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The record penalty imposed this week on Balfour Beatty and the fine against Geoconsult for their parts in the tunnelling collapse at Heathrow Airport in October 1994 were the culmination of five years' work for Health & Safety Executive investigators. Ric

When Balfour Beatty won the main civils works contract for Heathrow Express in January 1994, with Geoconsult as its specialist New Austrian Tunnelling Method consultant, neither could have imagined how badly things were to turn out.

Nine months into the £60M contract to construct the main tunnels and stations for the client BAA's £235M Heathrow Express rail link from central London to the airport, the project suffered one of Britain's worst tunnelling collapses. The site was the focus of national media attention as engineers fought for two weeks to contain and arrest the progressive collapse 30m below the heart of the nation's busiest airport.

Five years later the rail link is complete and hailed a success. Frenetic activity and unprecedented construction teamwork brought the project in just six months late and salvaged some credibility for the project team (NCE HEX supplement March 1998). Last year's British Construction Industry Awards even recognised the achievement with a special commendation for disaster recovery. 12

But the project has had its costs. Balfour Beatty has spent around £35M more than it anticipated, as has client BAA. Numerous insurance companies have also shelled out as costs soared to over £440M. The record fine of £1.2M against Balfour Beatty and £500,000 against Geoconsult plus costs of £100,000 each will dent not only balance sheets but also the reputations of the two guilty firms.

Both were prosecuted and found guilty under Sections 2(1) and 3(1) the Health & Safety at Work Act 1974 for failing to ensure the safety of their employees and others not in their employment while carrying out tunnelling work at the Central Terminal Area of Heathrow Airport. Balfour Beatty pleaded guilty to the charges, Geoconsult not guilty.

Evidence given in court painted a picture of a project which began in semi-chaos with management practices, quality control and checking procedures failing. Even the actions of those not in the dock were thrown into question. Client BAA's procurement strategy, lead designer Mott MacDonald's role - all came under scrutiny during the 26 day trial.

Nor did the HSE emerge unscathed. Judge Cresswell's criticism of its investigation and use of expert witnesses in its prosecution left the HSE paying all but £200,000 of its costs - that totalled £880,000 at the last count. The judge's ruling on the use of expert witnesses will certainly affect the way the HSE carries out its investigations in the future.

So how does a project go so wrong? The Heathrow Express rail link between London's Paddington station and Heathrow airport began life full of hope as a 70:30 joint venture between BAA and British Rail. It was to build the first new private heavy rail line for decades.

The BAA/BR HEX team was set up to manage the project under the then- radical New Engineering Contract. It included engineers from project manager Taylor Woodrow and permanent works design engineers from Mott MacDonald. In 1996 BAA took sole control by buying out BR's share in the project for £19.8M.

Under the conditions of the semi-bespoke NEC set up by BAA, main contractor Balfour Beatty was responsible for the design and technical supervision of its own tunnelling work using NATM, which was being used in London Clay for the first time. Balfour Beatty employed Austrian NATM expert Geoconsult to carry out design and supervision.

Most tunnelling on the project was to be carried out using two boring machines - one with a Dosco shield to construct the main twin running tunnels to the Central Terminal Area, the other with a Howden shield to construct the single bore to Terminal Four. But it was always the decision to use NATM to construct the stations at the Central Terminal area and Terminal 4 that required the most design time and caused the most anxiety.

Although the original design was to construct the underground station concourses and access tunnels with conventional segments, the HEX team was keen to use the potentially cheaper NATM sprayed concrete technique.

To prove the method - used with great success on the Channel Tunnel but in hard chalk rather than soft London Clay - BAA commissioned a £1.1M trial tunnel in 1992. Under the guidance of Mott MacDonald, Taylor Woodrow and Austrian tunnelling expert Dr Gerhard Sauer, contractor Kier-Lilley- Kunz successfully trialled three different adaptations of NATM and associated compensation grouting regimes. The results were used as the basis for contractors' tenders in 1993.

So when Balfour Beatty and Geoconsult began work in earnest in February 1994 they had no reason to doubt that the method would work.

And in reality it is perhaps only the NATM method which has survived the 'construction trial of the decade'. The HSE's prosecution raised questions about the management structure of the project and highlighted poor quality workmanship and supervision as key contributors to the collapse.

It successfully argued that disaster could have been prevented by the consultant whose monitoring instruments showed a collapse was likely weeks before it happened.

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