钙质砂固结排水剪切特性三轴试验

为给中国南海岛礁吹填钙质砂地基上基础设施提供设计与施工参考，通过一系列三轴试验研究了钙质砂固结排水剪切特性。定性分析了钙质砂应力-应变、体变与应力路径变化规律，非线性拟合试验数据获得了不同特征状态下钙质砂抗剪强度、内摩擦角和孔隙比的归一化表达式及其参数取值，进一步定性分析给出了抗剪强度、内摩擦角和孔隙比的非线性变化特征。研究结果表明：(1)围压小于300 kPa时钙质砂发生应变软化和剪胀；特征状态偏应力随围压或相对密度增大而变大，体变随围压(或相对密度)增大而增大(或减小);钙质砂排水剪切应力路径为一系列平行直线，围压越大应力路径越长。(2)不同相对密度下特征状态抗剪强度(或内摩擦角)具有较好归一性；峰值状态抗剪强度(或内摩擦角)大于相变状态，而相变状态大于临界状态；抗剪强度(或内摩擦角)为量纲一化平均主应力的幂函数(或对数函数),而相对密度对余量内摩擦角的影响随围压增大而减小直至消失。(3)在压缩平面内，特征状态孔隙比随量纲一化平均主应力增加而减小，且不同相对密度下临界状态孔隙比具有较好归一性；特征状态孔隙比可用负指数函数予以表达，该函数的上、下限与特征状态孔隙比实际极限值基本吻合。

Investigation of Shear Behavior of Calcareous Sand in Consolidated and Drained Triaxial Tests

To provide references for design and construction of infrastructures in the hydraulic fill foundation of calcareous sand in the coral reef of South China Sea, a series of triaxial tests were carried out to investigate the consolidated and drained shear behavior of calcareous sand. The stress-strain-volume change and stress path behavior of calcareous sand were quantitatively analyzed, and the normalized formulations and its parameters of the shear strength, internal friction angle and porous ratio at various characteristic states were put forward by means of the nonlinear fitting of test data, and the further quantitative analyses were made for their characteristics of nonlinear evolution. The research findings indicate that:① calcareous sand exhibits strain softening and volume dilation when the confining pressure is less than 300 kPa; the deviatoric stress at the characteristic states increases with the confining pressure and relative density, and volume strain increases with the confining pressure or it decreases with the relative density; the stress path upon shearing in consolidated and drained triaxial tests are a series of parallel straight lines and its length is also larger when confining pressure is higher. ② the shear strength or internal frictional angle at the characteristic states is well normalized in various relative density, and shear strength at peak state (PS) is over that at phase transformation state (PTS), and meanwhile shear strength at PTS is over that at critical state (CS); it is merely a power or logarithm function of normalized mean principal stress, and the effect of relative density on the excessive internal frictional angle decays with the confining pressure and finally disappears. ③ in the compression plane the characteristic state porous ratio decreases with the normalized mean principal stress, and the critical state void ratio is well normalized in various relative density; the characteristic state porous ratio can be characterized with a negative exponential function, the upper and lower limit of which are in agreement with the actual limits of the characteristic state porous ratio.