土体强度与变形尺度特性的理论与试验分析

Theoretical and experimental investigation on size effect characteristic of strength and deformation of soil

土体是一种颗粒介质,其强度与变形特性具有显著的颗粒尺度效应。采用胞元土体模型和三轴抗剪试验分析了土体强度和变形的尺度效应特性。根据土体中不同尺度颗粒间相互作用表现出的聚集和摩擦效应,提出了"基体-增强颗粒"土体胞元模型,胞元体由基体和增强颗粒组成,其中基体由微小土颗粒集成,而增强颗粒为砂粒,宏观土体则简化为由许多胞元体构成的介质。引入广义球应变和广义等效应变,基于应变能导出了考虑颗粒尺度效应的应力-应变关系以及屈服应力计算公式;同时,针对增强颗粒不同粒径和体分比的土体进行一系列三轴不排水抗剪试验,给出了应力-应变和屈服应力尺度效应的测试结果。试验和理论计算结果均表明,土体强度和变形的尺度效应随增强颗粒的体分比增加以及粒径的减小而增强,由此反映出土体强度和变形显著的尺度效应;土体强度和变形尺度效应的理论预测结果与试验具有较好的一致性。

Soil is a granular medium, and its strength and deformation characteristic behave marked grain size effect. Based on the theoretical model of cell element and triaxial shear tests, the analysis of grain size effect is presented. The matrix-reinforcing particles cell element model of soil is proposed according to cohesion and friction effect of interaction between particles of varying size. The cell element is composed of matrix and reinforcing grain. Many tiny grains are grouped into the matrix and reinforcing grain is a sand grain, so the macroscopic soil is simplified as a medium that consists of a number of cell elements. Introduced the generalized spherical strain and equivalent strain, the stress-strain relation and yielding stress formula are derived from strain energy accounting for the grain size effects. A series of triaxial undrained shear tests are performed for test samples with reinforced particles of different sizes and volumes fractions, and test results of stress-strain curves and yielding stresses are presented on the size effect. The experimental results and theoretical analysis show that the size effect of the strength and deformation of soil is increased with volume fraction raising and decreasing of particle size, which suggests strong size effect. The theoretical prediction of size effect is in good agreement with that of the test.