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循环动载下土体变形呈现的复杂各向异性,本质上依赖于土体微观组构特征的演化。为了揭示非比例循环动载下土体变形的微观机制,采用离散元方法模拟砂土的循环单剪行为。应用等幅剪应变的往复加载实现循环单剪应力路径,模拟得到了砂土的循环弱化、剪胀性、非共轴性及微观组构的演化规律。微观模拟表明,在循环剪切过程,土体表现为循环弱化行为,并最终趋于塑性安定状态。而试样组构主方向倾角和组构各向异性系数也会不断增大直至一个稳定值,同时主应变率、主应力轴和组构主方向旋转角度会存在一定的差异,即非共轴现象,随着单调剪切的进行,三者会逐渐趋于一致。土体的剪胀行为表现为循环压密性,而非共轴性呈现逐渐增强的演化规律。循环剪切过程中微观组构的主方向与应力主方向逐渐趋于一致,而微观组构各向异性呈现减弱的演化趋势。
The complex anisotropy of soil deformation under cyclic loading depends essentially on the evolution of soil microstructure. In order to reveal the microscopic mechanism of soil deformation under non-proportional cyclic loading, the discrete element method is used to simulate the cyclic single shear behavior of sand. The circular single shearing stress path was achieved by reciprocating loading with equal amplitude shear strain. The cyclic weakening, dilatancy, non-coaxiality and microstructure evolution of sand were simulated. Micro-simulation shows that in the cyclic shear process, soil behaves as cyclic weakening behavior and finally tends to plastic and stable state. The main dip angle and the anisotropy coefficient of structure will also increase to a stable value. At the same time, the main strain rate, the principal stress axis and the rotation angle of the principal direction will be different, that is, the non-coaxial Phenomenon, with the monotonous shear, the three will gradually tend to be consistent. The dilatancy behaviors of soil show cyclic compaction, while the non-coaxiality shows a gradually increasing evolution law. During the cyclic shear process, the main direction of micro-structure and the main direction of stress gradually converge, while the anisotropy of micro-structure shows a decreasing trend.