Abstract: The DoubleSidePilotExcavation is a popular method in the tunnel excavation since it is suitable for the excavations in the Class V (worst) rock mass and it can also reduce the effect of large span in the tunnel dimensions. However, it has the disadvantages of constrained work space and long construction periods. Consider the fact that the rock mass in the project was actually better than the Class V, the optimization of the conventional DoubleSideExcavation was possible. The excavation sequence of the conventional method of left, middle and right was changed to upper left, upper right, upper middle and then, lower left, lower right and lower middle. The improved procedure was numerically modeled using GEO5 finite element software and the results were compared with the conventional procedure in terms of stress in the surrounding rock mass, bending moment in the supporting structures and the subsidence of the ground surface. The comparison results indicate that the optimized procedure is safe a reliable and further, the headroom for the construction was also able to be increased and therefore, the efficiency could be improved.

Key words: DoubleSidePilotExcavation, Stress in Surrounding Mass, Bending Moment in the Supporting Structures, Ground Subsidence, Finite Element Analysis with GEO5