Download as PDF, PPTX
![LCC [Geotechnical capacity] of single pile in Uplift (Tension)
in clays by Static formulae
! =
#
$
%
&
. (
)% ! =
#
$
%*
&
+,
-)%
≯ 7 t/m2
LCC of pile in clay in compression
Qu= Qb + Qs – Wp
LCC of pile in clay in uplift
Qu= Qb + Qs + Wp
82](https://image.slidesharecdn.com/1-230321144202-d701c3a6/85/1-Pile-foundations-SL-1-143-pdf-82-320.jpg)
![● Driven Piles
● Tomlinson’s or Berezantsev’s method
● qb = PDNq
● For driven pile in sand
96
Piles in sandy/granular soils
фmod =
!"°$%
&
, if ф < 40°
If ф > 40°, Limit фmod =40°
The max base or tip or end bearing resistant in sand is limited to 11000kN/m2
bearing capacity factor [after Berezantsev et al. (1961)]
'( ≯ **"""+,/.&
'/ ≯ *""+,/.&
Limiting values,](https://image.slidesharecdn.com/1-230321144202-d701c3a6/85/1-Pile-foundations-SL-1-143-pdf-96-320.jpg)
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1. Pile foundations (SL 1-143).pdf
- 1. CV 725: PileFoundations Course Instructor: Dr. Babloo Chaudhary L-T-P : 3-1-0 Credit : Four (04) Department of Civil Engineering National Institute of Technology Karnataka, Surathkal
- 2. Contents q Introduction q BroadClassification of Piles q Load Carrying Capacity of Single Pile: Static Formulae q Field Tests (SPT and SCPT) q Load Carrying Capacity of Single Pile: Dynamic Formulae q Under-reamed Piles q Load Tests on Piles (IS: 2911-P4) 2
- 3. q Educational Qualificationand Experience v Name: Babloo Chaudhary v Affiliation: Assistant Professor Dept. of Civil Engineering, NITK v Specialization: Geotechnical Engineering 3 Faculty Introduction Degree/ Post Name of University Specialization M. Tech IIT Guwahati, India Geotech. Engg. PhD Kyushu University, Japan Geotech. Engg. Postdoc Kyoto University, Japan (2018 QS World Rank-13 in Civil & Str Engg) Geotech. Engg.
- 4. Students who completethis course will be able to appreciate/learn/understand. q Differences between shallow and deep foundations. A knowledge of the available types of piling and methods of constructing pile foundations. Importance of pile socketing, good geotechnical practices through case studies. q Determine the suitable type of pile and method of installation for the ground/site conditions and the form of the loading. q Evaluate load carrying capacity of single piles, group of piles and latrally loaded piles in sands and clays, group behavior. Use of relevant IS codes. Estimating safe load on piles from pile loading test. q To predict the behavior of the piles (including laterally loaded piles) once they are in the ground and subject to loading. 4 COURSE OUTCOMES(COs):
- 5. Stage No. Contents Approx. No. of Lectures 1 • Introduction,Classification of piles, Advantages and disadvantages. • Piles Subjected to Vertical Loads: Load carrying capacity of a single pile by different methods - static formulae, dynamic formulae, field tests (SPT, SCPT etc.), monotonic and cyclic pile loading tests, MLT. • Under-reamed piles • Piles resting on rock 16 2 • Pile groups • Pile groups (of vertical piles), pile group efficiency • Pile groups under an eccentric load or under a centric load and moment • Pile groups with vertical and inclined piles . 12 5 Course Coverage
- 6. Stage No. Contents Approx. No. of Lectures 3 • Miniproject • PG Student seminars 03 4 • Geotechnical and structural designs of piles and pile caps • Pile driving and pile installation 08 5 • Lateral load-carrying capacity of vertical piles (Matlock and Reese non-dimensional analysis, Broms' method etc.) • Settlement of Piles • Negative Skin friction 12 6 • PG Student Seminars 03 6 Course Coverage
- 7. Reference books § Varghese,P.C." Design of Reinforced Concrete Foundations", PHI § Tomlinson, M.J., "Pile Design and Construction Practice", E & FN Spon publishers § Poulos, H.G. and Davis, E.H. "Pile foundation design and analysis", John-Wiley and Sons § Broms, B.B. (1964), "Lateral resistance of piles in cohesive and cohesion soils" ASCE, Journal of soil mechanics and foundations, Vol. 90, pp. 27-63 and 123-156. § Nayak, N.V." Foundation Design Manual", Dhanpat Rai Publications. § IS2911 (Part 1, Sec 1-4), Part 2, 3, 4, 1S 456 & SPI6 § Swami Saran, "Analysis and Design of substructures (limit state design)", Oxford and IBM § Som, N. N. and Das, S.C. "Theory and practice of Foundation design", PHI § Karuna Moy Ghosh, "Foundation design in practice" PHI § Bowles, J.E. "Foundation Analysis and design. Mcgraw Hill § Das, B.M. "Principles of foundation engineering, CENGAGE learning India Edition § Punmia, B.C. "Soil Mechanics and foundations, Lakshmi Publications. § Kaniraj, S.R. " Design Aids in Soil Mechanics and Foundation Engineering, TMH § Gopal Ranjan and ASR Rao “Basic and applied soil Mechanics” New Age Int’l Publishers 7
- 8. Continuation Evaluation AssessmentTools 8 1. Quiz 2. Test 3. Assignments 4. Attendance 5. Seminars and reports 6. Tutorials 7. Term/mini project 8. Mid-sem exam 9. End sem exam
- 9. Evaluation Plan 9 Description Weightage Assignments,Quiz, Test, Tutorials, Seminar, class performance & attendance. 25% Mid Sem Exam 25% End Sem Exam 50%
- 10.
- 11.
- 12. Day/Period 1 7:55-8:50 2 8:55-9:50 3 10:05-11:00 4 11:05-12:00 Lunch Break 5 13:00-14:00 6 14:05-15:00 7 15:05-16:00 Mon CV725 Tue CV725 WedCV725 CV725 Thu CV725 Fri CV725 Time Table
- 13. Foundation Engineering Major Partsof Civil Engg Structures ØSuperstructure ØSubstructure or foundation q Foundation: It is substructure element which transfer the loads safety from structure to the earth. § It should safely transfer the load within permissible limit of settlement. § Supporting soil/earth must not be overstressed and not undergo deformation beyond permissible limit. 13
- 14.
