PROTECTING BASAL LINERS
When installed, a geomembrane should be protected against puncture, ultraviolet degradation, thermal and localised stress concentrations. These include indentations that lead to stress cracking. The most effective method of protecting a geomembrane has been proven to be a thick geotextile or geocomposite layer. GEOfabrics are market leaders in the manufacture and supply of high-performance geotextiles and geocomposites designed specifically for this application.
Cylinder Test (Environment Agency LFE:2/ BS EN 13719)
The selection of an appropriate geosynthetic protection layer is now made using the Cylinder Test. The Cylinder Test is recognised as the only method for determining the effectiveness of a material in protecting a geomembrane against the long-term effects of static point loads; it is designed to simulate the conditions expected in the base of a landfill.
The load applied includes the dead load of the waste mass and any overburden pressure due to the depth of the waste and restoration materials. That is, (depth of waste x waste density x acceleration due to gravity) + (depth of restoration materials x density of restoration materials x acceleration due to gravity). It is known that the HDPE continues to deform under constant load and also at higher temperatures (plastic deformation), therefore a safety factor of 2.5 is incorporated into the test.
GEOfabrics laboratories have conducted thousands of Cylinder Tests and built up a vast library of knowledge over many years. Using this expertise, we are able to assist designers in finding the most effective value engineered solution to leachate management and membrane protection.
The mechanism by which geotextiles cushion point loads from individual stones is complex, with the geotextile being the top layer in a system that includes the geomembrane and mineral layer underlying the membrane. In addition, the influence of temperature and time (creep) must also be considered.
Protection efficiency can be correlated with strength and modulus, and it is a clear indication that mass does not correlate with an improvement in product performance. Specification that are based on the unit weight of a product are entirely inappropriate. When referring to geotextile protectors, the role of fibre interaction is central to performance.
HPS Geotextiles are manufactured using a unique matrix of high tenacity, high surface friction fibres entangled such that a stone receiving a lateral load is transferred to produce an evenly distributed load to the membrane.
■ Isotropic properties: strength in all directions
■ UV stabilised – active carbon black
■ 100% virgin polymer fibres