Piles are structural members that are made of steel, concrete or wood. They are used to create a pile foundation, which are deep and whose cost is more than the foundation. Despite the cost, the use of piles is often necessary to ensure structural safety. The following list identifies some of the conditions that require a pile foundation:
Conditions requiring the use of pile foundation
1. Compressed or weak upper soil layer
When one or more top soil layers are highly compressible and too weak to support the load transmitted by the superstructure, piles are used to load into a loadbearing bedrock or a stronger soil layer as shown in figure-A. Is. When the cornerstone is not faced at the proper depth below the ground surface, piles are used to gradually transfer the structural load to the soil. The resistance of applicable structural weight is mainly obtained from abrasion resistance developed in the clay-pile interface. (See Figure-B)
2. Presence of Horizontal Forces
When subjected to horizontal forces (see Figure-C), the pile foundation resists bending, while still supporting the vertical load transmitted by the superstructure. This type of situation commonly comes up in the design and construction of earth retaining structures and the foundations of tall structures that are subject to high wind or earthquake forces.
3. Extensive soil presence
In many cases, detailed and collapse soil may exist at the site of the proposed structure. These soils can grow to a great depth below the surface of the ground. As the moisture content increases and decreases, the expanded clay swells and contracts, and the pressure of swelling can be considerable. If the shallow foundation is used in such circumstances, then the structure can be considerable loss. However, pile foundation may be considered as an alternative when piles extend beyond the active area, where swelling and shrinkage occur. (See Figure-D) Soils like loam are collapsible in nature. When the amount of moisture increases in these soils, their structures can be broken. The sudden decrease in the zero ratio of soil inspires the big settlements of the structures supported by the shallow foundation. In such cases, pile foundations may be used in which the piles are expanded into layers of stable soil beyond the area where moisture will change.
4. Subject to uplift forces
The foundation of some structures, such as transmission tower, offshore platform, and basement matte under the water table are subject to uplift forces. Sometimes the heap is used to oppose the uplift force for these foundations. (See Figure-E)
5. Soil Erosion
Bridge abutments and piers are usually built over pile foundations to avoid the loss of bearing capacity to shallow foundations due to soil erosion on the ground surface. (See Figure-F) Although many investigations, both theoretical and experimental, have been conducted in the past to predict the lifting capacity of piles in granular and aggregated soils, the mechanisms are not yet fully understood and will never be can be. Thus the design and analysis of pile foundations can be regarded as an art as a result of the uncertainties involved in working with certain subsoil conditions. This chapter discusses the current state of the art.