Seismic effort of blasting wave transmitted in coal-rock mass associated with mining operation

J, Cent. South Univ (2012)19: 2604-2610分SpDoI:10.1007/sll?71-0l2-1317-6springerSeismic effort of blasting wave transmitted incoal-rock mass associated with mining operationCAO An-ye(曹安业), DOU Lin-ming(窦林名)2, LUO Xun(骆循)ZHENG Y-dong(张益东)2, HUANG Jun-i(黄军利),K, Andrew2School of Mines, China University of Mining Technology, Xuzhou 221116, China2. State Key Laboratory of Coal Resource and Mine Safety(School of Mines, China University of Mining Technology ), Xuzhou 221116, China3. Exploration Mining, CSIRO, Brisbane, Queensland 4069, Austral4. Faculty of Safety Engineering, China University of Mining Technology, Xuzhou 221116, ChinaC Central South University Press and Springer-Verlag Berlin Heidelberg 2012Abstract: Microseismic effects during the transmission of seismic waves in coal and rock mass associated with mining operationwere studied by on-site blasting tests and microseismic monitoring in Lw704 of Southen Colliery, Australia, by using spreadvelocities, amplitudes and frequency contents as the main analysis parameters. The results show that the average P-wave velocity,mean values of combined maximal amplitudes and frequencies of the first arrivals are all reduced significantly along with goafexpanding and intensity weakening of overlying strata during mining process. A full roof fracturing can make the average P-wavevelocities, combined maximal amplitudes and frequencies of first arrivals reduce to about 69.8%, 92.2% and 60.0%, respectivelyThe reduction of the above seismic parameters reveals dynamic effects of the variation of strata structure and property to the wavetransmission and energy dissipation of blasting wave. The research greatly benefits further study on stability of surrounding rockunder the destructive effort by mine tremor, blasting, etc, and provides experimental basis for source relocation and parameteroptimization of seismic monitoring as wellKey words: seismic effort; blasting wave; transmission and attenuation rule; fracture zone; intensity weakening; geophone stationpropagdistance based on 60 shots1 Introductionquarry area in Istanbul. MANOJ and SINGH [6evaluated and predicted the blast-induced groundThe destructive effects of seismic wave on the vibration and frequency by incorporating rock propertiesroadway surrounding rock in underground mine, not only blast design and explosive parameters. XIA et al [71are influenced by failure mode and energy radiation of analyzed the situation of the vibration and thethe source, but also depend on the structure complexity deformation of the roadway under the shock of blastinginhomogeneity, discontinuity, etc)of the coal-rock mass. stress wave. The transmission rules of the stress wave inBecause of the isotropical property of energy radiation sandstone [8], halite [9], and limestone [10] have beenpattern of calibration shot, it can be specially used as the studied. MEHDI et al [11] studied the blast wavemain experimental method to study the influence of the propagation in the medium and the response of theproperty variations of the non-source factors(intensity of structure to blast loading. MANOJ and SINGH [12]coal-rock mass, propagation path, etc)on the proposed a new neural network for the prediction oftransmission and attenuation of seismic wave in ground vibration and frequency by all possibleunderground mine [1-3] There have been some influencing parameters of rock mass, explosiverelated-literature studies on the transmission rules of characteristics and blast design. KuZU et al [13] putblasting waves. YANG [4] discussed the properties of forward a method of modified scaled distances based onblasting transmission, energy, frequency and damage. empirical equations considering factors such asCENGIZ [5] studied the blast-induced shock wave blasting and geological parameters of rock mass forattenuation law in relation to the charge weight and the bench blasting in quarries. yE et al 14] carried out anFoundation item: Project(2010CB226805)supported by the National Basic Research Program of China; Project(2010QNA30)supported by theFundamental Research Funds for the Central Universities of China; Project supported by the Priority Academic Development Programof Jiangsu Higher Education. China; Projects(SZBF2011-6-B35, 2012BAKO4B06) supported by the National Twelfth Five-year KeyScienceTechnology Foundation of ChinaReceived date: 2011-07-26: Accepted date: 2011-11-14国煤化工Corresponding author: ZHANG Yi-dong, Associate Professor, PhD; Tel: +86-13952118118; E-mail: yuzhang@cumt.eduNMHG方数据J.Cent. South univ.