Dynamic Response of the Cross Tunnel with Ultra-Small Spacing Under Various Seismic Motions Using a Shaking Table Model Test

Abstract

ABSTRACT Different from a single tunnel, the cross tunnel with ultra-small spacing is characterized by high crossing risk, significant coupling of multiple effects, and difficulty in controlling stability. A shaking table model test was carried out to study the failure process and dynamic response of the cross tunnel with ultra-small spacing under seismic motions with various types and peak accelerations. The results show that the seismic damage of the cross tunnel model has significant failure stages. The deformation of the upper-span tunnel lining is cumulative progressive damage from the left wall to the invert, while the under-crossing tunnel lining is cumulative progressive damage from the left wall to the crown. The acceleration response of the model when inputting Wenchuan seismic motions is greater than that of El-Centro seismic motions, and the Wenchuan seismic motions may cause a peak lag in the acceleration response of the model. Compared with inputting El-Centro seismic motions, the 1st predominant frequency of the model increases while the 2nd predominant frequency decreases when inputting Wenchuan seismic motions. Additionally, the 2nd predominant frequency components are significantly amplified in the propagation of seismic motions from bottom to top through the lining structure. Although the energy ratio of the wavelet packet frequency components gradually tends from low-frequency bands to relatively high-frequency bands, the low-frequency bands still play a dominant role in the failure of the model.