NUMERICAL MODELING OF THE IMPACT OF EXCAVATING A NEW TUNNEL BENEATH A PRE-EXCAVATED TUNNEL AT A CROSS SYSTEM

Investigating the interaction between new underground spaces and existing underground spaces, and presenting appropriate solutions, is one of the most important geotechnical issues in development of infrastructure network. This paper investigates the impact of excavating a new tunnel below and crossing the pre-excavated tunnel for the case study of Tehran-North Freeway, Lot۰۲. The case study is variant East TU No. ۳۲ that passes under West TU۳۳-۱. The impacts of cross tunnel excavation were studied using numerical modeling in FLAC ۲D software. Numerical modeling was conducted on different geometrical section of acute cross of tunnels. The results of this study indicates that as tunnels approach each other, the uniformity of displacement contours diminishes, and an integration of displacement contours is observed. In addition, the critical sections of tunnels are different from displacement and yield zones factors. For displacement point of view, the critical effect of cross tunnel construction occurs on the section with maximum width between two tunnels. By decreasing the width between two tunnels, the yield zones around tunnels becomes more critical. These results were considered as fundamental issues during the design and construction of new tunnel.

Keywords:

Numerical modeling , Tunnel Cross , Tehran-North Freeway , Yield zone