Water threatened the integrity of one of the UK’s most important motorways – now hydrodemolition is playing a vital role in its renewal
It is a question many motorists must have asked: why are there tents on a motorway?
The blue mesh and scaffolding structures have been ever-present on the M5 in Oldbury for two years, during a £100m+ project to repair one of the UK’s longest motorway viaducts.
They contain the thousands of shards of concrete sliced from the structure during hydrodemolition operations which generate water jets that travel at speeds of up to 1,000 miles per hour.
The project to renew the 3.5km stretch of elevated motorway between Junctions 1 and 2 of the M5, is being carried out by a joint venture involving BAM Nuttall, Morgan Sindall, and VolkerFitzpatrick (BMV JV).
It is overseeing the concrete repairs on the carriageway deck and significant other modifications to the viaduct structure, which opened in 1970, and now carries 120,000 vehicles a day.
Sabre Jetting Services are working on the project on behalf of asset maintenance and repair specialists CRL and VolkerLaser.
“We work on a lot of motorways,” says Sabre Jetting Managing Director David Malin. “But this is the most complex and intensive hydrodemolition programme we’ve been involved with in 29 years of operations.”
The insidious effect of water, combined with salt spreading and the pounding impact of ever-heavier vehicles, has had the most impact on the viaduct.
It is apt, then, that hydrodemolition is playing a pivotal role in restoring the structure to an as-new condition.
Between four and 10 hydro-demolition teams – usually made up of two personnel – have been deployed at any one time.
A key task has been the removal of degraded concrete from around more than 320 joints between deck sections that make up both carriageways.
Once the water jetting is done, the cuts are finished with mechanical chisels. Corroded reinforcement is replaced, and damaged reinforcement welded. Then, fresh concrete can be poured.
It is a process that, typically, should take six days per joint, a speed made possible by good teamwork between contractors, and a key advantage of hydrodemolition.
Work began on the concrete repair project in April 2017. The southbound carriageway was repaired first, with a contraflow system set up on the northbound carriageway.
In September 2018, work switched to the northbound carriageway. Project works on top of the viaduct are forecast to finish in autumn 2019.
The volume of individual repairs has been significant. On the southbound carriageway, more than 6,000 repairs were carried out, considerably more than anticipated.
With concrete repairs completed, three specialist layers of sprayed material are being added to seal and waterproof the deck, ready for it to be resurfaced with asphalt.
Potable water needed for hydrodemolition has been supplied via a complex four-inch pipe network on the viaduct deck. Each individual hydrodemolition team needs 2.5 cubic metres of water an hour to be kept busy.
Europe’s largest scaffold scheme, erected under the viaduct, supports another network of pipes that drains wastewater into mobile filtration and settlement tanks (Siltbuster HD Units) provided by Sabre Jetting Services.
These capture sediments from the hydrodemolition activity and bubble CO2 through the water to achieve a PH level approved by the Environment Agency.
The process has allowed the filtered wastewater to be discharged into a river and canal that run beneath the motorway, instead of being tankered to an authorised disposal site, saving considerable time and money.
As well as being faster, hydrodemolition is generally healthier and safer than other forms of demolition as it eliminates the risk of vibration and associated injuries.
The jetting water also contains waste particulates, reducing dust pollution. This has particular importance with traffic passing by just feet away, and thousands of homes and businesses lining the route.
Sabre Jetting Services have been using hand-held water jetting lances, an approach that is proving well-suited to the project.
David Malin says: “Hand-held water jetting is quick to set up, breakdown and relocate, and takes up minimal space, so we can react rapidly to changing requirements, both between and during work shifts.
“With the large number of small concrete repairs, we’ve been having to work on, it has allowed us to deliver maximum productivity.”
The worksite might be over 3km, but it is barely 15 metres wide on each carriageway. It has meant control of access and vehicle movements have been key elements of BMV JV’s health and safety strategy whilst maintaining productivity and outputs.
This has made meticulous planning and a responsive approach to the needs of other construction interfaces essential to keep up with a “relentless” work schedule, says David Malin.
Working for two years through weather extremes, from sub-zero winters to the summer 2018 heatwave, on an exposed, elevated deck has also been a significant challenge for all contractors.
The jetting operatives work in an enclosed space, wearing heavy protective Kevlar clothing, controlling equipment that exerts significant force on them.
The wellbeing of the teams has been fully-considered throughout the project, with regular breaks, plenty of hydration and careful monitoring of health and safety implemented.
The viaduct is also getting an updated carriageway drainage system, an additional measure that should give the concrete deck better protection and a prolonged life.
David Malin says: “I’m certain hydrodemolition using high-pressure water jetting will have a role to play on the viaduct in the future. But road users will be glad to know that it won’t be on this scale again for many years to come.”
Setting hydrodemolition standards
Sabre Jetting Services are members of the Water Jetting Association (WJA), the industry body that represents water jetting contractors, manufacturers and training providers.
The WJA upholds standards with two codes of practice – the Blue Code for use of high-pressure and ultra-high-pressure water jetting equipment and the Red Code, for water jetting in drains and sewers.
It is also the UK’s largest water jetting training provider. City & Guilds-accredited courses are delivered by registered training providers and approved instructors. WJA: www.waterjetting.org.uk