(2012)19:2604-26102605experiment study on the transmission rule of blastingrocks around the geophone arrays were undisturbed,wave in deep underground by using seismic monitoring partial disturbed and fully disturbed by mining operationsystem. GAO et al [15-16] made a comparative analysis The shots locations are also shown in Fig. Iof the transmission rules of blasting wave in several7454900different rock masses on the ground7454800W703The property of coal-rock mass and stress field will(mined)LW704change continually during mining process, which makes7454700B(being mined)the transmission and attenuation rule of the seismic wavemore complex than that in the laboratory and surface site907454600Nowadays, there has been little experimental study on 5 7454500Dthe transmission rule of the seismic wave associated withLW705(unmined)coal mining, while the knowledge of this aspect is useful7454400for the risk evaluation and control of rock burst induced7454300LW706by dynamic effort from mine tremor, blasting, etc(unmined7454200Based on the blasting experiment and Siroseis658600658800659000659200659400659600microseismic monitoring results in the mining process ofEast length/mLongwall(LW)704 in Southern Colliery, Australia, thevariation characteristics of seismic parameters (wave200(b)velocities, amplitudes and main frequencies, etc)150influenced by the mining disturbance were studied in thiswork, for the purpose to reveal the influence factors of00transmission and attenuation rule of seismic wave andenergy dissipation associated with variations of goafcaving range and rock fracturing extenta Coal seamThe forth calibration shotThe third calibration2 Collection of calibration shots duringThe second calibratiThe first calibration油mining process100Geophone station160015001400130012001001000900Longwall chainage/n2.1 Microseismic monitoring layout in LW704Fig. 1 Layout of LW face, geophones, and calibration shots:Southern Colliery is located in the Bowen Basin of(a)Plan view;(b) Cross section along strikecentral Queensland. The German Creek(GC)Seam ismined 150 m below the ground surface. The immediate 2.3 Collection of signals of calibration shots androof stratum is composed of massive sandstones withmining-induced seismicitiesbedded siltstones The massive sandstone roof results inIn the first day of the mining operation, a set ofheavy weighting at the longwall face. In order to further three blasting tests were implemented in Borehole Sl, S2determine the fracturing processes and patterns of the and S3, respectively. In addition, only three mining-heavy roof associated with longwall mining, a micro- induced seismicities were recorded by the seismic systemseismic monitoring study was carried out at Lw704[7]. which means that the ray paths between the blastingThe microseismic system consists of 20 triaxial sources and geophone arrays have not been disturbed bygeophones with five in each of four deep boreholes mining operation. The plane view of the blasting sources,(named by A, B, C and D)across the longwall faceseismic events and geophones are shown in Fig. 2(a)(Fig. 1). This monitoring layout covers an area of2)When the Lw face was retreated to about 110 m,400 mx400 m and provides a better configuration for the another set of three blasting tests was implemented indetection of roof fracturing occurring in this areaBorehole Sl, S2 and S3, respectively. At that moment,the surrounding rock around geophone array"Awas2.2 Layout of calibration shotspartially destroyed by coal mining(Seen in Fig. 2(b))The variation rules of seismic waves along with The seismic features of blasting waves were thusroof caving were studied using calibration shots during influenced