The Role of Horizontal Probe Drill Data in Tunnel Excavations: A Case Study from Istanbul Bosphorus Tunnel

  • Aydin BAKIR Scientific Researcher, Geological Engineering Department, 34469 Maslak / İstanbul, Turkey
  • Vural YAVUZ Assoc. Prof. Dr., Civil Engineering Department, Turkish-German University, 34820 Beykoz / Istanbul, Turkey
Keywords: Bosporus Tunnel, Probe Drilling, RQD, TBM, Thrust Pressure, Tunneling


Research methods are needed during excavations with TBM (Tunnel Boring Machine) to ensure safe excavation conditions because it is not possible to see and continuously monitor the excavation face completely. One of the most dangerous conditions expected in the tunnels that will be opened underwater is sudden and high water ingress. To detect possible water ingress, one of the most reliable methods that can be used is to perform horizontal probe drills. With water flow, the dimension of the danger increases more if weak ground conditions and fault and/or crush zones are monitored intensively. Such conditions may cause serious damage to TBM, and sudden washing can cause collapse and deviations in the vertical and horizontal axes. In this sense, considering the negativities of the geological and hydrogeological conditions of the Bosphorus Tunnel passing beneath the Bosphorus Strait, it was set as a contract condition that TBM excavation would be performed according to the results of the horizontal probe drills. During the excavation along the tunnel route, horizontal probe drills were performed at an average of 36 m. The Instantaneous Advance Speed (IAS) with 1-cm intervals, Thrust Pressure (TP), Torque (TQ), and washing water thrusts of the horizontal probe drills were recorded in this respect. In this article, the Instantaneous Advance Speed (IAS) values recorded during drilling were normalized with torque and thrust values, respectively. In this way, the changes in advance speeds were determined, and it was determined whether these changes were caused by increased thrusts, and/or torque or lithological changes. The relations between normalized Instantaneous Advance Speed (IAS) values and the RQD values at the tunnel excavation level of 14 vertical drillings built on the tunnel route were revealed. These relationships showed that the speed of Instantaneous Advance Speeds decreased as RQD values increased. This study must be proceeded by analyzing statistical data with a database containing more vertical drilling data to develop the TBM performance prediction model in such a way that the relations between formation characteristics and horizontal probe drill performance are revealed based on horizontal probe drill data.


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