## 1 Introduction  
The non-uniform settlement caused by stratum creep and train cyclic load has a significant impact on tunnel structure safety and stability. At present, the backfill materials of expressway tunnel engineering are mainly flake stone concrete and low-strength-grade plain concrete [1; 2; 3]. [PERSON] [4] used the finite element calculation method by changing the elastic modulus of concrete elements and found that the deformation and stress of the tunnel surrounding rock and the internal force of lining were reduced greatly with the increase in the elastic modulus of backfill concrete at the top of the middle wall. [PERSON] et al. [5] used foam concrete to replace the traditional arch foot backfill material and verified the tunnel structure strength and anti-floating requirements through numerical model calculation, and successfully implemented it on site. [PERSON] et al. [6] carried out undrained cyclic triaxial tests of saturated soft clay under different confining pressures and consolidation modes, established an explicit model of cyclic cumulative pore pressure and verified the rationality of the model. Previous studies analyzed the long-term settlement of backfill under cyclic loading and its influence on tunnel stability through similar model tests [7; 8; 9] and indoor cyclic loading tests [10; 11]. The mechanical properties,durability and damage characteristics of backfill concrete have a crucial influence on the tunnel's stability. Stone flakes concrete and plain concrete usually have defects such as unequal particle size, large strength deviation and poor durability. [PERSON] has been grinding waste tires and using them as one of the concrete ingredients, as well as mixing them with cement and sand aggregate, etc., to make RC [12]. This new type of concrete has proper toughness [13] and low rigidity [14], and has been widely utilized in roads, bridges, railways, airport runways and other projects [15]. Rubber concrete has good durability, impermeability and corrosion resistance [16; 17; 18]; a large number of documents indicate that the incorporation of rubber particles can hinder the development of cracks in concrete, improve the toughness of concrete and inhibit crack propagation [19; 20; 21; 22; 23; 24]. [PERSON] et al. [25] found that the compressive strength and elastic modulus of rubber concrete decreased, but the deformation energy and absorption energy increased and the curvature ductility increased by 90%. [PERSON] et al. [26] conducted a drop hammer test on rubber concrete and found that, with the increase in the particle size and content of rubber particles, the impact resistance was better. [PERSON] et al. [27] found that, compared with ordinary concrete, the ultrasonic modulus of tire rubber concrete is greatly reduced, and the sound absorption performance is superior. In addition, rubber concrete also performs better ductility and stability than ordinary concrete after cyclic loading [28]. [PERSON] et al. [29] found that the rubber concrete has large deformation but good stability after cyclic loading, the optimal content of rubber particles is 5% and the optimal ratio particle size is 0.85 mm. [PERSON] [30] carried out a cyclic load test on an RC specimen under a confining pressure of 0-25 MPa. [PERSON] and [PERSON] [31] found that the main influencing factors of confining pressure on the cyclic performance of confined concrete are reloading modulus and plastic strain. The results show that the ductility of RC is higher than that of NC. Moreover, [PERSON] et al. [32; 33] analyzed the failure mode of concrete under cyclic loading with the characteristic of dissipation energy hysteresis, and studied the failure mode of concrete under monotonic loading and cyclic loading; the size and type of cracks were directly related to the loading method. Meanwhile, the energy dissipation rate increased with the increase in load level and reached the maximum value at peak strength.