三轴试验条件下城市生活垃圾土的变形强度特性

Investigation of the Deformation and Strength Properties of Municipal Solid Waste Using Triaxial Tests

在实验室对现场钻取的垃圾土样进行成分分析和试样制备,考虑填埋场内垃圾土的实际状态,采用三轴试验从试样尺寸、固结方式和应力路径等3个方面系统研究了垃圾土的变形和强度特性,试验结果表明:(1)直径分别为40mm和100mm两种尺寸的垃圾土试样的应力-应变关系具有相同的变化规律,偏应力随着轴向应变的增加逐渐增大,应变水平较大时应力-应变曲线呈上翘形状,应变超过30%仍没有出现屈服或达到峰值的迹象;轴向应变相同时,偏应力随着围压的增加而增大;轴向应变和围压都相同时,相比小尺寸试样,较大尺寸试样的抗剪强度较小.(2)得到了垃圾土的抗剪强度参数随轴向应变的线性表达式,小尺寸试样的黏聚力和内摩擦角分别约为较大尺寸试样的1.48倍和1.16倍.(3)等压固结、各向异性固结和K_(0)固结(3种固结方式的侧向土压力系数k分别为1.0、0.54和0.29)试验所得垃圾土的偏应力增量随着k值的减小而略有减小.(4)轴压不变围压逐渐减小的卸载试验结果表明,垃圾土的偏应力-轴向应变曲线类似双曲线形状,围压越大偏应力越大;围压减小到0后轴压持续增加的加载试验结果表明,垃圾土的偏应力-轴向应变曲线同样出现了上翘的形状,依然没有屈服或达到峰值,解释了高陡填埋场边坡能够保持长期稳定的现象.研究成果可为填埋场的设计及稳定性分析提供参考.

Composition analysis and specimen preparation of municipal solid waste(MSW)drilled from landfill were carried out in laboratory.Considering the actual status of MSW in the landfill,the deformation and strength behavior of MSW were studied systematically using triaxial tests from the following three aspects,such as specimen size,consolidation method and stress path.The stress-strain relationships of MSW specimens with diameters of 40mm and 100mm respectively have the same varying tendency,exhibiting a pronounced upward shape at larger axial strains.The deviatoric stress of the specimens continues to increases with axial strain without any distinct yielding failure or peak stress value even up to 30%axial strain.The deviatoric stress increases with confining pressure increasing at the same axial stain.And the larger-size specimen has a smaller shear strength than that of the smaller-size specimen with the same value of axial strain and confining pressure.The linear expressions are obtained for the relationship between shear strength parameters(cohesion and internal friction angel)and axial strain.The cohesion and internal friction angle of small-size specimen are about 1.48 and 1.16 times of large-size specimen,respectively.From the isotropic,anisotropic and K_(0)consolidation tiaxial test results with the corresponding lateral earth pressure coefficient k of 1.0,0.54 and 0.29,respectively,the deviatoric stress increment of MSW decreases with the reduction of k value.The stress-strain curves are similar to hyperbolic shape in unloading triaxial tests,and the greater confining pressure the greater deviatoric stress.The stress-strain curves also present upward shape without any yielding failure or peak value in the reloading triaxial tests with zero confining stress,which explain the phenomenon that the high and steep waste mass slope in landfill could maintain long-term stability.The above results provide a reference for design and stability analysis of landfill.