Light at the end of tunnel inquiry?

4:49pm Tuesday 30th August 2005

As Chiltern Railways commuters get back to their normal routine, the events surrounding the Tesco tunnel collapse are still under the microscope of the Health and Safety Executive.

The causes of the calamity, which blocked the line for seven weeks, are finally coming to light, as JENNA TOWLER discovers.

SEVEN weeks after a 30- metre section of the Tesco tunnel collapsed onto the main south Bucks rail line to London, trains are up and running again.

Bosses at Chiltern Railways were relieved to get their services back on track early last Saturday morning after passengers had endured weeks of replacement bus services and lengthened journey times.

On Monday, commuters got to work at full speed, with no problems, after all safety procedures were followed successfully.

The main objective over the last few weeks has been to get trains moving again through Gerrards Cross station. Now the causes of the disaster are being scrutinised.

Tesco and its contractors, Jacksons Civil Engineering, are working with officials from Network Rail, Chiltern and the Health and Safety Executive to identify what went wrong.

A spokesman for Chiltern Railways said: "The major cause of the collapse has been identified and remedial works have taken place over the last seven weeks to make it safe to run trains through the tunnel.

"Independent assessments by a number of different bodies have taken place, which have satisfied both Network Rail and the Health and Safety Executive (HSE) that it's absolutely safe to run trains again. Chiltern Railways has received written confirmation from Network Rail and the Health and Safety Executive," the spokesman added.

No more construction work will take place at the site until Tesco can prove to both Network Rail and the HSE that it can be done without threat to the railway.

The spokesman said: "All safety assessments so far have been based around opening the railway through the existing sections of the tunnel and, as such, no decision has been made on the future of the tunnel or will be made for some months."

Concerns about the design of the tunnel and its strength have been raised by commuters.

However, Chiltern Railways reassured its passengers, saying the design is in use in more than 1,000 locations worldwide, including the Channel Tunnel Rail Link, and the design is perfectly safe when correct construction methods are used. "In the area where the tunnel collapsed, they weren't," a spokesman said.

Who is to blame is still being probed by investigators at the HSE but the cause has been identified.

Roger Dickinson, the contract director at Network Rail said: "The covering method requires the space on each side of the tunnel structure to be filled before the roof is covered.

"The underlying cause of the accident is still subject to a HSE investigation, but initial views are that the loading sequence used in the construction of the tunnel was the major factor that caused the collapse."

An electronic monitoring system has been installed by Chiltern Railways to assist engineers and to monitor any possible movement. It takes readings from 400 points on the structure every three hours. The date of the final report from the HSE report is still unknown.

FACT FILE

• 29 damaged segments of the tunnel have been removed from the site.

• A further 34 undamaged sections adjacent to the collapse have also been removed.from the consrtuction area.

• 8,000 tonnes of fill from the collapsed area and a further 7,000 tonnes from the sides of the collapse have been taken away.

• All damaged track has been taken up and relaid.

• A laser monitoring system has been installed to monitor any future movement in the tunnel's structure.

• Infill material was placed on top of the tunnel with insufficient support at the sides which caused the tunnel to buckle.