Seismic Damage and Possible Influencing Factors of the Damages in the Melamchi Tunnel in Nepal Due to Gorkha Earthquake 2015

Nepal is a sensitive earthquake zone. On April 25, 2015, there was an Earthquake of 7.8 Mw. After that, more than 30 aftershocks of above 5 Mw occurred. One of the aftershocks was of 7.3 Mw which occurred on May 12. In this paper, the damages in the tunnel of the Melamchi water supply project due to this earthquake were assessed. Cracks were observed on the inside surface, wall, and crown of the tunnel. Distribution and characteristics of these seismic damages were investigated and summarised to assess potential influencing factors. The damages are categorized into the following patterns: lining cracks and spalling. Lining cracks are further divided into longitudinal cracks, transverse cracks, ring cracks, and inclined cracks. Influencing factors are discussed with respect to Earthquake parameters mainly being magnitude, depth and distance to epicenter. This paper presents the pattern of seismic damages occurred for different overburden depths and different rock types. Here, the analysis is done by observation and categorization of damages for different aspects of considered factors and there are some unusual results in damages for varying overburden depths. There were few unusual results as in the damage distribution for overburden depth and also for different rock types. The reason may be the occurrence of many considerable aftershocks and epicenter being very near, so the damages may have been accumulated after each shock. Also the distribution of rock types have influenced the damages. So one influencing factors may have its effects on the results while considering the other factor.