PILING & FOUNDATIONS
The benefits of displacement piling are not restricted to contaminated land.On one greenfield project it has helped speed up the process and keep things tidy. Claire Symes reports.
Eye-catching modern offices and laboratories fill Abingdon’s 100ha Milton Park, sandwiched between the M4 and the M40 in Oxfordshire.
Developer MEPC has been investing in the site for more than 15 years and its 316,000m2 of space is still growing.
In the latest spurt, a 50,000m3 complex of small business blocks is shooting up using techniques that minimise the impact on nearby tenants. Construction manager Glanville Projects is aiming for ‘business as usual’ at the park.
Contractor Roger Bullivant has just completed piling using continuous helical displacement (CHD) piling to keep noise and vibration levels low and avoid the cost and mess of taking spoil off site.
Bullivant piling contracts manager Jim Bourke says: ‘CHD piling was initially developed for contaminated sites to reduce the risk and cost of disposing of spoil and minimise exposure of workers to potentially hazardous materials.
‘Milton Park is not a typical candidate for CHD piling because there is no soil contamination, Glanville Projects chose the technique because of its performance benefits. If ground conditions are right, and there are no concrete delivery hold-ups, we can install up to 100 CHD piles in a day, which is very quick.’
The main access road to the latest site is from the busy A34 and travels through the core of the business park. The client was keen to avoid disturbing the site’s neighbours with noise and vibration during construction.
‘Using displacement piling techniques has saved around 30 lorry loads of spoil being transported through the park, ’ says Glanville Projects director Bill Brown. ‘This has not only reduced landfill costs but removes the potential for material to be dropped on the road.’
Bullivant’s CHD technique uses a bullet ended hollow stem shaft with a 600mm diameter helical auger section that displaces spoil laterally instead of bringing it to the surface.
Once the stem has been augered to the required depth, concrete is pumped down the 300mm diameter hollow shaft and the stem withdrawn, rotating in the reverse direction to form a solid pile. After the concrete is in place steel reinforcement is installed.
At 127 Milton Park, Bullivant has installed 131 CHD piles, up to 13m deep, through 1m of fill to found in the underlying Gault Clay. The 500kN capacity piles have been built on a regular grid to support three buildings that will be split into small business units from 150m2 to 200m 2.’CHD piling is best suited to cohesive soils and the ground at Milton Park was near perfect for the technique, ’ Bourke says.
‘We managed to complete the piling work at the site in just three days.’
Choice of piling technique was not the only unusual aspect of the contract. Procurement was unconventional in that there was no main contractor for the development. Brown says this method benefits everyone involved.
‘Glanville Projects is acting as construction manager for MEPC Milton Park and all the design consultants and trade contractors are employed directly by the client.
‘We were responsible for fasttracking the design and procurement phases of the work, eventually overlapping the two, to give significant time savings on the overall project programme.’
Now piling has been completed, the groundworks contractor is building cast insitu ground beams. Steel work contractors will follow on to install the unit’s steel framework.
‘Selection of fast construction techniques for every phase has enabled us to speed up delivery of the scheme. The first tenants will be moving in this September- less than nine months after work began, ’ says Brown.