Geomembrane Liner Installation
Enviroseal are one of the leaders in Geomembrane Installation in the UK and in Europe. Geomembrane lining systems have been around for over 50 years. As environmental concerns become more prevalent, these lining systems are a practical means to prevent pollutants from contaminating water sources. Geomembranes are a type of synthetic (actually geosynthetic) material that is comprised of impermeable membranes. In essence, a geomembrane liner is a synthetic hydraulic barrier. These systems can be utilized to contain hazardous waste byproducts, control odors, collect gas, preserve potable water sources, grow food in aquaculture applications, waterproof dam faces and control effluents. The benefits of using geomembrane lining systems are vast, especially if one considers the need for water quality improvement resources across the globe.
Of course, as with any versatile product, there are various types of geomembrane materials, each with its own set of unique characteristics. The following are some of the most commonly used geomembrane linings:
- Linear Low Density Polyethylene (LLDPE). LLDPE is a linear polymer featuring increased tensile strength and puncture resistance than its predecessor low density polyethylene (LDPE). LLDPE is manufactured by a process of copolymerization of ethylene (and other alpha-olefins such as butane and/or octane) at low pressure and temperature. LLDPE geomembranes tend to be incredibly flexible and stretches when introduced to stress. Notably, it is very resistant to chemicals.
- High-Density Polyethylene (HDPE) – Perhaps the most commonly used geomembrane liner, HDPE is both widely available and generally the least expensive. HDPE liners have excellent resistance to ozone and ultra-violent spectrum radiation, as well as notable chemical resistance. Typically, HDPE liners are utilized in landfills and mining operations. For large applications, HDPE provides the most efficient means to fulfill desired results.
- Flexible Polypropylene (FPP) – FPP geomembranes are more costly to install than polyethylene based liners, but it has a better reputation for being more flexible and has better crack resistance than HDPE. These linings are easier to install and repair after aging. The material is a resin that is co-polymerized with ethylene-propylene rubber and polypropylene.
- Ethyl Vinyl Acetate (EVA) – EVA is three times as flexible as LDPE and can withstand temperatures of 96°C. The material is known to be a good barrier, can withstand low temperatures, good stress resistance, waterproof and resistant to ultraviolet radiation. The material has very little odour. EVA is a copolymer of ethylene and vinyl acetate.
- The surface must be inspected immediately before the liner is placed. Any debris that could damage the liner or prevent an even/smooth deployment must be removed.
- The deployment of the rolls should be in a manner that will require the least amount of welding.
- The rolls are placed as pre-determined in the blueprint or design.
- If the lining is going over a slope it is laid vertically up and down the slope. Additionally, material that is deployed on a slope should be carefully unrolled and not simply unrolled freely downhill. On slopes that are curved, material may require a diagonal cut in order to ensure welds are perpendicular.
- The installers will take careful precautions to prevent wrinkling
- Anchor the linings as they are laid. Usually sandbags or tires are used.
Geomembrane lining systems require welding that should performed by qualified technicians.There are two primary welds that are commonly utilized in geomembrane installation:
- double hot metal wedge welding and
- extrusion welding. Double hot metal wedge welding is the preferred method and the most reliable.
- The surface area that will be welded should be free of debris or any foreign materials.
- If extrusion welding is used, oxidation must be removed by grinding and debris from grinding must be removed.
- Double welds are used frequently in order to create a channel of air between welds that facilitates testing.
- Trial welds are made on a regular basis.
- The seaming will be done vertically on the slope.
- The number of seams will be minimized on corners or odd-shapes. A maximum of 3 rolls can be welded together (using a T-joint configuration).
- No horizontal seams near the bottom of a slope or any high stress concentration
- To assist with vertical welding, panels are visibly marked with a line 140 mm from the outside edge of the material. With a double wedge weld, the overlap should be wider than the weld by at least 10 mm, and 50 mm with an extrusion weld.
- The overlaps must be dry and clear when welding begins.
- Trial seams are done at the beginning, middle and the end of each seaming period. The trial seams must always be done under the same conditions as the geomembrane seam is done. The trial seams must be 1 m in length and 0.3 in width.
- Using a field tensiometer, 5 welding samples will be done. The samples will be 2.5 cm wide and 30 cm long. If any of the samples fail – the entire operation will have to be repeated.
- If excessive wrinkling occurs (fish mouths) then the edges of the wrinkling is cut in order to create a flat overlap. The places that were cut will then be seamed. If the cutting caused an issue with the length of the overlap than a round or oval patch will be placed that must extend 15 cm from all sides.
- A non-destructive test is used to check the integrity of welds.
- For fusion welds an air pressure test is used. For extrusion welds either a vacuum test or spark test is used.
- A destructive test is used to evaluate the strength of the seam. Depending on the type of raw material used to make the geomembrane a sheer test or peel test will be done. A destructive test should be performed at the beginning and completion of every long weld, as well as at points that engineers designate.
Installation of Geomembrane Lining Systems
Installing geomembrane lining systems is a complicated process that is generally carried out by trained engineers and technicians. Various specialized welding techniques, site preparation, and installation expertise are required to ensure that any geomembrane lining system is properly employed. The following is a general, yet illustrative, geomembrane installation process:
Quality Assurance Inspection: The following items are reviewed to ensure quality geomembrane installation:
- Surface conditions met all requirements before the lining was laid
- The geomembrane rolls were deployed and identified correctly
- The anchor system was done correctly
- The anchor trench and the placement of the lining were all done correctly
- The correct welding equipment was used
- The quality control devices were operating correctly
- Verified the fusion welding seaming and/or extrusion welding seaming
- All repairs were completed
- Correct pipe penetration
- The seam crossings were accurate
- The installation was done per the original design
- The documentation of the installation was completed
Quality assurance is an ever present standard: before, during and once the project is complete. Supervisors maintain a presence on the work site at all times to ensure that all the geomembrane installation procedures are correctly implemented. Detailed logs are maintained to record work progress, as well as any issues that occur and how they were resolved. In turn, these records are reviewed by a field manager, providing one further layer of quality assurance inspection.
- Specifications of the geomembrane that will be used.
- The type of anchoring system that is needed.
- The quantity of geomembrane lining.
- Which quality controls will be in place.
- What are the weather conditions as temperatures play a significant role in if and how the installation process will be completed.
Receiving, Storing and Handling: The following factors need to be considered when the product arrives.
- It is required that each roll have an identification number and quality certificate.
- Unload the rolls with approved equipment to prevent damage. Spreader bars or lifting straps can be utilized to accomplish this.
- Visual inspection of the outside of the rolls should reflect that there are no holes, tears or bubbles. Any non-conformance damage that is identified will be noted and recorded. Non-conforming material will either be repaired to conformity, or used in a manner that is appropriate to its use.
- The surface of the storage area needs to be free of stones and any items that could puncture the linings, mud, grease and chemicals. The rolls can be placed on wood platforms or sandy mattresses. The surface should also not be near a heat source. Rolls should not higher than 3 on top of one another
- The storage location needs to be in a location that minimizes the handling of the lining.The actual geomembrane installation has many steps within the entire process.
While the installation process is an involved endeavor, the required effort only illuminates the utility of geomembrane lining systems as a proven commodity for pollution containment.