## 1 Introduction  
For a high rockfill dam built on deep overburden, the dam surface will produce large deflection deformation because of the large deformation of the dam body and foundation. If there is a geomembrane barrier on the upstream face of the dam, excessive deflection deformation will lead to cracking or even dislocation of the cushion and protective layers. This situation will endanger the safety of the geomembrane under pressure by water. A granular crushed stone layer, or porous concrete, is typically used as the cushion material in the geomembrane surface barrier of a low rockfill dam. However, existing research and engineering application experience have demonstrated that the granular material cushions cannot maintain stability [1, 2]. The porous concrete usually presents a higher elasticity modulus and an obvious brittle characteristic during compressive and flexural failure [3, 4]. Thus, these traditional cushion materials are not suitable as a cushion for the geomembrane surface barrier of a high rockfill dam. Polyurethane bonded aggregates are a new type of elastic honeycomb porous material composed of polymer glue and crushed stone. Polyurethane bonded aggregates were first applied to embankment surfaces in Europe for slope protection. The porous structure was used to eliminate the energy of the wave and water flow, thus reducing the erosion damage to the embankment [5, 6]. Polyurethane bonded aggregates have high strength and permeability. Moreover, they have low elastic modulus and good flexibility. Polyurethane bonded aggregates have stronger deformation adaptability than traditional materials such as porous concrete. Thus, they are well suited as a cushion material for the geomembrane surface barrier of a high rockfill dam [7]. However, there has not been any reportedresearch on the mechanical and deformation performance of a geomembrane surface barrier comprised of polyurethane bonded aggregates as the cushion material. Several researchers have studied the deformation behavior of geomembrane on different cushion materials. Based on the film tension theory, [PERSON] et al. (1996) proposed the design criteria of a geomembrane with different cushion layers [8]. [PERSON] et al. (1996) verified and improved the design criteria through laboratory model tests and proposed a calculation method for the safety factor of geomembrane puncture on different cushions [9]. [PERSON] and [PERSON] (2006) conducted puncture tests on 1.5 mm-thick high-density polyethylene (HDPE) geomembrane with a coarse gravels cushion under 3000 kPa-pressure and concluded that the geomembrane could be punctured under this extreme condition [10]. [PERSON] et al. (2008) obtained the puncture resistance of geomembranes with different thicknesses through puncture tests and pointed out that the puncture resistance of the geomembrane increases with increasing thickness [11]. [PERSON] and [PERSON] (2010) conducted laboratory tests to measure the strain of a geomembrane placed on cushions and concluded that the indentation and strain of geomembranes are affected by the shape and particle size of cushion material [12]. [PERSON] et al. (2013) and [PERSON] and [PERSON] (2014) derived the relationship between the contact-stress distribution and the particle size of cushion materials using the entropy theory [13; 14]. [PERSON] and [PERSON] (2018) used the image recognition method to measure the depression of a geomembrane formed by cushion particles and conducted simulation and analysis through the finite element method [15]. The previous research mainly focuses on the behavior of geomembranes on the cushion of granular materials. No research has been conducted on the failure characteristics of geomembrane and cushion of polyurethane-bonded aggregates under the non-uniform settlement deformation of the dam surface conditions. Thus, the influence of polyurethane bonded aggregates on the deformation of the geomembrane is unclear.