High Density Polyethylene(PE) Geomembrane Liner
Geomembrane is an essentially impermeable membrane used with soil, earth,rock and foundation as a requisite part of an engineered project.
High Density Polyethylene (HDPE) liner:
is the most widely used geomembrane in the world due to its inexpensive material cost. HDPE lining material is an excellent product for large applications that require UV and Ozone resistance, chemical resistance or high-quality installations. One of the main uses of HDPE is for landfill base liners, Waste lagoons, Pond lining, Aquacultures and mining applications where its chemical resistance is used to good effect. HDPE is best used as an exposed lining material, and has the UV resistance required for many years of outstanding service.
HDPE Geomembrane Sheet:
product is delivered in large rolls with a width of 1500mm and is a field assembled lining material that cannot be practically fabricated in the shop. All HDPE projects, regardless of size, must be installed by trained installers. HDPE offers the most cost effective liner for large projects. HDPE is available in thicknesses ranging from 0.70mm to 5mm.
HDPE Geomembranes Liners are manufactured from a nonpolar thermoplastic polymer which is chemically very stable but forms a melt above 140 °C, and so can be extruded at approximately 200 °C. Therefore in practice, HDPE geomembranes sheets cannot be glued by chemical processes and welding by thermal process is the jointing technology of choice.
Description of Welding Methods:
Areas to be seamed shall be free from dust\debris and dry. In no case shall HDPE Sheet overlap be less than 75mm HDPE Geomembranes sheets are to be sufficiently overlapped up to 150mm to secure sufficient good weld.
Weather conditions can be of extreme influence to the weld quality; therefore welding or Seaming is prohibited during rain without special protection. Seaming is usually prohibited at temperatures of less than + 4°c and above + 75°c. Subgrade must be maintained in good condition to guarantee permanent bearing capacity (in case welding equipment is dependent on ground pressure). Prior to commencement of welding, test welds are to be executed and tested to all weld parameters.
No vehicular traffic shall travel on the HDPE geomembrane sheet other than an approved low ground pressure Vehicle or equivalent
Sand bags or equivalent ballast shall be used as necessary to temporarily hold the geomembrane material in position under the foreseeable and reasonably - expected wind conditions.
Geomembrane placement shall not be done if moisture prevents proper subgrade preparation, sheet placement, or sheet welding.
The HDPE geomembrane shall not be allowed to "bridge over" voids or low areas in the subgrade.
The HDPE geomembrane shall rest in intimate contact with the subgrade.
Welding or Seaming shall primarily be performed using automatic fusion welding equipment and techniques. Extrusion welding shall be used where fusion welding is not possible such as at pipe penetrations, patches, repairs and short (less than a roll width) runs of seams.
Welding or seaming of HDPE Geomembrane is a thickness dependant technique that requires a minimum material thickness to create an effective weld without distortion. Extrusion welds in sheet less than 1.0 mm thickness are not recommended. Extrusion welds in 1.0 mm thick HDPE Sheet show some distortion and can sometimes be very difficult to prepare around intricate pipe penetrations and mechanical attachments. 1.5 mm thick HDPE Geomembrane sheet can be reliably extrusion welded in most situations and is recommended in most applications. Welds in 2.0 and 2.5 mm thick HDPE Sheet are excellent and are recommended in applications that require exceptional durability. Extrusion welds are very slow and are typically used only for repairs and details.
Hot wedge welders have become the technique of choice for HDPE installers over the past several years. Wedge welders are fast, produce excellent welds in HDPE sheet from 1.0 mm to 2.5 mm thickness, and can be easily tested. Hot wedge welders today produce two weld tracks separated by a small unbonded channel. By sealing off both ends of this channel, and then pumping it full of air, entire seams can be checked quickly and effectively.
Fishmouths or excessive wrinkles at the weld or seam overlaps shall be minimized and when necessary cut along the ridge of the wrinkles back into the sheet so as to effect a flat overlap. The cut shall be terminated with a keyhole cut nominal 10 mm diameter hole so as to minimize crack/tear propagation. The overlay shall subsequently be welded. The key hole cut shall be patched with an oval or round patch of the same base HDPE Sheet geomembrane material extending a minimum of 150 mm beyond the cut in all directions.