A historic bridge with a proud past creates challenges for the CML team
Thickley Wood footbridge at Shildon, in County Durham, merits a special place in railway history since it tells the story of the growth of Shildon sidings, growing from nothing in the earliest days of the railway, to becoming the biggest sidings in the world, superseded by Chicago, in 1927.
It is very wide, with seven spans over the Darlington to Bishop Auckland line, and Grade II listed because it was built in four different stages between 1857 and 1875. In its heyday there were 27 miles of tracks on the sidings, all filled with wagons delivering coal from the nearby Durham coal fields.
Bridges of this age inevitably suffer wear and tear and the work required was extensive, including:
- Removal of spans 1-3, including 3 stone piers to be replaced with a reinforced earth embankment and footpath access
- Removal and replacement of span 4
- Steelwork repairs and refurbishment of spans 5 and 7, including refurbished timber deck on span 5, and a lightweight concrete deck on spans 6 and 7
- Brickwork repairs on span 6
- New drainage systems, along with landscaping of surrounding areas, and over 300m of newly fabricated Estate Fencing.
Local stakeholders, such as FSDR (Friends of the Stockton & Darlington Railway) and Locomotion, the nearby railway museum, were keen to be involved and CML re-used stone and timber from the structure where possible, retaining a section of the bridge for FSDR for heritage purposes.
Following initial site clearance operations, the team installed temporary access roads, crane pads and large laydown areas to stable mobile cranes and the steel spans being removed and re-installed on the 7 span structure.
Spans 1-4 were removed within possessions and are being replaced by a reinforced earth embankment (‘Terramesh’). This system, using a combination of steel cages to face the new embankment and geo-fabric tensile straps installed in layers as the embankment is constructed, helps form the embankment with much steeper sides than possible with traditional embankment construction, reducing materials and land-take.
The system incorporates pockets of pre-seeded soil mixture up the face, which in springtime will germinate to leave attractive looking grass covered walls supporting one of the ramps and three of the old spans of the footbridge structure. A new bridge deck was installed on span 4 and steel work repairs and new parapets were constructed on spans 5 and 7. The new earthwork ramps are being installed on the South and North side of the bridge.
Weather has been a major factor with the planned lift of span 4 being delayed by 2 weeks due to high winds. A large crack was also identified on span 7 on one of the main bridge beams – a number of options are being considered to implement repair works. The new structure should be open in time for Spring 2019.