Calculation of the strength of cast and packaged concrete protective walls

Abstract

Purpose. The substantiation of the compliance of the selected cement-mineral mixture with the mining and geological conditions of the working location when calculating the parameters of cast or packaged walls, considering the intensity of concrete hardening over time, the compliance of the set strength of concrete with the expected load. Method. To substantiate the compliance of the physical and mechanical properties of the pressure mixture on the means of protection of the production from the side of the fake roof of the coal seam, the values of the limit strength of concrete for uniaxial compression, obtained according to standard tests in laboratory conditions, are used. At the same time, concrete samples are subjected to uniaxial compression, the surfaces of which must be smooth and parallel, which does not correspond to the mine conditions for the construction and operation of cast and packaged protective walls. Quick-hardening liquid mixtures are used in the construction technologies of cast and packaged security walls. For some time, necessary for the hardening of concrete, they are not able to perceive the pressure from the rocks forged by longwall. Therefore, the criterion for evaluating the stability of cast or packaged walls is the correspondence of the rate of growth of the strength limit of the wall to uniaxial compression with the load from the forged roof of the coal seam at the moment of timeτ. Results.The importance of the impact on the strength limit of the concrete wall of each of the factors that create the risk of its destruction has been established. At the same time, the ranges of change of these factors are considered. The largest influence (up to 33%) is exerted by the coal seam capacity factor km. The scientific novelty of the work consists in the integration of the influence coefficients of the factors that create the risk of destruction of the concrete protective wall: its structure; relief of forged and crushed rocks pressing on the wall; chemical aggressiveness of mine water, which is used to dissolve the mixture; the temperature of the mine environment and the power of the coal seam to obtain a formula for calculating the growth of wall strength over time. The practical significance of the work lies in the improvement of the method of calculating the strength of concrete protective walls over time by considering the factors that form the mine conditions of their construction and operation.