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RAIB report released into the penetration and obstruction of a tunnel between Old St and Essex Road

Rail Accident Investigation Branch (RAIB) has today released its report into the penetration and obstruction of a tunnel between Old Street and Essex Road stations, London, 8 March 2013.

A full copy of the report is available here.

Summary

Shortly after 10am on Friday 8 March 2013, the auger of a CFA piling rig penetrated the roof of a Network Rail tunnel near Old Street station in Hackney, London. The auger was being used to install piles for a mixed-use development on a site 13 m above the tunnel.

An accident was avoided because the driver of a passenger train travelling between Moorgate and Finsbury Park observed water pouring from the tunnel roof. Train services were stopped shortly before two sections of auger, each weighing 120 kg, fell onto the track.

The construction team were unaware that they were working above a tunnel because its alignment was not shown on the site plan, or on any map available to the design team, developer or the local planning authority. As a consequence, Network Rail had not been consulted and was unaware of the construction activity. The RAIB has determined that about half of the 39 proposed piles would have penetrated the tunnel.

RAIB’s investigation found that:

  • The tunnel, in common with some other railway tunnels in urban areas, particularly London, Newcastle and Glasgow, is omitted on most mapping, including all current and historic Ordnance Survey maps and plans. Although not relevant to the accident, maps showing underground railways often show a stylised, but incorrect, tunnel alignment.
  • The developer proceeded without understanding the significance of a Land Registry entry for the development site stating ‘so much of the sub-soil as was vested in the Great Northern and City Railway is excluded from the registration’. This railway company no longer exists but its assets, including the incident tunnel, have passed to other railway organisations.
  • The structural engineer and building contractors did not identify that an obstruction, found in an exploratory borehole before piling commenced, was part of a railway tunnel. 
  • Routine conveyancing searches undertaken when the developer purchased the site did not include the tunnel owner, Network Rail, because this organisation was not included in the options offered by the specialist conveyancing search provider.

Recommendations

As a consequence of this accident, RAIB has made five recommendations.

Recommendations addressed to railway infrastructure managers cover:

  • Informing developers and local authorities about the location of railway tunnels and associated subterranean structures when they are not shown on Ordnance Survey mapping.
  • Taking proactive steps to identify new developments above railway tunnels (a process already implemented by London Underground).

A recommendation to the British Standards Institution seeks an addition to the Code of Practice for Site Investigations (BS 5930), warning that some railway tunnels are not shown on Ordnance Survey mapping. A recommendation to the Department for Communities and Local Government relates to arrangements for making Railway Infrastructure Managers aware of all planning applications in the vicinity of railway infrastructure.

RAIB has also identified two learning points relevant to the construction industry: 

  • clients and design teams should be aware of the importance of information shown on land ownership records; and 
  • those conducting desk study investigations should be aware that not all railway tunnels are shown on Ordnance Survey mapping.
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