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University college challenge

Bringing US-style cancer care to UK patients has prompted Cementation Skanska to employ some cutting edge technology at a crowded central London site.

London’s University College Hospital (UCH), located east of Tottenham Court Road and to the south of Euston Road, has been expanding over the last decade into what will become Europe’s largest bio-medical university/hospital campus, combining leading edge medical research and patient care.

The latest addition, the new ambulatory cancer centre, will be the first of its kind outside of the US, when it opens in early 2012.

Minipiles are needed for about a quarter of the wall’s length where its centre line is only 600mm from the adjacent Rayne Institute

University College London Hospitals NHS Foundation Trust (UCLH), of which UCH is a part, has for a number of years been researching why cancer patients in the US seem to survive for longer than those in the UK. One of the main reasons, it concludes, is the existence of purpose-built cancer centres that focus on the personal needs of patients with different types of cancer.

As Sir Robert Naylor, UCLH chief executive, commented on launching the project in November 2008: “Treating elderly lung-cancer patients is quite different to treating teenagers with leukaemia. We plan to bring the best of US-style cancer care to London by building a centre where each floor is designed around the needs of patients with different cancers.”

The approach is completely new to the UK; the centre will provide patients, families and carers with educational, social, psychological and complementary therapy support alongside clinical treatment, with the main focus on day care and outpatient treatment.

Retaining wall

That is for the future; right now excavation at the Huntley Street site (formerly occupied by part of the original Elizabeth Garrett Anderson and Obstetric Hospital, - a similarly revolutionary institution in its day) is exposing the perimeter retaining wall of the two-level basement. The 70m by 30m rectangular box structure is formed by a combination of 1,200mm diameter rotary bored secant piles and 450mm diameter secant mini piles. All piles are constructed using recycled aggregate and reinforcement, part of the design team’s bid for a BREEAM excellent sustainability rating.

The minipiles are needed for about a quarter of the wall’s length where its centre line is only 600mm from the adjacent Rayne Institute. Foundation contractor Cementation Skanska started a three-month piling programme in November last year. All work was carried out from what was previously the single level basement of an earlier structure to occupy the site.

The site is underlain by the variable Lambeth Group, rather than its more ubiquitous cousin, the London Clay. With the potential for high permeability layers, consultant Arup specified the interlocking secant pile arrangement to minimise water inflow into the basement excavation.

Risk of groundwater inundation also meant many piles were fully cased during their construction, keeping bores dry and stable. This required casing depths of up to 20m for the 1200mm diameter piles and 13m for the minipiles.

To all intents and purposes the building load is carried entirely by the basement’s perimeter wall

Tight construction tolerances were very much order of the day during the piling. A particular challenge of the job, says Skanska’s bid leader project manager Zoë Baldwin, was the need to install King posts in alternate 1200mm diameter piles as the primary support for the original basement structure during the excavation phase.

Equally with an excavation depth of 8m in front of the minipile wall - that is 8m below the original basement level - great accuracy was required to ensure the piles correctly interlocked for the wall to be watertight.
Another challenge was creating 1400mm tall “box-outs” in many of the large diameter piles. This relatively novel approach involves incorporating polystyrene blocks within the pile reinforcing cage, creating voids in the pile concrete. This enables the structural steel fitters to access the pile reinforcement bars without having to break out the pile concrete.

In this case the design required Skanska’s biggest box-outs to date, as there is an unusually big shear connection into the wall.

This is because the perimeter retaining wall is also providing virtually all of the load capacity for the six-storey superstructure, designed by architectural firm Hopkins.

Bored piles

In fact there are four 1200mm diameter load bearing bored piles within the building, located just inside the minipile wall. These are needed because the minipiles could not support the required bearing loads, but to all intents and purposes the building load is carried entirely by the basement’s perimeter wall.

Cementation Skanska completed the pile installation in 13 weeks, despite having to work alongside the demolition works at the start of the contract. This, says Baldwin, required up to four rigs on the cramped site simultaneously and very detailed daily planning meetings were needed to ensure the foundations were executed safely.

The piled retaining wall is currently exposed to its full depth over about half of the site area. Given the proximity to existing buildings the wall is being closely monitored for movement during the bulk dig.
In addition to standard inclinometer measurements, the inclinometer tubes are fitted with fibre optic cables, and

Cementation is working with researchers from University of Cambridge to calibrate the fibre optic strain measurements against conventional measurements.

A key advantage is fibre optic sensing provides a continuous strain profile with depth and has the potential to be highly cost effective.

What is going on underground at this compact urban site is, it seems, every bit as innovative as the cutting-edge cancer treatment soon to commence in the building above.

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