为探究砂土液化的微观机理,根据室内试验中微生物反硝化反应气泡的生成速率,建立数值模拟的时效性关系,分别制取微生物处理0天、2天、3天和5天的高饱和砂土试样,采用CFD-DEM耦合方法模拟不同工况下砂土试样的循环三轴不排水剪切试验.依据砂土试样的力链分布、抗液化振次、孔压比、轴向应变和力学配位数在加载过程中的变化情况,从宏微观角度分析砂土试样的抗液化能力.模拟结果表明:含微生物气泡高饱和砂土的抗液化强度较饱和砂土有所提升;随着微生物处理时间的增加,砂土试样的饱和度降低,孔压比和轴向应变的累积变慢,抗液化能力增强.

The microbially induced calcite precipitation is a promising technology to improve ground, and the treated soil can be regarded as the structural one. In this study, firstly, based on the three-dimensional (3D) contact model for granulates incorporating rolling and twisting resistances and 3D bonds failure criteria, and considering both the slight plastic deformation of particles during collisions and the rate-dependency, a cyclic bonded contact model is established. A time-dependent relationship is then proposed to describe the denitrification reaction in reinforced sand. Next, the mechanical responses of microbially treated sands at different cementation and bubble contents are investigated by the coupled CFD-DEM in undrained-consolidated cyclic triaxial tests. The effects of biological bond and biological bubbles on the liquefaction resistance of sands are analyzed in link with the mechanism from macroscopic and microscopic scales. The results show that the coexistence of cementation and bubble does not increase the liquefaction resistance as expected in the form of "1+1=2". The presence of cementation enhances the liquefaction resistance of unsaturated sands evidenced by the decrease of excess pore water pressure ratio and axial strain, and the increase of coordination number. However, the presence of bubbles reduces the liquefaction resistance of cemented sands, where the number of cycles to the initial liquefaction decreases, the axial strain increases significantly in the tensile direction, and the coordination number decreases significantly.

月球表面存在不少的高陡边坡,其坡度一般都大于30°,月海区可达48.9°,月陆区甚至可达55.7°,这些高陡的边坡会严重影响未来月球资源开采等活动的安全.通过引入考虑范德华力和抗转动作用的月壤微观接触模型,采用离散单元法模拟了不同坡角下的月壤滑坡试验,对滑坡过程、滑坡机理及常见的工程灾害指标进行分析.结果表明:坡后体积一定,流滑距离会随着初始坡角的增大而增大;最终倾角几乎不受初始坡角的影响;滑坡过程中,当切坡倾角低于60°时,滑坡过程呈现流动状态,高于60°时,滑坡过程呈现类崩塌状态;滑体的最大速度随初始坡角的增大呈现抛物线式增长.

The discrete element method (DEM) is a numerical simulation method based on non-continuous medium mechanics,which can effectively analyze the macro and micro mechanical behavior responses of cemented granular materials.By using the three-dimensional discrete element commercial software PFC3D,a series of conventional triaxial compression tests for cemented sands with different cement contents and different confining pressures were simulated based on the microscopic cement contact model BPM to study the macro and micro mechanical behaviors of cemented sands.The results of simplified simulation showed that,compared with the pure sand specimen of the same initial void ratio,shear strength of the cemented sands was higher,the tested stress strain curve showed obvious strain softening,volumetric curve showed the dilatancy.The peak strength increased and the softening and dilatancy enhanced with the increases of cement content.With the increase of confining pressure,the peak strength increased and the dilatancy reduced;but the softening kept unchanged.In addition,the internal friction angle and the cohesion of the specimen were affected by the cement content and the confining pressure.

Influenced by construction technology, quality and environment in the construction process of rock-fill concrete gravity dam, natural cementation sands may have different cementation strengths between the sand particles. By using the microscopic model BPM of PFC3D, the distribution of the bond strength in cemented sand is defined as the normal distribution to study the mechanical properties of cemented soil with different bond strengths. The mechanical properties of cemented sands under different contents and variances are analyzed. The results show the strain softening and shear dilatation characteristics. And with the increase of cement contents, softening and dilatancy increase. When the deviatoric stress reaches the peak value, with the increase of the axial strain, the change of the volume is reduced by the shear contraction. The volumetric strain is changed from the shear shrinkage to dilatancy. With the assumption that the cementing of sample under the normal distribution cementation strength, the peak stress linearly grows with cement content, but charge of the normal distribution variances has a little influence on the cementation of strength.