LECTURE ON PILE FOUNDATIONS

BYDR.K.K.MOZA

SPECIAL ADVISORSIMPLEX INFRASTRUCTURES LIMITED

PILE FOUNDATIONPILES ARE COLUMN LIKE ELEMENTS IN A FOUNDATION WHICH HAVE THE FUNCTION OF TRANSFERRING LOAD FROM SUPER STRUCTURE THROUGH WEAK COMPRESSIBLE STRATA OR THROUGH WATER , ONTO STIFFER OR MORE COMPACT OR LESS COMPRESSIBLE SOILS OR ONTO ROCK.

THEY ARE STRUCTURAL MEMBERS OF RELATIVELY SMALL CROSS SECTIONAL AREA CAPABLE OF INTERACTING WITH SURROUNDING SOIL AND DEVELOPING SOIL SUPPORT.

PILES FIND APPLICATION IN FOUNDATIONS TO TRANSFER LOADS FROM A STRUCTURE TO COMPETENT SUBSURFACE STRATA HAVING ADEQUATE LOAD BEARING CAPACITY.

PILES TRANSFER AXIAL LOADS EITHER SUBSTANTIALLY BY FRICTION ALONG ITS SHAFT AND/OR SUBSTANTIALLY BY END BEARING.

THE INSTALLATION OF PILES DEMAND, CAREFUL CONTROL ON POSITION,ALIGNMENT AND DEPTH AND INVOLVE SPECIALISED SKILL AND EXPERIENCE.

HISTORICAL

• WOODEN PILES WERE DRIVEN INTO MIDDLE OF LAKE BOTTOM TO PROTECT HOUSES AND PROTECTION FROM INTRUDERS AND ANIMALS.

• IN BRITAIN THERE ARE NUMEROUS EXAMPLES OF TIMBER PILING IN BRIDGE WORKS AND RIVER SIDE SETTLEMENTS CONSTRUCTED BY ROMANS.

• TO TRANSFER LOADS FROM SUPERSTRUCTURE THROUGH WEAK COMPRESSIBLE STRATA OR WATER TO DEEPER SOIL STRATA CAPABLE OF WITHSTANDING THE LOADS WITH DESIRED F.O.S.

• TO CARRY UPLIFT LOADS WHEN USED TO SUPPORT TALL STRUCTURES SUBJECTED TO OVERTURNING FORCES FROM WINDS AND WAVES.

• TO CARRY LATERAL LOADS WHEN PILE IS SUBJECTED TO TRANSVERSE FORCES SUCH AS WIND , EARTHQUAKE, WATERCURRENT, EARTH PRESSURE MOVING VEHICLES, PLANT AND EQUIPMENT, IMPACT OF BERTHING SHIPS AND FROM WAVES.

• TO CARRY COMBINATIONS OF VERTICAL AND HORIZONTAL LOADS WHERE PILES ARE USED TO SUPPORT RETAINING WALLS,BRIDGE PIERS AND ABUTMENTS AND MACHINERY FOUNDATIONS.

FUNCTIONS OF PILES

LOAD TRANSFER MECHANISM IN PILES

Q=Qs+QbQ= ULTIMATE LOAD CARRYING

CAPACITY OF THE PILEQs= SHAFT RESISTANCEQb = END BEARINGAS = SURFACE AREA OF PILE SHAFT

Ab = CROSS SECTIONAL AREA OF PILE TOE

fs = UNIT SKIN FRICTION

qb = UNIT END BEARING RESITANCE

Qb = Ab. qb

Qs=fs.As

Q

PILE - TYPE & CLASSIFICATION

• BASED ON INSTALLATION– DRIVEN

» CAST IN-SITU CONCRETE» PRECAST CONCRETE» PRECAST JOINTED» PRECAST-PRESTRESSED CONCRETE» STEEL

– BORED» CAST IN-SITU CONCRETE» PRECAST CONCRETE GROUTED IN PRE-BORED

HOLES

PILE - TYPE & CLASSIFICATION

• BASED ON MATERIAL• CONCRETE, STEEL & TIMBER

• BASED ON FUNCTION• FRICTION, END BEARING OR COMBINATION

• BASED ON SHAPE• SQUARE, ROUND, HEXAGONAL OCTAGONAL, H OR I-

SECTION• BASED ON INCLINATION

• VERTICAL OR BATTERED (RAKER PILE)

