基于离散元的砂土在不同应力路径和剪切模式下的强度和临界状态行为

DEM investigation of strength and critical state behaviours of sand under axisymmetric stress paths with different shearing modes

本文通过离散元模拟的方法研究了砂土在不同轴对称应力路径和剪切模式下的强度和临界状态行为。其中,应力路径包括轴向压缩和轴向拉伸,而剪切模式包括常规三轴和恒定平均应力三轴。试样分为松砂和密砂两种,初始围压范围控制在100~900 kPa。当轴向应变(绝对值)接近45%时,所有样品均达到临界状态。模拟结果表明在相同围压下,偏应力的临界状态值是唯一的,与初始密度无关,但与应力路径有关:临界状态下轴向压缩的偏应力通常大于轴向拉伸的偏应力。应力比在临界状态下的值与剪切模式和围压均无关,但取决于应力路径。在围压一定的条件下,摩擦角在临界状态下具有唯一性,且不受剪切模式、应力路径和初始密度的影响,这表明Mohr-Coulomb准则(在轴对称条件下等效于Matsuoka准则)是有效的临界状态强度准则。在围压和剪切方式一定的条件下,孔隙率在临界状态下的值与初始密度无关。在临界状态下,不同试样机械配位数的差异是由平均应力的变化所引起的。

This paper investigates the strength and critical state(CS)behaviours of sand under axisymmetric stress paths with different shearing modes using discrete element method(DEM).The stress paths include axial compression(AC)and axial extension(AE),and the shearing modes include conventional triaxial(CT)mode and constant mean pressure(CP)mode.A series of dense and loose sand samples are generated for this purpose with confining pressures ranging from 100 kPa to 900 kPa.The CS is achieved for all samples after an axial strain(absolute value)of about 45%.The CS value of deviator stress is unique and independent of the initial packing densities for the samples with a given confining pressure,but the unique deviator stress under AC is generally larger than that under AE.The CS values of the stress ratio are independent of the shearing modes and the confining pressures,but are dependent on the stress paths.The CS friction angle for a given confining pressure is found to be unique and independent of the shearing modes,stress paths and initial packing densities,indicating that Mohr-Coulomb criterion(for axisymmetric conditions,equivalent to Matsuoka criterion)is an appropriate CS strength criterion.The CS value of void ratio is independent of the initial packing densities for a given confining pressure and shearing mode under a given stress path.The differences among the CS values of the mechanical coordination number are found to be attributed to changes in the effective mean pressures.