主应力轴变化下各向异性钙质砂的定轴剪切特性

Fixed-axis shear characteristics of anisotropic calcareous sand under variation of principal stress axes

为探究各向异性南海钙质砂的剪切特性,利用GDS空心圆柱扭剪仪,通过不同大主应力方向上的定轴剪切试验,对比分析了钙质砂和石英砂的原生各向异性,揭示了原生各向异性对强度和孔压的影响。结果表明:钙质砂和石英砂在强度上均表现出各向异性,随着大主应力方向角?(大主应力方向与竖直方向夹角)的增大,强度先降低后增加,在?=70°时最低;钙质砂原生各向异性更为显著,不同大主应力方向上钙质砂的强度变化幅度约为石英砂的1.4~1.5倍;钙质砂和石英砂破坏时的孔压值都随着?的增大而增大,破坏时的状态也都由趋于剪胀逐渐向趋于剪缩变化;与石英砂不同的是,钙质砂破坏时亨开尔孔压系数的最大值出现在?=70°,而非?=90°;钙质砂各应变分量开展程度在不同大主应力方向上表现出差异性,破坏时的径向应变随大主应力方向角变化幅度最小,破坏时的扭剪应变随大主应力方向角变化幅度最大。

In order to explore the shear characteristics of anisotropic calcareous sand,the GDS hollow cylinder torsional shear apparatus is used to compare and analyze the anisotropy of calcareous sand and quartz sand through the fixed-axis shear tests in different directions of large principal stress to reveal the effects of inherent anisotropy on strength and pore pressure.The results show that both the calcareous sand and the quartz sand exhibit anisotropy in strength.As the large principal stress direction angleα(the angle between the large principal stress direction and the vertical direction)increases,the strength decreases first and then increases,and reach the minimum whenα=70°.The anisotropy of calcareous sand is more pronounced,and the magnitude of change in strength of calcareous sand in different directions of large principal stress is about 1.4 to 1.5 times that of quartz sand.The pore pressure values of the calcareous sand and quartz sand both increase with the increase ofα,and the state of failure also gradually changes from tending to dilatancy to shrinking.Different from that of the quartz sand,the maximum value of Henkel’s pore pressure coefficient appears atα=70°instead ofα=90°.The radial strainεr at the time of failure has the smallest amplitude change with the direction angle of the large principal stress,and the torsional shear strainγzθhas the largest one.