BBGE is delivering thefinal stages of complex foundations work to prepare for the construction of the first railway station to straddle the Thames in London as part of the Thameslink Programme.
The ground engineering specialist mobilised to site following the demolition of the existing buildings, and completed a programme of significant geotechnical works.
The team comprising of BBGE, main contractor Balfour Beatty Civil Engineering and customer Network Rail overcame a number of challenges including working adjacent to a live railway line and above a live Underground track in small constricted spaces.
Additionally, as the site had been developed many times in the past, there were a number of obstructions encountered during the piling work including old brickwork, reinforced concrete and existing concrete and timber piles. BBGE devised a number of solutions to allow the team to overcome these obstructions.
To overcome the restrictions of working in a confined space and above the live Underground track, a Track Protection Structure (TPS) and a temporary King Post Wall was installed by BBGE and placed above the London Underground tracks to ensure no disruption to existing services and to create a safe working environment. The installation of the King Post Wall allowed the piling platform to be raised to a single level, thereby providing the required safe working space for the large piling rigs without any undue load being exerted on the TPS.
With the TPS and King Post Wall in place for a safer site, a combination of over 700 large diameter secant wall and bearing piles ranging from 600mm to 1000mm in diameter and up to 39 metres deep, with only 6m of headroom in some instances, were constructed. Additionally, there were also self drilled micro piles of 187mm in diameter which were installed up to 18m deep with only 3m of headroom.
Due to the unforeseen obstructions and in order to mitigate delays to the overall programme, double shift working was required and carried out in accordance with Network Rail regulations and with approval from the relevant authorities. This was achieved through careful selection of equipment and techniques whilst maintaining strict control on the environmental impact.
These measures brought about the additional benefit of unrestricted engineering hours for the installation of the piles. Due to the varying obstructions encountered, modifications to tools and equipment were essential; as such, BBGE redesigned the configuration of their augers and casing cutting teeth which resulted in reduced equipment downtime as well as greater certainty of the coring time.
Peter Coulthart, BBGE project manager, said:
“The development of Blackfriars Station is one of the most complex construction projects being undertaken in London. We have worked very closely with Balfour Beatty Civil Engineering and Network Rail throughout the process and early involvement was key to developing the initial solutions right through to the current stage which is nearing completion.”
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