Tunnels
GEOSYNTHETICS IN TUNNEL CONSTRUCTION
Modern tunnel design and construction involves engineered lining systems that provide effective long-term sealing for tunnels. Whether the tunnel is an internal tunnel or a cut and fill type, geosynthetics are required to effectively seal the tunnel. While the sealing or the barrier function is performed by a geomembrane; for the geomembrane to perform effectively over long term it needs to be protected from two critical design consideration.
Critical Design Consideration:
- Puncture Protection
- Hydrostatic relief
PUNCTURE DAMAGE
Synthetic geomembrane liners are sensitive to mechanical damage and need protection to resist puncture and wear due to abrasion caused by sharp stones in the subgrade or the overlying layer. The effective puncture resistance of the geomembrane can be considerably increased by using appropriate ALYAF needle-punched nonwoven geotextile.
The effective puncture resistance can be increased by a factor of 2 to 5 by use of appropriate geotextiles. This dramatic increase in puncture resistance of the geomembrane is made possible by needlepunched nonwoven geotextile by their ability to absorb point loads as well as through stress distribution.
Hence in typical tunnel sealing application the geomembrane is protected by sandwiching it between two thick robust layers of needepunched nonwoven geotextiles.
PUNCTURE DAMAGE
Synthetic geomembrane liners are sensitive to mechanical damage and need protection to resist puncture and wear due to abrasion caused by sharp stones in the subgrade or the overlying layer. The effective puncture resistance of the geomembrane can be considerably increased by using appropriate ALYAF needle-punched nonwoven geotextile.
The effective puncture resistance can be increased by a factor of 2 to 5 by use of appropriate geotextiles. This dramatic increase in puncture resistance of the geomembrane is made possible by needlepunched nonwoven geotextile by their ability to absorb point loads as well as through stress distribution.
Hence in typical tunnel sealing application the geomembrane is protected by sandwiching it between two thick robust layers of needepunched nonwoven geotextiles.
HYDROSTATIC PRESSURE
Tunnels are long term structures and their waterproofing is critical to their performance. A critical concern in waterproofing is development of hydrostatic pressures on the geomembrane that can overtime enter the tunnel through weak spots. Hence a prudent design intent is to install a system that would instantly intercept and drain the water away from the sealing membrane.An effective solution is the use of suitable ALFDRAIN geocomposites.
An engineered crush resistant biplanar net core made from HDPE to provide an effective drainage of water in its plane even under high compression loads.
A high strength engineered low elongation polypropylene nonwoven to act as a filter in allowing only the water to flow into the drainage core and not the soil fines.
A robust layer of thermally set polyester geotextile laminated to one side of the net core. The function of this layer is to prevent point loads on the geomembrane. Polyester is recommended here because of its superior heat resistance, lower creep property and better abrasion resistance.