ABSTRACT:

During the whole life of a tunnel lining, the concrete-rock interface is one of the weak areas. To study the shear strength of concrete-surrounding rock interfaces, a direct shear test with a flat interface was carried out. The mechanical properties of contact surfaces with different sawtooth parameters were simulated via MatDEM based on the discrete element method. The four tooth angles (0°, 15°, 30°, and 45°) and eleven normal stresses (0.5∼1.5MPa every other) were simulated. The results show that the shear strength increases with increasing normal stress for all four sawtooth angles. As the sawtooth angle increases, the shear strength increases due to the increasing cohesion and contact area. When the sawtooth angle is 15°, the failure occurs mainly along the interface. The fractures develop from the interface and the sawtooth is cut off when the angle is greater (30°and 45°) due to the mechanical occlusion.

INTRODUCTION

After drilling and blasting, the surface of the surrounding rock will produce a jagged surface, as shown in Figure 1. During the whole life of a tunnel lining, the concrete-rock interface will be one of the weak areas(Wang et al., 2014).

The mechanical properties of the rock-concrete interface have a significant importance. Many researchers have studied the shear failure behaviour of the rock-concrete interface. Saiang et al. (Saiang et al., 2005) concluded that the peak shear stress at the interface was composed of the bonding force and the frictional resistance by direct shear tests on concrete-rock assemblies. In the direct shear test of concrete-rock assemblies, Tian et al.(Tian et al., 2015) found that with increasing normal stress, the bond interface showed both abrupt and progressive damage. Meng et al.(Meng et al., 2022) developed a numerical model of synthetic rock mass (SRM) based on the particle flow procedure two-dimensional (PFC2D) and carried out numerical direct shear tests to discuss the effects of joint geometry, positive stress, joint roughness and joint aperture on the shear properties of unbonded joints.

In this article, laboratory direct shear tests were first carried out. The calibration of a MatDEM model is performed based on stress-displacement curves at the normal force of 0.5 MPa. The failure process and shear strength of rock-concrete interfaces with different tooth angles were then investigated.

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