On the selection of an appropriate excavation pattern for urban tunnels with big cross-section: A case study

Among various practical measures used for restriction of the ground surface settlement in such tunnels driven in soft ground, selection of an appropriate excavation method plays a significant role. In this paper, employing suggested diagram by Yu & Chern, corresponding values of Niayesh tunnel has been inserted into the diagram. Later, two excavation methods namely: central diaphragm and side drift methods have been suggested and numerically modeled using Finite Difference Method. Side drift excavation pattern has finally been selected since it causes less settlement. To reach an optimized selection of excavation sequence through side drift method, seven excavation patterns have thus been recommended and numerically modeled. Results have revealed that the first pattern causes the least amount of settlement. Consequently, the aforementioned excavation pattern has finally been considered as an appropriate excavation pattern encompassing optimum excavation sequence for Niayesh tunnel.