Bachy Soletanche constructs slurry cut-off wall

Bachy Soletanch has just completed a project for Urban Regen to carry out the construction of a slurry cut-off wall as part of preparation works for a new residential development.

Leading geotechnical specialist, Bachy Soletanche Limited has just completed a project for Urban Regen to carry out the construction of a slurry cut-off wall as part of preparation works for a new residential development based in Tonge Moor, Bolton.

The purpose of the slurry trench works were to permanently isolate the proposed built development within the site - preventing the ingress of any potential contaminants from the adjoining landfill via both permeable fill and natural ground.

Andy Tucker, site engineer for Bachy Soletanche commented: "Due to the depth of the underlying impermeable deposits, and restrictions of space imposed by the development layout - a vertical slurry trench cut-off wall was selected as the most appropriate type of barrier".

"This environmental measure was taken to prevent some of the issues raised on the risk assessment".

Bachy Soletanche's process prevents contaminant migration from outside the site through permeable horizons, which are within the made ground and the natural superficial deposits underlying the Northern and Western parts on the site.

Andy Tucker continued: "One of our considerations was that residents are living in close proximity to the site - therefore our aim was to ensure that operations do not affect them" .

Works began on site in February to construct the 270metres wall in clean soils - forming a permanent seal to protect the site.

The depth of the wall varies from 3metres to 13metres and is constructed using bentonite cement slurry as a support fluid through the soils.

Andy Tucker added: "The length of the excavated wall was on an incline which caused Bachy Soletanche to undertake the work in stepped individual sections along one part of the length of the wall, each approximately 10metres long".

"As a result, we were continually building bunds to surround the excavation which helps to control the final slurry levels".

"As the incline was not originally incorporated into our designs, we had to re-sequence the excavation method - eliminating any plans to go over schedule".

Once the slurry mix is installed into the wall, it will harden in-situ giving a near impermeable barrier to any potential contaminant.

In addition, a width of 1metre will offer the best cut-off point and future protection for the housing scheme as it is thicker than typical specified slurry walls.

Andy Tucker commented: "Normally 600mm is a sufficient thickness, yet the concentration of possible contamination means this width is preferable".

When the first sections were constructed and the slurry wall has taken on a sufficient setting time; the excavation to fill in the missing sections began.

After approximately one week, the wall is sufficiently set for the excavator to sit above the previously constructed section of the wall and excavate towards it.

Andy Tucker concluded: "The Jethro Street project was completed in early April ready for the housing scheme to continue apace.".

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