Highland Council awarded Strath Civil Engineering the contract to prevent flooding between Inverness and Dingwall. The site, on the banks of the River Conon, is flanked by the main road through the small town and the railway bridge. Major flooding has occurred 14 times over the past 200 years, highlighting the need for increased protection in the area.
The flood defence project aims to protect local communities from seasonal flooding, creating a safer environment for the surrounding town of Conon Bridge. Strath Civils subcontracted Aarsleff’s geotechnical department to install a value-engineered, sustainable slurry wall. The overall scheme will include site clearance, the installation of the slurry wall, and the construction of a much larger bund than is currently on the site.
The ground environment consisted of a high volume of gravels and boulders from 2m to target depth, causing logistical challenges to the working environment. This technique requires heavy equipment and machinery. Also, the time of year (December) naturally caused difficulties in delivering this particular technique. The team efficiently navigated both the adverse ground conditions and challenging seasonal weather uninterrupted.
Aarsleff worked within six metres of the River Conon and five metres from the adjacent live network rail bridge. The team used a 36ft long reach excavator to dig the 120m by 6m by 600mm trench before filling the vertically excavated trench with a standard slurry mix. Due to the cementitious content, the slurry hardens within about 24 hours to form the low permeability barrier, ultimately reducing groundwater flow. Aarsleff used a high replacement cementitious material in the bentonite slurry mix, producing maximal structural strength. The purposely designed mix also has the added benefit of significantly reducing carbon footprint. Considerations for this solution were designed against the compatibility of the contamination type and the materials used to construct the barrier walls.
Project director Neil Morrison commented: “We are delighted with Aarsleff’s overall service. As we are not a commercial contractor, the opportunity to work closely with the delivery team was greatly appreciated, and our final valuation was agreed with minimal hassle”.
Slurry walls can be quick to install, are typically low in cost, and resist organic contaminants. The installation proved to be an effective solution for our client - Strath Civil Engineering. Aarsleff is pleased to report that delivery was completed within three weeks, on time and in budget.
This article was paid for by Aarsleff Ground Engineering
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