The pneumatic cylinder mobile support system serves to protect the near-face area from rocks being ejected into the worked-out chamber and prevents the roof from collapsing when miming to the dip in thick steep beds using pillars, with the collapse or self-filling of mined-out spaces. At the first stage in support system development, laboratory tests were done to study the following aspects:the interaction between the support system and the lateral and overhead rocks; investigate and develop methods for support control; and evaluate the parameters of the stope face and support system stability in respect of fold formation.The support model and the testing installation were made to the scale of 1:20. The similarity between the model and natural conditions is provided by geometric s~m~larlty and also by the fact that all loads applied to the support model (distribution on the surface and flexing moments) should be in the same relative ratios as the respective loads on the prototype.We consider the conditions and similarity criteria in detail.The pattern of motion of the support system as the bed is worked and its sagging over the stope space are determined by the direction and magnitude of the loads from the overhead rocks. The model scale should be selected such that the mechanism of movement and deformation of the overhead rocks in the model correspond to the natural conditions. Studies [I, 2] have shown that granular material retains its properties when particle sizes relate to the smallest opemingdimenslon as 1:30 or less. For coal seams thicker than 6 m, this condition is met, because the particle size of filling material is not larger than 200 mm. When filling material of 0-6 --,was used in the model, the effective model width (bed thickness) should be at least 200 mm. The mechanism of deformation of granular material in the model will then correspond to the real processes.Meeting the first sdmdlarity condition implies that the second condition is also met to some extent. Basically, this similarity requires that the loads on the support from the transported rocks are determined by the mechanism of rock deformation.If the deformation mechanism in the model corresponds to natural processes, the load on the mobile support in the model would be determined as in situ according to [2] as or in nondimensional parameterswhere P(l~m~) is the ~ pressure on the mobile support system; a. bed dip; 8, shear angle of the transported rock from the bed floor; and C, a nondimensional coefficient determ~-ed by the internal friction and lateral pressure.Therefore, P(HLax) is the principal criterion for the model's s~m~larity to the natural conditions.The rocks transported in the worked-out space must also have equal internal friction coefficients tan 9 -idem, in addition to the adequate ratios of granular sizes. Because the sag of the support system in the near-face area is determined by the bending Institute of Mining, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk.
The use of rock strips to insulate horizons and maintain an interhorizon pillar in working steeply dipping coal seams wholly satisfies the requirements imposed on the working characteristics of interpanel supports. While securing the necessary yield and resistance to convergence of the side rocks, a rock strip enables us to avoid ingress of fires and clay bursts from overlying worked-out horizons and to reduce air leakage, and makes it possible to stow the worked-out area. The main problem is to get the necessary stability of the rock strip.At the IGD SO AN SSSR we have developed a method of making insulating rock strips, as follows [i]. The rock strip (Fig. i) is bounded above and below by a yielding guard support, in which the two rows are tied together by steel cables which give preliminary thrust of the rock strip with the side rocks. To avoid thrust of the beams of the guard support with the roof and floor of the seam, they are made compound and are laid overlapping.The theoretical scheme of stability of the rock strip is based on ideas of the deformation of a loose mass under conditions of pure shear in a confined state [2]. According to these investigations, deformation of a loose mass in a confined state in conditions of pure shear occurs with the formation of a block structure and sliding of the blocks relative to one another along the slip planes. In these conditions with deformation of the rock strip, the sllp planes must be formed at an angle to the direction of displacement of the strip, unfolded on opposite sides relative to the symmetry axis (Fig. 2a). The condition of equilibrium of the rock strip is then determined by the interaction, on the one hand, of the weight of the stowage material and, on the other, by frictional forces acting in the slip planes. Naturally, the greater the force tying the top and bottom rows of guard supports, the greater are the frictional forces developed in the slip planes and the greater is the stability of the rock strip. Thus, if any appreciable flexure of the stip is possible, it must be accompanied in the limiting state by the formation of a block structure, the strength of which depends on the frictional forces over the contact surfaces.Closer to these conditions of deformation of a rock strip is the character of the deformation of a loose medium behind a movable support. The processes of deformation of a loose medium with advance of the supports to the dip, studied by Revuzhenko et al. [3], show that a block structure is also formed in this case, characterized by initial displacement of block abed (Fig. 2b) with preservation of the primary structure within the Block. The condition of equilibrium of block abed is determined by interaction of the weight of the strip and by the friction over planes ab and cd. Owing to the small values of angle ~, in calculating the stability of the strip the slip planes can be arbitrarily drawn along the roof and floor of the seam. An increase in the weight of the strip will go into the reserve of stability.The above ideas concerni...
