Whenever possible, site selection should avoid areas where flooding or ground water pressure can occur. The lining "bottom" should be well above the water table. If the site selected is in an area where organics are in the soil, or if gases can be generated by chemical reaction, the design must allow for venting.
Surfaces should be level and free of all sharp rocks (all rock and stone greater than .05" diameter), objects, vegetation and stubble. (Soil sterilization may be necessary to kill roots and certain types of grasses.) The subgrade surface should provide a unyielding foundation for the geomembrane with no sharp or abrupt changes or break in grade. Proper compaction assures stability and support of the liner.
Groundwater should be taken into account and, if present, it will need to be controlled both during and after construction. One method for controlling groundwater is to develop a French drain system under the lining that allows the water to flow laterally under the lining without floating the lining.
A good design for an underdrain is to pipe it to the outside of the lake into a gravel sump. This allows the sump to run continuously during construction and, with the placement of an upright at this sump, the underdrain can be pumped if needed to relieve hydrostatic pressure and gas buildup under the lining system.
Side slopes should be no steeper than 3:1 whenever feasible. Contact Raven directly when site specifications or conditions differ. Slopes are usually hand-raked to achieve proper smoothness.
Receipt of Liner & Materials
Liner panels are fabricated into large sheets to minimize field seaming. These large panels are first accordion folded, then rolled up on a core.
It is recommended that the liners panels' protective covering not be removed until installation and that any uncovered panels be stored out of direct sunlight.
Panels are rolled on 6" cores and can be unloaded using a 10' section of schedule 80 pipe and handling straps.
We also offer 12 mil tarps to cover and protect delivered liner rolls.
To secure the edges of the lining in an earthen pit, an "anchor trench" is dug. Anchor trenches are approx. two foot wide by two foot deep (2' x 2') and one foot back from the crest of the berm (standard trench dimensions and depth vary according to project design)
Dirt removed should be raked out flat on the far side of the trench, away from the pit, to be used to backfill after the liner edges are laid out in the anchor trench, while allowing the panels to be unrolled along the berm.
Structures, piping, concrete, drains, and any associated work should be completed prior to lining installation.
The roll is raised by a loader, forklift, or other lifting equipment, and then unrolled in one direction, and unfolded in the other direction.
Take time when unloading and placing rolls of lining to avoid damage. Verify the location of a panel or sheet before unrolling and placement to avoid improper alignment. Sandbags are required to keep the panels in place during installation, exposed or covered. Care should be taken to avoid wrinkles in the seam areas and around mechanical attachments.
It takes considerable manpower to deploy a liner. It is "pulled" but not stretched. Minor wrinkles ensure the liner is installed in a relaxed condition. A ballast system (sand bags) and anchor trenches are used for all geomembrane installations.
Fabricating panels at one of our climate controlled facilities into essentially larger panels dramatically reduces the amount of field seaming a project requires. The lining material itself determines the types of field seaming techniques used.
The most commonly used process is heat fusion welding, which can be done with hot air or hot wedge.
Liner Attachments to Structure
The most commonly used methods for attaching to structures are Mechanical and Embedment Strip methods.
- Mechanical: Battens are typically 1/4" x 2" and are aluminum or stainless. (Pending corrosion resistance requirements.)
- Embedment Strip: A method using the same material as liner system - placed in concrete during concrete pour.
Creative methods to deal with special attachment needs are possible.
A pipe boot is a method of sealing the liner system to necessary pipes that penetrate the lining system. These can be fabricated in one of our facilities or on site during field construction.
These guidelines are for informational purposes and are intended as illustration or general information only. They are not intended as a guarantee or warranty. Raven Industries, Inc. assumes no responsibilities in connection with the use of this information.