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Motorway roadworks | BUILDING MAGAZINE

Motorway roadworks

Closing one of the busiest motorway junctions on the network for routine maintenance isn’t something you undertake lightly. Therefore, wherever possible the work will be done in phases in order to keep at least one lane clear so that traffic can continue to flow albeit slowly. However, meticulous planning and the careful choice of materials have vastly improved the speed and efficiency of maintenance on the motorway network.

Even so, temporary lane closures are not popular with anybody, every driver knows the aggravation caused when coned-off bottlenecks slow traffic flow for weeks on end, and every road maintenance worker will appreciate the danger of working in close proximity to live traffic.

This looked likely to be the situation at the M3-M25 interchange when it became necessary to begin replacing several expansion joints, a couple of years ago. Expansion joints span the entire carriageway so there is little scope for reducing traffic disruption, nevertheless Jackson Civil Engineer, the framework contractor responsible for the works, had a plan.

Rather than carry out the joint replacements in phases, Jacksons decided that if it closed the carriageway completely and worked round the clock, it could replace each joint in a single weekend. This, of course, would mean diverting traffic, but only for a relatively short period of time when the junction was a its least busy.

Jackson calculated that doing it this way meant not only that lane closures could be flagged for road users well in advance, but they could also be reduced by more than 90%. Safety would be improved immensely because workers would spend less time on the road and avoid proximity to live traffic.

The main challenge however, was the meticulous planning necessary to ensure snag-free execution of the works. Jackson planned what became known as the ‘weekend wonder shifts’ to run from 10pm on Friday evening to 5am the following Monday.

The work, which has recently been completed, saw six teams working in relays around the clock for 55 hours straight. Doing it in one hit meant also that there were none of the delays associated with conventional working patterns because there was no need to mobilise and demobilise the sites between shifts.

“Working in shifts is not new of course” says Jacksons framework manager Ryan Smith, “but it’s never been explored in this way on the M25”. Generally speaking, work cannot be done outside of permitted hours and Highways England’s payment mechanism (‘paymech’ for short) imposes hefty charges should this happen. Cramming such an ambitious operation into a narrow 55 hour window has never been attempted before.

“Previously we’d have installed a complex temporary works system using metal plates acting like individual drawbridges so that we could work under them in sequence. That method was an innovation in itself, says Smith, but it still drags the joint replacement operation out over an extended period. This is much quicker and safer”.

Smith explained that the key to making the ‘weekend wonder’shifts’ work within the 55 hour timescale was the concrete mix employed. Jackson’s concrete supplier, Axtel, had previously worked with the contractor to perfect a rapid-strength mix for pavement quality concrete (PQC) bay replacements on sections of the road that are paved with concrete rather than blacktop.

Smith says that Jackson realised it could use that same concrete mix- slightly ‘tweaked’ for the application – on joint replacements. Whereas a standard concrete mix for this type of work would take 21 days to cure properly, Axtel’s rapid cure mix can reach the required strength in ‘six to eight hours’.

While the rapid-cure concrete made the job possible, the challenge of planning and executing the ‘weekend wonder-shifts’ remained. Jackson organised the work into six consecutive shifts working back-to-back continuously over the weekend. Not only did the contractor have to ensure that each change-over happened smoothly and without undue delay, but also it had to ensure that its suppliers could deliver on time and without any difficulties.

The work was planned literally minute-by-minute says Smith, with numerous contingencies and escalations allowed for and strategic hold-points built into the programme. “It was like a military operation” he says, “We had to be able to give Highways England an assurance that everything was going to complete on time”.

The first two joint replacements were completed towards the end of 2019 and Jackson replaced two more identical joints at the same junction in November and December 2020.

“Productivity during the ‘weekend wonder-shifts’ is exceptionally high as they give us the opportunity to get the bulk of the removal and replacement of the joint done in one go. “It has been a real win for our client”.

Adopting the ‘weekend wonder-shifts’ allowed the contractor to deliver the schemes for just 30% of their predicted cost and with only 10% of the man-hours originally envisaged. Jackson estimates that the new method cut around three months from the project programme.

Road users also benefited hugely. “Essentially the traditional method would require approximately 160 road closures whereas the new method took around 12 closures give or take a few”. The closures were over a shorter period and so were less impactful than over a four-month period per joint”.

So impressed was Connect Plus with the success of this new method that it has changed its joint replacement strategy for the remainder of the contract. Besides the cost reductions and efficiency gains, the use of ‘weekend wonder-shifts’ improved safety, with workers spending less time on the road. In fact Jackson says that no incursions or safety observations relating to traffic management were reported on this job.

Other benefits have included environmental gains, with a reduction in the use of materials including asphalt, concrete and steel bolts, and an estimated 60 tonnes of CO2 being saved across the project.

Jackson Civil Engineering has shared its knowledge with other supply chain partners and areas beyond Highways England’s Area 5.