Deep rock masses have complex internal structures, which results in significant discreteness and blocky structures. With the increase in the depth of engineering construction and energy extraction, the unique pendulum-type waves emerge in deep blocky rock masses under the action of dynamic loads from mining and blasting, and they are characterized by low frequency, low velocity, large displacement amplitude and high kinetic energy, distinguishing them fundamentally from conventional seismic waves. Pendulum-type waves can induce alternating stress states of relative compression and separation within blocky rock masses, and may lead to rockburst disasters and even engineering-induced seismicity, thus posing great challenges to the safety of underground engineering such as tunnel construction and mining. In this paper, experimental research is conducted on the mechanical behaviors and typical characteristics of pendulum-type waves of multi-fractured blocky rock masses under static and dynamic loads. Firstly, the strength, deformation and failure mode were analysized based on uniaxial compression tests. The weak structural layers will significantly reduce the uniaxial compressive strength and enhance the ultimate deformation capacity of rock masses. Fractured rock masses have significant nonlinear deformation and may develop macroscopic fractures (vertical splitting failure, with the failure mode transitioning from brittle failure to ductile failure) at the stress level significantly lower than their uniaxial compressive strengths. Subsequently, based on the dynamic impact tests, the dynamic response, overall displacement, wave velocity and the mechanism of anomalously low friction were investigated, and the typical characteristics of pendulum-type waves, including the low frequency (177 Hz and 153 Hz in this experiment, which are much lower than the natural frequency of the rock itself), low velocity (about 900 m/s in this experiment, which is significantly lower than those of P-waves and S-waves), large displacement amplitude (it is more than two orders of magnitude larger than the deformation of an intact rock under an identical load) and high kinetic energy (The total kinetic energy accounts for 40% and 28% of the total energy in this experiment, which has its particularity and cannot be ignored) were quantitatively described. This study holds significant research importance for understanding the nonlinear waves in deep fractured rock masses and their dynamic behaviors, as well as for preventing and controlling engineering disasters in deep rock masses.

How to cite: Jiang, K., Qi, C., and Hu, X.: Research on the mechanical behaviors of multi-fractured blocky rock masses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5765, https://doi.org/10.5194/egusphere-egu26-5765, 2026.

Acoustic emission (AE) monitoring is widely applied to track damage development in brittle rock, although relating recorded signals to specific fracture mechanisms can remain uncertain, particularly when comparing thermal and mechanical loadings. This contribution presents a preliminary assessment of AE waveform characteristics measured during two heating-only experiments and two uniaxial compressive strength (UCS) experiments performed on 100 mm diameter basalt specimens containing a central axial circular hole. This geometry provides a consistent configuration that promotes stress redistribution and damage localisation around an opening, allowing fracture processes to be compared within a common specimen form.

Full AE waveforms were acquired throughout each test using broadband piezoelectric sensors coupled to the specimen surface, with pre-amplification and digital acquisition. Event features were extracted in the time and frequency domains, including rise angle, duration, hit counts, average frequency, peak frequency, peak amplitude, and amplitude distributions. Feature-space comparisons were then used to evaluate whether thermally and mechanically induced microfracturing exhibit separable signal characteristics.

The thermal experiments were associated with a single dominant fracture initiating along the shortest ligament between the aperture boundary and the nearest specimen edge. In contrast, UCS loading produced a more complex fracture network consistent with mixed tensile and shear microfracturing. Rise angle versus hits per duration plots indicated that thermal events occupied a more restricted region, whereas UCS events displayed a broader spread, which may reflect greater variability in source processes during complex damage evolution. Frequency-based comparisons further highlighted the differences: thermally induced events clustered mainly within a lower-frequency band (approximately 100-300 kHz), while the UCS tests exhibited an additional higher-frequency population (approximately 400-600 kHz), alongside the lower-frequency component. Amplitude distributions were also differed, with thermal events tending toward a narrower amplitude range relative to the wider distribution observed under UCS loading. Collectively, these observations suggest that the combined time-domain, frequency-domain, and amplitude-based AE features support mechanism-informed discrimination between thermally driven tensile fracture and mechanically driven complex fracture networks providing a basis for subsequent statistical or learning-based classification in coupled thermomechanical experiments

How to cite: De Alwis, A., Serati, M., Dyskin, A., Pasternak, E., Martin, D., and Williams, D.: Waveform signatures of acoustic emission from thermally and mechanically induced microfracture in centrally apertured basalt, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8596, https://doi.org/10.5194/egusphere-egu26-8596, 2026.

