Review of Studies of Mechanoelectrical Transformations in Rocks in Russia and Abroad

The problem of monitoring and forecast of dynamic manifestations of rock masses becomes immediate in the mining industry because of the growth of mining work intensity and changeover to the mining operations in deeper levels. The article presents a short review of the scientific works of foreign researchers for more complete and in-depth study of geophysical methods of control of the stress-strain state and bump hazard of rock masses

Determining the effect of the duration of alternating acoustic excitation on electromagnetic response parameters of the composite

The paper presents the results of the experimental investigation dealing with the effect of the alternating excitation acoustic pulse duration on the parameters of the electromagnetic emission caused by interaction of acoustic vibrations with inhomogeneities in the sample structure, piezoelectric inclusions and media interfaces of different dielectric properties. The model sample was epoxy resin with quartz sand as filler. The electrical component of the response was recorded with a capacitive transducer. The acoustic pulse was generated by piezoelectric transducer at frequencies of 57 kHz, 65 kHz, 74 kHz, 87.5 kHz and 94.5 kHz with the pulse duration varying from 10 ?s to 100 ?s. It is shown that the reduced duration of the acoustic action leads to dominance of the intrinsic frequency in the spectrum. A contribution of tensile pulses to acoustic electromagnetic transformation response generation is revealed

Experimental research of the influence of the strength of ore samples on the parameters of an electromagnetic signal during acoustic excitation in the process of uniaxial compression

Parameters of electromagnetic responses (EMRe) generated during uniaxial compression of rock samples under excitation by deterministic acoustic pulses are presented and discussed. Such physical modeling in the laboratory allows to reveal the main regularities of electromagnetic signals (EMS) generation in rock massive. The influence of the samples mechanical properties on the parameters of the EMRe excited by an acoustic signal in the process of uniaxial compression is considered. It has been established that sulfides and quartz in the rocks of the Tashtagol iron ore deposit (Western Siberia, Russia) contribute to the conversion of mechanical energy into the energy of the electromagnetic field, which is expressed in an increase in the EMS amplitude. The decrease in the EMS amplitude when the stress-strain state of the sample changes during the uniaxial compression is observed when the amount of conductive magnetite contained in the rock is increased. The obtained results are important for the physical substantiation of testing methods and monitoring of changes in the stress-strain state of the rock massive by the parameters of electromagnetic signals and the characteristics of electromagnetic emission

Electromagnetic Radiation Generated by Acoustic Excitation of Rock Samples

The paper presents an experiment on acoustic excitation of electromagnetic radiation (EMR) signals in skarn, sandstone, and magnetite ore samples. For the skarn and sandstone samples, the EMR signal amplitude was observed to decrease with increasing ultimate strength. Supposedly, this effect can be explained by assuming that EMR is generated when an acoustic wave propagates through an electrical double layer. The presence of piezoelectric inclusions (e.g., quartz) in the magnetite ore enhances the analog EMR signal and its spectral components

Studying electromagnetic signal of rock effected by acoustic impact under uniaxial compression

Physical modeling in vitro is a way to carry out basic laws of mechanoelectric transformations in a rock massive. In this paper we examined how rock mechanical properties influenced on parameters of electromagnetic signals (EMS) excited by the determined acoustic impulse under uniaxial compression. It has been determined that sulphides and quartz in rock samples from the Tashtagolsky iron-ore deposit (Western Siberia, Russia) promote transformation of a mechanical energy to an electromagnetic field energy which is expressed in an augmentation of an EMS voltage. An EMS voltage reduction at the change of the stress-strained state of the sample in the course of an uniaxial compression is observed with quantity augmentation of containing of high-conducting magnetite in rocks. The obtained results are important for a physical substantiation of the method of monitoring of the stress-strained state of rock massive by mechanoelectric transformation characteristics

Interconnection between parameters of rock samples electromagnetic signals and content of magnetite in the samples

The paper describes the results of studies of electromagnetic response parameters of samples of bearing strata and ore rocks from the Tashtagol mine on acoustic effects. Patterns of changes in amplitude-frequency parameters of electromagnetic signals for rock samples with different content of magnetite are experimentally found. The conducted research shows that the maximum amplitudes of electromagnetic signal spectral components increases in samples of the same mineral composition with the reduction of their ultimate strength. This is caused by heterogeneities, and defective areas which contribute to active transformation of mechanical energy into electromagnetic energy. For rocks, which contain magnetite, the emissivity depends not only on heterogeneities and defective areas, but on the quantity of high-conductivity minerals in their composition

Study of interrelation between electromagnetic radiation and rock strength

The paper presents the study of the electromagnetic radiation of real rock samples under acoustic impact. The test samples are made of kerns from the iron ore mine with different petrophysical features and strength. The study has shown that the electromagnetic radiation parameters are related to the sample strength. However, this dependence is not observed for samples with magnetite that can be due to individual structural-textural features and quartz inclusions

Application of an Integrated and Self-contained Electromagnetic Acoustic Recorder for Monitoring the Rock Mass Structure and Development of Geodynamic Processes in Ore Mines

The paper presents a block diagram of the recorder of electromagnetic and acoustic signals. The recorder provides monitoring of electromagnetic and acoustic signals under changing stress-strain state of heterogeneous materials and rocks. The analog amplifier input sensitivity of electromagnetic signals in 4 channels is 10 [mu]V, that of the electromagnetic signal intensity is 10 [mu] and that of acoustic signals is 50 [mu]V. The operating frequency range of recording is (1±100) kHz. The averaging of electromagnetic and acoustic signal amplitudes is performed within 1 or 5 seconds. The data on electromagnetic and acoustic emission materials is recorded in digital format in the internal memory of the recorder. The recorder operates off-line within 7 days. Repeated testing of the recorder in natural conditions of the Tashtagol mine showed that the changes in the amplitude and frequency parameters of electromagnetic signals (EMC) indicate the structural damage in mines made of rocks which differ in their electrical properties. Measurements of the intensity of electromagnetic signals enable monitoring the changes in the stress-strain state of rocks during and after blasting and other geodynamic phenomena