非饱和土真三轴双剪新强度准则及验证*

A new twin-shear true triaxial strength criterion of unsaturated soils and its validations

摘要:

已有非饱和土真三轴试验结果表明：中间主应力对其强度影响显著，但现有非饱和土强度公式多是基于未考虑中间主应力影响的Mohr-Coulomb强度准则而建立的。本文依据非饱和土的双应力状态变量理论，在俞茂宏双剪新强度准则的基础上，建立了适用于非饱和土的真三轴双剪新强度准则，并用文献非饱和粉砂刚性与柔性真三轴试验结果进行了验证。研究结果表明：本文分段线性的真三轴双剪新强度准则能反映非饱和土强度的中间主应力效应及其区间性与单轴拉压不等特性，且可线性逼近拓展的非线性Spatially Mobilized Plane准则；Mohr-Coulomb强度准则的预测值偏小、外接圆Drucker-Prager准则的预测值明显偏大，这两个准则对非饱和土的真三向应力状态及试验数据均不具有很好的适用性。

关键词:非饱和土;强度准则;真三轴试验;中间主应力;基质吸力

Abstract:

The true triaxial test results for unsaturated soils indicated that the intermediate principal stress affected the unsaturated soil strength significantly. However, most existing strength formulae of unsaturated soils were based on the Mohr-Coulomb strength criterion and did not consider the intermediate principal stress effect. On the basis of the new twin-shear strength criterion of Mao-Hong Yu and the two stress state variables theory, a new twin-shear true triaxial strength criterion is derived and validated by the rigid and flexible true triaxial tests of unsaturated silty sand available in the literature. It is shown that the new piecewise linear twin-shear true triaxial strength criterion proposed in this study can reflect strength characteristics of unsaturated soils, such as the effect and its range of intermediate principal stress and strength differences among uniaxial tension and uniaxial compression; the new twin-shear strength criterion can be a linear approximation of the extended nonlinear Spatially Mobilized Plane criterion; neither the Mohr-Coulomb strength criterion nor the circumscribed Drucker-Prager criterion has good applicability to true three dimensional stress states and test data of unsaturated soils, in that the predictions of Mohr-Coulomb strength criterion are small, whereas the predictions of circumscribed Drucker-Prager criterion are obviously large.

Key words:unsaturated soils; strength criterion; true triaxial test; intermediate principal stress; matric suction