ABSTRACT
Various theories relating to the ultimate bearing capacity of shallow foundations were presented in Chapters 2, 3, and 4. In section 2.12 a number of definitions for the allowable bearing capacity were discussed. In the design of any foundation, one must consider the safety against bearing capacity failure as well as against excessive settlement of the foundation. In the design of most foundations, there are specifications for allowable levels of settlement. Refer to Figure 5.1, which is a plot of load per unit area q versus settlement S for a foundation. The ultimate bearing capacity is realized at a settlement level of Su. Let Sall be the allowable level of settlement for the foundation and qall(S) be the corresponding allowable bearing capacity. If FS is the factor of safety against bearing capacity failure, then the allowable bearing capacity is qall(b) = qu/FS. The settlement corresponding to qall(b) is S′. For foundations with smaller widths of B, S′ may be less than Sall; however, Sall < S′ for larger values of B. Hence, for smaller foundation widths, the bearing capacity controls; for larger foundation widths, the allowable settlement controls. This chapter describes the procedures for estimating the settlements of foundations under load and thus the allowable bearing capacity.
