Cavity expansion and cone penetration resistance in anisotropic clay

Abstract

Due to strength anisotropy, the undrained shear strength of naturally deposited clay can vary with its position in the coordinate. When subjected to a spherical expansion, the undrained shear strength of clay yields the lowest value in the horizontal direction and the largest value in the vertical direction. To represent the nature of clay, a model based on the anisotropic undrained strength criterion has been developed in this paper to determine the anisotropic undrained shear strength under a spherical expansion condition. To simplify the model, the effects of in‐situ initial stresses, anisotropy, and the anisotropy of soil deformability are not taken into account here. Combining the spherical cavity expansion theory and the anisotropic undrained shear strength under spherical expansion conditions, a simplified limit pressure of spherical cavity expansion in anisotropic clay has been established. The magnitude of limit pressure is related to its position in the spherical cavity. Based on the limit pressure in spherical cavity expansion derived from anisotropic strength, the cone factor of an advancing cone has been derived to correlate the cone resistance and undrained shear strength of clay. The calculated cone factors uniquely correspond to the undrained shear strengths determined from different tests and are interrelated to each other in terms of strength anisotropy ratio Ar of clay. The accuracy of the calculated cone factors has been satisfactorily verified with laboratory and field CPTU results. However, it has also been found that the effect of strength anisotropy only becomes obvious when clay has a low rigidity and high strength anisotropy. If the strength anisotropy of clay is not considered, a less than 15% error on the value of the cone factor will result.