- 15. Purpose of aFoundation • To safely transfer the loads from superstructure to substructure • Settlements must be within permissible limits. Both total settlements and differential settlements are not desirable. • Earthquake resistant. • Minimum eccentricities between load, column, footing, pile group. • Economical in cost • Effective for problematic soils – able to take care of the problems associated (expected) to problematic soils. Ex.- Black cotton soil, soft clays, loose sands, dispersive soils, expansive soils etc. • Foundations must be structurally sound. (both geotechnical designs and structural designs). • Pile design – Structural member as a column subjected to compression. Long pile- long column with buckling flexure. 15
- 16. Foundation Engineering isall about settlements and bearing capacity § No settlement – Vey good § Uniform settlement - may hinder service lines § Differential settlement - Most dangerous, must be avoided Drainage is very important in all geotechnical engineering/ slope engineering projects 16
- 17. Types of Foundation ShallowFoundation Deep Foundation q Shallow Foundation § Transfer load to soil at a relatively small depth § less expensive & suitable for lighter structures. Ex-spread footings, strip footings, rafts foundations § !" # ≤ % q Deep Foundation § Transfer load to the firm strata at deeper layer inside the ground (rather than small depth) § more expensive & suitable for heavy structures, problematic soils, Ex- piles, piers, caisson foundation § !" # ≥ % Deep Foundation Moderate Deep % < !" # < %( Deep foundation !" # > %( 17
- 18. Combined and Strappedfooting Shallow foundations Isolated footing 18
- 19. Isolated footing Mat orraft footing Shallow foundations 19
- 20.
- 21.
- 22.
- 23. When to gofor deep foundation • Fill or poor soil condition on the top surface of the ground • To get acceptable bearing capacity is difficult. • To keep settlement of the structure within permissible limit • To carry heavy load from superstructures • Structures get large uplift forces • Poor soil condition- when ground improvement technique may be costlier. 23
- 24. Differences between shallowfoundation and deep foundation Sl.No Shallow Foundation Deep Foundation 1 Depth of embedment (D) to width of foundation (B) generally does not exceed one (01) L/D is generally greater than 15, where L is the length of embedment and D is diameter 2 Examples: strip footings, isolated footings, combined footings, raft or mat foundations Examples: Pile foundations, well foundations, caissons 3 Load is transferred to soil beneath at a shallow depth by bearing Load is transferred to a stratum deep below partly by bearing and partly by skin friction 4 Cannot resist tensile forces or pullout forces In case of tensile forces, resistance is only by skin friction or shaft friction 5 Cannot resist large lateral loads Can be designed to resist large lateral loads 24
- 25. Sl.No . Shallow Foundation DeepFoundation 6 Method of construction: conducted in open excavations and strata to which load is transferred Method of construction: Driven or bored. Only some idea of the strata can be obtained from bore holes and as such strata is not visible 7 Soil disturbance during construction: limited to very small zone Soil disturbance during construction: In case of pile foundations irrespective of method of construction, a large zone of soil is affected extending to the full length of the pile Differences between shallow foundation and deep foundation 25
- 26. Dead load: Selfweight of the structure Live load: Occupancy load due to people, furniture, etc. Wind load: Lateral load depends on the geographical location Horizontal Pressure below grade: Retaining wall/ water pressure on sheet piles Structural member forces Uplift forces Earthquake Note: LL Should be taken 100% for ground and first floor. As floor number increases, LL decreases. After 5th floor, LL to be kept 50% . Foundation Loads 26
- 27. Types of DeepFoundation q Pile Foundation q Piers Foundation q Caissons or well foundation Caisson Foundation Pile Foundation 27
- 28. Types of DeepFoundation q Piles- relatively slender column, generally less than 750 mm dia q Drilled Piers- shaft is drilled into soil and then filled with concrete q Caissons or well foundation - Dia more than 750 mm, designed as end bearing member Functional feature- almost similar Physical size and method of installation- difference 28
- 29. For unusual, skyscrapers,and high rise structures, Pile foundations are best 29
- 30. Pile foundations • Itis the kind of sub-structure, which transfers the heavy- loads through weak soil to the deeper and hard strata. • Almost all complex structures can be supported on pile • For unusual structures, the foundation cost will be several times more than the normal structures. • If we use piles, we need to spend more on sub-structure. • In usual structure with shallow foundations, only 15%of the total cost of the structure is reserved for substructure constructions. But, if we adopt pile foundations, cost of substructure can increase to 50%. • Due to this, pile foundation is kept as final option. 30
- 31. When to usepiles? Piles are commonly used § When foundation fails in acceptable bearing capacity(shear failure) and settlement. § When problematic soils are encountered. When soil near the surface undergoes large volume changes depending on environmental factors. § When soil at shallow depth cannot provide adequate support § When structure is expected to carry uplift loads § When large lateral loads act on foundation § When foundation is subjected to large eccentric loads, inclined loads and moments § When scouring of soil immediately below foundation is expected to occur § When a future construction with deep excavation is anticipated in adjacent area/adjacent site. 31
- 32. When to usepiles? Piles are commonly used § For Vertical Loads End bearing: It transfers the loads through weak soil to the deeper and hard strata. ØFrictional pile ØCombined 32
- 33. When to usepiles? § For Uplift force ØTension pile: Ex-electric transmission tower Offshore platform 33
- 34. When to usepiles? § For carrying inclined & horizontal load ØLaterally loaded pile: horizontal load acts perpendicular to the pile axis. Ex- pile below retaining wall, bridge abutment 34
- 35. When to usepiles? § For carrying inclined & horizontal load Ø Inclined piles: driven at an angle, carry large horizontal loads 35
- 36.
