Modren tunnel design and construction involves engineered lining system that provide effective drainage and a long term moisture barrier for the tunnel walls. After the excavation of the tunnel, the rock is sprayed with concrete(shotcrete) to smooth out the unevenness of the rock face. Either a geocompsite or needle- punched non woven geotextile i s then placed on the sprayed concrete and anchored using steel bolts coupled with polymer fastening discs. The Tunnel liner(HDPE mebrane) is then welded to the discs. After the weld testing a final concrete layer(ring concrete) is put in place.
The geotextile performs two primary functions:-
1. Protection of the linear from abrasion and puncture by protrusions from the base surface of the tunnel well.
2.Drainage of water seeping through the rock and sprayed concrete layer. The in-plane oermeability of the geotextile enables the water to flow to a subsurface drainage collection system. where it is directed awa from the tunnel