Experimental Study On Spherical Bulging Deformation Of Separated Composite Geomembrane Applied To Plain Reservoir

For the separated composite geomembrane used as the horizontal seepage control system in surrounding dam plain reservoirs,the air expansion phenomenon was caused by conditions including groundwater level rise,rapid decrease in the reservoir water,surrounding embankment construction,and geomembrane defect leakage.The air expansion deformation of separated composite geomembrane was simplified as the spherical bulging deformation under ring restrained condition to study the air expansion deformation of the separated composite geomembrane,the same type of geomembranes and the same specification of geotextiles used in the actual construction of Datun Reservoir are selected as test materials of separated composite geomembrane,the experimental scheme is designed,and the formulas for calculating stress and tensile stress are derived.Tests on spherical bulging deformation of separated composite geomembrane under ring restrained condition are carried out using an improved special test equipment for bulging deformation,the rules of bulging deformation and failure are summarized,and the main conclusions are as follows:(1)By comparing the calculation formulas of stress and tension stress of separated composite geomembrane,it is concluded that the calculation formula of tensile stress has obvious advantages and can better describe and analyze the mechanical characteristics of expansion deformation of samples.(2)The combination form is the most important factor affecting the expansion deformation of separated composite geomembrane while the size of clamp is a secondary factor,but the effect of loading rate on the expansion deformation of separated composite geomembrane is limited.(3)Because of the permeability of geotextiles,when geotextiles are located at the bottom of the sample and can directly contact with the pressure medium,it will not affect the mechanical deformation properties of the whole sample.It is considered that geotextiles located at the bottom of the sample can directly contact the pressure medium belong to the invalid position of bulging deformation.(4)Tensile stress and strain curves of separated composite geomembrane can be divided into “geotextile-like” and “geomembrane-like”.Tensile stress and strain curves of “geotextile-like”can be divided into three stages: linear,yield and strengthening failure.Tensile stress and strain curves of “geomembrane-like” can be divided into three stages: elastic,plastic and weakening failure.(5)The bulging failure of separated composite geomembrane is controlled by deformation,and the order of failure is that geotextile is prior to geomembrane.(6)For the separated composite geomembrane with the combination form of “geomembrane under geotextile”,when its expansion deformation reaches a certain height under the pressure,the pressure imposed by the upper geotextile is equal to the pressure of the single geotextile when it reaches the same height,while the pressure imposed by the lower geomembrane is equal to the pressure of the single geomembrane when it reaches the same height.