It is known that the ratio of rock stiffness around the mine workings and the stiffness of the surrounding strata has a crucial meaning for rock stability in the close vicinity of the underground excavation. Significant resources were invested for the research aiming to understand the failure mechanism using acoustic emission (AE) to evaluate the relationship between the parameters of AE and crack/fracture dimension/scale to determine statistical regularity of AE appearance before oncoming rock collapse and features of acoustic wave attenuation during its propagation via rock massive. However, the methodology of the rock stiffness assessments based on the AE parameters is still lacking.
The paper considers the physical basis for applying AE for stiffness assessment in underground conditions.
The rockburst understanding and assessment of their occurrence is in the mainstream of rock mechanics since the violating collapse of rocks towards the space of underground openings is a great cause of accidents during mining (Zhang et al. 2017a, He et al. 20017). Moreover, strong seismic events are largely responsible for the general community's increasingly declining acceptance of mining (Alber et al. 2009).
There are different approaches in the assessment of the probability of rockburst proneness (Zhang et al. 2017b) including local stress assessment at the wall/face of underground openings or/and in boreholes, using acoustic emission (AE) (Muhammad et al. 2021, Plenkers et al. 2022) or/and electromagnetic radiation (EMR) caused by rock fracturing (He et al. 2017, Lockner and Rehez 1994, Guha 2001, Thompson et al. 2009, Johnson et al. 2013, Goebel et al. 2014, McLaskey & Lockner 2016, Gibowicz & Kijko 1994, Frid & Mulev 2018). AE or seismic acoustic excitation is known to be induced by rock fracturing (Kim et al. 2015).
Stiffness is defined as the ability of the system to resist deformation in response to an applied load (Mendetsky 2016). It scales positively with the ratio of the applied stress to the induced strain. Variations in shear stiffness in the shear zone contributed to the emergence of a high slip potential, leading to seismic events (Sainoki & Mitri 2014). The effect of stiffness changes on instability in the underground opening was studied by Qin et al. (2006), who showed that the instability leading to coal bump depends mainly on the system stiffness ratio. Generally, the criterion of stiff loading can be written as follows (Kocheryan et al. 2016):
(equation)
Where Km and KF are stiffness coefficients of the loading system (rock mass) and fractured zone near the underground opening, respectively. If Eq.1 is invalid, the rock failure occurs in an abrupt and blast-wise form (so-called rockburst).
