Risk analysis for determination of a tunnel support pattern

Rock mass is inhomogeneous in nature. Data for underground structure designs are mainly obtained from site investigations and tests, but they are very limited. For this reason, uncertainty exists in the process of constructing underground structures in a rock mass. In the design a tunnel support pattern, the most important parameters such as advance rate and excavation method must be determined optimally. However, it is difficult to determine these parameters quantitatively. In addition, if these parameters are determined incorrectly, unexpected risk occurs such as the decrease in the tunnel stability or economic loss due to excessive amount of supports. In this study, a methodology to determine an optimal support pattern and advance rate for the design of a tunnel is introduced based on risk analysis. It can be confirmed quantitatively that the more the tunnel is supported, the higher the reliability index becomes and the more stable the tunnel is predicted to be. Also an optimal support pattern and advance rate can be determined quantitatively by performing a risk analysis considering the construction cost and the cost of losses that can occur due to the collapse of a tunnel. (C) 2005 Elsevier Ltd. All rights reserved.