Laboratory test and modelling of gas pressure under geomembrane subjected to the rise of groundwater in plain reservoirs

To investigate the development of pore pressures in the air-confined system with a rise of groundwater under a geomembrane, a laboratory test was conducted. Then, a numerical model with the consideration of the water-gas-solid three-phase system was developed based on the hydro-mechanical coupling theory for unsaturated soils. The model was validated by the experimental result and then a numerical study was conducted on the Datun plain reservoir. The result confirms the fact that the rise of groundwater is one of primary driving force for gas pressure under the geomembrane. When there is no surcharge over the geomembrane, air bulge would be produced. As the groundwater under the geomembrane replenished by water infiltration from groundwater around the reservoir, the gas pressure increases from the edge to the center of the reservoir and reaches the same final value with time. The increment of the pore gas pressure is significant during the increase of reservoir water, especially for the soils with larger compression strain. Thus, the coupled deformation is necessary to be considered for the regulating reservoir that undergoes the fluctuation of reservoir water frequently. •A laboratory test was conducted to understand the development of gas pressure with the rise of water table under geomembrane cover.•A numerical modelling method was developed base on the hydro-mechanical coupling theory of unsaturated soils, which could consider water-gas-solid three-phase.•The laboratory test was well simulated using the developed numerical method.•Numerical simulation was conducted relying on the real project of Datun plain reservoir.