THE SCHEME
Led by Hackney Borough Council, this mixed-use development programme included the expansion of New Regent’s College campus on Nile Street with the construction of a two-storey Pupil Referral Unit (PRU) school. This formed part of the Borough’s wider scheme to increase school spaces for local children. The development also featured a 29-storey residential tower and a seven-storey residential building, which have contributed £12m to Hackney council’s social housing regeneration budget. All three structures share a single storey basement and a central courtyard.
DESIGN AND PLANNING
Bachy Soletanche was appointed to design and build a secant wall to form the perimeter retaining wall, the bearing piles to support the new school building, the reinforcement for the residential tower settlement reducing piles (With geotechnical design by Pell Frischmann) and the temporary piles required to support the tower crane.
Bachy Soletanche began working closely with the main contractor, McLaren Construction, and the consulting engineer, Pell Frischmann, very early in the process, which enabled its in-house design team to offer its geotechnical expertise throughout the preconstruction phase. Bachy Soletanche’s design team continued to provide in-person technical support throughout the construction phase of Nile Street, which was greatly appreciated by the client and allowed them to achieve the various programmed piling start dates.
PILING OPERATIONS
Bachy Soletanche installed a total of 783 piles over a period of 45 days, operating a total of three rigs: the Soilmec R625, the Soilmec SF65 and the Liebherr LB24, which required the careful coordination and logistical planning of the team.
For the construction of the secant wall, the team opted for the continuous flight auger (CFA) technique to install the piles, which were designed in a Hard/Firm arrangement. The team first installed 347 primary piles that were then followed by 347 secondary piles. Each pile was 600mm in diameter and either 8m or 12m in depth.
Bachy Soletanche then installed 20 temporary piles to support the tower crane, 34 CFA bearing piles for the new school building and 35 LDA polymer piles for the reinforcement of the residential tower block. These piles ranged in diameter from 400mm to 900mm and were installed to depths ranging between 24m to 31m. During the ground investigation work, Bachy Soletanche suspected a layer of sand to be present in Lambeth Clay, which threatened to destabilise the pile boreholes when installing the deeper piles. However, by bringing in an on-site polymer plant, the team was able to quickly add in polymer support fluid when any unstable ground was encountered and thus mitigated any risk of pile destabilisation.
The early contractor involvement allowed Bachy Soletanche to develop a unified approach with all parties that ultimately led to the smooth and successful delivery of the contract, with all works completed on time and within budget.
The team received a result of 100% in its Client Satisfaction Survey in which it was commended for the design team’s contributions and for its highly experienced approach to the management and delivery of daily operations.
