Continuous GNSS Movement Monitoring in the Zone of Influence of Tuzla Salt Deposit Exploitation

Transcription

1 TS 5 GNSS and Indoor Navigation Continuous GNSS Movement Monitoring in the Zone of Influence of Tuzla Salt Deposit Exploitation Ruža Čeliković 1, Edis Imamović 1 1 Faculty of Mining, Geology and Civil Engineering, University of Tuzla, Univerzitetska 2, Tuzla, Bosnia and Herzegovina, ruza.celikovic@untz.ba, imamovic_edis1983@hotmail.com Abstract. The moving of the rock massifs and the ground surface in the area of mining activities creates a risk of damaging consequences and sometimes creates catastrophic consequences. Because of the possible negative consequences, monitoring is conducted for these processes, and the main segment is the geodetic monitoring. The urban part of the Tuzla city area is a dramatic example of the impact of underground exploitation. In order to monitor the impact of mining exploitation on the ground surface and the objects, periodic geodetic measurement have been conducted, starting in In addition to periodical measurements, GNSS measurements have been carried out since 2010 as well, at two locations (the location above the Tušanj pit, and since 2013 at the location Pannonica). Continuous monitoring in the zone of influence of mining works could provide a new quality in the prevention of the consequences of mining activities. Since, so far, this method has not been used for monitoring the movement of the terrain in the zone of influence of exploitation of Tuzla's salt deposits, the results of the analysis of the data collected in the process of continuous monitoring is summarized. Basic information on the movements of registered periodic geodetic measurements during the exploitation of deposits are given, in order to assess the impact of the Tuzla salt deposits exploitation. The aim of this paper is to display the possibilities/benefits of this technology concerning its implementation in monitoring the consequences of the mining activities through the analysis of the data collected so far on the continuous monitoring of the ground surface in the zone of influence of exploitation of Tuzla's salt deposits. Keywords: exploitation, GNSS, monitoring, movement, reference station. 1. Introduction Mining exploitation of mineral resources is one of the important factors related to disturbance of the natural environment. Underground mining of mineral raw materials means creating empty spaces within the mineral deposits, or deterioration of the natural balance in the rock massif, which has resulted in the development of massif movement processes that manifest themselves on the field 489

2 SIG 2016 International Symposium on Engineering Geodesy, May 2016, Varaždin, Croatia surface. The development of these processes in a particular area is a limiting factor in spatial planning. Monitoring and studying these processes, defining their spatial-temporal framework is necessary in order to protect the environment. The problem of the negative impact of underground exploitation is characteristic for the city of Tuzla (Bosnia and Herzegovina). The deposit of salt in Tuzla is located under the urban area and spreads over the area of over 2 km 2. The horizontal projection of the deposit has the shape of an ellipse, with the length of about 2500 m and width of about 900 m [Soklić 1964]. Extensive exploitation of deposits began in 1886, in the eastern part of river deposits Trnovac-Hukalo, by pumping salt water through deep wells (salt wells) and using the uncontrolled leaching method. The exploitation of rock salt through pits begian in In the period from 1983 to 1991, the so-called controlled leaching of the existing parts of the mine "Tušanj'' was carried out. Intensive production of salt water by means of the uncontrolled leaching method caused intense movements and deformations of the terrain in the urban area of Tuzla, causing damage and/or destruction of over 2,000 objects [Imamovic et al. 2015]. Due to the consequences of exploitation, a decision to stop the exploitation of Tuzla's salt deposits was reached. In the period from 2002 to 2004, the sinking of the pit was conducted. In the period from March 2006 to May 2007, a gradual suspension of salt wells exploitation was carried out. The official date of termination of the exploitation of Tuzla's salt deposits is 29/05/2007. Given the duration and method of the exploitation, the period of the massif consolidation is uncertain. In order to reduce the risk of the leaching impact zone of Tuzla salt deposits, the monitoring of rock mass and the surface, even after the suspension of exploitation, is scheduled. In addition to the periodic measurements needed to determine the movement of stabilized points, continuous monitoring of the critical area is planned as well. The areas above the submerged pits Tušanj and the area of the salt lakes Pannonica have been defined as the critical points. A GNSS receiver/ monitoring station that continuously collect data have been set up at these sites. Based on the data collected so far, the convenience of this method for this purpose may be evaluated. The basic features of the terrain shifts in Tuzla determined on the basis of previous periodic geodetic measurements in the period from 1956 to 2012 have been specified in order to consider the complexity of the problems. 2. Monitoring the ground surface movements in Tuzla Systematic geodetic measurements in the area of influence of Tuzla's salt deposits exploitation began in A network of fixed points was set up in 1955, in order to monitor and study the process of surface movement and to determine the boundaries of the exploitation influence [Zuber & Efendić 1975]. Since 1956 until 1991, geodetic measurement was conducted annually in order to determine the displacement of the stabilized points. A number of points changed over time. By 1991, about 1200 points were stabilized. For the given period, there were about 330 points with a known vertical displacement, and about 40 points with a known 490

