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.