Geotechnically massive strata behave as strong units, rather than the geologically massive description which describes the sedimentary formation. The consequence of such geotechnically massive units to mining is a series of problems associated with these units failing to break up into small blocks.
This paper deals with the determination of what constitutes geotechnically massive strata. This is essentially a function of the geology and the mechanical properties of the geological stratigraphic units that need to be combined into geotechnical units. The mechanical properties depend on the rock itself and on the structure in the form of joints and faults. The importance of anisotropic rock behaviour cannot be underestimated and neither can the variations in geology.
Structural plate and beam analysis is presented as a method to determine where and at what span the initial fall and subsequent goaf falls will take place. While this is elastic analysis, it should be appreciated that the stronger rocks which lead to massive strata conditions will behave more elastically, and therefore this method of analysis is considered justified in most cases. This approach is considered to be far more usable and reliable than complex numerical analysis, which generally lacks the range of real rock behaviour as a fundamental input and is frequently uncheckable. The use of these established analytical techniques lends confidence to the solutions derived from their use. The pre-existing stresses are important as they will control initial goaf formation.
Dynamic support loading is considered as is preconditioning to break massive units down so that they break in smaller blocks.
Ian Gray and Tim Gibbons, A structural engineering approach to longwall rock mechanics in massive strata, Proceedings of the 2023 Resource Operators Conference, University of Wollongong - Mining Engineering, February 2023, 18-35.