Pre- and post-failure ground behaviour: case studies of surface crown pillar collapse

Five case studies of collapse of surface crown pillars from Western Austral ia and the Northern Territory were analysed. It was found that there was a pattern in the geotechnical behaviour of the rock mass prior and after the collapse. The pattern indicated that the hangingwall was deteriorating year s or months prior to collapse. Weeks before, level pillars were collapsing and broken rock rilled down the stopes. Within days or even hours before th e collapse, rock noises and rock falls were reported in various parts of th e mines. To monitor different behaviour of the rock mass it is recommended that appropriate geotechnical instrumentation and monitoring be used. Deter ioration in ground conditions can be triggered by external sources like mas s blasting or a seismic event. After the collapse, the postfailure behaviou r in a from of further ground collapse and gradual movement continued for a number of years. (C) 1999 Elsevier Science Ltd. All rights reserved.