GDL were approached by Robertson Construction Group to develop an earthworks strategy for the new Scapa Hospital in Kirkwall, with a key project objective to maximise the re-use of site-won excavated materials in the works.
Prior to engaging with GDL, the original intent was to dispose of unsuitable earthworks materials off-site to landfill and import replacement granular materials for use in the works. We proposed the use of soil modification for fill-drying proposes and to increase the strength characteristics of the site-won materials which would ultimately allow their re-use as an engineering material on-site.
Prior to site start samples were recovered for feasibility testing and our ground modelling team worked closely with the Robertson Construction team to arrive at the optimum design levels for the initial construction platform. Working with the clients appointed engineers AECOM an alternative specification was agreed for upfill under both the building, hardstanding and car parking areas.
Our team mobilised efficiently to the island and completed the works over a five week duration, our programme efficiencies and approach allowed for follow on trades to commence works after week two.
The total amount of re-engineered fill placed and re-compacted to a structural specification was 15,000m<sup>3</sup>. Considering the equitant replacement volume that would have to be imported this is equivalent to 3,000 heavy vehicle movements which were removed from the project.
Compared with just 10 bulk powder deliveries that were required under our approach, we delivered significant improvements to the overall environmental and road safety impact of this project.
When compared with the alternative dig and dump approach, our total package of works was in the order of 40% cheaper than the traditional method.
Fill material where re-compacted to 95% compaction less than 5% air voids. A stabilised capping replacement layer through car parking and hardstanding areas achieved CBR values in excess of 30%.
Our approach in providing a completely engineered platform means greater speed of production and cost savings for follow on works.
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