Results of modeling of the operational conditions of a pneumatic cylinder mobile support system in the mining of thick steep beds

Abstract

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.