Bored Cast-In-Situ Piles

Hydraulically Operated Rotary

Piling Rig Salient Features:

FACTORS GOVERNING CHOICE OF TYPE OF PILE

• SUBSOIL CONDITION• LOCATION AND TYPE OF STRUCTURE• LOAD CHARACTERISTICS• LIMITATION OF TOTAL & DIFFERENTIAL SETTLEMENT• REQUIREMENT ON ACCOUNT OF NEARBY EXISTING

STRUCTURES• TIME FRAME AVAILABLE• DURABILITY

CHOICE OF TYPE OF PILESTEEL PILE

• USEFUL WHERE VERY HARD DRIVING IS REQUIRED• DEEPER PENETRATION INTO BEARING STRATA• CAPABLE OF CARRYING HIGH COMPRESSIVE LOADS WHEN DRIVEN ON TO A HARD

STRATUM• FASTER INSTALLATION• ROBUST, LIGHT TO HANDLE • ADVANTAGEOUS IN SITUATIONS WHERE GROUND HEAVE AND LATERAL DISPLACEMENT

MUST BE AVOIDED.• CAN BE READILY CUT DOWN OR EXTENDED WHERE LEVEL OF THE BEARING STRATUM

VARIES

DISADVANTAGES

– SUSCEPTIBLE TO CORROSION IN FREE WATER NEAR AIR-WATER INTERFACE IN MARINE OR RIVER STRUCTURES.

– MATERIAL COST VERY HIGH– HIGHER NOISE GENERATION DURING INSTALLATION

CHOICE OF TYPE OF PILE

TIMBER PILE• HIGH STRENGTH TO WEIGHT RATIO• EASY TO HANDLE AND CAN BE READILY CUT TO LENGTH AND TRIMMED AFTER DRIVING• CAN BE DRIVEN TO VERY LONG LENGTHS IN SOFT OR FIRM CLAYS BY SPLICING AND

JOINING • HAS INDEFINITE LIFE IN FAVOURABLE CONDITIONS OF EXPOSURE• MOST ECONOMICAL

DISADVANTAGES– LIABLE TO DECAY IN THE PORTION ABOVE GROUND WATER LEVEL– LIABLE TO BE DAMAGED WHEN USED IN MARINE STRUCTURES BY THE MOLLUSC-

TYPE BORERS WHICH INFEST THE SEA WATER– LIMITATIONS OF MAXIMUM LOAD CARRYING CAPACITY– LIGHTNESS OF TIMBER PILE MAY CAUSE PROBLEMS WHEN DRIVING GROUP OF

PILES THROUGH CLAYS OR SILTS– HEADS OF TIMBER PILES NEED TO BE PROTECTED AGAINST SPLITTING DURING

DRIVING BY MEANS OF A MILD STEEL HOOP

CHOICE OF TYPE OF PILEPRECAST CONCRETE PILES

• VERY MUCH SUITABLE IN APPLICATIONS WHERE AGGRESSIVE SUB SOIL CONDITIONS PREVAIL

• PROVISION OF PROTECTIVE COATING OF PILE SURFACES POSSIBLE• ADVANTAGEOUS IN SITUATIONS WHICH DEMAND USE OF DENSE CONCRETE (MARINE

AND RIVER STRUCTURES). CAN BE PROJECTED ABOVE GROUND LEVEL.• FASTER INSTALLATION• CONCRETE IN PILE CAN BE CHECKED FOR QUALITY AND SOUNDNESS BEFORE DRIVING ,

BETTER QUALITY CONTROL DURING CASTING ,• INSTALLATION OF PILES NOT AFFECTED BY GROUND WATER• USEFUL IN SITUATIONS OF FLOWING WATER/ARTESIAN WATER FLOW CONDITIONS IN

SUBSTRATA.• VARYING LENGTHS CAN BE PROVIDED BY ADOPTING A JOINTED TYPE.• METAL SHOES ARE NOT REQUIRED AT THE TOES OF PILES DRIVEN THROUGH SOFT OR

LOOSE SOILS INTO DENSE SANDS AND GRAVELS OR FIRM TO STIFF CLAYS. A BLUNT POINTED END IS JUST SUFFICIENT.

