µm) ⎜ ⎜ ⎟⎜ ⎟⎜ ⎟⎜ M ⎟ ⎟ ⎝ M 6 ⎟⎜ M 3 ⎠⎝ ⎠⎝ 1 ⎠- Calculate the cumulatieve percentage by mass of the sample passing each of the sieves from the general relationship: (% passing this sieve) = (% passing previous sieve)-(% retained on this sieve)Calculate the fraction passing the 63 µm test sieve by difference. The mass of fines lost by washing isequal to (M3-M4). To this is added the mass of any fine material (Mf) passing the 63 µm test sieve whendry sieved. ⎪ (M 3 − M 4 ) + M f ⎧ ⎫⎛ M 2 ⎞ Percentage passing 63 µm sieve = ⎨ ⎬⎜ ⎜ ⎟ 100 ⎟ ⎪ ⎩ M3 ⎭⎝ M 1 ⎠ReportingIn addition to the particle size curve and the usual sample identification data, the sheet should includethe visual description of the sample. This should be the description of the sample before testing, andmodified as necessary as a result of the additional information revealed by the test result. Any materialremoved before sieving, such as vegetation or an isolated cobble, should be reported.Tabulated data showing the percentage each sieve are sometimes required instead of, or in addition to,the grading curve. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 18. 14/06/2005 Soil mechanics laboratory manual 182.3 Hydrometer test BS 1377: part 2:1990Scope of the testThe hydrometer analysis is a widely used method to obtain the distribution of particle sizes in the siltrange (63-2 µm), and the percentage of clay minerals < 2µm. The test is usually not performed if lessthan 10% of the material passes the 63 µm sieve.The hydrometer analysis utilises the relationship among the velocity of fall of spheres in a fluid, thediameter of the sphere, the specific weights of the sphere and of the fluid, and of the viscosity of thefluid as expressed by the Stokes’ law.NOTE:The hydrometer is a very fragile device; it should be handled with care. Never hold it horizontal whileholding it on one side, the bulb is very heavy and the glass could break. Hold it on the bulb whenmoving it horizontal. When moving it in and out of a cylinder, keep it as straight as possible; a smallangle could break it.Apparatus used− soil hydrometer− two 1000 ml glass measuring cylinders, with rubber stops− thermometer− high speed stirrer− sieves 200 mm diameter; 63 µm, 212 µm, 600 µm, 2 mm and a receiver− balance readable to 0.01 g− drying oven, 105-110 °C− stopwatch readable to 1 s.− steel rule− four evaporating dishes− 1000 ml beaker− two measuring cylinder, 100 ml and 50 ml− wash bottle and distilled water− constant-temperature bath− glass rod: 12 mm diameter, 400 mm long− standard dispersant solution: that is 33 g sodium hexametaphosphate and 7 g of sodium carbonate in distilled water to make 1 litre solutionCalibrations and corrections of hydrometer readingsEach density reading taken on the hydrometer must first be expressed as a hydrometer reading, Rh’,corresponding to the level of the upper rim of the meniscus. This is done by subtracting 1 from thedensity and moving the decimal point three places to the right. For example, a density of 1.028 wouldbe a hydrometer reading of Rh’ = 28.Meniscus correction− Insert the hydrometer is a 1 L cylinder containing about 800 ml water.− By placing the eye slightly below the plane of surface of the liquid and then raising it slowly until the surface seen as an ellipse becomes a straight line, determine the point where the plane intersects the hydrometer scale. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 19. 14/06/2005 Soil mechanics laboratory manual 19− By placing the eye slightly above the plane of surface of the liquid, determine the point where the plane intersects the hydrometer scale.− Record the difference between the two readings as the meniscus correction, Cm. Rh = Rh’ + CmScale calibration of hydrometerCalculate the effective depth, HR (mm), corresponding to each of the major calibration marks, Rh fromthe equation: ⎛ V ⎞H R = H + 12 ⎜ h − h L ⎟ ⎝ 900 ⎠where:H = length from the neck of the bulb to graduation Rhh = length of the bulb = 159 mm for B.S. hydrometerVh = volume of hydrometer bulb = 70 ml for B.S. hydrometerL = distance between the 100 ml and the 1000 ml scale markings of the sedimentation cylinder Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 20. 14/06/2005 Soil mechanics laboratory manual 20Example: Rh length H Hr mm mm mm h 159 mm N= 16 Vh 72 ml 25 d1= 19 35 101.78 L 318 mm 20 d2= 38.5 54.5 121.28 15 d3= 58 74 140.78 10 d4= 77 93 159.78 5 d5= 97 113 179.78 0 d6= 117 133 199.78 -5 d7= 137 153 219.78Plot the relation between Hr and Rh as a smooth curve, and determine the relation.With this relation, we can calculate for each reading Rh the corresponding Hr. scale calibration hydrometer 250 200 150 calibration Hr 100 Linear (calibration) 50 y = -3.9286x + 199.71 R2 = 0.9999 0 -10 0 10 20 30 RhSample preparation− Dry the sample in an oven at 60-65°C.− Amount of dry sample − for sandy soil 100 gram − for clayey soil 50 gram− Weigh the soil to 0.01 gram− Place the soil in a 1000 ml beaker− If the sample contains organic matter (>0.5%) we have to remove this as follows:− Add 150 ml of hydrogen peroxide and stir gently for a few minutes with a glass rod− Cover with a cover glass and allow to stand overnight− Next morning heat the flask and stir gently, either on a low-heat hot plate or on a low gas flame. Agitate frequently by stirring or by shaking with a rotary motion. Frothing over must be avoided. If necessary, add more hydrogen peroxide in increments of about 100 ml until the oxidation process is complete. Very organic soils may require several additions of hydrogen peroxide, and the oxidation process may take 2 or 3 days. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 21. 14/06/2005 Soil mechanics laboratory manual 21− As soon as frothing has stopped, the volume of liquid is reduced to about 50 ml by boiling which decomposes any excess hydrogen peroxide− Transfer the contents of the conical flask to a funnel with a Whatman No 50 filter paper, and wash thoroughly with distilled water− Transfer the residue from the filter paper to container using a fine jet of distilled water from a wash bottle and dry the sample at 60-65°C.− Take the weight mp, weight after pre-treatment.Executing the testDispersion− Add 100 ml of the standard dispersing solution to the soil.− Shake the mixture thoroughly until all the soil is in suspension.− Transfer the soil with some distilled water to the cup of the high-speed stirrer and stir for about 1 hour.− Transfer the suspension to the 63 µm sieve placed on a receiver.− Wash the soil in the sieve with a maximum of 500 ml distilled water.− Transfer the suspension in the receiver into a 1000 ml sedimentation cylinder, this will be the sedimentation cylinder.− Transfer the material retained on the 63 µm sieve to an evaporating dish and dry it in the oven at 105 to 110 °C.− When cooled, sieve this material on the 2mm, 600 µm, 212 µm and 63 µm.− Dry and weigh the material retained on each sieve to 0.01 g.− Add any material passing the 63 µm sieve to the sedimentation cylinder.Sedimentation− Fill the sedimentation cylinder to the 1 L graduation mark with distilled water.− Place the sedimentation cylinder in the constant-temperature bath, set on 25 °C.− Place a second cylinder containing 100 ml of the dispersant solution and distilled water to exactly 1 L. in the constant-temperature bath: this is for calibration readings of the dispersant solution and for storage of the hydrometer between the readings.− Allow the cylinders to stand in the bath until they have reached the bath temperature (about 1 hour).− Insert a rubber stop in the sedimentation cylinder or close it off by hand and shake the cylinder vigorously to obtain a uniform suspension. Stir if necessary with a glass rod so that all material goes into suspension. The cylinder is inverted for a few seconds, and is then stood in the constant temperature bath. Without delay as soon as it is in the upright position, the stop-watch is started (zero time).− Remove the rubber bung and insert the hydrometer steadily and allow it to float freely. It must not be allowed to bulb up and down, or to rotate. However a quick rotational twist with the fingers on the top of the hydrometer will dislodge any air bubbles which may adhere to the side.− Readings of the hydrometer are taken at the top of the meniscus level at the following times from zero: 0.5 , 1 , 2 , 4 minutes.− The hydrometer is removed slowly, rinsed in distilled water, and placed in the separate cylinder of distilled water in the constant temperature bath.− Observe and record the top of the meniscus reading, Ro.− Insert the hydrometer for further readings at the following times from zero: 8 , 30 min; 2 ,8, 24 hours and twice during the following day. It is not essential to keep rigidly these times, provided that the actual time of each reading is recorded. Insert the hydrometer slowly about 15s before a reading is due.− Insert and withdraw the hydrometer very carefully to avoid disturbing the suspension unnecessarily.− Observe and record the temperature of the bath after every recording. If the temperature varies more than 1 °C another reading to determine Ro should be taken.− Use a suitable form to record your observations. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 22. 14/06/2005 Soil mechanics laboratory manual 22CalculationDispersion− Calculate the mass percentages according to the wet sieving procedure in paragraph 2.2Sedimentation− Calculate the effective depth Hr− Calculate the equivalent particle diameter D (mm), from the equation− η *Hr D = 0 .005531 ( ρ s − 1) t Where: η = dynamic viscosity of water at the test temperature (mPa.s), table 2.3.1 Hr = effective depth (mm) ρs = particle density (Mg/m3) t = elapsed time (min)− Calculate the modified hydrometer reading, Rd, from the equation Rd = Rh - Ro Where: Ro = hydrometer reading at the upper rim of the meniscus in the dispersant solution− Calculate the percentage by mass, K, of particles smaller than the corresponding equivalent particle diameter , D (mm), from the equation: ⎛ 100ρ s ⎞ K=⎜ ⎜ m(ρ − 1) ⎟R d , where m = mass of dry soil used (g) or mp = mass of soil after pre-treatment. ⎟ ⎝ s ⎠ ρs = particle density (Mg/m3)ReportingThe report shall affirm that the test was carried out in accordance with BS 1377: Part 2: 1990 and shallinclude the following information:1. the method of test used2. the results of the sedimentation analysis3. the results of the sieve analysis4. the method of pre-treatment5. the sieve curveTemperature Dynamic viscosity, η (°C) (mPas) 0 1.7865 5 1.5138 10 1.3037 15 1.1369 20 1.0019 25 0.8909 30 0.7982 40 0.6540Table 2.3.1 viscosity of water Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 23. 14/06/2005 Soil mechanics laboratory manual 23The Atterberg limitsThe Atterberg limits are the so-called consistency limits. Determining the Atterberg limits is a veryuseful method to classify cohesive soils. The concept is based on the fact that the consistency dependslargely on its water content. The Atterberg limits comprise the liquid limit (WL), the plastic limit (Wp)and the shrinkage limit (Ws). They define the boundaries between four stages of a soil.Most of the Soil Classification Systems for engineering purpose is, among other parameters,based on the consistency limits (See chapter 1-1). The classification of soils is not the onlyapplication of the Atterberg limits. There is also a good correlation with the strength of cohesivesoils, expressed in Cu , the undrained shear strength. The consistency limits have been used allover the world for many years and a lot of empirical relationships have been developed.There are four test devices for determination of the liquid limit. These devices are:Casagrande cup, according to the American standard: ASTM, 1995. D 4318Casagrande cup, according to the British standard: BS 1377: Part 2:1990Fall cone, according to the British standard: BS 1377: Part 2:1990 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 24. 14/06/2005 Soil mechanics laboratory manual 243.1 Liquid limit with Casagrande cup. BS 1377: Part 2:1990 (ASTM D4318)Scope of the testThe liquid limit of soil is the water content, expressed as a percentage of the weight of the oven driedsoil, at the boundary between the liquid and the plastic state. The water content at this boundary isarbitrarily defined as the water content at which two halves of a soil cake will flow together for adistance of 12-mm along the bottom of the groove separating the two halves, when the cup is dropped25 times for a distance of 1 cm at the rate of 2 drops/s.Note: The difference between the American and British Standard, is the difference in base plate of the Casagrande cup. The British standard defines a relative soft rubber base, the American standard a harder ebonite one. Because of this difference, the results of the British method are generally higher.Apparatus used- Casagrande cup, according the ASTM or BS standard.- Flat glass plate about 500mm square.- Mass balance accurate to 0.01g- Drying oven- Glass cup or tin dishes- SpatulasFig. 3.1.1 Casagrande apparatusSample preparationPlace the soil sample, weighing about 250 g, from the thoroughly mixed portion of the material passingthe No.40 (425-µm) sieve obtained in accordance with the used standard in a porcelain evaporating dish(about 114-mm in diameter) and thoroughly mix with 15 to 20 ml of distilled water by alternately andrepeatedly stirring, kneading, and chopping with a spatula. Mixing can also be done on a glass plate inthe case care shut be taken to keep the hole sample at the same moister content. Make further additionsof water in increments of 1 to 3 ml. Thoroughly mixes each increment of water with the soil aspreviously described, before adding another increment of water.Test procedureWhen sufficient water has been thoroughly mixed with the soil to produce a consistency that willrequire 30 to 35 lift and drops of the Casagrande cup to cause closure of the groovePlace a portion of the mixture in the cup above the spot where the cup Pests on the base. Squeeze it Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 25. 