Underwater Lining Using PVC
PVC Geomembrane Liner Placement Underwater in an Operating Irrigation Canal
Fred P. Rohe
Environmental Protection, Inc., 9939 US-131 South, Mancelona, MI 49659 USA
231-587-9108, Email email@example.com
For more than 40 years PVC geomembranes have been used to control seepage in irrigation canals. The United States Bureau of Reclamation is responsible for the construction and maintenance of many of these canals in the western United States. Environmental Protection, Inc. participated in the design and development of a prototype system to install a 30 mil PVC geomembrane liner and 3 inches (8 cm) of concrete underwater in an operating canal. This project, directed and funded by the U.S. Bureau of Reclamation, was the first of its kind anywhere in the world. Many different suppliers worked together to develop and implement a unique solution to this complex logistical problem. This paper will explain the process of installation of PVC geomembrane and concrete underwater in the Coachella Canal in southern California. This project was the beginning of a significant effort to conserve water resources and reduce canal maintenance and construction costs.
KEYWORDS: Geosynthetics, PVC Geomembrane, Canal, Irrigation, Thermal Welding, Case History, Geotechnical Design, Innovative Technologies
EPI was selected to provide a 30 mil PVC geomembrane liner for an experimental project by the U.S. Bureau of Reclamation. The project, titled "Coachella Canal In Place Lining Prototype, All American Canal Relocation, California," was the first of its kind anywhere in the world. After completion of the bidding process, the Bureau of Reclamation determined that Kiewit Pacific Company, of Santa Fe Springs, California, should be awarded the contract. EPI was contacted by the design engineers for Kiewit, regarding the supplying of the PVC geomembrane liner. The initial meeting in September of 1988 involved preliminary research regarding the feasibility of the preliminary design work done by Mr. William Giroux. Over the next several months, much research and development was done in order to solve the problems of handling the PVC liner during the inplace lining process. Since the project was being done on a fast track schedule, actual fabrication of much of the equipment was being undertaken while other development was being researched regarding the handing of the PVC liner material. Fabrication of the PVC geomembrane was completed during February and March of 1989, with shipment to California and actual placement of liner in the canal beginning in May of 1989.
Polyvinyl Chloride (PVC) was selected as the membrane lining material for the underwater application at the Coachella Canal. The Bureau's specification of PVC was based on many factors, including:
The availability of large panels. PVC was fabricated into panels 58.6' x 200'.
The PVC geomembrane is highly flexible and retains its properties over a wide temperature range. This permits the liner to conform to the subgrade better than other available geomembrane materials.
The PVC geomembrane is easily field spliced with solvent welding. The PVC also has very good puncture, abrasive, and tear resistance properties, which are important in minimizing damage during installation.
PVC has a proven history of use in canal lining for more than 30 years by the Bureau of Reclamation.
Since the lining of the canal was to be done in two passes requiring a longitudinal seam in the PVC liner down the center of the canal, it was necessary to use a geomembrane that could be sealed underwater. Since an un-bonded longitudinal seam would not provide the necessary seepage control the Bureau required, laboratory studies concluded that a vinyl swimming pool adhesive used to repair pool liners would be a suitable adhesive for this seam. Laboratory test results of seam strengths for the underwater seam proved comparable with normally fabricated field seams, even though these were constructed underwater. The seam also eliminated the seepage possibility at the longitudinal overlap.
There was also a concern that the freshly placed concrete would have a tendency to slough down the slope of the canal sidewalls. Initial design requirements called for the application of a 3.4 ounce per square yard non-woven geotextile fabric on the side slopes on top of the PVC. The final solution involved the contractor gluing this geotextile to the PVC liner at their facility in Santa Fe Springs. The liner panels were then refolded and rolled prior to installation at the project site. A factory laminated product, which will provide both the 30 mil PVC and a non-woven geotextile bonded to one or both sides of the liner is now available for future projects. This material is also used in tunnel lining applications and it saves considerable time and manpower in the placement of the two materials at the same time.
Since the PVC geomembrane fabricated material had never been used in this type of application, there was no data available as to how the membrane would behave during the underwater installation procedure. The preliminary design concept, proposed by Mr. Giroux, involved holding the PVC in a manner much like a garage door track supports the sides of an overhead garage door. The track design called for the inclusion of a hem in the liner material along both sides of the panel. This hem was to be filled with a rope to provide body and hold the liner securely in the guide track.
