A foundation is that part of a structure which transmits loads directly to the underlying soil. This chapter is concerned with the bearing capacity of soils on which foundations are supported, allied to the general philosophy of foundation design. If a soil stratum near the surface is capable of adequately supporting the structural loads it is possible to use either footings or a raft, these being referred to in general as shallow foundations. A footing is a relatively small slab giving separate support to part of the structure. A footing supporting a single column is referred to as an individual footing or pad, one supporting a closely spaced group of columns as a combined footing and one supporting a load-bearing wall as a strip footing. A raft is a relatively large single slab, usually stiffened with cross members, supporting the structure as a whole. If the soil near the surface is incapable of adequately supporting the structural loads, piles, or other forms of deep foundations such as piers or caissons, are used to transmit the loads to suitable soil (or rock) at greater depth. In addition to being located within an adequate bearing stratum, a foundation should be below the depth which is subjected to frost action (around 0.5 m in the United Kingdom) and, where appropriate, the depth to which seasonal swelling and shrinkage of the soil takes place. Consideration must also be given to the problems arising from excavating below the water table if it is necessary to locate foundations below this level. The choice of foundation level may also be influenced by the possibility of future excavations for services close to the structure and by the effect of construction, particularly excavation, on existing structures and services.