to a certain extent by the characteristicthemining process. These shots were set off at thevariations(poriness, integrity, hardness, etc) of coal-rockbottom of the boreholes (named S1, S2 and Smass in partial areasrespectively) located in the microseismic network. In the3)When the Lw face was retreated to about 450 mwhole mining process of LW704, three sets of eleven a set of two blasting tests was implemented in boreholeblasting tests(three, four and four tests in Sl, S2 and S3S2 and S3, respectively. At that moment, the surroundingrespectively) were carried out while the surrounding rock around geophone array"A","Bwas中匡煤化工CNMHG万方效据2606J.Cent. South univ.(2012)19:2604-261074549007454900EventEvent7454800LW face T7454800LW faceLW703LW704LW704E745470(my(being mined7454700( mined(being mined)2074546000745460074545007454500LW705LW705(unmined)(unmined)745440074544007454300Aw7067454300A LW706(unmined)(unmined74542007454200658600658800659000659200659400659600658600658800659000659200659400659600East length/mEast length/74549007454900EventEvent7454800LW face7454800LW faceLW704LW704(being minedLW703e 7454700(mined)BA(being mined)LW703E 7454 700(mined) B745460020745460074545007454500LW7057454400(unmined)7454400LW705S2:2(unmined7454300●ALW7067454300A(unmined(unmined)x<74542007454200658600658800659000659200659400659600658600658800659000659200659400659600East length/mEast length/mFig 2 Plan view of blasting shots, geophones, and mining-induced seismic events: (a) In first day of Lw704 mining;(b )Lw704retreated to about 110 m;(c)Lw704 retreated to about 450 m; (d)Lw704 retreated to about 550 mnearly fully destroyed by coal mining(Seen in Fig. 2(c). dissipation of blasting wave associated withThe attenuation extent of the blasting waves was further characteristic variations of coal and rock mass in miningincreased, while the ray paths between the two blasting processsources and three geophone arrays were largelyDyed by mining operation3.1 Variation rules of average p-wave velocities4)When the lw face was retreated to about 550 mIn the blasting tests, the locations of all calibrationthe geophone array"C"was entirely destroyed because shots and geophone stations are exactly known, and theof the collapse of surrounding rock around the borehole first arrivals of P-waves are also easily recognized(Seen in Fig. 2(d). Besides, the mining-induced Therefore, the average P-wave velocities of 'theseismicities were not recorded by the seismic monitoringcalibration shots in different mining periods can besystem. Until the LW face was fully mined out, the lastexactly calculated using linear regression method. Theset of three blasting tests was implemented in boreholeaverage spread velocity can be expressed asSl, S2 and S3, respectively. At that moment, thesurrounding rocks around all the geophone arrays were∑nearly fully destroyed by coal miningFj=13 Seismic efforts of calibration shotsassociated with fracturing extent ofoverlying strata∑[v-2-)-7)Considering the anisotropy of the real coal and rockmass, the average P-wave velocities, mean values ofcombined maximal (Comb. Max )amplitudes and(1)frequencies of the first arrivals were mainly studied, forthe purpose to reveal the attenuation rule and energy(-F)(0-m)H匡煤化工CNMHG万方效据J Cent. South Univ(2012)19: 2604-26102607whereri =(xi-x)2(v-yo)2+(zi-zo)which isFor the blasting borehole Sl, when the blasting teststhe distance between the blasting source and each I was carried out, the ray paths between the blastinggeophone; ijobs is the first arrival of pe in eachsource and geophone arrays havent been disturbed bymining operation yet(Fig. 2(a)), and the average spreadgeophone, and Tin is the number ofvelocity of blasting wave is comparatively fast(about4.06 km/s). When the test 2 was carried out, the raygeophone stations used for calculationTherefore, the average P-wave velocities of Sl, $2aths between the blasting source and geophone arrayS3 in different mining periods mentioned aboveA"have been partially destroyed by coal mining(Figassociated with variations of the goaf caving range and2(b)), and the average P-wave velocity is reduced to 3. 