Barrett Byrd Associates

Challenging ground conditions have led to use of highly durable foundation piles to support a heavily loaded extension to Europe’s largest radiator factory. Mike Walter reports

Increasing demand for new heating systems from house builders in eastern Europe has helped to drive forward development of a huge new warehouse at the Quinn Radiators site in Newport, south Wales. Up to half a million completed radiators with a combined weight in excess of 40,000t will be stored in the new 40m high warehouse, under construction on a tight footprint between two existing industrial units.

Accommodating such a large load on relatively soft Mercia mudstone has called for installation of a durable foundation system. Engineers from Roger Bullivant Ltd (RBL) were asked to design a piling solution that would pick up point loads from columns supporting the building and underpin a reinforced floor slab on which the warehouse would sit. Poor ground and the huge weight of the structure meant that each pile had to accommodate a large compression load of 1050kN.

The chosen foundation design features a uniform grid of 574 piles, each of which extends to 13m beneath the ground, and piles are created using a 600mm diameter continuous flight auger.

Each pile position is being bored using a powerful 7001 rig with a high torque motor, augering through made ground and an upper layer of sand and gravel, before cutting through 10m of weathered Mercia mudstone. At full depth, the auger is retracted and concrete pumped through a central shaft to draw concrete through the profile formed by the auger’s flight. Reinforcing cages of six T16 steel bars inserted by hand to a depth of 5m are giving each pile added strength.

Creating foundation piles using a continuous flight auger was preferred to precast concrete piles on account of the high anticipated loadings of the new warehouse and the close proximity of nearby buildings.

“Precast foundations would not have been suitable for use beneath the proposed building because of the high compressive load of 1050kN on each pile,” says RBL engineer Jason Honour. “In addition, the difficulty of driving heavily loaded precast piles into Mercia mudstone is well documented, and could have led to excessive settlement of the piles.”

RBL chose to specify large pile diameters of 600mm to achieve the desired loadings without boring to excessive depths. Using slightly narrower diameter piles that extend further into the ground may have increased the risk of the auger refusing at shallow depths.

“We were initially concerned that the ground conditions on site were such that the auger would refuse to bore into the weathered Mercia mudstone. But using such a large auger and a powerful rig meant that we were able to power right through it,” adds Jason Honour.

Positions for piles to support the perimeter of the new industrial unit had to be designed as close as possible to the two existing buildings, to prevent pile loadings increasing further, says RBL’s operations manager Nick Jonathan. “We are working as close as 900mm to an existing building on one side of the site. Piles created using a continuous flight auger create no lateral displacement of earth, so fortunately there is no risk of damaging existing foundations.”

Continuous flight auger piles are being installed at 3.6m centres and rely on both end bearing and skin friction to accommodate the compressive load. Tension loadings will be taken out by the reinforced floor slab, which is to sit on top of cast in situ pile caps.

Static tests applied to two piles using kentledge blocks confirmed the foundation could cope with one and a half times working load. Settlement was found to be less than 4mm and well within specification.

Back