结构性砂土力学特性三维离散元分析
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摘要
利用离散元法对结构性砂土的三轴试验进行了三维数值模拟并对其宏观特性进行了分析。首先将考虑胶结尺寸(宽度和厚度)的三维胶结接触模型导入离散元软件PFC3D中,对结构性砂土数值试样进行三轴试验数值模拟;然后对比分析离散元模拟与室内试验结果;最后从宏观力学角度对试验结果进行了分析。离散元模拟结果表明:结构性砂土与无胶结松散砂土表现不同,其在低围压时表现出应变软化和体积剪胀特征,并随胶结含量的增加或围压的减少而愈发显著,在高围压时则呈应变硬化和体积剪缩现象;低平均应力时,随胶结含量的增加,试样峰值内摩擦角、黏聚力以及内摩擦角均增加,其中黏聚力增加较为明显,随着平均应力的增加,峰值强度包线逐渐趋向于无胶结土。
The three-dimensional(3D) distinct element method(DEM) is employed to investigate the behaviours of cemented sands at the macro-scale in triaxial tests. A 3D bond contact model is implemented in a DEM commercial software(PFC~(3D)) to simulate the triaxial tests on cemented specimens, and the simulated data are compared with the experimental results. Finally,the underlying mechanism behaviour is discussed at the macroscopic scale. The DEM results show that, the structured sands and uncemented loose sands have different macroscopic behaviours. In the conventional triaxial compression tests, the strain softening and the shear dilation are more pronounced in the structured sands with the increasing cement content or decreasing confining pressure. Under high confining pressures, the specimens show strain hardening and shear contraction. Both the cohesion and the peak friction angle increase with the increasing cement content under relative low-mean stresses. As the mean stress increases, the strength envelops for cemented sands converge gradually to those for uncemented geomaterials.
The three-dimensional(3D) distinct element method(DEM) is employed to investigate the behaviours of cemented sands at the macro-scale in triaxial tests. A 3D bond contact model is implemented in a DEM commercial software(PFC~(3D)) to simulate the triaxial tests on cemented specimens, and the simulated data are compared with the experimental results. Finally,the underlying mechanism behaviour is discussed at the macroscopic scale. The DEM results show that, the structured sands and uncemented loose sands have different macroscopic behaviours. In the conventional triaxial compression tests, the strain softening and the shear dilation are more pronounced in the structured sands with the increasing cement content or decreasing confining pressure. Under high confining pressures, the specimens show strain hardening and shear contraction. Both the cohesion and the peak friction angle increase with the increasing cement content under relative low-mean stresses. As the mean stress increases, the strength envelops for cemented sands converge gradually to those for uncemented geomaterials.
引文
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[2]BROMS B B,BOMAN P.Lime columns-a new foundation method[J].Journal of Geotechnical and Geoenvironmental Engineering,1979,105(4):539-556.
[3]CLAYTON C R I,HIGHT D W,HOPPER R J.Progressive destructuring of Bothkennar clay implications for sampling and reconsolidation procedures[J].Géotechnique,1992,42(2):219-239.
[4]CUNDALL P A,STRACK O D L.Discrete numerical model for granular assemblies[J].Géotechnique,1979,29(1):47-65.
[5]JIANG M J,Yu H S,LEROUEIL S.A simple and efficient approach to capturing bonding effect in naturally microstructured sands by discrete element method[J].International Journal for Numerical Methods in Engineering,2007,69(6):1158-1193.
[6]JIANG M J,SHEN Z F,WANG J F.A novel three-dimensional contact model for granulates incorporating rolling and twisting resistances[J].Computers&Geotechnics,2015,65:147-163.
[7]JIANG M J,ZHANG F G,THORNTON C.A simple three-dimensional distinct element modeling of the mechanical behavior of bonded sands[J].International Journal for Numerical and Analytical Methods in Geomechanics,2015,39(16):1791-1820.
[8]WANG Y H,LEUNG S C.A particulate-scale investigation of cemented sand behavior[J].Canadian Geotechnical Journal,2008,45(1):29-44.
[9]ROTTA G V,CONSOLI N C,PRIETTO P D M,et al.Isotropic yielding in an artificially cemented soil cured under stress[J].Géotechnique,2003,53(5):493-501.
[10]JIANG M J,KONRAD J,LEROUEIL S.An efficient technique for generating homogeneous specimens for DEMstudies[J].Computers and Geotechnics,2003,30(7):579-597.
[11]LADE P V,OVERTON D D.Cementation effects in frictional materials[J].Journal of Geotechnical Engineering,1989,115(10):1373-1387.
[12]CUCCOVILLO T,COOP M R.On the mechanics of structured sands[J].Géotechnique,1999,49(6):741-760.
[13]LEROUEIL S,VAUGHAN P R.The general and congruent effects of structure in natural soils and weak rocks[J].Géotechnique,1990,40(3):467-48.