In carrying out mining, during drilling and blasting operations there is dynamic loading and disintegration of the rock mass. In order to calculate parameters for drilling and blasting operations it is necessary in this case to know the elastic properties of the rocks under dynamic loading.Elastic properties of rocks, of which the main ones are elasticity modulus and Poisson's ratio, are currently determined from the transit velocity of ultrasonic waves for which there are several methods of determination [i, 2].For this study we adopted a pulsed method of through sonic testing.The first arrival of a longitudinal wave and its amplitude are recorded on the screen of an electron beam tube; it is very accurate, and the results obtained have a clear physical meaning.In contrast to other methods it does not require an experienced operator.For the velocity of longitudinal waves there is a typical maximum value in unbounded material (solid rock), i.e., VM, and a minimum value in a material with one linear dimension (a thin bar), i.e., Vst. The procedure for determining these values in rocks by through sonic testing of specimens with finite dimensions has not yet been sufficiently studied.As shown by previous studies carried out on specimens of different materials [3][4][5], ultrasonic wave velocity depends not only on specimen transverse dimensions and length, but also on the relationship of these dimensions to the ultrasonic vibration (USV) wavelength. Thus, the research problem is reduced to determination of values of velocities V M and Vst, and refinement for regions of their existence in rocks using the pulsed method of through sonic testing by means of UKB-Im equipment with piezoelectric transducers having natural vibration frequencies of 150, i00, 60, and 25 kHz.In orderto carryout tests sandstone specimens were selected from several mines, open pits, and coal seams of the Volkov pit "Severnoi" in the form of lumps 20-25 kg in weight. From a single lump prismatic specimens 180-250 mm long and with a minimum cross sectional dimension from 75 to 1.7 ---were sawn out in a rock cutting machine. During testing specimens were shortened in steps of 20-30 --, which made it possible to vary the ratio r/A for different specimens from 2.1 to 0.027, and the ratio 5/I from 12.2 to 0.6, where r is half the least dimension of the specimen cross section, A is wavelength, and I specimen length.As a standard, use was made of round specimens made of steel d = 120 mm, aluminum di00 -,-, and acrylic plastic d -60 and i00 mm. During a test specimens were turned with specified stages to d -3-4 mm and the longitudinal wave velocity was measured in specimens of each diameter.In order to study the effect of specimen length on ultrasonic vibration velocity different diameter specimens of steel, aluminum, and acrylic plastic were used which during the test were reduced in length from 3000 to 20-30--,.Some results of studying the effect of specimen length on longitudinal wave propagation velocity are given in Fig. 1 plotted on coordinates K -...
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