By Matt Westhead, Engineering Director - Major Projects
Did you know that, on average, five motorway bridge strikes occur in the UK every day? The impact of these strikes can be severe, not only in terms of potential injury, but also their impact on our country’s transport infrastructure and the day-to-day lives of those caught up in the disruption and delays. In this blog, Matt explores what happens in the aftermath of a bridge strike and the importance of a rapid and collaborative response.
Following a bridge strike, it’s very much ‘all hands on deck’, with organisations, such as Highways England, working tirelessly to make sure the affected area is closed to traffic, the emergency services are called (if required), the accident site is safe and the necessary road diversions have been put in place. But what happens after a bridge strike? How is the bridge stabilised and the road re-opened as quickly as possible?
Keeping disruption to a minimum requires a high level of collaboration throughout the supply chain. When the clock is ticking and the day-to-day lives of those reliant on our infrastructure network are being impacted, all parties - from contractors through to specialist engineering firms, permanent works engineers to temporary works – need to work as one team.
Bridge strike response in action
A key example of this rapid and collaborative response in action was a lorry bridge strike on the M6 motorway in Lancashire, back in 2018. While the driver was, thankfully, not seriously injured, the collision resulted in the lorry wreckage being the only thing holding the bridge up. As a result, the motorway was forced to close in both directions until the wreckage had been removed.
Thanks to the expertise and successful collaboration between project partners, the bridge was successfully stabilised and reopened to traffic in just 24 hours. Here, we explore the five fundamental stages of responding to a bridge strike, beyond any initial and immediate threat to life.
Step One: Assess and inspect
When a bridge strike takes place, specialist engineering firms and contractors must quickly work together to first inspect the site and assess the damage and impact to the bridge’s structural integrity. The information gathered at this stage will help determine the extent of road closure required, the structural damage sustained and how any wreckage can be safely removed.
Following the M6 bridge strike, we were contacted by Kier Services on behalf of Highways England, with a request for our emergency response team to immediately head to the crash site. Once there, our engineers were able to assess how we could support the concrete bridge, while the safe removal of the wreckage was carried out.
Step Two: Design temporary support
Once the damage and structural stability of the bridge has been assessed, a bespoke temporary works solution can often be required to help provide immediate support and enable the bridge to be either fully or partially re-opened to traffic.
Given the M6 motorway is a major part of our country’s road network, making the bridge safe and opening it to traffic as soon as possible was an evident priority, and so our engineering team worked on designing a bespoke temporary propping scheme. The optimum solution consisted of two Mass 50 towers, each capable of supporting vertical loads of around 480kN, with base beams to spread the load on the carriageway. The scheme also featured header beams and hydraulic Hymat Jacks, which would help undertake the load transfer and support the existing bridge beams.
Step Three: Installation
A key stage of any project, the methodology and logistics can often be just as complex as the initial scheme design itself; perhaps even more so on a bridge strike. Making sure the temporary support is installed safely, without damaging or impacting upon the existing structure, is especially critical. As such, it’s important to work with a specialist company that has experience in installing temporary works schemes in complex and high-pressure situations, such as that encountered on an emergency infrastructure project.
On the M6 bridge strike, once the engineered design had been agreed by all parties involved, part of the propping scheme was first pre-assembled in the local Mabey Hire depot, before being delivered to site, contributing to a smoother, quicker and more efficient process. Once on site, our experienced in-house install team then worked through the night to complete the installation of the temporary props and jacks.
By 6am the following morning, within 24 hours of our emergency team first arriving on site, the bridge was stable, the lorry wreckage had been safely removed and all but one lane was re-opened to traffic.
Step Four: Futureproofing
Of course, as the name suggests, an emergency temporary works solution is just that – temporary. Once the primary objective of making the bridge safe and open to traffic is complete, the next step is to engineer a more ‘permanent’ temporary solution, providing a longer-term and sustainable means of support while a repair works plan is developed and undertaken.
Here, again working closely with the Kier and Highways England teams, Mabey Hire led the design and installation of a semi-permanent propping solution, which would allow the motorway to reopen in its entirety. Our team of engineers recommended the installation of our higher-capacity Mat 125 propping system at the original concrete pier position, with hydraulic Hymat Jacks on top to offer further support. This was engineered so as to remain in-situ for a minimum of six months, whilst a permanent replacement pier could be designed and fabricated.
Step Five: Monitoring
Despite being the final step in this blog, monitoring can be invaluable at all stages of a bridge strike response, providing important insight into the bridge’s structural behaviour, stability and live loads. This live data can be used to help ensure the safety of the site, both immediately after the impact and during remedial works, provide added assurance and inform the temporary works design.
On the M6 bridge strike, we installed a structural monitoring system while the ‘semi-permanent’ propping solution was being developed, providing valuable information on the bridge’s live load paths and articulation. Then, during the repair works, digital levels and displacement sensors were installed on the existing bridge abutment to monitor vertical, transverse and longitudinal movement, with pressure sensors also integrated within the temporary hydraulic jacks. All of this data fed into our Insite web-based portal, providing our teams with a real-time view of the bridge’s behaviour and helping us to ensure that all work was carried out as safely and efficiently as possible.
Providing an emergency response
In an emergency, whether it’s a motorway bridge strike or flooding, subsidence or a burst water main, a swift and expert response is key. At Mabey Hire, our emergency response team of engineers have been helping customers get communities back up and running for over 60 years, meaning you can rely on us to be there when you need us.
