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Abstract: Twin 8.5 m diameter, 10.5 km long parallel headrace tunnels under overburdens of up to 1 870 m with high horizontal stresses were excavated for the Neelum Jhelum Hydroelectric Project located in the Azad Kashmir region of northeast Pakistan using two main beam gripper Tunnel Boring Machines (TBMs). The TBMs were introduced to improve tunnel excavation rates and were the only realistic...