It has been established by previous investigations [1, 2] that the effectiveness of electrothermal and, in particular, low-frequency breaking of rocks depends mainly on physical properties-modulus of elasticity E, coefficient of linear expansion cz, electrical conductivity g, etc.Since low-frequency rock breaking is associated with their severe heating and melting in the region where the electrodes contact the rock, a study of the processes of the temperature effect on the physical properties is of considerable interest. In connection with this we investigated the temperature dependence of certain physical properties of the siderite ores of the Baikal deposit. The siderite of this deposit belongs to a type of sedimentary ores. Its composition contains the following elements and compounds-Fe, P, S, CaO, MnO, AlzO 3, and SiOz.The data in the literature concerning the physical properties of siderite ore pertain mainly to room temperature. There are no investigations into the effect of temperature on its physical properties.In this article we will examine the results of an experimental study of the temperature effect on the modulus of elasticity, coefficient of linear expansion, and electrical conductivity of siderite ore.When calculating thermoelastic stresses it is usual to consider that the physical properties do not depend on temperature. Actually this assumption is valid in a comparatively small range of temperature changes and not for all rocks. Therefore a study of the physical properties of rocks, in particular the electrical conductivity, modulus of elasticity, coefficient of linear expansion and their product oz. E in the temperature field is of great practical and theoretical value. In the laboratory of rock physics of the Moscow Institute of Radioelectronics and Mining Eleetro-J mechanics (MIRGEM) a method was developed which makes it possible to determine these magnitudes simultaneously in a temperature range from 0 to 900"C. This method is a development of the previously created ultrasonic impulse method which permits the determination of the modulus of elasticity by measuring the velocity of an ultrasonic impulse in a heated rock specimen. The investigations were carried out on specimens in the form of thin rods whose radius was many times smaller than the wavelength. Since the propagation velocity of ultrasound C D depends on the elastic parameters and the density p of the rock, then the modulus of elasticity E is found by the formula E=rThe block diagram of the device is shown in Fig. 1. A rock specimen which is clamped between two quartz rods about 20 cr n long is placed in an electric furnace. The rods simultaneously perform the role of a mechanical resistance inserted between the ultrasonic transformers and the specimen and of a restraint against longitudinal expansion of the specimens upon heating. The material of the rods, in addition to low heat conductivity, has the property of hardly changing its physical properties (in particular the coefficient of linear expansion and elastic constants) in...
Many workers [1][2][3] have shown that the structures and properties of real rocks are inhomogeneous in space and nonuniform in time. The inhomogeneity of the rock may be manifested in cracks, stratification, stress, inclusions, and cavities, and may be regular (smoothly varying) or random. The scale of inhomogeneities in the rock can vary over a very wide range; for example, cracks can be from 10 -7 cm to 1 cm wide and 10 -I cm to tens of meters long; inclusions and cavities vary from 10 -1 cm to several tens or hundreds of meters; and stress concentration zones have dimensions from tens of centimeters (around a borehole) to tens of meters (tectonic stresses).The chief problem of physical methods of surveying and monitoring is to discover and assess various types of inhomogeneity, i.e., to obtain an objective picture of the distribution of properties and of the state of the rock by making measurements in the solid rock and interpreting the results.The principal requirement imposed on physical methods of investigation and control of the properties and state of the solid rock is objectivity of the results in conjunction with technological feasibility of the measurer merits -i.e., detail and accuracy of measurement, reliability of interpretation, and attainability of quantitative data on the solid rock.At present there are many methods of investigating and monitoring the state of the solid rock -in particular physical methods based on wave fields of various types (elastic and electromagnetic waves and penetrating radiation), which are finding increasing application in engineering-geological surveys and exploitation control of the properties and state of the solid rock in mining. These methods are based on finding various types of inhomogeneity in the part of the solid rock under observation by means of changes in the parameters of the wave field which are used as indicative signs.Analysis reveals that the chief causes reducing the effectiveness of measurements in solid rock are experimental-methodological errors and inhomogeneity of the rock which is scarcely taken account of in present methods of control. The selection of an indicative sign for control and of a base for measurement without taking account of the statistical inhomogeneity of the rock will greatly reduce the reliability with which zones of high stress are distinguished near mine workings; the error in the estimation of the fissuring parameters of the rock may reach hundreds of percent.The maximum detail attainable in investigations of the spatial inhomogeneity of the rock is governed both by the absolute dimensions of the inhomogeneities and by the nature of their interaction with the wave field. Thus the measurement procedure and the methods of interpretation should be closely linked with the real structure of the rock. In other words, to increase the effectiveness of measurement it is necessary to match the parameters of the measuring system with the characteristics of the subject of investigation. Here by the parameters of the measuring system we ...
1, 2.3. E(-1) -----E(-3) = Ec-5~ = E(-7) = E(-9) ----E(+I ) =Ec+3 ~ = Er = Ec+Tt = = Ec+9) = E(+11) = Ec+13) = E(+,5) = 0,73 X t05 MPa ; Ec_2) =Ec+4t = =Ec+8 ~ = 0,89 X t05 MPa; Ec_4~ = t,2t >< t05 MPa ; e(-s) = 1,48X t0 ~ MPa ; E~-s~ = 1,38 • 105 MPa, E(-io) = E(.~B) = t,3 Xi0 s ,!MPa; E(+2) = =1,2X`105 MPa; /~c+12) = 0,91 X `105 MPa E(+I4) = 1,4X ~05 MPa; p0 = PC+6) = P(+IO) = ~t,4 X `10 4 N/m 3; PC-l) = toe-3) = Pc-St = PC-7) = PC-g) = A considerable body of experimental data has been accumulated over the past few years concerning acoustic emission (AE) and electromagnetic radiation (EMR) observed during cyclic loading of rock specimens [1][2][3][4]. These characteristics, known as emission memory effects (EME), indicate that under certain conditions rocks can retain and reproduce information on impacts experienced at an earlier time. Although the basic possibility of utilizing EME for quantitative estimates of stresses in a rock bed is obvious, no such estimates had been obtained before now. This was due to the following: it was unclear which of the stresses acting in a bed could be determined from EME in specimens or what effect was exerted on signal-to-noise ratios in monitoring dynamic loads experienced by rock when the core was extracted and processed. Also, how disruptions of the core might affect EME was not known. These questions are the subject of the present study.Institute of Mineralogic Studies, Academy of Sciences of the USSR.
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