1. Pile foundations (SL 1-143).pdf

CV 725: Pile Foundations
Course Instructor: Dr. Babloo Chaudhary
L-T-P : 3-1-0
Credit : Four (04)
Department of Civil Engineering
National Institute of Technology Karnataka, Surathkal

Contents
q Introduction
q Broad Classification 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

q Educational Qualification and 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.

Students who complete this 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):

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

Stage
No.
Contents
Approx.
No. of
Lectures
3
• Mini project
• 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

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

Continuation Evaluation Assessment Tools
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

Evaluation Plan
9
Description Weightage
Assignments, Quiz, Test,
Tutorials, Seminar, class
performance & attendance.
25%
Mid Sem Exam 25%
End Sem Exam 50%

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
Tue CV725
Wed CV725
Thu CV725
Fri CV725
Time Table

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
Wed CV725 CV725
Thu CV725
Fri CV725
Time Table

Foundation Engineering
Major Parts of 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

Purpose of a Foundation
• 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

Foundation Engineering is all 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

Types of Foundation
Shallow Foundation 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

Combined and Strapped footing
Shallow foundations
Isolated footing
18

Isolated footing
Mat or raft footing
Shallow foundations
19

Deep foundations
Pile foundations
20

When to go for 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

Differences between shallow foundation and deep foundation
Sl.No
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

Sl.No
.
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

Dead load: Self weight 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

Types of Deep Foundation
q Pile Foundation
q Piers Foundation
q Caissons or well foundation
Caisson Foundation
Pile Foundation
27

Types of Deep Foundation
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

For unusual, skyscrapers, and high rise structures, Pile foundations are best
29

Pile foundations
• It is 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

When to use piles?
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

When to use piles?
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

When to use piles?
§ For Uplift force
ØTension pile:
Ex-electric transmission tower
Offshore platform
33

When to use piles?
§ For carrying inclined & horizontal load
ØLaterally loaded pile: horizontal load acts perpendicular to
the pile axis. Ex- pile below retaining wall, bridge abutment
34

When to use piles?
§ For carrying inclined & horizontal load
Ø Inclined piles: driven at an angle, carry large
horizontal loads
35

Broad Classification of Piles
Length
Materials
of construction
Shape
Mode of
load transfer
Method of
installation
Use
Cross-section
Method of
formation
37

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

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

1. Based on length
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

2. Based on Materials
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

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
42

q Timber piles
43

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).
44

H-Piles
Steel Tubular Piles
q Steel Piles
45

Screw Piling
Box Steel Piles
Close end open Steel
pipe Piles
q Steel Piles
46

Precast
concrete
driven piles
q Reinforced Concrete (RC) Piles
RC
bored piles
47

Concrete on Steel Concrete on Timber
Composite Piles
Composite Piles
48

§ 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
49

3. Based on Shape 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.
50

Piles can be designed 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
51

End Bearing and Friction 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

Compression and Tension Piles
Leeward side
Windward side
Wind load
Tension piles Compression piles
GL
53

Free Standing and Rigid 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

• 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
• Pre-stressed Piles
5. Based on method of installation
Driven pile
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
• Pre-stressed Piles
5. Based on method of installation
Driven pile
Bored Pile
56

Driven Piles/ Displacement Piles / 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

Applications of driven piles
• 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

Applications of Bored Piles
• 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

Advantages of Driven Piles/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

v Unjointed types cannot 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

End enlargements will reduce skin
friction over shaft
62

Bored Piles/ Non-displacement Piles / 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

Advantages of Bored Piles/ 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

End Bearing and Friction 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

1. Concrete in shaft 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

Problems in bored concrete piles
67

6. Based on use
• 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
68

Geogrid reinforced Pile supported Embankments
69

Important Points
• Pile is 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

Dense sand up to
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= -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

Soft clay but
stiffness
increasing with
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= -8m
El= -16m
El= -2.5m
El= -6m
El= -3m
El= -5m
El= -6.5m
El= -18m
Firm
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

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
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

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

Load Carrying Capacity of a Single Pile
qStatic & Dynamic Formulae
qPile Load Test
75
qPile Driving Formulae
qCorrelation with Field Test Data (SPT, CPT, etc.)

