Analysis of a Field Study on Drainage Design and Control of Water Inrushes into Hongtu Tunnel, China

Abstract

Serious water inrush accidents occur frequently in the fault-prone area around Hongtu Tunnel, which encompasses several reservoirs and large bodies of water. In this study, a field test was used to identify the water inrush mechanism and the design characteristics of the tunnel’s drainage system, the impact of water gushing through the tunnel on the surrounding environment was analyzed, and the results were used effectively to guide the design and construction of a supporting engineering drainage system. The specific conclusions are as follows. The supply source of the water causing the inrush accident was far away from the tunnel. The groundwater flowed to the site of the burst through a groundwater network connecting a fault and rock fracture. Full-section curtain grouting reinforcement with a thin grouting ring was carried out first to meet the construction requirements of the tunnel face before further excavation in the water-rich fault zone, followed by postgrouting of the weak section after blasting for further construction of the new roadway to strengthen the water-blocking capacity of the excavated part. The use of curtain grouting and postgrouting together reduced the disruption to construction near the tunnel face and thereby sped up the new construction. The seepage pressure calculated using the equivalent penetration coefficient method was weaker than the water pressure borne by the support structure in the middle of the two rows of the annular blind pipes, which was an important reason the support structure cracked during the operational period; thus, a higher safety factor should be considered when using the equivalent permeability coefficient. These research results can serve as a useful reference for the design and construction of drainage systems in similar cases.