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Customer: Glasgow City Council
Value: £16.5 million
VHE were awarded Contract 1 as the Principal Contractor for the delivery of an ambitious design and build remediation scheme of a 50-hectare site.
Having previously carried out major remediation projects in Glasgow, such as the Commonwealth Games Athletes Village and successfully treating hexavalent chromium at Shawfield, this was yet another major success for VHE in the area.
Sighthill TRA aims to transform an existing residential and public open space into a new and improved development. The site, prior to its previous use, encompassed numerous industrial uses including chemical works, rail facilities, brickworks and engineering works.
VHE employed WYG as designer who met the requirement to implement earthworks while dealing with contaminant remediation, ground improvement and waste minimisation - all with consideration of the Masterplan (location of roads, structures, parks) integrated into the design and construction. The initial tender value of the contract was £10.79 million, however VHE identified value engineering and risk management potential that saw elements of Contract 2 (infrastructure works) be incorporated into Contract 1. These elements were relating to geo- environmental aspects. Rather than focus on the remediation elements in targeted areas VHE widened the scope to encompass all of the available site and utilised all the available material in its most economic and environmentally beneficial location to minimize waste overall, cross contamination potential and warranty issues.
With over 1,200,000m3 of material movements on the site the overall project benefited from a more seamless traceability and verification process. By negotiating an increased scope VHE saved the client time and money.
The site had been subject to upfilling with materials being deposited from the development of the M8 motorway, but more synonymously with Sighthill, waste from the former St Rollox Chemical works which produced nearly 1 million cubic metres of a by-product termed galligu. Galligu is manmade and does not conform to any classification (geo-technically or chemically) as it is variable in nature, colour, properties and composition as the process from which it came was developed over time and was not consistent.
The identification of galligu was fundamental to the successful remediation as this material could impact on ground water and potentially generate hydrogen sulphide gas. A major consideration throughout the project was the management and reduction of odours associated with H2S.
Due to varying periods of development, which included parkland and residential development, the conceptual model was extremely complex with material having been historically imported, relocated, mixed and exposed to different elements over time. The solution was to develop a strategy allowing different materials to be placed in different locations both on plan and in elevation. In some cases, these materials were treated to allow them to meet criteria. This required a significant pre-classification exercise with extensive planning, materials management, tracking and verification.
VHE introduced and employed combinations of techniques to maximise the reuse of materials on site through recovery and revival dealing with, above others, a material that is unique to the location and history of the site. This was undertaken around two primary schools and a recently completed housing development while accommodating other separate contracts through giving access, temporary possession and phased handover. All of this occurred without a reportable accident in over 250,000 man-hours and less than 20 complaints, most of which could be classed as inquiries.
To achieve the standard required by this transformation VHE undertook a pre-classification exercise involving nearly 400 trial pits and over 1,000 samples. A further 3,000 samples were tested chemically with more than 5,000 geotechnical tests undertaken. With historic odours being an issue and with the proximity of the schools, residents and adjacent businesses environmental management and monitoring were huge undertakings with over 10,000 readings taken for hydrogen sulphide in addition to dust, noise and vibration.
VHE installed 70 post works monitoring boreholes (gas and groundworks) and will be carrying out 2 years of post-works monitoring. VHE also treated and buried Japanese Knotweed and carried out grouting of historical mine drains.
The bespoke nature of galligu resulted in huge risk to the project but VHE’s resourcefulness, experience in ground modeling and maximising material capability developed a solution to manage the materials in order of hierarchy. Managing the most critical material resulted in the generation of unsuitable material from a former tip which VHE put together and executed a process of material recovery maximising its value, suitability and benefit of reuse.
Complex segregation using non-conventional plant, mechanical product selection, hand picking and sorting, rescreening crushing and treatment by stabilisation with reuse as biomass and recycled metals resulted in 99% recovery against a zero waste ideal. The overall solution to encapsulate the galligu in-situ using a slurry wall, which was up to 20 metres in depth and created using a 135 tonne long reach excavator, with 120,000m2 geocomposite clay liner avoided the removal of 700,000m3 of material. The discovery of additional previously unidentified galligu was managed on site to avoid any disposal with the management of over 1,200,000m3 material movements.
With the majority of the works self-delivered by VHE, including all the treatment processes, VHE were able to react to inevitable changes in what was encountered applying the most suitable treatment method for the material to optimise its end use. VHE’s approach meant that all material was classified, managed, placed and tracked with the maximum utilisation and benefit for the future works.
VHE worked closely with regulators throughout the project to develop acceptable solutions to issues as they arose and with the client in terms of their expectations for future development. VHE had to consider cultural heritage management and mitigation in terms of archaeology and historical stone circles that would be reincorporated into the final development and ecology matters also required significant stakeholder co-ordination.