Testing the shearing creep of composite geomembranes-cushion interface and its empirical model

An accurate description of composite geomembranes (CGs)–cushion interface behaviour (particularly creep behaviour) is of great importance. This paper presents a creep experiment method for studying the shearing creep characteristics of CGs–cushion interfaces. In this study, natural sand and sandy gravel cushion materials were tested for their creep characteristics with CGs. In the proposed method, the shearing creep curves of CGs–cushion interfaces in multi-stage loading are obtained, and they can be transformed to the creep curve at each specific loading level with Chen’s method. The results show that the power function and modified hyperbolic function exhibit perfect performance in fitting the displacement–stress and displacement–time relationships, respectively. An original empirical creep model for the CGs–cushion interface was established on the basis of these fitting means; it was found to exhibit superior performance in fitting and predicting the attenuation creep curve at each stress level. An accelerating creep model applicable to the accelerating creep phase is presented by using the Kachanov damage factor to reflect the accelerating creep damage to CGs–cushion interface. The study provides enhanced guidance for the engineering design and construction of structures incorporating CGs.