粗粒土在平面应变条件下的强度特性研究

使用河海大学新型真三轴仪,对粗粒土分别进行σ₃ 保持不变的等σ₃平面应变试验和 b =0 （即常规三轴压缩）、 b =0.25 的等σ₃等b[b=(σ₂ -σ₃)/(σ₁ -σ₃)]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 σ₃平面应变试验的应力路径介于 b =0 与 b =0.25 的等σ₃ 等b[b=(σ₂ -σ₃)/(σ₁ -σ₃)] 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 φ _tc 求平面应变条件下的破坏应力比 M _fp 的计算公式 M _fp =2.3sin φ _tc ,可较好地模拟试验结果。

Strength characteristics of coarse-grained soil under plane strain condition

Plane strain compression tests in which σ₃ keeps invariable and experiments in which both σ₃ and b[b=(σ₂ -σ₃)/(σ₁ -σ₃)] 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 M _fp [=( 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 M _fp =2.3sin φ _tc , which is verified by the test results of coarse-grained soil, is proposed to calculate the peak value of stress ratio, M _fp , under plane strain conditions from the angle of internal friction, φ _tc , obtained from conventional triaxial compression tests.