Review of Rib Failure Mechanisms in Underground Coal Mines

This project consisted of field measurement of rib deformation including monitoring of rib bolt loads and rib yield characteristics using a range of measurement techniques. The project aimed to assess the effectiveness of current industry rib support patterns with regards to the nature of rib deformation through field measurement and modelling. Dynamic rib failure mechanisms such as coal burst and outburst are not included in this assessment.

The project objectives were met through three case study examples at three different mines in New South Wales and Queensland.

The characteristics of the rib deformation highlighted the variation in mechanisms of rib deformation between the sites; from near rib slabbing at shallow depths, to shear failure of claystone bands, to high stress causing significant shear failure at depth into the rib. Despite this variation in behaviour, the rib support design applied is typically similar across the different mines and for different seams with similar overburden depth.

This project posed the questions “what is the role of rib support” and “should rib support be tailored to the site-specific mechanisms for rib deformation?” The monitoring to date suggests that the role of rib support is to minimise the progression of failure further into the rib by controlling kinematic failure and generating confinement of fractured/yielded rib. However, to effectively implement the appropriate controls, an understanding of site-specific failure mechanisms is required.

This study presents guidelines on key factors that should be considered when designing rib support, where site-specific failure mechanics are to be controlled. Also outlined in this study is a rib monitoring investigation approach that can be used to determine the specific rib failure mechanisms.