In mine investigations of loads acting on supports units under the influence of periodical rock pressures

In six mechanically supported longwalls of Dudar-Balinka coal fields, Hungary series of measurements were done by the author. They were aimed at recognizing the processes of rock mechanical and rock pressure character involved with the first collapse of arching over top roof formations. Measurements included the continuous recording of loads acting on the legs of some shield units /by PRESMET device/ and daily measurement of pressures on every prop set in longwalls. Finally the made characteristic data on the joint action of support and rock surroundings were represented by drawings of Mr 1:200 in scale. It was evidenced that the periodic pressure, involved with the collapse of top roof formations, doesn’t act /in a deterministic way/ on each shield unit. By it, as a stochastic phenomenon, the statistic assembly of all the shields in the long wall face is influenced. It was stated that relationship exists between the probability distribution of prop pressures and the characteristics of the process of roof failure. The measurements made it evident that the changes, accompanying the collapse of over-arched top roof layers, take place during five characteristic periods.