Application of risk analysis and assessment in tunnel design

A new risk analysis system for estimating the risk factors in tunneling is suggested in consideration of the complex effect in tunnel construction. It is verified that various risk factors can be expressed by stability and environment index using numerical and statistical analysis. Stability index includes the factors of safety of ground condition, the amount of ground settlement, condition of inflow and earthquake as a variable, and environment index includes vibration and noise by blasting under construction and train operation. The risk analysis of geotechnical stability factors were performed by classifying the factor of safety calculated SSR method, the damage of neighboring structure due to settlement, the groundwater inflow rate into the tunnel and the potential damage by the certain earthquake. Also, the environmental factors can be grouped into two aspects such as the construction stage and the operation stage; vibration, noise and the drawdown of the groundwater level caused by tunnel construction. Each risk factor was evaluated as a classified term to be the fixed quantity based on various probabilistic and statistic technique, then it was analyzed the distribution characteristic of risk along tunnel line. Then, the impact was evaluated that how much each risk factor influences on the construction cost with a tunnel construction period by analyzing social charge, so it is possible to perform reasonable tunnel design which was capable of minimizing the risk in the construction stage as well as the design stage. Finally, the applicability of quantitative risk assessment method using stability and environment index are evaluated and utilization method in designing tunnels in Korea is reviewed.