Tunnel Boring Machine Advance Ground Investigation in Rockburst-Prone Ground Conditions on Neelum Jhelum Project

Abstract

This paper details the methods by which various advance ground investigation methodologies were deployed on two Tunnel Boring Machines (TBMs) working on the Neelum Jhelum Hydro-power project. The project is located in the Azad Kashmir region of northeast Pakistan, in the foothills of the Himalayan range, with overburdens up to 1,870 m and high horizontal stresses, and with complex and challenging geology. The lack of previous project experience in similar conditions, required the use of a wide variety of geological prediction methods and systems. The geological phenomenon of greatest concern was rockbursts: although expected they nevertheless presented a significant danger to personnel and equipment. The ability to predict the likelihood, location, severity and number of rockburst directly impacts upon the tunnel safety and daily production rates. The advanced prediction methods used on this project include forward probing; Tunnel Seismic Tomography (TST), TBM boring parameter analysis, in-situ stress measurements, short term rockburst prediction and continuous microseismic monitoring. This paper describes the various methodologies and how the individual data was integrated on a day-to-day basis to support TBM operations.