Tunnel and Underground SpaceISSN:1225-1275(Print) 2287-1748(Online)한국암반공학회

There has been an increasing demand for 2-Arch tunnels in urban areas. However, as the collapse of 2-Arch tunnels due to uneven pressure occurred recently, interest in the stability of 2-Arch tunnels is being focused. At the construction site, considering the equipment operation and construction period, it is expected that the 2-Arch tunnel will be excavated on one side, causing uneven pressure to be generated on the central column. However, when evaluating the stability of the central column, Matsuda's relaxed rock load, which only considers the vertical load, is applied, resulting in under-applied load conditions. In this study, the stability assessment method of the central column was improved by considering the effect of asymmetric excavation. A numerical analysis was conducted simulating the construction stages according to asymmetric excavation, and the effects of uneven pressure on the central column according to parameters were analyzed. The element force generated in the central column was analyzed by linking the numerical analysis results to the structural analysis. The structural analysis results demonstrated that the section force of the central column increased due to the uneven pressure and exceeded the design strength under the unfavorable conditions. In addition, an Uneven Pressure Factor(U.P.F) was proposed as a method to consider the effect of uneven pressure on the existing under-applied relaxed rock load.