无黏性松散土石混合体剪切特性的结构效应及强度模型构建

Structural effects of shearing properties of loose cohesionless soil-rock mixture and development of strength model

综合室内直剪试验、DEM模拟和理论解析等手段,从多尺度角度揭示和表征了中低体积含石量下土石混合体的剪切破坏机制。试验结果表明,无黏性土石混合体的剪胀规律受控于基质密实度,块石体积含量(VBP)和外部法压的共同作用,其内摩擦角演化具有显著的非线性特征(VBP<30%),基于莫尔-库仑准则的强度分析会产生块石结构形成的表观黏聚力。DEM模拟揭示块石结构诱发特殊的细微观力学过程,土石接触力的分布不均匀、剪切带的不规则度是土石混合体与砂土剪切行为的关键差异。最后,基于中低含石量下土石混合体的工程地质特征与强度发挥机制的讨论,提出表征块石结构力学含义的新公式,通过理论分析发现Lindquist的修正强度模型是剪切应力传递的简化描述。初步构建物理意义明确的土石混合体新强度模型(等效粗糙度模型),通过对黏性和无黏性两类土石混合体的试验结果对比,验证新模型可有效预测中低含石量下土石混合体的非线性强度包线。

In this work,direct shear tests,DEM simulation and theoretical analysis were conducted to reveal and characterize the multi-scale failure mechanism of soil-rock mixtures with lower rock block proportions.The experimental results show that the shear dilatancy of soil-rock mixture is determined jointly by soil density,volumetric block proportion(VBP)and normal stress condition.Significant nonlinear characteristics appears in the internal friction angle evolution of cohesionless soil-rock mixture(VBP<30%),and the apparent cohesion induced by the rock block structure was generated from the strength analysis of Mohr-Coulomb criterion.Indicated by the DEM simulation results,the special mechanical pattern of soil-rock mixtures is formed by the block-in-matrix fabric on the micro and meso scale,such as the uneven distribution of contact force and the tortuosity of shear zone,which is distinguished from that of the homogenous sand matrix.Furthermore,based on the in-depth discussions on engineering geological characteristics and failure mechanism of soil-rock mixtures,a new formula was proposed to interpret the mechanism of the rock block structure.Through the stress transfer analysis,it was figured out that Lindquist's modified strength model is a simplified expression.Meanwhile,a novel strength criterion(equivalent roughness model)has been established,which presents the rationality in predicting the nonlinear strength evolution of soil-rock mixtures under medium to low VBP,in confrontations with the experimental results of cohesive and non-cohesive specimens.