89km/s, with the slight reduction of about 4.2%. In thefracturing extent, can be obtained from Eq.(1),seenfrom Figs. 3-5blasting test 4, the attenuation of blasting waves isincreased substantially, while the surrounding rocks=3. 89 km/saround all the geophone arrays are fully destroyed by380Test 1coal mining (Fig. 2(d)). Thus, the average P-waveTest 4relocity is reduced to 2. 58 km/s, with the reduction of330about 36.5%For the blasting borehole $2, when the blasting tests2801 and 2 were carried out, the ray paths between thep 2.58 km/sblasting source and geophone arrays can be regarded to4.06km/sbe undisturbed by mining operation yet. The average230P-wave velocities are 3.82 km/s and 3.70 km/srespectively, which are equivalent roughly to each other220280340400460520while considering the calculation error. MeanwhileArrival time/mswhen the blasting tests 3 and 4 were carried out, the rayFig 3 Velocity variations of si along with mining progresspaths between the blasting sources and geophone arraysB""C" have been largely destroyed by mining380operation, while the ray paths between the sources and=3.70km/s=229km/sgeophone array"A"and D" are partially destroyed. Dueto the comparatively large attenuation of blasting wavesthe average P-wave velocities in tests 3 and 4 are=2.27km/■一 Test 1reduced to 2.29 km/s and 2, 27 km/s. respectively withe300Test 3the reduction of about 39. 4%Test 4For the blasting borehole $3, when tests 1 and 2vp, =3.82 km/swere carried out, the ray paths between the blastingsource and geophones haven't been disturbed yet. The220average P-wave velocities are 4. 14 km/s and 4.07 km/s240260280300respectively, which are equivalent roughly to each otherArrival time/msFig. 4 Velocity variations of S2 along with mining progressWhen test 3 was carried out, the ray paths between thesources and geophone array“B”and“C” are partially600vp, 4. 14 km/sdestroyed, and the P-wave velocity is slightly reduced to550Test 13.88 km/s, with the reduction of about 6.3%. In test 4est 2Test 3the surrounding rocks around all geophones are fullyTest 4destroyed by mining. The average P-wave velocity issubstantially reduced to 1. 25 km/s, with the reduction ofE450about 69.8%0Therefore, with the goaf expanding and intensity=407kmweakening of overlying strata associated with miningv=1.25km/s350operation, the average P-wave velocities of blasting3.88km/ssources are reduced correspondingly in various degrees,300240260280300320340360which means that the more integrated and harder theArrival time/mscoal-rock mass is, the larger the transmission velocity isFig. 5 Velocity variations of s3 along with mining progressand vice versaH匡煤化工CNMHG万方效据2608J.Cent. South univ.(2012)19:2604-26103.2 Amplitude variations of blasting waveformsamplitude attenuation coefficient which presents theBecause of the coal-rock media damping effort, the attenuation degree in the wave transmission processseismic energy will be dissipated in various degreesMeanwhile, in the view of anisotropy of coal-rockduring the transmission process. Variations of maximal mass, the mean values of combined maximal amplitudesamplitudes of blasting waveforms recorded by the five of all five geophone stations in each geophone array aregeophone stations in each borehole were studied here. further considered. Then, the variation rules of meanFigure 6 shows the typical variation curves of maximal values of combined maximal amplitude of differentamplitudes as the transmission distance increases. Seen blasting sources(S1-S3)associated with mining processfrom Fig. 6, the maximal amplitudes of blasting were discussed. The results are shown in Tables 1-3waveforms recorded by different geophones in each From the results of difterent blasting tests in eachgeophone array decrease exponentially with the increase borehole, the mean values are almost gradually reducedof transmission distance which can be expressed asalong with the expanding of goaf caving and fracturingA ,=Ageextent during the mining process of Lw704. Seen from(2)the tables, taking test 1 (when there is nearly nowhere Ao is the maximal amplitude radiated by blasting disturbance by mining)as the basis, when test 4 wassource;Ai is the maximal amplitude