Shear Strength in Terms of Coulomb C-Intercept

Document Type : Original Research


Civil Engineering School, University of Birmingham, Birmingham


Foundation design is conventionally practiced by deriving the allowable bearing capacity in terms of shear strength and compressibility. Shear strength refers to the individual or combined contribution of drained angle of internal friction and undrained cohesion, at one of the three instances of peak (failure), residual, or critical (softened) states. Compressibility refers to the elastic and consolidation settlements; the predominance of which is a factor of soil permeability. Soil is conventionally examined by confined stressing on the wet stress-state surface, for the coefficient of volume compressibility to be determined. Ultimate bearing capacity is then reduced to a certain total settlement, and an arbitrary factor of safety of 3 is finally applied to cover uncertainties. Such a conservative approach however does not always successfully restrict the settlements beneath foundation. Although the shear strength has become a muchpracticed subject, there has been a certain lack of emphasis on a fundamental understanding of shear strength parameters, and even greater neglect of the correct choice of stress path for individual soil types so to derive such parameters in the most critical stress-hydraulic environment. For that reason, this work aims to critically review the shear strength literature for a better understanding of the internal angle of friction and c-intercept.