3 TS 5 GNSS and Indoor Navigation horizontal displacement [Čeliković et al. 2010]. After 1991, geodetic measurements were carried out on a reduced scale and in an unbalanced time shift. The geodetic measurement of the points in the network stabilized above the Tušanj pit was planned as a part of the project related to the soaking the pit "Tušanj". In the period since , five series of measurements with a time span of 5-8 months were carried out. The number of points observed by the series is variable, so there is a different number of points with known displacement [Čeliković 2006]. During and after the planned shutdown of salt wells, geodetic measurement was conducted as well. Since March 2006 to November 2012, 10 series of geodetic measurements were conducted. Geodetic measurements covered about 200 points, but there was a different number of points perceived in some series [Čeliković et al. 2014]. Geodetic measurements covered approximately 200 points, but there was a different number of points observed in certain series [Čeliković et al. 2014]. As a part of the Tuzla-Ravenna project, an expert team from the University of Bologna was involved in the realization of the first GPS measurements in the area of subsidence in the city of Tuzla in For the purposes of regional planning, Tuzla municipality launched in 2013 a new project of monitoring the ground surface in the impact zone of the Tuzla salt deposits exploitation. 3. Continuous monitoring the movement position of monitoring stations GNSS equipment for continuous monitoring was purchased and placed into operation within the frame of the NATO project Development of a Monitoring Project NATO EPS.EAP.SFP ): System to Counter manage the Risks of Subsidence Deformation on the Population of Tuzla (Bosnia),among other things. Since 2010, in addition to periodic ones, continuous measurements have been conducted as well. The continuous monitoring system consists of three GNSS stations the reference station Tuzla and the monitoring stations Tušanj and Pannonica. Equipment for continuous GNSS observations in Tuzla consists of: GNSS reference station (receiver GRX GNSS, antenna AT504 GG) Two GNSS monitoring stations (GMX902 GG receiver, antenna AX GNSS). These GNSS stations are connected to the system via internet. Software components of the system include Leica GNSS Spider and GNSS QC and Leica Geo Office [URL 1]. The reference station is set up at the site outside the zone of influence of leaching (Tuzla city administration building). Another GNSS monitoring station is set up at the site above the submerged pit Tušanj. Other monitoring stations are set up on the Pannonica site where intense shifts had been registered in the past. The antenna of the Tušanj station is fixed to the chimney of the boiler room 491

4 SIG 2016 International Symposium on Engineering Geodesy, May 2016, Varaždin, Croatia of the mine Tušanj, with a height of 30 m. The antenna of the Pannonica station is fixed to the stainless steel continuation of the screw embedded in the concrete body being 5 m high above the ground attached to a concrete base (1.5x1.5 m) buried 1.5 m in ground. In September 2011, the coordinates of Tuzla and Tušanj stations were determined in relation to a network of reference GNSS stations in BiH, i.e. positioning system FBiHPOS in ETRF2000 coordinate system. The coordinates of the Pannonica station were determined from measurements conducted on 3/21/2014. The coordinates of these stations, as well as the standard deviation (STDev) under which they are determined, are given in the table [Table 3.1]. Table 3.1 GNSS stations coordinates Station Latitude (φ) Longitude (λ) h (m) StDev Lat (m) StDev long (m) StDev h (m) Tuzla 44 31, ' 18 41, ' Tušanj 44 32, ' 18 39, ' Pannonica 44 32, ' 18 40, ' Figure 3.1 Location of the reference and the monitoring GNSS stations in the Tuzla area The spatial position of these stations is presented in the figure [Figure 3.1]. The figure marks the boundaries of the salt deposit as well as the subsidence 492

5 TS 5 GNSS and Indoor Navigation isolines of 0.5 m and 5.0 m, generated on the basis of periodic measurements during exploitation. The reference and the monitoring stations continuously collect data from GPS and GLONASS satellites. The information is forwarded via Internet to the server where it is processed and stored. The measurements taken in RINEX format are stored in files for a period of 1 hour with data measurements of 1 second and a period of 24 hours with the data measurements of 30 s. The system is intended to determine the coordinates of the monitoring station in real-time (RT), so RT measurement data are also stored on the server Measurement data taken in real time The measurement and the determination of coordinates are carried out every second. As a part of the installed program, the collected data are automatically processed, and coordinates of the stations Tušanj and Pannonica are calculated in real time, while the coordinates of the reference station Tuzla are fixed. The collected data are stored in files for a time interval of 1 hour, so that each file should contain 3600 entries. Thus formed recorded data are time series whose analysis can determine whether there is a trend, periodicity or cyclicality in changing the values of coordinates, and for longer or shorter periods of time. Table 3.2 presents the structure of the file containing the RT measurements data. Column 1 shows the time in the form hh mm ss, column 2 contains the date. Columns 3 and 4 are the values of latitude and longitude in the form ddmm, mmmmmm (degrees minutes and a minute part to 7 decimals). Columns 5, 6 and 7 contain a label for the type of solution, the number of satellites and estimated positioning errors (m). Column 8 presents the height (ellipsoidal) to three decimal places. Column 9 contains the value of GDOP (Geometric Dilution of Precision). Table 3.2 File structure containing RT measurements data Latituda Longituda Sol. (φ) (λ) No. Time Date typ (d.d. (d.d. sat. e mm.mm..) mm.mm..) qual. pos. Height h (m) GDO P 14:01: , , :01: , , In order to draw conclusions on the accuracy and reliability of the system, and positioning accuracy in real and near-real-time, the collected data were statistically analyzed. The data automatically formed from hourly RT files from different periods have been analyzed as statistical samples from the entire set. In order to analyze the accuracy of the coordinates, the deviations of the individual coordinates of the mean value determined for each RT-hourly files have been considered. For latitude (φ) and longitude (λ), the deviations are converted into linear sizes (dx and dy) according to the expressions: ( ) = = ( ) (1) 493

