Study of controlling catastrophe for roof strata in shallow seam longwall mining

In accordance with the occurrence behavior of roof strata and the breaking convergence characteristics of main roof in shallow seam longwall mining, this paper studied the catastrophe mechanism and the catastrophe control of main roof during the first weighting by using the initial post-buckling theory and the catastrophe theory, added the sufficient conditions of instability due to sliding for controlling rock blocks after the main roof breaking, perfected the criteria of step convergence of rock blocks for contacting and not contacting with the waste rock from fallen roof, determined the step convergence values, derived the formulae of support force for controlling the step convergence and ensuring the roof stability, and presented an application with the example of Daliuta 1203 face. It is pointed that the rock blocks are in a state of non-equilibrium after main roof breaking, the mechanism of the step convergence is instability due to sliding of structure; the step convergences before and after contacting with the waste rock from fallen roof have some determinate relations with the breaking convergence and the mining height respectively; the intense roof weighting is mainly caused by key roof block sliding; and controlling step convergence is essentially controlling sliding for rock blocks. The results also indicate that the synthetical application of initial post-buckling theory and catastrophe theory can determinate whether step convergence will take place before contacting with the waste rock from fallen roof in accordance with the occurrence state and structure characteristics of roof rock layer, can determinate the motion form after contacting with the waste rock from fallen roof according to mining height of working face and effective filled thickness, and can determinate the support force for controlling step convergences before and after contacting with the waste rock from fallen roof in accordance with the breaking span, the breaking convergence value and the friction coefficient.