Dáil Éireann debate -
Tuesday, 27 May 2003

Vol. 567 No. 5

Written Answers. - Dublin Port Tunnel.

Finian McGrath

Question:

362 Mr. F. McGrath asked the Minister for Transport if his attention has been drawn to the damage to homes by the construction of the Dublin Port tunnel; and if the 30 metre zone will be extended to a 60 metre zone in order to protect the interest of the residents. [14547/03]

Minister for Transport (Mr. Brennan)

The matters raised by the Deputy are matters for the contractor, Dublin City Council and the NRA.

I am informed by the NRA and Dublin City Council that the port tunnel passes under approximately 50 apartments and 334 houses. To date it has passed under close to half of these properties. From this total a small number of complaints have been received claiming damage to some properties. I understand that any verified damage connected with the tunnelling will be made good by Dublin City Council.

I understand that a number of measures are in force to ensure the safety of properties. All properties lying within a 30 metre zone of influence on either side of the tunnel have pre-construction and post-construction building condition surveys carried out by independent building surveyors. Any damage attributable to tunnelling works are covered by a property protection guarantee issued by Dublin City Council to all the property owners before the tunnelling works commenced. There is also provision for interim surveys should complaints arise during the construction period. The project's insurance loss adjusters are also available to assess any damages arising from property owners claims, if and as they arise.

I also understand that other significant measures have also been taken to monitor and ensure the safety of buildings over the tunnel including vibration monitors being installed at various properties to monitor any vibration from the works; and settlement surveys being carried out on an ongoing basis during tunnelling under houses and an extensometer being installed in certain boreholes along the route which remotely monitors ground movements in the rock before such movements appear at the surface and provides substantial information on the ground behaviour associated with the tunnelling.

Within the tunnel, monitoring of the tunnel walls is also carried out. This involves the setting up of deformation points which are regularly checked for position and movement. Any movement or misalignment will be registered. A 24 hour hotline and emergency response is in place and available.

This package of measures along with the other various controls and monitoring arrangements that exist represents a comprehensive approach to ensuring the safe passage of the tunnelling works under properties. It is in line with the best international practice and is part and parcel of the successful delivery of tunnels around the world.

In regard to the question of extending the survey area from 30 metres either side of the tunnel to a 60 metre distance, the NRA and Dublin City Council consider this unnecessary. The rationale behind the 30 metre "influence zone" is based on a prediction of ground impacts associated with the tunnel. Actual ground settlement results have corroborated the accuracy of the limit of this predicted influence zone. Any basis for change to the width of the zone would have to be guided by the actual settlements measured. I am informed that to date, settlement readings have not indicated a need to widen the "influence zone".