Návr otvírky, přípravy a dobývání ložiska žáruvzdorných jílovců Kamenná Horka

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Řešení problematiky dobývání žáruvzdorných jílovců ložiska Kamenná Horka

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The assessment of stress in an exploited rock mass based on the disturbance of the rigid overlying strata

Gravitational rules are used as the basis for the prognosis of vertical stress distribution in exploited rock masses. A decrease in stress in a worked-out area (decrease between the initial stress and the stress acting on the floor of the outmined seam) results in an increase in stress in the surrounding unworked area. The size of load in the floor of the worked-out area is determined by the degree of disturbance in the overlying strata rocks. An overall additional load in the surrounding rocks of the unworked area is determined based on the difference between the initial geostatic stress and the load in the floor of the worked-out area. The additional load, which is determined from the force of relieving the stress in the worked-out area divided by the periphery of the worked-out area, decreases per unit of length of the periphery of the worked-out area. Furthermore, the behaviour of stress in the direction of the worked-out area is calculated mathematically. In this way, the stress in the grid of points on the level of seams being mined can be calculated, and isolines of acting stress can be determined. As an example, we show calculations for a specific situation in a mine before rigid overlying strata failure and after the failure. After the rigid overlying strata failure, the additional stress decreased by approximately 40%.Web of Science50827

Some parameters of rockbursts derived from underground seismological measurements

A total of 240 three-component recordings from 80 rockbursts, which occurred in various coal mines in the Ostrava-Karviná Coal Basin (Czech Republic) between 1993 and 2005, was used to examine the decrease in maximum particle velocities ui (m/s) with a scaled distance of d = d/√E (m/√J) or d/3√E (m/3√J) and the rate of predominant frequencies of body waves. The energetic span of rockbursts was within the interval of E = 6.2 × 103 − 5.0 × 108 J, while calculated hypocentral distances d of four underground seismic stations varied from 0.6 to 7 km. The slopes b of regression straight lines for the maximum particle velocities ui (m/s) of P- and S-waves in the bilogarithmic scale correspond to the values of − 1.004, − 1.297, − 1.183 and − 1.527. The results of the linear regression are as follows: Pmax-waves ui = 1.184 × 10− 4 × d− 1.004 (m/s) (square root scaling) Pmax-waves ui = 3.055 × 10− 3 × d− 1.297 (m/s) (cube root scaling) Smax-waves ui = 5.280 × 10− 4 × d− 1.183 (m/s) (square root scaling) Smax-waves ui = 2.397 × 10− 2 × d− 1.527 (m/s) (cube root scaling). The evaluation of the abovementioned dynamic parameters was based on seismic events data gathered in the database of the regional seismic array, and calculations were carried out either by using special programs applied as part of the automated data processing in the computation center, or by usual linear regression approaches. The aim of the detailed analysis of the maximum particle velocity and predominant frequencies was a) to set up input data from underground seismological observations for laboratory experiments dealing with the comparison of rock mass behaviour under modeled laboratory conditions simulating manifestation of rockbursts, and b) to incorporate particle velocity into the design of support in order to control damage and evident devastation of workings by rockbursts. The investigation of peak particle velocities was based on the recognition that they are the best criterion to assess vibration damage to surface structures and in mines

Fatigue properties of intact sandstone samples subjected to dynamic uniaxial cyclical loading

In this paper, the fatigue behaviour of intact sandstone samples obtained from a rockburst prone coal mine and studied under dynamic uniaxial cyclic loading in the laboratory is presented. Tests were conducted on dry and saturated samples with loading frequencies ranging from 0.1, 1 and 10 Hz and amplitudes of 0.05, 0.1 and 0.15 mm. From the laboratory investigations, it was found that the loading frequency, as well as the amplitude, was of great significance and influenced the rock behaviour in dynamic cyclic loading conditions. The dynamic fatigue strength and the dynamic axial stiffness of the rock reduced with loading frequencies and amplitude. The dynamic modulus was found to increase with the loading frequency but decrease with the amplitude. In the case of the saturated samples, it was found that the dynamic fatigue strength reduced by approximately 30 per cent, while the dynamic Young's modulus reduced by about 20 per cent. From the presented study, the dynamic energy was found to be independent of the testing conditions while other rock properties were found to be dependent on these. Finally, it was concluded that rock would more readily succumb at low frequencies and amplitude than at high frequencies and amplitude for a given energy availability