A study on the sulfate erosion deterioration law and damage model of shotcrete in high geothermal tunnels

When building a tunnel in an environment rich in high‐temperature hot water, it is particularly necessary to pay attention to the influence of sulfate ions in underground hot water on tunnel shotcrete. In order to study the sulfate erosion mechanism and mechanical properties of shotcrete in a real high‐temperature hot water environment, this study was carried out by setting the curing temperature (20, 40, 60, and 80°C), humidity (55% RH, 95% RH), and erosion age (0, 15, 30, 60, and 90 d) as the test influencing factors; a full combination of dry‐wet cycle test was carried out, and the specimens under different conditions were analyzed macroscopically and microscopically. The results show that with the increase of the number of dry‐wet cycles, the quality of shotcrete increases first and then decreases, and the mechanical properties gradually decrease. In the early stage of erosion, the erosion product is mainly ettringite, and the macroscopic damage is aggregate spalling. In the later stage of erosion, the erosion product is mainly gypsum, and the macroscopic damage is expansion damage. Compared with standard curing, a certain degree of high temperature curing has little effect on the sulfate attack resistance of shotcrete, but when the curing temperature exceeds 60°C, the concrete is seriously damaged. Finally, by constructing the damage model of sulfate attack shotcrete, the variation of compressive strength of shotcrete with age after sulfate attack under different curing conditions was successfully predicted.