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Ground investigation
Geotechnical consultancy
Contaminated land assessment

Ground investigation of suspected contaminated land for residential development

April 7, 2022
by GEA

Case Study: Barlby Road Residential Development, W10

Architects: Stiff+Trevillion
Engineers: Conisbee
Client: Royal Borough of Kensington and Chelsea
Location: North Kensington, London
Sector: Residential
GEA Engineer: Alex Taylor, Senior Geotechnical Engineer
GEA services: Ground investigation; Contaminated land assessment; Reporting

The site and its requirements

The Royal Borough of Kensington and Chelsea’s New Homes Delivery Programme identified an area on Barlby Road as a potential location for the development of new homes for the borough.

Due to being located adjacent to a site that was formerly home to an old print works, it was suspected the residential development site contained some contamination. Prior to the submission of planning applications, GEA was contracted to conduct rigorous contaminated land assessments to prove the site would be suitable for its proposed use and inform any potential remediation works, as well as carry out comprehensive ground investigation works to advise the design of the new buildings.

The investigations

GEA began an initial phase of investigation in December 2020. Due to site access involving a steep slope, a demountable rig was used to drill three cable percussive boreholes. In situ Standard Penetration Tests (SPTs) were performed to determine the density of the soil. Samples of undisturbed clay were also taken, for subsequent strength testing in the laboratory, and a series of smaller boreholes drilled to install standpipes to facilitate future gas and groundwater monitoring and sampling, and to achieve greater coverage of the site with respect to investigating the potential presence of contamination.  

Although the risk associated with contamination was thought to be minimal, the Royal Borough of Kensington and Chelsea required thorough contamination testing and reporting. Additional tests for groundwater quality, soil vapour and ground gases were carried out to satisfy this requirement.

The development will include an indoor sports facility, housed by the single level basement of one of the new residential blocks. Located along the western boundary of the site, the basement excavation will take place in close proximity to existing Thames Water mains. Basement and watermain assessments also, therefore, comprised part of the brief to GEA, to inform the rerouting of these watermains which will take place prior to excavation, and the impact of ground movements resulting from the basement construction on the rerouted water main.  

Findings inform the design process

The comprehensive site investigations provide the client and engineers with the information they require with respect to the proposed residential development. The results gathered from the cable percussive boreholes have been used in the design of the piled foundations for the new buildings and the retaining walls for the basement, and the contamination assessments to determine the specification for ground gas protection.

The investigations evidenced that contamination levels are low and pose minimal risk. However, a gas resistant membrane within each of the buildings will be installed to protect against radon and ground gas ingress in accordance with the council’s requirements. A cover system in areas of soft landscaping will also be installed, with new, clean material being brought to site and laid in a thickness of 600 mm to provide a barrier between end users and any potential contaminated soil.

What’s next?

As site investigations come to an end, GEA is submitting a remediation method statement to the contaminated land team at the council. This is the final report required before construction can begin.  On completion of the remediation work, GEA will provide a verification report to confirm that the work has been carried out in accordance with the method statement, allowing the final planning condition to be discharged.

Construction is scheduled to start in the summer of 2022 and complete in mid-2024. When completed, the new residential development at Barlby Road will comprise four new residential buildings providing 83 new homes, a sports facility and a NHS dental practice extension, built around a central community garden. 

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