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Dynamic Compaction Rig in operation at Project True North site, Sheffield

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Consulting engineers Burke Green were

designing a new print works on the site of the

former wire works at Tinsley, close to the M1 in

Sheffield. The development, known as Project

True North, with a building footprint of some

55,660 m2required floor slab loads from 60 to

150kN/m2 and stanchion base loads of

175kN/m2. The site had been filled with

between 3.5 and 10.5 metres of colliery spoil

prior to the previous development some 20years before.

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Working as a sub-contractor to UK GSE Ltd

Pennine designed and carried out a dynamic

compaction solution to provide the required

bearing capacities. The method consists of

dropping a large weight on individual positions

(or footprints) on a grid pattern, the footprints

are filled and subsequent treatment passes

carried out. Design criteria were established by

comparing predicted and actual ground

response measured by heave tests; load tests

demonstrate overall effect. The deepest areas of

fill were treated with two passes of a 10 tonne

weight falling 15 metres on a 7.5 metre grid,

this was followed by two passes of 8 tonnes

falling 15 metres on a 5 metre grid. Where fill

was less deep the treatment was similar but

omitted the first two passes. A final tampingpass of 2 tonnes falling 5 metres completed the

sequence.

The design and performance was verified by 10

heave tests, 50 plate tests, 2 dummy footing

tests, 2 zone tests and 20 post-treatment CPT

tests. The 150,000 lump sum design and

construct package was completed in a 10 week

period during the summer of 2004.