DISADVANTAGES» ADDITIONAL REINFORCEMENT MUST BE PROVIDED TO WITHSTAND

HANDLING AND DRIVING STRESSES.» CAN BE CAST TO LENGTHS ONLY UP TO CERTAIN LIMIT. IN CASE OF LONGER

OR VARYING LENGTHS OF PILES,THEY HAVE TO BE CAST IN SEGMENTS ANDJOINTED TOGETHER.

» SPECIAL ARRANGEMENTS FOR CASTING,HANDLING AND TRANSPORTATION OF PRECAST SEGMENTS REQUIRED

» LIMITATIONS FOR LARGE SIZE PILES» UNSEEN BREAKAGE DUE TO HARD DRIVING CONDITIONS.» CANNOT BE DRIVEN IN CONDITIONS OF LOW HEAD ROOM» MORE NOISE /VIBRATION DURING INSTALLATION

CHOICE OF TYPE OF PILE

BORED CAST -IN-SITU CONCRETE PILES• ADVANTAGEOUS IN SUBSOILS WITH DEPOSITS OF LARGE SIZED GRAVELS OR BOULDERS OR

INTERVENING HARD STRATUM OR VERY STIFF TO HARD COHESIVE SOILS. • SOIL OR ROCK REMOVED DURING BORING CAN BE INSPECTED FOR COMPARISION WITH SITE

INVESTIGATION DATA.• LARGE DIAMETER PILES OF VARYING LENGTHS CAN BE INSTALLED TO SUIT VARIATION IN

LEVEL OF BEARING STATUM.• MATERIAL FORMING PILE IS NOT GOVERENED BY HANDLING OR DRIVING STRESSES.• CAN BE INSTALLED WITHOUT APPRECIABLE NOISE OR VIBRATION.• CAN BE INSTALLED IN CONDITIONS OF LOW HEAD ROOM.• DRILLING TOOLS CAN BREAK UP BOULDERS OR OTHER OBSTRUCTIONS WHICH CANNOT BE

PENETRATED BY DRIVING TECHNIQUES

DISADVANTAGES• SPECIAL CARE IS NEEDED IN SOFT OR LOOSE OR WATER BEARING GRANULAR SOILS TO

AVOID DEFECTS IN PILE SHAFT UNDER SUCH SITUATIONS. SPECIAL TECHNIQUES NEEDED FOR CONCRETING IN WATER BEARING SOILS.

• CONCRETE CANNOT BE INSPECTED AFETR INSTALLATION.• CONCRETE IN SHAFT LIABLE TO SQUEEZING OR NECKING IN SOFT SOILS WHERE

CONVENTIONAL TYPES ARE USED.• SPECIAL ARRANGEMENT REQUIRED FOR HANDLING AND DISPOSALOF MUCKGENERATED

DURING BORING OPERATION.• LOW END BEARING RESISTANCE IN LOOSE NON COHESIVE SOILS,• LIMITATIONS IN LOOSE NONCOHESIVE SOILS, USE OF TEMPORARY OR PERMANENT

LINER NECESSARY. • CANNOT BE EXTENDED ABOVE GROUND LEVEL WITHOUT SPECIAL ADAPTATION.• DRILLING A NUMBER OF PILES IN A GROUP CAN CAUSE LOSS OF GROUND AND

SETTLEMENT OF ADJACENT STRUCTURES.

BORED CAST-IN-SITU PILES USING HYDRAULIC DRILLING RIGS

DIAMETER UPTO 2 TO 2.5 M CAN BE INSTALLED UPTO A DEPTH OF 40 TO 60 M. ADOPTING SUITABLE TOOLS AND TECHNIQUES WITH HIGH POWERED DRILLING RIGS

THE SPEED OF INSTALLATION IS VERY FAST.

CAN BORE THROUGH ALL TYPES OF SOIL AND BOULDARY STRATA.

THE INTRICATE MECHANISM OF HYDRAULIC SYSTEM ENABLES TO MAINTAIN CONSTANT SPEED OF ROTATION UNDER HIGH TORQUE

THE ROTARY HAS SPECIAL ATTACHMENT TO INSTALL TEMPORARY CASING/PERMANENT LINER DURING BORING OPERATION.

