Foundation Area

an excavation in the ground intended for the installation of the foundations of buildings and other engineered structures. The foundation area is usually dug from the surface of the ground, but in some cases it may be excavated by caissons. The dimensions of the foundation area in terms of area and depth are determined by the design and function of the structure, the level at which soil capable of supporting the load of the structure lies, the depth at which the soil freezes, and other factors. When building on permafrost soils, consideration must also be given to the thermal interaction of the structure and the ground.

To ensure the stability of the foundation area, it is built with sloping sides whose steepness is determined by the angle of repose. This angle, in turn, is dependent upon the angle of internal friction and cohesion, the load, the moisture of the soil, and other conditions. The angle of repose is between 15° and 50° for different types of ground. When foundation areas are very deep, the sides are given varying steepness. Where there is unstable ground, the sides of the foundation area are protected against caveins and slides by matched barriers, struts, and other means. Groundwater is removed from the foundation area by pumps or by drawdown devices. Under difficult engineering and geological conditions, unstable ground is artificially reinforced by freezing, silicification, and bitumenization. Different types of earthmovers, such as excavators, scrapers, and bulldozers, are used to create the foundation areas for new structures. On flooded terrain, foundation pits are made by suction dredges and water-jet pumps. Special machines which operate on the boring principle are used to dig foundation areas for separate supports and columns.