Hook Embankment Failure
Issued to: All Network Rail line managers, safety professionals and accredited contractors
Date of issue: 30/11/2023
Location: Hook, Wessex, Southern region
Contact: Derek Butcher, Principal Engineer (Geotech), Southern Region
On Saturday 14th January 2023 a landslide occurred which closed the railway between Hook and Winchfield in Wessex Route (part of Southern Region). The landslip occurred during a possession for a track renewal.
Both the Down Fast and Down Slow lines were closed to traffic because of the landslip for a number of weeks causing disruption to passenger and freight operators.
A Level 2 (Local) Investigation has been completed and identified several underlying causes.
This Shared Learning highlights material available to familiarise employees and contractors of some of the risks associated with Earthworks.
Two days prior to event, there had been reports of a track defect and trains were required to be cautioned at 20mph until the Basingstoke P-Way attended to carry out an assessment and perform minor repairs by means of lifting and packing. The P-Way had not associated the track defects with a potential earthwork failure.
Based on the evidence available there was more than average rainfall at the time (5 months of rain fell in the 3 months prior to the landslip).
This led to a loss of strength of the clay embankment and the softer
alluvium below. The surrounding area at the bottom of the embankment and in surrounding fields was also pooled with water and a local river had overtopped.
The drainage at the bottom of the embankment was ineffective at removing the water and had not been maintained over a period of 10 years. The drainage had not been inspected prior to the failure occurring and this location was not listed as a priority.
The landslip required significant intervention and arrangements were put in place to run trains on two out of the four lines. There was effective co-operation and engagement between all key parties to plan what was required to make the site safe and to provide a suitable train service as soon as possible. This continued until the slope was fully repaired and normal working resumed.