Bachy Soletanche steps up the action at Shepherds Bush
Leading geotechnical specialist, Bachy Soletanche Limited, has completed a £1m+ piling contract at Shepherds Bush (Central Line) Underground station - constructing two shafts for step-free access from the underground platforms. The shafts were constructed for the redevelopment using the hard/firm secant wall piling method during a five month programme working for Morgan Est who is the Principal Contractor.
Shepherd’s Bush Central line is undergoing a major upgrade. It is expected that 60 per cent of people visiting the massive Westfield London retail and leisure development, which lies to the north of the Shepherd’s Bush site, will come by public transport. As a result, the project will help the station to accommodate the influx of people.
The project involves a number of redevelopments such as the remodelling of the ticket hall and step-free access created through the installation of lifts. New passageways and staircases will also increase the station’s capacity. In addition, the station will be modernised through the installation of upgraded security and information systems, and new ceiling, wall and floor surfaces.
The site is sandwiched between Shepherd’s Bush (Central Line) underground station, the bus station and the busy city centre roads, and Tom Stewart, Site Supervisor, at Bachy Soletanche explains the difficulties involved in the piling work:
“Careful co-ordination was essential to the smooth running of the project, as both sides of the site were tight and surrounded by traffic and pedestrians most of the working day.
The site consists of two sections - the east shaft and the west shaft - with the busy Shepherd’s Bush bus stand sandwiched between the two.”
The two shafts were constructed using the secant wall piling method, incorporating 900mm large diameter auger (LDA) piles, which were drilled to a depth of 19 metres for the east shaft, and 24 metres for the west shaft. As the west shaft was larger, sixty-eight piles were constructed compared to the fifty-six at the east shaft.
Tom Stewart commented
“Although the LDA process is more time consuming than other methods such as continuous flight auger (CFA) piling, the LDA process was utilised due to the accurate drilling tolerances required of better than 1 in 200 verticality, the 300mm cut on the female piles and the required concrete strength of 30n/mm2 in the female piles. Also, some of the tunnelling work could begin between the two shafts - meaning thirteen of the female piles from each shaft had full length steel beams inserted into the piles before concreting. the position of the beams gave little room for error as the male piles were cut full depth and with less than 50mm between the casings and the beams at surface level it was due to the skill and dedication of the piling team that they managed to drill all the piles.
The heavy duty rig has also helped the programme on the east shaft when work became hampered by existing reinforced concrete piles, which were discovered once drilling began. These piles had to be cored out to the new pile depth of 19 metres before Bachy Soletanche could progress and install the secant piles.
Tom Stewart added:
“Discovering the existing piles and having to stop works to core them out was a lengthy process, but as the heavy duty rig was already on site the coring process allowed the shaft to be installed in the original position without any design changes.
Aside from this minor obstacle, the project ran very smoothly with all works complete and the site cleared by the project deadline.”