The Rail Accident Investigation Branch (RAIB) is to look into events at Lamington viaduct, damage to which has closed the West Coast main line since 31 December.
RAIB reports that several trains passed over the viaduct on that morning, some at high speed, after the ground beneath one of the piers had been eroded by river scour. The damage was caused by Storm Frank.
At 07.35, the driver of a southbound service from Edinburgh Waverley to London Euston reported a dip in the track, and a temporary speed restriction was imposed. After the track had been inspected, track maintenance staff removed the speed restriction and remained on site to undertake minor remedial work (normal linespeed at the location is 120mph). After observing unusual track movement at 08.40 during the passage of another train at the normal linespeed, the speed restriction was re-imposed, and at 08.53 the line was blocked to all trains after a large crack was observed in one of the three viaduct piers located in the river.
Subsequent investigation has revealed a large hole beneath the pier, subsidence of the pier and damage to three of the steel bearings which support the bridge deck. Initial efforts to save the piers by pumping in fast-setting concrete were abandoned after the scale of the challenge emerged and part of another pier was damaged. The railway is now not expected to open until at least the beginning of March while repairs continue.
RAIB says it will examine actions in response to a scour risk assessment undertaken for Lamington Viaduct in 2005; actions taken when the approach of Storm Frank resulted in warnings of exceptionally heavy rain, likely to cause fast flow in the River Clyde; responses to the 31 December report of a track dip on the viaduct; the effectiveness of Network Rail’s processes intended to mitigate risks to structures, including scour related risks, due to extreme weather; and any underlying management factors.