Influence of hardness on the deformation and acoustic emission characteristics of rock-like models
Authors: 牛 耀 , Su Zhandong , Sun Jinzhong , Zhang Hao , Zhang Minglei , Wang Lei , Zhang Jianyong 
Published: November 2022

The deformation characteristics of fractured rock masses and the
acoustic emission (AE) (microseismic) characteristics of internal crack
propagation are important research topics to help evaluate and predict
the stability of rock masses. In this study, rock-like models of the
same scale but with different degrees of hardness were prepared by
changing the ratio of rock-like materials, and in each model, a fracture
of the same scale was prefabricated at the same position. Uniaxial
compressive deformation and AE tests were conducted on these rock-like
models. Based on the stress–strain relationship during the compressive
deformation of the models, the compressive deformation process could be
divided into four stages: stage I is the medium compaction stage; stage
II is the elastic deformation stage; stage III is the crack propagation
stage; stage IV is the model failure stage. The deformation test results
showed that the variation trends in the maximum principal strain with
time at measuring points on both sides of the prefabricated fractures
were the same. The maximum principal strain peaks at these measuring
points showed an opposite variation trend with the model hardness. The
deflection angle range of the local principal strain at the passive
loading end increased with the increase in the degree of hardness, while
that at the active loading end did not change significantly. The
relative displacement rate changed significantly mainly in the medium
compaction stage; the harder the rock-like model, the lower the peak
relative displacement rate. Based on the observation results of the AE
test of the rock-like models, the ring-down count vs time curve could be
divided into three stages: initial, growth and stable stages. The
initial stage corresponded to deformation stages I and II. In this
stage, the ring-down count of the hard rock-like model showed little
variation, and the cumulative ring-down counts increased gradually. The
growth stage corresponded to deformation stage III, where the ring-down
count increased sharply, and the harder the rock-like model, the higher
the growth rate of the cumulative ring-down counts. The stable stage
corresponded to deformation stage IV, where the distribution of the
ring-down count of the rock-like model with a relatively higher hardness
was sparse, and the cumulative ring-down counts were either stable or
increased steadily. Corresponding to the medium compaction stage (stage
I) and the crack propagation stage (stage III) of the rock-like model,
with the increase in the hardness of the rock-like model, the frequency
bandwidth of the peak frequency distribution of the AE signals of the
models tended to narrow. Corresponding to the elastic deformation stage
(stage II), with the change in the hardness, the frequency bandwidth of
the peak frequency distribution did not change significantly. The above
test results provide an experimental basis for studying the influence of
rock-like model hardness and prefabricated fractures on the deformation
process of model medium and fracture development.