- 37. Broad Classification ofPiles Length Materials of construction Shape Mode of load transfer Method of installation Use Cross-section Method of formation 37
- 38. Broad Classification ofPiles Based on length • Short Piles • Medium Piles • Long Piles • Very Long Piles Based on shape • Straight Sided / Cylindrical / Prismatic • Tapered • With Enlarged Base or Bell Bottom Shaped • Single or Multiple Under-reamed Based on method of installation • Driven • Bored • Vibration • Jetted • Cast In-Situ Piles /Bored Piles/Replacement Piles • Precast Concrete Driven Piles Or Preformed Driven Piles/ Displacement Piles • Driven Cast In-Situ Piles • Bored Precast Piles • Precast Jacked Piles • Precast Vibrated Piles • Precast And Jetted Piles Based on cross-section • Circular • Square • Hexagonal • H-section • I-section • Corrugated, Fluted • Based on load transfer • End Bearing Piles • Friction / Floating Piles • Compaction pile • Tension pile/Uplift Piles • Anchor Pile • Fender Pile • Sheet Pile • Rigid Piled Raft System • Inclined Piles/ Sloping Piles / Batter Piles 38
- 39. Broad Classification ofPiles Based on material of construction • Timber Piles • Steel Piles • Reinforced Concrete (RC) Piles • Composite Piles Rarely • Granular Piles Method of formation • Precast • Cast in-situ • Prestressed Based on use • Compaction Piles • Load Bearing Piles • Compression Piles • Uplift Piles / Tension Piles • Fender Piles / Dolphins • Inclined Piles • Micropiles / Root Piles • Bridge Approach Support Piles 39
- 40. 1. Based onlength TYPE LENGTH CASES Short Piles < 6m Common Medium Piles 6 TO 18 m Common Long Piles 18 TO 36 m Special Cases Very Long Piles 36 TO 60 m & MORE Exceptional Cases • On-shore piles are generally up to 20m long. • Off-shore piles can be up to 100m long or more. • Up to 20m length and 500mm dia piles can be precast driven piles /displacement piles. • Larger diameter and longer piles are bored cast-in-place piles /non-replacement piles. Classification of Piles 40
- 41. 2. Based onMaterials Classification of Piles Ø Timber Piles Ø Steel Piles Ø Reinforced Concrete (RC) Piles Ø Composite Piles - Rarely Ø Granular Piles/DJM Piles (Strictly Ground Improvement Technique) Note: • Timber piles/steel piles/RC piles are rigid piles and load transfer is by end bearing and shaft resistance. • Granular piles are not rigid and load transfer is by bulging in top portion. 41
- 42. q Timber piles •For temporary and lightly loaded structures up to a maximum load of 25 tons. • 2m to 8m long, lengths can be spliced. 200mm to 400mm dia with tip dia of 125mm to200mm. • Use is generally made of casuarina piles, bamboo piles, coconut piles, … • Timber piles have high strength to weight ratio. Easy to handle. • Can be cut to required length and trimmed easily after driving. • Dry (seasoned) timber is strong. Wet timber is weak • Problems of splitting heads, brooming in compact soils during driving and may require pre-boring • Liable for termite attacks. Not suitable for marine environments because of attack by molluscan type wood-borers. • Should be coated with a good wood preservative like creosote oil [225 to 250 kg/m3 of piles in freshwater and 350 kg/m3 of piles in saline water) • Should not be subjected to alternate wet and dry conditions due to groundwater table fluctuations Classification of Piles 42
- 43. q Timber piles Classificationof Piles 43
- 44. q Steel Piles •Steel piles are suitable for loads of around 40 to 125 tons • The foundation cost will be higher. • Used in different forms such as Steel H-Piles, Box (hollow) piles, Screw piles and steel pipe (tubular) with both open and closed end. • H- piles can be driven close to an existing structure as they produce very small soil displacement and used in the construction of bulkheads, trestles, retaining walls, bridges and cofferdams. • In case of open piles, after driving, the hollow space inside the pipe is normally, filled with concrete. • As its vulnerable to corrosion, an anti corrosive treatment such as cathodic protection may be necessary or have to provide extra steel (sacrificial steel). Classification of Piles 44
- 45. H-Piles Steel Tubular Piles qSteel Piles Classification of Piles 45
- 46. Screw Piling Box SteelPiles Close end open Steel pipe Piles q Steel Piles Classification of Piles 46
- 47. Precast concrete driven piles q ReinforcedConcrete (RC) Piles RC bored piles Classification of Piles 47
- 48. Concrete on SteelConcrete on Timber Composite Piles Composite Piles 48
- 49. § Straight sided/cylindrical/prismatic- circular, square, polygonal (hexagonal/octagonal) shapes, § H-section, I-section, hollow pipe etc.-Most common shape are circular and straight sided § Tapered § Corrugated § Fluted § With enlarged base or bell bottom shaped § Single or multiple under-reamed 4. Based on Shape Classification of Piles 49
- 50. 3. Based onShape and Cross-section Note: Most common shape are circular and straight sided Tapered Corrugated Fluted With Enlarged Base or Bell Bottom Shaped Single Or Multiple Under-reamed IS2911(Part-III) Straight Sided / Cylindrical / Prismatic (Circular, Polygonal shapes, H-section, I- Section, Hollow Pipe etc. Classification of Piles 50
- 51. Piles can bedesigned to resist all types of loads such compression loads, uplift or tension loads and lateral loads. Piles can resist large loads and large moments. • End Bearing Piles (Vertically loaded piles / compression piles ) • Friction/Floating Piles (Vertically loaded piles / compression piles ) • Single Piles & Pile Groups • Piers & Micropiles/Paliradice (Root Piles) • Free Standing Piles • Rigid Piled Raft System (RPRS) • Uplift Piles/Tension Piles (Vertically Loaded Piles / Tension Piles) • Raker Piles/Inclined Piles/Sloping Piles/Batter Piles (Laterally loaded piles) 4. Based on Load Transfer mechanism Classification of Piles 51
- 52. End Bearing andFriction Piles GL Qu Qs Qs Qb Qb Qu= Qb Qu= Qb + Qs Friction Pile or Floating Pile End Bearing or Point Bearing Pile Qu= Qs Combined Pile Qu Qu Hard Strata Skin Friction Where, Qu= Ultimate load Qb= Bearing resistance Qs= Skin friction resistance Qs >>Qb Qb >>Qs 52
- 53. Compression and TensionPiles Leeward side Windward side Wind load Tension piles Compression piles GL 53
- 54. Free Standing andRigid Piled Raft System GL Pile Cap GL Pile Cap WL Free Standing Pile group Rigid Piled Raft System Onshore Piles Offshore Piles Water Table 54
- 55. • Driven pile •Bored Pile • Vibration Pile • Jetted Pile • Cast In-Situ or cast in Place Concrete Piles/Bored Piles/Replacement Piles/Non-displacement Piles • Precast Concrete Driven Piles or Preformed Driven Piles/Displacement Piles/Non-replacement Piles • Driven Cast In Situ Piles • Bored Precast Piles • Pre-stressed Piles • Precast Jacked Piles • Precast Vibrated Piles 5. Based on method of installation Classification of Piles Driven pile 55
- 56. • Driven pile •Bored Pile • Vibration Pile • Jetted Pile • Cast In-Situ or cast in Place Concrete Piles/Bored Piles/Replacement Piles/Non-displacement Piles • Precast Concrete Driven Piles or Preformed Driven Piles/Displacement Piles/Non-replacement Piles • Driven Cast In Situ Piles • Bored Precast Piles • Pre-stressed Piles • Precast Jacked Piles • Precast Vibrated Piles 5. Based on method of installation Classification of Piles Driven pile Bored Pile 56
- 57. Driven Piles/ DisplacementPiles / Non-replacement Piles • Driven piles are deep foundation elements installed using impact or vibration hammers to a design depth or resistance. These piles displaces the soil adjacent to it. Note: End bearing and friction piles are driven type. 1. Placement of Pile 2. Installation of Pile 3. Repetition of process up to required depth 57