The hem/track development involved the use of a PVC jacketed nylon rope. In order to develop data as to the behavior of the liner in this application, EPI fabricated for Kiewit Pacific, several full size samples of the PVC liner. In addition, EPI fabricated a small section of liner 60 feet wide, which was furnished to Mr. Giroux at his office in Omaha, Nebraska. Mr. Giroux proceeded to do full scale testing with this liner sample at the YMCA pool in Omaha. From the data generated in these tests, he determined that support of the liner on the two outside edges would not be sufficient to control the final placement of the liner. The design was then modified to have two center guide tracks, one at the toe of the slope, and one at the centerline of the canal. The outside guides would be at the top of the slope, and at the outside edge of the three foot overlap in the canal bottom. The center guides posed a problem in that a hem type seam would be subjected to forces which would exceed the normal peel strength of the seams.
Canal Cross Section
The challenge for EPI was to develop a fabrication process which was both effective and cost competitive to provide the liner panels for this project. EPI developed a system whereby the ropes could be anchored into the PVC liner, and seams made with sufficient strength to resist the forces that would be placed on the liner during the underwater placement of the geomembrane. The final fabrication techniques are a proprietary process of Environmental Protection, Inc. The process was inspected in operation by the U.S. Bureau of Reclamation. All fabricated panels were tested for bonded seam strength and peel adhesion of the factory seams and a sample from each roll of material was supplied to the Bureau of Reclamation for physical property testing. In addition, all material that was supplied for the project was also tested for compliance with the project specifications.
The prototype project was to line 1.5 miles of the Coachella Canal near Niland, California. The canal at this section was approximately 110 feet wide and 9 feet deep. The side slopes of the canal were approximately 2.5:1. Since the canal was built in 1942 in the sandy desert soil, it was necessary to reshape the canal prior to the placement of liner and concrete. A machine to dredge the canal and place a new sub-base of crushed aggregate was also designed and built by Kiewit Pacific. This machine, affectionately known as the Trimmer, precedes the paving unit and reshapes the sides and bottom of the canal to line and grade.
After shaping is completed, the paving unit proceeds to travel along the canal, placing the PVC/geotextile composite in place directly in front of a slipform paving unit designed and constructed by Gomaco, of Ida Grove, Nebraska. After paving one half of the canal, the machine is turned around, and proceeds to pave the second half of the canal from the opposite direction. Based on design, speed, and availability of concrete, working 24 hours per day, it was estimated that the paving of 1.5 miles in one direction could be accomplished in approximately 3 days.
Liner Placement Schematic
The initial paving operation was started in May of 1989. At that time, the water usage requirements in Southern California were reaching their peak. It was necessary to be able to regulate the flow of water so that the many adjustments to all of the various operating systems of the paving unit could be accomplished in reasonable fashion. Initially, about 1,200 feet of lining was placed during early May. Serious problems were encountered with areas of soft soils in the bottom of the canal. As the weight of the concrete was added to the soil below the liner, a wave of mud was created oozing in front of the paving hopper. This mud would trap the liner sliding down in front of the hopper, causing it to snag or tear. Modifications would have to be made to the equipment to accommodate the soft substrate that underlies some areas of the canal bottom. The project was shut down for the 1989 season because of irrigation water usage requirements for the summer months and the time required for modifications.
During this time EPI did significant research and development on the use of wedge welders for thermal welding of PVC geomembranes. The intention was to develop methods to extend the PVC geomembrane installation season in Michigan. Starting earlier in the spring and working later in the fall would be an advantage. The use of thermal welding would provide the ability to weld PVC when weather conditions would not be favorable for chemical or adhesive seaming. EPI’s R&D eventually proved very prolific for the success of the Coachella Canal inplace lining project.
The project resumed in March of 1990. The concrete delivery system was redesigned using belt conveyors on one side of the canal and concrete pumps on the opposite side. Since it requires a minimum of 15 Cu. Yd. of concrete to initially charge the pavers hopper, the concrete delivery requirements are very large and critical to the success of the project.
The most significant modification was the addition of a series of five foot (1.6M) square pressure plates directly in front of the paver. The pressure plates extended the full width of the paver and 5 feet (1.6M) in front of the concrete hopper. The PVC geomembrane was placed in the bottom of the canal directly in front of the pressure plates. Each of the 12 pressure plates was fitted with hydraulic adjusting cylinders and pressure sensors. The pressure sensors were connected to a computer at the operator’s console. As the paver traveled forward placing concrete in the canal, the computer monitored the pressure exerted under the pressure plates in front of the hopper: