TUNNELING IN OPHIOLITHIC SERIES FORMATIONS: TUNNELS OF THE NEW HIGH-SPEED RAILWAY DOUBLE TRACK LINE - SECTION LIANOKLADI - DOMOKOS

Abstract

For the project “3rd phase of design of the new high speed double track line - section Lianokladi – Domokos (subsection: Ch. 0+000 - Ch. 13+500)” geological and geotechnical investigations and designs were implemented for tunnels and cut & cover of the subsection Ch. 9+685 - Ch. 12+254. The above subsection, a significant part of which is already constructed, includes three tunnels (SS1, SS2 and SS4) and one Cut & Cover (SS3). Tunnels SS1, SS2 and SS4 are of lengths 860m, 477m and 495m, with overburden 58m, 50m and 60m respectively and are driven in mountainous area consisting of ophiolithic series formations, mainly massive basalts with varying fragmentation, dolerites, spilitic intrusions and serpentinites. The above formations are characterised by variable fragmentation, weathering and degree of alteration. At places metamorphic basalt (amphibolite) is also encountered. Schist-chert intrusions and ophiolithic material with intense schistification, are considered of tectonic origin and are connected with the major and secondary compressive fault zone in the area. Limestone blocks inside the ophiolithic mass are also considered of tectonic origin. The narrow area of the alignment is characterized by the presence of normal and transverse faults, along with major joints crossing the rockmass. The formations along the tunnels, according to their engineering – geological behaviour, were separated to seven geotechnical units. Representative values for the geotechnical parameters of each unit were determined and analyses for the corresponding primary support categories were performed, using code UNWEDGE (RocScience) for rock-classes were behaviour of underground excavation is determined mainly due to orientation of joints and using code PHASE2 version 6.011(RocScience) for formations were behaviour of underground excavation is determined mainly by their strength and deformability.