Centre stage at new London theatre
Leading geotechnical specialist Bachy Soletanche Limited (BSL) has provided the first exceptional performance at London’s latest theatre – providing the innovative piling and foundation solution to support a new theatre and residential development in Islington Green. The theatre itself will be situated below ground level, with an adjoining residential complex above ground that will include luxury apartments and town houses.
During a sixteen-week programme, BSL provided a comprehensive piling and foundation solution for both the theatre and the residential complex, incorporating a test-piling programme completed before full foundation works began. The £950,000 contract combined large-diameter auger (LDA) rotary piling and continuous-flight auger (CFA) piling for bearing piles and a secant basement wall project.
Simon Marshall, Contract Engineer, commented:
“We selected the LDA process over CFA for the ninety low cut-off and contiguous bearing piles – which ranged between 600mm and 900mm in diameter. The reason for this was that the LDA process provided a significant saving in concrete, and the KCA-100 rotary piling rig was capable of removing any obstructions we encountered during the pile probing.”
“The CFA process was used to construct a hard-firm secant basement wall comprising of four hundred and forty-eight piles; each with a diameter of 750mm and a depth of up to 20m.” He added.
A total of 4000m3 of concrete and 130 tonnes of reinforcement was used during the project, with reinforcement cages fixed on site due to the considerable cost saving when compared with pre-fabrication off-site.
With the unusual luxury of sole occupancy of the site, BSL was able to work unimpeded throughout the project, even completing the front end of the programme one week ahead of schedule. Due to this time-efficiency during the initial probing, guide-walling and foundation piling, the secant piling that was due to begin during week five of the programme was able to commence at the beginning of BSL’s fourth week on site.
Simon Marshall commented:
“From Bachy Soletanche’s point of view, the entire Rose Theatre project ran very smoothly indeed. We were a week ahead of schedule after the first four weeks of the programme, and we enjoyed a great spirit of mutual cooperation with both Tolent Construction and the follow-on contractor Knight Build Limited.”
“Indeed, it was together with Knight Build that our design team developed the ingenious and unusual propping detail used in the centre of the deepest basement.” He added.
This propping solution involved the construction of three temporary works CFA piles in the centre of the deepest basement, providing an innovative centrepiece for a project that itself is characterised by architectural ingenuity.
In order for the CFA secant wall to achieve the optimum properties, extensive laboratory and batch trials were organised in advance of the main works. The correct cement mix was essential to the success of the project, as without the correct mix the quality (verticality) and production of the male piles would be placed in jeopardy. The mix trials were conducted with the cement provider for the project, Hanson Premix.
Following the trial period, a C10 mix of eighty percent PFA (pulverised fuel ash) replacement mix with a total cement content of 240kg per cubic metre was selected for female piles; gaining strength at 0.5N/mm2 each day. The C35 male piles used a standard DC2-S4 mix with thirty percent PFA replacement. The typical construction cycle lasted six days, with two days spent on female piles, and four days on male piles.
These trials contributed to the overall time-efficiency of the project, which was completed two weeks ahead of the time quoted in the tender. At the production peak, BSL was constructing twelve female piles per day with an average length of 14m, and seven male piles with an average depth of 20m.
Confirming BSL’s position as best supporting act, there were no significant remedial works required, and the secant wall was totally compliant with the Whitby Bird Piling Specification with respect to water-ingress. Simon Marshall added:
“The Rose theatre programme has been a great success in terms of both efficiency and quality, and I’m sure I speak for the entire team when I say it’s been a privilege to work on such an interesting and innovative project.”