14/06/2005 Soil mechanics laboratory manual 25down and spread it in the position shown in fig. 3.1-2. with as few strokes of the spatula as possible,care being taken to prevent the entrapment of air bubbles within the Mass. With the spatula (having ablade about 76-mm in length and 19mm in width) level the soil and at the same time trim it to a depthof 1 cm at the point of maximum thickness. Return the excess soil to the evaporating dish. Divide thesoil by firm strokes of the grooving tool along the diameter through the centreline of the cam followerso that a sharp, clean groove of the proper dimensions will be formed. To avoid tearing of the sides ofthe groove or slipping of the soil cake on the cup, up to six strokes, from front to back or from back tofront counting as one stroke, shall be permitted. Each stroke should penetrate a little deeper until thelast stroke from the back to front scrapes the bottom of the cup clean. Make the strokes with as fewstrikes as possible.Fig. 3.1.2 Casagrande cupLift and drop the cup by turning the crank at the rate of 2 revolutions per second, until the two halves ofthe soil cake come in contact at the bottom of the groove along a distance of about 12 mm.Record the numbers of drops required to close the groove along a distance of about 12-mm.Remove a slice of soil approximately the width of the spatula, extending from edge to edge of the soilcake in right angles to the groove and including that portion of the groove in which the soil flowedtogether, and place it in a suitable container (for example a matched watch glass).Weigh and record the mass.Oven-dry the soil in the container to constant mass at 110 °C and reweigh as soon as it has cooled butbefore hydroscopic moisture can be absorbed. Record this mass. Record the loss in mass due to dryingas the mass of water.Transfer the soil remaining in the cup to the evaporating dish. Wash and dry the cup and grooving tool,and reattach the cup to the carriage in preparation for the next trial.Repeat the foregoing operations for at least two additional trials with the soil collected in theevaporating dish, to which sufficient water has been added to bring the soil to a more fluid condition.Preserve after completion of the test the test sample if the plastic limit and plasticity index test has to bedetermined from the soil sample.The object of this procedure is to obtain samples of such consistency that the number of drops requiredclosing the grooveWill be above and below 25. The number of drops should be less than 35 and exceed 15. The testshould always proceed from the dryer to the wetter condition of the soil.CalculationCalculate the water content Wn of the soil, expressed as a percentageof the weight of the oven-dried soil, as follows: mass of water Wn = ∗ 100 mass of ovendried soil Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 26. 14/06/2005 Soil mechanics laboratory manual 26Preparation of the flow curve.Plot a "flow curve" representing the relationship between water content and corresponding number ofdrops of the cup on a semilogarithmic graph with the water content as abscissa on the arithmetical scale,and the numbers of drops as ordinate on the logarithmic scale. The "flow curve" is a straight line drawnas nearly as possible through the three or more plotted points. See fig. 3.1.3 Fig. 3.1.3Reporting-Report the liquid limit as the water content corresponding to the intersection of the flow curve with the 25-drop ordinate as the liquid limit of the soil. Round off this number to the nearest whole value.-Treatment of the soil.-The percentage material passes the 425 mµ sieve, if it was sieved. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 27. 14/06/2005 Soil mechanics laboratory manual 273.2 Liquid limit using the cone penetrometer BS 1377: Part 2:1990Scope of the testWith this test, one can obtain the liquid limit. This value is often used in classification systems, togetherwith particle size analysis.It is based on the measurement of penetration into the soil of a standardised cone of specified mass. Atthe liquid limit the cone penetration is 20 mm.Note: The results obtained with the cone penetrometer may be differ slightly from those with theCasagrande apparatus, but in most cases up to a liquid limit of 100 these differences will not besignificant.Apparatus used- Cone penetrometer with standard cone of mass 80 gr. sees fig 3.2.1- sample cup of diameter 55 mm and 40 mm deep- Flat glass plate about 500mm square.- 2 spatulas- wash bottle- drying oven- mass balance accurate to 0.01 g-Fig.3.2.1 cone penetrometerSample preparationWherever possible the test shall be carried out on soil in its natural state. With many clay soils it ispracticable and shall be permissible to remove by hand any coarse particles present, i.e. particlesretained on a 425µm test sieve. Otherwise these particles shall removed by wet sieving. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 28. 14/06/2005 Soil mechanics laboratory manual 28Sieve procedure-Take a sample of the soil of sufficient size to give a test specimen weighing at least 300 g. which passes the 425 µm test sieve.-Take a representative sample and determine its moisture content, Wn (in %)-Weight the remainder of the sample to an accuracy of within 0.01 g (M6)-Place the sample in a container under just enough distilled water to submerge it.-Stir the mixture until it forms a slurry.-Sieve the slurry through the 425 µm sieve with the minimum amount of distilled water until the water passing is virtually clear.-Collect the material retained on the 425 µm sieve, dry it at 105 °C and weigh it to an accuracy of within 0.01 g (M7).-Collect the fines in a receiver or large container if necessary, and let the fine particles settle.-After a suitable interval pour off any clear water above the suspension, and let it dry (warm air) until it forms a stiff paste.Calculation:From the sieved soil calculate the dry mass, Md (in g), of the initial sample from the equation: ⎛ ⎜ 100 ⎞⎟⎟ Md = ⎜⎜⎜ ⎟M 6 ⎜ 100 + Wn ⎟ ⎟ ⎝ ⎠WhereWn is the moisture content (in %)M6 is the mass of particles retained on 425 µm sieve (in g). ⎛ ⎜ Md − M 7 ⎞⎟⎟Pa = ⎜⎜⎜ ⎟100% ⎜ ⎝ Md ⎟⎟⎠WhereM7 is the dry mass of particles passing the 425 µm sieve (in g)Execution of the test- Thoroughly mix the sample on the glass plate using two spatulas, and if necessary add distilled water, to form a plastic material- Place the paste into an airtight container, and leave it standing for a curing period of 24 hour, or overnight, to allow water to permeate through the soil mass. For soil of low clay content, such as very silty soils, the curing period may be omitted.- Remove the soil from the container and remix with the spatulas for at least 10 min. Some soils (heavy clays) up to 40 min.- fill the sample cup with the soil and trim off excess material with the spatula to form a smooth even surface being careful not to trap any air bubbles- bring the point of the cone to the surface of the sample lower the dial gauge pointer to the top of the cone and set the gauge on zero- release the cone pressing the release button for 5 seconds- lower the pointer to the new position of the cone- Take a reading to the nearest 0.1 mm, it should be approximately 15 mm for the first test.- Lift out the cone and clear it carefully. Add a little more wet soil to the cup and take a second reading. If the second cone penetration differs from the first by less than o.5 mm, the- Average value is recorded, and the moister content is measured. If the second penetration is between 0.5 and 1 mm different from the first, a third test is carried out, and provided the overall Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 29. 14/06/2005 Soil mechanics laboratory manual 29 range does not exceed 1mm, the average of the three penetrations is recorded and the moisture content is measured. If the overall range exceed 1mm, the soil is removed from the cup and remixed, and the test is repeated.- take a sample of approximately 10 gram from the cup and determine its moisture content- To the remainder of the material add some distilled water and repeat the above procedure. This is done at least three more times to get a range (min. 4) of penetration values from about 15mm to 25 mm.- N.B. One must be careful not to add too much water at one time.CalculationThe moisture contents determined are plotted against the respective penetration depth, both on a linearscale. The liquid limit is defined as that moisture content where the cone penetrates 20 mm into thesample. This value is interpolated from a graph. See fig. 3.2.2.Reporting-The liquid limit is expressed to the nearest whole number.-Treatment of the soil.-The percentage material passes the 425 mµ sieve, if it was sieved.Fig 3.2.2 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 30. 14/06/2005 Soil mechanics laboratory manual 303.3 Plastic limit BS 1377: Part 2:1990Scope of the testThe plastic limit is often used together with the liquid limit to determine the plasticity index whichwhen plotted against the liquid limit on the plasticity chart provides a means of classifying cohesivesoils.It is the empirical established moisture content at which soil becomes to dry to be plastic.Apparatus- glass plate- 3 mm diameter metal rod- spatulas- drying oven- mass balance accurate to 0,01 gram.Sample preparationca. 20 gram of material is needed. The sample may be a disturbed sample. We only use material passingthe 425 µm sieve.Execution of the test.- Thoroughly knead the sample and if necessary mix with the distilled water for 10 min. to form a plastic ball.- Mould the ball between the fingers and roll between the palms of the hands so that the warmth of the hands slowly dries it. When slight cracks begin to appear on the surface, divide the ball into two portions each of about 10 g. Further divide each into four equal parts, but keep each set of four parts together.- One of the parts if formed into a thread about 6 mm diameter, using the finger and thumb of each hand. The thread must be intact and homogeneous. Using a steady pressure, roll the thread between the fingers of one hand and the surface of the glass plate. The pressure should reduce the diameter of the thread from 6 mm to about 3 mm after between five and ten back-and-forth movements of the hand. Some heavy clay may need more than this because this type of soil tends to become harder near the plastic limit. It is important to maintain a uniform rolling pressure throughout; do not reduce pressure as the thread diameter approaches 3 mm.- Mould the soil between the fingers again to dry it further. Form it into a thread and roll out again as before. Repeat this procedure until the thread crumbles when it has been rolled to 3-mm diameter. The metal rod serves as a reference for gauging this diameter. By "crumbling" is meant shearing both longitudinally and transversally as it is rolled. Crumbling must be the result of the decreasing moisture content only, and not due to mechanical breakdown caused by excessive pressure, or oblique rolling or detachment of an excessive length beyond the width of the hand.- The first crumbling point is the plastic limit. It may be possible to gather the pieces together after crumbling, to reform a thread and to continue rolling under pressure, but this should not be done.- As soon as the crumbling stage is reached, gather the crumbled threads and place them into a weighed moisture content container.- Repeat for the other three pieces of soil, and place in the same container. Weigh the container and soil as soon as possible, dry in the oven overnight, cool and weigh dry, as in the standard moisture content procedure.- Repeat stages on the other set of four portions of the soil, using a second moisture content container. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 31. 14/06/2005 Soil mechanics laboratory manual 31CalculationsCalculate the moisture content of the soil in each of the two containers. Take the average of the tworesults. If they differ by more than 0,5% moisture content, the test should be repeated.Reporting-The average moisture content referred to above is expressed to the nearest whole numbers and reported as the plastic limit.-The treatment of the soil.-The percentage of material passes the 425mµ sieve if it was sieved.RemarksFrom some soils the plastic limit cannot be determined. Crumbling occurs before you reach 3mm. orrolling of the soil is not possible.ReferenceHead K.H. (1982): Manual of Soil Laboratory Testing, Vol 1,Pentach Press, London Plymouth. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 32. 