What is the main principle behind friction piles?

The main principle behind friction piles is their reliance on soil adhesion and friction to transfer the load from the structure to the surrounding soil. This type of foundation is particularly useful in scenarios where the bearing capacity of the shallow soil layers is insufficient to support the structure. Friction piles achieve their support by mobilizing friction between the surface of the pile and the surrounding soil as the load is applied.

The effectiveness of friction piles is largely influenced by the characteristics of the soil, including its cohesion and density. As the pile is driven or excavated into the ground, the soil's frictional resistance and adhesion work together to provide the necessary support. This principle is vital for ensuring that the load is adequately distributed and managed by the pile system.

Other options discuss different aspects that are not directly related to the function of friction piles. The bearing capacity of rock pertains more to end-bearing piles, which rely on the rock substrate for support. The use of water for stability typically relates to the behavior of certain types of soil or methods of installation, not the fundamental principle of friction piles. Lastly, while concrete casing can be used in certain pile systems for durability and strength, it is not a defining characteristic of friction piles themselves.