# The Shear Behavior of the Curved Interface in Polyurethane-Concrete Composite Structures
## 1 Introduction
[13] studied the effects of polyurethane density, environmental temperature, and interfacial moisture content on the shear strength of polyurethane and concrete composite structures using the concentric push-out method. The results indicated that bond failure primarily occurred when the polymer was pushed out. Higher polymer density and temperature improved the bonding strength, whereas increased concrete moisture reduced it. [PERSON] et al. [14; 15; 16] investigated the effects of vertical stress, shear rate, and cycling frequency on the interfacial mechanical properties of polyurethane-concrete interfaces through a series of direct shear tests. The results showed shear softening behavior. Vertical stress increased shear strength and modulus, while higher shear rates reduced both. Cyclic loading significantly weakened shear strength, with greater impacts on cohesion than on friction angles. [PERSON] et al. [17; 18] examined the damage mechanism of polyurethane-concrete interfaces through direct shear tests, supplemented by acoustic emission technology and scanning electron microscopy. The results showed that a higher polymer density increased the bonding strength, with AE activity peaking during the failure stage. [PERSON] et al. [19] explored the influence of polyurethane density, concrete strength, and water on the interfacial mechanical properties of polyurethane-concrete interfaces through direct shear tests and scanning electron microscopy. The results indicated that poly mer infiltration into concrete pores enhanced the bonding strength. However, pre-wetted surfaces reduced polymer migration, leaving pores incompletely filled and weakening the bond. [PERSON] et al. [20] investigated the influence of normal stress on the shear performance of polyurethane-concrete interfaces through direct shear tests, corroborated by finite element simulations. The results showed that low-density polymers were more sensitive to normal pressure. The bond strength increased linearly with the polymer density, but increments gradually diminished, and peak displacement decreased. [PERSON], [PERSON], [PERSON], and others [21; 22; 23; 24] employed three-dimensional finite element analysis and full-scale tests to examine the mechanical response of drainage pipes before and after repair with polymer and cement grouting, as well as the effects of traffic loads on the longitudinal performance of large-diameter pipes. Their findings indicated that vertical displacement at pipe joints and under traffic loads was significantly greater than other pipe sections, suggesting potential shear stress in composite structures involving concrete pipes, polyurethane, and soil. [PERSON] et al. [25] argue that the exploration of interfacial shear mechanical properties in concrete should extend beyond monotonous planar structures. Such a singular planar approach merely scratches the surface of understanding interfacial shear behavior at the material level, neglecting the diverse interface configurations present in real-world engineering structures, including curved surfaces, irregular interfaces, multiple coexisting interfaces, joint surfaces, weak planes, and gradient distribution surfaces. [PERSON] et al. [26; 27] developed an analytical model for pipe-soil-polyurethane interaction based on elastoplastic theory. Using the Duncan-Chang EB nonlinear model, they verified the effectiveness of polyurethane grouting in repairing voided pipelines and demonstrated the advantages of polyurethane polymer impermeable walls. [PERSON] [28], drawing on the properties of polyurethane grouting materials and tunnel curtain grouting techniques, proposed treatment methods for water-leaking highway tunnels as well as quality inspection and evaluation methods for polyurethane curtain grouting. [PERSON] [29] conducted pre-grouting construction experiments for subways and tunnels, investigating the influencing factors and variation patterns of targeted grouting technology, and confirmed its effective repair outcomes.