Bailey Street Culvert Repairs for Torfaen County Borough Council
Edwards Diving Services Ltd. were appointed by Torfaen County Borough Council to inspect Bailey Street culvert, in particular to identify the scale of a known defect where scour of the invert and washout of the abutment was occurring.
EDS identified large scour damage, 10m long by up to 1m deep, to the stone invert of the masonry barrel with undercutting to one abutment over a 5m length and a wholesale collapse of the opposite abutment over a 3m length, with a further section suffering from movement. EDS developed a methodology to repair the damaged areas.
The methodology for repairing the culvert is summarised below:
- Create access across playing field with ground protection mats and temporarily removing fencing
- Install temporary propping of all unstable areas with sacrificial Acrow props
- Install water management measures (bypass pipes and 6” submersible hydraulic pump) followed by pollution control measures
- Pump ready mixed concrete (40m3) in to the invert void to stabilise the invert, fill undercutting to the abutment and prevent any further movement of the abutment wall
- Construct new abutment wall using dense concrete blocks, laid on flat and staggered to achieve circular profile, backfilled with pumped grout (also utilised to fill voids behind abutment wall downstream) in a number of lifts to reinstate the wall
- Apply steel mesh then spray apply structural render system to finish abutment reconstruction to tie in with original circular culvert profile
- Re-pointing and resetting of large masonry stones
Works were undertaken over a period of 4.5 weeks, which included additional scour remediation works upstream of the main repair area. Difficult access via a narrow manhole and chamber was overcome by dealing with local landowners to arrange access for large plant and equipment over their private property at the beginning and end of the contract. All other access was via the narrow manhole.
All pumped concrete was an RC32/40 mix, with an underwater additive (Sika UCS), provided as a pump mix with high slump and 10mm aggregate in order to enable pumping to the void.
The repair and maintenance work was highly commended by the Torfaen County Borough Council project supervisor, with the reinstatement of the large void preventing the possibility of a culvert collapse which may have had significant safety, cost and inconvenience implications for the local residents and Local Authority.