Numerical analysis of reverse shear behavior of granular soil with fines

Abstract

针对含细颗粒砂土的反常剪切行为，开展了双轴剪切试验的数值模拟，从宏细观角度分析了其反常剪切行为发生的内在机制。数值模拟结果表明，增加围压能提高含细颗粒砂土的抗剪切液化能力，该反常行为的根本原因在于围压上升使得粗细颗粒更有效地参与了力链传递，增加了颗粒间的接触，增强了土体的密实度。细颗粒在土骨架中的移动对砂土的液化起着至关重要的作用，而粗颗粒仅起次要作用。研究表明，细颗粒在剪切过程中会持续从有效土骨架中移出成为无效颗粒，而部分粗颗粒也因失去细颗粒的支撑作用会脱离土骨架，直至试样最终液化。细颗粒一般参与土骨架中的弱力链，而粗颗粒则一般参与强力链，导致细颗粒较粗颗粒更容易在土骨架中移动。 This paper describes an investigation of the reverse shear behavior of granular soil with fines by using the discrete element method(DEM) simulations of biaxial shear tests. The fundamental mechanisms underlying the so-called reverse behavior are scrutinized from both macroscopic and microscopic perspectives. The numerical simulation results show that the promotion of liquefaction resistance with increasing confining pressure tests mainly on the fact that as the confining pressure increases, both fine and coarse grains are to join the force chains more effectively, increasing the effective contacts between particles and thus enhancing the packing density of soil specimen as well as the stiffness of soil skeleton. The migration of fine particles in the soil skeleton plays a considerably important role in the liquefaction of granular soil with fines. It is found that during shear fine particles will be continuously dislodged into voids; and some coarse particles will also be removed from the soil skeleton due to the loss of the supporting effect from fine particles until the soil specimen is completely liquefied. In addition, fine particles are found to be mainly in weak force chains; while coarse particles are generally in strong force chains, and this has made fine particle more easily migrate in the soil skeleton as compared with coarse particles.