Bachy Soletanche adds levels to The Cube in Birmingham
Leading geotechnical specialist, Bachy Soletanche Limited (BSL) has recently completed piling works at the site of a planned iconic building, The Cube in Birmingham. The Cube will be the sister building of the Mailbox and is set to be a major new mixed use development including up-market apartments, retail outlets and the first roof-top restaurant to overlook the city.
The Cube has been designed by Ken Shuttleworth – one of the architects to contribute to the creation of the Gherkin in London – and is receiving a lot of interest with many of the apartments already sold. Once complete, the building will include 17 storeys and a five floor basement which has been designed to make the best use out of the premium 60 metres by 70 metres space.
BSL was awarded the £1.7 million piling works contract by BuildAbility to design and deliver a retaining wall. Working closely with the developers from an early stage in the project, a contiguous piled retaining wall was chosen to be installed around the perimeter of the site.
Steve Mallinson, contracts manager for Bachy Soletanche commented:
“We had many issues to consider in the design process due to the sites city centre location by the canal, its limited space and the buildings adjacent to the east and west sides of the site. We worked closely with the project team to provide a solution which satisfied all parties”.
Using the large diameter auger (LDA) piling technique, BSL installed 226, 900 mm diameter piles at 1050 mm spacings. These were drilled up to a depth of 24 metres. In order to carry out the process successfully, BSL skipped three piles – after installing the first pile – to avoid concrete flowing into the next borehole and therefore damaging the original pile.
However, when piling works commenced, BSL came across an unexpected problem of groundwater as Steve continued:
“We encountered up to 6metres of groundwater when boring out the 24 metre piles. As a result, we had to re-evaluate our methods of pouring the concrete into the bored pile.”
This required the use of a Tremie pipe which was put inside the reinforcement cage down to the toe of the pile. Concrete was then poured through the pipe and gradually lifted out as the concrete filled the pile.
“By filling the borehole from the base up, the groundwater is displaced to the top of the cast concrete.” Steve added.
Included in the design is a car lift in the southwest corner of the site. With space being at a premium, BSL replaced the LDA piles in this area with 24, 273 mm diameter minipiles bored to a depth of 24 metres. Another 54 minipiles were used to the west of the site alongside the LDA piles which were drilled to a depth of 12 metres in order to add further support to the adjacent building.
Finally, BSL constructed 30 king post piles to provide foundation for a ramp which is required for future building works. Each king post pile was formed in a 900 mm diameter pile, with a 400 mm square steel column concreted into the toe of the pile. These piles run in two parallel rows down the centre of the site.
With all the initial piling works complete, the site has been excavated exposing the piles between 14 metres and 19 metres to create a new ground level. BSL returned to the site after the excavation to construct 12 temporary anchors to hold back the retaining piles on the east side of the site.
BSL completed the piling project at the end of 2007.