不同围压加载方式下土石混合体变形破坏机制颗粒流模拟研究

Particle flow modelling of deformation and failure mechanism of soil-rock mixture under different loading modes of confining pressure

土石混合体是一种非连续、非均质的混合多相介质材料,在轴向荷载作用下,由于内部变形的不均匀性,其变形破坏受围压加载方式影响显著。考虑刚性和柔性两种围压加载方式,采用颗粒流程序（PFC2D）开展了不同含石量和块石空间分布下土石混合体的双轴试验研究,从宏细观上探究了土石混合体在不同加载方式下的变形破坏规律。数值模拟研究表明：在不同围压加载方式下,受侧向变形约束不同的影响,土石混合体在峰后表现出了不同的力学特性,且在刚性加载下,其峰值偏应力较柔性加载下的高;同时,土石混合体在不同围压加载方式下局部化剪切带的形成演化过程也是不同的,其破坏型式不仅取决于围压加载方式,同时也决于块石含量和空间分布,在刚性加载下,多表现为复杂的多叉型破坏,在柔性加载下,多表现为非对称单叉型鼓胀破坏,而且随着含石量增加,破坏型式由简单的单叉型向复杂的多叉型转变,即使在相同含石量下,块石空间分布不同,破坏型式也不一样;土石混合体在不同加载方式下表现出了不同峰后力学行为的根本原因是由于内部土石颗粒间接触力的传递演化规律的不同所致,而且其应力应变关系是内部颗粒间切向接触力的外在宏观表现。

Soil-rock mixture（S-RM） is a kind of discontinuous and inhomogeneous multiphase materials. Its deformation and failure are significantly affected by the loading mode of confining pressure due to the internal nonuniform deformation under axial loading. Considering different loading modes of confining pressure, the biaxial tests on S-RM samples with different contents and spatial distributions of rock blocks are conducted by the particle flow code（PFC2 D）, and their deformation and failure characteristics are investigated under different loading modes. The numerical results show that the S-RM exhibits different mechanical behaviors after the peak under different loading modes of confining pressure owing to the effects of different lateral deformation constraints, and the peak deviatoric stress under the rigid loading mode is higher than that under the flexible one. Meanwhile, the formation and evolution of the localized shear band in the S-RM under different loading modes are also different, and the shape of its shear band depends on the loading modes and the content and spatial distribution of rock blocks. The shape of the shear band shows the type ofcomplex multi-cross under the rigid loading mode and that of asymmetrical single-cross under the flexible loading mode, and with the increase of the content of rock blocks, it shifts from the type of single-cross to that of multi-cross. The shearband of S-RM is also different under the same content but different spatial distributions of rock blocks. The different mechanical behaviors of S-RM after the peak under different loading modes result from different evolutions of the contact forces between its internal particles, and the stress-strain relationship is the external macro-performance of the tangential contact force between the particles.