Tesco tunnel partial collapse in UK

In the UK, the partial collapse of a rail tunnel under construction over a live railway line at Gerrards Cross on 30 June has caused chaos, but given that a passenger train was held at a signal nearby, it appears that luck played a part in preventing a tragedy.

The work was being carried out by Jackson Civil Engineering on behalf of supermarket giant Tesco, who controversially obtained permission to build a new store over the top of the railway line. The contractor's £20M (US$35.6M) scope included the creation of a land platform over a 350m long stretch of the four track line by erecting 320m of precast concrete arches on piled foundations and filling over the arch with material imported by rail.

At 19:34hrs on 30 June, the driver of a train reported parts of the "Tesco tunnel" had collapsed. It later transpired that a 30m section of arch had collapsed onto the track approximately 80m from the south entrance to the tunnel leaving spoil up to six metres deep on the track. Network Rail, responsible for the UK's rail infrastructure, moved onto site and oversaw cleanup operations.

In the order of 10,000t of spoil had to be removed, with the track beneath the collapsed section being taken up as it was destroyed. Roughly a dozen arches adjacent to the collapsed section have also been removed. The Health and safety Executive (HSE) is investigating the incident and said "the focus of the investigation remains on the way the tunnel infill material was being placed over the concrete arch structure".

Following their own intensive investigation into the cause and extent of the damage, engineers advising Tesco believe they understand the causes of the tunnel collapse and were due to present their analysis, together with a plan to make the site safe for reopening, to Network Rail by 1 August. With associated reviews and remdials to the track and signalling, it is unlikely the tunnel will reopen before 15 August and the future of the scheme remains undecided.

The incident has fuelled speculation as to the impact this may have on insurers' willingness to take a view on providing cover for UK tunnel projects, especially as the contractor in this instance was not a recognised tunnelling specialist. Indeed, there has even been some dissention in the engineering press as to whether the arches constituted a tunnel at all or were better described as a canopy.