P62 In-mine Geoelectric Methods for Detection of Tectonic Disturbances of Coal Seams

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1 P62 In-mine Geoelectric Methods for Detection of Tectonic Disturbnces of Col Sems T. Ormos* (University of Misolc), Á. Gyuli (University of Misolc) & M. Dobró (MTA-ME Reserch Group for Engineering Geosciences) SUMMARY In-mine geoelectric methods - the geoelectric sem-sounding nd geoelectric trnsillumintion - were pplied for detection of fult zones in col mine. The mesured dt were interpreted using geoelectric tomogrphy lgorithm. Apprecible greements were found between the loction of tectonic zones predicted by the interprettion nd those observed during the mining extrction.

2 Introduction Efficiency nd sfety of col mining necessitte tht the tectonic nd strtigrphic fetures of the col deposits should be well nown. By surfce geophysics this informtion is generlly not obtinble with sufficient ccurcy. If one hits fult, pinch-out, or dirt bed during col-drwing, this would probbly not only reduce the output, but could even cuse wter inrush. Tectonic disturbnces of col series re trced by openings nd hedings, but these methods re expensive. However, there re geophysicl methods for which the necessry mesurements re crried out within the mine, nd by which even smller disturbnces of the col series cn be detected: the in-sem seismic reflection nd trnsmission methods (Krey, Arnetzl nd Knecht 1982) nd in-mine geoelectric methods (Csóás et l., 1986) The in-mine geoelectric methods The two in-mine geoelectric methods clled geoelectric sem-sounding nd trnsillumintion llow the determintion of tectonic nd strtigrphic disturbnces of col beds. Both re bsed on the fct tht col bed is lyer of high resistivity embedded in medium of considerbly lower resistivity. In the fult zones the roof nd floor lyers (of much lower resistivit get connected, so tht the pprent resistnce of the medium mesured by n equtoril verticl dipole rry is lower thn it would be in its undisturbed sitution. This decrese in pprent resistnce llows one to detect the tectonic disturbnces. The principle of the methods is shown in Fig. 1. The current electrodes A nd B nd the potentil electrodes M nd N re plced t the upper nd lower boundries of the col sem in n equtoril verticl dipole rry. For sem-sounding the dipoles re plced in the sme drift with distnce r between Figure 1. The scheme of sem-soundings nd sem-trnsillumintion. them. If two drifts re ccessible in the investigted re, we cn use geoelectric sem-trnsillumintion too. In this cse the current dipole is plced in one of the drifts nd the potentil dipole in the other. The dipole rry should cover the bed in fn-shped form s fr s possible. The pprent resistivities nd the pprent resistnces R of n undisturbed lyered medium with col sem cn be clculted by mens of the formule given in Csóás et l. (1986). Are of investigtion In order to detect tectonic disturbnces in-mine geoelectric mesurements hs been crried out in Cigel col mine of Hornonitrinse bne,.s. Prievidz, Slovi. Due to previous tectonic motions the col sem ws broen into blocs (Ssvári et. l ). The loction of the geoelectric investigtions nd the mesurement system re shown in Fig. 2. Sem-soundings were crried out in the drift long Figure 2. Mp of the geoelectric sem-soundings nd trnsillumintion mesurement system. with 200 m length. The current nd potentil electrodes were plced in verticl drillings reching the col-bedroc boundries. 21 verticl dipoles were used for the mesurement equidistntly; the distnce between them ws 10 m. The positions of dipoles re numbered from 01 to 21 on the mp. The reference points of the sem soundings re depicted on Fig. 2 too. (See blue points on the mp). Sem-trnsillumintions were mde on the re bordered by four drifts (Fig. 2.). The current nd potentil dipoles were plced similr with the sem-

soundings. 43 verticl dipoles - numbered from 01 to 43 - were mnufctured in the drifts. The drift signed 177 675-0 ws closed unfortuntely, so we cn t use it for mesurements.

This pprent resistnce mster curve cn be either mesured on sites without disturbnces, or clculted it with the nowledge of the geoelectric model prmeters (Csóás et l., 1986).

3 soundings. 43 verticl dipoles - numbered from 01 to 43 - were mnufctured in the drifts. The drift signed ws closed unfortuntely, so we cn t use it for mesurements. Geoelectric model of the investigted re In order to interpret the sem-soundings nd trnsillumintions mesurements it is necessry to now the pprent resistnce R of the non-disturbed col sem structure. This pprent resistnce mster curve cn be either mesured on sites without disturbnces, or clculted it with the nowledge of the geoelectric model prmeters (Csóás et l., 1986). To determine these model prmeters we performed dditionl drift sounding mesurements long the upper (roof sounding) nd lower boundries (floor sounding) of the col sem. From the mesured pprent resistivities the model prmeters of the structure (thicnesses nd resistivities) were estimted using 1D joint inversion procedure (Dobró et l., 1991) (Tble 1.). Using 11,0 Ωm roof 660,0 Ωm 5,5 m, col sem 20,3 Ωm 5,8 m, floor 0,8 Ωm 8 m, cly 200,0 Ωm 2 m, floor sem 1,0 Ωm deep floor Tble 1. Geoelectric model prmeter estimted by joint inversion these model prmeters pprent resistnce mster curve for sem sounding were clculted (Fig. 3). To compre these vlues with the mesured curve, the pprent resistnce curve is shown in Fig. 3b. mesured in non-disturbed col bed. Results of sem-soundings From the pprent resistnce mster vlues R nd from the mesured pprent resistnce vlues R (Fig. 4.) the sem sounding devitions E were computed for th dipole-dipole position with the formule: E =. The computed devitions mp is shown in Fig 5. R R R 3.) 3b.) Figure 3. Apprent resistnce R mster curves. ):clculted from model prmeter, b):mesured. Figure 4. Apprent resistnce R mp from semsoundings. Figure 5. Apprent resistnce devition E mp, with interpreted fults (isolines in %).

