Abstract
In recent years, the mountain construction method of tunneling in urban areas is being widely applied in Japan. In order to prevent damage to adjacent environment due to excavation in difficult geological conditions, ground improvement and reinforcement techniques are required. The steel pipe-reinforced multi-step grouting method has been applied to tunnel sites as an auxiliary construction technique for reinforcement. However, this technique has been usually employed empirically without much understanding with regard to its effect on the ground movement prevention. In this study, the three dimension simulations have been carried out for evaluating the displacement restraint effect of the steel pipe-reinforced multi-step grouting by changing its design pattern. As a result, a subsidence restraint rate became significant if the tunnel being excavated in soft ground conditions. In addition, the propriety of the proposed analysis is verified based on the field measurements of Nagasaki Oranda Slope tunnel and the future prediction of surface subsidence in the unexcavated region and the reinforcement effect of the reexamined auxiliary technique have also been investigated.
