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Loadings of legs in sections of mechanised supports by dynamic movements of roof and floor |
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Loadings of legs in sections of mechanised supports by dynamic movements of roof and floor Author: S. Szweda
Using results of measurements of the resultant force carried by hydraulic legs and of a vertical component of acceleration of a canopy, the sense of external loading of the section caused by the dynamic action of the rock mass and parameters characterising changes of the force in legs opposing the that external load was determined. The sense of external loading of the section of the mechanised support was determined assuming that it causes a linear motion of the canopy. This results from the initial conditions of the equation of the canopy movement (the conditions corresponding to the initial static load) that initially senses that the vertical component of the acceleration of the canopy and of the resultant force of the external load are the same. It was assumed on the basis of the observations of changes of the force in the legs during setting that in the case of dynamic movement of the rock mass on the support the average speed of the force increase in legs - wFn is at least 1.25 times bigger than the maximum value of wFn registered during setting of the section. As a result of the long-term measurements carried out in four longwalls, 37, recordings of dynamic processes at different times, of forces in legs, caused by dynamic movement of the rock mass were registered. In 9 cases of changes offerees in the legs were caused by external loads acting on the bases of the section. Looking for a relationship between parameters characterising changes of the force in the legs and the natural and technical conditions in situ, a clear statistical dependence between maximum force - Fm and an initial static force - Fslp was demonstrated. The dependence is valid both for changes of force in the legs caused by an external load acting from the roof and for a load acting from the floor. The coefficient of load increase, Kj, which characterises changes of force in the legs caused by external load acting on bases is significantly greater than that imposed on the legs by changes in roof loadings. Also the average rate of increase of force in.the legs is considerably greater in the case of an external load acting from the floor.
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2011