Geosynthetic clay liners (GCLs) are factory manufactured hydraulic barriers consisting of a layer of bentonite or other very low-permeability material supported by geotextiles and/or geomembranes, mechanically held together by needling, stitching, or chemical adhesives. Due to environmental laws, any seepage from landfills must be collected and properly disposed of, otherwise contamination of the surrounding ground water could cause major environmental and/or ecological problems. The lower the hydraulic conductivity the more effective the GCL will be at retaining seepage inside of the landfill. Bentonite composed predominantly (>70%) of montmorillonite or other expansive clays, are preferred and most commonly used in GCLs. A general GCL construction would consist of two layers of geosynthetics stitched together enclosing a layer of natural or processed sodium bentonite. Typically, woven and/or non-woven textile geosynthetics are used, however polyethylene or geomembrane layers or geogrid geotextiles materials have also been incorporated into the design or in place of a textile layer to increase strength. GCLs are produced by several large companies in North America, Europe, and Asia. The United States Environmental Protection Agency currently regulates landfill construction and design in the US through several legislations.[1][self-published source]
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The origin of GCLs can be traced back to when Arthur G. Clem filed a patent for preformed moisture impervious panels which combined bentonite clay with corrugated paperboard.[2] In , Arthur J. Clem filed a patent for a what would today be recognized as a GCL which combined bentonite clay, adhesive, and a geotextile.[3] In that same year, Arthur J. Clem established Clem Environmental Corp to put his invention into production.[4] The use of GCLs as a separate category of geosynthetics appears to have been in the United States in in solid waste containment as a backup to a geomembrane. The product was Claymax which is bentonite mixed with an adhesive so as to bond the clay between two geotextiles; one below (the carrier textile) and the other above (the cover textile) the bentonite in the center. About the same time a different product in Germany, Bentofix, was manufactured by placing bentonite powder between two geotextiles and then needle punching the three-components system together. The needle punching method of manufacture (US patent filed in ) gave the resulting composite material shear strength, a critical feature for installation on slopes.[5]
Other names used for GCLs since their initiation are "clay blankets", "bentonite blankets", "bentonite mats", "prefabricated bentonite clay blankets" and "clay geosynthetic barriers", the latter currently favored by the International Organization for Standardization (ISO).
The engineering function of a GCL is containment as a hydraulic barrier to water, leachate or other liquids and sometimes gases. As such, they are used as replacements for either compacted clay liners or geomembranes, or they are used in a composite manner to augment the more traditional liner materials. The ultimate in liner security is probably a three component composite geomembrane/geosynthetic clay liner/compacted clay liner which has seen use as a landfill liner on many occasions.
Differences between geosynthetic clay liners (GCL) and compacted clay liners (CCL) Characteristic Geosynthetic Clay Liners (GCL) Compacted Clay Liners (CCL) Material Bentonite clay, adhesives, geotextiles and/or geomembranes Native soils or blends of soil and bentonite clay Construction Factory manufactured and then installed in the field Construction and/or amended in the field Thickness ~ 6 mm 300 to 900 mm Hydraulic conductivity of clay[6] 10−10 to 10−12 m/s 10−9 to 10−10 m/s Speed and ease of construction Rapid, simple installation Slow, delicate and complicated compaction works Installed cost $0.05 to $0.10 per m2 Highly variable (estimated range $0.07 to $0.30 per m2) Experience Construction quality assurance and quality control are critical Highly workforce dependentGeosynthetics have gained widespread popularity in civil, geotechnical, environmental, coastal, and hydraulic engineering projects owing to their versatility and cost-effectiveness. Of note, over the past decade or so, Geosynthetic Clay Liners have replaced compacted clay liners in various applications, especially in terms of hydraulic performance and ease of installation. The Ocean Geosynthetics, prefabricated geosynthetic clay liners, find immense uses as cover systems, composite liners, protection barriers, storage tanks, canal liners, pond liners, and more.
There is a rapid expansion and growth in the geosynthetic clay liner market owing to the increasing prominence of infrastructure development. Moreover, rising awareness about geosynthetics being the environmentally-safe alternative has propelled their demand in the global geosynthetics market.
Geosynthetic clay liners are essentially two layers of geotextiles sandwiching a layer of sodium bentonite clay. The geotextiles are needle punched, physically bonded, or stitched for structural integrity. They may be woven or non-woven geotextiles, depending upon the project specification and applications.
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The GCLs are either made of polypropylene or bentonite. Bentonite is fine-grained absorbent clay, typically made of montmorillonite and swells on wetting. Application-wise, they find uses in geosynthetic sectors like roadways, railways, waste treatment, landfill mining, gas and vapor seals, ground engineering, agriculture, waterproofing, tunneling, etc.
The Ocean Geosynthetics’ prefabricated geosynthetic clay liners consist of high-quality bentonite liner encapsulated between two layers of geotextiles needle punched and then subjected to controlled heat treatment to thermally lock the layers and fibers in place, providing high shear strength. They find use as single or composite liners.
Here are some reasons why GCLs are largely replacing traditional compacted clay.
Natural sealant: The sodium bentonite characteristically swells on wetting with an affinity for water, acting as a sealant around penetrations, self-healing punctures, and also self-seam at overlaps.
Long-term performance: GCLs eliminate the problems of differential settlement and are less impacted by desiccation-rewetting cycles owing to the high plasticity and self-healing capabilities of sodium bentonite. The traditional compacted clay liners succumb to these conditions and crack up. The GCLs are invariably more resistant to varying weather conditions providing consistent performance over the long-term. The compacted clay liners, on the other hand, show a decrease in performance with varying moisture content, clay content, or density and are hugely dependent on weather conditions.
Ease of Construction and Installation: GCLs are the environmentally-friendly alternatives requiring less effort during installation and using up lesser natural resources, also taking up lesser air space. They are even easier to deliver just unrolling and overlapping as opposed to hauling, dumping, spreading, and compacting clay resulting in added construction time, increased logistics, and cost. While the clay liners use local aggregate, the manufacture of GCLs is in factory units with the quality of raw materials and products undergoing stringent testing measures during and post-production.
With benefits like self-healing, self-seaming, unaffected by wet/dry, freeze/thaw cycles, and excellent resistance to chemical and physical stressors, the Ocean Geosynthetics prefabricated geosynthetic clay liners show superior performance, are multifunctional, and yet cost-efficient.
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