CHOICE OF TYPE OF PILEDRIVEN CAST- IN- SITU PILES

•ADVANTAGEOUS IN LOOSE NON COHESIVE SOILS

•HIGHER COEFFICIENT OF EARTH PRESSURE AND CONSEQUENTLY HIGHER SKIN FRICTION ACHIEVABLE IN CASE OF NON COHESIVE STRATA

•ADJACENT GROUND GETS COMPACTED DUE TO LATERAL DISPLACEMENT OF SOIL

•FASTER PROGRESS

•NO MUCK GENERATION

•LENGTH CAN EASILY BE ADJUSTED TO SUIT VARYING LEVEL OF BEARING STRATUM

•ENLARGED BASE POSSIBLE

•MATERIAL IN PILE NOT GOVERNED BY HANDLING OR DRIVING STRESSES

DISADVANTAGES•PROPER DRIVING SEQUENCE IS REQUIRED TO AVOID GROUND HEAVE OR DAMAGE TO ADJACENT PILES AND STRUCTURES DEPENDING ON TYPE OF SOIL

•MORE NOISE/VIBRATION DURING INSTALLATION

•CONCRETE CANNOT BE INSPECTED AFTER INSTALLATION

•CANNOT BE DRIVEN WITH VERY LARGE DIAMETERS

•CANNOT BE USED IN RIVER OR MARINE STRUCTURES WITHOUT SPECIAL ADAPTATION

LOAD FROM SUPER STRUCTURE

• SHALL HAVE TO BE RESISTED BY GROUND

– SUPPORTING CAPACITY OF GROUND SHALL HAVE TO BE CHECKED W.R.T.

» SHEAR» SETTLEMENT TOTAL

DIFFRENTIALDISTORTION

SOIL INVESTIGATION• CARRIED OUT IN ADVANCE TO DEFINE

• STRATIFICATION• NATURE AND TYPE OF SOIL • VARIATION AND ITS EXTENT• DENSITY AND MOISTURE CONTENT• SHEAR STRENGTH• COMPRESSIBILITY• MODULUS

• GROUND WATER TABLE• SULPHATE/CHLORIDE/ANYOTHER

DELETERIOUS CHEMICAL• pH• SELECTION OF PILLING SYSTEM

SOIL INVESTIGATION

• NUMBER OF BORINGS AND INSITU TESTS• STRUCTURE TO BE CONSTRUCTED • EXTENT OF PILES• VARIATIONS IN SUB SURFACE CONDITIONS

