Dualistic effect of the deformation of protective structures made of broken rock in mine workings under static load

Abstract

Purpose is to reveal physical essence of the dualistic (double) nature of deformation effects and their influence on the mechanical properties of protective structures made of broken rock while unloading coal-bearing mass to ensure stability of side rocks and operational conditions of the development mine working within the working areas of coal mines. Methods. The deformation properties of protective structures made of broken rock was modeled on experimental samples during their static load in terms of uniaxial compression with the possibility of lateral expansion of the original material or its compressive stress. Findings. A dualistic effect of deformations for the conditions of uniaxial compression of protective structures was revealed. Under the effect, a complex transformation of volume and shape occurs in the structures caused by the process of relative changes in the backfill material volume. The observed phenomenon occurs within the range of 0.12 ≤δV ≤ 0.32 and the values of the compaction coefficient of broken rock being 1.13≤k con. ≤ 1.47, depending on the granulometric composition of the source material and its bulk density. It was established that under conditions when broken rock is compressed, there is an effect of forming the bearing capacity of protective structures, which is observed when a relative change in the volume of backfill material is 0.14 ≤ δV ≤ 0.38, and its compaction factor reaches 1.16 ≤ kcon. ≤ 1.59. Depending on the homogeneity degree of the backfill material of protective structures, when comparing the values of kcon., a dualistic (double) effect is manifested in the difference of deformation characteristics of broken rock under uniaxial and compressive stress, reaching two or more times. Originality. A regularity was established that determines the relationship between compaction factor kcon. of broken rock and a relative change in the volume (δV) of backfill material, which makes it possible to evaluate bearing capacity of protective structures, being under static load in a stress-strain state. Practical implications. The research results can be used to substantiate the selection of a method to protect development mine working with flexible supports made of broken rock. To clarify the assessment of bearing capacity of such structures, it is advisable to carry out specific field studies in mine conditions.