Rock pressure manifestations during changes in resistance in MK-powered hydraulic support systems in the nadbaikaimskii-I seam in the Kuzbass

Abstract

622.831 : 622.284-523.3 and V. T. GorokhovThe All-Union Scientific-Research Mine Survey Institute (VNIMI) has been conducting experiments since 1964 on powered supports in the Kuzbass in order to examine thoroughly the reaction between these supports and the surrounding rock. From the engineering point of view, the object of the experiment was to define the optimum calculated, working, and initial setting loads for hydraulic supports. The experiments involved a program of continuous variation of working and setting load; caved rock was suspended on the restricting parts of the powered support section.OMKT units [1][2][3][4] were used for the investigations. This paper gives the results of an investigation into the force reaction of the supports and rock in face 22 of the Nadbaikaimskii-1 seam at the 7th November Colliery in the Leninugol' area of the Kuzbassugol' group, with a sequential variation of forward and trailing support load settings in an MK face equipment. The face length was 60rn, the working pillar, 400 m. The face was divided by a 6-8 m wide pillar starting on the top at the worked-out pillar and was bounded at the bottom by face entry 24. There were no faults in the face area; the gradient was 2-3 ~ total seam thickness, 2.6-2.7 m, and the worked thickness, 1.75 m. Two 0.1 and 0.4 m argillite bands in the lower part of the seam were not mined. The coal was of average hardness. The working depth was 70 m. Argilltte lies 5-7 m above the seam, and is overlain by sandstone.Holes were drilled to examine the structure and mechanical properties of the roof. Examination of the core showed that the argillite contained a number of weak inter-bed interfaces (with slide surfaces), coal bands and plant residue. Table 1 gives breaking strength perpendicular to stratification for various interfaces in the argtllite.To break down the immediate roof into packs and to evaluate the fluctuating thickness of the beds, it is assumed that bed separation occurs along interfaces with average strength (0.04-0.06 kg/cmZ). Fairly thick beds are present only in the IV and VI bands; the overhang in these beds can reach as much as 4.5-5.0 m (Table 2, graphs 9 and 10). Thicker beds are to he expected above pack VI, with a caving interval correspondingly larger. The MK equipment has been described in [5].To carry out measurements on eight supportsecti0ns in the center of the face (from 25 to 32), a measuring station was instrumented (57 sections in the whole face). Pressure gauges were arranged on all the props in these sections, and the 32nd section was fitted out with self-recording gauges designed by the A. A. Skochinskii Mining Institute. The period of observation can be broken down into three stages; the first, with a setting load in the props of 40 tons, and of 80 tons in the section; a second period with pressures of 80 and 160 tons, respectively, and a third period with 54 and 108 tons, respectively (the prop valves were changed over on the measuring station only in the second and third periods).At the beginning of obse...