土工膜与土界面剪切特性细观研究

MESOSCOPICAL STUDY ON INTERFACE PROPERTIES BETWEEN GEOMEMBRANE AND SOIL

填埋场衬垫系统中,土与土工膜界面剪切强度较低,易造成失稳破坏。目前国内外学者主要采用室内试验对土与土工膜界面的宏观剪切特性进行研究,而对界面剪切特性的细观研究较少。为了从细观角度研究土与土工膜界面的剪切特性,本文采用Esy S-particle程序对土工膜与土界面直剪试验进行了离散元数值模拟分析。采用摩擦接触模型模拟砂土;采用黏结模型颗粒模拟土工膜,通过紧密排列土工膜颗粒以模拟土工膜的光滑表面。通过室内拟合试验,选取和校准材料的细观参数。分析结果表明,离散元模型能较好的模拟界面应力-应变关系;剪切带的厚度约为两倍平均土颗粒直径;剪切带中的土颗粒发生较大位移,孔隙比增大,而剪切带之外的土颗粒位移和孔隙比变化较小;随着剪切位移的增加,颗粒间接触力逐渐向左端集中,力链方向由垂直逐渐倾斜。

Geomembrane has been commonly used as barriers in landfills in combination with soils. However,the soil-geomembrane interfaces may become the potential planes of weakness within the system along which failure may occur. Therefore,many laboratory tests have been conducted by researchers to investigate the interface shear behaviors. However,it is difficult to directly investigate the material interactions and mechanisms occurring at soilgeomembrane interfaces through common laboratory tests. In order to investigate the mesoscopical interface properties between geomembrane and soil,a serial of numerical direct shear tests are carried out using a modified three dimensional DEM code,Esy S-particle. In this paper,the sand is modeled with cohesionless frictional interactions,while the geomembrane is modeled with bonded particles. In order to precisely simulate the smooth surface of the geomembrane,the distance between two nearest bonded particles has been adjusted to a small value.Suitable mesoscopic discrete element parameters of the sand and geomembrane have been calibrated by numerical triaxial tests and tensile tests,respectively. The numerical interface direct shear tests are performed under the same conditions as the laboratory tests, and the simulation results are compared to experimental data. The DEM simulation result shows that the DEM simulation is capable of reasonably predicting interaction behavior betweengeomembrane and soil. The shear band thickness is approximately 2 times of the average particle diameters. During the shear process,the particles inside the band undergo large horizontal relative displacements,while particles outside the area are driven by an upward motion. And the void ratio inside the shear band sees an increasing trend during the shear process,whereas no obvious change is observed outside the area. The distributions of contact force chains are small and homogeneous at the beginning of the shear,during the shearing,the contact force chains are concentrating to the left part of the sample,and the orientations of the forces changed from nearly vertical to diagonal.