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The safety angle

Extensive piling for a managed motorways scheme on the M1 is well under way, with safety considerations to the fore. NCE reports.

Geotechnical specialists Bachy Soletanche and Carillion Piling are currently working on an £18M geotechnical contract as part of the M1 junction 10 (Luton) to junction 13 (near Milton Keynes) managed motorways with hard shoulder running scheme. The work is being carried out for main contractor Costain Carillion joint venture whose client is the Highways Agency.

The piling and soil nailing works are to facilitate the conversion of the existing hard shoulder to a peak time running lane, as well as improvements at junctions 11 and 12, installation of improved sign gantries and construction of emergency refuges, over its 25km length.

Design by Costain Carillion’s consultant URS Scott Wilson allows the work to be carried out without the need for additional land take. The work is phased between the three junctions on only one carriageway at a time to minimise traffic disruption while keeping the workforce safe.

Piling and soil nailing

Piling and soil nailing works are due to last up to 90 weeks. The project involves inserting 250 continuous flight auger (CFA) piles of 750mm diameter and up to 20m long, with vibrated full length reinforcement cages to support gantries. A further 1,600 CFA piles of 750mm diameter will be inserted for contiguous bored pile walls up to 11m long in the emergency refuges, and 22,000 hollow stem and solid bar soil nails between 5m and 12m long will also be used to stabilise the new cuttings and embankments.

The embankments are made up of a variety of fill materials, and the cutting slopes are generally within clay with flints over chalk. The clay with flints layer is up to 5m deep and is thought to have originated from prolonged weathering of outcrops of the Woolwich and Reading beds, while the chalk formation occurs as upper chalk, middle chalk, grey chalk and chalk marl along the length of the route.

Safety considerations have been paramount as work takes place close to live traffic and overhead power lines. As a result the Bachy Soletanche and Carillion Piling JV has used guarded soil nail rigs with innovative safer operator platforms, improved guarding and auger cleaning for CFA piling, rope access systems for work on the slopes, mobile grouting trailers, a new anti erosion Geoweb securing system, and most recently a combined mobile grout powder silo, grout mixer and pumping unit that minimises dust, manual handling and packaging waste.

CFA piles

The CFA piling and soil nailing works have been successfully completed to programme, on both carriageways between junction 10 and junction 11 northbound, junctions 12 and 13 northbound and most recently between junctions 10 and 11 southbound.

Geotechnical works are due to begin this month on the southbound carriageway between junctions 12 and 13.

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