V. Frid

Electromagnetic radiation method for rock and gas outburst forecast

Abstract An increase of rock and gas outburst hazard changes different geophysical parameters of rocks near mine workings. We consider a new modern method of rock and gas outburst forecast that relies on registration of electromagnetic radiation caused by rock fracture. Features of electromagnetic radiation were investigated at different mine situations, and relationship between a buildup of rock and gas outburst hazard and an appearance of anomalous electromagnetic radiation of rocks was revealed.

Electromagnetic radiation associated with induced triaxial fracture in granite

A study has been made of the electromagnetic radiation (EMR) emitted during triaxial compression of granite. Changes in EMR activity with loading are shown to be strongly correlated with changes in Poissons ratio but not with Youngs modulus.

Fracture area calculation from electromagnetic radiation and its use in chalk failure analysis

Fracture area calculation from electromagnetic radiation and its use in chalk failure analysis A. Rabinovitch*, V. Frid, D. Bahat, J. Goldbaum The Deichmann Rock Mechanics Laboratory of the Negev, Israel Physics Department, Ben Gurion University of the Negev, PO Box 653, 84105, Beer-Sheva, Israel Department of Geological and Environmental Sciences, Ben Gurion University of the Negev, PO Box 653, 84105, Beer-Sheva, Israel

Parametrization of electromagnetic radiation pulses obtained by triaxial fracture of granite samples

We have accurately measured and parametrized individual pulses of electromagnetic radiation (EMR) obtained during a fracture experiment. Analysis of the parameters shows that they follow a log-normal distribution. Results indicate no dependence between fracture lengths and widths.

Experimental and theoretical investigations of electromagnetic radiation induced by rock fracture

Frid, V., Bahat, D., Goldbaum, J., Rabinovitch, A. 2000. Experimental and theoretical investigations of electromagnetic radiation induced by rock fracture. Isr. J. Earth Sci. 49: 9‐19. There is a general agreement in the literature that the technique of measuring electromagnetic radiation (EMR) emitted from cracked rock is a good candidate for forecasting of earthquakes. Our immediate objective in pursuing this goal is to correlate EMR with crack dimensions in micro-scales (mm–cm), coupling it with the understanding of atomic-scale phenomena for coherently understanding the EMR process. We review some of the results obtained in this laboratory. They include the isolation, both experimentally and theoretically, of an individual EMR pulse. Individual EMR pulse parameters are correlated with crack dimensions: the time from pulse origin up to its maximum is proportional to the crack length, and the frequency of the EMR pulse relates to the crack width. Individual EMR pulses are classified both according to their length and according to their location on the stress–strain curve. We find that the key elastic parameter for EMR characterization during triaxial compression is the Poisson ratio: the lower the Poisson ratio, the higher the EMR activity. Amplitudes of EMR and their changes with loading are shown to be independent of crack mode (tensile vs. shear), they are only dependent on the entire crack area. In order to experimentally overcome load limitations we introduce a new sample shape, the truncated cone, that fails more readily than standard cylindrical samples.

Similarity and dissimilarity of electromagnetic radiation from carbonate rocks under compression, drilling and blasting

