Model Test for the Seismic Response of an Entrance on a Shallow-Buried Double-Staggered Mountain Tunnel

The theoretical analysis of the seismic response of tunnels is still insufficient. The shaking table test is an effective way to study the earthquake resistance of tunnels; because of the complex nonlinear constitutive model of rock soil and the complicated seismic dynamic equation. In the LEBUGUOLAJI tunnel, the similarity ratio is 1:30. A thermal molten mixture of river sand, oil, and fly ash is used as the similar material of the surrounding rock, and gypsum is used as the similar material of the tunnel lining. A strain gauge is symmetrically pasted inside and outside the tunnel model lining to monitor the strain stress, and a structural accelerometer is installed on the tunnel model and shaking table to invert the surrounding rock of the model. The earthquake damage characteristics and engineering shock absorption measures of a shallow-buried double-staggered tunnel are determined using the large shaking table model test. Results show that the surrounding rock of the tunnel model exerts obvious enlargement effect on the input seismic wave, and its frequency spectrum changes. The seismic wave in frequency bands below 15 Hz is strengthened, whereas those in other frequency bands are attenuated. The seismic response of the tunnel is reduced by the confinement effect of rock and soil. On the basis of the similarity ratio of the model test, 45 m can be used as the fortification length of the tunnel entrance. The weak link of the tunnel portal section is the wall angle and the 45° of arch shoulder on the tunnel slope. The seismic damage in the gap section of the tunnel is more serious than that in other parts of the tunnel in the entrance. Thus, the rock and soil volume can be increased at the staggered area to enhance the rock and soil constraints of the site in design. A strong dynamic interaction occurs in the shallow-buried double-hole staggered mountain tunnel under seismic wave action. The seismic response of the tunnel with a large damping structure can be effectively reduced to minimize the damage of the lining strain.