14/06/2005 Soil mechanics laboratory manual 324.1 Density BS 1377: Part 2:1990Scope of the testThe bulk density of a soil, ρ, is the mass per unit volume of the soil deposit including any water itcontains. The dry density, ρd, is the mass of dry soil contained in a unit volume. Both are expressed inMg/m3, which is numerically the same as g/cm3.Three methods are specified. The first applies to soils that can be formed into a regular geometricshape, the volume of which can be calculated from linear measurements. In the second the volume ofthe specimen is determined by weighing it submerged in water. In the third the volume is measured bydisplacement of water.Apparatus used:- calliper with accuracy of 0.1mm- balance with accuracy of 0.01g- cutting and trimming tools- ParaffinLinear measurement methodThis method is suitable for the determination of the density of a sample of cohesive soil of regularshape.The sample is mostly extruded from a sample tube but can also be shaped in a cube or rectangular blockfrom a undisturbed soil sample- The specimen volume is calculated from the average value of several calliper readings (3 at least) for each dimension of the sample- Weight the trimmed specimen to an accuracy of 0.1 % (m)- Calculate the volume, V of the specimen.CalculationsThe bulk density can be calculated: m ρ= VIf the moisture content, W (in %), of the soil is known, calculate the dry density of the specimen, ρd (inMg/m3), from the equation: 100 ρ ρd = 100 + WExpress the density and dry density of the soil specimen to the nearest 0.01 Mg/m3Remark:In practice we often use a (density) cutting ring to prepare a cylindrical sample with a fixed volumeImmersion in water methodThis method determine the bulk density and dry density of samples of natural or compacted soil bymeasuring its mass in air and its apparent mass when suspended in water. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 33. 14/06/2005 Soil mechanics laboratory manual 33- Trim the soil sample, until a specimen is produced measuring at least 100 mm in each dimension.- Weigh the specimen to the nearest 1 g (Ms)- Fill al l the surface air voids of the specimen with a material that is insoluble in water, e.g. plasticine or putty and weigh to the nearest 1 g (Mf)- Coat the specimens completely by dipping in molten paraffin wax. Allow the waxed specimen to cool and weigh to the nearest 1 g (Mw)- Measure the apparent mass of the specimen while suspended in water to the nearest 1 g (Mg)CalculationsCalculate the volume of the specimen, Vs (in cm3), from the equation: ⎛ Mw - Mg ⎞ ⎛ M w - Mf ⎞ Vs = ⎜ ⎜ ρwater ⎟ − ⎜ ρρ ⎟ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠Where,Mw is the mass of specimen and wax coating (in g);Mg is the apparent mass of specimen and wax coating when suspended in water (in g)Mf is the mass of specimen after making up surface voids with filler (in g);ρρ is the density of paraffin wax (in g/cm3)Calculate the bulk density of the specimen, ρ (in Mg/m3), from the equation: Ms ρ= VsWhere, Ms is the mass of the soil specimen (in g)Water displacement methodThis method used the water displacement and mass of a specimen, to calculate the bulk density and drydensity.The sample is prepared like the water immersion method and put in a water container with siphonoutlet. By taking the weight of the water coming out, the volume can be calculated.ReportingThe report shall include the following information:Data on the sampleProject name, location, and date of sampling, sample number, depth below terrain (in case of aborehole)Type of sample (core, block or other), sample dimensionsThe sample transport and storage conditionsThe density should be reported to the nearest 0.01 Mg/m3The report should specify the type of test. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 34. 14/06/2005 Soil mechanics laboratory manual 344.2 Natural Moisture Content BS 1377:part 2,1990Scope of the testThe objective of the test is to determine the water content of a soil sample as it was sampled in the fieldor at the moment of testing for the accurate determination of in-situ water content, the sampling,storage, transporting and handling precautions should be such that the water content remains within 1%of the in-situ value.Apparatus used- balance accurate to 0.01 gr.- sample container (watch glasses or tins)- oven (24 hr at 105°C ±5°C)- dessicatorSample preparationThe quantity of the soil sample required for an accurate measurement of the natural water content isdependent upon the particle size of the sample.- fine grained material use 30 g- medium grained material use 300 g- coarse grained material use 3000 g-Execution of the test- weigh the sample container to 0,01 gr. accuracy M1- add the material to be tested and weigh again M2- place container with sample in the oven for 24 hours at a controlled temperature of 105 °C- cool the sample in the dessicator- weigh the oven dry and cooled sample M3Calculations mass of water M2 - M3 Moisture content W = = ∗ 100% dry mass of sample M3 - M1With help of the moisture content W, we can calculate the dry density, with the following calculation: mass insitu Dry density = ∗ 100 100 + WReporting- Data on the sample- Project name, location, date of sampling, sample number, depth below terrain (in case of bore hole)- Type of sample (core, block, disturbed, or other), sample dimensions.- lithology, particle size, density, natural moister content- The sample transport and storage conditions- The water content should be reported to the nearest 0.1%. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 35. 14/06/2005 Soil mechanics laboratory manual 354.3a: Particle density small pyknometer method BS 1377:part 2,1990Scope of the testThe objective of the test is to determine the density of the soil particles finer than 2mm.Apparatus used- Two 50mL density bottles (pyknometers) with stoppers- A rod small enough to go through the neck of the density bottle.- A constant temperature water bath in the range from 20-300C ± 0.2 0C- A vacuum desiccator- A desiccator containing anhydrous silica gel.- Balance accurate to 0.001 gr.- Oven (24 hr at 105°C ±5°C)- Vacuum system- A wash bottle containing air-free distilled water- A small riffle-boxSample preparationAt least two specimens, each between 5g and 10g shall be obtained by riffling. The specimens shall beoven dried at 105°C to 110°C and stored in an airtight container.Execution of the test- Wash the density bottles, dry, cool and weigh to the nearest 0.001g (m1).- Transfer the soil specimen to the density bottle. Weigh the bottle, with stopper to the nearest 0.001g (m2)- Add enough air-free distilled water to cover the soil in the bottle. Place the bottle, without stopper in the vacuum desiccator. Reduce the pressure gradually to about 25kPa. Leave the bottle for at least 1 hour under vacuum until no further loss of air is apparent- Release the vacuum and remove the desiccator lid. Stir the soil in the bottle. Before removing the stirring rod wash off any soil particles with a few drops of air-free water. Replace the lid of the desiccator and repeat the vacuum procedure as specified before- This procedure is repeated until no more air is evolved from the soil.- Remove the density bottle from the desiccator and add more air-free water until full. Insert the stopper and immerse the bottle up to the neck in the constant-temperature bath. Leave the bottle in the bath for at least 1 hour so that the bottle attains the temperature of the bath.- If there is an apparent decrease in the volume of the liquid, remove the stopper, add more liquid to fill the bottle and replace the stopper. Return the bottle to the bath and again allow the contents to attain the constant temperature..- Remove the bottle from the bath and wipe it dry. Weigh the bottle with stopper, soil and water to 0.001g (m3)- Clean out each bottle, fill it completely withy de-aerated water, insert the stopper and immerse in the constant temperature bath as before. If necessary fill the bottle as specified before.- Take the bottle out of the bath, wipe it dry and weigh it to the nearest 0.001g (m4) Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 36. 14/06/2005 Soil mechanics laboratory manual 36Calculations m 2 -m1 Particle density = ρs = (m 4 -m1 )-(m3 -m 2 )WhereM1 = mass of density bottleM2 = mass of bottle and dry soilM3 = mass of bottle and soil and liquidM4 = mass of bottle and liquidIf the result of the two samples differs more than 0.03Mg/m3 the test shall be repeated.ReportingThe method of test usedThe average value of the particle density of the soil specimen to the nearest 0.01 Mg/m34.3b Particle density large pyknometer method BS 1377:part 2,1990Scope of the testThe objective of the test is to determine the density of non-cohesive soil containing particles finer than20mm. Coarse particles should be broken down.Apparatus used- A pyknometer, a glass vessel of nominal 1L capacity designed for a screw-top lid, fitted the following a corrosion-resistant screw ring a conical cap of corrosion-resistant metal with a cone-angle of 75 o to 78o and with a hole 6 ± 0.5mm diameter at its apex- A glass about 300mm long and 6mm diameter.- A thermometer range 0°C to 50°C readable to 1°C- Balance accurate to 0.5 gr.- Oven (24 hr at 105°C ±5°C)Sample preparationTake a sample of about 1.5kg. Coarse particles should be broken down.At least two specimens, each of about 400g shall be obtained by riffling. The specimens shall be ovendried at 105°C to 110°C and stored in an airtight container.Execution of the test- Clean and dry the pyknometer and weigh to the nearest 0.5g (m1).- With the screw top removed transfer the soil specimen into the bottle. Weigh the bottle, with screw- top assemble to the nearest 0.5g (m2)- Add water at a temperature of within ± 2°C of the average room temperature to about half fill the pyknometer. Stir the mixture thoroughly with the glass rod to remove air trapped in the soil.- Fit the screw cap assembly and tighten so that the reverence marks coincide. Fill the pyknometer with water.- Agitate by shaking the pyknometer, or by rolling it on the bench, while holding one finger over the Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 37. 14/06/2005 Soil mechanics laboratory manual 37 hole in the conical top. Allow air to escape froth to disperse. Leave the pyknometer standing for at least 24h at room temperature constant to within 2°C.- Top up the pyknometer with water so that the water surface is flush with the hole in the conical cap.- Dry the pyknometer on the outside and weigh the whole to the nearest 0.5g (m3)- Empty the pyknometer, wash it thoroughly and fill it completely with water at room temperature.- Dry the pyknometer on the outside and weigh to the nearest 0.5g (m4)- Repeat the test using the second sample. If the results differ more than 0.05 Mg/m3 repeat the test.Calculations m 2 -m1 Particle density = ρs = (m 4 -m1 )-(m3 -m 2 )WhereM1 = mass of pyknometerM2 = mass of pyknometer and dry soilM3 = mass of pyknometer and soil and liquidM4 = mass of pyknometer and liquidIf the result of the two samples differs more than 0.5Mg/m3 the test shall be repeated.ReportingThe method of test usedThe average value of the particle density of the soil specimen to the nearest 0.5Mg/m3 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 38. 14/06/2005 Soil mechanics laboratory manual 385.1 Vane test BS 1377: Part 7 1990Scope of the testThe vane test is a test, which can be carried out both in the field and in the laboratory.The undrained shear strength of soft to firm cohesive soils can be determined without the sample beingdisturbed by preparation. This method may be used when the sample is too sensitive or soft to enable acompression test.Apparatus used-Laboratory vane test apparatus see fig 5.1-1Sample preparationAn undisturbed sample should be cut and trimmed to a diameter of 37.5mm with a length of about75mm. Place the trimmed sample centrally into the sample container belonging to the equipment. Fillthe annular space between the wall of the container and the sample with molten wax.Alternatively we can clamp a sample container with an undisturbed sample on the base plate of the vaneequipment the sample shut be of sufficient dimensions such that the shearing force applied by the vaneis not hampered or influenced by forces originating from the extremities of the sample.Three tests on one sample material should be sufficient if the results are reasonably constant.Execution of the test (for numbers see fig. 5.1-1)Peek value- a choice of spring is made dependent upon the stiffness of the ground : weak ground: spring 2kg.cm firm ground: spring 8kg.cm- measure the dimensions of the vane- clamp the sample container in the clamping attachment or in a other way vertically below the vane shaft- Lower the vane gradually without disturbing the soil sample so that the top of the vane is at least 10mm below the surface of the sample.- bring the maximum pointer in contact with the (strain)angle indicator- note the reading on the circular graduated scale- operate the torque applicator handle with a rate of 1 revolution per second or used the motorized drive unit until the maximum shear resistance of the soil is reached. At this point failure occurs and the torque decrease but the maximum pointer remains in the position indicated the maximum angular deflection of the spring. Warning: If the (strain)angle indicator rotate for more then 180 degrees stop the test and repeat with a stiffer spring.- record the reading of the maximum pointer as the peek value.Remoulded value- after reading of the (strain)angle indicator rotate the vane rapidly two complete revolutions, to remould the soil.- After stopping rotation wait for a few seconds and slowly apply torque as been done for the peek strength .- Record the reading of the maximum pointer as the remoulded valueRepeat the test at least twice. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 39. 