Evaluation of two different drainage systems for rock tunnels

• Drainage of water in tunnels is important but costly and work intensive activities.
• A new drainage system, Rockdrain, was installed and tested in a Swedish rock tunnel.
• The Rockdrain system was compared with a conventional drainage system.
• Both methods were evaluated for technical, environmental and economic performance.
• The Rockdrain system showed significant improvements over the conventional system.

Water penetration and dripping in tunnels is almost always a significant problem which is usually solved with the help of a tunnel waterproofing drainage system mounted where drips and leaks are detected. Today’s drainage systems are made of foamed polyethene (PE) mats which are covered with shotcrete. These are relatively expensive, complex to install, sensitive to mechanical impact, and often have a much shorter expected lifetime than the tunnel. In this study, a new type of drainage, Rockdrain, was studied and compared with the present drainage system. The systems were evaluated with respect to technical, environmental, and economic aspects. A field test was performed with the Rockdrain system and compared with installation of a traditional system. Laboratory tests were performed on especially the different shotcrete layers used in the Rockdrain system. The environmental evaluation was performed by Life Cycle Assessment (LCA) and the economic evaluation was performed by Life Cycle Cost (LCC) analysis. The results indicate that the Rockdrain system has a good drainage function, is significantly cheaper than the current system, has a longer expected lifetime, is easier to install, and is less sensitive to mechanical impact.

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