Determination of Active Zones below Footings

To predict structure settlement, a designer must know the thicknesses of active (deformation) zones that develop under structure foundations. Numerous methods have been offered to calculate active zone dimensions, generally based on the assumptions that active zone thicknesses are functions of the applied load values, physical and mechanical properties of supporting soils, and footing depths, as well as footings geometry and dimensions. This paper presents a method for estimating active zone dimensions, based on the knowledge of soil structural pressure values, σ_sz (structural pressure value, σ_sz, is the maximum stress value for which only recoverable deformations may be observed). The applicability of the obtained equations were verified, using only the results of tested square footings supported by similar quasi-elastic cohesive soils in which physical and mechanical properties did not vary significantly. It was assumed that the stresses applied to footings decreased linearly with depth, and that no friction existed between soils and footings. The paper presents empirical relationships between footing settlements, active (deformation) zone thicknesses, and footing dimensions.