At pit 5-6 of the Prokop'evskugol' Group, during the winning work in the Vnucrennii seam, from cross-cut 13 (level+ 60 m, northern panel of pit 6, south) by the shield system with gravity-flow stowing, measurements were made of strata convergence to determine the effect of moving stowage on convergence of seam rock.Seam Vl Vnutrennii is 2.8-8.0 m thick, with a dip of 85-75". The coal is of medium hardness, with cleavage cracks, and is crushed in the hanging and foot walls. The roof is medium-strength argillite, and has thread-like cracks. The immediate floor is weak siltstone with argillite bands, with total thickness of 0.5 m; the main floor is fissured siltstone of medium strength. The seam has not been affected by over-or underworking.Figure i shows the arrangement of the measurement points. The first datum points in the roof and floorof the seam were located in headings before extraction was begun in the first pillar for a period of 35 days, and then with one pillar in advance.The measurements lasted 396 days, during which three pillars were extracted. Pillar 736 (3rd) was extracted with a 6-month break, caused by absence of stowing material. Figure 2 shows the working face arrangement and the roof convergence pattern.The first pillar (70,/) was extracted in 6,/ days, the second (708) in 43 days; extraction of the upper half of fine third pillar (,/86) took 29 days (up to the lengthy break), and the whole of this pillar 8 months (including the stoppage).Over a period of 35 days (before beginning work 30.5 m from the minus level) convergence of strata in the solid coat in the first pillar ahead of the wirming face was 6 mm; at a distance of 12.5 m it was '7.5 ram. The average convergence rate was 0.17 and 0.21 ram/day, respectively. CZ3C3 V--lrnDm ---nr-nE3n OOOO Z J 32 3r 29
28--27"20~r26 .
7~15 708
Crushability of the ore in the kinetics equation is defined by the characteristic time for crushing, T, which is needed to reduce the coarse-class content in the mill by e (e is the natural--logarithm base). It is also defined by the index m, which determines the form of the dependence. The mathematical model permits the prediction of mill productivity in relation to its operating regime and the composition of its mineral mixture.1. 25 3.LITERATURE CITED E. I. Shemyakin, V. I. Revnivtsev, N. N. Faddeenkov, and A. S. Petrov, "One approach to an est~m-te of energy consumption while breaking up ore," 0bogashch. Rud., No. 6, 158 (1981). C. E. Andreev, "The content of the coarse class in a mill determines its productivity," Obogashch. Rud., No. 2, 38 (1962 Thick steep beds with faults are usually worked by a system of sublevel caving, which is characterized by a high loss of coal, high fire hazard, prolonged development working, and impossible mechanization of stoping work.The possibility of working such disrupted areas with a rising order is limited by the instability of overhanging coal beds that create hazardous conditions for work at the stone face. For that reason, attempts have been made to work thick steep beds by decending horizontal layers with pne,---tic filling of worked-out space [i]. But low cost-effectlveness systems due to the absence of ways and means for mechanized coal excavat:ion or support of near-face space led to abandonment of this principle.Research and development is now underway to create a system for working of thick steep seams by horizontal layers in descending order with a solidifying fillitng of the workedout space [2,3]. An important aspect of this process is creating a stable ceiling of the solidifying filler. Tests at Nogradskaya mine of Prokop'evskugol' Ente]--prlses show tl~at, under unfavorable mining and geologic conditions, the layer of solldlfy~tng can collapse, and individual fall-outs can occur when the filling mass is not formed properly.This necessitates installing an additional support for the artific:lal ceiling.Foreign experience with a system of horizontal layers of working i~n descending order with solidifying material used to fill the worked-out space also conf~s the need for supporting the artificial ceiling to prevent the collapse of blocks and foz'matlon of fall-outs. For additional support, a raft of beams and metal net is used, resting on stakes or bang,nfrom rods fixed in the overhead layer [4]. In the latter case, this additional support does not limit the choice of the height of the horizontal strip and allows cCntlnuous excavation of the underlying sea,, by stoplng and tunneling machines. The introduct:ion of additional support, however, increases the labor costs of development working and z~akes the utillty of this process questlonable in areas outside of structures requiring spec:lal protection. For that reason, and also in view of the fact that the mines of the Prokep'~vsk-Kiselev deposit lack an adequate material base for development working with a solldi...
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