Stent laid the foundation for the station's 28.5M facelift and began piling in late September for main contractor Tolent Construction. The consulting engineer is Arup.
Bearing pressures on the underlying tunnels meant it was not possible for piling rigs to cross the tunnels. This required a low loader to move machines around the sensitive site. Plant positioning drawings were also needed for each pile.
The soils generally consisted of fill material overlying clays to rock head. But at two pile locations a 3m band of sand and gravels began at a 15m depth.
The foundations, designed for loads up to 40,000kN, are permanently cased down to below the invert level of the tunnels. Site workers pieced together full length cages (up to 37m long) for the piles that have up to 7m rock sockets. The job comprised seven piles at 750mm diameter and six at 1.2m.