These investigations were performed during the actual working of seam III (1.9 m thick, dip 4-5 ~ ) in the Severnaya colliery of the Tashkumyr field.The immediate roof of the coal seam was siltstone, 0.3 m thick, overlain by siltstone and argillite, 3.5 m thick.Siltstones and argillites formed the floor. Mining was by the system of long pillars along the strike.The longwalls (length 150 m) were equipped with KM-87D mechanized aggregates.To determine the character of bed separation of the wall rocks atdifferent depths from the exposed roof surface we installed deep bench marks in the airway.Paired bench marks were installed in i0 cross sections in the conveyer road and the airway.Deep bench marks were installed in boreholes 9 m long at the following distance from the exposed roof surface:P~ 2.0 m, P~ 3.8 m, Pa 6.0 m, P= 7.5 m, and Pt 8.6 m. Figure 1 shows a diagram of a deep measuring station.Observations on the deep and paired bench marks gave a picture of the fracture pattern of the roof rocks. Figure 2 shows the bed separation pattern of the roof; it will be seen that the abutment pressure zone, which influences the bed separation of the immediate roof rocks, extends for 30 m ahead of the minlng-out face. The bench marks installed in the rock mass to a depth of 5 m are displaced far more markedly than the deeper ones.
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