In assessing the stability of mine workings we need reliable indices of the strength of the solid rock in situ. Determination of these indices is one of the most complex problems in rock mechanics owing to the presence of many types of defects in the rocks. Pocks, being of geolo~cal origin, differ fundamentally from other solids in the arrangement' development, and dimensions of their defects. We can distinguish three categories of defects in terms of the methods of analyzing their influence on the strength properties and of their geometrical parameters.The first catagory includes micro-and macrmiefects more or less uniformly scattered throughout the rock. Such defects are found in all solids. They include lattice defects, microfissures, various inclusions, etc. We will refer to these defects as dispersed or random. The second category of defects is characterized by the natural fissuring. Here we will consider only those properties of the fissuring which influence the strength properties of the rock. We distinguish between endogenic and exogenic fissuring. Endogenic fissures form three mutually perpendicular systems, the fissures of one of these systems are approximately parallel to the stratification. The number of systems of exogenic fissures depends on the number of cycles of action of the tectonic forces. ~ogenic fissure systems lie at oblique angles to the plane of stratification. In sedimentary rocks endogenic fissures are almost ubiquitous, but exogenic fissures are found only in regions subjected to tectonic processes.

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...

Authors who have dealt with the influence of the scale factor have studied it only for the cases of compression and tension. Some of them give a method of processing test results [1][2][3][4][5][6][7][8]. There are scaroely any papers on fiexural tests, and those which have been published [4,5] analyze individual probiems in the processing of test results.In this article I consider some questions concerning the method of processing, analyzing, and presenting research results on the influenceofthe seam factor in flexure, using as an example some experimental data obtained in field and laboratory tests on limestone under flexure. The field tests were performed in Pit 8 of the "leningradslanets" group. In the floor of a working we partly cut and tested four cantiiever beams and four embedded onboth sides [6]. In the laboratory we tested 21 beams of various dtmensiom made from samples taken from the in situ beams. The load was imposed in stages which were kept until rapid deformation increase stopped, and the flexure was measured and the displacement of the fixed parts monitored. The stages were 250-500 kg for the field tests and 4-8 kg in the laboratory tests. Load relaxation was performed only for the laboratory tests in four to five stages with recording of the residual flexures. The loads were measured by oil manometers with a scale division of 1 kg/cm z, which corresponded to a load of 25 kg in the field hydraulic apparatus, and 4 kg in the laboratory apparatus. The displacements were measured by clock gages with scale divisions of 0.01, 0.002, and 0.001 ram.The results of the laboratory and field tests are plotted in Figs. 1 and 2.The fiexural strengths of the beams and the moduli of elasticity were calculated from the usual formulas for strength of materials. The functional coefficients of deformation were calculated with the aid of formulas for the modulus of elasticity with elastic fiexure instead of geueral flexure.To study the influence of the scale factor, the experimental data must be divided into groups according to each dimensional parameter. For compression, tension, or shear tests, according to the statistical theory of strength [7][8][9], for this parameter we take the cross-sectional area or volume of the test bodies. Under flexure, for equally long beams, it is more convenient, in order to elucidate the influence of the scale factor on the strength, to take as the dimeusional parameter the moment of resistance of the cross section, W, and for the deformation index, the moment of inertia of the cross section, I. In particular cases, as the dimensional parameters, instead of W and I we can, for beams of circular cross section, take the diameter d and correspondingly d 2 and d ~, and for rectangular beams with constant width and height, h 2 and h a.We should note that in connection with results on the influence of the dimensions of beams on their deformation (see Fig. 2), by the term "scaie factor" we shall in future mean the influence of the dimensions of a body on its strength and deformation indic...