基于状态曲面的非饱和土强度准则及其验证

考虑体变对非饱和土土-水状态的影响，将状态曲面函数引入传统的Vanapalli强度公式得到与孔隙比相关的抗剪强度准则，新准则使用饱和土的强度参数和两条不同孔隙比对应的土-水特征曲线。选择一种尾矿砂和高岭土的混合土料为研究对象，进行一系列的土-水特征曲线试验、吸力控制的等向压缩和三轴剪切试验。试验结果表明，新准则能更准确地预测非饱和土的强度，证明了传统强度预测的误差主要来源于忽略了体变导致的土-水状态变化，并提出在不同应力空间内精确地获得抗剪强度包线的方法，合理地解释了强度包线斜率在净应力-强度平面内随吸力增大、强度包线形状在吸力-强度平面内随净应力发生变化的特性。

Experimental verification of an unsaturated shear strength criterion based on the state surface expression

Considering the influence of the volumetric behavior on the soil state, a void-ratio-dependent shear strength criterion for unsaturated soils is proposed by introducing the state surface expression into the Vanapalli’s shear strength equation. The saturated shear strength parameters and two series of soil water characteristic curve (SWCC) corresponding to different void ratios are employed in the proposed criterion. A series of SWCC tests, isotropic compression tests and suction-controlled triaxial tests are performed on a soil mixture of tailing sand and speswhite China kaolin. The testing results indicate that the proposed criterion can provide a more accurate prediction of shear strength for unsaturated soils than that of convention prediction using a unique SWCC. It is proved that the principal source of errors in the conventional estimation of shear strength is related to the evolution of soil state caused by the volume change. Moreover, a method for accurately identifying the failure envelopes in different stress spaces is developed. Several mechanical characteristics of unsaturated soils, including an increase in the slope of failure envelope with suction in net stress versus shear strength plane and the influence of the net stress on the shape of the failure envelope in the suction-strength plane, are reasonably interpreted by this method.