The stabilisation of soils has been performed for millennia. It was recognised before the Christian era began that certain geographic regions were plagued with surface materials and ambient conditions that made the movement of armies and goods difficult, if not impossible, over the paths between villages and towns.
The Mesopotamians and Romans separately discovered that it was possible to improve the ability of pathways to carry traffic by mixing the weak soils with a stabilising agent like pulverised limestone or calcium. This was the first chemical stabilisation of weak soils to improve their load carrying.
Jump forward a few years to the war in Vietnam, the US military were looking for methods for rapid stabilization of weak soils for support of its missions worldwide. Over the past 60 years they had used cement and lime these being the most effective stabilisers for road and airfield applications, but although with careful analysis of ground conditions and the make-up of the existing soils these traditional stabilisers did have a remedial effective. They urgently needed a stabiliser that could be used quickly without having to carry out extensive site tests that would increase the strength of the prevalent soft clay type local soils rapidly to support the landing and take-off of heavy C-17 and C-130 aircraft traffic on their temporary airfields.
Various combinations of plasticisers were tested as additives to the cement to find an amalgam that could cope with the varying levels of moisture and prevailing air temperature. Laboratory tests confirmed that one particular application where chemical additives and hydrogels were added to a cement base mix increased the strength and toughness by a factor of over 100% whilst still retaining the degree of flexibility of surface the military were looking for.
The fore runner of our proprietary SMR soil stabiliser was born.
Early uses of SMR in the UK
Success in Stabilising Recycled Aggregate
Despite being the Highway Authority with the largest U.K. network, (some 12900 km) and having reputedly one of the strictest Street Works regimes in England; Devon County Council have been very receptive to the use of SMR Soil Stabiliser by Utility Companies since its introduction in late 1999.
Initial trials were carried out by John Kennedy (Civil Eng) Ltd, (now Balfour Beatty Utility Solutions Ltd) on behalf of South West Water and under strict monitoring by Devon County Materials Laboratory. The trials encompassed numerous laboratories and field tests including C.B.R. and compressive strength testing, frost heave susceptibility tests and air void testing of wearing course applied onto SMR reinstatements. In all of the tests carried out, the SMR bound reinstatements were proven to outperform control reinstatements using Type 1 GSB.
Following these trials, permission was granted to South West Water for use of SMR in footway reinstatements under clause S1.5 of the SROH, New Roads and Street Works Act 1991, (more commonly referred to as the HAUC spec).
Based on the success of SMR in use in footway reinstatements and further trials in carriageways, the approval to South West Water was extended in December 2000 to include reinstatements in Type 3&4 carriageway.
The approvals permit SMR treated spoil to be used as a replacement for traditional materials up to and including Road base levels. Under the revised SROH introduced in June 2002, performance criteria set down for alternative materials in Appendix A9 to be used at these levels deem the material to be classified as an NFSMR (non flow able structural material for reinstatement).
To date, SMR has been used by South West Water on over 100,000 reinstatements within the footways and carriageways of Devon, without a single failure or recorded defect.
The fact that use of SMR mixed with excavated spoil eliminates the need for imported backfill material and eliminates the need to remove spoil to landfill since it is re-used, it means that the following environmental benefits have been realised.
- Approx 150,000 Tonnes of Landfill Capacity have been preserved.
- Approx 150,000 Tonnes of Primary Aggregate have been preserved.
- Approx 300,000 Tonnes of Material movements have been avoided, reducing both pollution and disruption to the road going public.
In addition to the substantial environmental benefits, both South West Water and Devon County Council are more than happy with the performance of the SMR reinstatements, since nearly 5 years and 100,000 completed reinstatements on, there is still to be a single reported failure. Zero failure means zero remedial works, means zero traffic disruption.
Major financial benefits are also achieved, typically a saving of £40.00 per cubic metre is enjoyed by Utility Companies using SMR when compared to traditional methods, and these savings, currently running at around £18,000,000 can be further increased should the Utility Co. adopt a 1st time – single visit – permanent reinstatement policy.
The successful use of SMR in the UK is not limited to Devon and South West Water, although both must be considered as pioneers in the adoption of this highly sustainable and environmentally ideal technique. SMR is currently approved for use by in excess of 130 Local Highway Authorities nationally and has been used, without a single reported failure, on over 500,000 reinstatements, saving close to a million tonnes of landfill capacity and a similar quantity of primary aggregate. As word spreads, and the success stories increase, breaking down the industry’s “traditional approach” and its inherent resistance to change, more and more Utility Companies, Civils Contractors, and Highway Authorities will adopt SMR as their first option on footway and carriageway reinstatements.
Current uses of SMR in the UK
With a proven record of success in trench fill reinstatements, the stabilising properties of SMR have transferred over very easily to general land stabilisation applications, including the improvement and strengthening of weak or unstable soils, and the recovery and encapsulation of contaminated soils, the drying out and re-engineering of troublesome clay, chalk and sulphate bearing soils.
Over the next few years, the quality and reliability consistently achieved by SMR stabilisation will establish this product as the first choice solution for ground stabilisation.