Slurry Walls with Geomembrane
Pictures
Click the thumbnails to view larger versions of the images
Contact information
- Dan Adams
- geotechnique@keller.co.uk
Membranes
The passage of landfill gases such as Methane and Carbon Dioxide, along with vapours produced by hydrocarbons and other VOC's, can be controlled using insitu cement/bentonite slurry wall barriers and venting systems.
For the purposes of gas control, Keller normally incorporates HDPE membranes within their slurry walls.
The Membrane acting as the primary gas barrier with the slurry wall being used to provide a high level of secondary protection, whilst at the same time containing any residual contamination or leachate flow.
The HDPE liners used are usually supplied in panels, which are lowered into the bentonite/cement slurry using specially weighed frames. The panels are connected using proprietary interlock systems.
Alternately, where gas or vapour control is required without a slurry wall. Keller can install deep columns or gravel trenches as the venting medium. In unstable soils these would also be constructed using biodegradable mud’s as temporary support and can also incorporate 'barriers' in the form of HDPE liners. Collection pipes can be laid within the trenches to channel the gas to ventilation stacks.
Under Slab Ventilation
On sites that are producing harmful gases, the under slab ventilation system is frequently designed separately from the foundations - often reducing the choice and adding considerably to the cost. By considering both operations as an integrated package, it is possible to obtain maximum savings in both areas whilst ensuring a highly effective solution. Keller's whole project approach can be tailored to maximise the use of the ventilation medium in terms of load distribution whilst reducing the cost of the foundation and substructure, providing s complete gas barrier.
For prevention of gas migration, particularly above the ground water table, a secondary barrier is placed in the Keller Slurry Wall. This typically comprises a continuous geomembrane liner installed insitu before a set of the slurry takes place.
Construction
Construction of the wall proceeds under the temporary support of a bentonite slurry or self-hardening bentonite/cement slurry according to wall depth and excavation technique.
Dependent on the wall depth, the geomembrane is lowered into the wall as either a continuous sheet or roll, or in interlocking panels for deeper walls.
To complete the composite wall self-hardening bentonite/cement slurry encapsulates the flexible liner.
