Back-analysis of Shimizu Tunnel No. 3 by distinct element modeling

The paper presents a numerical back-analysis of the response of Shimizu Tunnel No. 3 during construction. The 1.1 km long Shimizu Tunnel No. 3, which was completed in Japan in 1998, is a research tunnel along the proposed Tomei II highway. It was excavated in a region consisting mainly of soft to hard sedimentary rocks, such as locally weathered sandstone, underlain by interbedded sandstone and mudstone, using a sequential tunneling technique known in Japan as the “TBM pilot and enlargement method” along with NATM techniques. The tunnel response was analyzed using “ground characteristic curves” and the “convergence-confinement method” which were adapted to the distinct element method (DEM) and the computer code UDEC. Parametric analyses were performed to study the behavior of the wide tunnel geometry under various conditions. The results of the simulations using UDEC and the convergence-confinement method yielded results which are comparable to the monitored data on tunnel deformation and tunnel support loads.