採掘跡天盤の崩落, 沈下に関する模型実験

抄録

This paper describes a scale model study of strata mechanics related to the development of fracture zone above a goaf as a longwall face is advanced. The laminated roof strata were made of tens of sand-plaster sheets with 1cm of thickness whose strength was lowered down to 1kg/cm² by adding some detergent. The experimental results showed the bottom stratum of immediate roof collapsed as its span became long enough to crack at the ends. The progressive failure of the laminated roof followed the initial fracture until the goaf was filled with caved fragments, and resulted in a trapezoidal fracture zone. After the transient caving, the fracture behind the face support turned in a steady fashion that was either continuous or periodic depending upon whether the caving was within the immediate roof or not.
The experimental results can be well explained by a structural model in which a beam is assumed to be continuous along the full span before failure, but to be torn in two jointed on its upper surface at the mid-span after cracking at the ends. The largest span of any roof stratum, at which it can be competent to its own weight, seems to be determined from the fracture criterion of a beam lying on elastic foundation in cooperation with the caving angle. Finally the caving angle is formulated in terms of the geometrical and mechanical properties of the roof beam on the basis of the limit equilibrium of the beam segment. The structural model described in this paper appears to be relevant to not only interpreting the development of roof caving behind a longwall face, but also predicting the load applied on the face supports.