Abstract: To study the degradation characteristics of the gypsum breccia that surrounds tunnels in a seasonally supplemented groundwater environment, a case study on gypsum breccia is conducted for a tunnel project in Shanxi. Wettingdrying cycle tests for 1, 3, 6, and 10 cycles are carried out considering the effect of flow rates of 0, 10, and 20 L/h. The law describing the corrosion and water absorption behavior of gypsum breccia under the action of the wettingdrying cycles at different flow rates is systematically analyzed in this paper. Based on the results of uniaxial and triaxial compression tests, the law describing the degradation of the mechanical parameters of gypsum breccia under different wettingdrying cycles and flow rates is then explored in more detail. The results show the following. (1) The wettingdrying cycle and water flow cause degradation of the gypsum breccia. The effect of the wettingdrying cycle on the gypsum breccia mainly involves a reduction in the degree of connection between particles, whereas the water flow aggravates the corrosion of the gypsum breccia and erodes the loose particles on the surface of the rock. (2) The mechanical indices of gypsum breccia including the uniaxial compressive strength, elastic modulus, friction angle, and cohesive strength show a downward trend as the flow rate and the number of wettingdrying cycle increase. When the flow rate is 20 L/h, after 10 wettingdrying cycles, the uniaxial compressive strength of the gypsum breccia is reduced by 72.86%, the elastic modulus is reduced by 75.67%, the friction angle is reduced by 70.69%, and the cohesion strength is reduced by 57.58%. The elastic modulus is degraded the most, followed by the uniaxial compressive strength, friction angle, and cohesion.

Key words: tunnel, gypsum breccia, groundwater environment, wettingdrying cycle, physical properties, degradation , law