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Class note for btech students lce 463 pavement structure-soil interaction


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Class note for btech students lce 463 pavement structure-soil interaction

  1. 1. SIGNIFICANCE OF CBR TEST <ul><li>It is very important & a simple penetration test developed to evaluate the strength of subgrade soils for roads & airfields construction </li></ul><ul><li>The California Bearing Ratio (CBR) is a measure of the supporting value of the subgrade </li></ul><ul><li>It is merely a value and it is integral to the process of road design </li></ul><ul><li>In IRC:37-2001, the total crust thickness of the pavement is decided based on CBR value of subgrade for a given traffic </li></ul>
  2. 2. PLATE LOAD TEST (IS:1888-1982) <ul><li>The subgrade modulus is defined as the load intensity ‘p’ applied on the standard plate per unit deflection i.e. k=p/d, where the value of deflection d = 1.25 mm </li></ul><ul><li>The plate load test was originally devised to find the modulus of subgrade reaction of prepared subgrade soil in the Westergaaard’s analysis for wheel load stresses in cement concrete pavements. </li></ul>
  3. 3. APPLICATION OF THE PLATE LOAD TEST <ul><li>K-value is used in the analysis of stresses in rigid pavements. </li></ul><ul><li>The value of radius of relative stiffness (ℓ) depends upon the properties of the pavement slab & the subgrade modulus (k) </li></ul><ul><li>The relation b/w ‘k’ & ‘ℓ’ can be had from the equation below: </li></ul><ul><li>ℓ = [ Eh 3 / 12 k (1-µ 2 )] 0.25 </li></ul><ul><li>K-value has the following applications in pavement design & evaluation apart from the above: </li></ul>
  4. 4. Contd … <ul><li>Repeated plate load test is carried out to find the subgrade support in flexible pavement design by ‘McLeod’ method of flexible pavement design </li></ul><ul><li>The exact load-deflection behaviour of the soil or the pavement layer in-situ for static loads is obtained by conducting plate load test at the site </li></ul><ul><li>The loaded area may be kept equal to the actual loaded area under the design wheel load in field </li></ul><ul><li>The supporting power of the soil subgrade or a pavement layer may be found for the evaluation of pavements </li></ul>
  5. 5. Contd.. <ul><li>The elastic modulus values and the ratio of E1/E2 are found by carrying out plate load tests on the subgrade and the base coarse layer, in flexible pavement design using Burmister’s elastic two layer theory </li></ul><ul><li>Similarly, the ratios E1/E2 and E2/E3 are made use of the design using elastic three layer theoryplate load tests on the subgrade and the base coarse layer, in flexible pavement design using Burmister’s elastic two layer theory </li></ul>
  6. 6. EQUIPMENT & PROCEDURE <ul><li>Equipment: </li></ul><ul><li>Bearing plate </li></ul><ul><li>Loading equipment </li></ul><ul><li>Instruments to measure the applied loads & resulting settlement or deflection </li></ul><ul><li>Bearing plate </li></ul><ul><li>It consists of a mild steel plate of dia 750 mm & thickness 25 mm </li></ul><ul><li>Smaller bearing plates of dia 450 or 300 mm & thickness 25 mm may also be used </li></ul>
  7. 8. Bearing plates <ul><li>Stiffening plates of dia 600, 450, 300 & 225 mm and thickness of 25 mm are used to prevent bending of the large plate of dia 750 mm during application of heavy loads </li></ul><ul><li>It consists of a reaction frame or a dead load and a hydraulic or screw jack of capacity 15,000 kg </li></ul><ul><li>The reaction frame may suitably be loaded to give the reaction load of about 15 tonnes on the plate </li></ul><ul><li>The load applied may be measured either by a proving ring with dial gauge assembly or a load cell </li></ul>Loading equipments
  8. 9. Settlement measurements <ul><li>It may be made by means of three or four dial gauges with an accuracy of 0.01 mm, fixed on the periphery of the nearing plate from an independent datum frame/ bar </li></ul><ul><li>The datum frame should be supported far from the loaded area </li></ul>
  9. 10. PROCEDURE <ul><li>Preparation of test are & seating </li></ul><ul><li>Test set up </li></ul><ul><li>Seating the plate </li></ul><ul><li>Loading procedure & calculation </li></ul><ul><li>Corrections for k-value- (i) Correction of k-value to </li></ul><ul><li>account for smaller plate size </li></ul><ul><li>(ii) Correction of k-value to account for subsequent soaking of </li></ul><ul><li>subgrade </li></ul><ul><li>(iii) Correction of k-value to account for other factors </li></ul>
  10. 11. Preparation of test area & seating <ul><li>The test site is prepared & loose material is removed so that the 750 mm dia plate rests horizontally in full contact with the surface of soil subgrade </li></ul><ul><li>If the k-value of natural ground is to be ascertained, the top soil is stripped off & removed up to a depth of about 250 mm </li></ul><ul><li>If the test is to be got conducted on the compacted fill or subgrade, care is to be taken that the test is conducted at the dry density & moisture content of the soil that are likely to exist subsequent to the construction </li></ul>
  11. 12. Preparation of test area & seating <ul><li>In order to ensure full contact of the plate, oil is applied on the bottom of the plate and the plate is rotated to mark the irregularities and high spots of the seating surface is trimmed </li></ul><ul><li>For granular soil with gravel particles, after leveling of the surface by a straight edge, it may be necessary to apply a thin layer of plaster of Paris & allow the same to set before applying the load </li></ul><ul><li>The level surface of the plate is checked using a bubble tube place on the plate in different positions </li></ul>
  12. 13. Test set up <ul><li>The bearing plate is seated on the prepared surface & the stiffening plates are placed one above the other in the decreasing order of the dia </li></ul><ul><li>The reaction load frame is set up above the center of the plate </li></ul><ul><li>The loading jack is placed centrally above the top of the set of plates & the proving ring with dial gauge b/w the loading jack & the reaction load frame in order to measure the load applied </li></ul><ul><li>Additional spacer discs or cylinders may be required to be placed b/w the jack/load measuring device & the reaction load frame </li></ul>
  13. 16. Test set up <ul><li>Three or four dial gauges are to be uniformly spaced and set up near the rim of the bearing plate from an independent datum frame or bar in order to measure the settlement readings due to load application </li></ul><ul><li>The supports of this datum are placed away from the loading plate as well as the supports of the loading frame such they are not affected by the loading operations </li></ul>
  14. 17. Seating the plate <ul><li>After seating the bearing plate & setting up the loading and settlement measuring devices are installed, a seating load of 310 kg is applied on the 75 cm dia plate, equivalent to a pressure of 0.07 kg/cm 2 for light traffic pavements </li></ul><ul><li>Seating load of 620 kg, or seating pressure of 0.14 kg/cm 2 is applied for heavy traffic pavements </li></ul><ul><li>The seating load may be held till there is no significant settlement and then it is released </li></ul><ul><li>Cyclic loading under seating load may be applied if required, to obtain good seating </li></ul>
  15. 18. LOADING PROCEDURE & CALCULATION (METHOD-1) <ul><li>The seating load applied is released & the load reading is set to zero </li></ul><ul><li>All the settlement dial gauge readings are either set to zero or the initial dial reading are noted corresponding to zero load </li></ul><ul><li>Then the load is applied by means of the jack and it is increased to sufficient magnitude to cause an average settlement of about 0.25 mm and the load is retained, observing the settlement dial readings </li></ul><ul><li>When there is no appreciable increase in settlement or when the rate of settlement is less than 0.025 mm per minute, the load dial reading & the settlement dial readings of the individual dial gauges are noted </li></ul>
  16. 19. Contd… <ul><li>The average of the three of four dial readings is taken as the average settlement of the plate corresponding to the applied load </li></ul><ul><li>The load is then increased till the average settlement increase to a further amount of about 0.25 mm , and the load and the settlement dial readings are noted as before </li></ul><ul><li>The procedure is repeated till the total average settlement of the plate is not less than 1.75 mm </li></ul>
  17. 20. Observation sheet Approx. settlement, mm Settlement dial readings, division Av. Settlement,d mm Load dial (proving ring dial) reading dividions Load/unit area p, kg/cm 2 Remarks 1 2 3 4 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75
