FOUNDATION

in engineering and architecture, is the formation upon which a building or structure is reared. In erecting a building, for instance, the surface earth is removed, and the building begins when the natural formation of the place is reached. The nature of this formation depends entirely on the locality of the structure. In one place it may be clay, which, when level, forms a very good foundation; in another, running sand, which forms an exceedingly bad one. It is e ential that the foundation should not move, and, consequently, clay on a hillside, for instance, is to be avoided if po ible, as clay so situated is apt to slip. Running sand is out of the question, unle specially treated. The permanence of the foundation being a ured, its merit from one point of view is measured by the load it can carry per square foot. The following table gives the usual permi ible loads (Colonel Seddon):— Material ge aterial. per sq. ft. Hard rock.. ce So. Rock, of strength of good concrete a6 bio), GR Very soft rock Ae coe es Firm earth and hard clay 1 to 1:5. Clean dry gravel and clean sharp sand, prevented from spreading sideways 1 to 1:5. In places where running sand, or an unreliable formation, is encountered, piling is often used. Wooden piles, which may be anything up to 100 feet long, are driven downwards into the ground, sometimes two or three being driven one above the other, so that the deepest one may go down some 300 feet. The piles may be wooden beams or they may be made of concrete. They are driven into the ground by a pile-driver. On the top of these piles a concrete raft is usually formed, which consists of a flat layer of concrete from, say, 3 iuches to 5 feet thick. This concrete platform or raft is allowed to set, and upon it the building is erected. Submerged foundations are another important cla which requires special treatment. This cla includes the foundations of breakwaters, bridges, . It is usual to form such foundations with Portland cement, which is thrown, in sacks, into the sea or river, where the foundation is required. In course of time these sacks of cement form a solid ma . Upon this artificial ‘bed of rock’ the structure is raised. In bridge-work every effort is made to find natural and firm foundations for the piers, but it may be nece ary to reinforce these with concrete in the artificial way described above. Each of the columns of the Tower Bridge in London is raised on a bed of granite lying on the natural clay bed of the river.— BIBLIOGRAPHY: W.M. Patton, A Practical Treatise on Foundations; C. E. Fowler, Ordinary Foundations, dies the Coffer-dam Proce for iers.