Complications and Prospects of the Hydrogeological Substantiation of Drainage in Deep Tunnels
Currently, many automobile tunnels are being designed and put into operation in urban areas including Moscow. This is associated with the need of the city to unload the motorways in the absence of sufficient-free areas for the construction of land routes. Experience of operation has shown the expediency of building such facilities on the city territory. Several deep tunnels were commissioned in Moscow including the northwestern tunnel, 27 m deep and 3.1 km long.
The Alabian-Baltic tunnel has been under construction since 2006. A great difficulty in its operation is created by groundwater that seeps into the tunnel. In winter these leaks lead to icing on the road which can trigger accidents. Unfortunately, it has not been possible to completely seal the tunnel to the present day. All this determines the need for water drainage. However, closely located houses, many of which have already suffered from construction, as well as the passing subway tunnel, require careful justification for such solutions.
Currently, the most dangerous for the accident-free operation of the tunnel is the water inflow into it. Breakthroughs of water-saturated sands or the process of forced mass suffusion was observed in several sections. This process could manifest itself both as a sudden arrival of quicksands into the pit and breakthroughs of water-saturated sands through interbeds of clay soils. It was the main reason for the decompaction of the soil massif containing the tunnel, the anomalously large and uneven sediment of buildings, and the formation of dips.
A numerical hydrodynamic model was created within the framework of the work. The model analyzed various options for the organization of drainage, including the zero option (without drainage). It is shown that between the technologically altered level in the aquifer and the bottom of the tunnel, a significant difference in altitude remains, which leads to seepage of groundwater into the tunnel. Analysis of possible technical solutions to reduce water inflows in the tunnel has shown that a permissible option is a forced drainage inside the contour of the wall in the ground.