Imperial College London

Secured under a JCT D&B contract, Careys is principal contractor and principal designer, coordinating all temporary and permanent works designs and delivering the full scope under a self-delivery model, with specialist subcontractors where required.

Extensive engagement with LUL was required for the installation of eight huge, braced pair steel beams over the Central Line to form new road and pedestrian access. We worked closely with LUL to enable the continued use of their transport services and works were part-delivered overnight to minimise disruption. Operatives holding LUL Sentinel certification were overseen by our designated rail interface manager.

A full-height hoarding segregated the works from the LUL assets and protected the existing services on a trackside retaining wall before piling works commenced. Permanent sheet-piled wing walls formed the bridge abutments, with bored piling to form the foundation. The slew radii, collapse radii and downrating of crane capacities all met LUL standards.

A full trigger level assessment and action plan was agreed for the piling works, with trackside monitoring stations on adjacent buildings and survey points on the retaining wall. The beam installation required a specialist crane and lifting team to position them to millimetre accuracy.

A significant feature of the works is the construction of a new highway which runs from the new bridge over the LUL lines into the development plot. The newly constructed carriageway was built following the installation of the new sheet piled retaining wall and incorporates new cycleways, crossing points and security features to control access.

Construction of the carriageway was phased to manage the access requirements of the university bus route, as well as servicing of the adjacent academic buildings. Significant utilities corridors incorporating HV, LV and DNO networks were constructed under and adjacent to the new access road, with Careys self-delivering the installation of all of these works including a new potable water network built under a self-lay agreement with Thames Water.

Construction of a new basement box within the footprint of the site and in proximity of the LUL Central Line was also a large feature of the project. With a footprint of circa 1,500m􀉜, the single storey basement was originally based on a contiguous pile wall comprising 900mm diameter piles. During the tender stage, our design team undertook detailed assessments of the ground conditions and water table, determining that a secant piled wall solution was more appropriate. To support this design change, carbon calculations were undertaken on the secant wall option to prove the embodied carbon levels were equal to those for the original design option.

The basement incorporates a 600mm thick slab, along with CFA piles, pile caps and columns to support a 850mm cover slab that will support the weight of 2m of landscaping fill above. Working with propping suppliers, we designed 'blister' upstands and enhancements to the capping beam to allow propping above the capping beam level to assist in the construction sequence of the finished cover slab.

Ground remediation entailed extensive onsite testing, selective excavation/reuse and treatment of asbestos soils at Careys’ onsite laboratory.

To meet the client’s reuse strategy, the bulk of excavated material and concrete was processed and returned for use on site as aggregate and 6F5. Our asbestos manager calculated an environmentally compliant and commercially efficient solution whereby 3088t of asbestos-, hydrocarbon- and metalimpacted soils were reused following treatment and retesting. In total, we reused 10,000t of soil and stones, with 17,000t of recyclate returned to site.

The measures to reduce nuisance and disruption for residents, businesses and campus users included:

• Selecting construction plant and methodologies with regard for minimising noise and vibration. Acoustic blankets used to prevent sound transfer and dust management also controlled by using dampening techniques and employing plant to capture dust at source.
  

• Noise, dust and vibration levels measured using automated sensors that provide real-time readings and alerts allowing us to respond to any breaches and employ corrective action.
  

• A Sustainability Advisor and Qualified Ecologist to ensure we are protecting the local environment.
  

• A robust traffic management plan. The existing Depot Road bridge remained open as usual and access for vehicles, pedestrians and cyclists remained, but with minor re-routing once on campus. These diversions were signposted.