Up to the latter part of the nineteenth century, when Portland cement first carne into general use for making concrete, the majority of buildings were built directly off the ground. Walls of stone or brick were built on a bed of rough stones or brick footings and timber framed buildings on a base of rough stones or brick. As walls were built their weight gradually compressed soils such as clay, sand or gravel to form a sound, adequate foundation.
Local experience of the behaviour of soils and rocks, under the load of buildings, generally provided sufficient information to choose a foundation of the required depth and spread by this method of construction.
Where a small variation of the degree of compression of soils under buildings occurred the natural arching effect of the small, bonded units of stone and brick and the flexibility of lime mortar would allow a transfer of load to the sound foundation without damage to the building.
Fig. 1 Brick fottings.
From the beginning of the twentieth century concrete was increasingly used as a foundation base for walls. Initially concrete bases were used for the convenience of a solid, level foundation on which to lay and bond stone and brick walls. Brick walls which, prior to the use of concrete, had been laid as footings, illustrated in Fig. 1, to spread the load, were built on a concrete base wider than the footings for the convenience of bricklaying below ground. This massive and unnecessary form of construction was accepted practice for some years.
With the introduction of local and, more recently, general building regulations in this century, standard forms of concrete foundations have become accepted practice in this country along with more rigorous investigation of the nature and bearing capacity of soils and rocks.
The move from the practical, common sense approach of the nineteenth century to the closely regulated systems of today has to an extent resulted in some foundations so massive as to exceed the weight of the entire superstructure above and its anticipated loads. This tendency to over design the foundations of larger buildings has been exacerbated by the willingness of building owners to seek compensation for damage, caused by the claimed negligence of architects, engineers and builders who, in order to control the amount of premium they pay for insurance against such claims, have tended to over design as an insurance.