Page 6 - Deep Basements Project Examples

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Deep Basements - Example Projects

Subsea 7 Office HQ, Sutton, Surrey Services
Robust Monitoring Approach Keeps Network Rail Ÿ Site investigation
on Track
Ÿ Temporary Works Design
The project was for construction of a high-tech HQ office in
Ÿ Numerical and Ground Modelling
Sutton for offshore engineers Subsea 7. The £40m new
building has five storeys above ground plus a 20,000m³, Ÿ Observational Methods Approach
5m deep basement including a car park. Ÿ Monitoring of Network Rail Asset

Construction of the new building car park ramp had the The catalyst for these design changes was CGL's
potential to undermine the neighbouring Network Rail supplementary site investigation around the basement
South West (NRSW) line. Other critical constraints for the perimeter and CGL's focus on understanding realistic
basement included the need for temporary retaining geotechnical design parameters, hydrology and predicted
works to provide working space and to protect sensitive ground movement modelling in structured chalk.
fuel storage tanks, existing trees, neighbouring buildings,
highways and sewers. The main achievement of the project was delivery of a
substantial basement alongside the railway that involved
CGL partnered with Galliford Try (GT) as geotechnical only minimal temporary works on three sides with none at
Temporary Works Engineer and CGL also advised GT on the NR boundary, which benefitted from observational
ground movements. methods backed by robust monitoring.

Liaison with NRSW was undertaken by CGL which CGL used ground modelling software including WALLAP,
identified the need for specifically targeted supplementary GWALL, FLAC Slope and PDISP to justify the proposed
site investigation, slope stability analysis, temporary works scheme and efficiencies in both temporary and permanent
design and exemplary multi-hierarchy protocols for works.
monitoring and trigger level action and contingency
planning. The robust monitoring scheme paid dividends in providing
reliable data to justify efficiencies in design. An example of
Following successes using Observational Methods in chalk this was the back analysis of King Post deflections to justify
for previous projects, a pragmatic approach was adopted early prop removal ahead of constructing the ground floor
for a cost saving combination of open cut excavation and slab.
King Posts with robust monitoring controls, as opposed to
a contiguous pile wall solution.

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