Deterioration behavior of gypsum breccia in surrounding rock under the combined action of cyclic wetting-drying and flow rates

The cyclic wetting-drying (W-D) phenomenon, which is a part of weathering processes, plays a vitally important role in affecting rock materials’ properties. In this paper, the gypsum breccia, an environmentally sensitive rock, was taken as the research object, which has the characteristics of high solubility. The deterioration behavior of gypsum breccia under W-D cycles with different flow rates was investigated. A one-dimensional water saturation test was conducted to study the coupling mechanism of water saturation-dissolution of gypsum breccia. A series of W-D cycle tests with different flow rates (0, 10, and 20 l/h) for gypsum breccia were conducted to reveal its deterioration behavior. Furthermore, the influence of these effects on the stability of the tunnel was discussed. The results show that gypsum breccia has a coupling behavior of water saturation and dissolution in the water environment. The effect of W-D cycles is the primary reason for the formation of visible cracks in gypsum breccia, while the flowing water will wash away the loose particles caused by the action of W-D cycles and accelerate the development of visible cracks and dissolution in gypsum breccia. The combination of these two actions gradually deteriorates the self-stability of the surrounding rock, which eventually leads to lining damage due to overload. The study can provide references for the engineering design of tunnels in gypsum breccia.