Process of rock failure is one of the important phenomena in the rock mass. Authors present the monitoring of process of rock failure in laboratory conditions by several methods in this paper. Measurement of acoustic emission, gas permeability and volumetric deformation are methods enable to record the changes of behavior of rock sample in the process of deformation. On the other hand the measurement of ultrasonic wave velocity, analysis by computer tomography or by optical microscopy properly note the changes of failure after the process of deformation. Increasing of gas permeability, number of acoustic emission and volumetric deformation in uniaxial or triaxial stress conditions recognizes creation of micro and macro fracturing in the process of deformation. Computer tomography and ultrasonic wave velocity measurement are susceptible methods to determine the density changes after strength measurement. The visualization of microfractures in thin or polished sections prepared from test specimens is enabled by application of conventional or fluorescent optical microscopy.


Laboratory measurement of stress and strain properties of rock samples belongs to basic destructive tests necessary for assessment of behaviour of rock massif especially due to anthropogenic activity in this environment - constructing of engineering constructions, extracting mineral raw materials, constructing of underground storage etc. The presence of interconnected discontinuities such as cracks, fractures and joints significantly affects both elastic and transport properties of rocks and rock masses. Where the discontinuities are randomly oriented and the state of stress is hydrostatic, the rock might be expected to exhibit isotropy in physical properties. A rock or rock mass containing a system or systems of interconnected, aligned cracks will behave in an anisotropic manner in its elastic and transport properties (King et al. 1995).


Elastic and transport properties have been studied not only during loading of test specimen, but also after peak strength, both in uniaxial or triaxial state of stress or after heating and cooling at present. The test specimens after the loading were analysed by various methods - computer tomography, measurement of elastic wave velocity, optical microscopy.

2.2 Stress - strain tests with measurement of gas permeability

The universal mechanical press ZWICK 1494 with maximum force output of 600 kN and servo control and triaxial cell KTK 100 for measurement in triaxial state of stress with maximum confining pressure of 100 MPa was used for stress-strain tests. Triaxial cell is adapted to inserting into ZWICK press and to gas passage experiments. The triaxial cell KTK 100 was used for the laboratory tests for simulation of stress conditions in rock massif and for measurement of gas permeability (ASTM Standard D4525. 1990, Konečný jr. et al. 1999). Confining pressure in the triaxial cell was applied by the hydraulic pressure of oil. The compressed nitrogen was applied as a reference gas. Upstream pressure of the gas was 3 MPa and it was constant during the measurement. The volume rate of the gas was measured by the flowmeters with the range from 5 to 600 cm3min-¹.

This content is only available via PDF.
You can access this article if you purchase or spend a download.