14/06/2005 Soil mechanics laboratory manual 39CalculationCalculate the difference between the initial reading and the reading at the peek and remoulded valueThis difference gives the angle of torque of the spring. Multiply the outcome by the spring factor (isindicated on the spring) and dived the outcome by 180 this give the torque in kgf.cm recalculate thisvalue in N.mm. Average the values obtaining for the different test.If one result differs appreciably from the others (more then 20%) it should be discarded.Calculate the vane shear strength of the soil, τv in kPa Mτv = * 1000 KM= measured torque in N.mmK = constant which depends on the dimensions of the vane. ⎛H D⎞K = πD 2 ⎜ + ⎟ ⎝ 2 6⎠D = vane diameter (mm)H = vane height (mm)Reporting-The average undisturbed and remoulded shear strengths in KPa-The highest and lowest measured values-Type of testing machine-Size of the vane-Indicate the horizon at with the test was executedFig. 5.1.1 Laboratory vane apparatus used at DGM Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 40. 14/06/2005 Soil mechanics laboratory manual 405.2 Shear strength with Triaxial test BS 1377: part 8 1990Scope of the test:The measurement of the effective shear strength parameters for cylindrical specimens of saturated soilwhich have been subjected to isotropic consolidation and then sheared in compression, under a constantconfining pressure, by increasing the axial strain.The test maybe performed consolidated or unconsolidated under drained or undrained conditions, withthe possibility of measuring pore pressure and volume change.Overview test set-upThe triaxial test set up maintenance the following apparatus (fig 5.2.1)1- Triaxial test frame controls.2- Pressure controller air regulator3- Control panel controls.4- Triaxial cell controls5- Load ring controls.6- Strain transducer Strain transducer max. 25 mm 0.01mm.7- Pressure transducer Pore pressure transmitter.8- Volume change apparatus controls9- Bladders controls air-water cylinder.Fig. 5.2.1 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 41. 14/06/2005 Soil mechanics laboratory manual 41Description of testThe sample is enclosed in a thin rubber membrane, which is sealed against the pedestal and the top capon the sample by rubber O-rings.The sample is placed on the base plate of a triaxial cell. The removable cap of the cell is placed over thesample and the total triaxial cell is placed in the triaxial frame.The cell can be filled with (de-aired) water, and with the air regulator we can established the desiredcell pressure (σ3).A piston, movable with little friction through a bush in the top cap of the triaxial cell, rest on the top capof the sample. The upper end of the piston touches a dynamometer, consisting of a metal ring and a dialgauge, which measures the decrease in vertical diameter when a force is applied to the ring. The force isfound by multiplying the dial gauge reading by a calibration constant. (See calibration chart)The triaxial frame has a stepper motor and screw jack assembly, which can provide a constant platenspeed. This causes a compression of both dynamometer and sample.The rate at which the sample is compressed is depending on the kind test (CU, UU, or CD), and type ofmaterial to be tested. A dial gauge just below the dynamometer measures the settlement of the sample.With a pressure transducer, the pore pressure can be measured.And with the automatic volume change apparatus, we can measure the amount of water going in or outthe sample.During the practical we will execute an unconsolidated undrained test (UU), this is a normally not muchperformed test. (No effective stresses are measured)Sample preparationSpecimens shall have a height equal to about twice the diameter, with plane ends normal to the axis.The diameter is normally between 35 and 100 mm.Undisturbed specimens shall be prepared with the minimum change of the soil structure andmoisture content.The method of preparation shall depend on whether the sample received in the laboratory is containedin a tube of the same internal diameter as the specimen to be tested, or in a tube of larger diameter, or asa block sample.Preparing the sample from a block sample.Cut out an approximately rectangular prism of soil slightly larger than the final dimensions of thespecimen. Make the ends of the prism plane and parallel.Put the prism in a soil lathe (fig 5.2.2) and cut off the excess soil in thin layers. Rotate the specimenbetween each cut until a cylindrical specimen is produced. Take care to avoid disturbance due to torsioneffects. Remove the sample from the soil lathe. Cut to the required length and make the ends plane andnormal to the specimen axis to within ½ °.A handy way to establish this is by putting the sample in a catch tube, and cutting away the surplus.With the aid of the levelling ring (fig.5.2.4), smooth the ends of the sample by placing the ring on theend of the catch tube and giving the ring a few turns.Do this to both ends of the sample and make sure that the sample does not slide up and down in thecatch tube. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 42. 14/06/2005 Soil mechanics laboratory manual 42Fig. 5.2.2, Soil lathePreparing the sample from sample tube. (See fig. 5.2.3)- Push the sample tube into the block sample; be sure the sample is long enough.- Place the sample tube in the extruder- Put on the inner side off catch tube mineral oil or silicone crease- 1 = Extruder 2 = Sample tube 3 = Catch tube Fig. 5.2.3 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 43. 14/06/2005 Soil mechanics laboratory manual 43- Fasten the catch tube with the fastening fork to the outside of the extruder- By turning the screw of the extruder, press the sample out of the sample tube into the catch tube.- Separate the sample in the catch tube from the remainder in the sample tube with help of a thread saw- With the aid of the levelling ring (fig.5.2.4), smooth the ends of the sample.- Placing the ring on the end of the catch tube and giving the ring a few turns- Do this to both ends of the sample and make sure that the sample does not slide up and down in the catch tube.- 1= Catch tube 2= Sample trimmer 3= Porous discs 4= SpecimenFig 5.2.4, Catch tube and sample trimmer.- Take the weight from sample with catch tube, by subtracting the weight of the catch tube we can calculate the bulk density (fill in your test form).- Place footcap and topcap on the ends of the sample.- Remove the sample carefully out the catch tube- Measure the height and diameter of the sample. (Fill in your test form).Test ProcedureThe procedure describes the test set up for an unconsolidated undrained testIn order to obtain a reasonable assessment of the C and φ values, three experiments should be done onthree different undisturbed samples of the same soil at three different cell pressures.- Place the sample with the foot piece and cap on the base of the pressure cell- Place a membrane inside the membrane application tube and fold the ends over the outside of the tube, to fit the membrane snugly against the inside wall of the tube wall suck on the hose to create a vacuum between tube and membrane- Slide the membrane application carefully over the sample (see fig. 5.2-4) Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 44. 14/06/2005 Soil mechanics laboratory manual 44 1 = Membrane application 2 = Sucking tube 3 = Membrane 4 = Base pedestal of the pressure cell 5 = Pressure capFig.5.2-4- Remove the suction (vacuum) between the tube and membrane- Roll the membrane ends off of the application tube onto the footpiece and cap- Seal the membrane to the base pedestal using two rubber O-rings- Remove air pockets from between the membrane and the specimen by light stroking upwards- Seal the membrane to the pressure cap with two rubber O rings- Roll the extra membrane back over the rubber ring- Place the cap of the pressure cell over the sample and onto the base plate and fasten it securely with the tie rods- Press the piston carefully onto the cap making sure that the piston falls into the circular hole in the sample cap- Bring the load plate from the triaxial frame up (see the operation instructions from the triaxial Apparatus), until the piston is into contact with the dynamometer (no vertical pressure is exerted on the sample)- Open the air vent on the cap off the cell and fill the cell with de-aired water- Close the vent tightly- Build up the desired pressure in the cell with the air regulator cell pressure and control panel (see the operation instruction of these apparatus)- Bring the strain gauge in contact with the datum bar on the top of the cell and adjust to read zero- Adjust the dynamometer to read zero- Select the machine speed.- Start the test and note values of the dial gauge from the dynamometer at certain strain intervals see test form- Continue the test until a constant reading is obtained on the dynamometer or at 20% strain- Stop the test and remove the pressure from the cell, with help from the air regulator cell pressure.- Bring down the base plate from the triaxial machine- Open the air vent and drain the water out the cell Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 45. 14/06/2005 Soil mechanics laboratory manual 45- Remove the sample from the cell and sketch the failure pattern- Determine water contentReportingAfter executed at least 3 test with different cell pressure (σ3), we can calculated the deviator stress (σ1-σ3)m (in kPa), given by P/As ∗ 1000 in kPaP = is the axial force in N, dial gauge reading times calibration factor (note: the dial gauge reading isalready corrected for the applied cell pressure (σ3) and friction from the piston).As = area cross section of the specimen, this area will change during the compression stage so we needto make a correction: The corrected area is given for each strain reading on the test form.Graphically plot the values of deviator stress against the displacement (in percentage)Calculated the major principal stress σ1 (in kPa), given by σ1=(σ1-σ3) + σ3 whereσ3 is the cell pressure (kPa)Graphically plot the values σ1 and σ3 on the horizontal axis.Draw the Mohrs circles and measures the values for the internal angle off friction (φ) and cohesion (c).Calibration chart for load measuring ring 2.0 kN compression.Temperature at calibration 20 ° Cring serial number 00010105 Gauge reading 0.001 mm Load kN 245 0.2 481 0.4 725 0.6 965 0.8 1214 1.0 1459 1.2 1705 1.4 1955 1.6 2201 1.8 2449 2.0 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 46. 14/06/2005 Soil mechanics laboratory manual 465.3 Direct shear test BS 1377: part 7 1990Scope of the testThe direct shear test is used to measure shear strength, friction angle and cohesion of soils for stabilityanalysis of foundation, slopes, and retaining walls.The test may take place under drained, undrained or consolidated-undrained conditions.Fig 5.3-11-Frame EL 28-0072-Thyristor controlled drive unit3-Gear box4-Load ring5-Weight hanger6-Lever arm (beam) with counter balance7-Displacement transducer8-Loading yokeDuring the practical we will execute the unconsolidated undrained test!Description of testThe direct shear test is used to determine the shear strength of soils on predetermined failure surfaces.The principle of the direct shear test is illustrated in Fig, 5.3.2. The soil sample confined inside theupper and lower rigid boxes is subjected to the normal load N. This load is applied by the yoke which isplaced on the loading cap and by putting weight on the hanger the specimen is loaded axially. Becauseof the length of the beam the applied weight has to multiply with a factor 11. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 47. 14/06/2005 Soil mechanics laboratory manual 47Fig 5.3.2The shear force T shears the sample; this force is applied by the motorised drive unit and measured withhelp of the load ring.If A is the area of surface CD, the shear stress τ acting on surface CD is equal to T/A, and the normalstress σ is equal to N/A. The soil shear strength is the shear stress τ that causes the soil to slip onsurface CD. It can be defined by Mohr-Coulomb theory: τ = C + σ tan φWhere c is the cohesion and φ is the friction angle.During the test, the stress state is not completely defined: τ and σ are only measured on the horizontalsurface, but are undetermined on other surfaces.Therefore, the stress path during direct shear cannot be represented. However, the Mohr circle can bedrawn at failure, assuming that the failure plane is horizontal and the stress state is uniform.Sample preparationSpecimens of either cohesive or non-cohesive soil may be tested in the shear box. Preparationprocedures depend on the type of soil.The size of the largest particle shall not exceed one-tenth of the height of the specimen.Loss or gain of moisture by the sample shall be avoided at all stages of preparation.Normally three similar specimens are prepared, for testing under three different normal pressuresPreparation of specimen of undisturbed cohesive soil, 10∗10∗2 cm (other sizes are possible).- Place the bottom plate.- Place the lower porous plate.- Determine the weight of the sample cutter- Push the sample cutter in the soil sample; trim it with the wire saw and spatula.- Weight the specimen in the cutter to 0.1 g, and calculate the initial mass (Mo ) of the specimen.- Push the specimen out of the cutter and into the shear box keeping its upper face horizontal, until it is bedded on to the lower porous plate.Preparation of specimen of cohesion less soil.The procedure depends on whether the soil is dry and can be poured, or damp and needs to be tamped,or saturated. The sample shall not contain a significant amount of material passing a 63 µm test sieve,to avoid segregation of fine particles, and is therefore referred to as sand. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 48. 14/06/2005 Soil mechanics laboratory manual 48Dry sand:- Determine the depth from the top surface of the upper half to the top of the base plate (h1).