Project:  1-3 Grosvenor Square
Date: 10/04/2015 – 25/08/2015
Client: Lodha Developers Structural Engineer: AKT II Contract Value: £150,000
Awards: Shortlisted for Ground Investigation Project of the Year 2016

Overview of Deliverables

This corner plot is located in the prestigious Grosvenor Square in the heart of London and was until recently occupied by the Canadian High Commission. Lodha Developments propose to demolish the existing 5 storey, single basement steel framed building and construct a new eight storey building approximately 62m long by 44m wide, with three levels of basement below the majority of the site, extending to 21m bgl. The building is attached to the north to the building occupied by the Italian Embassy and to a masonry building to the east. The Jubilee Line tunnels run under the site at approximately 30m bgl.

Concept were appointed to provide geotechnical and environmental advice for the development to the Structural Engineers AKT II group. The deliverables of the project were:

• Phase 1 Geo-environmental Desk Study and basement impact assessment: review and identification of geotechnical and environmental risks to the geology, hydrology and urban development of the area; proposals for site investigations to provide information for the reduction/elimination of risks and to assist the design.

• Geotechnical and environmental Investigation: site works involving the drilling of 8 boreholes up to 30m deep to establish the ground conditions and trial pits; geotechnical and environmental sampling; ground water and gas installations and monitoring; geotechnical laboratory testing.

• Structural investigation and assessment: fabric survey of the steel structure; trial pits and coring to expose and establish the foundation details of the existing and adjacent buildings; in-situ and laboratory structural testing; structural assessment report.

• Phase 2 Environmental Interpretative report: determination of contamination risk and providing recommendation for the handling of the spoil from the development.

• Geotechnical Interpretative Report: Collation and review of the available information, recommendation of geotechnical parameters to be used in the design; preliminary assessment of ground movements and their effect on the adjacent buildings and infrastructure; recommendations and parameters for retaining wall and basement design; recommendations on appropriate methods of construction for the basement; recommendations for monitoring of adjacent buildings and infrastructure.

• Geotechnical support to the structural engineer during detailed design stage: detailed analysis of anticipated ground movements and soil-structure interaction; retaining wall analysis.

All works followed and adhered to the current standards and guidelines, EC7, BS5930, the UK framework for the assessment of contaminated land and Westminster’s Basement development guidelines.

Competencies

1-3 Grosvenor Place is situated in the heart of Mayfair and was a challenging and highly complex project which required careful coordination and the combination of a variety of skills to ensure its successful completion within the time frame and available budget. Concept’s combination of geotechnical, environmental and structural capabilities and considerable experience in ground and structural investigations enabled us to effectively advise the client on all aspects of the works. Our competencies demonstrated in this project included:

• Geotechnical Investigations
• Design of temporary works
• Underpinning advice
• Geotechnical design of foundations and retaining walls
• Advice on deep basements and excavations
• In-house ground Investigations in urban environment, above LU tunnels
• In-house UKAS accredited laboratory testing
• Assessment of soil movements
• Geotechnical interpretation and advice
• Geo-environmental assessment of contamination risks
• Environmental investigation

Numerical analysis required at detailed design stage will be provided by our experienced external consultants stated in the CV section. Landscape advice, topsoil and sediment assessment if required will be provided by our external consultant stated in the CV section.

Value added initiatives

The demolition and reconstruction of the deep basement in the heart of London above the running Jubilee line tunnels poses significant risks for the tunnels and surrounding infrastructure and buildings. The risks are associated with short term and long term ground movements as well as possible impact on the hydrology of the area, issues with dam effects and water ingress into the tunnels and adjoining properties and potential damage caused by the construction activities. Concept identified these risks at desk study stage and was able to effectively design the investigation and provide appropriate recommendations and design measures for their elimination.

Our considerable expertise both in geotechnical design as well as investigation enabled us to provide our client with a tailor made one stop service that encompassed all the investigation needs of the project as well as the geotechnical input required for the detailed design stage. This eliminated the need of appointing separate geotechnical consultants and contractors resulting in significant cost savings, and simplification of the logistics associated with the management of the investigation and design phases of the project.

Our significant urban experience allowed us to correctly identify the risks of the development and provide the most appropriate and economical advice to mitigate them.

Our knowledge of working in London Underground and TfL projects enabled us to provide the client with expert advice on the logistics of working within exclusion zones, adjacent to sensitive structures and infrastructure.

Locations

The investigation was carried out prior to the demolition of the existing building within its basement and congested surrounding areas. Careful consideration was given to the location of the boreholes so that they did not lie within the LU exclusion zone. The coring and exposure of the foundations of the adjoining buildings was expertly carried out to avoid any damage to the neighbouring properties. Close liaison with stakeholders was vital in achieving the investigation objectives whilst ensuring their cooperation.

Programme

10/04/2015 – 25/08/2015
The detailed design phase is on-going. Additional phases of investigation have been added to further clarify the design.

Recourses Utilised

The Project Director was Milan Dedic, MICE who has over 25 years’ experience in the geotechnical design and investigation and guided and reviewed the production of the interpretative reports and geotechnical design. The environmental assessment was overseen by our environmental consultant Christian Wilkinson, SiLC. The investigation was coordinated by our Ground Investigation Technical Director David Hammond who has over 25 years’ experience in complex ground investigations. All geotechnical testing was carried out by our in- house UKAS accredited laboratory.

The site work was project managed by Concept’s degree qualified Project Managers and was carried out by our in-house NVQ qualified experienced corers and drillers.

Percentage of sub consultants used

25% for the disciplines stated in the previous section.