**friction pile**. Here one of the embedded surfaces is the pile surface.

**End bearing piles**are piles that transfer the load to the lower stratum. Specially designed piles will transmit the load by both the means.

Contents:

**Suitability of Pile Foundation in Construction**

The pile foundation is generally employed in the following type of soil strata:
- Area with compact or hard stratum, underlying soil is soft material, sand or clay
- The area with clayey soil with soft stratum overlying the firm layer. Here the open foundations lead to high settlement
- Dense or stiff soil with soft clay overlaid. Here the open foundations can be spaced closely to reduce the pressure that is transmitted to the soft layer
- Alternative layers of clay- soft layer and thick in nature
- Sandy strata with high water table. This brings difficulty for excavation

**Spacing of Pile Foundation in Pile Group Construction**

The piles must be arranged in such a way that the force exerted by one of the piles on the other is least. In the case of friction piles, this factor is very important. This is because the soil surrounding the piles are in a stressed condition. This force exertion will affect the frictional resisting capacity of the neighboring piles.
The influence lines of a cluster of piles on the surrounding ground are shown in the figure-1. The lines show the stress intensities at a point. More the distance from the pile edge surface, lesser is the stress intensities. So, this provides an idea on the minimum spacing that must be provided between the two piles.
**Fig.1: Pressure Distribution represented by Influence lines in the case of End Bearing Piles**

**Fig.2: Pressure Distribution represented by Influence lines in the case of Friction Piles**

**End bearing piles: Spacing S = 2.5d + 0.02L**

**Cohesion Piles: Spacing S = 3.5d + 0.02L**

*d*is the diameter of the pile and

*L*is its length. The standard also stipulates for pile capacity till 300 kN, the distance from the edge of the pile to the pile stem must be 100mm. For higher capacities, the mentioned distance must be 150mm.

**Maximum Pile Foundation Spacing**

The Maximum pile spacing should be decided by considering two factors:
- The design of pile cap
- Overturning Moments

**Soil Friction Factors for Pile Foundation**

The skin friction factors help in the preliminary estimation of the pile capacity. The value of the soil friction factor varies from driven to bored piles. This factor can be used only for preliminary calculations.
Before a final decision is taken, a full-scale load test must be carried out. The table-1 shows the approximate skin friction factors in saturated clay. Here Ro is the consolidation ratio.
**Table.1: Skin FrictionÂ Factors of Saturated Clay**

Pile Length in meters |
Clay Driven Piles Normally Consolidated |
Over Consolidated Clay- Driven Pile |
Over Consolidated Clay- Bored Pile |

20 | 0.3 | 0.3 |
0.15 |

40 | 0.2 | 0.2 |
0.1 |

60 | 0.15 | 0.15 |
0.08 |

**Read More:**

**Capacity of Pile Group and Efficiency**

**Determination of Piles Settlement by Load Test**

**Concreting of Pile Foundations â€“ Workability and Quality of Concrete for Piles**