- Determine the combined thickness of plates to be used for the test (tp).- Prepare a quantity of soil somewhat larger than required and determined its mass to 0.1 g.- Place the bottom plate.- Place the lower grooved plate.- Place or pour the sand directly into the assembled shear box until the appropriate thickness.- Level the surface- Place the upper grooved plate firmly on the specimen.- Measure the distance from the top of the shearbox to the surface of the grooved plate. (h2).- Weight the total of the unused soil, and determined the initial mass of the specimen (mo).Saturated sand:- Determine the depth from the top surface of the upper half to the top of the base plate (h1).- Determine the combined thickness of plates to be used for the test (tp).- Place the bottom plate.- Place the lower porous plate.- Place the grooved plate.- Prepare a quantity of soil somewhat larger than required and determined its mass to 0.1 g.- Boil the sand in water for 10 minutes- Place the saturated sand into the shearbox and compact it by vibration to achieve the desired density.- Place the upper grooved plate firmly on the specimen.- Place the upper porous plate.- Measure the distance from the top of the shearbox to the surface of the porous plate (h2).- Collect all surplus sand, dry and weight it, and determine the dry mass of the specimen (mo) by difference.- Execution of the testPlace the shear box in the sleigh.- Fill the shear box from the bottom up with: (see fig 5.3.3)- Bottom plate- Porous drainage plate- Grooved plate (grooves up, at right angles to shear motion)- Sample, (with help of the wooden push block)- Grooved plate (grooves down, at right angles to shear motion)- Porous drainage plate- Top plate with ball bearingN.B. In the case of drained experiments use the grooved plates with the holes. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 49. 14/06/2005 Soil mechanics laboratory manual 49Fig 5.3.3- Apply the normal force by placing the load hanger on the ball bearing. The force is applied by placing the slotted weights on the bottom of the hanger. For greater normal forces the slotted weights can put on the hanger from the lever arm. (see fig 5.3-1)- Select the shearing speed, for sand a rate of 1 mm/min, for sand the effect of the displacement rate on the friction angle is generally negligible within the range 3 to 0.1 mm/min.- For cohesive material the shearing speed depends of the type of test, for an undrained test a rate to approximately 1mm/min. should be fast enough to approach the undrained condition.- Adjust the position of the box such that it is in contact with the screw applying the shearing force and the arm of the top half of the shear box is in contact with the load-measuring device.- Install the measuring devices to obtain the vertical and horizontal displacement, and take the initial reading.- Apply the normal force by placing the load hanger on the ball bearing. The force is applied by placing the slotted weights on the bottom of the hanger. For greater normal forces the slotted weights may be hung from the lever arm. (see fig 5.3.1)- Start the motor and record the readings on the measuring devices at regular intervals (for example, every 30 seconds) until a constant value is obtained for the load-measuring device.CalculateCalculate the initial moisture content, Wo (in %), from the equation Mo - MdWo = ∗ 100 Mo is the initial mass of the specimen (in g). Md Md is the final dry mass of the specimen.Calculate the initial dry density, ρd (in Mg/m3), from the equation Md ∗ 1000ρd = A is the plan area of the specimen (in mm2) AH o Ho is the initial height of the specimen. (Ho= h1-h2-tp). For an undisturbed sample, Ho is equal to the height of the cutter.Determine the shear force by correlating the load ring displacement with the force using the calibrationchart.Calculate the shear stress.τ = P/A × 1000 (in kPa) P = Shear force (in N) A = Is the initial plan area of the specimen (in mm2)Plot the displacement against the shear stress and determine the maximum shear stress.Calculate the normal stress at the moment of the maximum shear stress. (Failure points).σn = F/A (in kPa) F = mass on the hanger (or equivalent mass if a Lever-arm is used.)Determine the C and φ values by plotting the max. Shear stress against the normal stress. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 50. 14/06/2005 Soil mechanics laboratory manual 50Calibration chart for load measuring ring 4.5 kN compression.Temperature at calibration 20 ° CRing serial number 1155-7-13080 Gauge reading 0.001mm Load kN 387.2 0.6 512.2 0.8 770.2 1.2 1029.6 1.6 1283.8 2.0 1546.0 2.4 1804.4 2.8 2068.2 3.2 2332.2 3.6 2596.4 4.0 2929.6 4.5Typical values of effective cohesion intercept C′ and effective friction angle φ′ for various fine-grainedsoils (drained test).Case record water Plasticity C′ φ′ Content (%) index PI ( %) (kPa) (deg)Kimola Canal 53 27 4.9 28Trondheim embankment - 2-14 8-20 31-35Slope failure in variegated clay shale 20 24 7.4 24London clay failures 31 52 12 20Field test in Oslo clay 30-38 23 8.8 24Kaolin - 32 25.8Seven Sisters Dikes 48 67 13.8 15Table 1.Undrained shear strength of claysConsistency description Undrained shear strength (kN/m²)Very soft < 20Soft 20 – 40Soft to firm 40 – 50Firm 50 – 75Firm to stiff 75 – 100Stiff 100 – 150Very stiff or hard > 150 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 51. 14/06/2005 Soil mechanics laboratory manual 516.1 Consolidation test BS 1377: Part 5: 1990Scope of the test:Consolidation can be defined as the plastic deformation or void-ratio reduction of a soil mass, which arefunctions of time and excess pore pressure.When fine grained soils are subjected to changes in load due to construction, their deformation takesplace not only at the time of the load application, but also continues for very long time periods whichmay last several years. The long-term settlement of fine grained soil layers is primarily controlled byconsolidation, a physical process in which the interstitial water that is under excess pressure slowlydiffuses through the compressible matrix of soil particles. After the excess pore pressure has completelydissipated, fine-grained soils can also deform due to their viscous nature.The properties that characterise the amplitude and rate of deformation are determined in theconsolidation test.Fig 6.1-11- Consolidation frame2- Consolidation cell3- Displacement transducer4- Loading yoke5- Counter balance weight6- Beam7- Beam support jack8- Weight hanger Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 52. 14/06/2005 Soil mechanics laboratory manual 52Description of testA prepared soil specimen is put in a consolidation cell (fig 6.1-2); which is mounted on the cellplatform from the consolidation frame.The loading yoke is placed on the loading cap and by putting weight on the hanger the specimen isloaded axially. Because of the length of the beam the applied weight has to multiply with a factor.(Depending to which hole of the beam the hanger is connected) The stress is held constant until theprimary consolidation has ceased. This can take a few hours to a few weeks, depending of the load andsample material.During this process water drains out of the specimen, resulting in a decrease in height which can bemeasured with the displacement transducer at suitable intervals.Sample preparationThe inside diameter of the cutting ring shall be not less than 50 mm and not greater than 105 mm. Theheight of the ring shall be not less than 18 mm and not greater than 0.4 times the internal diameter.Undisturbed specimens shall be prepared with the minimum change of the soil structure and moisturecontent. The method of preparation shall depend on whether the sample received in the laboratory iscontained in a tube of the same internal diameter as the specimen to be tested, or in a tube of largerdiameter, or as a block sample.For the practical you will get a clay block sample, from which you will prepare a specimen with helpfrom the cutting ring.Fig 6.1.2- Measure the diameter and height of the cutting ring, with an accuracy of 0.1 mm- Weigh the ring to an accuracy of 0.1 gram- Lubricate the inner face of the ring lightly with silicon grease, to minimise side friction- Place the sample on a glass plate- Push the cutting ring into the sample cutting away surplus soil from the outside of the ring as the sample enters it, until the top surface projects a few millimetres above the top of the ring- Cut of the soil projecting above and below the ring with the wire saw (see fig. 6.1.2) and flat ten both sides carefully with the spatula- Remove soil particles sticking to the outer side of the ring- Weigh the specimen with ring Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 53. 14/06/2005 Soil mechanics laboratory manual 53 Test procedure Assembly of the consolidation cell - Place the cell body on the cell base - Place the bottom porous disc on the cell base - Put the cutting ring with specimen centrally in to the cell with its cutting edge uppermost. - Fix the ring retainer around the ring, so that it is securely held, and tighten the clamping screws - Place the upper porous disc - Place the loading cap centrally on topClamping screws Loading capUpper porous disc Cell body Ring retainerUnder porous disc Cutting ring Cell base O-ring Fig.6.1-3 - With the loading Yoke swung forward and resting on the beam, place the consolidation cell centrally on the frame platform - Adjust the counterbalanced loading beam so that when the loading yoke just make contact with the loading cap the beam is slightly above horizontal position - Raise the beam a little more above horizontal position and hold it there with the support jack - Swing the loading yoke vertical above the loading cap and slowly lower it - Adjust the supports jack so that the bull just touches the seating. - Add a small weight to the hanger (the seating pressure on the specimen shall not exceed 2 kPa) - Bring the displacement transducer in contact with the loading yoke and set it zero. If not otherwise indicated by the laboratory assistant, the test has to be done for tree load increments starting with a load giving a stress of 174 kPa on the sample. Normal procedure is to double the stress at each stage. The applied stress range will therefore be 174, 347, 694 kPa. - Add the first load to the hanger to give the required pressure of 174 kPa. (take away the seating load) - Start Winclips program. (trigger on the vertical displacement transducer, 0.1 mm) - Add water to the cell - Measure with suitable intervals the vertical displacement; the following periods of elapsed time from zero are convenient. 0,10,20,30,40,50 s 1,2,4,8,15,30 min. 1,2,4,8,24 hours -Plot the readings of the dial gauge or the settlement against time to a logarithmic scale (See fig. 6.1-4): Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 54. 14/06/2005 Soil mechanics laboratory manual 54Fig.6.1-4After 24 hours, the decision must be taken whether or not to apply the next load increment.If the dial reading versus log-time shows a flattening out from the steep part of the curve to a straightline which is less steeply inclined, as in figure 6.1-4, it indicates that the primary consolidation phase iscomplete and that the next load increment may be applied. If the straight line representing secondarycompression has not yet been established, the load should be left unchanged for another 24 hours.When it has been established the loading stage may be terminated:- Applied the second load on hanger, to give the required new stress (347 kPa)The procedure has to be carried out at the same way as done for the first load increment.Repeat this procedure for a third load increment.- After completion the last load increment takes out the consolidation ring Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 55. 14/06/2005 Soil mechanics laboratory manual 55- Remove the porous discs carefully, any soil adhering to them should be scraped off and returned to the sample- Wipe the outside of the ring dry and weight the sample with the ring- Place sample with ring in the oven for 24 h.- Take the dry weight, to calculate the moisture content and dry-weight.ReportingCalculate the bulk mass density and moisture content before and after the test.Calculate the dry density (if no material has been lost during the test).Plot the settlement versus log-time curve, and analysis has to be made following Casagrandes method,to determine the coefficient of consolidation Cv for each increment of loading.The principle of the method is illustrated in fig 6.1-4.Locate the corrected zero point by marking off the difference in ordinates between any two points onthe initial (convex-upwards) portion of the curve having times in the ratio 1:4, and laying off an equaldistance above the upper point. Repeat this operation using two other pairs of points having times in thesame ratio, and take the average as the corrected zero compression point (d oDraw and extend the tangents to the two linear portions of the laboratory curve, i.e. at the point ofinflexion, and the secondary compression portion. Their intersection gives the compressioncorresponding to theoretical 100 % primary compression, denoted by d100 .From the zero and 100% points, locate the 50 % primary compression point, d50, on the laboratory curveand obtain its time, t50 (in min).Calculate the coefficient of consolidation with the following equation: 0.026 H 2Cv = Expressed in m2/year t 50 H1 + H 2With: H = were, 2H1= Height of specimen at start of a loading incrementH2= Height of the specimen at the end of that incrementt50 = time for 50 % consolidation, expressed in minutes. