饱和黏土不排水抗剪强度各向异性的热力学本构模型研究

基于饱和土体TTM（Tsinghua thermodynamic soil model）热力学本构模型分析研究了饱和黏土的不排水抗剪强度各向异性问题。模型及试验研究表明：非等向或固结历史是引起土体强度各向异性的重要原因,固结应力比越小,不排水强度各向异性越大。不排水加载过程中主应力轴的方向对土体不排水抗剪强度和变形有着重要影响。一般而言,当主应力轴方向从0°旋转到90°时,土体的不排水抗剪强度逐渐下降,峰值应变却逐渐增大。此外,非等向固结会导致土体主应力与主应变的非共轴性。利用TTM理论模型,对Kaolin Clay 和Boston Blue Clay的不同试验结果进行了模拟验证和预测。结果表明,TTM理论模型具有反映和预测应力引起的饱和黏土强度各向异性和应变软化等特性的能力,同时也具备精准描述主应力轴旋转等复杂路径下饱和黏土的强度和变形特征的能力。

Thermodynamic constitutive model for anisotropic undrained shear strength of saturated clays

An approach is proposed for the undrained strength anisotropy of saturated clays based on a thermodynamic constitutive model, TTM (Tsinghua thermodynamic soil model). The model analyses and experiments indicate that the anisotropic consolidation or K₀ consolidation can be an important cause for the strength anisotropy of geotechnical materials, and the strength anisotropy becomes more significant with the decrease of the consolidation stress ratio K_c. During the undrained loading, the direction of the principal stresses has a huge influence on the undrained strength and deformation of soils. Generally speaking, with the rotation of principal stresses from 0°to 90°, the undrained shear strength decreases while the peak strain increases. Besides, the anisotropic consolidation causes the non-coaxiality of the principal stresses and strains. Based on the proposed model, simulations and predictions are made for various test results of Kaolin clay and Boston blue clay, which indicate that TTM is able to show and predict the strength change and deformation behavior of soils under complex stress paths caused by the strength anisotropy, strain softening and rotation of direction of the principal axis of stress.