On made up ground and ground with poor bearing capacity where a firm, natural bed of, for example, gravel or sand is some few metres below the surface, it may be economic to excavate for isolated piers of brick or concrete to support the load of buildings of some four storeys in height. The piers will be built at the angles, intersection of walls and under the more heavily loaded wall such as that between windows up the height of the building.
Pits are excavated down to the necessary level, the sides of the excavation temporarily supported and isolated pads of concrete are cast in the bottom of the pits. Brick piers or reinforced concrete piers are built or cast on the pad foundations up to the underside of the reinforced concrete beams that support walls as illustrated in Fig. 11. The ground beams or foundation beams may be just below or at ground level, the walls being raised off the beams.
The advantage of this system of foundation is that pockets of tipped stone or brick and concrete rubble that would obstruct bored piling may be removed as the pits are excavated and that the nature of the subsoil may be examined as the pits are dug to select a level of sound subsoil. This advantage may well be justification for this labour intensive and costly form of construction.
Fig. 11 Pad foundation.