The study of barrier fracture in relation to earthquake and rockburst prediction
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One of the simplest models of earthquakes and rockbursts was studied in laboratory conditions in which the fracture was initiated in a barrier between two preexisting faults. The treated models were built of concrete; during the construction of the models, the stress concentrators were inserted inside the models. This arrangement enabled the shear displacement to occur during uniaxial loading of the model. The tests were made on the series of models, the sizes of which were mutually varying more than one order. In the process of the barrier fracture propagation, the following were investigated: the time and space changes of local deformations as well as the acoustic emission, velocities and amplitudes of elastic waves, electrical conductivity and proper electro-induction. The process of barrier fracturing can be understood in three fundamental stages. In the course of the first stage, the density of small tensile cracks increases considerably, while the volume in which they exist is gradually enlarged. In the second stage, as the result, of these cracks coupling, longer shear cracks are created. During the coupling, due to the development of numerous regions of unstable deformation, the zones of nonequal rigidity arise in the treated medium, distributed within it in a mosaic-like pattern. In the third stage, the main fracture is prepared and formed with simultaneous unloading of the surrounding medium. The process of crack forming is gradually localized into a more narrow zone.
The second and third stages of fracture forming are reflected in variations of all the above-mentioned physical parameters which are therefore identified as the precursors of the main fracture. By means of the series of precursors it is possible to find the reliable prediction of a barrier fracture.
Key wordsEarthquake modelling fracturing process precursors of failure
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