Abstract: Due to environmental pollution, the underground structure gradually deteriorates, which causes severe long-term stability problems of the underground structure. In this study, the immersion erosion tests were first carried out on concrete specimens by soaking in the 50 g/L Na2SO4 solution, 50 g/L NaCl solution and landfill leachate containing 50 g/L Na2SO4 + 50 g/L NaCl, respectively. Then the gas permeability under different confining pressures, chloride permeability and mechanical properties of the eroded concrete specimens were studied. The results show that the permeability coefficient of the specimens after immersion in different solutions is closely related to the confining pressure. Under the same erosion time, the permeability coefficient gradually decreases with the increase of confining pressure. The permeability of the specimen under continuous immersion by landfill leachate increases linearly with the time of erosion, and the lower the confining pressure is, the greater the rate of the increase is. While the permeability of the specimens exposed to Na2SO4 and NaCl solutions decreases first and then increases. Generally, under immersion in three kinds of solutions, the permeability sensitivity of specimens to confining pressure is improved. The uniaxial compressive strength of the specimens after exposed to different solutions is divided into two stages: linear increase and slow decrease. However, the strength of the specimen exposed to landfill leachate is the lowest. The elastic modulus also presents a similar pattern. At the same erosion depth, the free chloride content of the specimen after the landfill leachate erosion is 20%?50% lower than that of the specimen after the erosion of the NaCl solution. In addition, the erosion degree of the concrete specimen by the chloride ions in the landfill leachate is lower than that of the concrete specimen by the NaCl solution. Compared with uniaxial compressive strength and chloride diffusion coefficient, the gas permeability changes the most obviously by the erosion, which is more suitable for evaluating the long-term stability of the concrete structure. The research results can provide a theoretical basis for the long-term stability analysis of underground structures under corrosive environment.

Key words: landfill leachate erosion, underground structure, permeability, mechanical properties