• DEPTH OF BORINGS SHALL NOT BE LESS THAN• 1.5 TIMES ESTIMATED LENGTH OF PILE IN SOIL BUT

MINIMUM 30M• 8-10 TIMES DIAMETER OF PILE IN WEAK/JOINTED

ROCK < 6M• 3-5 TIMES DIAMETER OF PILE IN GOOD ROCK < 3M

• ACTUAL DEPTH IS GOVERNED BY LOAD DISTRIBUTION

SOIL INVESTIGATION PROGRAMME• FIELD TEST• BORING

• SHELL AND AUGER• DRILLING MACHINE

–MECHANICAL–HYDRAULIC

• SUBSURFACE PROFILE• CONDUCTING SPT 1.5 M INTERVAL OR CHANGE

OF STRATA• EVALUATING IN-SITU DENSITY AND MOISTURE

CONTENT• CONDUCTING VANE SHEAR TEST IN COHESIVE

SOIL AT REGULAR INTERVALS

SOIL INVESTIGATION PROGRAMME

• FIELD TEST• CONDUCTING PRESSURE

METER/ELECTROMETER/GOODMAN JACK TEST AS DESIRED LEVEL

• COLLECTING UNDISTURBED/REPRESENTATIVE SAMPLES FROM EVERY STRATA ENCOUNTERED FOR LABORATORY TESTING

• COLLECTING WATER SAMPLES FOR CHEMICAL ANALYSIS

• PLATE LOAD TEST FOR SUB GRADE MODULUS • DYNAMIC CONE PENETRATION TEST • STATIC CONE PENETRATION TEST

SOIL INVESTIGATION PROGRAMME• LABORATORY TESTS

• ON REPRESENTATIVE SAMPLES• GRAIN SIZE ANALYSIS• ATTERBERG LIMITS• SPECIFIC GRAVITY

• UNDISTURBED/REMOULDED SAMPLES• COMPRESSIBILITY TESTS• TRIAXIAL COMPRESSION TESTS

(UU/CU/CD)• UNCONFINED COMPRESSIVE STRENGTH

SOIL INVESTIGATION PROGRAMME

• LABORATORY TESTS

• ON ROCK CORES

• UNIAXIAL COMPRESSIVE STRENGTH• POINT LOAD INDEX TEST

CODE OF PRACTICE REQUIREMENTSIndian Standards

1. IS:2911 (Part I/Sec1)-1979- Indian Standard Code of Practice for Design and Construction of Pile Foundations Part-I Concrete Piles Section 1 Driven Cast in-Situ Concrete Piles

2. IS:2911 (Part I/Sec2)-1979- Indian Standard Code of Practice for Design and Construction of Pile Foundations Part-I Concrete PilesSection 2 Bored Cast in-Situ Piles

3. IS:2911 (Part I/Sec3)-1979- Indian Standard Code of Practice for Design and Construction of Pile Foundations Part-I Concrete Piles Section 3 Driven Pre Cast Concrete Piles

4. IS:2911 (Part I/Sec4)-1979- Indian Standard Code of Practice for Design and Construction of Pile Foundations Part-I Concrete Piles Section 4 Bored Pre Cast Concrete Piles

5. IS:2911 (Part 2)-1979- Indian Standard Code of Practice for Design and Construction of Pile Foundations Part-2 Timber Piles

6. IS:2911 (Part 3)-1979- Indian Standard Code of Practice for Design and Construction of Pile Foundations Part-3 Under Reamed Piles

7. IS:2911 (Part 4)-1979- Indian Standard Code of Practice for Design and Construction of Pile Foundations Part- 4 Load Test on Piles

British StandardsBS 8004: 1986 – British Standard Code of Practice for Foundations

∫ ⎟⎠⎞

⎜⎝⎛−=

dzdp

cdP

EASS czzoz

11 τ ∫−=z

z ZCdzPP0

Elements of Load Transfer

Ps

Z

γz σzPz

σz σz Sz τz Pz

Pp

P

L

Sz = Vertical displacement of any pile section at depth Z

MH S

deflection slope

Reese Matlock Analysisγ Mt

B.M Soil reactionpile S.F

M Elastic Condition

p = Ezyv+dv

M+dM

V

Pile element and forces

Fixed HeadFree Head

EITMB

EIHTA tYY

33

+EIHTF y

3

Deflection =

EITMB

EIHTA tss

33

+Slope =

HTBHTA mm +

TMBHA t

vv +

HTFmB.M =

S.F =

12tpp MB

THA

+ THF pS.R =

T = Relative Stiffness

51

h

EITη

= 41

sKEIT =For Sands For Clays

Cohesionless soil

Type of Soil ηh (kg/cm3)Dry Submerged

Loose sand 0.260 0.146Medium sand 0.775 0.525Dense sand 2.075 1.245

Very loose sand underRepeated loading or

Normally loading clays

- 0.040

Cohesive soil

CU (kg/cm2) Ks (kg/cm2)

0.2 to 0.4 7.751 to 2 48.802 to 4 97.75

More than 4 195.50

Piles Subjected to Downward Drag (Negative Skin Friction)

original

∆p

lowered

original

GW

GW

σx

Z

σx

Remoulded

σx

Z

p

Fill

Settlements in normally consolidated or preconsolidated soft clays due to an effective vertical stress generated by lowering of water table.

Remoulding of soft clay may cause consolidation resulting into negative drag.

Consolidation of soft layer around pile due to recent fill or deposit.

• Piles driving capacity mainly from friction:Negative drag taken as 0.2 to 0.3 times the Undrained

shear strength multiplied by the area of pile shaft embedded in compressible soil.

• End bearing Piles:Negative drag taken as 0.5 times the Undrained shear

strength multiplied by the area of pile shaft embedded in soil.

