Abstract: The expansion stress of swelling rock in the contact with water has an adverse effect on the long-term safety of the subway tunnel structure. Previous studies mainly considered the volume expansion of swelling rock, but lacked the consideration of the softening effect during the expansion process. For this reason, through laboratory tests, the material components, softening characteristics, and expansion parameters of swelling rock are obtained, and the elastic softening effect of swelling rock in the expansion process is revealed. An equivalent simulation method of humidity and temperature expansion considering elastic softening is proposed based on the recognition that the volume expansion caused by humidity and temperature are similar. The determination methods of elastic softening parameters, expansion equivalent temperature boundary conditions, and expansion zone are given. The simulation procedure has been established. The above method is applied to the long-term safety assessment of the sandy mudstone section of the interval tunnel of Chongqing Metro Line 18, and the results show that the expansion stress calculated by the new method is closer to reality than the classical equivalent simulation result of humidity and temperature. Finally, the thickness of the expansion zone and the degree of elastic softening that affect the calculation results are discussed. Recommendations for the disposal of the swelling tunnel section are also put forward. This work can be used as a reference for long-term safety evaluation of swelling rock tunnels, and has a certain guiding role in preventing and controlling swelling disasters of underground engineering.

Key words: deeply-buried subway tunnel, swelling rock, elastic softening, equivalent expansion of humidity and temperature