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湛江黏土是一种具有高结构强度的灵敏性黏土,其强度包络线在固结围压达到结构屈服应力时存在明显转折,为了考察小应变条件下该黏土的动剪切模量随围压水平演化规律,开展了原状样与重塑样在不同围压水平下的共振柱试验与三轴CU试验,探讨考虑土体结构性损伤影响的动剪切模量表征方法。结果表明,重塑土最大动剪切模量Gmax随有效围压的变化可用Hardin公式很好表征,而原状土Gmax随有效围压的变化呈现先增大后减小特征,其转折点对应围压大于结构屈服应力,但最大动剪切模量与不排水剪切强度比值或经孔隙比函数归一化后的最大剪切模量随有效围压变化的转折特征点与结构屈服应力相当。出现上述现象的缘由在于该黏土Gmax同时受土体压硬性的正效应与结构损伤的负效应双重影响,当固结压力小于结构屈服压力时,正效应占主导,反之则相反。针对Hardin公式未考虑结构性损伤的影响与难以延伸极端应力水平的不足,提出具有更广适宜性的描述模式。基于不同固结压力下该黏土的静刚度与微观结构演变性状,阐明了结构性损伤对其动剪切模量影响的物理机制,并间接印证了提出表征公式的合理性。
Zhanjiang clay is a kind of sensitive clay with high structural strength. Its strength envelope changes obviously when the consolidation confining pressure reaches the structural yield stress. In order to investigate the dynamic shear modulus of the clay under confining pressure Horizontal evolution of the original shape and remodeling samples carried out under different confining pressure levels of the resonant column test and triaxial CU test to explore the impact of structural damage of soil dynamic shear modulus characterization method. The results show that the maximum dynamic shear modulus, Gmax, of the remolded soil can be well characterized by Hardin’s formula as a function of the effective confining pressure. However, the Gmax of the undisturbed soil increases first and then decreases with the change of effective confining pressure. The turning point corresponds to the confining pressure Which is larger than the structure yield stress. However, the turning feature point of the maximum shear modulus normalized to the ratio of the maximum dynamic shear modulus to the undrained shear strength or the void ratio as a function of effective confining pressure is comparable to the structural yield stress. The reason for the above phenomenon is that the clay Gmax is affected by both the positive effect of soil compressive rigidity and the negative effect of structural damage. When the consolidation pressure is less than the yield stress of the structure, the positive effect dominates and vice versa. In view of the fact that Hardin’s formula does not consider the influence of structural damage and the difficulty of extending the extreme stress level, a more appropriate descriptive mode is proposed. Based on the static stiffness and the microstructure evolution of the clay under different consolidation pressures, the physical mechanism of the structural damage on the dynamic shear modulus is clarified and the rationality of the proposed formula is indirectly confirmed.