Longwall Visual Analysis, which is a software package that continuously monitors shield pressures and shearer position in longwall mines, can provide a Cavity Risk Index that can be used by mines to assess the likelihood of instabilities, Hoyer said.

“LVA displays live charts of data, such as shield leg pressures, loading rates, and yield frequencies,” he said.

“Data analysis techniques were applied to historical data records from multiple longwall sites in order to develop a Cavity Risk Index.

“The CRI indicates the risk of roof cavities developing, and it is based on pressure trends that indicate significant yielding and loading rates spanning a region of relatively low support.”

LVA has been running on 19 Australian longwalls for up to four years and as a result a very substantial database of shield pressure trends in a wide range of longwall situations has been collected.

This database has been analysed to develop indicators that will give operators and geotechnical engineers advance warnings of developing conditions such as weighting events and difficult roof conditions.

Case studies from different longwalls show that the CRI can give real-time advanced warning of the formation of roof cavities with their anticipated location on the face, Hoyer said.

“The limited number of case studies done so far indicate that the predictions have a high degree of reliability, but more work is required to quantify this.”