- 58. Applications of drivenpiles • Can be used for all types of construction, particularly in aggressive soil conditions • Well suited to sites where the ground conditions are highly variable as they are driven to a set or pre-determined resistance • A good foundation choice when you have very thick layers of soft soil and/or a high water table that would be problematic for a traditional drilled pile • Small sizes piles can be used for underpinning houses and light buildings, limited headroom, difficult access • Medium size piles can be used for foundations for new buildings, infrastructure, floor slabs and load transfer platforms, lateral support for earth retention in conjunction with king post walls • Large size pile can be used for wind turbines and pylons, river bridge foundations, bridge abutments and piers, marine construction 58
- 59. Applications of BoredPiles • As heavy foundations, securing deep excavation especially close to existing buildings as well as stabilizing and retaining slopes • In a variety of infrastructure projects such as tunneling, road or bridge construction as well as flood protection • Retain ground alongside an excavation pit or close to adjacent buildings, often combined with other techniques such as ground anchors or soil nails • For slope stabilization to prevent landslides, or protect existing buildings 59
- 60. Advantages of DrivenPiles/Displacement Piles v Material forming pile can be inspected for quality and soundness before driving. v Not liable to 'squeezing' or 'necking'. v Construction operations not affected by ground water. v Projection above ground level advantageous to marine structures. v Can be driven in very long lengths. v Can be designed to withstand high bending and tensile stresses. 60
- 61. v Unjointed typescannot readily be varied in length to suit varying level of bearing stratum. v May break during driving, necessitating replacement piles. v May suffer unseen damage which reduces carrying capacity. v Uneconomical if cross-section is governed by stresses due to handling and driving rather than by compressive, tensile, or bending stresses caused by working conditions. v Noise and vibration due to driving may be unacceptable. v Displacement of soil during driving may lift adjacent piles or damage adjacent structures. v End enlargements, if provided, destroy or reduce skin friction over shaft length. v Cannot be driven in conditions of low headroom. Disadvantages of Driven Piles/ Displacement Piles 61
- 62. End enlargements willreduce skin friction over shaft 62
- 63. Bored Piles/ Non-displacementPiles / Replacement Piles 1. Setting, drilling and casing insertion 2. Steel reinforcement insertion 3. Concrete pouring with Tremie pipe 4. Casing retraction Note: Bored piles can be drilled to depths in excess of 60m and typical diameters range up to 2.4m. 63
- 64. Advantages of BoredPiles/ Non-displacement Piles 1. Length can readily be varied to suit variation in level of bearing stratum. 2. Soil or rock removed during boring can be inspected for comparison with site investigation data. 3. In-situ loading tests can be made in large-diameter pile boreholes, or penetration tests made in small boreholes. 4. Very large (up to 7.3m diameter) bases can be formed in favourable ground. 5. Drilling tools can break up boulders or other obstructions which cannot be penetrated by any form of displacement pile. 6. Material forming pile is not governed by handling or driving stresses. 7. Can be installed in very long lengths. 8. Can be installed without appreciable noise or vibration. 9. No ground heave. 10. Can be installed in conditions of low headroom. 64
- 65. End Bearing andFriction Piles GL Qu Qs Qs Qb Qb Qu= Qb Qu= Qb + Qs Friction Pile or Floating Pile End Bearing or Point Bearing Pile Qu= Qs Combined Pile Qu Qu Hard Strata Skin Friction Where, Qu= Ultimate load Qb= Bearing resistance Qs= Skin friction resistance Qs >>Qb Qb >>Qs 65
- 66. 1. Concrete inshaft liable to squeezing or necking in soft soils where conventional types are used. 2. Special techniques needed for concreting in water-bearing soils. 3. Concrete not inspected after installation. 4. Enlarged bases cannot be formed in cohesion less soils. 5. Cannot be extended above ground level without special adaptation. 6. Low end-bearing resistance in cohesion less soils due to loosening by conventional drilling operations. 7. Drilling a number of piles in group can cause loss of ground and settlement of adjacent structures. Disadvantages of Bored Piles/ Non-displacement Piles 66
- 67. Problems in boredconcrete piles 67
- 68. 6. Based onuse • Load Bearing Piles- Compression / Tension/ Lateral load • Compaction Piles- in Loose sand ( Ground Improvement) • Compression Piles- To resist predominantly compression load • Uplift Piles / Tension Piles- To resist predominantly uplift load • Fender Piles / Dolphins- To resist predominantly lateral load in case of sea structure • Inclined Piles • Micropiles / Root Piles • Bridge Approach Support Piles Classification of Piles 68
- 69. Geogrid reinforced Pilesupported Embankments 69
- 70. Important Points • Pileis not a framed structure. • Pile is a slender section. • Skin friction always acts in opposite direction to the motion of piles. • During the uplift of pile, there will be no end-bearing, the resistance of the pile will be only due to shaft / skin friction acting downwards. • During berthing of ships on jetties, ships hit the jetty. Due to this there will be large lateral load and hence piles will be provided under jetty. • While driving the precast pile into the ground, we can infer the strata based on the energy required to hammer the pile in to the ground. For, hard strata, we require large energy to drive, whereas in soft soils, piles sink by itself. • In case of bored piles, if we come across water tables, it is difficult to install pile. In such conditions, we adopt Tremmie concreting. • Black cotton soil causes problem only in light structures. But, not much in heavy structures. 70
- 71. Dense sand upto great depth Stiff clay or stiff silt and clay up to great depth Stiff clay Soft clay up to great depth Soft clay Rock Soft clay Med, Dense sand extending deep Loose sand up to great depth (a) (b) (c) (d) (e) (f) El= 0m El= 0m El= 0m El= 0m El= 0m El= 0m El= -3m El= -6m El= -15m Suggest a Suitable Foundation Spread Foundation Spread Foundation Spread Foundation Deep Foundation, Pile Cast in-situ Pile with bulb 1) Raft 2) Densify with vibrofloatation driven pile- Densify 71
- 72. Soft clay but stiffness increasingwith depth (to a greater depth) Soft Medium Medium Soft clay Compact Sand Hard Clay (extending deep) Misc. Fill Loose Sand Medium Dense Sand Compact glacial fill Rock (g) (h) (i) El= 0m El= 0m El= 0m El= -8m El= -16m El= -2.5m El= -6m El= -3m El= -5m El= -6.5m El= -18m Firm Suggest a Suitable Foundation Raft Foundation Otherwise frictional Pile-Best Bored and cast in situ Pile with bulb formation in hard clay Driven and cast in situ pile extending upto med dense sand or upto compacted glacial fill 72
- 73. Misc. fill Misc.Fill Rock (j) (k) (l) El= 0m El= 0m El= -2m El= --2.5m El= -4.5m Medium firm clay Medium dense sand El= -12m El= -30m Rock Soft clay El= 0m El= -12m Soft Clay Medium dense to dense sand El= -18m El= -45m Rock Loose sand and soft clay Suggest a Suitable Foundation 1) Pile in upper dense sand layer 2) Replace upper 2m thick poor fill with compacted fill material &provide spread foundation 1) Low-medium load – pile on dense sand layer 2) Heavy load – driven steel pile on the rock strata 1) pile –since rock is 4.5m depth 2) If basement is there, best to lay base slab resting on the rock 73
- 74. Pile foundation qDesign requirement •Safety: Adequate factor of safety against shear failure of soil qsafe =qult/FOS where q- bearing capacity • Serviceability: acceptable amount of settlement (including immediate consolidation and secondary compression). • Max load that satisfies both the conditions is allowable bearing capacity, qa 74
- 75. Load Carrying Capacityof a Single Pile qStatic & Dynamic Formulae qPile Load Test 75 qPile Driving Formulae qCorrelation with Field Test Data (SPT, CPT, etc.)
