沉积角对净砂宏微观力学特性影响的离散元分析

Discrete element analysis of effects of sedimentary angle on macro-micromechanical properties of pure sand

由颗粒定向排列导致的初始各向异性对净砂力学特性影响明显。为探究这一影响,首先采用自编的离散元软件生成4种不同沉积方向的椭圆颗粒净砂样,并分别对4种试样进行双轴压缩试验;其次,通过将离散元模拟结算与室内试验结果对比以验证该方法的可行性;最后,通过分析模拟结果研究沉积方向所产生的影响。结果表明:4种试样均出现应变软化及剪胀现象;随着沉积角δ的增加,试样具有由应变软化逐渐向应变硬化发展的趋势,试样的剪胀性逐渐减弱;在δ=0°时试样取得最大峰值内摩擦角和最大残余内摩擦角,且随着δ的增大试样的峰值内摩擦角先降低然后基本不变,残余内摩擦角逐渐减小;颗粒排列初始优势方向基本与沉积方向平行,但随着轴向应变的增大,颗粒排列优势方向逐渐向平行于加载面方向旋转,接触点的优势方向由最初垂直于沉积方向逐渐向垂直于加载面方向旋转,且这两种旋转的改变幅度随着沉积角δ的增大而增大;而强接触力的优势方向始终垂直于试样的加载面。

Initial anisotropy caused by granular arrangement effects the mechanical behaviors of pure sand evidently.In order to study such effects,pure sand specimens consisting of elliptical particles at four different sedimentary angles（δ） are prepared by the self-developed software NS2 D firstly,and then biaxial compression tests are conducted on those DEM specimens.Secondly,the simulated results are compared with those of laboratory tests to validate this method.Finally,the influence of δ is studied by analyzing the simulated results.The results show that all of these four specimens show strain softening and shear dilation phenomenon.With the increase of δ,the strain softening phenomenon of stress-strain curve tends to become strain hardening,and shear dilation phenomenon becomes more and more unapparent.The peak and residual internal friction angles achieve the maximum when δ=0°.With the increase of δ,the peak internal friction angle decreases and then keeps constant,while the residual internal friction angle decreases.The initial principal direction of particle arrangement is parallel to the sedimentary direction.With the increase of axial strain,the principal direction of particle arrangement rotates to the direction parallel to the loading plane gradually,and the principal direction of contact rotates from perpendicular to sedimentary direction to perpendicular to the loading plane.And the increments of both rotations aforementioned increase with the increase of δ.The principal direction of strong contact force is perpendicular to the loading plane all the time.