In this study, a case study was introduced for the design of a twin tunnel along high speed national highway Route 12 from Damyang to Sungsan. It was related to determine the optimal tunnel support pattern and excavation method based on a risk analysis in order to incorporate the uncertainty of ground properties. To this end, three alternatives with different amounts of support and excavation method were selected and risk analysis was performed by applying Monte Carlo simulation technique, respectively. Stability of the tunnel was quantified by the factor of safety. To improve the result, the 729 cases of the combination of ground properties (deformation modulus, cohesion, and internal friction angle) satisfying a Gaussian distribution were generated and applied. Also, stability of the tunnel was confirmed by analyzing the distribution of both displacement and shotcrete bending stress.