Abstract:

Most studies investigate the mechanism of tunnel seismic damages due to earthquakes by numerical simulation and physical model experiments. However, limited by inevitable simplifications, assumptions and boundary problems, the above methods deviate more or less from the real situation. Therefore, this research acquire the seismic response of a rock tunnel through in-situ monitoring. Five accelerometers were installed in a highway tunnel in southeast Taiwan, four on the same tunnel section, one on another. Since the monitoring started from 2014, there are four earthquake events exceed Richter magnitude 4.0. The acceleration records show that in general, the predominant frequencies of accelerometers installed in different locations inside the tunnel are similar with the predominant frequencies of the two neighboring seismic stations. Such similarity in predominant frequencies possesses the best consistency along the slope dip direction, and the worst along the vertical direction.

1 Introduction

Cases of tunnels damaged in earthquake had been reported worldwide, including scientific articles on a single earthquake event (Kawakami 1984, Asakura & Sato 1998, Wang et al. 2001, Yashiro et al. 2007, Wang et al 2009, Shen et al. 2014), or research papers that include multiple events (Dowding & Rozen 1978, Sharma & Judd 1991, Ulusay et al. 2002, Aydan et al. 2011, Asakura et al. 2008). It is known that under the attack of earthquakes with moment magnitude larger than 6.0, underground structures may, but not bound to, display local or complete collapse (Aydan 2017). Aydan (2017) classified tunnel damages into three types, 1.portal damage, 2.shaking induced damage and 3.permanent ground deformation induced damage. Part of portal damages and almost all of the permanent ground deformation induced damages are caused either by faulting or slope movements. This research concerns the shaking induced damages of tunnels.

Barred by the complexity of wave scattering, superposition of wave source with multiple frequency, or the composition of waves of different types, the universal analytical solution for seismic response of a tunnel in a general earthquake event is still absent. Therefore, the authors embarked on acquiring coseismic records of a mountain tunnel. Five accelerometers were installed in a highway tunnel in southeast Taiwan, four on the same tunnel section, while one on another (Kung 2015, Chiu et al. 2015). Four seismic events produced more than 80 gal (cm/s2) Peak Ground Accelerations (PGAs) in the two neighbouring seismic stations, which are less than 10 km to the case tunnel, since 2014. The acceleration records were then processed, and transformed into Fourier frequency spectra. Base on comparison between the seismic responses of the seismic stations and the accelerometers in the tunnel, a preliminary conclusion is given.

This content is only available via PDF.
You can access this article if you purchase or spend a download.