Engineers defend plan for Dublin Port tunnel

ENGINEERS involved in designing the proposed Dublin Port Tunnel have strongly defended their controversial scheme against accusations from Marino residents that it could destabilise their homes.

Speaking to The Irish Times in advance of a special meeting of city councillors last Friday called to discuss the £130 million tunnel project, its designers sought to allay the fears of local residents. The designers said the tunnelling method would not represent a safety hazard.

The engineers from Dublin Corporation, Ove Arup and Partners and the Austrian firm, Geoconsult also denied the proposed dual carriageway route linking Whitehall with Dublin Port had been consciously designed as the first phase of an eastern bypass.

The Marino Development Action Group, which represents 2,400 households in the area, has said the recently published environmental impact statement (EIS) on the port tunnel had served only to increase their fears and worries about this project.

These fears have given rise to concern among the project team that the city council might not agree to adopt the required statutory variation of the city plan to allow the tunnel to proceed. Friday's special meeting showed councillors still had serious concerns.

Mr Gerry Murphy, the corporation's project engineer, defended the EIS, which was prepared by Ove Arup and Geoconsult. It had covered issues such as vibrations and construction disturbance, and pledged "before and after" surveys on the effects on housing.

"The issues are addressed in the £15. The vibration controls are defined as severe, adverse or moderate. The time effect on each property as the tunnel passes under is set out and it says that vibrations will be restrained to a level that will not cause even cosmetic damage."

Mr Murphy said the corporation was "concerned that people are afraid" of the project, but he felt this was due to a misunderstanding of a report by Britain's Health and Safety Executive, (HSE) which examined tunnel collapses involving the New Austrian Tunnelling Method (NATM).

"What the HSE report said was that NATM was as safe as any other tunnelling method, but this message hasn't got across," he said, adding that all of its recommendations which were relevant would be "taken on board" to ensure complete safety.

Mr Murphy said the HSE report was dealing particularly with London clay, whereas all the tunnelling under 273 houses in the Marino area at an average depth of 16 metres (53 feet) was through limestone rock and so the risk of collapse would be negligible to non-existent.

Mr Johannes Wageneder, of Geoconsult, said trial bores had shown that the limestone under Marino was ideal for tunnelling. Even the compacted boulder clay which lay along one third of the route not under any of the affected houses would not present any difficulties.

Mr Ciaran de Burca, senior engineer with Dublin Corporation, denied the line of the tunnel had been moved eastwards to run under Marino. He said the proposed route, of the six options examined, was chosen specifically to minimise the effect on residential properties.

Mr Wageneder said the aim was to choose an alignment for the tunnel which was in rock, as far as possible. Other considerations, apart from cost, included minimising its effect in terms of severance, heritage, recreation, townscape, ecology, noise, air quality and disturbance.

He agreed NATM had been chosen because it was a more economical method of tunnelling though he pointed out that contractors bidding for a design and construct tender for the twin tunnel could propose using more conventional building methods.

The fact that the tunnelling method had not been decided might explain why Marino residents found the £15 somewhat vague and uncertain.

Mr Wageneder said the designers still believed that NATM is "the most appropriate method". However, he denied that Geoconsult was "married" to the Austrian system, which involves spraying concrete on the exposed face of a newly bored tunnel to form its structure.

Asked about the spiralling cost, from an initial estimate of £104 million in 1994 to £130 million today, he said the latest figure included VAT, inflation and some additional elements.

The design team emphatically rejected claims that adopting the HSE report's 97 safety recommendations for NATM could add up to £50 million to the overall cost. "These are things we would normally have to do anyway in order to fulfil our obligations", Mr Wageneder said.

Mr Murphy stressed the corporation wanted the HSE's recommendations implemented to the letter.

Asked about the design of the interchange at Whitehall, where the airport motorway would run directly into the tunnel and traffic bound for the city centre would have to get off, the engineers said this had been done to minimise its environmental impact on houses in the vicinity.

Mr Sean Mason, project co-ordinator, said computerised traffic modelling had shown the new route would result in a "marginal increase" in commuter traffic.

He said the port access route would permit the installation of bus lanes, or light rail lines, on Drumcondra Road. The port route would be tolled to discourage car commuters.

Asked if the tunnel would cause such traffic chaos in the north port area that it would have to be extended to form a full eastern by pass, Mr Murphy said this was "absolutely not the case". However, he agreed with the EIS assessment that another Liffey bridge would be needed.

This bridge, costing up to £8 million, is not included in the port tunnel's budget. It would run across the river either on the alignment of Macken Street or Castleforbes Street, in the Grand Canal Docks.