The performance specifications for today’s traffic tunnels require a nearly dry environment without dripping from penetrating water. This is to avoid the formation of ice (icicles) as well as hazardous dripping on equipment, such as overhead contact lines in railroad tunnels.
All tunnels are currently pre-grouted with cement or similar material, both to avoid environmental impact, such as reduced groundwater levels, and to achieve an environment in the tunnels that is as dry as possible. When it comes to achieving a dry environment, it is seldom enough with pre-grouting. Post-grouting is also necessary. This hunt for leaks is exceedingly costly, time-consuming and inefficient, which is the reason why in recent years, drains have instead been installed to channel water from ceilings and walls into the tunnel drainage system at the bottom.
The drains are normally made of extruded polyethylene plastic (about 50 mm thick) that are attached to the rock with bolts. Because polyethylene is flammable, the drains must be covered with shotcrete, and because the drains in themselves constitute a shell construction, exposed to suction and compression strain that is especially significant in railroad tunnels, this shotcrete must be reinforced to a thickness of about 80 mm.
These drains have major drawbacks. They are both extremely resource-demanding during installation and constitute a fire hazard, and their life cycle is short relative to the context – about 40 years compared to about 120 years for other structural elements. Overall, the figures for both the construction’s LCC (Life Cycle Cost) and LCA (Life Cycle Assessment) will be very high.
When carrying out repairs or upgrades, the construction necessitates the use of equipment that requires considerable space, entailing long tunnel closures and consequently significant disturbances to traffic.
There are now alternative solutions, but even these have major drawbacks, such as the inability to inspect underlying rock mass, high costs for operation and maintenance, as well as poor resistance to fire.
It is against this background that RockDrain has been developed, through an innovative new approach.