recorded by carried out, the mean values in each borehole are reducedgeophone after wave transmission; r; is the distance substantially, with the reduction ranging from 58.49%tobetween blasting source and geophone; n is the92.19%40yA1494R2=09929B30R2=08485D15Dy=4×105e00174x月EE4=63729e0243xy1=50551025R2=0.9341y3=638|3e003542-09596目答R2=0.8266R2=0.9669y2=346130e0318R20.746y2=22914e00241R2=0.776310015020250300350400450C0150200250300400Distance/mDistance/mFig. 6 Typical combined maximal amplitude variations of blasting shots in difterent geophone stations: (a) SI in Test 1;(b)S2 inTest 1Table 1 Mean values of combined maximal amplitude variations of si calculated by different geophone arrays (10 mGeophoneTest 1Test 2Test 4arrayMax amplitudeChange/%Max amplitudeChange/%Max amplitude Change/%A1280.00113011.7292.19B14.900.0130012.751.80879217.100.0018.20643530000Table 2 Mean values of combined maximal amplitude varations of $2 calculated by different geophone arrays(10 m/s)GeophoneTest 1Test 2Test 3Test 4array Max amplitude Change/% Max amplitude Change/% Max amplitude Change/% Max. Change/%A32.900.00288112.4376676.73,7l38.72B20.200.00134633.372.521.979025C36810.0046.5426438.457704D30.240.0026.ll-13.6679373.7870176.82CNMHG万方效据J Cent. South Univ (2012)19: 2604-26102609Table 3 Mean values of combined maximal amplitude variations of S3 calculated by different geophone arrays(10 m/s)Test ITest 2Test 3Test 4Geophone arrayMax amplitude Change/% Max amplitude Change/% Max amplitude Change/% Max amplitude Change/%o3.610.006.250.005.24-16.163.5143.843.5742.88BCD27.990.019.5630.1218.1035337.300.006.747.675.8919.323.03-5849The seismic energy is proportional to the square of of fracturing extent during mining process. In addition,waveform amplitude, so the dissipation rules of energies because of the surrounding rocks around the geophoneare similar to amplitude variations. According to thearray"B"are mostly destroyed by mining operation, theamplitude results, with the goaf expanding and intensity mean frequency of first arrivals is reduced to above 60%,weakening of overlying strata, compared to the intact while the frequency reductions in other three geophonecoal-rock mass, the seismic energies transmitted to the arrays range from 20% to 30%recording stations will be reduced to 16% of that at leastand 0.006 at most4 ConclusionsIn addition, by the variation rules of velocity andamplitude mentioned above, the variations of dynamic1)With the goaf expanding and intensity weakeningstress drops caused by blasting shots can also be obtained. of overlying strata associated with LW704 mining, theAccording to formulas pa =pvp(PPV)n and average P-wave velocities of blasting sources in eachPa=pvs(PPV)s[18], because of the reductions of borehole are reduced correspondingly in various degreesspread velocities (vp, vs), the maximal amplitudes Especially, when the surrounding rocks around geophone(normal vibration velocity (PPn)n and tangential arrays are largely destroyed by mining operation, thevibration velocity(PPV) ), and rock densities with the reductions of average P-wave velocities reach 36.5%o,fracturing expanding during mining process, the dynamic39.4% and 69.8%, respectivelydisturbance on the surrounding rock caused by stress2)The amplitudes of blasting waveforms recordeddrop pa and pa is also weakened largely.by different geophones in each geophone array decreaseexponentially with the increase of transmission distance3.3 Frequency variations of blasting waveformsIn addition. the mean values of combined maximalThe main frequency of waveform is determined by amplitudes in each borehole are also reduced graduallyfailure characteristic of seismic source itself, and the during the mining process of LW704, with the reductionhigh frequency part is also affected by damping effect of ranging from 58.49% to 92. 19% when last tests arecoal-rock medium in its transmission process. Taking the carried outcase of borehole S2 as example, Fig. 7 shows the3)The main frequencies of waveforms are alsovariations of mean frequency of first arrivals. Seen from affected by damping effect of coal and rock medium inFig. 