- 76. Load Carrying Capacity(LCC) of Single Pile in Compression in Clays Qu= Qb + Qs – Wp Qu = qb*Ab + qs*As Where, Qu =Load Carrying Capacity Qb =End Bearing resistance (Tip resistance) Qs =Skin friction resistance (Shaft resistance) Wp =Weight of the pile (Generally ignored for smaller dia piles) qb =Unit bearing resistance Ab= c/s area of Shaft tip qs =Unit Skin Resistance As = Surface area of Piles shaft qStatic Formulae GL Qs Qb Qu Wp 76
- 77. Qu = Qb+ Qs Qu = qb Ab + qsAs qb= CpNc Cp is average cohesion at pile tip Nc is bearing capacity factor = 9 qs = αC C- average cohesion over pile shaft α- adhesion factor GL Qs Qb Qu Wp Load Carrying Capacity (LCC) of Single Pile in Compression in Clays qStatic Formulae 77
- 78. C1 C2 C3 Ci Cn Qu = Qb+ Qs Qu = qb Ab + qsAs = qb Ab + ∑"#$ % &'"('" = qb Ab + ∑"#$ % ∝" *"('" In Layers Soil Load Carrying Capacity (LCC) of Single Pile 78
- 79. Adhesion factors • Adhesionand Cohesion? Soil type N value ‘C’ Value in kN/m2 Adhesion factor (α) Avg. α value Soft Clays <4 1 to 25 1.0 1.0 Medium Stiff Clays 4 to 8 25 to 50 0.4 to 0.7 0.55 Stiff Clays 8 to 15 50 to 100 0.3 to 0.4 0.35 Hard Clays > = 15 > = 100 0.25 to 0.3 0.28 Also, C= N/16 to N/20 kg/cm2 79
- 80. Note: The value ofadhesion factor depends on the Undrained Shear Strength of clay and may be obtained from the graph given below mentioned in IS:2911 (Part 2&3) 80
- 81. Adhesion of clayson surface of piles Clay Pile Asperities Smear Zone 1. Adhesion/ Cohesion 2. Angle of friction/ Angle of internal friction 81
- 82. LCC [Geotechnical capacity]of single pile in Uplift (Tension) in clays by Static formulae ! = # $ % & . ( )% ! = # $ %* & +, -)% ≯ 7 t/m2 LCC of pile in clay in compression Qu= Qb + Qs – Wp LCC of pile in clay in uplift Qu= Qb + Qs + Wp 82
- 83. Mobilization of PileResistances (Only Skin Resistance) Settlement Load (Qu) 0.5-1.0% of Pile dia Qu Qs Ex: For 800mm dia, Settlement = ½” to 1” 83
- 84. Mobilization of PileResistances (Only End Bearing Resistance) Qu Qs Settlement Load (Qu) 5- 20% of Pile dia Ex: For 800mm dia, Settlement = 6” 84
- 85. Mobilization of PileResistances (Both Skin and End Bearing Resistance) Qu Qs Settlement Load (Qu) 0.5-1.0% of Pile dia Ex: For 800mm dia, Settlement = ½” to 1” Qb Qs Qb 85
- 86. Allowable Load onPile (Factor of Safeties) Qa= !" #.% = !'(!) #.% Overall F.O.S =2.0 Qa= !) *.+ + !' #.+ F.O.S against Skin friction = 1.5 F.O.S against End bearing = 2.5 86
- 87. Problem Determine the loadcarrying capacity of the pile shown in the figure. Clay A has undrained cohesion of 35 kPa. Clay B is having undrained cohesion of 45 kPa. Clay C has undrained cohesion of 80 kPa. Assume M30 grade concrete being used and Fe500 steel. Percentage of steel is 2%. Diameter of pile is 500mm. Clay A Clay B Clay C C = 35kPa C = 45kPa C = 80kPa 10m 12m 6m 87
- 88. Clay A Clay B ClayC C = 35kPa C = 45kPa C = 80kPa Dia of pile= 500mm Grade of concrete= M30 Grade of steel= Fe500 Ast=2% 10m 12m 6m Given that Solution: 88
- 89. Geotechnical capacity (Compressive) Bearingresistance, Qb = CpNcAp = 80 x 9 x (!/4 x 0.52) = 141.37kN Skin friction resitance, Qs = QS1+QS2+QS3 = (! x 0.50 x 10 x 1.0 x 35 )+ (! x 0.50 x 12 x 0.95 x 45 ) + (! x 0.50 x 6 x 0.58 x 80) = 459.78+ 805.82 + 437.31 = 1702.91 = 1702.91 kN Solution: IS2911(Part 1/Sec 1): 2010 89
- 90. Ultimate load, Qu= Qb + Qs = 141.37+992.6 = 1133.97 kN Allowable load, Qa = (141.37/2.5) + (1702.91/1.5) = 56.5 + 1135.27 = 1191.77 kN Geotechnical Capacity(uplift) = 1135.27 kN Qa(uplift) = 1135.27 kN 90
- 91. Structural Capacity(comp) =0.25fckAc = 0.25x30x !/4 x5002x10-3 = 1472.6kN Structural Capacity(uplift) = 0.87fyAst = 0.87x500x(2/100)x!/4x5002x10-3 = 1708.2kN Overall, Qall(comp) = 1191.77 kN Qall(uplift) = 1135.27 kN 91
- 92. 92 LCC of SinglePile in Sand: Compression Static Formula
- 93. Critical depth ofPiles in Sand due to Arching effect ● The critical depth is the depth up to which the vertical stress increases linearly. Below the critical depth, the stress remains constant. ● The maximum effective overburden pressure at tip should correspond to critical depth (Zc). ● Clay- depends on alpha only ● Sand- depends on Depth, phi, unit weight, Critical depth 93
- 94. 10D 20D 30D 40D Depth Here, D isdia of pile PDi= γ(15D) PDi= γ(20D) PDi= γZ PDi= γ(15D) PDi= γ(20D) • 15D is critical depth for loose sand, ф≤ 30° • 20D is critical depth for dense sand, ф≥ 40° • Interpolate for ф in between 30°and 40° 94 Loose sand Dense sand Concept of Critical depth Lc L-Lc Arching effect Normal full state IS 2911 (Part 1/ Sec 1):2010
- 95. Modified Friction Anglein Case of Driven Piles in Sands ф mod ф mod = (40+ф )/2 and фmod >40 If ф > 40, Limit фmod =40 ф 3D 3D Dilatancy effect 95 Driven Piles in Sands
- 96. ● Driven Piles ●Tomlinson’s or Berezantsev’s method ● qb = PDNq ● For driven pile in sand 96 Piles in sandy/granular soils фmod = !"°$% & , if ф < 40° If ф > 40°, Limit фmod =40° The max base or tip or end bearing resistant in sand is limited to 11000kN/m2 bearing capacity factor [after Berezantsev et al. (1961)] '( ≯ **"""+,/.& '/ ≯ *""+,/.& Limiting values,
- 97. Qu= Qb +Qs Qu =qbAb + qsi Asi Qu =qbAb + ∑ qsi Asi qb = PDNq + ! " YDNy Qu Qs Qb Ki PDi PDi ith layer Nq= Bearing factor as per IS: 2911 Nγ = Bearing factor as per IS: 6403 PD= Effective overburden pressure at pile tip 97 LCC of Single Pile in Sand in Compression Static Formula Type equation here.
