Core sampling work which ruptured a water main led to the partial collapse of a bridge over a railway line in Leicestershire, a Rail Accident Investigation Branch (RAIB) investigation has found.
In August 2016 a bridge across the Midland Main Line in Barrow-upon-Soar, Leicestershire, collapsed and a large volume of masonry fell onto the railway lines below.
When the incident happened, core sampling work was being undertaken to investigate subsidence in the footpath on the south side of the bridge, which was built around 1840.
Investigators found that one of the bridge’s side walls collapsed when coring had reached about 1.4m below ground, causing water to appear on the surface. Debris included a length of cast iron water main and the core sampling rig.
Barrow bridge collapse RAIB
The RAIB said: “Two of the four railway lines through the bridge were completely obstructed and there was debris on a third. There were no trains on the immediate approach to the bridge at the time of the collapse.”
The bridge had already been weakened by a full-height vertical crack, and there was a probability the nearby water main already had a small leak, although the investigation found that before the incident there was no imminent risk of the wall collapsing.
“The coring work on the night of the incident disturbed the pressurised water main and it ruptured. The consequent release of water behind the wall quickly overloaded it and caused the wall to overturn about its base,” said the RAIB.
“Underlying the incident was the lack of understanding of the risk posed to the structure and to the open railway from coring in proximity to the water main.”
The RAIB has called for tougher requirements for bridge examiners to report evidence of underground services and any changes since the previous inspections, to enable a possible connection to be drawn between a water main and observations of defects on a bridge.
It also said there must be enough engineering input to risk assessments for intrusive investigations and masonry repairs on bridges carrying water services.