Longitudinal Seismic Analysis of Cast-in-Place T-Type Cross Utility Tunnel

Based on the principle of the longitudinal response-displacement method and combined with the full-state input method with sinusoidal stratum displacement, a shell-spring finite element model of a cast-in-place T-type cross utility tunnel was used to systematically study the internal force, deformation and damage response of the utility tunnel under different seismic motion amplitudes and incident angles, with a focus on the most unfavorable internal force and deformation modes of the utility tunnel. In addition, a comparison was made between cast-in-place T-type cross utility tunnels and prefabricated T-type cross utility tunnels in the literature. Results indicate that under the moderate earthquake, when the incident angle of seismic waves is 45°, the axial force at the utility tunnel section reaches its peak value, forming the most unfavorable axial force mode. When the incident angle of seismic waves is 90°, both the shear force and bending moment reach their peak values, forming the most unfavorable shear and moment modes. Under the major earthquake, at an incident angle of 45°, the joint opening and compressive deformations can be up to 24.17 mm and 29.80 mm, respectively, representing the most unfavorable deformation mode. The distribution zones of tensile damage in the utility tunnel under the major earthquake vary significantly as the incident angle increases. The overall damage of the utility tunnel reaches its maximum at an incident angle of 45°, far exceeding the tensile damage threshold. It is indicated that there are significant differences between cast-in-place T-type cross utility tunnels and prefabricated T-type cross utility tunnels in terms of internal force and deformation, which are mainly attributed to the differences in connection modes and stiffness between tunnel segments. The overall stiffness of standard segments of the cast-in-place utility tunnel is significantly higher than that at the deformation joint. Consequently, the peak internal force response mainly occurs at the standard segments, while the peak deformation response mainly appears at the deformation joints. The findings in this paper may provide a reference for the seismic design of cast-in-place T-type cross utility tunnels.