  18. 21. Modulus of subgrade reaction (k) <ul><li>K = p/d = p/0.125 kg/cm 3 </li></ul><ul><li>p = pressure corresponding to average settlement, d = 0.125 cm, obtained from the graph, Settlement Vs Pressure </li></ul>0.5 0 0.1 0.2 Mean load pressure, kg/cm 2 Mean settlement, ∆ cm p kg/cm 2 K = p/ ∆ K = p/0.125 kg/cm 2
  19. 22. LOADING PROCEDURE & CALCULATION, METHOD-2 <ul><li>After the application of seating load & hold it for sufficient time, without releasing the seating load, the settlement dial gauges are set to zero and an additional load of 3100kg (31kN) is applied </li></ul><ul><li>If the test is conducted on relatively weak cohesive soils (which is indicated by average settlement exceeding 1.25 mm under 3100kg load on the plate), the applied load is held until the rate of settlement is less than 0.05 mm per minute and after that the readings are noted </li></ul>
  20. 23. Contd… <ul><li>If the test is conducted on granular soils or on relatively strong cohesive soils (which is indicated by average settlement reading much lower than 1.25mm under the applied load of 3100 kg on the plate), additional load of 1550kg is applied on the plate (without releasing the load already applied) and the settlement observations are recorded when the rate of settlement is lower than the specified rate </li></ul><ul><li>This process of applying of applying the load increments are continued until the total load applied on the plate is 9300kg(93kN) </li></ul><ul><li>This load is held for 15 minutes or until the rate of settlement is less than 0.02 mm per minute </li></ul>
  21. 24. Correction of k-value to account for smaller plate size <ul><li>This case is oftenly practiced where soil with high bearing capacity is encountered </li></ul><ul><li>In such case, very heavy reaction load is needed to conduct standard plate bearing test using 75 cm dia plate to find the standard k-value </li></ul><ul><li>If the reaction load available is not adequate, a plate of dia smaller plate size of 30 cm is often adopted </li></ul><ul><li>For design of rigid pavement for highways, plate size of 30 cm is often made use of for determination of k-value </li></ul>
  22. 25. Contd.. <ul><li>In such cases, k 1 is determined using smaller or non-standard plate of radius a 1 , and this value is to be multiplied by a correction factor in order to determine the subgrade modulus, k corresponding to the standard plate dia 2a = 75 cm </li></ul><ul><li>The subgrade modulus k 1 of a soil is inversely proportional to the radius a 1 of the plate & therefore k.a. is a constant </li></ul><ul><li>Hence, if ‘k’ is the subgrade modulus corresponding to standard plate of radius ‘a’, then: </li></ul><ul><li>ka = k 1 a 1 </li></ul><ul><li>k= k 1 a 1 /a </li></ul>
  23. 26. Contd… <ul><li>Thus, the ratio (a 1 /a) is the correction factor to be applied to the subgrade modulus k 1 determined using non-standard plate of radius a 1 </li></ul><ul><li>If a 30 cm dia is used for finding the subgrade modulus k 30 , the corresponding factor to be applied to obtain the k 75 -value corresponding to standard plate of dia 75 cm is = 15/37.5 = 0.4 </li></ul><ul><li>i.e. k 75 = 0.4k 30 </li></ul>
  24. 27. Correction of k-value to account for subsequent soaking of subgrade <ul><li>K-value found by plate load test depends on the moisture content & density of the soil at the time of testing </li></ul><ul><li>Subsequent increase in moisture content of the subgrade due to soaking of the soil will result in decrease in k-value (ks) </li></ul><ul><li>For the purpose of pavement design, it is necessary to determine this decreased k-value (ks) under the highest possible field moisture content or under soaked condition </li></ul>
  25. 28. Contd.. <ul><li>As it is not practicable to conduct plate load tests in the field every time under such adverse moisture condition, a simplified approach is adopted to apply a correction factor for typical soil </li></ul><ul><li>The correction factor to be applied is determined from the results of two sets of consolidation tests carried out on undisturbed soil samples collected from the same location of the subgrade </li></ul><ul><li>One consolidation test is conducted on sample at the field moisture content & the other test after allowing the specimen to absorb water in the consoli-meter and getting saturated </li></ul>
  26. 29. Contd.. <ul><li>The first undisturbed soil specimen at the field moisture content is placed in the consolido-meter and a load equivalent to the seating load to cause a pressure of 0.07 kg/cm 2 on the specimen is applied </li></ul><ul><li>This seating load is allowed to remain on the specimen until there is no further settlement as indicated by the consolidation dial gauge and the initial settlement dial reading is set to zero </li></ul><ul><li>An additional load is applied to cause a pressure of 0.7kg/cm 2 on this consolidation test specimen and allowed to remain till there is no vertical movement & then the settlement dial reading is recorded </li></ul>
  27. 30. Contd… <ul><li>The deformation or settlement of the specimen under the applied load is given by difference between the initial and final readings of the settlement dial & let this value be = d, mm </li></ul><ul><li>The second specimen is placed in the consolidometer with water in it and is allowed to get saturated under the initial applied seating pressure of 0.07 kg/cm 2 and the load is allowed to remain on the sample till there is no vertical movement and then the initial dial gauge reading is set to zero </li></ul><ul><li>An additional load is applied to cause a pressure of 0.70kg/cm 2 on this soaked specimen and is allowed to remain till there is no vertical movement & then final settlement dial reading is recorded </li></ul>
  28. 31. Contd.. <ul><li>The difference between the initial & final readings of the settlement dial of the soaked specimen is determined = ds mm </li></ul><ul><li>The settlement value, ds of soaked specimen will be higher than the settlement value d of the unsoaked specimen </li></ul><ul><li>The ratio (d/ds), which is less than 1.0, is taken as the correction factor to be applied to estimate the soaked subgrade modulus ks </li></ul><ul><li>The estimated value of subgrade modulus under soaked condition, ks is given by: </li></ul><ul><li>Ks =k d/ds </li></ul>
  29. 32. Correction of k-value to account for other factors <ul><li>Under the heavy loads, the large bearing plate of 75 cm dia may bend at the centre w.r.t. the rim </li></ul><ul><li>A correction factor to account for the bending of the plate may be applied using chart </li></ul><ul><li>Correction may also be required to be applied on the load-deflection curve, when it deviates from the straight line, particularly when the loads applied on the plate are high, upto 9300 kg load when the subgrade modulus exceeds 5.55 kg/cm 3 </li></ul>
  30. 33. DYNAMIC CONE PENETROMETER TEST <ul><li>Applications & Principle of the test: </li></ul><ul><li>It is a field test equipment widely used for the evaluation of the properties of the materials at site, such as subgrade soil and the materials below the pavement without the need to cut open the pavement layers </li></ul><ul><li>The basic principle of the test is based on the fact that the resistance to penetration of a standard cone pushed into a layer depends on the strength characteristics of the materials in the layer including its dry density & moisture content </li></ul>
  31. 34. IT’S USEFULNESS <ul><li>It is useful for assessing the boundaries between different layers with different strength and density & thus to estimate the thickness of the layer </li></ul><ul><li>It is generally used to evaluate the properties of soil layers in the field, up to a depth of 800 mm without an extension rod and up to 1200 mm with an extension rod </li></ul>
  32. 35. EQUIPMENT <ul><li>Steel rod having 15.8 mm dia with a replaceable cone tips. The tip has an included angle of 60 degrees and a dia of 20 mm at the base </li></ul><ul><li>Hammer of 8 kg is used & which is dropped from a fixed ht of 575 mm, a coupler assembly and a handle for holding the rod in a vertical position </li></ul><ul><li>A hammer of 4.6 kg wt. may be used on weak materials, where 8.0 kg hammer may produce excessive penetration per blow; however the standard drop ht is to be maintained same </li></ul>
  33. 36. EQUIPMENT <ul><li>A vertical scale graduated in increments of 1.0mm or measuring rod longer than the longest drive rod, if the drive rods are not graduated </li></ul><ul><li>Disposal cone tips </li></ul><ul><li>Extraction jack, if disposal cone tips are not used </li></ul><ul><li>Tools for assembling the DCP test equipment at the test site </li></ul>