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 56. 14/06/2005 Soil mechanics laboratory manual 567.1 Proctor test BS 1377:Part 4: 1990Determination of dry density/moisture content relationshipScope of the testCompaction of soil is the process by which the solid particles are packed more closely together,usually by mechanical means, thereby increasing the dry density of the soil. The dry density, whichcan be achieved, depends on the degree of compaction applied and on the amount of water presentin the soil. For a given degree of compaction of a given cohesive soil there is an optimum moisturecontent at which the dry density obtained reaches a maximum value.For cohesion less soils an optimum moisture content might be difficult to define.Note: For highly permeable soils such as clean gravel’s, uniformly graded and coarse clean sands,the results of the laboratory compaction test may provide only a poor guide for specifications onfield compaction The laboratory test might indicate meaningless values of moisture content in thesefree-draining materials and the maximum dry density is often lower than the state of compactionwhich can be readily obtained in the field. For these soils the test description for determination ofmaximum and minimum dry densities for granular soils would be more appropriate.Three types of compaction test are described, each with procedural variations related to the natureof the soil: 1-Light manual compaction test, using a 2.5 kg rammer. 2-Heavy manual compaction test, using a 4.5 kg rammer.For both these tests a compaction mould of 1 L. internal volume is used for soil in which allparticles pass a 20 mm test sieve.If there is a limited amount of particles up to 37.5 mm size, equivalent tests are carried out in thelarger CBR mould. Specifications for compaction by rammer in the CBR mould are based on thesame compactive effort per unit volume of soil as in the 1L compaction mould. For a series of testson a particular soil, one size of mould should be used consistensily. 3-Compaction with a vibration hammer, in the CBR mould (See chapter 7.2)Apparatus used- A cylindrical mould with an internal diameter 105mm and an internal effective height of 115.5mm. Detachable base plate and removable extension collar figure 7.1.1.- Metal rammer:Light test: 50 mm diameter face, weight of 2,5 kg, sliding freely in a tube which controls the height of drop to 300 mm figure 7.1.2.Heavy test: 50 mm diameter face, weight of 4.5 kg, sliding freely in a tube, which controls the height of drop to 450 mm- Jacking apparatus for extracting the compacted material from the mould.- 20 mm and 37.5 mm British Standard sieves.- CBR mould, as described in chapter 7.2- Balance readable to 5 g.- Watertight containers or strong polythene bags- A drying oven capable of maintaining a temperature of 105 C to 110 C.- A steel straightedge, about 300 mm long and 3 mm thick, with one bevelled edge.- Mixer, min 5 litres. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 57. 14/06/2005 Soil mechanics laboratory manual 57Fig. 7.1.1 British standard compaction mould Fig 7.1.2 Ordinary test rammerSample preparationThe quantity of soil required, depend on the size of the largest particles present and if the particles aresusceptible to crushing during compaction.Determine the approximate percentage by mass of particles in the soil sample passing the 20 mm and37.5 mm test sieves.For soils not susceptible to crushing, one sample only is required for test and it can be used severaltimes.- Original bulk sample, is air dried and weighed = w1- Particles larger than 20 mm should be removed by sieving with the 20 mm and 37.5 mm BS sieve.- The amount of material retaining on the sieves has to be weighed and as a percentage from the total mass calculated.- On the basis of these percentage the soil can be assigned to one of the grading zones (1) to (5) in table1, and the minimum mass of soil required can be determined.Table 1Grading Minimum Minimum Type ofzone Percentage Mass of prepared mould passing test sieve soil required used 20 mm 37.5 mm A B % % kg kg1 100 100 6 15 1L2 95 100 6 153 70 100 15 404 70 95 15 40 CBR5 70 90 15 40x Less than 70 Less than 90 Test not applicableA = Soil particles not susceptible to crushing.B = Soil particles susceptible to crushing.- Depending on the soil type, a suitable amount of water should be added Light test: Sandy + gravely soils: 4-6% (200-300 ml water on 5 kg of soil) Cohesive soils: 8-10 % below the plastic limit Heavy test: Sandy + gravely soils: 3-5% (150-250 ml water on 5 kg of soil) Cohesive soils: 15 % below the plastic limit- Thorough mixing in of the water is essential. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 58. 14/06/2005 Soil mechanics laboratory manual 58Execution of the test- Weigh the mould = m1- Connect the extension collar to the mould Add loose soil to the mould. Using the 1L or CBR mould, place a quantity of moist soil in the mould that when compacted it occupies a little over one-third of the height of the mould body for the “ordinary” test and one-fifth for the “heavy” test- Place the guide tube gently on the soil and hold it vertically.- Now the soil should be compacted by 27 blows for the 1 L mould and 62 blows for the CBR mould.- First 4 blows according to the pattern of fig. 7.1.3- After this, the rammer should be moved, according to fig. 7.1.3 between the successive blows. With this, the blows are uniformly distributed over the whole area.- Place a second, approximately equal, layer of soil in the mould and compact it with 27 or 62 blows in the same way as described above.- Repeat with: Ordinary test, third layer. Heavy test, third, fourth and fifth layer.- The compacted surface in the extension collar should be about 6 mm above the level of the mould body.(see fig 7.1.4)- Remove the extension collar carefully and cut away the excess soil and level off the top of the mould. Any small cavities, resulting from removed stones, should be filled up with fine material.Fig. 7.1.3 Sequence of blows fig 7.1.4-Weigh the soil + mould (m2).-if necessary execute the CBR test (chapter 7.2)Fit the mould on to the extruder and jack out the soil. Break up the sample on a tray.Now the moisture content has to be measured by taking three representative samples.Break up what is left over from the compacted sample and mix it with the remainder of the preparedsample.Add an increment of water, approximately as follows:-Sandy+ gravely soils 1-2% (50-100 ml of water to 5 kg of soil).-Cohesive soils: 2.4% (100-200 ml of water to 5 kg of soil).Mix in the water thoroughly for each increment of water added.Repeat the compaction part so that at least 5 compactions are made. Of course, the range of moisturecontents should be such that the optimum moisture content is within that range. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 59. 14/06/2005 Soil mechanics laboratory manual 59Fig 7.1.5 graph of dry density-moisture contentCalculationsCalculate the Bulk density, ρ: m2-m1Bulk density ρ = Mg/m3 VWherem1 = mass of mould and base platem2 = mass of soil and mould and base plateV = volume of the mould.Calculate the average moisture content, W %, for each compacted specimen.Calculate the corresponding dry density: 100 ρ ρd = Mg/m3 100 + WWhereρd = the dry density (Mg/m3)W = the moisture content (%)Plot each dry density, against the corresponding moisture content, W. Draw a curve of best fit to theplotted points and identify the position of the maximum on this curve. Read off the maximum drydensity and the corresponding moisture content, which is the optimum moisture content for this degreeof compaction. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 60. 14/06/2005 Soil mechanics laboratory manual 60The curve for 0, 5, and 10% air voids may be plotted on the same graph. These curves are calculatedwith the following equation: Va 1−ρd = 100 1 W + ρ s 100 ρ wwhere ρd = the dry density (Mg/m3) ρs = the particle density (Mg/m3) ρw = the density of water (Mg/m3) Va = the volume of air voids in the soil, expressed as a percentage of the total volume of the soil (equal to 0%, 5 %, 10 % for the purpose of this plot. W = the moisture content (%)An example of such a graph is given by fig. 7.1.5.Reporting- Description of the soil- The maximum dry density for the stated degree of compaction is reported to the nearest 0.001 Mg/m3.- The optimum moisture content is reported as follows: Below 5%: to the nearest 0.2% From 5% to 10%: to the nearest 0.5% Exceeding 10%: to the nearest 1%- The percentage of stones retained on the 20mm sieve is reported to the nearest 1%.- Which procedure was followed; British Standard 2.5kg rammer method British Standard 4.5kg rammer method- Whether the test was carried out on a single sample or on separate batches.RemarksIt is possible to combine this test with the CBR testReferences:- K.H. Head (1982), Manual of Soil Laboratory Testing: Vol. 2, Pentech Press, London.- BS 1377:Part 4: 1990 Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 61. 14/06/2005 Soil mechanics laboratory manual 617.2 Californian bearing ratio test BS 1377:Part 4: 1990Scope of the testThis method covers the laboratory determination of the California Bearing Ration (CBR) of a compactedor undisturbed sample of soil.The principle is to determine the relation between force and penetration when a cylindrical plunger witha standard cross-section area is made to penetrate the soil at a given rate.At certain values of penetration the ratio of the applied force to a standard force, expressed as apercentage, is defined as the California Bearing Ratio (CBR).The Californian Bearing Ratio test, or CBR-test, is an empirical test, which is used as an importantcriterion in pavement design. With this test, the bearing value of highway sub-bases and sub-grades, canbe estimated.Apparatus used- Motor-drive compression machine, with a constant penetration rate of 1 mm/min.- The load-measuring device depends on the CBR-value. With a CBR value up to 30%, a load ring with a range of 0-10Kn is needed. A seating load of 50N has to be applied. With a CBR value above 30%, a load ring with a range of 0-50KN is needed. A seating load of 250N has to be applied.- The displacement-measuring device must have a range of 25 mm and scale units of 0.01 mm.- A standardised CBR mould, fittings and tools.- 20 mm and 37.5 mm British Standard sieves.- CBR mould, as described in chapter 7.2- Balance, capable of weighing up to 25 kg readable to 5 g.- Watertight containers or strong polythene bags- A drying oven capable of maintaining a temperature of 105 C to 110 C.- A steel straightedge, about 300 mm long and 3 mm thick, with one bevelled edge.- Mixer, min 5 litresFig 7.2.1 General arrangement for CBR test Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 62. 14/06/2005 Soil mechanics laboratory manual 62Sample Preparation.The CBR test shall be carried out on material passing the 20 mm test sieve. If the soil contains particleslarger than 20 mm, the test material must be sieved with the BS 20 mm sieve. If this fraction is morethan 25 % the test is not applicable.The moisture content of the soil shall be chosen to represent the design conditions for which the testresults are required. Where a range of moisture contents is to be investigated, water shall be added orremoved from the natural soil.After bringing the sample to the required moisture content the soil shall be thoroughly mixed and shallnormally be sealed and stored for at least 24 h before starting compaction.The mass of soil required for the test shall be calculated or estimated. When the density or air voidscontent of a compacted sample is specified the exact amount of soil required for the test can becalculated as follows.Dry density specification, the mass of soil M1 (g), required to just fill the CBR mould of volume (cm3) isgiven by the equation: VmM1 = (100 + W ) ρ d 100% 100Where W = the moisture content of the soil (%) ρd = the specified dry density (Mg/m3) Vm = volume of the mould (m3)Air voids specification, the dry density ρd (Mg/m3), corresponding to an air voids content of Va (%) isgiven by the equation: Va 1−ρd = 100 1 W + ρ s 100 ρ wwhere ρd = the dry density (Mg/m3) ρs = the particle density (Mg/m3) ρw = the density of water (Mg/m3) Va = the volume of air voids in the soil, expressed as a percentage of the total volume of the soil (equal to 0%, 5 %, 10 % for the purpose of this plot). W = the moisture content (%)Compactive effort specification: About 6 kg of soil shall be prepared for each sample to be tested. Theinitial mass shall be measured so that the mass used for the test sample can be determined aftercompaction by difference, as a check.To make comparison possible, the soil conditions (Bulk density, moisture content on dry density) haveto be known.Table 7.2-1 gives an overview from the sample preparation methods for the CBR test.Six methods are described in the British Standard for the preparation of disturbed samples for the CBRtest. In methods 1 and 2 static compaction is used to achieve a specified density.In the other methods, dynamic compaction by hand or mechanical rammer, or by vibrating hammer, isused, either to achieve a specified density in method 3 and 4 or to provide a specified compactive effort Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 63. 14/06/2005 Soil mechanics laboratory manual 63in methods 5 and 6.table 7.2-1- The sample has to be divided in equal parts of weights according to the number of layers mentioned in table 7.2-2. This is because the compaction takes place in stages, in order to get an optimal compaction.