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Monday, May 27, 2024

Christmas at Milverton

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Leamington Spa in Warwickshire is a cosmopolitan town famed for its café culture and its medicinal waters. This popular destination draws in plenty of visitors, many of whom arrive along the Leamington Spa and Coventry Line that crosses Milverton Viaduct. This 220 metre long structure was built in 1844 and is situated on the edge of Victoria Park, which was opened in 1899 in celebration of Queen Victoria’s Diamond Jubilee.

Today, the viaduct spans the River Leam, several public footpaths leading to the park and a roundabout. The masonry structure of the viaduct had been suffering from long term water ingress which was causing significant damage that would shorten its operational life if intervention did not happen.

Usually on schemes like this, the waterproofing is taken care of first and then any other planned remedial works can follow. However, such was the weakened state of Milverton Viaduct that structural repairs were needed just to get the viaduct in a fit state to withstand the impact of the core works that would need to take place.

Preparatory work

Work began late in 2012, just as the dark nights were taking hold. Principal contractor Story Contracting’s first task was to remove the thick undergrowth that had built up in most of the viaduct’s sixteen spans. Once that was gone, repairs to the masonry could commence. These included the usual mix of stitching, repointing and recasing, along with some highly skilled work rebuilding damaged feature stonework. The extent of deterioration in the structure meant that almost every square metre of each span required some sort of attention.

A variety of access methods was used along the viaduct’s length. Cherry pickers were the preferred option and, where ground conditions weren’t suitable for them, scaffolding was used. For the spans above the public highways temporary traffic management was needed to access the works which were carried out at night to minimise any disruption. Rope access techniques were adopted for the three spans that crossed the river.

Earlier works to strengthen the structure had included the installation of more than sixty tie rods through the spandrel walls and through some of the piers. On this scheme each of these tie rods was ultrasonically tested to ensure their continuing integrity. Several of the pattress plates were cracked or broken and repairs to these were completed before they were all blasted and painted in order to enhance their appearance and long-term life.

No Christmas dinner

The core waterproofing works were scheduled for a 129-hour possession beginning late on Christmas Eve. In the lead up to this Story Contracting established a trackside compound 200 metres from the southern end of the structure, near Leamington Spa station. This needed to be big enough for the 2,000 tonnes of new ballast, 150 precast concrete sections, and nearly 1,000 new sleepers that the project required, along with having space for all of the spoil that was coming off the structure.

Across the country Christmas arrived, turkey dinners were enjoyed and the core possession was underway. Story Contracting removed both tracks from the structure and excavated the ballast and fill material down to the new formation level.

The track removal works were sequenced so that the first line was removed by RRVs working from the one adjacent. Once the first line was out, the second was lifted using road-rail tracked excavators working on the ballast bed. When all of the rail and sleepers were removed the spoil ballast and fill material was excavated progressively back along the bridge towards the access. It was loaded into dumpers and transported back to the cut positions in the track where it was transferred into spoil boxes ready to be removed to the compound by RRV.

With the track gone and the fill removed the tie rods were now buried just below the surface. Their positions were identified and precise engineering control of the excavation depth was used to ensure that none were exposed or damaged by the plant working on the viaduct.

All of the works on the structure had to be carefully orchestrated throughout the construction process. Strict control of the position and movement of each plant item was enforced to ensure that none of the arches were unevenly loaded at any time.

Putting it all back together

One hundred and fifty precast concrete L-shaped parapet units, supplied by Ballymena-based Moore Concrete Services, were next placed along the entire length of either side of the viaduct on a screed bed that was laid to provide a level base and to set the height of the units. They were placed in sequence, working along the viaduct away from the access. As the installation of the precast parapets progressed, an in-situ cast reinforced concrete slab was laid that tied everything together.

Fortunately, the weather during the possession was relatively warm and the contingency measures that were in place to ensure the supply of concrete and its protection on site in the event of low temperatures were not needed.

Once the concrete had sufficiently cured, a loose laid waterproofing system was installed along the viaduct by specialist contractor VolkerLaser. This was lapped up the sides of the precast and welded to an insert in the concrete. At the ends of the viaduct, the waterproofing was tied into a new deck end drain that discharged to ground level soakaways.

The track reinstatement followed the track removal process in reverse. Ballast was delivered to the end of the viaduct by RRV and trailer from the compound. Dumpers forward-tipped the ballast onto the structure and it was distributed and levelled by a road rail laser dozer supported by a tracked RRV. Once fully graded and compacted, the first line’s sleepers and rails were installed. This then allowed the second line to be completed by RRVs running on track. RRVs fitted with a clamshell and hauling trailers full of new ballast then dropped the top stone before the tamper arrived, with a tamping bank attachment kept handy in case of tamper breakdown.

Welding and stressing was done and followed by a final run through with a profile bucket and a ballast brush. Guard rails were fixed to the new timber sleepers along the full length of the viaduct to complete the core works and the possession was handed back four hours early.

Story Contracting’s multi-skilled engineering and project delivery teams provided a full track and civil engineering service. On Milverton Viaduct this ensured that the entire needs of the project were integrated throughout the planning and delivery stages and removed any interface issues between trades that could potentially lead to difficulties on site.

The success of this integrated approach resulted in the Story Contracting team delivering the project ahead of programme, on budget and, most importantly, without any accident or incident.


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