Extensive and intricate piling work for new lift shafts as part of tunnel works on a metro station upgrade at Shepherd’s Bush, London, has been completed by subcontractor Bachy Soletanche.

The piling contract, valued at more than US$2M, involved secant wall construction to sink two shafts during a five month job for main contractor Morgan Est. Some tunnelling work is to take place between the shafts on the site where the metro station continues to operate as normal. Details were not made available.

Bachy drilled 900mm diameter auger piles to a depth of 19m for the east shaft and 24m for the west. A total of 56 and 68 piles were placed for the east and west shafts, respectively. The subcontractor used large diameter piling (LDA) to achieve tight tolerances of one in 200 vertically, and 300mm cuts in female piles, which also needed to achieve concrete strength of 30N/mm2.

In addition, for each shaft there were 13 female piles with full length steel beams inserted for further strengthening as part of the preparation for follow-on tunnelling works, Bachy said in a statement. It added that tight tolerances for positioning were critical as the male piles had to be cut to full depth, leaving less than 50mm between casings and the beams.

While undertaking the secant piling, Bachy ran into problems with existing reinforced concrete piles at the east shaft area. The old piles were cored out to full 19m depth, the lengthy process done using kit already onsite to enable the works to continue where planned without design changes.

Shepherd’s Bush station is being upgraded with step free access and a larger ticket hall amongst other works. The modernisation will benefit the thousands who will visit the neighbouring retail and leisure complex being built to the north.

Late last year, Morgan EST won a US$63M contract to improve access and relieve pedestrian congestion at the station under its framework agreement with London Underground.

Bachy Soletanche hard at work constructing the secant walls to allow for future shaft sinking