Structural damage effect on dynamic shear modulus of Zhanjiang clay and quantitative characterization

The Zhanjiang clay is a kind of sensitive clay with high structural strength, whose failure envelope has a significant breakpoint when the confining pressure reaches the structural yield stress. The resonant column tests and CU triaxial tests are performed on undisturbed and remoulded specimens to investigate the evolution rules of dynamic shear modulus with confining pressure under small strain, and the characterization method for dynamic shear modulus considering the structural damage effect is also discussed. The results show that the values of G_max of remoulded and undisturbed specimens with the confining pressure are different: the former can be well described by the formula of Hardin, while the latter increases initially then decreases; and confining pressure at the the turning points are higher than the yield stress, however, the turning points of the ratio of shear modulus to shear strength or the normalized shear modulus by the void ratio function with confining pressure are close to the yield stress. The reason is that the values of G_max of the structured clay are influenced by both the positive effect of compressive hardening and the negative effect of structural damage, and the former is predominant when the confining pressures are less than the yield stress, otherwise it is opposite. Focusing on the deficiencies of the formula of Hardin without considering the structural damage effect and difficultly extending to the extreme stress level, a widely suitable expression mode is proposed. Based on the change of static rigidity and microstructure of Zhanjiang clay with consolidation pressure, the physical mechanism of influence of structural damage on dynamic shear modulus is illustrated, and the rationality of the proposed formula is confirmed indirectly.