Researches into mechanical properties of rocks are mostly done under static (quasistatic) loading. In nature, however, rocks are also often subjected to dynamic (vibration) loading as a result of propagation of seismic waves due to e.g. earthquakes, rockbursts, blasting operations, etc. This type of loading can be simulated on a modern press, MTS 816 Rock Test System, purchased by VSB-Technical University of Ostrava.
Whereas in the past, especially stress-strain and energy characteristics in the course of dynamic (cyclic) loading were observed on this test system, recently research has focused mainly on the observation of rheological properties during this loading. In the course of observation of energy characteristics of mechanical loading, anomalies were found before achieving the limit of ultimate strength. The cause of them is probably the action of energies other than mere mechanical energy. For this reason, research focused on the determination of temperature changes in the course of rock dynamic loading as one of possible causes of the occurrence of mentioned anomalies. During the observation of rheological properties under dynamic loading, tests were carried out both in creep regime and in relaxation regime, at various levels of average load or strain and at various vibration parameters (frequency, amplitude). The submitted article presents some results from the above-presented researches.
In the framework of researches, many tests in various cyclic load regimes were carried out. At first, the tests were conducted at a cyclic load in the regime of constant -rate of loading up to the rupture of test specimen. In this regime, both simple compression tests and oblique shear tests were performed. In the course of this research, energy anomalies, which could be explained by conversion of part of strain energy into another form of energy, were found out before damaging the specimens of rock. For this reason, some energy properties of rocks subjected to dynamic load were also observed and the temperature of rocks was measured.
Lately, research has focused especially on the rheological properties of rocks subjected to dynamic load. Tests of rheological properties at a dynamic load were conducted both in creep regime and in relaxation regime, at various levels of average load or strain and at various parameters of vibration (frequency, amplitude). Rock specimens were stressed especially in the range of frequencies that corresponded to frequencies of seismic wave propagation in the course of rockbursts (less than 30 Hz).
The submitted paper will deal with findings obtained in the course of this research, especially with results of tests in the rheological regime of load.
For dynamic loading, rock testing equipment MTS 816 was used. This system is able to produce the maximum compression force of 1015 kN and the maximum tensile force of 650 kN. The stiffness of the press is determined at 26.108 N/m. The more detailed characterization of the test system was described e.g. in (Šancer 2008, Petroš 2007).
