The Effects of Excavation of Divergence Tunnel from Double-Deck Tunnel on Stability of Underground Common Duct

Abstract

The objectives of this study is to figure out how the common duct is affected by excavating the divergence tunnel from the double-deck tunnel through a numerical analysis. A computer software, Midas GTS NX had been used for analyzing numerically the situation of divergence tunnel which is splitted from the main lane of deep underground of double-deck is excavated toward ground direction. A volume loss of tunnel has been changed to 1, 3 and 5 percent at each phase. Thus, the numerical analysis was conducted for situations of divergence tunnel, approaching to common duct which is laid 2.5m from ground, in the direction of 36˚,45˚ from the main line tunnel and the distance between common duct and divergence tunnel has been applied to 5m, 10m and 30m, according to the degree. As a result of the effect of the divergence tunnel on the stability of the common duct, the larger the volume loss of the divergence tunnel, the larger the influence on the common duct. Except when the divergence tunnel was excavated directly bellow the common duct, the longer distance between the divergence tunnel and the common duct, the more stable common duct was. The common duct was more unstable when the tunnel was excavated downward than the side of the common duct.