非饱和黏土的张拉-剪切耦合强度研究

Research on tensile-shear coupling strength of unsaturated clays

非饱和黏土中液相与固相基质间的相互作用,依据其形成机理的不同可分为毛细作用和物理-化学作用,目前建立的非饱和土强度模型多是基于毛细机理建立的,忽略了后者对土体强度的贡献。现有非饱和土强度理论仍建立在土体受压缩剪切作用的基础上,不适用于分析土的抗拉强度和拉剪耦合强度。为了能够全面地、合理地描述非饱和黏土的强度作用机制,建立了一个适用于非饱和黏土的二元介质压剪强度模型,将非饱和黏土抽象为理想毛细部分和理想吸附由两个理想部分组成,针对两者分别建立了理想强度公式,利用参与函数反映土中两种理想部分所占的比重,描述实际情况下土体的强度特征。在压剪强度模型的基础上,通过考虑非饱和黏土中的拉剪联合作用,建立了非饱和黏土的张拉-剪切耦合强度模型,给出了张拉-剪切耦合强度公式。利用强度模型对非饱和黏土的压剪强度及张拉-剪切耦合强度进行预测,预测结果和已有试验数据的对比结果表明所建模型能够较好地描述非饱和黏土的强度特征。

The interactions between liquid phase and solid matrix in unsaturated clays can be divided into capillary effects and physicochemical effects according to their formation mechanism. The physicochemical effects(that is, the adsorption effects) become significant at low saturation degrees. However, current strength models for unsaturated soils almost are established on the basis of capillary mechanism; and the contribution of adsorption effect to soil strength is neglected. Furthermore, the existing strength models for unsaturated soils apply only to compressive-shear soils but not to the tensile and tensile-shear soils. A binary-medium compressive-shear strength model is firstly proposed, involving the capillary and adsorption effects. The unsaturated clay is assumed to consist of two ideal parts, i.e. the ideal capillarity part and the ideal adsorption part, and then the corresponding ideal strength formulas are established. Furthermore, a participation function is used to reflect the degrees of capillary effects and adsorption effects. A tensile-shear strength model of unsaturated clays is secondly developed considering the various combinations of tensile-shear in unsaturated soils based on the compressive-shear strength model; and then the tensile-shear coupling strength formulas are obtained. Finally, predictions are performed on the compressive-shear strength and tensile-shear strength. Comparison between predicted results and existing test results shows that the proposed model can well describe the strength of unsaturated clays.