Creep Characteristics And Prediction Method Of Geomembrane And Geotextile Interface In Liner System

The liner system of modern sanitary landfill is often composed of compacted clay(CCL),geomembrane(GM),geotextile(GT),geogrid(GG)and geocomposites.The shear strength of the adjacent interface of these protective materials is less than that of the landfill itself,which makes the interface of geosynthetics slip first to consume the shear force in the system under the same shear stress.Therefore,most of the existing landfill instability cases are sliding failure along the weak interface of geosynthetics in liner system.At present,scholars at home and abroad have carried out a series of research work on the interface of CCL-GM,geosynthetics and the creep of geosynthetics in liner system.However,there are few researches on the creep characteristics of geosynthetics under long-term stress.Based on the above situation,this paper mainly carries out systematic research from the following three aspects:in the first part,the improved direct shear apparatus is used to study the shear characteristics of the interface between geomembrane and geotextile;In the second part,the creep characteristics of the interface between geomembrane and geotextile are studied through the indoor creep test;In the third part,four kinds of typical empirical creep model fitting creep test curves are compared and analyzed,and accurate and effective prediction methods are proposed and verified.Through carrying out the above content,the following research results have been achieved:(1)The shear stress of the interface between geomembrane and geotextile can be divided into three stages:elastic stage,strain softening stage and stable stage.Among them,the strain softening stage of smooth geomembrane geotextile interface is the most obvious,and the strain softening stage of column point geomembrane geotextile interface is not obvious.There are only elastic stage and stable stage,which is mainly due to the"tillage"phenomenon of column point in the interface.With the increase of interface normal stress,the growth rate of shear stress also increases in the elastic stage,and the interface needs to reach the peak strength and residual strength at a larger shear displacement.Under four different normal pressures,the peak shear strength of the column point geomembrane filament geotextile interface is the largest.In addition,the vertical and parallel stress directions of braided geotextile warp have little influence on the shear characteristics of the interface,so the influence of different stress directions of braided geotextile warp on the interface can be ignored.(2)The creep test curve of the interface between geomembrane and geotextile can be divided into deceleration creep stage and constant velocity creep stage.At the initial stage of deceleration creep,the creep displacement increases linearly with time,and then the creep curve gradually bends from a straight line to an arc,and the creep rate gradually decreases;In the stage of constant velocity creep,the creep curve tends to a straight line,the creep displacement growth rate tends to a fixed value,and the creep rate almost remains unchanged.Under the same normal stress,the instantaneous displacement of interface increases with the increase of shear stress;Under the same shear stress level,the instantaneous displacement of interface increases with the increase of normal stress.When the interface is under phase normal stress,the creep displacement and creep rate increase with the increase of loading shear stress;Under the same shear stress level,the larger the normal stress is,the larger the creep displacement and creep rate are.For the interface between geomembrane and woven geotextile,the vertical or parallel direction of warp of woven geotextile has little effect on the creep behavior of the interface.(3)Logarithmic function,power function,hyperbolic function and other function types(such as near logarithmic function)are only suitable for describing the attenuation creep curve or short-term non-attenuation creep curve.Among the four types of empirical models,the near logarithmic function model is the best to predict the 3-day creep displacement of geomembrane geotextile interface.For the prediction of non-attenuation creep displacement under long-term load,the formula is used (?) can achieve better prediction effect.