Stability Analysis of Surrounding Rock of Shallow-buried Subway Tunnel with Small Spacing under Different Working Conditions

The effects of support types and stress release rates before initial support were obtained regarding the stability of the surrounding rock of shallow-buried tunnels with small spacing and then an optimal construction plan chosen. Five working conditions for a shallow-buried tunnel with small spacing in the Dalian subway were numerically simulated. Variations in vertical and horizontal displacement of the surrounding rock were examined under changed stress release rate before initial support, advanced small pipe support, and support of grouting cement mortar behind initial support. Also, the maximum compressive stress of surrounding rock with a shotcrete layer and changes in axial forces of the plastic zone of surrounding rock and anchor bolt were obtained. It was shown that systematic bolts and shotcrete support, grouting behind the initial support, and twenty percent of stress release before the initial support, applied to a shallow-buried tunnel with small spacing with IV level surrounding rock, yielded the rock more suitable. These results could provide guidance for the design and construction of similar engineering projects.