Geosynthetic liners for landfills have become standard practice throughout the industry unless the project is located in an area with plentiful stable clay.
The lining system used usually consists of the following:
- A prepared subgrade.
- A GCL (Geosynthetic Clay Liner). This is a liner containing bentonite clay. Bentonite has a very low permeability. The GCL is placed under a HDPE liner. Should the HDPE liner puncture locally the bentonite layer is a secondary line of defence. The bentonite effectively seals the puncture.
- A HDPE Layer. Generally, 2mm HDPE is used. This layer is welded continuously in place. The operation is subject to close Quality Processes to guarantee integrity.
- A Protection geotextile to protect the HDPE from the filter layer above. The filter layer is a coarse gravel which is placed under the landfill materials to collect the liquids (leachate) which separates out from the solids. The protection geotextile is tested under pressure with the HDPE and the filter gravel to verify its characteristics
Figure 1 Pressure Test for Protection Geotextile
- A Filter layer made up of 9.5-32 (May vary) sized gravel. River gravels are generally smoother and rounded and have less angularity and tendency to puncture the membrane under pressure. This layer is generally of the order of 300 thick. The layer often includes a system of drainage pipes to improve the overall permeability of the system.
- A separation Geotextile. This is a high permeability geotextile designed to allow leachate through to the filter layer and keep out solids, which have the potential to block the filter.
There are lots of other components to a lined landfill system which are not mentioned here.