Studies on rock conditioning for hard rock tunnelling by a mobile laboratory

Very high abrasivity and squeezing properties of graphitic schists excavated by a large diameter hard rock TBM generate a huge challenge for the contractor company in High Speed Railway Tunnel between Ankara and Istanbul. These characteristics result in very high wear rates of cutting tools and other metal parts and very high torque requirement of the TBM, in addition to very frequent downtimes. The basic aim of this study is to determine effects of additives through rock conditioning on performance of TBM used to excavate the tunnel. All of the rock/muck conditioning laboratory tests is performed on graphitic schist samples, which are the most common lithology through the alignment, in a special mobile laboratory designed by IKSA Company. The tests performed to analyze abrasivity, clogging and sticking characteristics of graphitic schist are presented. Based on the results, during excavation, foam concentration and expansion ratio are suggested as 1% and 8, respectively; water addition should be at least 10% (plus natural water content) and foam injection ratio should be around 80%. Bentonite slurry addition in 2.5% concentration to muck is suggested at 5%. The contractor applied the suggested conditioning system by modifying the TBM equipment to suit the suggested conditioning system.