7, the frequencies of first arrivals in each geophone its transmission. Taking the case of Borehole S2, a fullarray are also reduced gradually, along with expanding roof fracturing can make the mean frequency of firstarrivals reduce to over 60%120Test I4) According to the test results, the intensity口Test曰Test3weakening of coal-rock mass can make the seismic四Test4energies radiated by mine tremors or blasting shotsdissipate largely, reducing the destructive efforts on thesurrounding rocks around roadways or working faces60Additionally, the spread velocity variations mean that theset velocity used for seismic event location needs to be三40adjusted correspondingly, according to goaf variationduring mining process, to ensure the location accuracy ofseismIc monitoringABCGeophoneReferencesFig. 7 Sketch map of frequency of first arrival of S2 associatedwith minins[U] CAO An-ye. Research on seismic effort of匡煤化工ofCNMHG万方效据2610J.Cent. South Univ.(2012)19:2604-2610coal-rock massassociated with mining and its application D]25(3):30t-304.( in Chinese)Xuzhou: China University of Mining and Technology, 2009.(in [11] MEHDI S C, GHODRAT K, MARIUSZ Z. Numerical analysis ofChinese)blast-induced wave propagateFSI and ALE muIti-materia[2] CAO An-ye, Fan Jun, MU Zong-long, GUo Xiao-qiang. Burstformulations [J]. Int J Impact Eng, 2009, 36: 1269-1275failure effect of mining-induced tremor on roadway surrounding rock [12] MANOJ K, SINGH T N. Prediction of blast induced ground[] Journal of China Coal Society, 2010, 35(12): 2006-2010.(invibrations and frequency in opencast mine: A neural networkapproach [J]. J of Sound vibration, 2006, 289: 711-725[3] CAO An-ye, DOU Lin-ming, YAN Ru-ling, JIANG Heng. [13] KUZU C, FISNE A, ERCELEBI S G Operational and geologicalClassification of microseismic events in high stress zone [J]. Miningparameters in the assessing blast induced airblast-overpressure inScience and Technology, 2009, 1916):718-723 (in Chinesemarries []. Applied Acoustics, 2009, 70: 404-411[4] YANG Sheng-quan. Study on theory and application of blasting [14] YE Gen-xi, JIANG Fu-xing, GUo Yan-hua, WANG Cun-wenvibration cumulative effects [D]. Changsha: Central South University,Experimental research on seismic wave attenuation by field2002.(in Chinese)microseismic monitoring in deep coal mine UJ]. Chinese Journal of[5] CENGIZ K. The importance of site-specific characters in predictionRock Mechanics and Engineering, 2008, 27(S):1053-1058.(inmodels for blast-induced ground vibrations [J]. Soil Dyn EarthquakeEng,2008,28:405414[15] GAO Ming-shi. Study on the strong-soft-strong structure control[6] MANOJ K, SINGH T N. Prediction of blast-induced groundmechanism of roadway surrounding preventing rock burst [D]vibration using artificial neural network []. Int J Rock Mech Min SciXuzhou: China University of Mining and Technology, 2006. (in009,46:1214-1222[7] XIA Zhi-xi, MIAO Xie-xing, MAO Xian-biaD. Analysis of ground [16] GAO Ming-shi, DOU Lin-ming, ZHANG Nong, MU Zong-long,hock wave on deep buried tunnels [J]. Henan Science, 2004, 22(1)WANG Kai, YANG Bai-shun. Experimental study on earthquake88-91.(in Chinesetremor for transmitting law of rockburst in geomaterials [J]. Chinese[8] WU Wen, XU Song-lin, YANG Chun-he, BAI Shi-wei. TestingJournal of Rock Mechanics and Engineering, 2007, 26(7)tudies on response behaviour of rock salt to impacting []. Chinese1365-1371.(in ChineseJoumal of Rock Mechanics and Engineering, 2004, 23(21): [17] GUO Hua, LUO Xun, ZHOU Bin-zhong, POULSEN B, KELLY M3613-3620.(in Chinese)CRAIG S, ADHIKARG D Southern colliery Lw704 geotechnical[9] KOU Shao-jin, YU Ji-lin, YANG Gen-hong. Testing studies onstudy[r]. ACARP Project 759, Australia, 2000attenuation mechanics of stress wave in limestone [] Journal of [18] GUO Ran, PAN Chang-liang. Theory and technology of hard-rockMechanics, 1982, 14(6): 583-588. in Chinese)burst-prone mining [M]. Beijing: Metallurgical Industty Press, 2003[10 LI Xi-bing, CHEN Shou-ru, GU De-sheng. Dynamic strength of rock41-42.(in Chinese)under impulse loads with different stress waveforms and durations U](Edited by YANG Bing)Journal of Central South Institute of Mining and Metallurgy, 1994H匡煤化工CNMHG万方效据