- 98. LCC of SinglePile in Sand in Compression Static Formula Qu= Qb + Qs Qu =Ab (0.5 D γ Nγ +PDNq) + Asi ∑ Ki PDi tanδi Qu Qs Qb i=1 i=n Ki PDi ith layer Where, Nq= Bearing factor as per IS: 2911 Nγ = Bearing factor as per IS: 6403 PD= Effective overburden pressure at pile tip Ki =Co-efficient of earth pressure for ‘i’th layer Pdi = Effective overburden pressure for ‘i’th layer δi = angle of internal friction b/w pile and soil ‘i’th layer D= diameter of the pile Note: Usually 0.5 DNγ is neglected since the dia (D) is small PD 98
- 99. Qu= Qb +Qs qs =Ki *PDi *tanδi Ki PDi ith layer PDi PDi Ki Pdi tanδ 99 LCC of Single Pile in Sand in Compression Static Formula K= 1 to 1.5 –Bored piles K= 2 to 3 – driven piles
- 100.
- 101. Nγ Values (IS 6403:1981) Bearingcapacity factor, Nq and Nγ 101 Nq Values IS 2911 (Part1/Sec1 ):2010 IS 2911 (Part1/Sec2): ):2010 Driven Piles Bored Piles
- 102. Values of Kand ф Qu = Qb + Qs = qbAb + ∑"#$ % ('()() qs = ∑"#$ % (+" ∗ -." ∗ /0%1") K= 1 to 1.5 –Bored piles K= 2 to 3 – driven piles 1 = 3 102
- 103. K and δfor piles and soils system Sand particles can stick in asperities Sand particles ! = # Pile 103 Ranjan & Rao, 1991 Broms (1966) recommended values of K and δ for driven pile in sands Murthy (2001)
- 104. 10D 20D 30D 40D Depth PDi= γ(15D) PDi= γ(20D) PDi=γZ PDi= γ(15D) PDi= γ(20D) IS 2922 (Part 1/ Sec 1):2010 For the piles longer than 15D to 20D, max effective overburden stress at the pile tip should correspond to the pile length to 15D (30°) to 20D (40°). 104 Loose sand Dense sand Concept of Critical depth Lc L-Lc Arching effect Normal full state
- 105. Allowable Load ● AllowableLoad, !" = !$ % ● F-Factor of safety =2.5 to 3.0 ● End bearing resistant in sand for bored pile is ½ to 1/3 of the value for driven pile. !& &'()* +,-) = 1 2 − 1 2 !& *(,3)4 +,-) ● ● For bored pile in sand, K=1-sinΦ; range of K= 0.3 to 0.75 (avg value 0.5) ● 5 = 6 – for bored pile in dry soil. Reduced value if slurry is used during excavation 105
- 106. Allowable Load 106 Qu= Qb+ Qs Qu =Ab (0.5 D γ Nγ +PDNq) + Asi ∑ Ki PDi tanδi IS 2911(part 1): 2010 For driven pile in loose to dense sand (! =30° to 40°), %& = 1 to 2 For bored pile in loose to dense sand (! =30° to 40°), %& = 1 to 1.5
- 107. Meyerhof (1976) Method 107 qb= PDNq Limiting Value for point or end bearing resistant qb = 50Nq tan! − #$%&$ &'%#& − (% )*/m2 qb = 25Nq tan! − ,-. /--&$ &'%#& − (% )*/m2 Meyerhof (1976) bearing capacity factors
- 108. Qu= Qb +Qs – Wp = qbAb + qsAs = qbAb + ∑"#$ % qsiAsi qb = CNc + PDNq + $ & YDNy qsi = ∑"#$ % ((")" + +",-"./%0") Qu Qs Qb ith layer 108 Soil 1: Sand Soil 2: Clay Soil 3: Sand Arching effects Increase in frictional angle –driven piles LCC of Single Pile in Compression C- Φ Soils Static Formula Layered soils
- 109. Qu= Qb +Qs – Wp = qbAb + ∑"#$ % qsiAsi qb = CNc + PDNq + $ & YDNy qsi = ∑"#$ % ((")" + +",-"./%0") Qu H1 Qb 109 Soil 1: Sand Soil 2: Clay Soil 3: Sand § Arching effects § Increase in frictional angle –driven piles H2 H3 1$ 2$ 13 23 1$H1 1&H2 13H3 Qb = qbAb = (PDNq + $ & YDNy) Ab QS = ∑"#$ % qsi Asi = (+$,-$./%0$) AS1 + ((&)&) AS2 + (+3,-3./%03) AS3 ∝2 9& LCC of Single Pile in Compression C- Φ Soils Static Formula Layered soils
- 110. Qu= Qb +Qs – Wp = qbAb + ∑"#$ % qsiAsi qb = CNc + PDNq + $ & YDNy qsi = ∑"#$ % ((")" + +",-"./%0") Qu H1 Qb 110 Layer 2: Clay Layer 3: Sand § Arching effects § Increase in frictional angle –driven piles H2 H3 12 32 ∝2 6& 1$H1 1&H2 12H3 Qb = qbAb = (………………….) Ab QS = ∑"#$ % qsi Asi = (… … … … … . .) AS1 + (… … … … … …) AS2 + (… … … … ……) AS3 Layer 1: Clay ∝1 6$ LCC of Single Pile in Compression C- Φ Soils Static Formula Layered soils
- 111. qb = PDNq+ ! " #′D%#′ PD = &1H1 + &2H2 + &′2'( 2 + &′3H3 Qu H1 Qb 111 Sand Sand § Arching effects § Increase in frictional angle –driven piles H3 Sand LCC of Single Pile in Compression C- Φ Soils; Layered soils; Static Formula Effects of Ground water table &1 '′2 GWT H2 &3 &2
- 112. Example: (1) A concretepile is driven in a sand(ϕ=40o) of uniformly deposited. Length and dia of the pile are 12m and 300mm respectively. average dry unit weight of the sand is 18kN/m3. Neglect the effects ground water table. Find out the safe load capacity of the file. FoS=2.5 and Nq = 137 (2) Solve example 1 if water table is at a depth of 2m from ground surface Solution: 112
