Environmental Engineering

Bachy Soletanche has a wealth of experience, throughout the world, in applying novel solutions to the containment and/or treatment of contaminated soil and groundwater. Those solutions are the result of a unique combination of unrivalled geotechnical and geo-environmental knowledge and our ongoing research and development programme.

Slurry Wall Cut-Offs
Slurry walls are an effective means of preventing the mitigation of water, contaminated water and leachate.

We use a variety of excavation techniques, depending upon depth and ground conditions, and employ a bentonite cement slurry mix to stabilise the trench and form the permanent cut-off wall.

The thickness of the wall is normally 600mm, but this can be increased to 1.5m if necessary.

Slurry Walls with HDPE Membrane
For situations demanding increased security, such as containment of landfill gas, or where post construction ground movements may be significant, a high-density polyethylene membrane can be included in a standard slurry wall.

This technique has been applied to depths up to 32m.

The membrane is installed into the slurry trench, before setting, on frames between 2m and 6m wide. The frames are withdrawn from the trench leaving the membrane in position. Panels are jointed in the trench using “Geolock” interlocking clutches incorporating Hydrotite.

Thin Cut-Offs by Vibwall
A Vibwall is ideal for creating cost effective, temporary isolation cells, where groundwater or soil can be decontaminated. Heavy H-shaped lances equipped with grout pipes are driven into the ground and grout is injected to leave an H-shaped grout column. The lance is then re-driven in successive positions to create a continuous wall generally between 60mm and 80mm thick. In suitable ground the technique can achieve a depth of 25m.

Landfill Gas Venting
Gas relief wells control the migration of landfill gases by drawing them out from the body of the tip, or by intercepting lateral spread.

The location, arrangement and interlinking of the boreholes are carefully designed to provide active or passive extraction systems and for larger sites, there is the possibility of harnessing and utilising the energy of the landfill gas.

Cut-Offs by Soil Mixing
The Cutter Soil Mixing (CSM) wall provides a cost effective solution for the rapid construction of retaining and cut-off walls by mixing soil in situ with a cement / bentonite grout.

Like traditional walls, the CSM wall consists of adjacent male and female panels, with thickness typically ranging from 500mm to 1000mm.

Depending on soil conditions and specific project requirements, the soil is mixed and grouted, following pre-determined procedures during the drilling and the extraction phases.

Soil Mixing
Soil mixing can also form vertical containment barriers. Traditionally this has been carried out by mixing vertical columns (utilising either single or multiple augers) which are overlapped to form the barrier. Techniques using this method include Colmix and Trenchmix.

Permeable Reactive Barriers
We are leading providers of “active” barriers, which allow the passage of groundwater with simultaneous decontamination. These barriers can be either continuous or with defined flow paths that can be engineered to control and monitor the treatment process more effectively.

Our innovative, patented “Panel Drain” system can be easily incorporated into slurry walls to provide “gates” where inflow and outflow quality can easily be monitored, and the reactive material replaced or regenerated as necessary.

This solution is ideal for working sites, providing insurance against future contamination and supporting pollution containment or gradual cleanup.

Treatment of Contamination
Treatment can be carried out on site using either ex-situ or in-situ methods to chemically stabilise and/or solidify contaminated ground or waste. Desk studies, laboratory trials and full scale trials are carried out as necessary to ensure that the treatment will be effective.

In-situ treatments can be applied using the patented Colmix process, which utilises overlapping contra-rotating augers to introduce and fully mix the reagents and soil whilst compacting to minimise volume increases.

Ex-situ treatments are carried out with a range of equipment specifically selected to provide cost effective and efficient solutions in each and every case.