Dedicated to advancing the use of fabricated geomembranes through education, research, and technology transfer.

WHY?
Factory fabrication reduces field welding, reduces installation time and costs, allows modular construction and provides consistent seam and liner quality.

PROJECT SPOTLIGHT

Columbus UpGround Reservoir (2011-2013)

GEOMEMBRANE APPLICATION: 
Geosynthetic bottom liner system to prevent water migration into solutioned limestone bedrock underlying reservoir
MATERIALS USED:
37 million square feet (3.4 million sq m) of 40 mil (1.0 mm) fPP geomembrane and 43 million square feet (4.0 million sq m) of 10 oz (283 g) nonwoven cushion geotextile
MEMBER COMPANY: 
EPI
PROJECT DESCRIPTION

The John R. Doutt Upground Reservoir is a 9.2 billion gallon (27.6billion liter) off-stream raw water storage containment reservoir for Columbus, Ohio. The reservoir covers a plan area of 785 acres (314 hectares) and covers primarily farmland. The reservoir area is underlain by glacial till that contains large pockets of high hydraulic conductivity sands and gravels. These permeable materials are about 6 m (20 ft) thick in some areas, which essentially brings the underlying fractured limestone bedrock in close proximity to the bottom of the reservoir. Therefore, reservoir water could seep into the underlying soil and bedrock and increase solutioning of the limestone and possibly destabilize the reservoir. As a result, the designers decided to install a geosynthetic bottom liner system across the reservoir to minimize leakage and connection with the underlying limestone bedrock. The geosynthetic liner system did not extend up to near the embankment crest because the upstream portion of the embankment consists of low hydraulic conductivity soil and could be exposed to ultraviolet light and wave action.

LESSONS LEARNED 

The use of factory fabrication allowed the project to move at a much faster rate and resulted in higher quality seams than what would have been possible with field fabrication, i.e., onsite welding. Because the geomembrane was primarily factory fabricated, 78% of all seams were performed under controlled factory conditions so only 12% of the seams were field welded. One of the biggest project challenges was the shear size of the project and the compacted clayey subgrade when it rained. The relatively flat site simply did not drain surface water, which resulted in ponding and softening of the clayey subgrade. This necessitated re-working of the subgrade and other challenges for the earthwork contractor. Luckily, most of the geosynthetics were installed during dry summer conditions so the factory fabricated geomembrane panels were able to cover a lot of prepared subgrade every day to reduce damage due to rainfall. The fine-grained particles of the clayey subgrade did create issues with the field seaming of the large fabricated panels. The clay particles were so fine that they actually embedded into the geomembrane surface and could not be physically cleaned off before field seaming. This resulted in a 25% of the field seams failing project specifications. Conversely, 100% of all of the factory seams exceeded project seam strength requirements. Therefore, having large factory fabricated geomembranes panels allowed the project to be completed on budget and well ahead of schedule. The Electric Leak Location Survey (ELLS) was also highly effective in locating hidden damage to the geomembrane.

HOW THE USE OF FABRICATION IMPROVED THIS PROJECT

Factory fabricated panels allowed the project to be completed at a much faster rate than was possible if all seaming was performed in the field, i.e., field fabrication. In the summer of 2012, factory fabricated geomembrane panels were being placed at an average rate of 12 panels per day (125’ x 250’ each, 31,250 sq ft or 38.1 m x76.3 m each, 2,907 sq m). That is an average is 375,000 square feet (34,884 sqm) per day in place, tested, and covered with a 10 ounce (283 g) nonwoven cushion geotextile every day for protection. The factory fabricated seams were higher quality, approximately 9% stronger in peel strength and over 9% stronger in shear strength, than what was possible in the field due to onsite contamination of fine-grained subgrade clay particles. For more information on this important project, please see the attached article: Stark, T.D., Hernandez, M.A., and Rohe, D.S.(2020). "Geomembrane Factory and Field Thermally Welded Geomembrane Seams Comparison,” Geotextiles and Geomembranes Journal, 48(4), August, 2020, 454-467, https://doi.org/10.1016/j.geotexmem.2020.02.004.

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