Shear Stress Transfer,Strength Characteristics And Safety Control Of Composite Liner Systems

Geosynthetics are widely used in municipal solid waste landfill,mainly including:geotextile(GT),geomembrane(GM),geosynthetics clay liner(GCL), geocomposite(GC) and etc.Liner systems is a new geotechnical structures consisting of the geosynthetics and soil with many features like sealing,impermeable and drainage.The use of liner systems for landfill design and construction brings many advantages.Tensile failure of geosynthetics and slide of the landfill along the liner systems may be attributed to the lower interface strength witin liner systems,the paper systematically studied the shear strength characteristics of liner system interface, as well as the shear transfer mechanism within liner systems,at last the stability of the landfill were analyzed.The main conclusion is as follows:(1) The different geosynthetics show different tensile properties.The tensile strength and tensile stiffness of Geogrid are larger,but the tensile strength and tensile stiffness of non-woven geotextile are smaller(2) The shear strength of GM/GT interface is affected by the surface roughness of GM.The shear strength of textured GM/GT interface is much larger than that of smooth GM/GT interface.(3) The loading rate and shearing effect play an important role related to bentonite extrusion from the prehydrated GCL/GM specimens. Bentonite extrusion exerts a significant influence on the shear strength of the hydrated GCL/GM interfaces.The loss in the large-displacement shear strength is approximately equivalent with 7.6°in terms of interface friction angle.The influence of bentonite extrusion on the peak shear strength showed a magnitude of 3.5°in terms of interface friction angle.(4) The shear transfer mechanism within liner systems must follow the two principles:(1)the interface with the smallest peak shear strength would be easily sliding at first;(2) The shear stress which the interface transfered can not be greater than the peak strength of the interface.(5) In this paper,a large-scale ramp test of the liner system was developed with a higher stress level.Two group tests on the stability of liner system were studied.The experimental results of GT/GM liner system show that,when the external shear stress is less than the peak shear strength of the GT/GM liner systems,the interface would not reach a residual shear condition,and when the external shear stress is greater than the peak shear strength of the GT/GM interface,the GT/GM interface would trend to reach a residual shear condition.The experimental results of GT/GM/GCL liner systems show that when the external shear stress is greater than the peak shear strength of the GT/GM interface and GM/GCL interface,even the peak shear strength of the GM/GCL interface is less than that of GT/GM interface,slide would happen along the GT/GM interface,and the the GM/GCL interface with the minimum peak shear strength is stable.(6) The highly compressible characteristics of MSW have a key impact on development of residual strength for the liner system on landfill slope. In addition,the slope gradient and landfill height also exert an important influence on the residual strength development.The slope gradient and height is greater,the liner system interface on the slope is easier to reach a residual shear condition,highly compressible characteristics of MSW, slope gradient and height have a less impact on the development of residual strength for the liner system on landfill base Generally the liner system on landfill base play its peak shear strength.(7) The selection of the strength paramete for a multi-layer liner system was recommended that:(1) determine the interface in the composite liner system that exhibit the lowest peak strength for the full range of normal stresses encountered along the bottom liner system;(2) uses the peak interface shear resistance with the the lowest peak strength along the base and the residual interface shear resistance with the the lowest peak strength along the sideslope(8) Leachate level,base length,landfill height,slope gradient and interface strength are the five key factors on the safety factor of slide along the liner system.Among them,the increase of leachate level will,landfill height and slope gradien would reduce the safety factor;but the increase of base length and the interface strength would improve the safety factor. Seleting a liner systems with a larger interface strength,controlling leachate levels,increasing the base length and choosing a suitable landfill height would keep the landfill peration of an effective measure.