Deep foundation - Pile group - load carrying capacity

Pile group

1. PILE GROUPPILE GROUPPILE GROUPPILE GROUP

7. LOAD CARRYING CAPACITY OF PILE GROUP

9. Group Efficiency,

12. NEGATIVE SKIN FRICTIONNEGATIVE SKIN FRICTION

13. 
Negative friction is a downward shear drag acting on a pile due
to the downward movement of the surrounding compressible soil
relative to the pile.

Figure shows the pile passing through a
recently constructed cohesive soil fill. The
soil below the fill is completely consolidated
Negative Skin FrictionNegative Skin Friction
soil below the fill is completely consolidated
under its overburden pressure.

14. FRICTIONFRICTION
NEGATIVE SKIN FRICTIONNEGATIVE SKIN FRICTION

17. 
Negative Skin Friction will occur due
to the following reasons:

When the surrounding compressible soil
has been recently filled.

If the fill material is loose cohesion less soil.
By lowering the ground water which
Cont...Cont...

If the fill material is loose cohesion less soil.

By lowering the ground water which
increases the effective stress causing
consolidation of the soil with resultant
settlement and friction force being
developed on the pile.

It also occurs when the fill is over the peat
or a soft clay stratum.

18. 
Cont...Cont...

19. Factors governing the selection of pilesFactors governing the selection of piles

The bearing capacity of soil

Characters of structure,

Types of loading

Length of the pile in relation to the load and type of soil,

Availability of the materials,

Installation technique like driven or bored

Spacing and Symmetry of piles in a group

Spacing and Symmetry of piles in a group

Location of pile in the group

Location of pile cap i.e. above or below soil

Shape of the pile cap, etc.

Drainage conditions in soil

Factors causing deterioration,

Ease of maintenance,

Estimated cost of types of piles, taking into account the initial
cost, life expectancy and cost of maintenance and,