Permeability mechanism of PVC-P geomembranes based on low-field NMR technology

The permeability of plasticised polyvinyl chloride (PVC-P) geomembranes (GMBs) is of significant importance to the safe operation of impermeable structures and even entire projects. To avoid the drawbacks of the traditional method of adopting the permeability coefficient to characterise permeability, this paper presents a mathematical model of porosity and seepage discharge based on the results of the vertical permeability test and porosity obtained from low-field nuclear magnetic resonance (NMR) tests. This paper also explores the applicability of porosity to evaluate permeability combined with the dynamic distribution of pores and pore radius. The results show that low-field NMR technology with ¹H (isotope of hydrogen) atoms as the probe can accurately measure the distribution of pores and pore radius in the PVC-P GMB. The proportion of micropores (Mic), mesopores (Mes) and macropores (Mac) and the shrinkage or development of pore radius are primarily responsible for the variation of porosity. Porosity is closely correlated with seepage discharge, and the constructed model can accurately predict seepage discharge. Furthermore, porosity can provide technical support for the evaluation of the permeability of PVC-P GMBs and the selection of appropriate GMBs for engineering design.