粗粒土在平面应变条件下的强度特性研究

Strength characteristics of coarse-grained soil under plane strain condition

使用河海大学新型真三轴仪,对粗粒土分别进行3保持不变的等3平面应变试验和b=0(即常规三轴压缩)、b=0.25的等3等b[b(2 3)/(1 3)]试验,研究了粗粒土在平面应变条件下的应力路径、破坏时的中主应力系数、内摩擦角及破坏应力比的特点。试验结果表明,等3平面应变试验的应力路径介于b=0与b=0.25的等3等b试验之间;粗粒土在平面应变条件下破坏时的中主应力系数b介于0.15～0.2之间;粗粒土在平面应变条件下的内摩擦角比常规三轴压缩条件下的大5%～7%,而破坏应力比则比常规三轴压缩条件下的小13%～18%。最后提出一个由粗粒土常规三轴压缩试验测得的内摩擦角φtc求平面应变条件下的破坏应力比Mfp的计算公式Mfp=2.3sinφtc,可较好地模拟试验结果。

Plane strain compression tests in which σ3 keeps invariable and experiments in which both σ3 and keep constant are performed on coarse-grained soil by means of the true triaxial apparatus recently developed in Hohai University.The characteristics of stress paths,parameter b at failure,angles of internal friction and peak values of stress ratio Mfp[=（q/p）fp] of coarse-grained soil under plane strain conditions are studied.The experimental results show that the stress paths of the plane strain tests exist between the b-constant tests in which b equals 0 and 0.25;the parameter b at failure is between 0.15 and 0.2 for coarse-grained soil under plane strain conditions;the angles of internal friction of coarse-grained soil under plane strain conditions are 5%~7% larger than those under triaxial compression conditions while the peak values of stress ratio of coarse-grained soil under plane strain conditions are 13%~18% smaller than those under triaxial compression conditions.Finally a formula expressed as Mfp=2.3sinφtc,which is verified by the test results of coarse-grained soil,is proposed to calculate the peak value of stress ratio,Mfp,under plane strain conditions from the angle of internal friction,φtc,obtained from conventional triaxial compression tests.