- 113. 113 Example: Determine theallowable pile load capacity of the 400mm dia driven concrete pile as shown in the figure below. Loose Sand Soft Clay ! = 30o, "sat =16 kN/m2 Cu = 15kN/m2, "sat =18 kN/m2 3m 4m 15m Dense Sand ! = 40o, "sat =20 kN/m2
- 114. • Under-ream pilesare very useful for expansive soils (e.g. black cotton soil). • It is bored cast in-situ concrete pile • It can have with one or more bulbs or under-reams. The bulb is formed by enlarging the stem of the pile near the bottom in a double conical shape. • Piles are connected at their top by plinth beams. • Piles are provided under every wall junction (no point load to bear on plinth beam) Under-reamed Pile 114
- 115. Bucket length + 0.55D Boredcast in-situ under-reamed piles (longitudinal section ) (a)Single under-ream pile and (b) Multi under-ream pile φ1 = 45° and φ2 = 30 ° to 45 ° 115 Under-reamed Pile
- 116. Use of Underreamed piles • To provide anchorage to the foundation for preventing its movement in a vertical direction due to alternate swelling and shrinkage of the expansive soils caused by seasonal changes in the moisture content (Tensile stresses). • To provide additional bearing area through the enlarged bulb in firm strata, underlying the top weak or filled-up ground. • To obtain adequate load-carrying capacity for downward, upward, and lateral loads and moments. • To take the foundation below the scour level. 116
- 117. qDesign Assumptions forUnder-ream piles : 1) The piles should resist the imposed loads as a structural member with adequate factor of safety. 2) The soil supporting the pile should withstand the loads without shear failure or excessive settlements with adequate factor of safety. 117 q The load-carrying capacity of under-ream piles is derived from the following three components: 1) Point-bearing resistance at the toe of the pile. 2) Skin friction resistance along the pile stem. 3) Skin friction on the soil cylinder between the extreme bulbs. However, when piles are subjected to uplift, the point-bearing resistance at the toe will not be present.
- 118. Design Considerations ofUnder-Ream Piles as per IS – 2911 (Part III)—1980 1) Minimum Grade of concrete: M-15 or M-20 concrete with respective minimum cement content of 350 or 400 kg/m3 2) The minimum length of under-ream piles, in deep deposits of expansive soils = 3 to 3.5 m below GL. 3) Minimum diameter of stem, D in mud= 250mm and if harmful constituents like sulphate present, min. D=300mm 4) Bulb diameter, Du = 2.5 D. 5) The maximum vertical spacing between under-reams is 1.5 Du for 300mm dia and 1.25Du for dia >300mm piles. 118
- 119. 6. Minimum depthof top most bulb= 2Du or 1750mm for expansive soils 7. The number of bulbs in a pile = Maximum 2 (Restricted). 8. The minimum c/c spacing of under-ream piles in a group =1.25Du to 1.5Du 9. Location of bottom most bulb from toe= Bucket length +0.55D 10. For a pile group with piles at a spacing of 2 Du, the group capacity = the sum of the load-carrying capacity of the individual piles in the group. 11. For a pile group with piles at a spacing of 1.5 Du, the safe load assigned per pile should be reduced by 10%. Design Considerations of Under-Ream Piles as per IS – 2911 (Part III)—1980 119
- 120. Safe loads forunder-reamed piles as per IS – 2911 (Part III)-1980 120
- 121. Under-reamed piles: LCCby Static Formula (Compression ) Qu = Qb1 + Qb2 +Qs1 + Qs2 Qb1= Cp. Nc. Ab ………..(1) Ab = !D2/4, Cp= Cohesion at pile tip Qb2= Cb. Nc. A0 ………..(2) Cb= Cohesion below lowest bulb, A0 = ! (Du2-D2) /4 Qs1 = αi. Ci. Asi ………..(3) This is due to adhesion Qs2 = Cj. Asj ………..(4) This is due to cohesion between top and bottom under ream Qs1 Qs2 Qb2 Qb1 Qu 121
- 122. Qu = Qb3+Qs1 + Qs2 Qb3 = Ct Nc A0 Ct = Cohesion at top of top most bulb or under ream A0 = ! (Du2-D2) /4 Under-reamed piles: LCC by Static Formula (Uplift) Note: When the number of bulb is increased from one to two, the load carrying capacity increases by about 50%. Qs1 Qs2 Qb3 Qu 122
- 123. LCC of SinglePile by using SPT Tests 123
- 124. ● It isan in-situ test especially for Cohesion less soils. ● Its conducted in a bore hole using standard split spoon sampler. ● SPT value (N) means, the number of blows required for 30 cm penetration. ● The value of ф and C values of a soil depend on the N-number ● Hammer weight = 65 kg ● Height of fall = 75 cm ● The test is reported as ‘refusal’ and the test is halted if 50 blows are required for any 150 mm penetration. Standard Penetration Test (SPT) 124
- 125.