- Dropping a certain weight several times, from a certain height performs the compaction.- Ensure that the blows are evenly distributed over the surface- Table 7.2-2 gives the details of the compaction, depending on the required way of compaction.Type of compaction Rammer No. of Blows per Mass drop layers layers (kg) (mm)BS ‘ordinary’ 2.5 300 3 62(BS 1377)BS ‘heavy’ 4.5 450 5 62(BS 1377)Intermediate 4.5 450 5 30Vibrating hammer 30-40* (vibration) 3 (60 s)ASTM ‘Standard’ 5.5 lb 12 in 3 61 56Modified AASHO 10.0 lb 18 in 5 61 56* Downward force (kgf) to be applied.Table 7.2-2 Compaction in CBR mould equivalent to BS compaction mouldExecution of the test.- The load-measuring device is connected to the compression machine.- The cylindrical plunger, diameter 49,5 mm and cross-sectional area of 1935 mm2 and a length of 250 mm, is connected to the load-measuring device.- The mould with the sample and the surcharge weights is placed in the machine. Each surcharge ring Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 64. 14/06/2005 Soil mechanics laboratory manual 64 of 2 kg is equivalent to about 70-mm thickness of superimposed construction.- The plunger must be seated on top of the specimen and must be able to move freely from the surcharge weight.- The seating load has to be applied by weight.- Adjust the displacement-measuring device to read zero.- Switch to motor drive and start the loading, with a loading rate of 1 mm/min.- Reading of the load-measuring device has to be taken with every 0,25 mm displacement.- After 7,5 mm penetration, the machine can be stopped.- After removing the sample from the mould, the moisture content has to be determined.Calculation- The data, obtained with the test, have to be plotted in a load penetration diagram.- The load at 2,5 and 5,0 mm penetration has to be read from this diagram.- The same has to be done from the diagram of the standard CBR test, with a CBR value of 100%, see figure7.2.2 for the standard load for 2.5 and 5 mm penetration.- The CBR-value is then: load at 2.5 mm penetration from test CBR = × 100% load at 2.5 mm penetration from standard- The same calculation is done for 5 mm penetration.- The highest of the two is then the CBR-value.Correction- The load-penetration curve is normally convex upwards. Figure 7.2.2, test 1- If not, a correction has to be applied: figure 7.2.2, test2- From the inflection point, the tangent has to be drawn until it cuts the horizontal axis.- This cutting point must then be taken as the new origin point and a new penetration scale, starting with zero at this new point, must be added.Reporting- Data on the sample.- Type of sample, disturbed, undisturbed etc.- Lithology, weathering grade, particle size distribution, moisture content and natural moisture content.- Data and testing procedure.- Description of the testing machine and stress rate used.- Type of load- and displacement measuring devices.- Way of compaction used.- Table with all readings.- Load penetration diagram, if necessary with construction of the direction.- C.B.R.-value. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 65. 14/06/2005 Soil mechanics laboratory manual 65Fig 7.2.2 Tree types of load penetration curve from CBR tests: Test 1, no correction required Test 2, correction required Test 3, correction as (B) may not be valid.RemarksUsually, the CBR-test is combined with the proctor test.References- K.H. Head (1982), Manual of Soil Laboratory Testing: Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 66. 14/06/2005 Soil mechanics laboratory manual 66Permeability testsIntroductionThe permeability of a soil is a measure of its capacity to allow the flow of a fluid (a liquid or a gas ingeneral water) through it.The principle is that soil consists of solid particles with voids between them. In general the voids areinterconnected, which enables water to pass through them. The degree of permeability is determined byapplying a hydraulic difference across a sample of soil, which is fully saturated and measuring theconsequent rate of flow of water. The "coefficient of permeability" in expressed in terms of a velocity.The flow of water through soils of all types, from gravel’s and sands to clays, are governed by the samephysical laws. The difference between the permeability characteristics of extreme types of soil ismerely one of degree, even though clay can be ten million times less permeable than sand. Clays are notcompletely impermeable, although they may appear to be so if the rate of low through them is notgreater than the rate of evaporation loss.The method used for measuring permeability depends upon the characteristics of the material.Permeability tests on natural disturbed soil are probably carried out more frequently in-situ than in thelaboratory, but field inspection and testing is beyond the scope of this laboratory guide.There are two types of laboratory tests for the direct measurement of the permeability of soils:Constant head test-for soils of high permeability, such as sands. The constant head test is a permeabilitytest in which water is made to flow through a soil sample under a constant difference in head orhydraulic gradient.Falling head test- for soils of intermediate and low permeability, such as silts and clays.The falling head test is a permeability test in which the piezometer tube used for measuring the headalso provides the water, which passes through the sample, and therefore the level falls during the test.For the indirect assessment of permeability careful inspection of the soil, together with a properlyconducted particle size analysis, are required. These procedures are useful either when it is notpracticable to make a direct measurement, or as a check on direct measured values. Permeability canalso be derived from data obtained during an oedometer test. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 67. 14/06/2005 Soil mechanics laboratory manual 678.1 Constant head test BS 1377 part 5Permeability of granular soils.Scope of the testThis method covers the determination of the coefficient of permeability by a constant head method forthe laminar flow of water through granular soils.The procedure is to establish representative values of the coefficient of permeability of granular soilsthat may occur in natural deposits as placed in embankments, or when used as bases courses underpavements. In order to limit consolidation influences during testing, this procedure is limited todisturbed granular soils containing not more than 10% soil passing the 63-um sieve.Fundamental Test ConditionsThe following ideal test conditions are prerequisites for the laminar flow of water through granular soilsunder constant head conditions.1. Continuity of flow with no soil volume change during a test.2. Flow with the soil voids saturated with water and no bubbles in the soil voids.3. Flow in the steady state with no changes in hydraulic gradient.4. Direct proportionality of velocity of flow with hydraulic gradients below certain values, at which turbulent flow starts.Apparatus usedPermeameter set-up fig 8.1.1 consist of:- Permeameter cell conform the standard- Two discs of wire gauze or porous material fitting inside the cell- A vertical adjustable reservoir tank capable of maintaining a constant –head of water supply- A supply of clean de-aerated water to the constant head reservoir- A discharge reservoir with overflow to maintain a constant level.- A set of manometer tubes connected to the cell with flexible tubes including a (pinch) valve- Filter material of a suitable grading for placing adjacent to the perforated plates at each end of the permeameter. The grading of the filter material depends on the particle size distribution of the test sample. The filter material grading limits should lie between four times the 15% passing size and four times the 85% passing size of the test sample. The material should be well graded between those limits.- Measuring cylinders of 100 mL, 500mL, and 1000mL capacity- A large plastic funnel- A scoop for placing soil in the funnel- A scoop small enough to fit inside the permeameter- A flat-ended tamping rod long enough to reach to the bottom of the permeameter and about 10mm diameter.- A calibrated thermometer reading to 0.5 oC- A stopwatch readable to 1 s.- A balance readable to 1 g.- A steel rule graduated to 0.5mm- Internal calliper.Sample preparationSample- A representative sample of air-dried granular soils, containing less than 10% of the material passing the 63µm sieve and equal to an amount sufficient to satisfy the requirements prescribed in (2) and Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 68. 14/06/2005 Soil mechanics laboratory manual 68 (3) below, shall be selected by the method of quartering.- A sieve analysis shall be made on a representative of the complete soil, prior to the permeability test. All particles larger than one-twelfth of the diameter of the permeameter cell shall be removed. The percentage of the oversize material shall be recorded.- From the material from which the oversize has been removed, select by the method of quartering, a sample for testing equal to an amount approximately twice that for filling the permeameter chamber.- Take a small portion of the selected sample for moister content and particle density determinations.- Weight the remainder of the prepared sample to 1g (m1)Fig. 8.1.1 Constant head test Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 69. 14/06/2005 Soil mechanics laboratory manual 69Preparation of the specimens- Make the following initial measurements: (see fig.8.1.1) Inside diameter, D, of the permeameter. Distances between manometer outlets X1, X2.- Record the weight of the remaining air-dried sample, W1, for unit Weight determinations.- Assemble the base plate, with perforated base, to the permeameter cell body.- Place the graded filter material in the bottom of the cell to a depth of about 50mm and place a wire gauze or porous disc on top.- Place the prepared soil into the permeameter in such a way as to give a homogeneous deposit at the required density or voids ratio. The final height:diameter ratio of the test sample shall be not less than 2:1. Placing and compaction shall be done by one of the following methods. A. Hand tamping: Place the soil sample in at least four uniform layers, each with a thickness of about ½ the diameter. Avoid segregation. Tamp each layer with a controlled number of standard blows with the tamping rod. B. Placing under water: Thoroughly mix the prepared soil with de-aerated water and place the mixture in a suitable funnel fitted with a bung and length of flexible tubing. Support the funnel so that the tubing reaches to about 15mm above. Connect the control valve on the base of the cell to the de-aerated water supply and allow de-aerated water to enter the cell to a height of about 15mm above the porous disc. Release the soil and water mixture into the cell, raising the funnel so that the end of the tubing is just at the water surface, which shall be maintained at about 15mm above the surface of the placed material by admitting moor water through the base valve. Continue until the cell is filled to the required level. This will result in a saturated sample in a loose condition. If higher density is required, tamp or vibrate the material during placement.- Place the upper wire gauze or porous disc on top of the prepared sample.- Place the graded filter material on top of the disc to a depth of at least 50mm- Release the piston in the top plate and withdraw it to its fullest extent.- Fit the top plate- Lower the piston carefully and bed the perforated plate on the filter material. Hold the piston down firmly and tighten the locking collar in this position.- Record the height of the test sample, L in mm as an average of three measurements- Dry the soil left over and determines the mass to the nearest 1g (m2), so that the dry mass of the soil used in the test sample can be obtained by difference m1- m2.Saturation- Fill the permeameter cell with water and saturate the sample as follows. (if the sample is placed under water start with step 4) 1. Connect the control valve on the base of the permeameter to the de-aerated water supply. Open the top connection and the air bleed to atmosphere, and close the connections to the manometer tubes 2. Allow de-aerated water to enter the cell and slowly percolate upwards through the sample until it emerges first from the air bleed, which is then closed, and then from the top connection. 3. Measure the length of the sample again, and record the average measurement, L (in mm) 4. Close the control valve. Connect the de-aerated water supply to the permeameter top connection, and connect the control valve at the base to the discharge reservoir, without entrapping air. 5. Set the inlet reservoir at a level a little above the top of the permeameter cell and open the supply valve. Open the manometer tube valves and ensure that no air is trapped in the flexible tubing. The water in all tubes shall reach the level of the reservoir surface. 6. The cell is now ready for test under the normal conditions of downward flow. 7. If a test with upward flow is required.(investigation piping effects), fit the control valve connected to the discharge reservoir, to the top of the cell and connect the de-aerated water supply to the base. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 70. 14/06/2005 Soil mechanics laboratory manual 70fig 8.1.2Test procedure, downward flow fig 8.1.2.- Adjust the height of the inlet reservoir to a suitable level. Often a hydraulic gradient of 0.2 is suitable.