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Slope engineering: Rock solid team

tecco g65 3 stainless gb cambrian rail campaign 2

Collaboration to reduce the risk of rockfalls on a rail route in north Wales has created wider benefits than just a safer railway

The 190km Cambrian Line through mid- and north Wales has been described as one of the most scenic rail routes in Britain but this beauty brings geotechnical challenges. 

Work by Network Rail Wales route asset management had identified six sites that were a particular risk for rockfalls and an innovative partnership is close to completing remediation of these hot spots.

Delivery of the work brought together contractor Alun Griffiths and Design Delivery Network Rail in a collaboration that secured the project the UK Geotechnical Team of the Year award at the 2018 GE Awards. The collaboration for the Cambrian Rock Cutting Campaign has delivered much wider benefits than the initial aim of risk reduction, with investment in staff skills, reduced long term maintenance and improved engineering value.

The line hugs the coastline to follow the path of least resistance, according to Design Delivery Network Rail senior design manager Jonathan Fullilove.

“But there are still steep slopes and rock cuttings, which means that the route has a long history of issues with rockfalls,” he says.

“An investigation into a fatal train derailment in 1883 said that the only solution to prevent further rockfall risk would be to tunnel the route, but this was – and still is – uneconomic.”

While there are known high risk sites, Fullilove says that the nature of the area can result in unexpected risks.

“A fallen tree up the mountain can re-direct a stream to a new area within hours and result in a rockfall where previously there was not a problem.”

Until this scheme was instigated, patrolmen would walk the line following bad weather or following reports of rock falls from train drivers.

“It’s a rural line with low passenger number, but it is regionally important,” says Fullilove. 

The six sites selected for remedial work under the campaign were identified through a condition approach and risk assessment.

We considered letting the work under a traditional design and build contract but given the challenges of the work we were worried about the potential of adversarial issues,” says Fullilove.

tecco g65 3 stainless gb cambrian rail campaign

tecco g65 3 stainless gb cambrian rail campaign

The coastal location of some of the sites led to the use of higher grade materials to maximise servicelife

“We wanted to ensure there was communication throughout the supply chains, which led to the work being let under a lump sum with Design Delivery Network Rail taking on the design risk and Alun Griffiths taking responsibility for quality.”

The aim was to develop a better solution with the savings reinvested in the work.

At the outset of the contract the partners set about finding synergies in culture, project metrics and health and safety aims to align the companies 

in a bid to work as closely together as possible. It was these efforts that secured the project an award at the 2018 GE Awards.

Judges for the category said: “This team demonstrated clearly that it had gone beyond what it needed to do and won because it didn’t have to do it that way, but chose to.”

They also said that the team had used every opportunity to invest in the future of people, methods, relationship and equipment and praised the innovative approach taken to achieve common goals and the strongly aligned cultural values.

As well as working with schools on the dangers of playing near rail lines and talking to the local community about the work, Alun Griffiths retrained local forestry and agricultural workers in rope access techniques and construction to create a local workforce and a skills legacy.

“We had staff in north Wales but they didn’t all have the skills we needed, so we trained them as well as recruiting more local staff,” says Alun Griffiths senior construction manager Jason Shannon.

Alun Griffiths also trained a number of Network Rail staff in rope access to allow them to be on site and see the issues first-hand to aid decision making processes.

According to Shannon, this enabled more informed and faster decisions to be made when it came to scaling and spot rock bolting.

“We wanted to blur the lines between the teams,” says Fullilove.

This resulted in the two partners working closely on buildability and safety issues during the design stages.

Shannon believes the approach has worked and created many efficiencies.

“We looked carefully at equipment and wanted to minimise the risk of hand arm vibration exposure, so we invested in a long reach road/rail excavator to undertake the rock bolting from track level,” he says.

“As a result, less than 1% of the rock bolts have been installed by hand so far.”

The project made extensive use of 3D modelling during design, which Fullilove says was an unusual step given the size of the project sites.

But he believes it aided the optioneering process.

While the project was let on a lump sum, the focus was on value rather than lowest cost, which led to more being invested in the material used to maximise the service life and minimise long-term maintenance costs on the route.

“The coastal environment of some sites presents a challenge to the conventional material used for rock bolting and meshing,” says Shannon.

“We wanted a 120 year design life for the solutions and needed to consider the total lifecycle costs rather than just the construction costs.”

This led the team to work with Geobrugg and Dywidag to use stainless steel rock bolts and rock fall attenuation mesh.

“This added around 3% to the project budget but lowered the whole life costs so the investment was valuable,” says Shannon.

The Tecco G65/3 stainless steel mesh used on the project has been specially developed by Geobrugg for sites in exposed marine environments or where there is a risk from salt spray resulting from road de-icing.

The mesh used on the Cambrian scheme has a 3mm wire and a tensile strength of 1,650N/mm2.

With a high proportion of the sites close to the seashore, this solution was essential. Network Rail’s aim was to move away from using conventional galvanized products without really considering the environment and the life cycle.

The team also worked with Dywidag to undertake some research and development during the early stages, which led to shorter and smaller diameter rock bolts being used, saving around £500,000 which is being reinvested back into the work.

Having the project team on site also allowed for some reactive remedial work when a rockfall occurred at the Penhelig Portal during other work nearby, which also saved on costs for Network Rail.

In total almost 16,000m2 of rock mesh and 2,893 rock bolts with a total drilled length of over 10km has been installed over three years.

The work is not yet complete but already it has removed the need to have patrolmen checking the route and created a 120 year design life for the areas that have been treated. Further work is now expected to be undertaken by the project team in Network Rail’s CP6 investment programme.

While the engineering may be completed, the long-term outcome of the work will benefit rail users for years to come. Fullilove believes that it is the set-up of the contract and companies involved that made it a success.

 

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