The external water pressure on a deep buried tunnel in fractured rock

Underground tunnels are increasingly built at greater burial depths for water conservancy and hydropower projects. The safety of these tunnels is threatened by high external water pressure during construction and reservoir operations. In this research, external water pressure was considered to be a relative incremental water pressure, instead of an absolute value: it thus depended on several factors, such as the excavation, lining, and grouting zone of tunnel. The calculation thereof was deduced. Also, a coupled model was used to calculate the external water pressure. This model incorporated a fractured network model (DFN) into an equivalent continuous medium model (ECM). The results showed that calculated hydraulic heads matched measured values when using the coupled model, rather than the continuous model, in the areas where fractures and fault zones were well-developed. Furthermore, external water pressures were predicted using the verified coupled model during the emptying and filling of diversion tunnels with water. (C) 2015 Elsevier Ltd. All rights reserved.