Home
>
Beneficial properties of LLDPE geomembranes in mining and waste landfill applications
Products
Technical note
4 Min read
Geomembranes are impervious sheets of polymeric material primarily for containment of liquids or gases; prevent or limit the migration of fluids. They represent a branch of engineering materials called geosynthetics which are specifically designed to enhance the building properties of natural soils that have been deemed deficient from an engineering point of view.
HDPE geomembranes have been the material of choice across the world for general waste containment application
due to its excellent chemical resistance and high mechanical strength. For heap leach pads in mining and capping of landfills, LLDPE geomembrane have been found to be better suited to address the specific applications’ needs due to its stiffness is generally only one quarter that of HDPE.
Technical benefits of LLDPE geomembrane
Flexibility of geomembrane in landfill capping
Geomembrane used in the capping of landfills is generally not in direct contact with waste and therefore
chemical compatibility is of secondary concern. Focus on geomembrane selection shall be waste settlement and its impact on the geomembrane’s integrity arising from its ability to deform.
Index tensile test following ASTM D6693 is a widely used method to check the tensile strength and elongation
properties of geomembranes. This test however does not take into account the flexibility properties of geomembrane when it is deformed three dimensionally as typically illustrated in Figure 1. The values obtained from ASTM D6693 is not representative of “real life” condition and therefore cannot be used for design.
Multi-axial tensile test is a performance test that better represents the geomembrane’s performance for landfill capping.
Solmax’s LLDPE Series was tested in the multi-axial direction following ASTM D5617 to provide a more complete
information for designers where the information is not specified for HDPE geomembrane. Multi-axial tensile test
simulates a void beneath the geomembrane or differential settlement which may stress the geomembrane beyond.
The multi-axial break strain result of Solmax’s LLDPE Series in comparison to the industry standards are shown in Figure 4.
On the account of the superior flexibility performance of Solmax’s LLDPE Series, it is recommended that LLDPE
geomembrane be used for landfill capping instead of standard HDPE geomembrane.
Puncture resistance of geomembrane in heap leach pads
Mining heap leach pad design with crushed rock ore fill height exceeding 100 m is becoming a norm. As such,
puncture resistance of the two dimensional geomembrane impermeable barrier is of utmost concern.
ASTM D4833 is the common index test prescribed to check the puncture resistance of polyethylene geomembranes. In simple terms, this test method measures the force required to puncture a geomembrane with a flat metal rod. The force required to puncture HDPE geomembrane is higher than LLDPE implying that HDPE is better. However, results obtained from this test method are misleading as ASTM D4833 is merely an index test and the significant contribution of liner flexibility was not considered.
Contact Solmax’s technical and sales representatives for more details.
A performance test following ASTM D5514 called large scale hydrostatic puncture test is a more appropriate test to evaluate “real life” puncture resistance of geomembranes. A large piece of geomembrane typically the size of 600 mm2 is placed on top of site representative material and pressure is applied. The test will then measure the pressure required to puncture the liner. This test is not regularly done on every liner as part of manufacturing quality control because it takes time to perform.
Solmax has tested its LLDPE Series in accordance with ASTM D5514 against gravel size of 20 – 40 mm and the
results compared with HDPE geomembrane is tabulated in Table 1 below.
Figure 5: Overview (Bedding before testing)
Figure 6: Overview of exposed face (after pressure release)
Greater flexibility and ability to accomodate and take the shape of the subgrade, ASTM D5514 clearly shows that Solmax’s LLDPE Series has a superior puncture resistance comparing with HDPE geomembrane when placed under tests that simulates the actual field condition. ASTM D5514 particularly simulates the geomembrane’s resistance to puncture in mining heap leach pad application.