Apex One

Ensuring safety, compliance, and efficiency for complex urban sites

Key Site Challenges

This development is situated directly above the newly extended Northern Line at Nine Elms, making it a highly complex engineering challenge. The proximity to major transport infrastructure required innovative structural solutions to ensure the stability of the building while minimising the impact on the tunnels below.

To the east, the site is bordered by a Network Rail viaduct, limiting construction access and design flexibility.

To the south, an access road further restricted site operations and logistics.
Directly beneath the site, two underground tunnels from the Northern Line extension added further complexities, requiring careful engineering to prevent excessive loading or structural impact.

Our Solution

To support the building while avoiding excessive loading on the tunnels, we designed a reinforced concrete grillage of transfer beams spanning across the tunnel exclusion zones at ground floor level. These beams varied in depth from 1m to 2.35m and were supported by 1.2m diameter, 50m deep rotary bored piles. This solution ensured that the load was transferred safely into strata located below the depth of the tunnels, thereby mitigating risk.

Basement Redesign:

At Stage 4, we redesigned the basement layout to sit alongside the tunnels rather than cantilevering over them, as was initially planned in the Stage 3 design. This redesign significantly reduced stress on the tunnels and lowered the overall construction cost. Working closely with the architects, we also relocated bike storage and plant rooms to accommodate the new basement layout.

Construction Monitoring:

Throughout the construction process, the tunnels were continuously monitored. This proactiveness helped de-risk the site and provided reassurance to stakeholders, including Network Rail and TfL.

Key Outcomes

Simplified Construction Process: The revised basement design allowed for more efficient construction, reducing complexity and associated costs.
Risk Mitigation: By avoiding direct loading on the tunnels and ensuring continuous monitoring, the project significantly reduced potential structural risks.
Strong Third Party Collaboration: We successfully coordinated with the necessary third parties, securing the approvals and maintaining good working relationships with Network Rail, TfL, and Thames Water.

Third-Party Approvals

Due to the constrained nature of the site, several third-party approvals were required before and during construction:

• Network Rail approval was obtained to ensure that the nearby rail viaduct and supporting infrastructure were not compromised.
• TfL approval was necessary to confirm that the design and construction methods would not negatively impact the Northern Line tunnels.
• Thames Water approval was secured to manage any potential effects on local utilities and drainage systems.