The rock in the area of the proposed Dublin Port Tunnel is less consistent than previously thought and is probably significantly fractured in several places, a Trinity College Dublin geologist has said.
Prof Adrian Phillips told the inquiry into the Dublin Port tunnel motorway scheme that potential "fracture zones" in the rock have significant implications for the risks associated with constructing the tunnel in its present form as well as for the cost of construction.
He told the inquiry that "significant geological structures" had not yet been "properly reported on". Before continuing with the construction of the tunnel section, Dublin Corporation would be well advised to carry out an assessment of risks associated with those structures and to consider the costs of addressing them, he argued.
Prof Phillips was a witness for the Marino Development Action Group, but stressed he was not being paid a fee for his evidence.
He disagreed with the evidence of Ms Irmina Porschle of Geoc onsult, who had agreed in her testimony that apart from two zones "the rock of the remainder of the corridor is pretty well undifferentiated". Ms Porschle's company, Geoconsult, had helped carry out an environmental impact study for Dublin Corporation.
Taking issue with Ms Porshcle's evidence, Prof Phillips said the internal coherence of the rock mass varied "quite considerably" and that could cause potentially serious problems at fault zones. He identifies a possible seven places where there could be fracture zones. As a result "the idea of the rock body being homogeneous and unfractured doesn't seem to be consistent with the bore hole data", he said.
Such zones had been associated elsewhere in Dublin with mechanical and chemical decomposition of the rock, which would weaken the rock structure, he said. They could have "zones of influence" of 10 or more metres in width and were "in no way insignificant" as a geological feature.
The rock surface was also "very irregular", with some of the irregularities being caused by "ancestors" of the present-day Middle Arch stream and Grace Park stream.
The inquiry also heard evidence of the health risks associated with traffic passing through the proposed tunnel. Mr Seamus Murphy, the principal of St Joseph's Co-educational School at East Wall Road, said a great number of students at the school were suffering from breathing problems and the location of the Dublin port toll plaza 160 metres away would be of only moderate benefit to them.
He also feared the impact of the 43-month construction period on the children. While the school was not opposed to the construction of the tunnel, he said the health of the children had been disregarded.