  34. 38. TESTING PROCEDURE <ul><li>The tips of the cone is checked carefully from any damage before the test </li></ul><ul><li>All the connections should be tightened securely </li></ul><ul><li>The DCP assembly if held vertically by the operator & the cone is seated such that the top of the widest part of the cone is flush with the surface the layer to be tested </li></ul><ul><li>The initial reading of the graduate drive rod is noted to the nearest mm </li></ul>
  35. 39. <ul><li>The hammer is released from the standard drop ht & the penetration readings and the corresponding number of hammer blow is determined </li></ul><ul><li>The penetration readings & the corresponding number of hammer blows may be recorded in increments of about 10 mm penetration </li></ul><ul><li>Alternatively, the penetration scale readings may be recorded after a set of 5 or 10 blows </li></ul><ul><li>The no. of blows b/w each reading may be decided depending upon the extend of penetration or the resistance to penetration offered by the material </li></ul>
  36. 40. <ul><li>For hard pavement layers like granular sub-base/stabilized layers, the readings may be taken at every 5-10 blows whereas for weak soil layers, it may be appropriate to record readings for every blow or two blows </li></ul><ul><li>However, too less readings are recorded, there is a possibility of missing the weak spots and it may be difficult to identify the boundaries of different layers accurately </li></ul><ul><li>If the total depth of penetration is more than 400 to 500 mm, the extension rods of the DCP are to be used </li></ul><ul><li>The metre scale has to be detached from the base plate and the bottom rod is to be split to accept the extension rod and the test is continued </li></ul>
  37. 41. DATA & RECORDING OF RESULTS <ul><li>Table 1 shows the format for the recording of the data and some typical observations taken during a DCP test for computation of the penetration rate or the DCP value </li></ul><ul><li>A graph is plotted with the cumulative values of number of blows on the X-axis and the depth of penetration in mm on the Y-axis </li></ul><ul><li>The DCP value of a layer of material is the penetration value in mm per blow at that depth </li></ul>
  38. 42. DATA & RECORDING OF RESULTS <ul><li>The penetration rate or the slop of the plot represents the strength characteristics of the material in the layer </li></ul><ul><li>The change in penetration rate or change in slope of the curve indicates change in material type </li></ul><ul><li>The boundaries between the layers and the depth of the layers may be identified by the change in the rate of penetration </li></ul>
  39. 43. Format for recording data Sl no No. of blows Penetration, mm Cumulative no. of blows Cumulative depth, mm 1 0 33 0 0 2 10 53 10 20 3 10 83 20 50 4 10 104 30 71 5 10 125 40 92 6 10 145 50 112 7 10 165 60 132 8 10 183 70 150 9 10 200 80 167
  40. 44. Format for recording data Sl no No. of blows Penetration, mm Cumulative no. of blows Cumulative depth, mm 10 10 218 90 185 11 10 230 100 197 12 10 252 110 219 13 10 275 120 242 14 5 295 125 262 15 5 314 130 281 16 5 333 135 300 17 5 352 140 319 18 5 370 145 337 19 5 390 150 357 20 5 405 155
  41. 45. Typical plot of no of blows Vs depth of penetration SUBGRADE SUB-BASE COURSE 170 MM BASE COURSE 200 MM SURFACE COURSE 50 MM
  42. 46. INTERPRETATION OF RESULTS <ul><li>Correlations have been established by various agencies b/w DCP value and the CBR values, so that the results can be compared & later used for pavement design </li></ul><ul><li>Correlations have also been established b/w the rate of penetration and the resilient modulus of the soil layers </li></ul><ul><li>The DCP may also be used to check the quality of construction at the site </li></ul>
  43. 47. <ul><li>The penetration rate per blow is used to estimate the CBR value or the shear strength using appropriate correlation </li></ul><ul><li>The general equation recommended by some of the organizations are given below: </li></ul><ul><li>US Corps of the Engineers: For all soils except for CL & CH soils having CBR value less than 10% </li></ul><ul><li>CBR = (292)/(DCP) 1.12 </li></ul><ul><li>Where, DCP is the penetration per blow </li></ul>INTERPRETATION OF RESULTS
  44. 48. <ul><li>For CL soils with CBR < 10, </li></ul><ul><li>CBR = 1/(0.017019xDCP) 2 </li></ul><ul><li>For CH Soils, CBR = 1/(0.002871 x DCP) </li></ul><ul><li>TRRL of UK (vide Road Note 8, with 60 0 cone) </li></ul><ul><li>Log 10 (CBR) = 2.48 – 1.057 Log 10 DCP (mm/blow) </li></ul>
  45. 49. MERIT & DEMERIT OF DCP <ul><li>The DCP can be used to assess the density of a fairly uniform material & therefore, DCP may be used to check the quality of construction especially the amount of compaction </li></ul><ul><li>The test is intended to evaluate the in-situ strength of a material under existing field conditions </li></ul><ul><li>Weak spots beneath the pavement may be identified & rectified </li></ul><ul><li>DCP doesn’t measure the density directly </li></ul><ul><li>Difficult to work on granular layers, crusher run macadam, wet mix macadam etc. </li></ul><ul><li>Thick layers of bituminous surface & binder course should be removed by core drilling, prior to starting the DCP test </li></ul><ul><li>The cone will have to be replaced after 15 tests in hard material hence not economical </li></ul>
  46. 50. RELATIVE DENSITY TEST IS:2720, P-14 <ul><li>Relative density is an arbitrary character of sandy deposit </li></ul><ul><li>In real sense, relative density expresses the ratio of actual decrease in volume of voids in a sandy soil to the maximum possible decrease in the volume of voids i.e. how far the sand under investigation can be capable to the further densification beyond its natural state </li></ul><ul><li>Determination of relative density is helpful in compaction of coarse grained soils and in evaluating safe bearing capacity in case of sandy soils </li></ul><ul><li>For very dense gravelly sand, it is possible to obtain relative density greater than one. This means that such natural dense packing could not be obtained in the laboratory </li></ul><ul><li>Porosity of a soil depends on the shape of grain, uniformity of grain size and condition of sedimentation </li></ul><ul><li>Hence porosity itself does not indicate whether a soil is in loose or dense state </li></ul><ul><li>The degree of compaction of cohesionless soil can be stated in terms of relative density </li></ul>
  47. 51. RELATIVE DENSITY TEST <ul><li>This information can only be obtained by comparing the porosity or void ratio of the given soil with that of the same soil in its loosest and densest possible state and hence the term, relative density is introduced </li></ul>DEFINITIONS Relative density or density index is the ratio of the difference between the void ratios of a cohesionless soil in its loosest state and existing natural state to the difference between its void ratio in the loosest and densest states Where, e max = void ratio of coarse grained soil ( cohesionless) in its loosest state e min = void ratio of coarse grained soil ( cohesionless) in its densest state e = void ratio of coarse grained soil ( cohesionless) in its natural existing state in the field
  48. 52. EQUIPMENT CONSIST OF <ul><li>Vibrating Table: </li></ul><ul><li>Steel table with a cushioned steel vibrating deck. It has a frequency of approx. 3600 vibrations per min under 115 kg load. Suitable for operation on 220 V, 50 Hz, single phase, AC supply </li></ul><ul><li>Cylindrical Metal Unit Weight Mould, 3000 ml capacity </li></ul><ul><li>Molds. Cylindrical metal unit weight molds of 0.1 and 0.5 cu ft capacity </li></ul><ul><li>Guide Sleeves </li></ul><ul><li>Surcharge Base Plates </li></ul><ul><li>Surcharge Weights </li></ul><ul><li>Surcharge Base Plate Handle </li></ul><ul><li>Dial Indicator Gauge Holder </li></ul><ul><li>Dial Indicator </li></ul><ul><li>Calibration Bar </li></ul>
  49. 53. EQUIPMENTS
  50. 54. Calibration <ul><li>Determine the volume of the mold by direct measurement and check the volume by filling with water as provided in a) </li></ul><ul><li>Determine the initial dial reading for computing the volumes of the specimen as provided in b) </li></ul><ul><li>a) Volume by Direct Measurement. Determine the average inside diameter and height of the mold to 0.001 inches. Calculate the volume of the 0.1 cu ft mold to the nearest 0.0001 cu ft and the 0.5 cu ft mold to the nearest 0.0001 cu ft. Calculate also the average inside cross-sectional area of the mold in square feet </li></ul>
  51. 55. b) Initial Dial Reading. Determine the thickness of the surcharge base plate and the calibration bar to 0.001 inches using a micrometer. Place the calibration bar across a diameter of the mold along the axis of the guide brackets. Insert the dial indicator gage holder in each of the guide brackets on the measure with the dial gage stem on top of the calibration bar and on the axis of the guide brackets. The dial gage holder should be placed in the same position in the guide brackets each time by means of match marks on the guide brackets and the holder.
