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To establish the technical requirements for powered supports in thin and moderately thick inclined and steep seams, to be worked by piUars conforming to the strike or to the dip, we have studied the laws governing rock pressure in production faces in relation to the chief mining, geologlcal and technical factors (thickness and gradient of the seam, composition and structure of the roof, direction of advance, face length). We have aLso made a quantitative evaluation of the variations in bed pnsitlon and fa~ting of seam sectors in pits in the Prokop'evsk-KLselevsk field in the Kuzbass and in the Central Area of the Donbass. The present paper analyzes andsummarizes the results of many years' research by VNIMI (All-Union Scientific-Research Mine Surveying Institute).A study of the composition and structure of the surrounding rock in coalfields with inclined and smep seams showed that in sectors where the bed position persismd and which were located at a considerable distance from large faulr~ and curves in the folds, the surrounding rocks had petrographic composition, physlcal and mechanlcal properties, endogenic jointing, and exfoliaflon slmilar to those in deposRs with level seams. Therefore in these conditions the roof strata can be divided into the same classes in terms of cavability as those for level seams.At the same time, it was established that in sectors where the dip of the beds varied (flexures) and those 1ocamd near faults and joinra in the folds, the surrounding strata were broken up by exogenic (oblique) jointing and caved in a markedly different way to that in non-fissured rock. Therefore, in calculatlng the working resistance of the supports we must distinguish the class of fissured rocks.In most cases the immediate roof and floor of steep and inclined seams display exogenic jointing. The density of the fissures and the cohesive force in them depend upon the petrographic composition of the rock and the structural nature of the zones, so the lateral strata can he unstable throughout the zone (in the case of argillites) or at points where p1ica~ve and disjunctive dislocations are present (sIRstone and sandstone). Therefore, in designing powered supports, a11 lateral strata (regardless of composition) mustbe considered as unstable elements which aUow only limited exposure (prolonged exposure must not exceed 2-3 m t and brief exposure not more than 6 m 2 over a period of 10-15 minutes). The roof bar and bed must ensure sufficiently good contact with the side walts over the whole area to be supported.A study of the mode of occurrence of inclined and steep seams shows that they display marked variation in thickness, strike and gradient and are generally much more disturbed than level seams.Taking the leogth of districts as 300-400 m to the strike and 80-120 m to the dip, the variation in thickness in most cases (55-60%) is 120-25 (Kuzbass) and • (Donbass) in relation to the mean.In the majority of disr in the Kuzbass and the Donbass the distance between faulm with throw >0. 8-1.2 m is 120-180 m and 300-500...

SPANThe effect of the depth of a working on the span and fracture pattern of sedimentary rocks in the roofs of coal seams has been inmfficiently investigated. The conclusions drawn by investigators are conflicting.Slesarev [1] and Kuznetsov [2] assume that since the first act in disintegration of the roof is its segregation into layers, which depends primarily on the composition and structure of the rocks, when one is determining the span (caving interval) of the roof it may be regarded as a bandof noncoheslve layers which are broken up by tensile strains when bent under the effect of their dead weight and the increased load exerted by the thinner and weaker overlying layers, Le., the 1Lmiting spans are independent of depth and are determined by the thickness of the layers an d their strength.Other investigators assume that depth is alto one of the principal factors determining the value of the span and the fracture patrem of the roof. However, they do not agree on the degree of influence of this factor.For example, Borisov [3] assumes that after primary segregation of the roof into layers the bearing capacity of the latter is determined by the value of the abutment pressure, which pins the layers against the abutments; under all conditions, the increase in this pressure with depth leads to a steady decrease in the value of the roof span.According to Kuznetsov [4l the structure.of the rock mass must also be taken into account when deal/rig with this problem. The caving Interval of a roof composed of thin layers of weak rocks is pract/cally Independent of depth, because the layers break up largely as a result of bending: However, if the roof contains thick layers of hard rocks, the caving interval depends on depth, because the part played by the increase in load exerted by the overlying rocks in the abutment pressure zone is intemffied. The fracture pattern will then be different: the layers are broken up as a result of shear (splitting).From an analysis of the stress in the roof of the abutment pressure zone, we postulated that i~ the roof contains rocks with poor cohesion between the layers we are most likely to observe fracture with primary layer segregation and layerwise displacement [5]. Stratified roofs with good cohesion between the layers, and massive roofs, exhibit layerwtse disintegration only at small or medium depths. At great depths the fracture pattern of such a roof changes radically: In the abutment pressure ~ne, ahead of the workIng face we observe inclined fissures, along which the roof rocks are displaced as blocks. We proposed the followIng equation for determining the critical dept h of transition to block caving:q cos p (/t r-k~k) t --4kxk3k tgt p where S is the cohesion, p is the angle of internal friction, q is the density, k is the coefficient of lateral presmre, and k t and ks are the concentration factors of the maximal and minimal components of the stress mnsor.For an experimental investigation of the dependence of the primary caving span on the depth of the mine working, the All-Union...

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