Keltbray Piling were appointed by Ardmore Construction for the piling works at 257-259 City Road, London. The original scope of works comprised a cantilever contiguous pile wall and 900mm diameter bearing piles for the construction of a new 25 storey tower with double basement.
As a direct result of the Keltbray works at 151 City Road and after close inspection of the ground investigation report, we recommended the use of a partially propped secant piled wall to limit the horizontal deflection along the sensitive boundary with the deep lying LUL Northern Line. Also, to speed the basement excavation process and keep the internal space as free from temporary works as possible, Keltbray designed and installed a connecting contiguous piled buttress wall behind and perpendicular to the secant wall.
The 900mm diameter Continuous Flight Auger (CFA) secant piled wall was installed to a verticality of 1:75 with hard/firm piles spaced typically at 0.7m c/c.
Piles were designed in accordance with Eurocode 7 and during the installation of the secant wall a rotary bored rig was mobilised to site to install a 780mm diameter preliminary test pile. The test pile was instrumented with Brillouin Optical Time-Domain Reflectometry with support from Cambridge University as well as traditional strain gauges.
Unusually for the laminated bed lithogy of the Lambeth Group, the rotary bearing piles were bored dry and concreted within 30 minutes of exposing the base. This methodology was adopted for the test pile, which performed extremely well allowing all subsequent contract bearing piles to be installed at the reduced diameter of 780mm.
This reduction in diameter ensured increased bearing pile production rates allowing the overall piling programme to be completed on time and to budget.
- Client : Ardmore
- Location : London
- Value : £830,000