  52. 56. <ul><li>Obtain six dial indicator readings, three on the left side and three on the right side, and average these six readings </li></ul><ul><li>Compute the initial dial reading by adding together the surcharge base plate thickness and the average of the six dial indicator readings and subtract the thickness of the calibration bar </li></ul><ul><li>The initial dial reading is constant for a particular measure and surcharge base plate combination </li></ul>Sample Select a representative sample of soil. The weight of sample required is determined by the maximum size of particle as follows:
  53. 57. Maximum Size of Soil Particle Weight of Sample Required(lb.) Pouring Device to be used in Minimum Density Test Size of Mold to be used(cu. ft.) 3 inch 100 Shovel or extra large scoop 0.5 1 – ½ inch 25 Scoop 0.1 3/4 inch 25 Scoop 0.1 3/8 inch 25 Pouring Device (1&quot; diameter spout) 0.1 No 4 (4.75 mm) 25 Pouring Device (1/2&quot; diameter spout) 0.1
  54. 58. <ul><li>Dry the soil sample in an oven at a temperature of 230 ± 9 F (110 ± 5C). Process the soil through a sieve with openings sufficiently small to break up all weakly cemented soil particles </li></ul>
  55. 59. <ul><li>Preparation of the Sample </li></ul><ul><li>Dry the soil sample in a thermostatically controlled electric oven </li></ul><ul><li>Cool in the sample in a desicator </li></ul><ul><li>Segregate soil lumps with out breaking individual particles </li></ul><ul><li>Sieve it through the required sieve size </li></ul>
  56. 60. Minimum Density Procedure <ul><li>Select the pouring device and mold according to the maximum size of particle as indicated on the chart in Sample section. Weigh the mold and record the weight. Use oven dried soil </li></ul><ul><li>b) Place soil containing particles smaller than 3/8 inch as loosely as possible in the mold by pouring the soil from the spout in a steady stream while at the same time adjusting the height of the spout so that the free fall of the soil is 1 inch. At the same time, move the pouring device in a spiral motion from the outside toward the center to form a soil layer of uniform thickness without segregation </li></ul>Determine the minimum density (zero relative density), (maximum void ratio) as follows:
  57. 61. b ) Fill the mold approximately 1 inch above the top and screed off the excess soil level with the top by making one continuous pass with the steel straight-edge. If all excess material is not removed, an additional continuous pass shall be made but great care must be exercised during the entire pouring and trimming operation to avoid jarring the mold Contd… ….. c) Place soil containing particles larger than 3/8 inch by means of a large scoop (or shovel), hold as close as possible to and just above the soil surface to cause the material to slide rather than fall onto the previously placed soil. If necessary, hold large particles back by hand to prevent them from rolling off the scoop. Fill the mold to overflowing but not more than 1 inch above the top. With the use of the steel straightedge (and the fingers when needed), level the surface of the soil with the top of the measure in such a way that any slight projections of the larger particles above the top of the mold shall approximately balance the larger voids in the surface below the top of the mold d) Weigh the mold and soil and record the weight
  58. 62. Maximum Density Procedure <ul><li>a) Dry Method : </li></ul><ul><li>Mix the sample of oven dried soil to provide an even distribution of particle sizes with as little segregation as possible </li></ul><ul><li>Assemble the guide sleeve on top of the mold and tighten the clamp assemblies so that the inner wall of the sleeve is in line with the inner wall of the mold. Tighten the lock nuts on the two set screws equipped with lock nuts. Loosen the clamp assembly having no lock nuts. Remove the guide sleeve. Weigh the empty mold and record the weight </li></ul><ul><li>Fill the mold with soil by the procedure specified in b) or c). Min. Den. Proc </li></ul>Determine the maximum density (100 percent relative density, minimum void ratio) by either the dry or wet method as follows:
  59. 63. <ul><li>Attach the guide sleeve to the mold and place the surcharge base plate on the soil surface. Lower the surcharge base plate, using a hoist in the case of the 0.5 cu ft mold </li></ul><ul><li>Set the vibrator control at maximum amplitude and vibrate the loaded specimen for 8 minutes. Remove the surcharge weight and guide sleeve from the mold. Obtain and record dial indicator gage readings on two opposite sides of the surcharge base plate, average, and record the average. Weigh the mold and soil, if this has not been done in the minimum density determination or if an appreciable amount of fines has been lost during vibration. Record the weight </li></ul>
  60. 64. b) Wet Method <ul><li>The wet method may be conducted on oven dried soil to which sufficient water is added or, if preferred, on wet soil from the field. If water is added to dry soil, allow a minimum soaking period of ½ hour </li></ul><ul><li>Fill the mold with wet soil by means of a scoop or shovel. Add sufficient water to the soil to allow a small amount of free water to accumulate on the surface of the soil during filling. The correct amount of water can be estimated by a computation of the void ratio at expected maximum density or by experimentation with the soil. During and just after filling the mold, vibrate the soil for a total of 6 minutes. During this period, reduce the amplitude of the vibrator as much as necessary to avoid excessive boiling and fluffing of the soil, which may occur in some soils. During the final minutes of vibration, remove any water appearing above the surface of the soil </li></ul>
  61. 65. Wet Method <ul><li>Assemble the guide sleeve, surcharge base plate, and surcharge weight as described in Paragraph a) 4). </li></ul><ul><li>Vibrate the specimen and surcharge weight for 8 minutes. After the vibration period, remove the surcharge weight and guide sleeve from the mold. Obtain and record dial indicator gage readings on two opposite sides of the surcharge base place. Carefully remove the entire wet specimen from the mold and dry to constant weight. Weigh dry specimen and record </li></ul>
  62. 66. Calculations <ul><li>Minimum Density </li></ul><ul><li>Calculate minimum density in pounds per cubic foot, as follows: </li></ul>٧ d min = Ws/Vc Maximum Density. Calculate maximum density, in pounds per cubic foot as ٧ d max = Ws/Vf
  63. 67. Where: Ws = weight of dry soil, pounds Vc = calibrated volume of mold, cubic feet Vf = volume of soil, cubic feet = Vc – (Ri – Rf ) / 12 x cu. ft. Rf = final dial gage reading on the surcharge base plate after completion of the vibration period, inches Ri = initial dial gage reading, inches A = cross-sectional area of mold, square feet Density of Soil in Place. Determine the density of the soil in place, Yd, in a compacted fill or a natural deposit in accordance with either the Method of Test for Density of Soil in Place by the Sand-Cone Method ASTM Designation: D1556 or the Method of Test for Density of Soil in Place by the Rubber-Balloon Method ASTM Designation: D2167
  64. 68. <ul><li>d) Relative Density. Calculate relative density, Dd, expressed as a percentage as follows: </li></ul>Dd = ٧ d max ( ٧ - ٧ d min) ٧ ( ٧ d max - ٧ d min) X 100 or in terms of void ratio: Dd = ( emax - e) ( emax - emin) x 100 Where: e = the volume of voids divided by the volume of solid particle emax = void ratio in loosest state emin = void ratio in most compact state
  65. 69. Tests used for evaluating the strength properties of soils <ul><li>(1) Shear Tests </li></ul>Direct Shear Test Triaxial compression Unconfined Compression (2) Bearing Test Plate Bearing Test (3) Penetration Tests California Bearing Ratio Test Cone Penetration Test
