Cardinal Pole Catholic School has approximately 1,006 pupils aged between 11 and 19. Our work helped to unify the school on a single site, for the first time in its history. We overcame significant engineering challenges to build the new school: the twin bore Channel Tunnel Rail Link lies approximately 25 metres below the site, which a concrete retaining wall divides into two levels.

A colour works, and a paint and varnish factory previously occupied the lower level; where we placed the school building. As a result, there were unsafe levels of contamination, including heavy metals. A thick layer of impermeable clay separates the contamination from the London Basin Aquifer, which underlies the area.

To eliminate the cost of removing the contaminated material from site and keep the loads on the tunnel within permissible limits, we designed a steel frame with lightweight concrete floors for the new building. Due to the contamination, we selected piles as the best foundation solution, to minimise the amount of material to be exported. As the piles would penetrate the clay layer, the Environment Agency were concerned that this could pollute the aquifer with contaminated groundwater. To prevent this, we selected small diameter continuous flight augured piles, with concrete pumped under pressure at the same time as the pile is bored, as the lowest risk solution.

To avoid damage and enable a favourable spread of load down to the tunnel, we designed the piling to end well above the tunnels. The depth of the tunnels varies across the site and we carefully considered the interaction between the foundations and the tunnels and modelled the effects on the tunnels with finite element analysis.

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