PILE FOUNDATION.pptx

pile foundation

1. PILE FOUNDATION

2. Types of foundation 1) Shallow Foundation Eg : Single footing, Strap footing, Raft foundation etc. 2) Deep Foundation Eg : Pile foundation, Well foundation, Pier foundation etc.

3. What is Pile Foundation…? A Pile foundation is a kind of deep foundation, can be defined as a slender column or long cylinder made of materials such as concrete or steel which are used to support the structure and transfer the load at desired depth either by end bearing or skin friction

4. Requirement of Pile Foundation The upper strata is very weak and compressible Irregular structure having chances of differential settlement Resist horizontal forces in addition to vertical load. Earth pressure for earth retaining structure and high wind and seismic forces for tall structures. Foundation soil is susceptible to Erosion and Scour Suitable for transmission tower, Off-shore platform which are subjected to uplift Expansive soil (Black cotton soil) which swells and shrinks as water content changes, Piles are used to transmit the load below active zone.

5. CLASSIFICATION OF PILES BROAD CALSSIFICATION DRIVEN (DISPLACEMENT PILES) BORED (NON DISPLACEMENT PILE) ON THE BASIS OF MATERIAL TIMBER STEEL PCC RCC PSC COMPOSITE

6. CLASSIFICATION OF PILES Method of construction Driven precast piles- Driven in Soil by applying blows of heavy Hammer on the top Driven cast in situ piles- Driving a casing with closed bottom end, later filled with concrete. Casing may or may not be withdrawn . Bored precast piles- A bore is excavated inside soil and a pile casted in yard put into it. Bored cast in situ piles – Excavating a bore into ground and filling it with concrete.

7. CLASSIFICATION OF PILES Mode of load transmission 1. End bearing piles Transmit the load through their bottom tip to a hard strata 2. Friction piles Transmit the load through skin friction between pile surface and surrounding soil 3. Combined End Bearing and Friction pile Transfer the Load by both skin friction and end bearing.

8. CLASSIFICATION OF PILES... contd SECTIONAL AREA CIRCULAR SQUARE TUBULAR OCTAGONAL H-SECTION SIZE MICRO (MINI) PILES (<150 mm) SMALL DIAMETER PILE (>150 mm < 600 mm) LARGE DIAMETER PILE (>600 mm)

9. SELECTION OF TYPE OF PILE: driven or cast-in-situ ? Availability of Space : Driven Piles require large areas and head room since it needs larger and heavier driving rigs Proximity to Structures : driving cause vibrations in ground which may cause damage to nearby structures Reliability : Precast driven piles ensure good quality of material, uniform section of piles Cast in situ piles can be formed to any desired length and no cutting of pile or addition to length required

10. SPACING OF PILES Minimum Centre-to- centre distance between piles Shall be governed by Practical aspects for installing the piles, Diameter of pile, and Nature of load transfer to the soil and possible reduction in the capacity of group of piles thereby

11. Spacing… contd FOR END BEARING PILES Pile founded on Hard strata and deriving the capacity mainly from end bearing, Minimum spacing 2.5D 2.0 D for piles resting on rock FOR FRICTION PILES Sufficiently apart to avoid overlapping zones of soil Not less than 3 D MAX SPACING 4 D

12. INSTALLATION OF pile…

13. TREMIE CONCRETING Minimum cement content not less than 400 kg/cum and slump between 150-180 mm The tremie should be water tight and a hopper attached to its head by a water tight connection. Tremie pipe should have minimum dia of 200 mm for pile dia more than 600 mm. A steel plate or ball shall be placed at bottom of hopper and the hopper is filled with concrete. The first charge of concrete sent by removal of this plate and ball. The tremie should always be kept full of concrete and should always remain inside concrete.

14. Tremie concreting… contd Concreting of pile should be uninterrupted In case of interruption, shall be resumed within 1-2 hr. Tremie shall not be taken out and raised and lowered time-to-time to prevent concrete to set. In case of withdrawal of tremie for any reason, the tremie may be inserted 60 cm to 100 cm in old concrete and resume the concreting. Top of concrete should be min 600 mm above cut off level to remove all laitance and weak concrete.