  66. 70. <ul><li>This is the simplest and oldest and the most common test for evaluating the shearing resistance of soils </li></ul><ul><li>In this test, the failure of the specimen is caused along a pre-determined plane b/w the two halves of the shear box in which the soil is placed </li></ul><ul><li>It is comprising of lower & upper halves coupled together with two removable pins with space to place the soil specimen, base plate, grid plates, porous stone plates and loading pad </li></ul><ul><li>The lower frame is held stationary and an upper one that can be moved in a horizontal direction </li></ul>Direct Shear Test
  67. 71. <ul><li>Soil with maximum particle size of 4.75 mm are generally tested under drained conditions </li></ul><ul><li>Shear box of larger size may be taken for gravelly soils </li></ul><ul><li>The internal dimensions of the shear box and the plates are such that the soil specimen is of size 60 x 60 mm cross-section and thickness of about 20mm for soil passing 4.75 mm IS sieve </li></ul><ul><li>The surfaces of contact b/w the soil and the porous stones are grooved in order to prevent slippage b/w the sample and the stone surfaces </li></ul><ul><li>A vertical load is applied and then the horizontal shearing force is applied to the upper frame </li></ul>
  68. 72. Shear Box Test Apparatus
  69. 74. <ul><li>Both the vertical & horizontal displacements are measured with the help of the dial gauges </li></ul><ul><li>The normal load is varied and the maximum horizontal load to cause shear failure for each normal is measured </li></ul><ul><li>The horizontal shear loads are applied at the desired strain rate (usually at 0.1 to 0.2 mm/min) and the readings of shear load (indicated by dial gauge readings) and corresponding longitudinal displacements are recorded at regular intervals </li></ul><ul><li>The test is continued up to failure load (maximum value of shear load) or 20% of longitudinal displacement, whichever occurs first </li></ul><ul><li>The values of failure shear load and corresponding displacement are recorded </li></ul>
  70. 75. Observation Sheet Details of specimen: Dimensions: Moisture content: Rate of strain: Normal load applied: Area: Weight: Bulk density: Date of Testing: Shear displacement Corrected area Shear force dial gauge reading Shear force Shear stress Vertical dial readings
  71. 76. Cross section area correction <ul><li>The corrected cross section area of the specimen at failure shear load is calculated from the relation: </li></ul><ul><li>Corrected area = A 0 [(1- Ә )/3] </li></ul><ul><li>Where, A 0 is the initial c/s area of the specimen in cm 3 and Ә is the horizontal displacement in cm </li></ul><ul><li>The values of norm stress and shear stress at failure are calculated from the corresponding corrected area of c/s for each of the normal loads applied (Refer Table 2) </li></ul>
  72. 77. Table 2. Summary of direct shear test results Test No. Shear displacement at failure Corrected area Normal load applied Normal stress Shear force at failure Shear stress at failure
  73. 78. <ul><li>By repeating the direct shear test at different magnitude of normal load, a graph is plot with normal stress values on the X-axis and shear stress values on the Y-axis </li></ul><ul><li>The values of cohesion, C and angle of internal friction or the friction of angle , Ф are obtained from the graph </li></ul>
  74. 79. <ul><li>From the mean straight line joining the four or more points, the values are obtained </li></ul><ul><li>Unit of cohesion, kg/cm 3 = intercept on Y-axis, corresponding to zero normal stress </li></ul><ul><li>Angle of shearing resistance or angle of internal friction, Ф = slope of the normal stress – shear stress line </li></ul>
  75. 80. Advantages of direct shear test <ul><li>It is a simple test </li></ul><ul><li>Easy to conduct the test </li></ul><ul><li>Less time consuming in comparison to TCT </li></ul>
  76. 81. Disadvantages <ul><li>There is non-uniform shear stress distribution within the failure plane </li></ul><ul><li>Drainage condition cannot be controlled </li></ul><ul><li>The failure is forced to take place along the pre-determined horizontal surface passing through the two halves of the shear box, and not through the weakest plane within the specimen </li></ul><ul><li>In view of the above limitations, for more precisely determining shear strength of soils, TCT is preferred </li></ul>
  77. 82. T RIAXIAL C OMPRESSION T EST <ul><li>This test overcomes the deficiencies of the direct shear test </li></ul><ul><li>The specimen is first subjected to an all-round pressure ( σ 3) and then the axial stress is increased till the specimen fails in shear </li></ul><ul><li>In this test, the plane of failure is not pre-determined </li></ul><ul><li>In this test, the cylindrical specimen (ht. to dia. ratio of 2) is enclosed in a water-tight rubber membrane and is placed inside the a transparent perspex cylinder </li></ul>
  78. 83. Principle of triaxial shear test
  80. 85. <ul><li>The specimen is capped with a metal disc at top and a porous stone disc at bottom </li></ul><ul><li>The pressure of liquid inside the chamber can be brought to a desired value ( σ 3 ) </li></ul><ul><li>The vertical load to the specimen is provided by piston until the specimen fails & the normal load applied starts decreasing </li></ul><ul><li>The total vertical pressure on the specimen ( σ 1 ) is equal to ( σ d + σ 3 ) </li></ul><ul><li>The normal pressure applied on the specimen is also called deviator stress ( σ d ) </li></ul>
  81. 86. <ul><li>This deviator stress ( σ d ) is obtained by dividing the vertical load applied by the area of cross section of the specimen </li></ul><ul><li>The experiment is repeated for various lateral pressure ( σ 3 ) as required </li></ul><ul><li>To find out the values of cohesion & angle of internal friction, tests are repeated at three or four different lateral pressure values such as 0, 0.75, 1.5, 2.25 & 3.0 kg/cm 2 </li></ul><ul><li>The advantage of the test lies in the facilities of observing the specimen through the transparent cell </li></ul>
  82. 87. <ul><li>The deformation of the specimen in the vertical direction is also measured </li></ul><ul><li>The analysis of the results is done by a Mohr’s diagram </li></ul><ul><li>Mohr’s circle is drawn by constructing a semi-circle whose centre is at a distance of ½ ( σ 3 + σ 1 ) from the origin and having a diameter equal to the deviator stress, σ d equal to σ 1 - σ 3 </li></ul><ul><li>By inspection, a common tangent is drawn to all such circles </li></ul><ul><li>This is known as Mohr’s rupture envelope </li></ul>
  83. 88. <ul><li>The intercept of the envelope line on the Y-axis gives the value of cohesion, C, and the slope of the line gives the value of the angle of internal friction, Ф </li></ul><ul><li>For plotting the best envelope line, a number of semicircles are needed </li></ul><ul><li>Though theoretically, two would be sufficient </li></ul><ul><li>Generally, three or more semicircles are drawn, having different values of the lateral confining pressure </li></ul>
  84. 89. Correction for area of cross section <ul><li>It is mandatory to correct the deviator stress values for the increased area of cross section of the specimen due to loading </li></ul><ul><li>Assuming that the volume of specimen remains constant and the area of cross section of the specimen increases uniformly </li></ul><ul><li>Then, the corrected value of deviator stress σ d is calculated from the relation given below </li></ul><ul><li>σ d = P / Ao [1-( ∆ / Io )] </li></ul><ul><li>Where, P= applied load, Ao = original area of cross section, </li></ul><ul><li>∆ = deformation of specimen, Io = original length of specimen </li></ul>
  85. 90. Mohr’s circles
  86. 91. Observation Table
  87. 93. <ul><li>The triaxial test can be performed under a variety of conditions as per highway engineer requirements </li></ul>Application 1 Unconsolidated undrained test It is performed on cohesive soils for determining stability of high embankments during construction or immediately after construction 2 Consolidated undrained test Performed on cohesive soils for stability of high embankments during construction and the long-term stability
