Bridge repairs to trough bearings using epoxy resin
Oxford Hydrotechnics were approached by the client to devise a solution to bearing erosion caused by excessive trough movement during train activity on the track above.
The problem was deemed to be the result of excessive vertical movement of cast iron troughs on their bearings, particularly when the bridge was carrying a train load above.
A total of four locations had sustained the damage, and in one location, a trough had slipped downwards by approximately 50mm. Another trough was seen to visibly move during train movements above.
The issue had resulted in Network Rail being forced to reduce the line speed on the section of track that passed over the bridge as a precautionary measure and urgent remedial works were scheduled. Proposed solutions included masonry pinning using helical ties and some form of grouting solution to arrest the movement of the troughs.
As Oxford Hydrotechnics were involved from an early stage, H2OX engineers were able to have a direct input into the devised solution.
It was deduced that, as there was no evidence of spoil falling out of the bridge, the bearing areas had been subjected to a crushing action only, and that this would not have created large voids within the structure.
H2OX engineers concluded that a cementitious grouting solution would not necessarily work, as it would not have been of a low enough viscosity to flow through the pulverised engineering brickwork.
H2OX proposed an alternative approach, using a very low viscosity epoxy resin (Oxford Hydrotechnics’ EP1390 product) which would allow permeation through the brickwork.
A temporary propping system was installed beneath the bridge, with H2OX inflating several grout bags to ensure full support whilst the work took place.
A grid pattern of injection ports was then drilled into the bearing area at the end of each trough, almost through to the extrados of the arch.
Injection packers were then installed at a shallow depth, allowing resin to flow into the structure, permeating the crushed brickwork and curing at a high compressive strength (>80N/mm2).
A Lily CD15, two component epoxy injection pump was used; due to its controlled mixing, injection and manoeuvrability. The epoxy resin was injected until refusal. Particular emphasis was placed on filling the interface between the trough ends and the bearing brickwork to prevent future movement.
Further epoxy injection was then carried out along the upper sides of the trough to further reinforce the brickwork.
Following completion, including a 48hr period to allow adequate curing time for the epoxy resin, the temporary propping system beneath the bridge was removed and the line speed of the track above was restored to its former limit.
The project took a total of 9 shifts from start to completion, using both day and night shifts, delivering quick and highly successful results for the client.
H2OX used 89.5 kg of EP1390 during the project and treated 8 trough ends (average 11.2kg per bearing area). A further 89kg of resin was then used to reinforce the upper lip areas along the sides of the troughs.