Rising to the challenge

UK-based Asset International Structured Solutions is rising to the challenge of making way for a new four-lane highway without compromising mainline railway access. As the steel rail tunnel was lifted into place, it also secured the project the accolade of the world’s largest lift.

Asset ISS has been in the business of the design and manufacture of wide-span steel structures since 1954. The company, which is part of Hill and Smith Holdings plc, offers Multiplate and StrenCor galvanised steel products for use in tunnels, underpasses, culverts, bridges and storage across a range of applications from railway access to wildlife protection.

The original concept of corrugated steel pipe was introduced by ARMCO in the US in 1896, with the first being manufactured in Crawfordsville, Indiana. Since that time, it has become a major drainage material and construction tool throughout the world.

Corrugated, galvanised steel has a long and proven international record in successful civil engineering applications. The use of corrugated steel in underpasses, culverts and bridges has proven time and time again that substantial savings can be made in both design and installation times when working with the material.

With a range of varied experience and projects successfully delivered worldwide, Asset ISS was an easy choice for Carmarthenshire County Council, based in Wales, UK, for the Morfa to Berwick Coastal link road project. The Council was presented with the challenge of working with contractors and designers to create a new highway route, whilst ensuring that not only was the mainline railway access assured in the long-term, but also that minimum disruption occurred during installation.

As projects regarding rail and public highway access become increasingly demanding and time constrictive, structural design and manufacturing teams such as Asset ISS are being called upon to be creative but practical, and both cost and time-effective.

Richard McTavish, Director of Asset ISS and a qualified Structural Engineer, explains further. “Over the years our role as manufacturer and supplier has evolved and changed considerably, and we are willingly rising to the new challenges that customers bring to the table.

“More often than not with each new project, we’re presented with a unique set of variables along with extremely tight restrictions that often involve public access and safety, along with the challenges of limited space and schedules of road and rail traffic. The Carmarthenshire project was one of the recent challenges we faced as a team of designers, engineers and manufacturers. It has so far been delivered on schedule whilst also saving on costs.”

The project, delivered by the main contractor Costain, was commissioned by Carmarthenshire County Council in West Wales as part of its UK£6.8 million pound coastal link-road project, in Llanelli. Initiated in May 2007 and due to complete in January 2008, the partnership between the Council, Costain and Asset ISS has resulted in the delivery and installation of the large span, corrugated steel rail tunnel via the world’s largest lift into place. The tunnel, supplied by Asset, has a span of 15.5 metres and measures over 52 metres in length.

The existing rail tunnel was formerly an at-grade railway connecting London and South Wales with a mainline passenger and goods rail link. The new four-lane highway to be created will cross over the rail line at an angle and the corrugated steel rail span, which forms the tunnel, will accommodate the high-speed rail traffic below.

When making it’s decision, Carmarthenshire County Council considered several types of overpasses but due to the skew of the road over the railway and the associated requirement for large approaches, these alternatives were deemed too costly. As a result, they chose to install the 52.8m long tunnel over the open railway and cover it with imported material, with the roadway then spanning the tunnel.

The Council elected to use Asset’s StrenCor steel bridge structure, because it offered the large span needed to accommodate locomotives combined with strength and durability. StrenCor’s corrugation profile also permits construction of longer, wider spans in a variety of configurations.

StrenCor is a deep corrugated structural plate type II, which is known as Bridge Plate. The lightweight modular panels can be transported efficiently and economically to virtually any location and then easily assembled in-situ.

“The unique demands of this project meant StrenCor was an ideal solution for planners,” says McTavish. “It has large annular corrugations offering additional stiffness, meaning greater spans can be achieved compared with other corrugated steel structure products.

“StrenCor modular panels can be delivered to even the most remote destination and then assembled adjacent to the job site, and moved into place using relatively light equipment. This means reduced closure times and lower installation costs, making it ideal for railway underpasses and a wide-variety of other installations,” he adds.

Properly designed and installed, StrenCor structures can last over 120 years and are relatively maintenance-free during their lifetime, unlike conventional bridges that frequently require substantial retrofits.

The link road will open up land for development in South Llanelli, reduce traffic congestion, and will also improve access to the National Wetlands Centre and the new Jack Nicklaus designed Machynys golf course. The Council says the link road will bring a huge boost to the local economy, creating hundreds of jobs and improving the highway network.

Carmarthenshire County Council Project Manager Adrian Harries, comments: “Using a corrugated steel structure has enabled us to create a far lower embankment profile than would normally be associated with a conventional crossing, with significant savings afforded to the project.”

The development has presented some unique challenges, as trains have not been stopped to accommodate the lifting of the tunnel sections. Instead, contractors have had to work around train timetables and have been allocated specific time slots by Network Rail.

“The tunnel has been lifted into place in three sections linked together with in-situ closure rings,” explains Nigel Hancock, Costain Project Manager. “The work has been undertaken over five separate weekends during night-time rail possessions. Timing has also been a critical factor, as some engineering and passenger trains were still being allowed through the works.

“Now the tunnel is in place, all three sections will be joined together and the backfill operation will begin. This involves the construction of the reinforced earth embankment utilising a concrete panel system,” he adds.

Because of the strategic and economic importance of the main London to South Wales rail line, and in order to minimise any disruption to commuters and rail travellers, the decision was taken not to cancel the trains.

During the three stages of the tunnel being lifted into place, the tunnel sections were assembled on a temporary site adjacent to the final site. This also presented contractors with a challenge because it is sandwiched between two live rail lines, is flanked by electricity cables, and is on land saturated by water from the nearby Millennium Wetlands Centre, making the surrounding environment a key consideration of the project delivery.

Each of the three sections weighed in at a total of 43 tonnes and measured around 16.9 meters. A team of approximately 12 people were present to oversee each stage of the lift. The completed tunnel is now in place, ready for backfill work to begin. The link-road project is due for completion by January 2008.