Abstract: The process of change and distribution of effective additional stress acting on a foundation base, the tensile stress of foundation concrete reinforcing bars and vertical deformation of foundation soil were investigated via methods of field monitor and data analysis. It shows that the contribution to settlement, influenced by dewatering of foundation pit, made by effective stress increment of soils overlying foundation base, should not be neglected; that the compressive stress acting on foundation base cannot be simply assumed as a uniform load, and the situation of the largest vertical deformation occurring does not keep in line with the working point of the largest stress; that the settlement values of foundation base in different places are usually different, and settlement at the centre of a large foundation maybe not the largest; that during the period of construction, the tensile stress of concrete reinforcing bars changed with time alternately, and the maximum tensile stress is just about 25%, which is far lower than the allowable strength of the reinforcing bars. The modulus of deformation of deeper sandy soil is usually larger than that of shallower sandy soil, but the empirical coefficient of settlement calculation of deeper sandy soil is smaller than that of shallower sandy soil. The conclusions mentioned above can offer a reference to the design of large concrete footing and layered sandy foundation bases.