SMR Applications: Ex-Situ Stabilisation
Where: MOD Longmoor
When: June 2016
Background
An integral part of the training estate for the British Army, the Longmoor Site on the Surrey/Hampshire border had undergone many changes since its acquisition in 1863 but this existing culvert was no longer effective and needed completely replacing.
R&W Langley, as the main contractor, had won the contract for the major culvert replacement plus embankment stabilisation, as well as extensive gabion basket and mattress works but upon commencement discovered that the spoil was retaining too much moisture and therefore unsuitable for the planned disbursement across the site.
Problem
The soil on the Longmoor Site was totally saturated with more than 45% moisture being present, so in order to re-use it elsewhere on the site this needed to be reduced to below 12%. In total around 1500m3 (3,500 tonnes) of spoil material was involved and the timeline for the overall project was already extremely tight.
New material could have been imported to meet immediate project requirements, with the existing moisture retaining soil sent to landfill but this would add transport cost plus increase the environmental impact of the project. Alternatively, the saturated material could have be left to naturally dry for longer on the site, however, this would significantly push back the completion date resulting in costly time delays to the project and there was still no guarantee of a positive outcome and the material could still need to go to landfill. The main contractor R&W Langley therefore turned to soil stabilisation specialists SMR (UK), to deliver a solution.
Solution
Because of access issues and in order to minimise overall vehicle movements on and off the site, SMR (UK), working in collaboration with Richardson Recycling, a Hub partner, set up a processing plant on site using a specially modified Powertrack 800 screener and mixer to add the SMR (Stabilised Material for Reinstatement) additive. This Batch‑Mix approach significantly shortened the overall time required to reduce the retained water percentage with a two-man crew working over a 10 day period to treated all 3,500 tonnes of material.
Under normal circumstances around 2% of SMR Batch-Mix would typically be added to the soil but when soil samples were sent away and tested the most favourable mix ratio of 4% was identified as this blending of the SMR and soil would guarantee the stability and performance of the material. This ultimately resulted in the moisture content being reduced to below the required target, thus removing the need to import a sub base product, send the spoil to landfill while at the same time delivering real financial savings.
A total of ten batches were blended, ranging in size from around 100 tonnes at the start and end of the process, with each of the main batches being around the 400-500 tonnes mark. Compression test blocks were created as part of the delivery process so that cube tests could be taken on each batch and these were subsequently tested. After the initial seven days soil strength of between 2.2 and 5.3 Newton/m2 was achieved, rising to between 4.3 and 8.7 Newton/m2 after 28 days.
Benefits
The benefits of using SMR on the Longmoor Culvert project included:
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Reduction of landfill – All excavated material was recycled and re-used on site, resulting in zero material being sent to landfill, with no tipping fees and no additional transportation costs.
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Reduction of Carbon Footprint – By Batch-Mixing the SMR with the spoil on-site not only were additional lorry movements avoided but the projects delivery time was reduced to just 10-days with a two-man crew treating all 3,500 tonnes of material.
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Saving in lorry movements – Had the alternative solutions been implemented around 4000 additional lorry movements would have been required on this project with all the associated environmental impact, additional staffing, operational and landfill costs.
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Delivery schedule maintained– By using SMR the original delivery schedule was maintained and the success has resulted in additional opportunities for the main contractor.
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Cost savings – Despite the SMR processing costs not being part of the original tender, because there were no additional land fill fees or transportation costs the project was still cost effective.
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SMR produces a high quality structural reinstatement material – This consistently outperforms traditional materials such as Type1 GSB plus dries out and stabilises excess moisture for optimum compaction. It also bonds soil particles together increasing density and strengthening the soil by as much as 600%.