- 126. Importance of Nvalue • The N value indicates the relative density of the cohesion less soil and the unconfined compressive strength of the cohesive soil. • If the soil is compact or stiff, the penetration number is high. • In general, the greater the N-value, the greater is the angle of shearing resistance. • The consistency and the unconfined shear strength of the cohesive soils can be approximately determined from SPT number N. 126
- 127. Correction for ‘N’value 1. Overburden Correction: • In granular soils, the overburden pressure affects the penetration resistance. • If the two soils having same relative density but different confining pressures are tested, the one with a higher confining pressure gives a higher penetration number. • Confining pressure increases with depth. • Higher the confining pressure, higher will be the N-value. N' = CN. N CN = 0.77 log10 (1905/ σo’) N' = Corrected value N= Field recorded value CN = Correction factor 127
- 128. 2. Dilatancy correction It’sto be applied when N' obtained after overburden correction exceeds 15 in saturated fine sands and silts. N' >15 is an indication of a dense sand. In such a soil, the fast rate of application of shear through the blows of a drop hammer, is likely to induce negative pore water pressure in saturated fine sand under undrained condition of loading. The increase in shear resistance will results in SPT value higher than the actual one. Correction for ‘N’ value If N' > 15; N"= 15+ (N'-15)/2 If N' < 15; N"= N' 128
- 129. Qu H1 Qb 129 Sand Sand H3 Sand LCCof Single Pile in Clay: Compression !1 !3 !2 H2 Qu= Qb + Qs – Wp = qbAb + ∑#$% & qsiAsi qb = CpNc = 5NpNc qsi = ∑#$% & ((#)#) = ∑#$% & ((#*+#) C=5N Qu= Qb + Qs = qbAb + ∑#$% & qsiAsi = CpNc Ab + ∑#$% & ((#)#) Asi = 5Np×-× Ab + ∑#$% & ((#*+#) Asi = 45NpAb + ∑#$% & (*(#+iAsi) qu - kN/m2 Ab &As - m2 Using SPT ‘N’ values
- 130. 130 LCC of SinglePile in Cohesionless Soil: Compression Using SPT ‘N’ values- IS Code 2911(P1/S1) Qu (kN) = 40N !" # $p + % &'s (.* Qb Should not exceed 400NAP qFor non-plastic silt or very fine sand Qu (kN) = 30N !" # $p + % &'s (.+ Minimum FOS= 2.5 Where, N = avg N value at pile tip Lb - Length of penetration of pile in the bearing in m D - dia or minimum width of pile in m Ap - C/s area of pile tip in m2 % & - Avg N along the pile shaft As – surface area of pile shaft Qb Should not exceed 100NAP qFor saturated cohesionless soil, ultimate load capacity of driven pile
- 131. 131 LCC of SinglePile in Cohesionless Soil: Compression Using SPT ‘N’ values Qu = ! " #$ of the driven pile QS = ! % #& of the driven pile qFor bored & cast in situ pile in sand qFor driven & cast in situ pile in sand For cast pile qu and qs can be same as that of driven pile
- 132. 132 LCC of SinglePile in hard Rock § When crushing strength of rock is more than characteristic strength of pile concrete/material, then the rock should be deemed as hard rock. The pile resting directly on hard rock may be loaded to their structural strength /capacity LCC of Single Pile in Weathered/soft Rock Qu (kN) = CulNc !"# $%& + '()# !"* %& Where Cul - Shear strength of rock below base of the pile in kN Nc – Bearing capacity factor =9 Fs- factor of safety = 3 (generally taken) + = 0.9 01223415616 782 = Avg shear strength of rock in the socketed length of pile in kN/m2 B- min width of pile shaft or diameter of the pile shaft in m L- socketed length of pile in m Note: for N≥ 60, =>?>84 @= >3 A1 235=@61016 ?= B1?>ℎ1016 032D 0?>ℎ10 >ℎ?5 =3@E
- 133.
- 134. Correlation between N-value,Relative density, ф value N-Value Denseness Relative density ф value 0-4 Very loose <15 <28⁰ 4-10 Loose 15-35 28⁰-30⁰ 10-30 Medium 35-65 30⁰-36⁰ 30-50 Dense 65-85 36⁰-42⁰ >50 Very dense >85 > 42⁰ 134
- 135. Static Cone PenetrationTest (SCPT) • Cone is pushed in to the soil at a steady speed and the resistance offered by the soil is determined. The resistance is called 'Cone resistance'. • It consists of Steel cone, friction jacket, mantle tube, sounding rods, gauges etc. • Suitability for: soft clays soft silts, medium sands & fine sands. • Unsuitable for: (1) Gravelly soil & soil for having SPT N value greater than 50. (In dense sand anchorage becomes too cumbersome & expensive), (2) Filled-up earth since erroneous values may be obtained due to the presence of loose stones, brick bats, etc. • It has arrangement to measure cone tip resistance (end bearing) and side friction. 135
- 136.
- 137. Equipment details • Coneapex angle= 60°15’ • Base diameter of cone = 35.7 mm • Cross-sectional area of cone= 10 mm². • Friction sleeve area= 150 cm² as per Std practice. • Rate of travel into the soil= 1 to1.5 cm/s. • Each time cone assembly shall penetrate a depth of 35mm • The sounding road is a steel rod (dia= 15mm) which can be extended with additional rods of 1m length each so you can conduct the test for up to the required length • For manual operation, the driving mechanism must have a capacity of 20 to 30 KN and for mechanical operation, the driving mechanism must have a capacity of 100 KN. 137
- 138. Procedure for conductingSCPT • To obtain only qc, the cone is pushed (II).. • To obtain only fs, friction sleeve is pushed (III). • For obtaining total resistance value, the sounding rod connected to cone-friction jacket assembly is pushed (IV). • The sounding apparatus should be provided with hydraulically operated measuring device by which the pressure developed is indicated on the gauges. 138 qc fs (qc+fs) (I) (II) (III) (IV) GL
- 139. Determination of Endbearing resistance 139
- 140. Correlation with Penetrationtest data qDriven Piles in Sand vUsing Cone Penetration resistance (SCPT) • Unit point resistance of driven pile, qb= static cone resistance = qc • Skin friction resistance for driven pile, Meyerhoff (1956) • Displacement pile, !" = $% ('()) + ,-//+ (limited to 100 ,-//+) • Where, 9: (;<=) =avg field value of cone penetration resistance in kg/cm2 over the pile length 140
- 141. Determination of Skinfriction resistance 141
- 142. Correlation b/w SPT‘N’ value and Static cone resistance, qc 142 qc-kN/m2 Just for guidelines. It may vary depends on grain size water table, Atterberg limit, etc.
- 143. Dynamic Cone PenetrationTest • It is useful for cohesion less soils. • Dynamic load (Hammer blows) is applied by a 65 kg hammer falling through a height of 75 cm. • The number of blows required for 30 cm penetration is taken as 'Dynamic cone resistance'. • The blow count for every 30cm penetration is made to get a continuous record of the variation of the soil consistency with depth. • The test is normally not suitable for cohesive soils or very loose cohesion less soils. 143