SIMPLEX FOUNDATIONS is installing 649 piles for the £58M phase one of the Blenheim Centre, a large redevelopment in Hounslow, Middlesex.
This phase consists of a 48,000m 2 public plaza, 334 apartments on eight floors above a 7,000m 2 supermarket, a medical centre, retail units and basement parking for 400 cars.
Simplex, working for main contractor and parent company Norwest Holst Construction under a £750,000 subcontract, arrived on site in early December. Its first task was to put in three preliminary test piles, two 600mm diameter and one 500mm diameter, designed with a safety factor of 2.
While workers tested these piles, main pile installation, designed using a factor of safety of 2.5, continued until Christmas. After satisfactory test results, the design was changed to a safety factor of 2.
The foundation contractor is using three main pile sizes for the project: 112, 750mm diameter; 352, 600mm diameter; and 185, 500mm diameter piles with depths ranging from 10-32m. All piles are being integrity tested. Six working test piles in a range of diameters and three tower crane base piles are also needed.
Simplex is installing the piles using rotary auger techniques with two Andes/5000 Watson rigs and a standby hydraulic Soilmec 312 piling rig.
It is also using an Andes service crane to install and extract casing and to install pile reinforcement cages. The temporary casing ranges from 3-9m in length.
The ground at the site has been excavated down 2m, leaving a further 3.5m of sand and gravels, with London Clay below.
Because a railway line runs past the site, Simplex has fi tted the rigs with jib arrestor ropes and slewing restraints.
Piling is due to fi nish at the end of this month.