Underground » Strata Control and Windblasts
The aim of this report is to discuss the roof failure mechanisms in development roadways within coal mines. This is achieved by a discussion of failure modes within the rock mass and how they interact to cause the commonly observed gross deformation of the roof.
The commonly observed deformation or failure modes of the overall roof are sheared roof, guttered roof, cantilevered roof and sag. These failure modes form when the internal self-supporting capability of the roof strata is compromised.
The nature of the self-supporting action and the stress conditions typically encountered in mining is presented.
An overview of the contribution and action of reinforcement, together with the requirements for roadways is presented.
It was found that under low stress deformation conditions, the roof is essentially self-supporting and only requires reinforcement to maintain the bedding and joint integrity.
As deformation increases, reinforcement is required to maintain the support structures in the roof section. Increasing deformation and stress compromises the internal support structures and secondary reinforcement support is required to maintain stability. At extreme stress - deformation levels, it is not cost effective to attempt roadway stabilisation. In many cases the roof may be able to be somewhat controlled, however the floor may heave dramatically to close the cross section available for equipment. In such cases mine re-design is recommended.
The concept of providing patterns for various deformation modes is not appropriate as it requires site specific consideration of the geology, stress fields and mining geometries. Rather, a general overview of the approaches is presented.