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Piling and soil nailing support massive M1 widening project

Work to convert hard shoulder to traffic lane is carried out next to live traffic.

Geotechnical specialists Bachy Soletanche and Carillion Pilling are currently on site for an £18M project to improve the M1 between junctions 10 and 13 for a Costain/Carillion joint venture.

The piling and soil nailing works will enable the conversion of the hard shoulder to a peak time running lane.

Other improvements include the erection of 60 improved sign gantries and emergency refuges over the 25km length of the scheme.

The design by the Highways Agency’s engineer, Parsons Brinckerhoff, and Costain/Carillion’s engineer, Scott Wilson, has eliminated the need for additional land take.

Phased work

The work is phased between the three junctions on one carriageway at a time to minimise traffic disruption and to comply with health and safety regulations.

The project is using 250 750mm diameter continuous flight auger (CFA) gantry piles up to 20m long, with vibrated full-length reinforcement cages. As well, 1,600 750mm diameter CFA piles will be used for the contiguous bored pile walls supporting the emergency refuges. The new cuttings and embankments will be stabilised with 22,000 hollow stem and solid bar soil nails.

The embankments are made up of a variety of fill materials, and the cutting slopes are generally within clay with flints over chalk.

Clay and flints

The clay with flints layer is up to 5m deep and is thought to have originated from prolonged in situ weathering of outcrops of the Woolwich and Reading beds. The chalk formation occurs as upper chalk, middle chalk, grey chalk and chalk marl along the length of the route.

High levels of safety have been paramount as work takes place close to traffic and overhead power lines.

This has led to a number of innovations by the joint venture, including the introduction of guarded soil nail rigs with a safe operator platform, improved guarding and auger cleaning for CFA piling, rope access systems, mobile grouting trailers, and a new Geoweb securing system.

These developments ensure work can be completed within the project’s 90-week time frame with minimised safety risks.

Piling and soil nailing works for the 90-week programme have recently been successfully completed on both carriageways between junctions 10 and 11 and have started between junctions 12 and 13 northbound.

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