Deformation as a process to transform shape and volume of protective structures of the development mine workings during coal-rock mass off-loading

Abstract

Purpose is to assess deformation characteristics of protective structures while coal-rock mass off-loading to ensure wall rock stability as well as operating conditions of the development mine workings in coal mines. Methods. In a laboratory environment, uniaxial compression of protective structures has been applied on the models to identify the influence by deformation processes on the changes in their rigidness resulting from the shape and volume transformation. Findings. Under the deformation of rigid structures in the context of a safe strain resource, potential energy of their changes in shape is 4.1-6.5 times higher than the one of changes in volume. Beyond the safe deformation resource when critical level of the specific potential strain energy has been exceeded, strength of protective structures is not sufficient to restrict wall rock movement limiting their use. If relative volume variation in the rigid protective structures is δV > 0.06-0.082 then they lose their stability. Under such conditions, structural rigidity decreases by 14-22%. If pliable wooden protective structures are used then relative 0.62 ≤ δV ≤ 0.72 volume change doubles their rigidity. In the circumstances, the potential shape change energy is 2.1 times higher than the volume change energy; the abovementioned favours temporary compaction of wooden components of the compressive structure while improving its resistivity. Originality. Regularities of changes in the specific potential deformation energy of protective structures depending upon their shape and volume variation in terms of uniaxial compression have been identified. Practical implications. To ensure stability of wall rocks and maintain operating conditions of the development mine wor-kings, it is reasonable to apply pliable wooden protective structures which will help restrict roof and floor movements after their compaction. Insufficient residual strength of rigid protective structures, resulting if they lose their stability, provokes rock failure within the working areas of coal mines.