UPGRADING M4 MOTORWAY BRIDGES

NEW BRIDGE INSTALLATION TECHNIQUES REDUCE POSESSION TIMES

We need to keep the road network moving. Highways England asked Balfour Beatty Vinci Joint Venture (BBV JV) and Cleveland Bridge to improve the M4 between Junction 3 at Hayes, Middlesex, and Junction 12 at Theale in Berkshire.

That stretch was a two-lane dual carriageway, which meant upgrading 11 bridges to make room for an extra lane. In addition, the bridge over the River Thames at Bray needed widening to support a new ‘smart’ motorway – but every effort had to be made to reduce disruption and delays for road users. On average, the M4 carries 130,000 vehicles per day.

We were delighted to play a key role in the project, helping to develop new installation techniques for some of those bridge replacements that reduced the all-important possession times.

EARLY CONTRACTOR INVOLVEMENT

The M4 is a major arterial route out of London and the main strategic route between London, the West of England and South Wales. This project included upgrades to ‘smart’ motorway, an additional lane for traffic, and technology to help smooth vehicle flows – many specialist contractors were involved.

Nigel Fletcher, our CEO: “We’re huge advocates for getting everyone round a table to talk about final installation plans, as early as possible in the project. Too often, logistics for transportation and installation are left late in the day – but with bridge-building and design expertise to hand, and our team’s logistics insights, we ensured value and mitigated the risks.”

REDUCING OVERALL POSSESSION TIME

To limit disruption, most of the new bridges were built next to the structures they were replacing. Access was restricted, with only so much space for temporary bridge assembly works. Precise planning of all follow-on trade work was essential.

For each bridge, girders were delivered in paired sections. These ranged in length from 15m to 36m, and weighed from 26t to 63t. Our team lifted them onto temporary stillages, so the splice connections could be bolted together. Once connected, we used our Self-Propelled Modular Transporters (SPMTs) to transport the fully paired girders to the bridge site. From there, they were craned into place with our LTM 1800D, a 1,000te mobile, fast-rigging telescopic crane.

OVERCOMING CHALLENGES

One of the most challenging parts of this project was the installation of the 80-metre, 385 tonne bridge at Monkey Island. Our joint installation crews had to contend with extremely poor winter weather conditions – and we had to contend with a pandemic.

• We put stringent safety protocols in place, far more rigorous than those usually found on a site like this. We also enhanced company-wide risk assessments, provided additional PPE, and reduced the risks for the members of our crew who were working in close proximity – rigging our SPMTs, for example. This particular challenge, we overcame through mechanical aids. It’s a practice we’ve carried over post-pandemic, reducing risk all round for our teams.
• The installation at Monkey Island included assembly and disassembly of the crane at the roadside, overnight, before the motorway reopened in the early morning. This is where early planning and access to our in-house heavy-lifting inventory adds value and confidence, and reduces concerns for clients.
• By getting involved early, we could allocate our cranes months in advance, and make sure we had the right configuration of SPMTs available. Osprey has one of the highest capacity fleet of SPMTs in the UK, with steering capabilities that allow precision positioning to +/- 2 mm of heavy loads.

Once complete – ahead of schedule – we then moved on to the next structures. Among these was the Thames Bray bridge, an extension to an existing bridge.

NEW INSTALLATION TECHNIQUES

Thames Bray was designed to match the existing haunch girder bridge, and is also the only bridge to carry the M4 itself, while the others carry roads or footpaths over the motorway. It comprised two back spans, which we put together in three paired sections per span. These weighed in excess of 160te each.

The bridge was welded together on-site before installation – we developed a unique system for doing this. Those back spans were tied to the abutments with specially tensioned cables, sourced from and installed by a specialist subcontractor from Italy. Once the back spans were installed and stabilised, the central span, weighing around 100te, could be put in place.

WORKING BETTER, TOGETHER

From the outset, getting involved early meant our engineering teams could identify more ways to support our client. Working better, together, the installation of all the formwork and parapet falsework before final installation meant we could reduce possession times – it’s an approach that’s been adopted industry-wide, since.