IMPORTANT PROVISIONS OFIS:2911 Spacing of Piles

In case of piles deriving their capacity mainly from end bearing minimum centre to centre spacing of pile shall be 2.5 times the diameter of the shaft. In case of piles deriving their capacity mainly from friction, spacing of piles shall not be less than 3 times the diameter of the shaft. In case of piles resting on rock, the spacing of 2D may be adopted.

Factor of Safety

Minimum factor of safety on ultimate bearing capacity computed by static formula shall be 2.5

Reinforcement in Pile

The minimum area of longitudinal reinforcement of any type or grade within the pile shaft shall be 0.4% of the sectional area calculated on the basis of outside area of the casing or the shaft.

Minimum clear cover to all main reinforcement in pile shaft shall not be less than 50 mm.

Minimum diameter of the links or spirals shall be 6 mm and their spacing shall not be less than 150 mm.Generally aspacing of 300mm is considered more appropriate and practical.

Design of pile cap

The clear overhang of the pile cap beyond outermost pile in the group shall normally be a minimum of 150mm.

The pile should project 500mm into the cap concrete

Temporary casing/Permanent liner

Minimum length of 2m of temporary casing shall be provided for each bored pile unless otherwise specifically desired. Additional length of temporary casing may be used depending on conditions of strata, GWL etc.

For aggressive action of ground water for marine situations piles shall be formed with permanent casing(liner)

Tremie Method

For 25mm down aggregate, the tremie pipe should have a diameter not less than 200mm. For 20mm down aggregate tremie pipe should have a diameter not less than 150mm.

All piling above 600mm diameter should however be done with 200mm diameter tremie pipe.

Drilling Mud (Bentonite)

Requirements of Bentonite suspension

Liquid limit: shall be 400% or more

Sand content of Bentonite powder:shall not be greater than 1%

Density of bentonite suspension:shall be between 1.03 and 1.05 g/ml for freshly prepared suspension. However the density of bentonitesuspension after mixing in the bore hole may rise upto 1.25g/ml and should be brought down to atleast 1.10 g/ml by flushing before concreting

Marsh Cone Viscocity : Shall be between 30 to 45 secs

pH Value : Shall be between 9 and 11.5.

Concrete

Minimum slump of concrete shall be 125mm and maximum of 180mm

Slump of concrete shall be between 150 to 200 mm for concreting under water by tremie method

Minimum grade of concrete shall be M-25 Minimum cement content in concrete shall be 400 kg/m3. When concreting under water or drilling mud, 10%additional cement shall be used.

Concreting operation should not be taken up when specific gravity of bottom slurry is more than 1.12

Where cut off level of pile is less than 1.5m below working level, the concrete shall be cast to minimum of 300mm above cut off level. For each additional 0.3m increase in cut off level below working level, an additional coverage of 50mm shall be allowed.

When concrete is placed by tremie method, concrete shall be cast to the piling platform level to permit overflow of concrete for visual inspection or to a minimum of 1m above cut off level.

Control of Alignment during Pile Installation

For vertical piles, an angular deviation of 1.5% in alignment and , for raker piles , a deviation of 4% should no be be exceeded.

Piles should not deviate more than 75 mm or D/4 whichever is less from their designed positions at the working level for piles upto 600 mm diameter ( 75 mm or D/10 whichever is more in case of piles greater than 600 mm diameter).

z

τc0 0

Very high

Very low strength

Y

P

Buckling

P

z

P

τc0 0

Y

P

Buckling in very weak surrounding soil

General shear in strong lower layer

τc0 0

Y

P

P

Z Uniform Strength

Z

τc0 0

Y

P

P

Skin Friction Predominant

ROCK ANCHORS / SOIL ANCHORS

504

200

Load Test Measurement by OsterbergCell.

• Osterberg Cell is a sacrificial jack like device attached to the reinforcing steel cage or other support structure.

• After the concrete reaches the desired strength the test is conducted by inducing hydraulic pressure to the cell.

underwater strain transducer and accelerometer mounted on pile

Pile Integrity Test

strain transducer and accelerometer mounted on a pile

Pile driving analyzer

Slide 212

SIL1 DR. K K MOZA, 25/03/2008