Case Studies

Ground remediation and engineering never throws up two projects that are the same, with each having their own specific challenges and opportunities. At G&J we use the experience we have acquired over the years to inform future designs and to aid continual improvement, but we never assume the solution for the last project will be appropriate for the next. Below are just some of the diverse projects we have been a part of.

Former Nursery and Landfill, South-East England

It is often the small / medium sized sites that cause the greatest headaches! A former nursery site was the proposed location of a new residential development of approximately 45 dwellings. Initial investigations found a former landfill encroached onto part of the site, while elevated concentrations of lead were noted along with the presence of asbestos fibres.

Subsequent investigation works based on a 20m grid found that low-level asbestos contamination was essentially a feature of the Made Ground across the site (including that beneath the concrete slab), while high concentrations of methane and carbon dioxide were present within the landfill, which would potentially preclude development in this area.

Removal of asbestos impacted soil would have been prohibitively expensive, so a robust cover system was proposed to prevent exposure. This involved leaving the concrete slab in place (where present) and placing a no-dig layer of coarse aggregate beneath a 600mm cover of clean soil in garden areas.

A programme of continuous gas monitoring and subsequent detailed quantitative assessment of the gas risks demonstrated that development could proceed on the landfill with appropriate gas protection measures installed.

Agricultural Building Conversions, Midlands
In rural areas, many agricultural buildings such as barns and stables lie unused and / or in a poor state of repair. In many cases, such buildings can be revived through converting to residential use. Given their past use, planning conditions usually require land contamination surveys to be undertaken to ensure a safe development.

G&J have undertaken Phase I Desk Studies and Phase II Ground Investigations to satisfy planning requirements for many such developments across counties including Leicestershire, Northamptonshire, Lincolnshire and Warwickshire.

The most cost-effective option is often to combine a Phase I survey with an exploratory investigation, whereby a small number of near surface samples are taken at the same time as the site inspection. In our experience, this is usually sufficient to satisfy the Local Authority and avoids the additional expense of a separate Phase II investigation.

Former smokeless fuel and organic chemicals production facility, Derbyshire
A 50ha site heavily contaminated with organic chemicals, most notably phenolic compounds and aromatic hydrocarbons, presented numerous challenges from the potentially significant risks to human health and environmental receptors, to the mitigation of odours and the management of large quantities of excavated materials.

Using a large amount of pre-exisiting investigation data, supplemented by analysis of our own, G&J produced Detailed Quantitative Risk Assessments which formed the basis of the remedial targets that would be the benchmark for the remediation works.

G&J worked closely with the remediation contractor on a solution that combined ex-situ bioremediation, the use of odour control layers and the strict management of material movements. We provided overall supervision of the works and undertook all validation sampling, analysis and reporting. The eventual success of the project owed much to the robust verification works, the collection and presentation of the necessary data and regular meetings with the project team and the Local Planning Authority.

Remediation, Earthworks and Mine Treatment – West Midlands
A 13ha former industrial estate in the West Midlands presented an array of challenging ground conditions that would need to be overcome to provide a suitable residential development platform. Principal among these were the presence of around 50 mineshafts and underlying mine-workings, soils contaminated with chlorinated solvents and Made Ground up to 8m thick.

G&J were involved at all stages from Ground Investigation and Risk Assessment to the preparation of the Earthworks and Remediation Strategies, and the verification of the works. Close engagement with the Local Authority, NHBC and Coal Authority was key to a successful strategy involving complex risk assessments, ground improvement using a combination of Rolling Dynamic Compaction (RDC) and Rapid Impact Compaction (RIC), and the intensive investigation and treatment of mine-workings. The overall strategy provided a safe development platform suitable for traditional shallow foundations.

Small Residential Development, St Albans
Another example of a seemingly straight forward investigation on a small site being the source of disproportionately significant challenges!

A residential development of six semi-detached dwellings was proposed on land occupied by part of the rear gardens of three existing residential properties. The challenges began with access to the site, which was via a narrow gap to the side of the existing property, and was compounded by very soft, wet ground that provided very little traction for vehicles.

Initial investigations by a tracked window sample rig found variable, sometimes unstable, upper ground conditions, which included medium volume change potential soils, and due to the presence of trees this potentially meant foundations deeper than 2.5mbgl, and therefore a requirement for deeper boreholes.

Although access was a problem for larger rigs, there is always a solution, which is this case was a demountable percussion rig that was able to reach the required depths and provide the necessary information to design the final foundation solution.

Former MOD Fuel Depot, Gloucestershire
The development of a 6.5ha former fuel depot required a full range of geo-environmental and geotechnical services to make the site suitable for a residential development. These included a Phase 1 Desk Study and Preliminary Risk Assessment, Phase 2 Site Investigation, Earthworks Specification, Remediation Strategy, Supervision and Verification.

The site included four large redundant fuel tanks that were partially buried, being cut into the natural slope of the site. Cut and Fill earthworks were necessary to provide a suitably level development platform, while hydrocarbon contamination was present that required addressing through bioremediation to eliminate significant risks to human health and the environment.

In addition, a nearby landfill was considered to be potential source of ground gases, and a robust risk assessment and Conceptual Model was necessary in order to demonstrate that this not present a risk to the development.

Closed Landfill and Lagoon, West Midlands
A site with a particularly complex history, G&J were appointed to undertake a ground investigation on a closed landfill, which rises up to 25m above the surrounding ground and lies adjacent to a lagoon which was known to have been used for the disposal of chemical waste.

The site was formerly the location of a brickworks which resulted in deep excavations where clay had been extracted. The pits were backfilled over time with waste, which included foundry sand and other industrial and household wastes, during various phases of disposal. This was initially to ground level, but later deposition raised ground levels well above the surrounding areas. The lagoon was reportedly used for the disposal of calcium phosphate and white phosphorous by a nearby munitions manufacturer.

The purpose of the investigation works was to provide information to help explore potential redevelopment options for the site. This involved establishing the thickness and properties (chemical and geotechnical) of the fill materials, assessing the stability of the slopes and identifying the primary contamination risks in terms of soil and water contamination and the generation of ground gases.