Anisotropic bounding surface model for natural structured clays

Natural clays are usually structured clays due to their grain cementation during the long deposition process,and exhibited anisotropic deformation behavior originating from the anisotropic arrangement of grains.A pragmatic bounding surface model was proposed for natural structured clays with emphasis both on structure and anisotropy.An anisotropic tensor and a structural parameter were involved in the formulation of the bounding surface,which served as a reference surface for defining plastic yielding and modulus.The initial anisotropy of natural clays was described by properly assigning the initial value of the anisotropy tensor,which depended mainly on the initial stress state.The anisotropy induced by the following loading process was described by an evolution law of the anisotropic tensor.Through assigning an initial value to enlarge the bounding surface the high intact stiffness and peak strength behavior of structured clays were described,and appreciable reduction of stiffness and strength due to destructuration were considered by assigning the structural parameter a descending function with the accumulation of plastic strain.Validity of the model was verified by the test data of several structured clays.