Block elbowing, the process in which rotating blocks push neighbouring blocks apart, influences both geological deformation and the stability of mining excavations in blocky rock masses. A clearer understanding of elbowing is essential for improving rock mass modelling and maintaining the safety of engineering structures. To this end, we analyse a chain of stiff blocks connected by springs, with one or two end active (driving) blocks – the blocks whose rotation is externally induced. All other - passive blocks - have translational and rotational degrees of freedom. The results show that block rotation is sequential (starting from driving blocks) producing a rotational wave with strongly configuration-dependent rotational patterns.

Opposite to a single driving block system, a double-driving block system exhibits more complex behaviour, as the active blocks may rotate in the same direction (Case I) or in opposite directions (Case II). In Case I passive blocks can exhibit anticlockwise rotation that is opposite to the clockwise rotating driving blocks, while in Case II all passive blocks do not rotate at all.

Further deformation patterns arise from block geometry, introduced by varying block corner rounding to represent spheroidal weathering. The results reveal a transition from reversible to irreversible passive block kinematics. Reversible responses include either clockwise rotation followed by full recovery or no rotation. The boundary between these types of block behaviour is defined by a linear relationship between the active-passive and passive-passive contact friction coefficients, with the intercept related to block corner rounding. In contrast, irreversible kinematics characterised by residual rotation emerge only for highly rounded blocks. This irreversible behaviour is restricted to short block chains and disappears in chains of five blocks suggesting a critical size of the Cosserat like zone with independent rotational degrees of freedom. This study provides new insights for modelling the stability and long-term evolution of blocky rock masses.

How to cite: Zhang, M., Dyskin, A., and Pasternak, E.: Non-linear rotational waves and complex rotation patterns in a chain of blocks with elbowing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8985, https://doi.org/10.5194/egusphere-egu26-8985, 2026.

The subject of this study is the process of hydraulic stimulation of a tectonic fault, leading to induced seismicity. We consider a scenario in which fluid injected near ​​an existing fault, causing a localized change in pore pressure and a reduction in effective stresses. This, in turn, initiates slippage of the fault segments and the formation of a slip zone, the size and slip velocity of which determine the magnitude of the resulting seismic events. The goal of this study was to develop a relatively simple model for estimating the potential magnitude of induced seismic events based on a limited set of governing parameters. The primary objectives of the study were to identify the key factors that have the greatest impact on the characteristics of the slip zone and to determine how fluid injection parameters (rate and injected fluid volume) affect earthquake magnitude by changing slip dynamics. The model obtained is based on the results of a series of numerical experiments analyzing the hydromechanical behavior of the fault under various injection conditions. The modeling was performed using a two-parameter rate-and-state friction law, which, unlike a single-parameter model, allows for a wider range of slip regimes to be simulated and accurately describes the transition from stable slip to dynamic failure.

The functional relationships were established between the initial system parameters and the key obtained slip characteristics. It was shown that the final slip zone length is almost linearly related to the length of the initial unstable zone, and the maximum slip velocity increases exponentially with increasing pore pressure rate. At the same time, in the area of high loading rates, the saturation of the sliding velocity is observed at a characteristic level, which leads to a limitation of the possible magnitudes of earthquakes induced by fluid injection.

How to cite: Turuntaev, S., Baryshnikov, N., and Riga, V.: Estimation of potential magnitudes of induced seismic events based on direct numerical simulation of fluid injection near an active tectonic fault., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11339, https://doi.org/10.5194/egusphere-egu26-11339, 2026.