土体介质强度尺度效应的理论与试验研究

为考虑土体微细观结构特征对其宏观强度特性的影响，根据土颗粒的大小及其连结性状，以一定的尺寸界限将土体分成基体和加强颗粒2种介质，基于应变梯度理论，引入适应基体与加强颗粒变形相容性要求的几何协调微裂纹概念，建立可描述土体强度尺度效应并具有多尺度理论框架的基体–加强颗粒模型。该模型揭示土体的强度与内禀尺度、应变梯度、基体性质以及加强颗粒的粒径和级配有关。设计一系列非饱和重塑土的三轴固结不排水剪切试验以研究土体的强度尺度效应并定量计算反映土体强度尺度效应的内禀尺度参量。试验结果表明：土体的屈服应力随加强颗粒粒径的减小而增加且与加强颗粒含量之间呈线性关系，与内禀尺度之间呈抛物线关系；内禀尺度随加强颗粒的粒径和含量以及基体液性指数的增加而增加且与加强颗粒含量之间呈抛物线关系；土体屈服应力的试验结果与基体–加强颗粒模型的预测结果一致。研究成果对土体的强度理论发展有一定的参考价值。

THEORETICAL AND EXPERIMENTAL STUDY OF SIZE EFFECT OF SOIL STRENGTH

According to the size and connecting characters of soil particles，soil is discomposed into two components as matrix and reinforcement particles respectively with a certain size demarcation to investigate the influence of the microstructures on soil strength. Based on the strain gradient theory and the notion of coordinated microcracks required for the compatible deformation between the matrix and the reinforcement particles，a multi-scale “matrix-reinforcement particle” model is established to study the size effect of soil strength which indicates that the soil strength is related to the intrinsic length scale，the strain gradient，the properties of the matrix as well as the size and gradation of the reinforcement particles. A series of consolidated and undrained triaxial compression tests on unsaturated remoulded soil were designed to study the size effect of soil strength and to determine the intrinsic length scale quantitatively. The results show that：the yield stress of soil increases with the decrease in the reinforcement particle size and has a linear relation on the reinforcement particle content；moreover，the relationship between the yield stress and the intrinsic length scale could be presented as parabolic function；the intrinsic length scale increases with the increase in the matrix liquidity index，the particle size and particle content of the reinforcement particles；and the relationship between the intrinsic length scale and the reinforcement particle content can be presented as parabolic function. The experimental data can be well fitted to the “matrix-reinforcement particle” model. The research results are significant to the development of strength theory of soil.