Disaster mechanism of shield tunnel under sequential disasters of earthquake and post-earthquake fire

Significant casualties and economic losses can result from a strong earthquake followed by a fire in a shield tunnel. This study employed a numerical thermal- -mechanical coupling method, validated with test data, to examine the dynamic response and disaster mechanisms of shield tunnels subjected to seismic events and subsequent fires. The analysis focused on the effects of post-earthquake fires on the deformation and internal forces of a shield tunnel, considering seismic amplitudes, fire characteristics, and soil properties. The findings indicate that (1) the extent of initial damage caused by an earthquake is a critical determinant of the fire resistance of a shield tunnel. A post-earthquake fire exacerbates the stress and deformation of the structure. When compared to scenarios involving only a fire or an earthquake, the deformation of the structure increased by 241.6% and 85.6%, respectively, whereas the bending moment increased by 31.6% and 254.6%. (2) Temperature rise curves significantly affect the rate of temperature increase, deformation, and internal force in the tunnel structure during the initial stages. Despite similar maximum temperatures, the prolonged combustion and resultant degradation of structural mechanical properties considerably impair the integrity of the tunnel. (3) The constraining effect of the soil on the tunnel strengthens with an increase in the shear wave velocity, which can effectively mitigate the initial seismic damage to the structure. Consequently, the deformation of the structure decreases, and the axial force of the segment increases, which can prevent the opening of the segment. These results provide technical insights that can enhance the comprehensive disaster prevention capabilities of shield tunnel structures.