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

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

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

Adhesion factors
• Adhesion and 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

Note:
The value of adhesion 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

Adhesion of clays on surface of piles
Clay
Pile
Asperities
Smear Zone
1. Adhesion/ Cohesion
2. Angle of friction/ Angle of internal friction
81

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

Mobilization of Pile Resistances
(Only Skin Resistance)
Settlement
Load
(Qu)
0.5-1.0% of Pile dia
Qu
Qs
Ex: For 800mm dia, Settlement = ½” to 1” 83

(Only End Bearing Resistance)
Qu
Qs
Settlement
Load
(Qu)
5- 20% of Pile dia
Ex: For 800mm dia, Settlement = 6”
84

(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

Allowable Load on Pile
(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

Problem
Determine the load carrying 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

Clay A
Clay B
Clay C
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

Geotechnical capacity (Compressive)
Bearing resistance, 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

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

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
LCC of Single Pile in Sand:
Compression
Static Formula

Critical depth of Piles
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

10D
20D
30D
40D
Depth
Here, D is dia 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

Modified Friction Angle in 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

● 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,

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.

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

Qu= Qb + Qs
qs =Ki *PDi *tanδi
Ki PDi
ith layer
PDi
PDi
Ki Pdi tanδ
99
Static Formula
K= 1 to 1.5 –Bored piles
K= 2 to 3 – driven piles

Nγ Values
(IS 6403:1981)
Bearing capacity factor, Nq and Nγ
101
Nq Values
IS 2911 (Part1/Sec1 ):2010 IS 2911 (Part1/Sec2): ):2010
Driven Piles Bored Piles

Values of K and ф
Qu = Qb + Qs
= qbAb + ∑"#$
%
('()()
qs = ∑"#$
%
(+" ∗ -." ∗ /0%1")
K= 1 to 1.5 –Bored piles
K= 2 to 3 – driven piles
1 = 3
102

K and δ for 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)

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

Allowable Load
● Allowable Load, !" =
!$
%
● 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

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

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

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

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&
C- Φ Soils
Static Formula
Layered soils

Qu= Qb + Qs – Wp
= qbAb + ∑"#$
%
qsiAsi
qb = CNc + PDNq +
$
&
YDNy
qsi = ∑"#$
%
((")" + +",-"./%0")
Qu
H1
Qb 110
Layer 2: Clay
Layer 3: Sand
§ Arching effects
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$
C- Φ Soils
Static Formula
Layered soils

qb = PDNq +
!
"
#′D%#′
PD = &1H1 + &2H2 + &′2'(
2 + &′3H3
Qu
H1
Qb 111
Sand
Sand
§ Arching effects
H3
Sand
C- Φ Soils; Layered soils; Static Formula
Effects of Ground water table
&1
'′2
GWT
H2
&3
&2

Example:
(1) A concrete pile 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
Example: Determine the allowable 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

• Under-ream piles are 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

Bucket length
+ 0.55D
Bored cast 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

Use of Under reamed 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

qDesign Assumptions for Under-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.

Design Considerations of Under-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

6. Minimum depth of 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

Safe loads for under-reamed piles as per
IS – 2911 (Part III)-1980
120

Under-reamed piles: LCC by 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

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

LCC of Single Pile by using SPT Tests
123

● It is an 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

Importance of N value
• 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

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

2. Dilatancy correction
It’s to 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

Qu
H1
Qb 129
Sand
Sand H3
Sand
LCC of 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
LCC of Single Pile 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
LCC of Single Pile 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
LCC of Single Pile 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

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

Static Cone Penetration Test (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

Equipment details
• Cone apex 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

Procedure for conducting SCPT
• 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

Determination of End bearing resistance
139

Correlation with Penetration test 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

Determination of Skin friction resistance
141

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.

Dynamic Cone Penetration Test
• 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

1. Pile foundations (SL 1-143).pdf

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à 1. Pile foundations (SL 1-143).pdf

Similaire à 1. Pile foundations (SL 1-143).pdf (20)

Dernier

Dernier (20)

1. Pile foundations (SL 1-143).pdf