1. S S SUBMITTED BY:- CHARU BHARDWAJ civil engineering 0804300010
PILE FOUNDATION
S S SUBMITTED BY:-
CHARU BHARDWAJ
civil engineering

2. DEFINITION
Pile foundation is a deep foundation used to transfer the loading to a deeper, more competent strata at depth if unsuitable soils are present near the surface. This is usually done when depth >3 m below finished ground level. In pile foundation, piles of different material in different manner are used.

3. Continued
Piles are relatively long , slender members that transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata of high bearing capacity.
In addition to supporting structures , piles are used to anchor structures against uplift forces and to assist structures in resisting lateral and overturning forces.

4. NECESSITY OF PILE FOUNDATION
When the strata at or just below the ground surface is highly compressible and very weak to support the load transmitted by the structure.
Pile foundations are required for the transmission of structure loads through  deep water to a firm stratum.
In case of expansive soil, such as black cotton soil, which swell or shrink as the water content changes, piles are used to transfer the load below the  active zone.

5. CLASSIFICATION OF PILE FOUNDATION
Pile foundation is classified into 3 categories as given below:
According to type of pile:-
End bearing piles
Friction piles
Settlement reducing piles
Tension piles
Laterally loaded piles
Piles in fill

6. According to type of construction:
Continued
According to type of construction:
Precast driven piles
Driven cast-in-situ piles
Bored cast-in-situ piles
Bored pre-cast piles
Driven steel piles
Driven timber piles

7. According to type of material used:-
Continued
According to type of material used:-
Timber piles
Steel piles
Pre-stressed concrete piles
Composite piles

8. FACTORS INFLUENCING CHOICE OF PILE
Location and type of structure
Ground conditions
Durability
Cost

9. LOADS APPLIED TO PILES V M H
Combinations of vertical, horizontal and moment loading may be applied at the soil surface from the overlying structure.
For the majority of foundations the loads applied to the piles are primarily vertical.
For piles in jetties, foundations for bridge piers, tall chimneys, and offshore piled foundations the lateral resistance is an important consideration.

10. continued
The analysis of piles subjected to lateral and moment loading is more complex than simple vertical loading because of the soil-structure interaction.
Pile installation will always cause change of adjacent soil properties, sometimes good, sometimes bad.

11. Modes of failure The soil failure is always caused by punching shear.
The failure mode of pile is always in buckling failure
mode.

12. Ultimate capacity of axially loaded single pile in soil
Like a shallow foundation, a pile foundation should be safe against shear failure and also the settlement should be within the permissible limits.
The methods for load carrying capacity are grouped in 4 categories given below:
Static Methods
Dynamic Methods
In-situ penetration tests
Pile load test

13. Static methods Qu
These methods give ultimate capacity of individual pile, depending upon characteristics of the soil.
Qu = Qp + Qs
where, Qu = ultimate failure load
Qp = point resistance of pile
Qs = shaft resistance developed by friction b/w soil and pile shaft. Qs Qp

14. Static methods for driven piles in sand
Qu = Qp + Qs where Qp = qpAp and Qs = fsAs qp is ultimate bearing capacity of soil Ap is area of pile tip fs is average unit friction b/w sand and pile surface As is effective surface area of pile in contact with soil

15. Static methods for driven piles in saturated clay
Qp = qpAp qp = unit point resistance equal to ultimate bearing capacity qu = cNc + qNq Nq = 1 for cohesive soil Nc depends upon D/B ratio and it varies from 6 to 9. Qs = caAs unit adhesion b/w clay and pile shaft (Ca )= αc’ α is adhesion factor c’ is average cohesion along shaft length

16. Static methods for bored piles
Bored piles in sand:-
Qu = (q’Nq)Ap + Ʃ(K ’v tan (As)i
where ’v = effective vertical pressure
lateral earth pressure coefficient (K)= 1-sin
tan = coefficient of friction b/w sand  concrete
Bored piles in clay:-
Qu = c.Nc .Ap + c’As
where As = area of shaft
 depends upon pile type and method of drilling

17. DYNAMIC METHODS Engineering news record formula:- Qu = (Whh)/(S+C)
where, S = penetration of pile per blow
C = constant(for drop hammer,C= 2.54cm  for steam hammer,C = 0.254cm)
h = efficiency of drop hammer
(b/w 0.70.9 for single acting hammer and
b/w 0.750.85 for double acting hammer
b/w 0.80.9 for diesel hammer)
Note:-A factor of safety of 6 is usually recommened.

18. continued Danish formula:- Qu = (W.h.h)/(S+0.5So)
where So = [(2hWhD)/(AE)]^0.5
So = elastic compression of pile
D = length of pile
A = cross–sectional area
E = modulus of elasticity of pile material
Note:- The allowable load is found by taking factor of
safety of 3 to 4.

19. continued Hiley formula:- Qu = (W.h.b.h)/(S+ 0.5C)
where, h = efficiency of drop hammer
h = height of free fall of ram or hammer
S = final penetration per blow cm
C = sum of temporary elastic compression
of pile, dolly and ground
b = efficiency of hammer blow

20. IN- SITU PENETRATION TEST
Standard penetration test
Dutch cone test

21. PILE LOAD TEST
Static pile load test is the most reliable means of determining the load capacity of a pile. The test procedure consists of applying static load to the pile in increments up to a designated level of load and recording the vertical deflection of the pile. The load is usually transmitted by means of a hydraulic jack placed between the top of the pile and a beam supported by two or more reaction piles. The vertical deflection of the top of the pile is usually measured by mechanical gauges attached to a beam, which span over the test pile.

24. Soil Mechanics and foundation engineering by K.R.Arora
References
Soil Mechanics and foundation engineering by K.R.Arora

25. THANK YOU