15. Tremie concreting

16. Overloading When a pile in a group, designed for a certain safe load is found, during or after execution, to fall just short of the load required to be carried by it, an overload up to 10 percent of the pile capacity may be allowed on each pile. The total overloading on the group should not, however, be more than 10 percent of the capacity of the group subject to the increase of the load on any pile being not more than 25 percent of the allowable load on a single pile.

17. PILE LOAD TEST Initial Load Test – Test conducted on pile at the initial stage of project to find the design load of pile. It is done on non working piles. Routine Load Test – Test conducted on working pile to check its capability to take working load without exceeding permissible settlement .

18. PILE LOAD TESTING Purpose of Initial Load Test Arrive at safe load by applying FOS on ultimate load capacity determined from tests To provide guidelines for setting up limits for acceptance of routine tests To have a check on safe load calculated by static or dynamic formulae

19. PILE LOAD TESTING Initial Test For small size projects ( total piles less than 1000) , a minimum of two tests For large projects ( piles more than 1000), a minimum of two tests for first 1000 piles and additional one test for every additional 1000 piles and part thereof Initial test piles should be installed by the same technique, same type of equipment as that proposed for working piles The test load in INITIAL TEST shall not be less than 2.5 times the estimated safe load Initial pile load test shall preferably be carried out before taking up the piling job

20. PILE LOAD TESTING Routine Test On 0.5 percent of total number piles subject to a minimum one test, can be increased to 2% depending on nature of strata . Purpose It is carried out on a working pile with a view to check whether pile can take the working load assigned to it Detection of any unusual performance contrary to the findings of initial test. Workmanship

21. ACCEPTANCE CRITERIA FOR ROUTINE TEST The routine test shall be carried out for a test load of at least 1.5 times the working load The maximum settlement at the load being not greater than 12 mm for piles up to 600 mm dia 18 mm or 2 percent of pile dia whichlever less for piles of dia more than 600mm

22. PILE LOAD TESTING METHODS Maintained Load Method : applicable for both initial and routine test Cyclic Method : this method is used in case of initial test to find out separately skin friction and point bearing load on single piles

23. MAINTAINED LOAD METHOD Pile Head should be chipped off till sound concrete met. The projecting reinforcement cut off or bent suitably and pile head finished smooth . Test should be carried out by applying a series of vertical downward incremental load, each increment being about 20 percent of safe estimated load on pile Each stage of loading shall be maintained till the rate of movement of the pile top is not more than 0.2mm/h or until 2h have elapsed, whichever is earlier subject to a minimum of 1 h The test load is maintained for 24 hours

24. MAINTAINED LOAD METHOD Vertical loading on single pile shall be continued till one of the following takes place : In case of Initial Load Test: Applied load reaches 2.5 times the safe estimated load; or Max settlement of pile exceeds a value of 10 percent of pile diameter in case of uniform dia piles and 7.5 percent bulb dia of under-reamed piles.

25. MAINTAINED LOAD METHOD In case of routine load test : Applied load reaches 1.5 times the working load ; or Max settlement of pile exceeds a value of 12 mm for piles dia up to and including 600mm and 18 mm or maximum of 2 percent of pile dia whichever is less for piles of dia more than 600 mm.

26. safe load initial test The safe load on a single pile will be least of the following (A) For piles upto 600 mm dia : Two third of the final load at which total displacement attains a value of 12 mm 50 % of the final load at which the total displacemnt equals 10 % of the dia. of pile for uniform dia piles and 7.5 percent of bulb dia for under-reamed piles.

27. SAFE LOAD-INITIAL TEST FOR PILES MORE THAN 600 MM DIA : Two-thirds of the final load at which the total displacement attains a value of 18mm or maximum of 2 percent pile diameter whichever is less. 50 % of the final load at which the total displacemnt equals 10 % of the dia. Of pile for uniform dia piles and 7.5 percent of bulb dia for under-reamed piles.

28. Load settlement curve SAFE LOAD ( piles upto 600 mm dia ) Least of 2/3 P1 or ½ P2

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