Case Study
Ex-situ soil stabilisation for a culvert renewal project
This case study illustrates the successful application of SMR through our Ex-Situ method, at the MOD Longmoor site in 2016. Overcoming saturated soil challenges, SMR offered an innovative solution resulting in landfill reduction, carbon footprint savings, preserved delivery schedule, and high-quality reinstatement material.
Problem Statement
The Longmoor Site on the Surrey/Hampshire border had undergone many changes since its acquisition in 1863, but the existing culvert was no longer effective and needed to be completely replaced.
R&W Langley, as the main contractor, had won the contract for the major culvert replacement and embankment stabilisation. However, upon commencement, discovered that the spoil was retaining too much moisture and therefore unsuitable for the planned disbursement across the site.
The existing saturated soil, with over 45% moisture content, posed difficulties in achieving effective disbursement and reusability across the site. Around 3,500 tonnes of spoil material needed to be treated to reduce moisture content below 12%, and the project timeline was already constrained.
The SMR Solution
For this project, new material could have been imported to meet immediate project requirements, with the existing soil being sent to landfill. However, this would add transport cost and increase the environmental impact of the project. Alternatively, the saturated material could have be left to naturally dry for longer onsite.
However, this would significantly push back the completion date, resulting in costly time delays. Also, there would be no guarantee of a positive outcome, and the material could still need to go to landfill. Therefore, the main contractor, R&W Langley, turned to soil stabilisation specialists SMR (UK), to deliver a solution.
To address the challenges, SMR (UK) collaborated with Richardson Recycling to set up an on-site processing plant. We stockpiled SMR Batch-Mix on-site and utilised a specialised Powertrack 800 screener and mixer for this ex-situ process. This process significantly reduced the retained water percentage to below the required target. Over a 10-day period, a two-man crew treated all 3,500 tonnes of material with an optimal mix ratio of 4% SMR additive. Compression test blocks were employed for quality assessment.
Benefits
Landfill Reduction: Zero material was sent to landfill, avoiding tipping fees and extra transportation costs.
Carbon Footprint Savings: Batch-Mixing on-site minimized lorry movements, resulting in a reduced carbon footprint.
Lorry Movements Reduction: Avoided approximately 4,000 additional lorry movements, reducing environmental impact and costs.
Delivery Schedule Preservation: The original delivery schedule was maintained, yielding additional opportunities.
Cost Savings: Despite processing costs, the project remained cost-effective due to eliminated landfill and transportation expenses.
Conclusion
The treatment process yielded impressive results. Soil strength improved from 2.2 to 5.3 Newton/m2 after 7 days, and further to 4.3 to 8.7 Newton/m2 after 28 days, ensuring stability and performance of the material.
By utilising Ex-Situ Stabilisation with SMR, the MOD Longmoor project successfully overcame saturated soil challenges, resulting in environmental benefits, cost savings, and the delivery of high-quality structural reinstatement material.
