In another large project, this time in England, the Pennine Group has been inserting more than 50,000 linear metres of stone columns at a 30ha site in Kettering, Northamptonshire.
The £600,000 project, for a food distribution depot for William Morrison Supermarkets, is on a steep site over a backfilled opencast ironstone quarry.
Carillion is the main contractor for the 80,000m 2 composite clad steel portal frame structure.
Site investigations found fill of varying composition, consistency and compaction at depths of up to 8m. Ground improvement design incorporated a lime stabilised reinforced soil raft.
Pennine contracts engineer Ralph Cook says: 'Very tight total and differential settlements were specified by the client's engineers.
The site sloped north east to south west with elevation changes of up to 10m, so a major cut and fill exercise was necessary to level it. Also, a final floor level was selected to ensure no material needed to be carted away.
'The western part of the site contained up to 8m fill, whereas to the east, outside the quarry, bedrock occurred at depths of less than a metre, ' Cook says. 'This posed more problems associated with differential settlements, with soils outside the quarry relatively incompressible and those within being variably compressible.' Pennine used stone columns to the full depth of the made ground with column spacing varying according to structural loads and settlement criteria.
Ground work was completed this spring and the main job is due to finish in August.