In the last few years, engineers have been under increased pressure to meet environmental sustainability requirements as environmental concerns have increased. When considering a landfill liner system, this is especially relevant; since the primary purpose is to protect soil and groundwater from pollution caused by hazardous landfill contents. Therefore, testing and design verification are essential for engineers to prove that their liner system design meets the required standards and specifications.
Environmental considerations are important, but it is also critical to proving the long-term integrity of the liner system that is necessary to obtain an operating license. Several site-specific factors impact the performance of a liner system and how well it retains its leak-free status. Some of these factors are the aggregate size and shape available near the construction site, the ability to obtain the required clay liner density and the moisture content. These factors should be considered during the testing and verification of a liner system.
Laboratory testing of a liner system design
Typically, a liner construction test is performed in a controlled laboratory environment. While it is a widely used method, laboratory tests are not always the most effective option for a few reasons:
- It is expensive.
- There is a long lead time to obtaining results as it takes time to ship material to the laboratory, and testing demand is high.
- Laboratories fail to replicate the conditions and challenges present on the construction site of a lining system. Among them are achieving the required density and moisture content in the compacted clay liner and how the aggregate layer naturally lies when spread over the geotextile.
Considering the limitations of laboratory tests, we can conclude that onsite testing of a liner design provides results that better represent the performance of the system.
Onsite testing of a liner system design
TANDM Technologies has developed an onsite test that addresses the shortcoming and challenges of laboratory testing. The test is an adaptation of the ASTM D5514 – Large Scale Hydrostatic Puncture Testing of Geosynthetics and the Hornsey and Wishaw test method and performed following these steps:
A test pad is constructed with a minimum size of 1m x 1m. The liner is constructed following the normal process, with a foil test sheet positioned below the geomembrane.
A 310mm x 310mm load plate is placed on the aggregate layer. A mechanical jack is placed on top and jacked against a vehicle to introduce the required load. The load is applied gradually over 15 minutes and monitored for any possible settling.
After 24 hours, the load is removed, and the liner system is carefully deconstructed to recover the foil test sheet. The locations of the most severe indentations are identified and scanned to determine the maximum strain induced in the geomembrane.
Several different liner designs can be tested simultaneously to determine the optimal design and loading parameters.
Benefits of onsite testing
With the TANDM method, testing costs and time are significantly reduced, while results are generated based on the actual construction process. The complete testing process can be witnessed by engineers, and the results are available mere hours after the test is completed. As a result, engineers can make any required changes to the design or obtain confirmation of their design meeting specifications to proceed with construction.
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