Void existing in the close vicinity of mountain tunnel lining is one of the causes that lead tunnel lining to damages. These damages include cracks and chip off-falling and may further develop into failure of tunnel lining. During the construction of mountain tunnel, void behind primary lining can be generated by overbreak and lack of backfilling, and its existence has been proved in many cases by advanced detection devices such as ground penetrating radar. To ensure the safety of tunnel lining as well as the personnel, discuss of the effect of void behind lining is necessary. Moreover, since most of the mountain tunnel in China are excavated by drilling and blasting method, the impact of tunnel face's blasting should be considered when analyzing the void's influence. Based on the monitoring data collected from in-situ test in Zhujiawu Tunnel, a numerical model considering tunnel face's blasting impact is established to study the influence of the void behind lining in both static and dynamic states. The numerical model is verified by the primary lining's oscillation velocity data, which was monitored near the tunnel face. According to the simulation, voids clearly reduce the tunnel lining's FOS in static condition, and enlarge the oscillation velocity of tunnel lining and surrounding rock in blasting striking. By comparing the oscillation velocities of lining in void and non-void situation, an amplification factor can be defined to describe the effect of voids in blasting impact condition. This factor can be used for assessing the risk of specific void behind tunnel lining.

1. Introduction

Void behind mountain tunnel lining is one of the main causes of lining damages. Damaged tunnel lining is dangerous on the lining serviceability, for instance, Rebunhama tunnel concerning an accident caused by spalling of tunnel lining (Asakura and Kojima 2003). Many researchers have studied the effect of voids behind lining. Leung and Meguid (2011) conducted an experimental study on earth pressure using mechanically adjustable lining system, and confirmed that local contact loss or void would change the distribution of earth pressure. Meguid and Dang (2009) discussed the effect of erosion voids using analytical and numerical analysis in which the bending moment and thrust force changes due to the void were evaluated. Ahmed and Ansell (2012) studied the response of hard rock tunnel shotcrete when exposed to blasting striking by using structural analysis and discussed the safety of shotcrete. But few studies have focused on the voids influence when coupled with blasting impact.

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