  88. 94. Modulus of deformation or Modulus of elasticity “E” Besides finding the values of c & Ф of the soil, the load-deformation characteristics of the soil are often judged from the stress-strain curves The value of modulus of elasticity “E” or more appropriately, the modulus of deformation, Ed is also obtained from the stress-strain diagram The modulus of deformation is the ratio of stress to strain at an arbitrary point on the stress-strain curve This point may be decided based on allowable % of strain or anticipated stress value Ed = σ d / ε where, ε is the selected strain value and σ d is corresponding value of deviator stress obtained from the triaxial test at selected value of confining pressure σ 3
  89. 95. Usefulness of triaxial test <ul><li>Analysis of stability of slopes of highway embankments, knowing the shear strength parameters C & Ф of materials, the shearing resistance of the material can be worked out using Coulomb’s equation, </li></ul><ul><li>S = C + σ tan Ф </li></ul><ul><li>Settlement analysis of high embankments </li></ul><ul><li>Design of retaining walls </li></ul><ul><li>Design of well foundations </li></ul><ul><li>Design of shallow footings </li></ul>
  90. 96. <ul><li>Modulus of deformation “ Ed” values of soil subgrade and other pavement materials are determined from triaxial test results </li></ul><ul><li>These values are made use of in the analysis of stresses in the pavement layers and in design of pavements </li></ul><ul><li>Triaxial test results on bituminous mixes are made use of in one of the methods of bituminous mix design </li></ul>
  91. 97. U NCONFINED C OMPRESSION T EST <ul><li>This tests are carried on cohesive soils and stabilized soil specimens </li></ul><ul><li>It is a very simple test and it is easy to carry out on specimens having adequate compressive strength </li></ul><ul><li>This test is very useful for stabilized soil mixes and cohesive/ clayey soils in order to determine or compare the compressive strength values </li></ul><ul><li>However, the test results are not useful to find the C and Ф values of soil specimens </li></ul>
  92. 98. <ul><li>It may be considered as a special case of trial axial compression test when the lateral confining pressure σ 3 is equal to zero </li></ul><ul><li>Therefore, the cylindrical test specimen may be directly placed in a compression testing machine and the compressive load applied </li></ul><ul><li>The test apparatus comprising of a strain-controlled compression testing machine with proving ring assembly to measure load applied, dial gauge to measure deformation. Apart from these, moulds & tools to prepare test specimens </li></ul>
  93. 99. <ul><li>The maximum size of particle in the test shall not exceed one-eight of the specimen dia. </li></ul><ul><li>Cylindrical specimens of dia. 38 mm or more, having ht. to dia. ratio 2.0 to 2.5 are prepared using either undisturbed or remolded samples </li></ul><ul><li>The initial length, diameter and weight of the test specimens are measured </li></ul><ul><li>Then, the test specimen is placed in the CTM, load and deformation dials adjusted and compressive load is applied at controlled strain rate of 0.5 mm per minute </li></ul><ul><li>The loading test is continued until the load sustained start decreasing after reaching a maximum load value P </li></ul>
  94. 100. <ul><li>or until the axial deformation of the specimen is 20% of the original length and the maximum load and corresponding axial deformation values are recorded </li></ul><ul><li>The axial strain at failure , e is given by: </li></ul><ul><li>e = ∆/ Lo </li></ul><ul><li>where, ∆ is the change in length of the specimen at failure and Lo is the initial length of the specimen </li></ul><ul><li>The average area of cross section A of the specimen at the failure strain is given by: </li></ul><ul><li>A = Ao/(1-e) </li></ul><ul><li>where, Ao is the initial average area of cross section of the specimen </li></ul>
  95. 101. <ul><li>Compressive strength σ o of the specimen is given by: </li></ul><ul><li>σ o = P/A </li></ul><ul><li>where, P = the failure load and A is the average cross section area of the specimen at failure load </li></ul>For an UCT, the Mohr’s circle rupture passes through the origin The envelope than becomes a straight line parallel to the x-axis at a distance of c . The radius of circle is also c Thus, c = qu/ 2, where, qu = unconfined compressive strength The bearing capacity of clayey soils under footings can be determined from the following formula qd = 5.70 c ----------------- (1a) = 2.85 qu ---------------- (1b)
  96. 102. Advantages <ul><li>In this test, the lateral pressure is taken as zero, hence, it becomes extremely simplified </li></ul><ul><li>It can be used in the field because of its simplicity & undisturbed samples can be tested easily </li></ul><ul><li>It is one of the convenient immediate tests on saturated or nearly saturated clays </li></ul><ul><li>In any case, since the UCT is conducted on saturated clays, a safe assumption can be made that Ф = 0 </li></ul>
  97. 103. Disadvantages <ul><li>The exact determination of c & Ф is not possible since only one circle is drawn </li></ul>
  98. 104. Factors affecting soil strength <ul><li>Soil type </li></ul><ul><li>Particle size distribution </li></ul><ul><li>Dry density </li></ul><ul><li>Moisture content </li></ul><ul><li>Extent of confinement </li></ul><ul><li>Permeability </li></ul>
  99. 105. Soil type <ul><li>Granular soils have generally higher strength than fine-grained soils </li></ul>
  100. 106. Particle size distribution <ul><li>The size, shape and distribution of the particle determine the internal friction and cohesion </li></ul>
  101. 107. Dry density <ul><li>The degree of compaction of soils governs its strength to a great extent </li></ul>
  102. 108. Moisture content <ul><li>The amount of water contained in a soil affects the density, the cohesion and internal friction of soils </li></ul>Sandy soils in dry state Loose Ф = 28.5 0 -34 0 c = 0-1.0 MN/m 2 Dense Ф = 35 0 -46 0 c = 0-2.0 MN/m 2 Silty soils Loose Ф = 27 0 -30 0 c = 0-3.0 MN/m 2 Dense Ф = 30 0 -35 0 c = 0-4.0 MN/m 2 Clayey soils Ф = 0 0 -15 0 c = 0.7-14.N/m 2
  103. 109. Extent of confinement <ul><li>Soils like sands exhibit greater strength when confined than when unconfined </li></ul>
  104. 110. Permeability <ul><li>The rate of drainage of water as loading takes place affects the soil strength. The more effective the drainage, the better is the shearing resistance </li></ul>
  105. 111. PERMEABILITY TEST <ul><li>Permeability of soil is the ease with which water can flow through it </li></ul><ul><li>Confining of road construction, it is taken into account for sub-surface drainage considerations of a pavement structure </li></ul><ul><li>The basic law on permeability is based on Darcy’s law </li></ul><ul><li>It is given by </li></ul><ul><li>Q = k x i x A </li></ul>Where Q = quantity of flow or discharge K = coefficient of the permeability of the media I = hydraulic gradient A = C/s area perpendicular to the direction of flow
  106. 112. Factors affecting coefficient of permeability <ul><li>Particle size of soil </li></ul><ul><li>Particle shape of soil </li></ul><ul><li>Relative distribution (gradation) </li></ul><ul><li>Degree of saturation </li></ul><ul><li>Degree of compaction </li></ul><ul><li>Connectivity of water passages </li></ul><ul><li>The coefficient of permeability is determined either in the laboratory by </li></ul><ul><li>the constant head test </li></ul><ul><li>the falling head test </li></ul>
  107. 113. Factors affecting coefficient of permeability <ul><li>The coefficient of permeability depends on several factors, most of which are listed below: </li></ul><ul><li>Shape and size of the soil particles </li></ul><ul><li>Void ratio, permeability increases with increase of void ratio </li></ul><ul><li>Degree of saturation, permeability increases with increase of degree of saturation </li></ul>
  108. 114. Influence of degree of saturation on permeability of Madison sand
  109. 115. Influence of degree of saturation on permeability of compacted silty clay
