To secure long-term structural safety of underground openings for radioactive waste disposal, the proper structural safety analyses are required. Especially, the structural analysis for underground openings should consider the effects of groundwater pressure. The objective of this study is to develop the structural dynamic analysis method for saturated rock masses by blasting. This study presents a parameter study on the structural response of a circular tunnel subjected to finite cylindrical charge. Two calculations (one for dry medium and the other for saturated medium) are performed