The rehabilitation of a 150 year old railway culvert damaged by overloading and lack of maintenance

This masonry culvert is over 150 years old and carries the Berks and Hants railway line over an unnamed tributary of the River Dun at Little Bedwyn in Wiltshire.

The problem

The barrel is constructed of three rings of red brickwork. It has a span of 1.8m and a rise at the crown from the springing level of 1.09m. The thickness of the barrel is 315mm. The culvert has a brick invert with a length of 10.5m. A previous Detailed Inspection Report had identified that the culvert was in very poor condition with extensive cracking and dropped (by up to 110mm) and missing brickwork. Movement under live load was also observed. In fact, the report stated that the culvert was in such a state of disrepair that it would be dangerous to enter for any future inspections. The barrel, therefore, had to be extensively propped and before the areas of faulty brickwork could be identified.

The Goldhawk solution

Before the MARS System MARS System could be installed, it was found that part of the barrel had to be re-cased and dropped and missing bricks were repositioned/replaced and pinned. When re-casing, a maximum of three bricks were taken out and replaced at any one time. Given the very limited workspace available, this was an extremely time-consuming operation.

The design railway loading comprises an LM71 train with 4No 2.55 tonne axle loads at 1.6m centres. The value of ⍺ was taken as 1.1 and the dynamic factor was calculated at 3.98.

The recommended system to bring the barrel up to this capacity was calculated at a double layer of 6mm stainless steel super 6 Helibars at 210mm centres for circumferential reinforcement and 8mm stainless steel Betinox reinforcing bars at 450mm centres as longitudinal reinforcement. 6mm stainless steel Helibar hooked radial pins were inserted at every intersection of transverse and circumferential bars.