1. IntroductionNumerous investigations have examined differentaspectsofelectromagneticradiation(EMR)emittedbyfracture [1–6]. For example, it was noted that anincreaseofYoungmodulus,strength,andloadingrateenhancestheEMRamplitude[3,7–9].IndividualEMRpulseswerecarefullyinvestigatedunderuniaxialandtriaxialstiffcompression[8–11].AnexampleofanEMRpulsefromchalkcompressionisshowninFig.1.Itisknownnowthatapropagatingcrackconsistsofatomicbondseverage,whichexcitesatomic(orionic)oscilla-tions along the crack surfaces. These oscillations(Rayleigh-typewaves)induceelectromagneticradiation.Hence,eachcrackconstitutesasourceofanindividualEMRpulse.TheEMRamplitudeisafunctionofthecrackarea[12,13];thetimefromthepulseorigintothemaximumofitsenvelope,isproportionaltothecracklength;thefrequencyoftheEMRpulseisrelatedtothecrackwidth[12,13].AnanalysisoftheEMRpulsesemanating during uniaxial compression [14] showedthatindividualshortpulses(ofdurationof0.5–6ms,Table1)arecorrelatedwiththestageofindividualmicro-cracksformation;multi-pulsestringsarecorre-lated with the crack coalescence stage;andlengthypulses(ofdurationof30–400ms,Table1)arecorrelatedwithrockfailure.All these investigations were carried out in thelaboratory.Large-scaleEMRstudiespriortorockburstsinminesandtoearthquakes(EQ)arealsoregistered.Thus,Khatiashvilli[15]carriedoutaninvestigationofEMRintheTkibullideepshaft(Georgia)priortoanEQofa5.4magnitude.Theregistrationpoint(attheshaft position) was located 250km from the EQepicenter.PriortotheEQitself,anincreaseofintensityofthelowerpartofthespectrum(1–100kHz)andacorrespondingdecreaseofintensityofhigherfrequen-cies(100–1000kHz)wereobserved.NesbittandAustin[16]registeredEMRinagoldmine(2.5kmdepth).Frid[17,18]observedEMRanomaliesbeforerockburstsandgasoutbursts.Itisclaimed[19]thatanabnormallyhigh-EMRleveloccurshoursorevendaysbeforeanEQ,afterwhichEMRdecreases.Rikitake[20],analyzing60EQeventsmeasuredinJapan,alsoshowedthatEMRisa‘‘short-term’’precursor,withanestimatedmeantimepriortoan EQ of B6h. It was assumed [21–25] that theanomaliesofEMRpriortoanEQwereduetoadeformationoftheEarthsurface,whichresultedintheformation of micro-fractures and in friction of thenearbyrockblocks.Parrotetal.[26],afteradetailedconsiderationofalargenumberofEMR–EQinvestigations,remarkedthatalthoughtheexistenceofEMRinrelationtoseismicand/orvolcanicactivitieswereclear,EMRselectionoutofahostofartificialsignalsremainedasignificantproblem. Nevertheless, investigations of EMR as aprecursortolarge-scalefailurecontinue.In this work, we present the results of ourEMR investigations on carbonate rock fractureboth in the large scale (blasting in an openquarry) and in the micro-scale (drilling in the lab)and show the similarities and dissimilarities oftheseEMRresultstoourpreviousEMRlaboratorystudies during regular compression tests in thelaboratory.

Calculation of Electromagnetic Radiation Criterion for Rockburst Hazard Forecast in Coal Mines

Abstract— Intensive micro-fracturing of rock close to mining operations accompanies an increase in the likelihood of rockbursting. This fracturing causes an increase of the electromagnetic radiation (EMR) level by up two orders of magnitude, depending on the mining environment. Several examples of this enhanced EMR are presented in this paper. We first treat the EMR theoretical criterion of rockburst hazard in coal mines and compare it with the empirical criterion of EMR activity that was revealed on the basis of more than 400 different hazardous and non-hazardous situations in underground coal mines. Only the following parameters are needed to estimate the EMR criterion of rockburst hazard: limiting value of gum volume, mine working width, coal seam thickness, and coal elastic properties.

Electromagnetic radiation method water-infusion control in rockburst-prone strata

An electromagnetic radiation (EMR) method associated with rock fracture was employed to study water infusion in rockburst-prone coal strata. Measurements of EMR activity during borehole drilling revealed that a hole nearing a stress peak excites a sharp increase in EMR activity. Water pressure increase/decrease excited EMR activity up to the coal stratum transition to residual stress. An absence of EMR activity during water pressure changes could be a criterion for water infusion performance.

Exploration via electromagnetic radiation and fractographic methods of fracture properties induced by compression in glass-ceramic

The fracture properties of glass ceramic induced by compression were investigated by combined electromagnetic radiation (EMR) and fractographic methods. The study of a transparent sample enabled us to elucidate the sequence of crack nucleation, growth and interaction, and the ultimate longitudinal splitting under incremental increase of uniaxial stress in five stages. The fracture process was accompanied by some 18 EMR pulses. The short EMR pulses (of a duration of 0. 8–1.5 μs) occur under low stresses (0.36–1.7 MPa) in association with microcracking at the sample outer surface. Medium pulses (durations of 15–25 μs) are associated with stresses of up to 65 MPa and are correlated with crack limited growth outside the specimen. A lengthy pulse (duration of more than 40 μs) occurs under greater stresses (112 MPa) and correlates with the longitudinal splitting at failure. A return to the 17–20 μs range occurs for the post-failure cracking during stress relaxation.

Comparison of electromagnetic radiation and acoustic emission in granite fracturing

The electromagnetic radiations and acoustic emision from two granite samples under compressive loading are studied in experiences. The two samples exhibit respectively plastic and brittle character. Differences in observed signals for these two samples are considered to be related to their different compositions.