三维柔性边界构建方法及其对砾质土变形发展影响的#br#离散元数值研究

文章基于离散元平台，开展了砾质土三轴排水试验的模拟，改进了交错式球颗粒柔性边界的构建方法和展卷式恒定水力围压的模拟方法。并针对不同砾石组构的三轴排水试验，采用颗粒流平台(PFC3D)分别建立了传统刚性边界和球颗粒柔性边界的三维离散元模型。从宏观破坏形态和微观力学性能、剪切带演化、边界处力链发展等对比研究边界模拟方法对模拟砾质土变形发展的影响。结果表明：刚性边界和柔性边界条件下，土试样破坏形态显著不同，前者呈现压塌式破坏形态，后者破坏时在试样内部形成一个非对称“X”形的条状剪切带，更接近于实际室内三轴剪切试验结果；柔性边界条件下边界处的力链分布均匀，强度均衡，而刚性边界条件下，边界处力链的演化过程中会出现明显的应力盲区和应力集中现象。结合宏微观分析可知，在离散元模拟中应采用柔性边界。

Three-dimensional flexible boundary construction method and its influence on the #br#deformation development of gravel soil by discrete element simulation

 Based on the discrete element platform, the drained triaxial tests of gravel soil were carried out. For these tests, the method of staggered spherical particle of constructing the flexible boundary and the unfolding method of applying the constant confining water pressure were improved. By using particle flow code (PFC3D), three-dimensional discrete element models of traditional rigid boundary and spherical particle flexible boundary were established, respectively, for numerical simulations of drained triaxial tests with different gravel contents. Furthermore, the effects of boundary conditions on the simulation of the deformation and development of gravel soil were studied from the perspectives of macro-failure morphology and micro-mechanical properties, shear zone evolution, and development of force chains at the boundary. The numerical results show that: in the cases of rigid boundaries, the failure of the specimen occurs earlier, which is inconsistent with the results of the laboratory test; while in the cases of flexible boundaries, the failure of the specimen occurs later, conforming well with the laboratory test; With the flexible boundaries, the uneven bulging deformation at failure can be observed in the middle of the specimen, and the inside asymmetric X-shaped shear band is formed, while with the rigid boundaries, the deformation of the specimen appears to be the collapsed failure. Based on the comparison of distribution and evolution of the boundary force chain between the two boundaries, it is found that the force chain of the flexible boundary is evenly distributed with more balanced strength; for the rigid boundary, however, stress blind zones and stress concentration may occur with the evolution of the force chain. Hence, based on the macro and micro analyses, it is recommended to apply the flexible boundaries rather than rigid boundaries for better numerical simulations.