AN ANISOTROPIC CONSTITUTIVE MODEL CONSIDERING DILATANCY EFFECT AND ITS APPLICATION IN CAVITY EXPANSION

The overconsolidated clay in natural sedimentary site has both anisotropy and dilatancy properties, but there are few constitutive models that can accurately describe the above properties at the same time, and it is even more rare to apply the model to the analysis of soil cavity expansion stress field. Three points of work have been done in this paper. (1) Based on the UH model of overconsolidated clay, the phase transformation stress ratio with the overconsolidation degree is introduced, and the dilatancy behavior affected by the overconsolidation degree is reflected by the non-correlated flow rule. (2) The modified rotation-hardening rule is adopted to drive the rotation axis of the yield surface and the plastic potential surface by the increment of plastic strain to reflect the initial anisotropy and the stress-induced anisotropy under cyclic loading. The three-dimensional modified UH model is obtained by using the transform stress method based on SMP criterion. (3) A self-similarity method is proposed to simulate the cavity expansion of soil. The measured data show that the normal or slightly overconsolidated clay is in the volume shrinkage deformation mode under shear loading, the moderately overconsolidated clay is in the shear contraction and then dilatancy deformation mode, and the severely overconsolidated clay is in the complete dilatancy deformation mode. K₀ consolidated clays exhibit higher shear stiffness and slightly higher residual strength. The proposed model can describe the dilatancy law and anisotropy properties. The three-dimensional constitutive equation and self-similarity method of the revised UH model are used to analyze the distribution of soil stress field for cavity expansion under the conditions of over-consolidation and K₀ consolidation. A series of laboratory tests and in-situ tests of various types of clay are compared with the prediction of the proposed model and analytical solution method. The rationality and applicability of the proposed model and analytical method are verified.