  110. 116. <ul><li>Composition of soil particles : </li></ul><ul><li>For sand & silt this is not important; however, for soil with clay minerals this is one of the most important factors </li></ul><ul><li>Permeability in this case depends on the thickness of water held to the soil particles, which is a function of the cation exchange capacity, valence of the cation, etc. </li></ul><ul><li>the coefficient of permeability decreases with increasing thickness of the diffuse double layer </li></ul><ul><li>Soil structure: Fine grained soils with a flocculated structure have a higher coefficient of permeability than those with a dispersed structure </li></ul>
  111. 117. <ul><li>Viscosity of the permeant </li></ul><ul><li>Density & concentration of the permeant </li></ul>
  112. 118. Determination of coefficient of permeability in the laboratory <ul><li>The four most common laboratory methods for determining the coefficient of permeability of soils are: </li></ul><ul><li>(i) Constant-head test </li></ul><ul><li>(ii) Falling –head test </li></ul><ul><li>(iii) Indirect determination from consolidation test </li></ul><ul><li>(iv) Indirect determination by horizontal capillary test </li></ul>
  114. 120. TEST METHODS Constant head permeability test Variable Head Permeability Test Q = k x i x A
  115. 121. Constant-head test <ul><li>This method is suitable for more permeable granular materials </li></ul><ul><li>The soil specimen is placed inside a cylindrical mold, and the constant head loss,h, of water flowing through the soil is maintained by adjusting the supply </li></ul><ul><li>The outflow water is collected in a measuring cylinder, and the duration of the collection period is noted </li></ul><ul><li>From Darcy’s law, the total quantity of flow Q in time t can be given by </li></ul>
  116. 122. Constant-head Method
  117. 123. Falling –head test This method is suitable for fine-grained soils The soil specimen is placed inside a tube, and a standpipe is attached to the top of the specimen Water from the standpipe flows through the specimen The initial head difference h1 at time t=0 is recorded
  118. 124. and water is allowed to flow through the soil such that the final head difference at time t = t is h2
  119. 125. Where h1 = initial head, h2 = final head, t= time interval a = cross-sectional area of the liquid stand pipe A =cross-sectional area of the specimen L = length of specimen Clean sand, clean gravel & sand mixture Pervious (good drainage) Fine sand, sandy silt & silt Slightly pervious (poor drainage ) Practically impervious (poor drainage) Homogeneous clay Up to 10 -4 10 -7 10 -5 10 -6 10 -8 10 -9 Or
  120. 126. Broad classification of soils as per IS:1498 4.75 MM Soil group Value as Subgrade Value as subbase Drainage characterisitics Compaction Equipment Unit dry wt (g/cc) CBR value,% Subgrade modulus (k) kg/cm 3 GW Excellent Excellent Excellent RTR, SWR 2.0-2.24 40-80 8.3-13.84 GP Good to ex Fair to G Excellent RTR, SWR 1.76-2.24 30-60 8.3-13.84 GM Fair to G Fair to G Fair to P RTR, SFR 1.76-2.24 30-60 8.3-13.84 GC Good Fair Poor to PI RTR, SFR 1.84-2.16 20-30 5.53-8.30 SW Good Fair to G Excellent RTR 2.08 -2.32 20-40 5.53-11.07 SP Fair to G Fair Excellent RTR 1.68-2.16 10-40 4.15-11.07 SM Fair to G Fair to G Fair to PI RTR, SFR 1.60-2.16 10.2-40 4.15-11.07 SC Fair to P Not Suitble Fair to PI RTR, SFR 1.60-2.16 5-20 2.77-8.30 ML,MI Poor to F Not Suitble Fair to P RTR, SFR 1.44-2.08 15 or less 2.77-5.53 CL, CI Poor to F Not Suitble Impervious RTR, SFR 1.44-2.08 15 or less 1.38-4.15 OL,OI Poor Not Suitble Poor RTR, SFR 1.44-1.68 5 or less 1.38-2.77 MH,CH, OH Not suitble Not suit Impervious RTR, SFR 1.28-1.68 5 or less Less than 2.5 GRAVEL SILT SAND COARSE SAND MEDIUM SAND FINE SAND CLAY 2.0 MM 0.425 MM 0.075 MM 0.002 MM
  121. 127. Highly expansive in nature & will have less permeability
  122. 128. CLAY MINERALS <ul><li>Composition & structure of clay minerals </li></ul><ul><li>Clay minerals are complex silicates of aluminum, magnesium, and iron </li></ul><ul><li>Two basic crystalline units form the clay minerals: </li></ul><ul><li>(1) a silicon-oxygen tetrahedron, and </li></ul><ul><li>(2) an aluminum or magnesium octahedron </li></ul>
  123. 129. Silicon-oxygen tetrahedron It consists of four oxygen atoms surrounding a silicon atom It consists of six hydroxyl units surrounding an aluminum (or magnesium) atom Aluminum or Magnesium octahedral units
  124. 130. Silica sheet Gibbsite sheet Silica – gibbsite sheet The tetrahedron units combine to form a silica sheet Combination of the aluminum octahedral units forms
  125. 131. Each silicon atom with a positive valance of 4 is linked to four oxygen atoms with a total negative valance of 8 However, each oxygen atom at the base of the tetrahedron is linked to two silicon atoms This leaves one negative valance charge of the to oxygen atom of each tetrahedron to be counterbalanced The combination of the aluminum octahedral units forms a gibbsite If the main metallic atoms in the octahedral units are magnesium, these sheets are referred to as brucite sheets When the silica sheets are stacked over the octahedral sheets, the oxygen atoms replace the hydroxyls to satisfy their valance bonds
  126. 132. Kaolinite mineral <ul><li>This is the most important clay mineral belonging to this type </li></ul><ul><li>Other common clay minerals that fall into this category are serpentine and halloysite </li></ul>
  127. 133. Illite & Montmorillonite minerals The most common clay minerals with three-layer sheets are illite and montmorillonite A three layer sheet consists of an octahedral sheet in the middle with one silica sheet at the top and one at the bottom Repeated layers of these sheets form the clay minerals
  128. 134. Illite mineral Montmorillonite mineral Illite layers are bonded together by pottasium ions
  129. 135. The negative charge to balance the pottasium ions comes from the substitution of aluminum for some silicon in the tetrahedral sheets Substitution of this type by one element for another without changing the crystalline form is known as isomorphous substitution Montmorillonite has a similar structure to illite. However, unlike illite there are no pottasium ions present, and a large amount of water is attracted into the space between the three sheet layers
  130. 136. What is sensitivity of clay soils? <ul><li>It is the ratio of the unconfined compressive strength in an undisturbed state to that after remolding is known as sensitivity </li></ul><ul><li>The sensitivity can be expressed as in eqn: </li></ul><ul><li>Unconfined compressive strength, undisturbed </li></ul><ul><li>Unconfined compressive strength, remolded </li></ul><ul><li>A clay is sensitive when the values of the sensitivity range between 4 and 8 , and extra sensitive when values of 8 or more are encountered </li></ul>S =
  131. 137. FSI Usefulness This test helps to identify the potential of a soil to swell which might need further detailed investigation regarding swelling and swelling pressures under different field conditions Take two 10 g soil specimens of oven dry soil passing through 425-micron IS Sieve Each soil specimen shall be poured in each of the two glass graduated cylinders of 100 ml capacity In the case of highly swelling soils, such as sodium bentonites, the sample size may be 5 g or alternatively a cylinder of 250 ml capacity may be used
  132. 138. Free Swelling Index
  133. 139. One cylinder shall then be filled with kerosene oil and the other with distilled water up to the 100 ml After removal of entrapped air ( by gentle shaking or stirring with a:tglass rod ), the soils in both the cylinders shall be allowed to settle Sufficient time (not less than 24 h ) shall be allowed for the soil sample to attain equilibrium state of volume without any further change in the volume of the soils The final volume of soils in each of the cylinders shall be read out
  134. 140. Free swell index, percent = (Vd – Vk) / Vk x 100 Where V d= the volume of soil specimen read from the graduated cylinder containing distilled water, and Vk, = the volume of soil specimen read from the graduated cylinder containing kerosene.
