The choice of a waterproofing system depends upon the type and construction of the tunnel as well as the geological criteria. Tunnels through rock generally deal only with seepage through cracks in the rock, a condition in which there is no head of water. In these cases, waterproofing is applied only on the vault. This is called partial or umbrella waterproofing. In the case of tunnels in frable or loose rock, however, one often encounters springs and water running through the strata. These conditions require the tunnel to be fully wrapped in waterproofing material designed to withstand the expected hydrostatic pressure.
Application Rock Tunneling / Umbrella System
no hydrostatic pressure, ground water level is below tunnel footings
tunnel wall condition
shotcrete min 3" thick
geotextile/ drainage layer nailed at intervals onto tunnel wall using PVC-disk, 2pcs/sq.ya.
membrane 1.5mm, 2.0mm, 2.5mm, 3.0mm welded to pvc-disk. Joints welded by hot wedge machine or hot air.