The proposed Dublin Port Tunnel is now likely to cost £196 million, according to the latest estimate, The Irish Times has learned. This is almost double the price quoted three years ago.
The controversial project, which would link the M1 motorway with the port largely via a twin-bore tunnel running underneath Marino, is the most expensive road scheme contemplated in the Republic, costing much more than the £100 million-plus Lee Tunnel in Cork.
The latest estimate, which includes VAT, takes into account changes in the design of the port tunnel brought about by the need to neutralise strong opposition from local residents, particularly in Marino and Whitehall, who feared its impact on their homes.
Though now approved by Dublin City Council for inclusion in the city plan, the scheme had to be redesigned to relocate its portals from Whitehall further north along the M1 and to tunnel deeper under Marino to avoid damaging some 300 homes along the route.
Before these major changes were made by the designers, a consortium involving Ove Arup and Partners and the Austrian tunnelling specialists Geoconsult, the price was put at £130 million - significantly more than the original estimate of £104 million in mid-1994.
It was this figure that persuaded the then Fianna Fail-Labour coalition to double the capacity of the port tunnel to a four-lane dual carriageway. The Dublin Transportation Initiative had proposed a two-lane single carriageway, estimated at £88 million.
Because of its strategic importance in catering for the port, which is handling record levels of trade, and reducing the volume of port-related traffic using the city's streets, the project qualifies for 85 per cent grant-aid from the EU Structural and Cohesion funds.
A portion of the additional cost is attributable to the need to take account of a long list of recommendations made by Britain's Health and Safety Executive in a major report on the safety of what is known as the New Austrian Tunnelling Method (NATM).
Unlike conventional tunnels, where a concrete retaining structure is built as the tunnel is bored, NATM involves spraying concrete on the exposed face of a newly bored tunnel, which forms the structure when it sets. The main reason why it is favoured is that it's cheaper.
The British HSE report was commissioned following the "catastrophic failure" during construction of an NATM tunnel at Heathrow Airport in 1994. The accident caused a crater at the surface and so destabilised an office building it had to be demolished.
However, while the Dublin Port Tunnel project team has insisted that the choice of tunnelling method will ultimately be a matter for the contractors to decide, the £104 million estimate which persuaded the government to double its capacity was based on using NATM.
The report of the consultants examining an underground option for the long-delayed Luas light rail project - expected in April - will also have an impact on the port tunnel, as it is expected to produce the first firm estimate of the likely costs of tunnelling in the city.
