Geotechnical monitoring and analyses on the stability and health of a large cross-section railway tunnel constructed in a seismic area

A field test was conducted in Jinpingyan tunnel located in the area influenced by the 2008 Wenchuan Earthquake. The settlement of the surrounding rock, the internal displacement of the surrounding rock, the pressure between the surrounding rock and the primary support, the internal force of the support arch, the axial force of rock bolts, the pressure between the primary support and the secondary lining, and the strain of the secondary lining were measured to analyze the stability and health of the surrounding rock under the traditional supporting structure. For the phyllite tunnel located in the Wenchuan Earthquake seismic effect area, the traditional I-shape steel arch was used to control the deformation because of its large stiffness during the earlier stage of deformation of the surrounding rock. Over time, the deformation rapidly increased in the later period. The crown settlement increased quickly in a three-stage growth pattern until the values exceeded the deformation allowance. Shotcrete layer cracking and slabbing occurred at the crown and the shoulder. It can be concluded that the traditional supporting structure did not satisfy the stability requirement of tunnel, especially for the sections with extreme risk of large deformation in this seismic area.