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The influence of the depth of an exploited seam on stresses around the shaft |
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The influence of the depth of an exploited seam on stresses around the shaft Authors: T. Majcherczyk, M. Lubryka
The paper deals with the influence of mining exploitation, carried out in the area of the shaft pillar, on the stress around the shaft. The paper also presents the results of measurements of vertical and horizontal dislocations in three shafts in the vicinity of which mining had taken place for some time. Numerical calculations of the state of stress around the shaft were carried out using Cosmos/M software. The problem was treated as a 3D task. The model of rock mass contained one heading and a shaft. The qualities of rock mass were changed from 5 GPa to 20 GPa using a variable module for the coefficient of linear elasticity and changing the exploitation depth from 400 m to 800 m. An analysis of results was made for cross sections at distances between 50 m and 500 m from the shaft axis to the face of the longwall face. Changes of the coefficient of vertical stress concentration on the shaft section for a given distance between the shaft and the face are analysed in the paper. The coefficient decreases in a hyperbolic manner as the distance between the face and the shaft increases. As the depth of exploitation increases, its serious influences on the shaft are discernible at greater distances from the shaft. For a coefficient of linear elasticity of the rock mass E = 20 GPa, the distance at which the influences cease to be significant is as follows: depth = 400 m, distance = 270 m; depth = 600 m, distance = 320 m; depth = 800 m, distance = 360 m. The change of depth only slightly influences the value of the coefficient of vertical stress concentration. However, its value increases in proportion to the increase of rock mass rigidity. As the result of maximum vertical stresses occurring at levels of 50 to 150 m above the exploited seam, damage may appear in the shaft in this zone. The bigger the value of Young's module, the longer the distance from the shaft to the [alfa] =1.05 iso-line of vertical stress coefficient. In view of these findings, workings at great depths allow the dimensions of the shaft pillars to be reduced significantly.
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2011