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Piling ahead

Piling work on the M1 widening continues apace.

Advance geotechnical works planning has helped speed progress on the M1 widening scheme between junction 6a at the M25 and junction 10 at Luton.

This major and high profile Highways Agency scheme is being undertaken by a Balfour Beatty/Skanska joint venture, employing Atkins as designer supported by Gifford.

Following the initial award of the contract to Balfour Beatty/Skanska, an integrated contractor-consultant team was established.

Its major focus was on the geotechnics of the scheme, which crosses an area dominated by chalk mantled by flinty clay. The construction team concentrated on getting the most out of the collaboration between designers and contractors.

Piling is just about complete for the first section of the scheme. Planning for this work had to account for a tight construction programme, dominated by limited motorway lane possession periods and traffic management requirements.

When work began on the scheme design, the contractor established a working team comprising consultants Atkins and Gifford, the JV's construction managers, and piling subcontractors Stent and Skanska Cementation Foundations.

The team reviewed the ground conditions on a site by site basis, giving particular attention to the presence of groundwater.

Two types of pile were selected;continuous flight auger piles and open hole rotary bored piles.

A programme of advance preliminary pile testing was also carried out so that on site pile testing could be eliminated. Pile testing also made it possible to review the main works piling design as work progressed.

Eight preliminary pile tests have been carried out at depths of 11m to 18m. These showed that the skin friction in the chalk was better than expected.

Solution features are a regular characteristic of chalky ground, so a plan to tackle them had to be developed before piling got underway. This enabled the piling subcontractors to prepare longer piles for these sections of the project, using data from site investigations.

Solution features have been relatively infrequent and not caused significant delays.

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