Investigation on the Causes of Abnormal Increase of Water Inflow in Underground Water-Sealed Storage System

Water inflow is a crucial factor in underground water-sealed storage for both safety and operation costs. Water inflow control measurements have mainly focused on the grouting of the cavern regardless of considering the influence of the access tunnel (i.e. the water flows directly through the fissures connecting the access tunnel and tanks after the access tunnel impoundment). In this study, the water control measurement related to access tunnel was investigated in certain project. First, based on monitoring data before the operational condition (including water inflow, groundwater level, and operating water level), the water inflow variation laws were explored in different construction phases. Then, the cause for abnormal increase in the water inflow after the access tunnel impoundment was explored using cross-correlation analysis and linear regression. Finally, some novel recommendations were provided for avoiding the abnormal increase in water inflow after the access tunnel impoundment: (1) zones with great fracture density or zones of water leakage should be identified through a geological survey and grouted before the access tunnel impoundment; (2) the access tunnel should avoid intersecting the advantage trend of fissures at a large angle to the greatest extent possible, and the layout of the access tunnel could be changed from the "wrap-around" to "direct-type" configuration; (3) smaller cross-section sizes and shorter lengths should be adopted for the access tunnel to retain proper functioning of the access tunnel and reduce the possibility of hydraulic connections between the access tunnel and tanks.