块石强度对土石混合料剪切特性的影响

Effect of the strength of rock blocks on the shear characteristics of soil-rock mixtures

块石强度的不足是引发土石混合料大型填方工程失稳破坏的重要原因之一。为深入探讨块石强度对土石混合料剪切特性的影响,弥补当前土石混合料研究领域的不足,以重庆市某超高填方工程为依托,采用室内大型直剪试验和PFC离散元数值模拟展开系统研究,揭示块石强度影响土石混合料剪切变形特征、峰值抗剪强度、裂隙扩展过程、能量响应方式的宏观规律和微观机制。结果表明:高应力水平下,由块石强度引起的剪切特性差异显著,硬岩土石混合料呈现应变硬化特征,软岩土石混合料则以应变软化为主;土石混合料的剪切过程基本符合线性莫尔–库仑强度理论,且随着块石强度的增大,混合料的内摩擦角、峰值抗剪强度均增大,而黏聚力表现出"先增大后减小"的变化趋势;块石强度越大,剪切过程中粒料间裂隙开展就越完全,裂隙密度越大;硬岩改造作用强烈,往往形成断面复杂的剪切面,软岩混合料剪切面形态与纯土体相差不大;剪切过程中,硬岩土石混合料以摩擦耗能为主,软岩混合料则主要通过塑性变形、调整块石空间位置吸收、贮存变形能。最后,基于PFC数值模拟技术进一步拓展分析,提出考虑块石强度的土石混合料抗剪强度预测模型。

The insufficient strength of rock blocks is one of the most important reasons for the instability of large soil-rock mixture(S-RM) filling bodies. In order to deeply explore the influence of the strength of rock blocks on the shear characteristics of the S-RMs and to make up for the deficiencies in the current research field,systematic research was conducted utilizing indoor large-scale direct shear test and discrete element numerical simulation(PFC) based on a great filling project in Chongqing. The macroscopic performances and microcosmic mechanisms of the block strength affecting the shear deformation,the peak shear strength,the crack extension process and the way of the energy response of the S-RM were revealed finally. The results show that,under a high axial pressure,the shear characteristics of the S-RMs with different distinct block strengths are remarkably different. The stress-strain relationships for hard and soft rock mixtures are respectively characterized by strain hardening and strain softening. The shearing process is basically consistent with the linear Mohr-coulomb strength theory,and with increasing the block strength,the internal friction angle and the peak shear strength of the mixture increase while the cohesion shows a trend of increasing first and then decreasing. The greater the block strength,the more complete the fracture development and the greater the fracture density. The hard rock shows a strong remolding ability which makes the mixture tend to form a shear plane with a complex cross-section,while the shear plane of the soft rock mixture is almost the same as that of plain soils. In the shearing process,the hard rock mixture dissipates the energy mainly in the way of friction,while the soft rock mixture absorbs and stores deformation energy mainly through the plastic deformation and the adjustment of spatial positions between rock blocks. Finally,PFC numerical simulation software was adopted to further expand the analysis,and a shear strength prediction model of S-RMs was proposed.