Research On Interaction Of Geomembrane, Mineralwaste Residue And Cushion

This thesis reviewed the history and current situation of the research ontailings disposal. Environment significance of using geomembrane as bottomliner of tailings disposal facilities was discussed. Analytical solutions totensile stresses and strain in geomembrane were deduced for geomembraneinstalled on tailings stack slopes. In theoretical analysis, the supporting effectof the foundation or bottom anchor bench on tailings was considered and theshear stress exerted on geomembrane by tailings was modified accordingly tobetter simulate the field condition. A numerical model was established toanalyze the interactions between tailings and geomembrane installed onmountain slopes using FLAC. The main contents are described as follows:(1) Forces applied on geomembrane in tailings stacks were analyzedbased on the force equilibrium analyses of a tailings element. Conditionsunder which tensile stresses develop in geomembrane were determined.Analytical solutions to tensile stresses and strain in geomembrane werederived for different tailings materials, slope angles, slope heights andcushion materials. The shear stress applied on geomembrane by tailings wasmodified to take the supporting effect of foundation into consideration. Theanalytical solutions with and without a stress reduction coefficient werecompared. The comparison showed that the calculated tensile stresses ingeomembrane were more reasonable by incorporating a stress reductioncoefficient.(2) The finite difference software FLAC7.0was used to simulategeomembrane installed on tailings stack slopes. Two methods were used: onewas to simulate the liner-tailings interaction using a single interface and theother was to simulate geomembrane using a beam element. The general trend of the variation of tensile stresses with slope height from the two numericalmethods was similar to that from the analytical solution. In both numericalmethods, the interface shear strength between geomembrane and cushionlayer was fully mobilized. However, the tensile stresses from the numericalmodel with the beam element were less than those from the numerical modelwith the single interface. This is because the relative movement betweengeomembrane and tailings decreased due to a relative movement betweengeomembrane and cushion layer and accordingly, the shear stresses appliedon geomembrane by tailings decreased when a beam element was used tosimulate the geomembrane. Comparison between the analytical andnumerical solutions showed that the tensile forces in geomembrane from thenumerical model using the single interface were the largest, but the tensileforces from the numerical model using the beam element might be a betterrepresentation to the actual field condition.(3) The influences of pore water pressure on tensile stresses ingeomembrane were analyzed. The results showed that: under saturatedconditions, the shear stresses applied on geomembrane by tailings decreasedbut the interface shear strength of the geomembrane-cushion interface didn’tchange. As a result, the tensile stresses in geomembrane decreased. Bothanalytical and numerical solutions showed that tension in geomembranedeveloped only in the case when a geomembrane-cushion interface frictionangle of10°and a slope of1:1were used. The analyses indicated that thegeomembrane is less vulnerable to downdrag of tailings in a fully saturatedcondition than in a dry condition as long as the integrity of the geomembranewas ensured.