North West, Premier Rail

Challenging tunnel project wins industry recognition

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Chorley Tunnel, National Rail Award

A challenging £7.5 m project including major works to Chorley Tunnel to enable future line electrification and involving lowering of the track within the tunnel, as well as the restoration of 16 listed stone arches at the tunnel approach, has won industry recognition.

Other elements of the project comprised the demolition of a road bridge at Harpers Lane, the reconstruction of the River Chor Aqueduct and an earthworks stabilisation scheme.

The development, which was carried out for Network Rail by main contractors Murphy Group, has won recognition in both the Institution of Civil Engineers Awards and the North West Regional Construction Awards, as well as being shortlisted for a National Rail Award.

The project, which involved 24/7 working during a six week blockade of the Chorley line, was originally programmed for completion during separate possessions for the various works over a two year period.

Chorley Tunnel, National Rail Award

Murphy engaged into Early Contractor Involvement with Network Rail, design partner Amey and Track Slab subcontractor, Stobart Rail, to create a detailed programme to undertake the entirety of the works in one blockade, resulting in significant cost savings for Network Rail.

Because the original Chorley tunnel cross section had insufficient clearance to allow for the future installation of the overhead line equipment, a scheme was designed to lower the tracks through the tunnel and replace the existing ballasted track with concrete slab track, sited directly on top of the existing brick invert to the tunnel.

Lowering the track required digging down to expose the bottom of the tunnel – although this alone did not achieve the required height, so it was necessary to notch into the tunnel base.

To achieve this safely, Murphy designed a bespoke solution allowing them to keep the tunnel-breaking to a minimum. This involved breaking out the tunnel in small sections, then installing the track slab as they went along, so that everything broken out behind the contractors was already filled with concrete.

The magnitude of the track lowering work in the 113 m long tunnel also necessitated extensive works on the tunnel approaches. This included a significant amount of sheet piling in front of the retaining walls on all four corners of the tunnel approaches in order to safeguard the integrity of the walls while the track lowering works were carried out.

Chorley Tunnel, National Rail Award

The stone flying arches on the approach to Chorley Tunnel and dating from 1841 were removed in 2008 and were meant to be reinstated later, but could not be installed as they were originally, because their height would have been too low for electrification, in the same way that the tunnel was. The arches are unique – there are no other examples of this type anywhere on the network.

The arches had been removed in their entirety, so they were still complete. The work involved dismantling them block by block (numbering all the blocks), then rebuilding each one over a specially made weathering steel arch to support the stonework and raise the height of each arch when installed on to the retaining walls at each side of the track.

Following close liaison with planning authorities and English Heritage, Murphy achieved a £600,000 saving for Network rail by designing the weathered steel alternative to the more costly original client specification for stainless steel arches.

Brick buttresses were then constructed to provide additional strengthening for the arches.

A further element of the project involved the demolition and reconstruction of a road bridge at Harpers Lane, and the reconstruction of the River Chor Aqueduct.

The aqueduct incorporated three stone arches with a cast iron trough on top. The works involved the demolition of the central arch, strengthening the other two arches with concrete and facing them with stone, and replacing the whole of the cast iron aqueduct trough with a fibre reinforced polymer material.

The overall project was completed some 48 hours ahead of schedule.

The benefits for Network Rail, were significant. There were a lot of historic problems at the site such as wet beds, drainage and ground issues, which resulted in Network Rail maintenance teams having to attend the site to undertake remedial works on a monthly basis.

There issues have now been resolved which, combined with maintenance-free solutions which Murphy identified, have resulted in a significant cost and time saving associated with ongoing maintenance.

The success of this highly commended scheme saw it reported in the BBC news and other local and national press. Following the successful completion, Murphy have recently been awarded the Farnworth Tunnel scheme of a similar nature. This has allowed for continuity of resources and for the company to apply the lessons learned to future schemes.

Chorley Tunnel, National Rail Award

 Bolton Stone

Bolton Stone specialise in the delivery of all types of masonry work with a focus on Listed structures, as well as new masonry and infrastructure works such as bridges, parapets and retaining structures. The firm was formed in 1999 and since its inception have worked with a varied range of clients acting as masonry framework contractors on local government municipal buildings, highway structures, rail and infrastructure schemes, banks, building societies, architects practices, as well as undertaking restorative works on listed properties and monuments.

