To create two road tunnels under an existing motorway in Raalte in the Netherlands, Genap submerged two prefabricated geomembrane panels to create a groundwater barrier along the tunnel ingress and egress for each ramp, i.e., a total of four prefabricated panels for each tunnel. The motorway could not be closed to traffic for more than 48 hours so the contractor had to tunnel under it. The two panels for each ramp are about 32,500 ft² and were unrolled and welded together on site to create a panel of about 65,000 ft² for each ingress and egress ramp. The groundwater barrier system consists of a 40 mil thick PVC geomembrane underlain and overlain by a cushion geotextile. After the underwater excavation of the ingress and egress ramps (see upper left photo), the geomembrane was pulled across the water with rope hems (see upper right photo) and then submerged (sunk) to create the groundwater barrier system. After the geomembrane was pulled across the water body, the nonwoven geotextile was pulled across the water with rope hems (see lower left photo) and then submerged to create the groundwater barrier system. The cushion geotextile was prefabricated in five panels instead of two because of the thickness of the material. These five panels were stitched together on site before pulling it across the water surface to be submerged. These five panels created a cushion geotextile of the same area, 65,000 ft², as the geomembrane. The underlying cushion geotextile was already installed before pulling the geomembrane across the water. After performing a geo-electric leak location survey that showed the geosynthetic construction was 100% watertight, the ramps were partially backfilled with ballast sand. The tunnel area was dewatered to permit construction of the ingress and egress ramps to the tunnel after it was dewatered (see lower right photo). The tunnel was open for traffic and the groundwater barrier system is maintaining a dry area even after dewatering ceased. This project shows that a geosynthetic groundwater barrier system is effective, which obviates the use of significant concrete along and below the ramps. In addition, the groundwater barrier allowed the soil along the sides of the ingress and egress ramps to be seeded to grow grass.
Submerging geosynthetics is possible and not known to many contractors; however, coordination between different construction activities is important and should be worked out before construction commences.
HOW THE USE OF FABRICATION IMPROVED THIS PROJECT
Seaming the individual rolls of geomembrane at the confined site (see upper left photo) was not possible because of the level of water tightness required, time available, and site access and logistical constraints. The use of prefabricated geomembrane panels also resulted in only one seam or weld being performed on site, which reduced construction time, costs, and equipment needed. In addition, the prefabricated panels were created in the exact shape of the ingress and egress ramps, which resulted in no waste generation on site.
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The FGI Pond Leakage Calculator Geomembranes v. Compacted Clay Liners
Fresh water is a precious resource with demands rising daily and supply greatly fluctuating. Only two (2) percent of all water on Earth is fresh water with the other 98% being salt water. This 2% of fresh water is comprised of: 87% ice, 12% groundwater, and 1% rivers and lakes. Thus, only 13% of the available freshwater is readily accessible. Therefore, it is imperative that we capture and hold these limited water resources for agriculture, domestic use, and industry and also protect valuable groundwater from surface or subsurface contamination.
The FGI’s Pond Leakage Calculator is a Microsoft EXCEL spreadsheet based on Darcy's Law of Seepage and provides a comparison between leakage rates from a canal, pond, or reservoir constructed with compacted fine-grained soils and a geomembrane liner system. The Leakage Calculator allows the user to input the size of the containment basin (including length, width, depth, side slope angle and freeboard), the anticipated level of hydraulic conductivity of the compacted soil or geomembrane liner, and the relative cost of water in dollars per acre-foot of water.
The Calculator then calculates the volume of the basin in gallons, a comparison of leakage rates between the compacted soil and geomembrane liner systems in gallons, and the cost of the leakage based on the cost of water per acre-foot to replace it. This Calculator is designed to help consultants, engineers, architects, and end users decide how to line their canals, ponds, reservoirs, and basins to capture and/or protect valuable fresh water. The Calculator does not consider variances in construction quality and operational techniques on the long-term effectiveness of the chosen liner system. The FGI has additional research and publications to help with other aspects of successful water containment applications.
Types of Geomembranes Four (4) popular types of geomembranes are available for pond liner systems. These four (4) geomembranes in ALPHABETICAL order are: (1) EPDM, (2) reinforced polyethylene (RPE), (3) Polypropylene (PP), and (4) Polyvinyl Chloride (PVC). EPDM (Ethylene Propylene Diene Monomer) geomembranes are unreinforced and have been used for the construction of ponds of varying kinds. EPDM geomembranes are made from rubber and can be welded together with tape and primer. EPDM can be reinforced or unreinforced. RPE geomembranes have a high tensile strength and puncture resistance because they are reinforced. RPE geomembranes also can be welded with heat. PP geomembranes can be unreinforced or reinforced depending on the application. Reinforced PP geomembranes also have a high tensile strength and puncture resistance because they are reinforced. PVC geomembranes are also unreinforced and have been used successfully for decades in water canals, ponds, and reservoirs. PVC geomembranes can be welded with heat and/or solvents.
Please click below to access FGI’s Pond Leakage Calculator.
Moderators: Jordan Wiechmann, Intertape Polymer Group and Jen Miller, Fabricated Geomembrane Institute
The Fabricated Geomembrane Institute at the University of Illinois has created a group titled, “Women in Geosynthetics (WIG)” in order to promote the advancement of women in the geosynthetics industry through education, networking and mentoring opportunities. Audience participation is the focus of this highly interactive discussion
The discussion will include, but is not limited to the following points of interest:
– How can we recruit MORE women into the Geosynthetic Industry?
– How can we create more opportunities in the industry for women?
– What types of educational opportunities are out there to educate women throughout the industry?