ABSTRACT
Twin 8.5 m diameter, 10.5 km long parallel headrace tunnels subject to overburdens up to 1,870 m with high horizontal stresses were excavated for the Neelum Jhelum Hydroelectric Project in northeastern Pakistan using two main beam gripper Tunnel Boring Machines (TBMs). Both TBMs started headrace tunnel excavation in January and February 2013. After 2.4 km, both TBM tunnels experienced regular rock bursts and a severe rockburst occurred at 5.8 km which disabled one TBM for 7.5 months and caused substantial damage to the tunnel lining in the second TBM tunnel. This paper will comprehensively explain the microseismic (MS) monitoring system and the report format produced from the recorded data. Analysis of the MS data relative to the location along the tunnel axis, horizontally, and vertically across the tunnel, radially around each TBM and relative to overburden, and the interrelation between the two TBM tunnels will be discussed for various sections where applicable.
