珊瑚砂动剪切模量预测的应变-损伤状态耦合模型

对南海饱和珊瑚砂进行了4类不同加载模式的不排水动三轴试验,研究了不同相对密度Dr和平均有效围压σ'0下加载第一周的动剪切模量比G1st/G0与剪应变幅值γa的关系,G1st/G0受Dr的影响很小,随σ'0的增大而增大。由于分级加载过程中土体结构与相对密度发生改变,在γa3×10-4时,应变控制的分级循环加载获得的G1st/G0-γa曲线位于等应变幅值循环加载获得的G1st/G0-γa曲线的上方。结合两类试验结果,给出了饱和珊瑚砂的G1st/G0-γa模型。基于弹性应变能理论,提出了可以描述土体损伤状态的状态参数Pd(damage parameter),探究了不同加载模式下动剪切模量比G/G0随土体损伤状态参数Pd的发展规律。在双对数坐标中,同一应变幅值下的(1-G/G0)-Pd可用直线表示,其斜率与应变幅值γa和历史加载过程中的最大应变幅值γa,max有关。结合G1st/G0-γa和G/G0-Pd关系,给出了可以同时反映应变幅值和破坏状态影响的珊瑚砂动剪切模量预测模型。

Coupled shear strain-damage state model for prediction of shear modulus of coral sand

Four series of cyclic triaxial tests with different loading forms are conducted on saturated coral sand from Nansha Islands. The relationships between shear modulus ratio G_1st/G₀ of the first loading cycle and shear strain amplitude $\gamma_{a}$ under different relative densities D_r and effective confining pressures $\sigma_{0}^{'}$ are studied. D_r shows no influence on G_1st/G₀, and G_1st/G₀ increases with the increasing $\sigma_{0}^{'}$. When γ_a is larger than 3×10^-4, the G_1st/G₀ -$\gamma_{a}$curves obtained from the strain-controlled multistage loading tests (UMγ-CTX) are higher than those obtained from strain-controlled single-stage loading tests (USγ-CTX) because of the change of the soil structure and the relative density during the reconsolidation process of UMγ-CTX. A new damage parameter P_d is proposed based on the elastic strain energy theory, and the relationships between shear modulus ratio G/G₀ and damage parameter P_d under different loading forms are studied. The (1-G/G₀) - P_d curves are almost linear in the log-log coordinate, and the slopes are dependent on the shear strain amplitude $\gamma_{a}$ and the maximum shear strain amplitude $\gamma_{a.max}$. Based on the G_1st/G₀ -$\gamma_{a}$and G/G₀ - P_d relationships, a new G/G₀ prediction model is proposed to predict the shear modulus of coral sand considering the effect of coupled shear strain amplitude and damage state.