Dight, PM 2026, 'The rock in rock reinforcement: linking fracture mechanics, structural geology and ground support', in D Cumming-Potvin & J Wesseloo (eds), Ground Support 2026: Proceedings of the 11th International Conference on Ground Support in Mining, Australian Centre for Geomechanics, Perth, pp. 1-18, https://doi.org/10.36487/ACG_repo/2625_47
(https://papers.acg.uwa.edu.au/p/2625_47_Dight/)
Abstract: A significant requirement for ground support design in dynamic situations is an understanding of how the rock fractures due to induced stress and seismic wave impact from a burst. This is often referred to as the bulking factor, although this paper will expand on the concept. The bulking factor governs the deformation experienced by the support system and is what the system is designed to manage by limiting deformation or controlling it. The bulking factor is defined by 2 mechanisms. The first is the extensional fracturing or spallation observed on the surface of the exposure, and the second is the apparent shearing of the rock adjacent to the spallation. Both these ‘mechanisms’ occur in a biaxial stress field where the induced stress is parallel to the surface and a response to the shear wave motion emanating from the burst. This story is incomplete and fails to capture the field observations of the remnant support bending before shearing. Surface-wave-induced block rotation provides one possible explanation for the observed bolt bending. Surface waves cause most of the damage from earthquakes in buildings and infrastructure. Surface-wave behaviour underground has received comparatively little attention, however. There is the observation that 80% of failures attributed to bursts occur at depths below the surface within the first 50 to 70% of the minimum opening dimension. Deeper failure, which is often more extensive along strike, is sometimes referred to as ‘shakedown’. It may be attributed to the presence of structural control where the extent of failure is related to the size of the burst event, the rock shear wave velocity, the wavelength and the dominant frequency of the event. Without a comprehensive understanding of the structural geology, the location of these events is considered random. This paper will show that knowing how rock fails is a necessary component of ground support design and implementation.

Keywords: biaxial, spallation, extensional failure, shakedown, stress measurement, strainburst, rockburst, shear wave velocity, Rayleigh wave, bulking, rock mechanics