Seismic Assessment of Shotcrete Support in Jointed Rock Tunnels

Shotcrete as a permanent support system is common for many underground openings. However, the performance of the same under seismic loading conditions has not been thoroughly considered, especially in jointed rock tunnels. This paper presents a numerical study using the two-dimensional distinct element modeling (DEM) technique to understand the performance of shotcrete in jointed rock tunnels under seismic loading conditions. The study analyses the spalling of the shotcrete under actual earthquake conditions. The normal force and bending moment acting on the shotcrete have been studied for the presence of joints under static and seismic loading. The increased spalling in the intersection regions between rock joints and shotcrete was observed in the study with localization of stress and moment concentrations. Parametric studies have also been conducted to analyze the effect of joint, shotcrete and seismic factors on the stability of shotcrete. The studies indicated spalling under the action of seismic loads commonly near points of intersection between shotcrete and joint. The position of spalling along with the forces and moments acting on the shotcrete has been found to be highly influenced by incoming wave frequency and amplitude.