BACK-ANALYSIS OF DEFORMATION AND MOHR-COULOMB STRENGTH PARAMETERS BASED ON INITIAL STRAIN METHOD

Abstract

This note proposes a numerical procedure in which both deformation modulus and Mohr-Coulomb strength parameters are back-calculated from a load-displacement response monitored in the field. The back-analysis of nonlinear constitutive parameters contains the difficulty that most nonlinear constitutive models employ stress as the fundamental variable to govern the change in deformation modulus and to specify the yield criterion, and that the stress is little sensitive to the change in deformation modulus. This difficulty is easily solved by applying the initial strain method for nonlinear stress-strain analysis, because the stress calculated by the method does not directly depend on the tangent modulus of rigidity. By combining a hyperbolic stress-strain equation, FEM based on the initial strain method and mathematical programming technique, the procedure allows to correct unknown soil parameters until the difference between calculated and monitored load-displacement curves decreases sufficiently. The proposed procedure is applied to some hypothetical case studies of in-situ testing and its validity is verified. The result indicates an important role of the initial stresses within subsoil, because the effects of friction angle and cohesion can be evaluated separately, only when the confining pressure exceeds a certain value.