FACTORThe method of studying creep under the effect of a bending load [1][2][3][4] is simple and reliable owing to fulfilment of the St. Venant principle. It gives all the necessary information for studying uniaxial creep: stress, modulus of elasticity, and change in deformation in time, described by the equatione(t)=e(0) 1 + 1--a where s (0 ) is the deformation at the moment of stress, a and 6 are parameters of the creep nucleus, and t is the time in seconds.The value of s(0 ), determined from the equationdepends on the loading parameters, because Eben d=K 4 B Ha ,~ y 'where L, B, and H are the length, breadth, and height of the beam being bent, Ap is the increment of the transverse load, Ay is the increment of sag, and K is a constant --I + 2.95 (H2/L 2) -0.02 H/L.Erzhanov [1] used the method of repeated loading so as to exclude the effect of irreversible deformations on gbend. It should be emphasized that although reference [1] mentions the scale factor, it was not studied in detail.The aim of this report is to determine the optimal specimen size at which repeated loading by bending, giving minimum elastic deformation, does not distort the modulus of elasticity. In this case, study of creep does not require special determination of the modulus of elasticity, and the test results become more representative.We performed tests on specimens of Tastagol' iron ores with 59.2% and 34.2% Fe, and coals and sandstones of the Prokop'ev-Kiselev coalfield in the Kuzbass.Anisotropy of the properties was allowed for by specific orientation of the schistosity during bending of the specimens relative to the effective stresses. The beam span L was kept constant for each series of experiments, while the square cross section varied; this enabled us to take account of the scale factor's effect.The duration of the nominally instantaneous load was stable; thus, with the same stress level, we obtained different loading rates for different cross sections of the specimens.
ROCKS UDC 622.02Many years of research on the mechanical properties of rocks in the Kuzbass have confirmed the opinion that a dislocated sedimentary series has a wide range of variability of properties, both round the perimeter of the region and depthwise. It is exceedingly difficult to establish any kind of regularity in their spatial distribution in order to assess the geomechanical conditions in deep horizons. However, if we base ourselves on the genesis and geological history of the geological bodies regarded as complex natural systems, their behavior can be represented by statisti: cal-probability methods. The larger the region of space occupied by the rock under investigation, the more certainly we can judge the overall variability of its properties.Our investigations were based on engineering-geological sampling in a system of uniformly spaced boreholes (about 70) along six survey lines covering the whole of the Prokop'evsk region to a depth of 1000 m. By a specially developed combined method [1] we obtained, in a unified scheme, over 20 parameters of the strength, deformation, and creep properties, characterizing the state and properties of the rocks of the main structures of the region and the coal fields therein ("Koksovaya," "Nogradskaya," "Ira. Kalinina," "Tyrganskaya," "Ziminki," and "Prokop'-evskaya"L The resultant copious information gives us grounds to subject the estimates of the rocks to the strike and in depth to a complex interpretation, which enables us to delineate the geological structure of the region in respect of a number of features. This enables us to establish the position of the boundaries between the rocks composing the mass, and hence to divide up the aggregate of measurements of rock properties into parts. The method makes it possible to check the relationship of the rocks by means of their properties regarded as a whole.In a mathematical plan the problem reduces to estimating the uniformity of the multidimensional geological aggregates in n-dimensional space by means of the criterion V k [1, 2]. This criterion is based on the idea that a set ofn successive values of the indices is uniform if, of n-1 values of V k computed for n -1 variants of the division of the random sequence into two, none exceed the permissible value of • for one degree of freedom and the given significance level a. For a multidimensional aggregate Vk is defined as E tl '.
We suggest a combined test method based on indentation of a plane punch. The main problem in devising a combined test method was to obtain, in a single scheme of loading on a limited piece of rock, a complex of strength, elasticity, plasticity, and creep characteristics. The method which was devised permits testing on rocks in a complex state of stress either in atmospheric conditions or under varying hydrostatic pressure. The method is sensitive to anisotropy of the properties of the rocks.The basis of our suggested test scheme was a scheme of loading by indentation of a plane punch. The scheme of loading in a complex state of stress has an elastic solution with the possibility of interpretation of the stress compenents by tests on isotropic and transversely isotropic media such as sedimentary rocks [1][2][3][4][5][6][7].According to the well-known contact problem in the theory of elasticity, the pressure under the base of a circular plane punch of radius a pressed into an elastic half-space by a force P, with a pressure q(x, y) in the region A outside the punch, is given by P(x, y) = --.
Mining operations in the lower existing horizons in the Prokop'evsk-Kiselevsk coals in the Kuzbass is greatly complicated by rock pressure, which increases with depth. To investigate the conditions under which rock pressure develops and to predict its effect on the efficiency and safety of the mining systems used we need to know the properties and structural characteristics of the whole of the country rocks within a specific sector of the mine or take.This communication gives the results of investigations into the structural characteristics and properties of the country rocks enclosing the principal coal seams of this coalfield: the IV Vnutrennyi, Gorelyi, and Moshchnyi. About 40% of the reserves of the coalfield are contained in these seams. They have maximum thickness and are generally accorded priority in working; this usually predetermines the sequence and intensity of mining of the whole series or group of seams in the series. The wall rocks of these seams consist largely of thick beds of strong arenaceous rocks, the overall thickness of which is 45-80 m. Exposure may lead to sag over extensive areas, creating dangerous abutment pressure concentrations at the marginal zones of the coal seams being woEked.To predict manifestations of rock pressure, primarily abutment pressure, we need to know the overall thickness of the roof and floor rocks, which actively interact with the marginal sectors of the solid coal and have been termed [I, 2] the "active roof" and the "active floor." These conuepts are somewhat arbitrary because the overall thickness of the roof and floor rocks which exert an influence on the operating conditions of the sys=em "roof--coal seam--floor" depends on n,~,~rous factors: geological, technical and engineering.From investigations of cross sections of mine workings and 120 prospecting boreholes (up to 1200 m deep) and on the basis of a comparative assessment of the results of field measurements of displacements of underworked and overworked rock masses, for the principal seams of the Prokop'evsk-Kiselevsk coalfield we propose to take the active roof thickness as 50 m (which corresponds approximately'to a sixfold-eightfold thickness of the coal seam or layer), and the active floor thickness as 20 m.These assumptions enabled us to compare the quantitative ratio of the lithological composition and variability of structure of the active roof and floor of the principal coal seams in the Prokop'evsk region. St was established that the rocks of the active roof and active floor are mainly sandstones and siltstones (75-90%). The amount of argillites in the active roof varies from 7 to 15%, and in the active floor from I0 to 25%. This pattern is traced throughout virtually all the mining fields of the region; on this basis we can infer that the wall rocks of the principal thick se-m-exhibit relatively the same quantitative ratio of the lithologic varieties and are predominantly strong and not readily caved.The structural characteristics of the rocks of the active roof and active floor are primarily du...
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