A pile is basically a long cylinder of a strong material such as concrete that is pushed into the ground to act as a steady support for structures built on top of it. Pile foundations are used in the following situations: When there is a layer of weak soil at the surface. This layer cannot support the weight of the building, so the loads of the building have to bypass this layer and be transferred to the layer of stronger soil or rock that is below the weak layer. When a building has very heavy, concentrated loads, such as in a high rise structure, bridge, or water tank. Pile foundations are capable of taking higher loads than spread footings.