Speaking about the project, Andrew Howe from Bolton Stone commented:

“We were commissioned by J Murphy & Sons to carry out the dismantling and reconstruction of the masonry flying arches. We also acted for Murphy’s when dealing with the conservation officers to help design suitable fixing methods and mortar specifications to satisfy the heritage aspects of the work.

“We have a long standing working relationship with J Murphy & Sons and this project gave us the opportunity to demonstrate our skill levels whilst working on an important Listed rail structure. This scheme has also shown how our knowledge of heritage work can help contractors deliver their projects to the standards demanded by the client.”

The firm pride themselves on assisting with specialist elements of projects and helping contractors fill the knowledge gap. Andrew added:

“We pride ourselves on knowing we have achieved the goals of the client, contractor, conservation authorities and being able to preserve important historical structures for future generations.”

Topdrill

 Topdrill specialises in geotechnical services across the railway infrastructure offering services ranging from ballast sampling to in-depth mining surveys. Having started in 2006, Topdrill has built up a dedicated team of engineers and drillers who in turn have developed strong relationships with the company’s client base to provide detailed investigations tailored to the railway environment.

Topdrill have been working on an array of projects throughout the United Kingdom, recently completing works on the North West Electrification, Midland Mainline Electrification, Doncaster to Immingham Gauging Project and Derby Remodelling. All four projects required differing approaches to ground investigation, and all brought differing problems that required resolving prior to their successful completion.

Work on Chorley Tunnel started with J Murphy & Sons back in 2011, with initial works taking place prior to the Lancashire Triangle Electrification works. This aspect of the project provided the team with a better understanding of how to make the tunnel viable for the passage of electrified trains.

Topdrill’s involvement included carrying out numerous cores within the tunnel to ascertain specific tunnel dimensions, ballast sampling to understand if it was possible to lower the track within the tunnel, and to understand the natural strata below. Additional works included trial pitting to locate tunnel foundations and the central culvert, and installing boreholes above the tunnel to understand the ground that had been backfilled on top of the tunnel once built.

Roger Price of Topdrill, said:

“Chorley Tunnel was part of a much larger project, which also included Farnworth Tunnel and numerous bridges and retaining walls stretching from Manchester Victoria to Blackpool. The tunnels were seen as a major part of the project due to the works required to make them viable for electrification.

“The levels of project management and the dedication of the staff who were involved in carrying out such detailed investigations – during months of midweek nights – is testament to J Murphy & Sons and Topdrill.”

Roger added:

“Topdrill prides itself on being a proactive geotechnical specialist on the railway. As for Chorley Tunnel and the other projects named here, Topdrill has effectively co-ordinated and delivered efficient ground investigation to the client requirements.”

Jamestown

 Jamestown who are experts in manufacture of specialist steelwork, were chosen by J. Murphy & Sons as the preferred supplier of the 16No steel arch sections at Chorley Tunnel. The pieces were made by Jamestown at their hugely impressive steel fabrication plant, and then shipped direct to Chorley for installation by J. Murphy’s team.

“We were delighted to be involved with the supply of complex steelwork to such an important project, and we are equally delighted with the successful installation,” said Jamestown General Manager, Mr Fiacre Creegan.

Jamestown’s work involved the forming of 16No steel plate girders, curved to a radius to exactly mirror the radius of the original stone arches. Jamestown also manufactured the girder end sections complete with stiffeners/backing plates and connection plates to exactly match the required on-site fixing detail.

In the past Jamestown has supplied all the significant steel components for several other prestigious rail bridges including Foxhall Lane, Customs House/Excel and many others. Supply of heavy bespoke complex structural steel components up to 100Te in weight and up to 70m in length is Jamestowns’ speciality; and with their recently acquired facility, have now the capacity to make even bigger, longer, heavier components.

“We have always found J. Murphy & Sons to be an excellent working partner. We look forward to further collaboration in the future, as we expand our operations in the UK. We take pride in successfully exceeding our clients’ requirements and the entire Jamestown team in Ireland and in the UK, is dedicated to ensuring our continued growth and success,” said Mr Creegan.

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