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Title: COMPARISON OF EFFICIENCY OF IN-SITU METHODS FOR CONTROLING THE STRESS STATE OF PILLARS UNDER ULTIMATE LOADS
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COMPARISON OF EFFICIENCY OF IN-SITU METHODS FOR CONTROLING THE STRESS STATE OF PILLARS UNDER ULTIMATE LOADS
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1314-2704
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English
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20
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1.2
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There are quite a lot of borehole methods for measuring stress in rock mass, the description of which is given in different works. However, the determination of the comparative effectiveness of various methods under in-situ conditions when creating ultimate loads on pillars in a mine is given for the first time in this article. The article describes the results of instrumental monitoring by various stress methods of two slightly inclined (at an angle of 14 ° to the horizon) pillars with dimensions 4 ? 4 m and 6 ? 4 m (with pillar height 1.0?1.2 m) during a full-scale experiment conducted in a mine at a depth of 345 m from the surface in order to cause rockbursts in these pillars. The compressive strength of rocks in pillars is ?? = 140 MPa.
The experiment was carried out in 4 stages. The loading of the tested pillars in each of which ranged from 10% to 30% of the initial state due to the destruction of neighboring pillars. The span of an unfastened working from the test pillars to adjacent supporting pillars at the final stage of the experiment was 60-70 m (with a working height of 1.2 m). The time interval between the stages of the experiment was ~ 1 year. After each stage of loading the tested pillars, there were performed the following experiments of borehole stress measurements by the unloading method (in the face measurement version), by core disking in boreholes and by monitoring the destruction of borehole walls, and by the ultrasonic method. The borehole stress graphs were obtained during measurements at every stage. It has been established that the most complete information on stresses, at their level up to 80-90% of the ultimate stresses (by the compressive strength), is provided by the unloading method in the case of face measurements. At a stress level of 90-100% of the maximum, qualitative information on the stresses is provided by the core disking method and the borehole contour distortion control method. The ultrasonic method does not allow obtaining information on the magnitude of the stresses that are close to the limiting ones, in view of the flattening of the dependence of the velocity of ultrasonic waves on the load at limiting stresses. A comparison of the stress control efficiency by each of the methods has been performed. |
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conference
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20th International Multidisciplinary Scientific GeoConference SGEM 2020
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20th International Multidisciplinary Scientific GeoConference SGEM 2020, 18 - 24 August, 2020
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Proceedings Paper
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STEF92 Technology
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International Multidisciplinary Scientific GeoConference-SGEM
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SWS Scholarly Society; Acad Sci Czech Republ; Latvian Acad Sci; Polish Acad Sci; Russian Acad Sci; Serbian Acad Sci & Arts; Natl Acad Sci Ukraine; Natl Acad Sci Armenia; Sci Council Japan; European Acad Sci, Arts & Letters; Acad Fine Arts Zagreb Croatia; C
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491-502
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18 - 24 August, 2020
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website
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cdrom
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6920
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pillars; stress state; boreholes; ultimate tensile strength
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