Sir, - As part of a research project funded by Forbairt and industry, we have been studying the rock fracture systems of the Dublin area and their potential for locating geothermal (hot water) energy sources. Costing of proposals to put the Luas system in tunnels under central Dublin needs detailed knowledge of the rock conditions there. In the case of the proposed Dublin Port tunnel, detailed plans and costings were based on data collected from 100 bore-holes and from a variety of detailed geophysical surveys. Such detailed information is neither available nor obtainable under the city-centre section of the Luas route.
However our own research, as well as data made available from the Geological Survey of Ireland, makes it clear that tunnelling will involve taking very serious risks of damage to buildings and of major cost over-runs. Tunnelling will be in the hard limestone strata into which Dublin's rivers, such as the Liffey, Stein, Poddle, Bradoge, Oxmanstown, Viceregal and Camac, have in the past cut deep canyons down to 45 metres below the present sea level. These channels probably formed where the underlying bedrock was highly fractured. The channels were subsequently filled with river sand and gravel when the sea rose to its present level after the end of the last ice age.
These buried channels are certain to have large volumes of water in them. Tunnelling through solid rock along the proposed Luas route will involve boring into these sand-filled channels, resulting in the risk of flooding, tunnel collapse and damage to the foundations of large buildings. While the exact position and depth of these buried channels is uncertain, some of them probably lie beneath present-day river courses. However, the buried ancient channel of the Liffey, reaching a depth of 45 metres below sea level, does not follow the present river course, but runs northwards from Islandbridge towards Drumcondra to join the buried channel of the river Tolka and then curves south-east to Ringsend. The proposed underground tunnels are likely to intersect at least eight of these channels.
EU Commissioner Monika Wulf-Mathies would certainly be right to cancel EU funding for Luas if the underground option is chosen. There are safer and more rational ways of spending EU taxpayers' money. It is, however, possible that underground rail tunnels just might run into the hot water that is of interest to our research. - Yours, etc.,
Adrian Phillips, and Alex Densmore,
Geology Department, Trinity College, Dublin.