Comparison of microseismic monitoring and actual rockbursts in twin TBM tunnels in the Lower Himalayas

摘要

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. The first TBM completed mining in October 2016 and the second TBM completed mining in May 2017. Rockburst characteristics were compiled on both TBMs to create a database for analyzing trends, patterns, etc. Microseismic monitoring commenced on both TBMs, six months after a severe rockburst. The aim of the microseismic monitoring was to collect details of each seismic event, analyze this data and produce a daily report each morning which provided a record of the previous day's seismic activity. Correlation of rockburst characteristics and microseismic activity improved the ability to predict the likelihood, location, severity and number of rockburst events for the following day