The pprent resistnce devition mp (Fig. 4.) computed by mens of the sem sounding dt mesured in the drift 171 227-20 shows clerly the view of tectonic zone (red lines long the 30%).

The vritions of pprent resistivity re minly influenced by the inhomogeneities of the col deposit.

4 The pprent resistnce devition mp (Fig. 4.) computed by mens of the sem sounding dt mesured in the drift shows clerly the view of tectonic zone (red lines long the 30%). Results of sem-trnsillumintions In order to determine the distribution of the inhomogeneities of col bed we hve developed n in-mine geoelectric tomogrphy method. The vritions of pprent resistivity re minly influenced by the inhomogeneities of the col deposit. In the geoelectric tomogrphy lgorithm we relte the locl reltive chnge in pprent resistivity nd the reltive difference between the mesured ( R ) nd clculted ( R ) pprent resistnces s 1 R R ρ ρ E = e( da with E = nd e( = A R ρ L L where is the surfce of integrtion lying in the plne of the col sem, is its re. Expnding the locl inhomogeneities in series by Chebishev polinomils e( = N M n= 0 m= 0 B nm T ( x) T n m ( A n overdetermined set of inhomogeneous liner equtions cn be derived for the unnown B nm coefficients. After solving it, the e( distribution of the inhomogeneities cn be clculted nd plotted. Figure 6. Apprent resistnce R mster curve for tomogrphy, clculted from model in Tble 1. The high (negtive) devition zones in the in-mine geoelectric tomogrphy mp (Fig. 7.) clculted from the semtrnsillumintions mesurements re interpreted s tectonic zones (red lines). Figure 7. Apprent resistivity devition e mp, from geoelectric tomogrphy, with interpreted fults. Comprison of results from in-mine geoelectrics nd observtion by exploittion The mesurement re ws extrcted in the mentime nd mp of the observed tectonic fult zones hs been given by the collegues t Cigel mine (Fig. 8). The tectonic zones observed during the mining extrction re depicted by blue colour. So it is possible to compre the predicted in Fig. 5. nd Fig. 7. (red coloured lines) nd the observed fult zones in Fig. 8. This comprison shows, tht ll the min observed tectonic fults were predicted in the interprettion of sem-sounding nd sem-trnsillumintion (tomogrphic) mesurements. There re some less ccurte predictions in the tomogrphy mp ner the closed drift As is well-nown the full tomogrphic coverge cn pprecibly increses the ccurcy nd relibility of the tomogrphic reconstruction, which ws not vilble in our mesurements.

Conclusions In order to detect tectonic disturbnces two previously developed in-mine geoelectric method were used in Cigel col mine of Hornonitrinse bne,.s. Prievidz, Slovi.

5 Conclusions In order to detect tectonic disturbnces two previously developed in-mine geoelectric method were used in Cigel col mine of Hornonitrinse bne,.s. Prievidz, Slovi. The interprettion of our in-mine geoelectric sem-sounding nd sem-trnsillumintion mesurements showed the existence of tectonic fult zones in the investigted col sem structure. The mesurement re ws lter extrcted nd the observed tectonic fult zones were mpped. It ws found tht there is good greement between the predicted nd the observed fults. The ccurcy of predictions is reduced in the zones of tomogrphiclly poor coverge. Our experiences show tht the pplied geoelectric methods re quic, ccurte nd economic under mine conditions. Figure 8. Comprison between the fults predicted in the interprettion of geoelectric mesurements (red colour) nd observed in the mining extrction (blue colour). Acnowledgements This reserch wor ws supported by the Ntionl Science Reserch Fund of Hungry (project No. T049852, T nd K62416). The uthors re grteful for the support. As member of the MTA-ME Reserch Group for Engineering Geosciences one of the uthors thns lso the Hungrin Acdemy of Science for the support. References Breitze, M., Dresen, L., Csóás, J., Gyuli, A. nd Ormos, T. (1987): Prmeter Estimtion nd Fult Detection by Three-Component Seismic nd Geoelectricl Surveys in Col Mine, Geophysicl Prospecting 35, Csóás, J., Dobró, M., Gyuli, Á. (1986): Geoelectric determintion of qulity chnges nd tectonic disturbnces in col deposits. Geophysicl Prospecting 34, Dobró, M., Gyuli, Á., Ormos, T., Csóás, J., Dresen, L., (1991): Joint inversion of seismic nd geoelectric dt recorded in n underground col mine. Geophysicl Prospecting 39, Gyuli, A., Dobró, M., Ormos, T. (2005): Experimentl geoelectric mesurements in the col mine Cígel. Report (in Hungrin). University of Misolc, Ssvári, T., Pndul, B., Kondel, J., Zelená, S.: Determintion of frcture zones using geoelectricl methods in soft - col deposits in Cigel nd Novy (Upper Nitr bsin, West Crpthins) (in Slovin). Sbor. vedecych prci Vysoe soly bnse - Technice univerzity Ostrv, rd stvebni (Trnsctions of the VSB - Technicl University of Ostrv, Civil Engineering Series), No. 2, 2006, Vol. VI, pp

INVESTIGATION OF BURSA, ESKIKARAAGAC USING VERTICAL ELECTRICAL SOUNDING METHOD

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