Effect of Compressibility on Bearing Pressure of Soft Ground

Most theories of bearing capacity of foundations on or in ground are based on the assumption that soil is incompressible and its stress–strain behavior is rigid-perfectly plastic following Mohr–Coulomb failure criteria. Menard (1957) proposed a theory for estimation of limit pressure for pressure meter that incorporates compressibility of soils in the form of rigidity index, $$I_{\text{r}} = G/c_{\text{u}}$$ (ratio of shear modulus to undrained shear strength of soils). Vesic (1973) derived compressibility factors for cohesive–frictional soils for the estimation of the ultimate bearing capacity of footings. The present study focuses on the variation of bearing pressure factor $$(N_{{\text{cf}}} = q/c_{\text{u}} )$$ for circular footings on soft ground with settlement, for a wide range of rigidity indices $$(I_{\text{r}} )$$ . Finite element axisymmetric analysis is carried out to evaluate the bearing pressure, q, versus settlement responses for circular footings for a range of $$I_{\text{r}}$$ from which $$N_{{\text{cf}}}$$ is obtained at different settlement ratios (SR). Perfectly rigid plastic response, i.e., incompressible soil is achieved for $$I_{\text{r}} = 5000$$ at SR of 0.25%. Normalized $$N_{{\text{cf}}}^{\prime}$$ (ratio of $$N_{{\text{cf}}}$$ of compressible soil to that of incompressible one) are derived as function of rigidity index, $$I_{\text{r}}$$ for different normalized $${\text{SR}}^{\prime}$$ (ratio of SR of compressible to incompressible soil).