Underground » Mining Technology and Production
This study was commissioned to provide a greater understanding of the ground caving process and the implications to longwall support operation and design. The major focus of the study was on the caving events which cause rock falls on the longwall face or which cause operational problems.
A study of adverse caving events on longwall faces has been undertaken utilising computer simulation of the ground fracture process and stress redistribution about longwall panels during extraction. Mine monitoring of support pressure, subsidence and stress distributions were undertaken to provide validation data for the models.
The primary aim of the modelling is to simulate the caving mechanics:
- to understand the key factors influencing ground behaviour and,
- to assess the interaction of longwall supports on ground behaviour,
- to assess the operational issues in dealing with the ground behaviour as defined.
The work contained within this report was done in association with ongoing studies at a number of mines. The work at individual sites has been reported to the minesites and the reports are included. The main body of this report is targeted to discuss the outcomes from the study. The detail of individual sites is contained within the attached reports.
Caving simulations were undertaken at the following minesites:
- Moranbah North
- South Bulga
The minesites studied represent a significant range in the geological and geotechnical characteristics of the overburden strata. The range extends from a massive sandstone (20-30m thick) to very weak interbedded strata.
Definition of Adverse Caving Events
An adverse caving event is one which causes delay and or damage to the mining equipment due to a fall of ground and convergence of the supports. The nature of adverse caving events is variable over the minesites studied and ranges from rock falls ahead of the longwall shields to significant and rapid closure of the shields under a sudden caving event. The cause and nature of these events is discussed in the report.