Assessment of Local Strain of PVC-P Geomembranes Induced by Particle Cushion Layers

This study investigates the deformation of plasticized polyvinyl chloride (PVC-P) geomembranes (GMBs) on uniform cushions and flat-rounded gravel cushions using a self-developed testing apparatus for GMB deformation and a three-dimensional (3D) laser scanner. Based on the principle of square voids equivalent to circles, the void width-depth ratio was adopted to quantify voids within granular cushions. The models between strain and void width-depth ratio, as well as gradation parameters, were established. The gradation parameters of flat-rounded gravel cushions satisfying the deformation requirements were determined for GMBs as anti-seepage materials in basins of pumped storage power stations. The results demonstrate that the areal strain of the PVC-P GMB is consistently greater than its linear strain for uniform cushions. From the perspective of engineering safety, the areal strain is recommended to characterize the deformation of PVC-P GMBs. The GMB areal strain on flat-rounded gravel cushions exhibits an allometric function with the width-depth ratio and non-uniformity coefficient, and an Exp2P function with the maximum limiting particle size, with all determination coefficients exceeding 0.99. Based on the areal strain less than 20% of its elastic strain threshold, the granular cushion should satisfy a non-uniformity coefficient in the range of 15.3 to 20.7, and the maximum limiting particle size is between 4.75 and 23.54 mm, the PVC-P GMB can maintain elastic deformation behavior, which extends its service life in practical engineering. These findings contribute to a deeper understanding of the local deformation behavior of PVC-P GMBs on cushion layers. The gradation parameters satisfying the deformation requirements for particle cushion layers provide technical guidance for cushion layer design for the application of PVC-P GMBs in pumped storage power stations.