Effect Of Loading Rate And Loading Medium On Bulging Deformation Of Geomembrane(Geotextile)

For the plain reservoir with horizontal seepage control,the pore pressure under the geomembrane has different accumulation forms,affected by the reservoir leakage,surrounding precipitation,groundwater rise and reservoir operation,the porous gas compression under the geomembrane will lead to air bulging problem,the extrusion of porous liquid will lead to hydraulic bulging problem.The problem of air bulging and hydraulic bulging can be attributed to the bulging deformation problem,the two kinds of pressure media will affect the mechanical properties and failure forms of the bulging deformation of the geomembrane(geotextile).In addition,with the different growth rate of pore pressure,the response of geomembrane and geotextile to bulging deformation is different,which will affect the material properties.In order to study the influence of different pressure medium and loading rate on the bulging deformation of geomembrane(geotextile),the air bulging test and hydraulic bulging test of geomembrane,geotextile and composite material of two materials were carried out on the same test platform by using the improved test equipment.The mechanical propertie,failure characteristic and mechanism of impermeable material under different pressure medium and loading rate are summarized.The main conclusions are as follows:(1)The improved bulging deformation test equipment can better realize the co MParison of different impermeable materials in the air bulging test and hydraulic bulging test,the results show that different pressure media will affect the mechanical properties and failure characteristics of the material.(2)When the geomembrane reache the maximum bulging pressure during the air bulging test,tearing failure occurs,and the failure form is relatively regular;when the maximum bulging pressure is reached in the hydraulic bulging test,a secondary plastic stretching phenomenon will occur,resulting in linear tearing failure,or produce a bulge damage in the center,and the direction of the cracks during failure is mostly parallel to the direction of the production texture.(3)The failure mode of geotextile in the bulging test all showed tearing failure;the cracks damaged by hydraulic bulging are mostly linear,crescent and spindle shape,and the damage range is small;the air bulging damage produces extremely irregular cracks with a large damage range.When the geomembrane and geotextile are combined,the bursting height is basically the same as that of a single geotextile,the damage surface of the geomembrane and geotextile is reduced,and the tearing pattern is also consistent;the tearing damage caused by air bulging test is obviously greater than that caused by hydraulic bulging test,so the leakage damage caused by air bulging test may be greater.(4)Under the same loading rate and pore size conditions,different pressure medium will affect the reaction rate of material deformation and the uniformity of the deformation area,and affect the strength of the material.In the air bulging test,the area of the test material that is uniformly deformed in the early stage is larger,and the deformation response is faster,making the bulging pressure of the air bulging test smaller than the hydraulic bulging test;the bulging height and bulging pressure of the geomembrane during the hydraulic bulging test are both greater than the result of the air bulging test,the difference in the result become more obvious as the thickness increases,but the pressure medium has little effect on the bursting height of geotextile and the composite material of geomembrane and geotextile.(5)Under the same pressure medium and aperture conditions,the loading rate will affect the response time of the bulging deformation of the geomembrane(geotextile),which in turn affect its mechanical propertie and failure morphology.The faster the hydraulic loading rate,the greater the maximum bulging pressure of the geomembrane,the greater the tensile stress when the geomembrane yields,and the smaller the range of secondary plastic stretching;the faster the air pressure loading rate,the greater the bursting pressure of the geomembrane,the smaller the bursting height,the tearing failure will occur directly.The bursting pressure of the geotextile and its tensile stress at the time of failure both increase with the hydraulic loading rate,while the bursting height decreases accordingly.The results of this paper can help to fully understand the bulging deformation process and failure mechanism of geomembrane and geotextile under different loading rates and medium conditions,and provide theoretical and technical reference for the mechanical properties detection and improvement design of the membrane cloth materials.