- Open the control valve at the base to produce flow through the sample. Allow the water levels in the manometer tubes to become stable before starting measurements.- Place a measuring cylinder of suitable capacity under the outlet from the discharge reservoir and simultaneously start the timer- Measure the quantity of water collected in the cylinder during a given interval of time. Alternatively record the time required to fill the cylinder up to a given volume.- Record the levels of water in the manometer tubes. If the levels indicate a significant non- uniformity of the hydraulic gradient remove and replace the sample.- Record the temperature of the water in the discharge reservoir.- Repeat the measurement at least four times.- If needed the hydraulic gradient can be increased by increasing the height of the inlet reservoir.CalculationsCalculate the rate of flow q1 and q2 etc. in mL/s during the period of each observation. Q1q1 = etc. twhere:q = the rate flow in mL/sQ1 = is the volume of water (mL) collected from the outlet reservoir during the time interval tt = time interval in s Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 71. 14/06/2005 Soil mechanics laboratory manual 71Calculate the hydraulic gradient, I, between the uppermost and lowest manometer: hi= ywhereI = the hydraulic gradienth = the difference between the two manometer levels in mmy = the height difference between the corresponding manometer connections on the cellCalculate the coefficient of permeability, k in m/s, for one set of readings: ⎛ q ⎞⎛ R ⎞k = ⎜ ⎟⎜ t ⎟ ⎝ i ⎠⎝ A ⎠wherek = the coefficient of permeability in m/sq = the rate flow in mL/si = the hydraulic gradientRt= the temperature correction factor for the viscosity of water, derived from table 8.1.1 to standardize the permeability to 20 oC.A = the area of cross section of the sample in mm2.Table 8.1.1: temperature conversion tableLaboratory temperature, T in oC Correction factor Rt 5 1.5 10 1.3 15 1.15 20 1 25 0.885 30 0.8If a test have been carried out on different hydraulic gradients, plot the calculated values of rate of flow,q against hydraulic gradient, i. ∆qDraw the straight line of best fit through the plotted points and determine its slope ∆iWhen a range of hydraulic gradients is used the coefficient of permeability of the sample may becalculated from the equation: ⎛ ∆q ⎞ ⎛ Rt ⎞k =⎜ ⎟⎜ ⎟ ⎝ ∆i ⎠ ⎝ A ⎠Calculate the dry mass and of the initial sampleCalculate the dry density ρd with the volume measurements of the sample in the permeameter cell ρsIf we know the particle density ρ s we can also calculate the void ratio, e = −1 ρd Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 72. 14/06/2005 Soil mechanics laboratory manual 72Reporting results- Information on the method used including the standard followed.- The particle size distribution curve.- The proportion and size of oversize material removed before preparing the test sample.- The method of placing and compacting the test sample.- The dimensions of the permeameter- The dry density and if required the voids ratio- The coefficient of permeability, k in m/s, to two significant figures, for laminar flow corrected to 20 o C.- The coefficient of permeability for other conditions, if relevant- A plot of coefficient of permeability, k on log scale against density or voids ratio if appropriate. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 73. 14/06/2005 Soil mechanics laboratory manual 738.2 Falling Head Permeability Tests.Permeability of fine soils.ScopeThe falling head permeability test is used for measuring the permeability of soils of intermediate andlow permeability (less than 0.0001 m/s), i.e. silts clay, a relatively short sample is connected to astandpipe, which provides both the head of water and the means of measuring the quantity of water,flowing through the sample.Several standpipes of different diameters are normally available from which can be selected thediameter most suitable for the type of material being tested.Note: This test is not covered by British Standards, or by ASTM Standards. The procedure describedbelow follows generally accepted practice.Preparation of apparatus.If the areas of cross-section, a, of the three manometer tubes are not known, they should be determined.See that the cell body is clean and dry, and weigh to the nearest 0.1 g, m1. Measure the mean internaldiameter, D, to the nearest 0,5 mm.Preparation of sample.A cylindrical test specimen may be obtained from a block sample of soft or fairly firm clay by pushinga U-100 cutting shoe, which has a sharp cutting edge. The block sample should be firmly supported ona flat surface, but the sides around the sampling location should not be laterally restrained. The tubeshould be pushed in squarely with a steady pressure, for a distance of about 90 mm. Beforewithdrawing the tube it should be rotated one complete turn to shear off the soil at the end.The sample may be prepared in the usual manner with its axis vertical, for measurement of verticalpermeability, or with its axis horizontal (or parallel to bedding) for measurement of horizontalpermeability (or permeability parallel to bedding). It is essential to ensure that the sample is a tight fit inthe cellbody, and that there are no cavities around the perimeter through which water could pass. Gapsor cavities should be well packed with the fine matrix portion of the soil, or with plasticine. Close thecell.Weigh the sample in the cell to the nearest 0.1 g, m2.Use some of the soil trimmings for determining the moisture content of the sample.Test procedure.Control that valves A, B, C, D, E, and F are closed.Place the permeameter cell containing the sample in the cylinder (see figure).Fill the cylinder with de-aired water.Open valve B and F and when the water has reached level 1 close valve B.Open valve A and start the vacuum pump (50 cm Hg) Due to this vacuum the test sample will becomesaturated with water from the bottom to the top.Close valve A if the water reaches level 2 and stop the vacuum pump. 7. Open respectively valves C, Dand E as long as necessary to fill respectively the tubes 3, 4 and 5.Close valve F.Fill the cylinder up to level 6 with water.Choose for the permeability measurement tube 3, 4 or 5 depending on the expected permeability of thesample.Measure the start level in the tube y1.Open the valve of the in 10 mentioned tube and open valve B. 13.Measure after a certain time interval,t, the water level in the 10 mentioned tube y2.Repeat this several times until you measure a constant value. 15.Measure the water level in the cylinderhO. Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 74. 14/06/2005 Soil mechanics laboratory manual 74Close all the valves.Calculation.The permeability of the sample is calculated by: ⎛ h1 ⎞ 3.84 ∗ a ∗ L ∗ log⎜ ⎟ ∗ 0.00001 Kt = ⎝ h2 ⎠ (m/s) A∗tWhere: Kt = permeability (m/s) a = cross section area of used manometer tube (mm2). A = cross section area of sample in permeameter cell (mm2). t = measured time interval (s). L = length of sample (m). h1 = start level manometer tube = y1 - hO (m). h2 = end level manometer tube =y1-hO (m).If necessary the permeability can be expressed as the permeability at 20 °C by multiplying it by a factorobtained from the temperature conversion table 8.1.1.RemarksPermeability can also be derived from data obtained during an oedometer test.References: Manual of Soil laboratory Testing. Volume 2: Permeability Shear Strength and Compressibility Tests. By: K.H. Head, Pentech Press London, Plymouth.fig 8.2.1 permeameter test falling head Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 75. 14/06/2005 Soil mechanics laboratory manual 759.1 Pocket penetrometer, Heavy duty pocket penetrometerScope of the testThe pocket penetrometer is intended for in situ soil investigation at the surface. It is a lightweight andeasily transportable device for classifying cohesive soils in terms of consistency, determining theapproximate unconfined compressive strength and the estimation of the undrained shear strength.WarningThe readings obtained from the pocket penetrometer do not replace laboratory test results due mainly tothe fact that a small area penetration test is inherently liable to give misleading results. The instrumentshould not be used for obtaining foundation design data. The pocket penetrometer should be regarded as asimple tool to aid the engineer in exploration and in checking and comparing similar types of soil.ApparatusThe pocket penetrometer is composed of a steel tube, a spring, a flat-tippedmeasuring pin, a drag unit, and a scale. When pushing the instrument into theground, the pin encounters a force of the ground. This force compresses thespring. A drag unit is taken along during this operation, which shows on thescale the maximum that has been encountered.The heave duty penetrometer has 3 interchangeable points. The standard pointhas a diameter of 6.35mm. The readings on the penetrometer are given for thispoint the range is up to 1MPa. The largest point, diameter 8.98mm has a areatwice the standard point. The values read on the scale must be divided by 2.Range up to 0.5MPa. The smallest point has a section half of that of thestandard. The values read on the scale must be multiplied by 2. Range up to2MPaTest procedureBefore using the penetrometer ensure that the sliding indicator, is fullyextended to the "0" position. Smooth the surface of the area to be tested. Thepenetrometer is placed perpendicularly on the soil surface and pressure isexerted until the calibration mark (approx. 6 mm) is level with the surface.(with the heavy duty penetrometer up to the narrowing) The penetrometer isnow extracted from the soil and the equivalent unconfined compressivestrength can be read from the scale in MPa.Be sure that the sliding indicator not slides back if the penetrometer isextracted from the soil.The heavy duty penetrometer has a special designed penetration rod whichallows relatively deep penetration of the soil (up to 6cm). This reducemistaken and uncertainties typical of shallow measurements which are oftenaffected by remoulding, drying etc. of the surface.Calculation and interpretation of the test resultsThe calibration of the instrument is based on many tests on clays ranging fromsoft to very hard. These tests were run concurrently with unconfined Figure 0.1.1: Pocketcompression tests on the same series of samples, and the scale readings on the penetrometerpenetrometer correspond to unconfined compressive strength.For the standard point (6.35mm diameter)r readings as indicated on the scaleFor the largest point (8.89mm diameter) readings divided by 2For the smallest point (4.55mm diameter) readings multiplied by 2.In theory, the undrained shear strength of purely cohesive materials can be obtained by dividing the UCSreading by two.Report your values in kPa Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 76. 14/06/2005 Soil mechanics laboratory manual 769.2 Pocket Hand vane testerScope of the testThe vane is used to measure the in-situ undrained shear strength in clays. It is primarily intended for use intrenches and excavation at a depth not influenced by drying and excavation procedure.The range of the instrument is form 0 to 120kPa when two different sizes of vanes are used. The accuracyof the instrument should be within 10% of the reading.ApparatusThe measuring part of the instrument is aspiral-spring. When the Body is turned, the springdeforms and the Dog plate and the Bogy of theinstrument get a mutual angular displacement.The size of this displacement depends on thetorque, which is necessary to turn the vane. Bymeans of a graduated scale on the dial plate theshear strength of the clay is obtained.Two sizes of four-bladed vanes are used: 19mm(readings on the outer-scale) and a 33mm(readings on the inner-scale), which makes itpossible to measure shear strength of 0 to 28 and ,0 to 120 kPaTest procedure- Connect required vane to the inspection vane instrument. Note: When coupling and uncoupling vanes and rods always use both spanners to avoid straining the spring which could ruin the accuracy of this calibrated instrument- Remove the plastic cover- Push vane into the ground to a depth of about 70-80mm with as little sideways movement as possible. N.B.: Do not twist inspection vane during penetration.- Make sure that the pointer needle is set to the zero reading.- Turn body clockwise with a constant speed equivalent to one complete revolution in a minute.- When the pointer needle is not increasing anymore (stays on the same reading) or the pointer even falls back, failure and maximum shear strength is obtained in the clay at the vane.- Holding the body firmly, allow it to return to zero-position. N.B.: Do not allow the body to spring back.- Note the reading on the graduated scale. N.B.: Do not touch or in any way disturb the position of the pointer needle until the reading is taken.- Write down the reading together with position of hole and depth.- When the reading is taken pull the vane up.- After use always put back the plastic cover over de body.Special procedure Geotechnical Laboratory of DGM, Thimphu Bhutan
  • 77. 14/06/2005 Soil mechanics laboratory manual 77When measuring the shear strength at greater depths we can ad extension rods, the friction between theclay and the extension rods can be appreciable preferable we take the measurements in a borehole.CalculationsWith the 19mm vane we read from the outer scale directly the undrained shear strength in kPaWith the 33mm vane we read from the inner scale directly the undrained shear strength in kPaReport your value as the undrained shear strength determined with the hand vane. Geotechnical Laboratory of DGM, Thimphu Bhutan