ESTIMATION OF NONLINEAR CONSTITUTIVE PARAMETERS BASED ON MONITORED MOVEMENT OF SUBSOIL UNDER CONSOLIDATION

Described is a numerical procedure to back-analyze the nonlinear constitutive parameters and permeability from the monitored movements of subsoil under two-dimensional consolidation. The difficulty in the back-analysis of nonlinear constitutive parameters lies on the fact that most of the nonlinear constitutive models employ the stress as the fundamental variable to govern the change in the deformation moduli and to specify the yield criterion, and that the stress is little sensitive to the change in deformation moduli. At first, the authors devise a simplified hyperbolic stress-strain model in which the shear strain is the variable controlling the decrease in deformation modulus and in which the shear strength is not related to the confining pressure. The unknown soil parameters to be back-analyzed are the initial tangent moduli of rigidity, the shear strengths and the permeabilities in multiple soil layers. By combining FEM and mathematical programming technique, the procedure allows to correct the unknown soil parameters until the differences between calculated and measured quantities decrease sufficiently. The proposed procedure is verified by calibrating the performance of the procedure being applied to hypothetical case studies. Subsequently the procedure is applied to actual case studies and comparisons are made with the results obtained by assuming the linear elastic behaviour of soil deposit. By applying the proposed procedure of back-analysis to the observational procedure in construction phase, one can get the rough estimate of shear strength at each time stage of construction.