  135. 141. Laboratory observations Initial Reading Final Reading Difference in Reading   FSI, %   Soil + Water Kerosene Soil + Water Kerosene 13 11 17 11 6 54.5 13 11 16.8 11 5.8 52.7 14 12 18.2 12 6.2 51.7 13.5 12 18 12 6 50.0 13 11 16.8 11 5.8 52.7 14 11 17 11 6 54.5 13.5 11 16.5 11 5.5 50.0 13.5 11 16.8 11 5.8 52.7 13.5 11 16.7 11 5.7 51.8 14.5 11 17 11 6 54.5
  136. 142. Unsuitable fill material for embankment construction <ul><li>Materials from swamps, marshes & bogs; </li></ul><ul><li>Peat, log, stump & perishable material; & soil that classifies as OL, OI, OH or Pt </li></ul><ul><li>Material susceptible to spontaneous combustion; </li></ul><ul><li>Salt-infested soils with pH>8.5 (sodic soil) IS:2720 P-26 </li></ul><ul><li>Clays having LL>70 & PI > 45 </li></ul><ul><li>FSI > 50 % </li></ul><ul><li>Materials in a frozen condition; </li></ul><ul><li>Fill materials with soluble sulphate content > 1.9 gm of sulphate (expressed as SO3) per litre </li></ul>
  137. 143. Importance & functions of each layer of pavement & subgrade <ul><li>EMBANKMENT </li></ul><ul><li>Whenever it is required to raise the grade line of a highway above the ground level from considerations of topography, vertical alignment, ground water depth and drainage etc. an embankment is needed </li></ul><ul><li>It should be so design to protect the subgrade from getting damaged due to capillary rise of ground water </li></ul><ul><li>It should act ready drainage of surface water, ensure the need of the geometric design standards </li></ul><ul><li>It should possess stable slopes & must not undergo excessive settlement </li></ul>
  138. 144. Elements of embankment design <ul><li>The important elements in embankment design are: </li></ul><ul><li>Selection of top width, height & side slope </li></ul><ul><li>Stability of slopes </li></ul><ul><li>Settlement analysis </li></ul><ul><li>Selection of fill materials </li></ul><ul><li>Drainage of embankment </li></ul><ul><li>Embankment design on marshy ground </li></ul>
  139. 145. S UBGRADE L AYER <ul><li>The performance of the pavement is affected by the characteristics of the subgrade </li></ul><ul><li>The desirable properties that the subgrade should possess include strength, drainage, ease of compaction, permanency of compaction and permanency of strength </li></ul><ul><li>The total crust thickness of flexible pavement is decided based on subgrade strength in terms of CBR value for a given traffic condition </li></ul>
  140. 146. Sub-base layer (Flexible pavements) <ul><li>The purpose of sub-base layer is to permit the building of relatively thick pavements at low cost & to provide a stress-distributing medium which will spread the load applied to the surface so that shear and consolidation deformations will not take place in the subgrade </li></ul><ul><li>Sub-base consist of selected materials, such as natural gravels, that are stable but that have characteristics which make them not completely suitable as base course </li></ul><ul><li>They may also be of stabilized soil or merely select borrow </li></ul>
  141. 147. Sub-base layer <ul><li>Thus, the quality of sub-bases can vary within wide limits, as long as the thickness design criteria are fulfilled </li></ul><ul><li>A sub-base can be of lower quality and it generally consists of locally available materials </li></ul><ul><li>A sub-base is a layer of material b/w the base & subgrade </li></ul>
  142. 148. Base course <ul><li>The base course is defined as the layer of material that lies immediately below the wearing surface of a pavement </li></ul><ul><li>Sometimes the material under a rigid pavement is called a subbase </li></ul><ul><li>In case of flexible pavements, the base course lies close to the surface </li></ul><ul><li>Therefore, it must possess high resistance to deformation in order to withstand the high pressure imposed on it </li></ul>
  143. 149. <ul><li>The function of the base course varies according to type of pavement </li></ul><ul><li>Base courses are used under rigid pavement s for (i) prevention of pumping </li></ul><ul><li>(ii) protection against frost action </li></ul><ul><li>(iii) drainage </li></ul><ul><li>(iv) prevention of volume change of the subgrade </li></ul><ul><li>(v) increased structural capacity </li></ul><ul><li>(vi) expedition of construction </li></ul><ul><li>To prevent pumping, a base course must be either free draining or it must be highly resistant to the erosive action of water </li></ul>
  144. 150. <ul><li>To provide drainage, the base may or may not be a well-graded material, but it should contain little or no fines; it may sometimes be stabilized with asphalt </li></ul><ul><li>A base course need not be free draining to provide structural capacity, but it should be well graded and should resist deformation due to loading </li></ul><ul><li>To provide resistance to deformation, many times it becomes necessary to stabilize the base course with cement or bitumen </li></ul><ul><li>Base courses & sub-bases are used under flexible pavements to increase the load-supporting capacity of the pavement by providing added stiffness & resistance to fatigue as well as building up relatively thick layers to distribute the load through a finite thickness of pavement. This is the prime requirement of the base course </li></ul>
  145. 151. Wearing Surface <ul><li>The upper most layer is the wearing course and is usually thinner than the lower binder course </li></ul><ul><li>The purpose of the wearing surface is to provide a safe and smooth riding surface </li></ul><ul><li>The surface must possess skid resistance, resist load and non-load associated fracture & resist permanent deformation (ruts, etc.) </li></ul><ul><li>Many functional & structural requirements are placed on the surface </li></ul><ul><li>The type of surface depends largely upon the load that will apply to the pavement as well as upon economics and availability of construction materials </li></ul>
  146. 152. <ul><li>In general, smaller size of aggregates and slightly more bitumen are incorporated in this layer than the binder course </li></ul><ul><li>The binder course is a transitional layer b/w the base course and the surface course </li></ul><ul><li>A tack coat is applied at the interface of the surface and binder courses </li></ul><ul><li>A prime coat is used b/w the binder & base </li></ul><ul><li>A seal coat may be applied to the top of the surface course </li></ul>
  147. 153. Poisson’s ratio The Poisson’s ratio, µ is the ratio of the strain normal to the applied stress to the strain parallel to the applied stress
  148. 154. Applications <ul><li>The influence of Poisson’s ratio µ, is usually small for most of the pavement materials </li></ul><ul><li>In determination of stresses in concrete slabs, Poisson’s ratio is a property that is needed </li></ul><ul><li>The µ for clayey subgrade varies from 0.4 to 0.5 and a value of 0.5 is used for the wet condition </li></ul><ul><li>The µ for sand can be assumed 0.35 </li></ul><ul><li>Typical values of µ for unbound granular material lie between 0.2 and 0.5 </li></ul><ul><li>For bituminous mixes, the µ value range from 0.35 to 0.50 </li></ul><ul><li>At low temperatures, the µ value of bituminous material is low, while it increases with the increase in temperature </li></ul>
  149. 155. THANKS