Numerical Simulation Analysis Of Working Performance Of Flexible Plugging Structure In Karst Funnel Reservoir

There is a serious seasonal water shortage in karst areas in southwest China,one of the main ways to solve this problem is to build a reservoir to store water.Due to the special geological environment in the karst area,the problem of leakage at the bottom of the reservoir is outstanding.Adopting appropriate reservoir bottom plugging measures is the key to solving this problem.Currently,there are few studies on karst funnel reservoirs,and the bottom plugginge technology is not mature enough,so what kind of suitable plugging scheme is choosed has become a key problem to be solved urgently.This paper relies on the Chongqing Technology Innovation and Application Demonstration Project"Karst Funnel Bottom Suitability Plugging Reservoir Forming Technology and Engineering Demonstration"(No.:cstc2018jscx-msybX0328),takes the Cizhuwan Reservoir project under construction in Pengshui County as the background and adopts the numerical simulation analysis method to carry out the research on the working performance of the flexible plugging structure of karst funnel reservoir.The main research work and results of the thesis are as follows:(1)Aiming at the topography,geological conditions and reservoir function of the Cizhuwan Reservoir Project Area in Pengshui County,the flexible plugging structure of“filled stone-rolled clay-composite geomembrane”and the flexible plugging structure of“filled stone-asphalt concrete panel”are proposed.Through analysis,it is determined that the structure and material composition of the“filled stone-rolled clay-composite geomembrane”plugging scheme(from bottom to top)are:rolled limestone block stone replacement(thickness 2m)+rolled gray rock slag Material(thickness 2m)+rolled clay layer(thickness 3m)+HDPE geomembrane(2 layers)+clay layer cover(thickness 0.5m)+limestone crushed stone(thickness 20cm)+dry block stone(thickness 20cm);the structure and material composition of the“filled stone-asphalt concrete panel”plugging scheme(from bottom to top)are:rolled limestone block boulder replacement(thickness 5m)+rolled limestone fragment stone transition layer(thickness 1m)+crushed limestone gravel cushion(thickness 1m)+asphalt concrete panel(thickness 0.9m).(2)Aiming at the plugging scheme of“filled stone-rolled clay-composite geomembrane”,MIDAS/GTS software was used for numerical simulation analysis,and the influence of working conditions,filling method,filling shape,filling thickness and filling material characteristics on the working performance of the flexible plugging structure was discussed.Research shows:under the condition of checking the flood position,the maximum structural settlement is 24.33cm,and the maximum tensile stress also reaches a maximum of 82.95 kPa,;the stratified filling can reduce structural settlement and reduce the maximum tensile stress;as the shape of the filling gradually changes from concave to horizontal and then gradually becomes convex,the structural settlement gradually increases,but the maximum tensile stress gradually decreases;with the thickness of the rolled clay layer increases,the structural settlement increases slightly,and the maximum tensile stress does not change regularly,when the thickness is2m,the maximum tensile stress is 87.25kPa,and when the thickness is 2.5m or more,the structural stress is better;according to the analysis of the characteristics of the filled materials,the characteristics of the rolled clay material have the greatest influence on the working performance of the structure,especially for its parameters K and n,the K value of the rolled clay should be controlled at 200 or below,while the value of n should be controlled at 0.6 or above.(3)Aiming at the plugging scheme of“filled stone-asphalt concrete panel”,MIDAS/GTS software was used for numerical simulation analysis,and the influence of working conditions,filling method,filling shape and filling material characteristics on the working performance of the flexible plugging structure was discussed.Research shows:under the condition of checking the flood position,the maximum structural settlement is 24.38cm,and the maximum tensile stress also reaches a maximum of267.44 kPa;the stratified filling has less influence on the settlement of the structure,but the maximum tensile stress of the design flood condition is reduced to 50.80 kPa,the decline is huge;as the shape of the filling gradually changes from concave to horizontal and then gradually becomes convex,the structural settlement gradually increases,but the maximum tensile stress has a large decrease;according to the analysis of the characteristics of the filling materials,the K and n parameters of the asphalt concrete material and the R_f of the crushed stone boulder material have a great influence on the structural performance;the value of the parameter K of the asphalt concrete material should be controlled at 255 and below,while the value of n should be controlled at 0.38or above,and the value of R_f of the rolled boulder stone material should be controlled at around 0.9.