6 SIG 2016 International Symposium on Engineering Geodesy, May 2016, Varaždin, Croatia ( ) = cos( ) = cos( ) ( ) (2) wherein: value 1' expressed in radians, φi, φs, λi, λs individual and secondary coordinates φ and λ (dd mm. mmmmmm), dx (m) the difference of the individual and mean values of the coordinates in the direction of the meridian, dy (m) the difference of the individual and mean values of the coordinates in the direction of the parallels, φ latitude for Tuzla (φ 44.5 ), R = m, the radius of the Earth. The chart below provides the overview of the differences between the individual and the average values of the coordinates for the RT measurements during one hour in order to illustrate the accuracy of determining the coordinates using this system. A transformation of the movable mean value has been performed within the pace of 60, which corresponds to the time interval of one minute [Figure 3.2]. differences (m) differences (m) differences (m) differences (m) 0,01 0,005-1E-17-0,005-0,01 0,01 0,005 1E-17-0,005-0,01 0,02 0,01 0-0,01-0,02 0,01 0, ,005-0,01 1 Tušanj g. - variations latitude (dx) in the time interval 02:33:50 do 03:33:50 dx 60 per. Mov. Avg. (dx) Tušanj g. - variations longitude (dy) in the time interval 02:33:50 do 03:33:50 dy 60 per. Mov. Avg. (dy) Tušanj g. - variations in height(dh) in the time interval 02:33:50 do 03:33:50 dh 60 per. Mov. Avg. (dh) Panonika g. - variations latitude (dx) in the time interval 02:34:55 do 03:34:54 dx 60 per. Mov. Avg. (dx) Figure 3.2 Variation of the RT coordinates Tušanj and Pannonica over a period of one hour t(s) t(s) t(s) t(s) 494

7 Data analysis for the Tušanj monitoring station TS 5 GNSS and Indoor Navigation A great number of one-hour RT files have been statistically processed within the analysis of Tušanj station data. Doing so, the mean, the standard deviation, and a range within the one-hour samples have been determined. The maximum standard deviation of coordinates is m. The maximum standard deviation of height is m. Assuming a normal distribution of probabilities, the uncertainty of the coordinates amounts to m with a 95% level of confidence. The interval of scattering of the mean hourly coordinates for a full set of mean hourly coordinates is up to m, thus the specified accuracy can be considered real. Figure 3.3 presents the variation of the 50 mean hourly RT coordinates of the Tušanj station, determined for different hours/dates of the specified period. The differences of the mean values for the entire set and the mean hourly RT coordinates are: 2 mm for x, 5 mm for y and 9 mm for the height being within the scattering interval of the mean hourly coordinates at this station. Based on the results of the statistical data processing gathered at the Tušanj station, a conclusion may be reached about the precision of positioning in nearreal time, or the time interval of one hour. differences (mm) 6,0 3,0 0,0-3,0-6, Variations mean hourly RT coordinate Tušanj in the period do dx dy datum differences (mm) 20,0 10,0 0,0-10, Variations mean hourly RTheight Tušanj in the period do Figure 3.3 Variation of the mean hourly RT coordinates at the Tušanj monitoring station for the period The conducted analysis of RT measurement data at the ''Tušanj'' station has shown that there is no expressed trend of change of the ''Tušanj'' station coordinates Data analysis for the Pannonica monitoring station dh At the monitoring station 'Pannonica', the data have been collected since March In May 2014, significant changes were observed in the value of the coordinates of the station 'Pannonica.' Significant changes of coordinates coincided with enormous amounts of rainfall in the Tuzla area [Table 3.3]. The datum

8 SIG 2016 International Symposium on Engineering Geodesy, May 2016, Varaždin, Croatia mean hourly RT coordinates of the Pannonica station for several dates, as well as the differences of the neighbouring coordinates are given in table 3.3. Table 3.3 Results of statistical processing of the hourly RT files of the Pannonica monitoring station Mean Mean Mean dx dy dh dd Pano Date lat (dd long (dd h mm mm mm mm Ni(0 ) mm.mm) mm.mm). (m) The changes of the mean hourly RT coordinates of the Pannonica station in relation to the initial coordinates are visible from the graphic representation [Figure 3.4]. Referring to the figure 3.4, it is evident that there is a trend of change of coordinates with a strong jump in May The rate of change of coordinates also has an expressed periodicity. According to the data from the table, the total horizontal shift of the Pannonica station until 21/01/2016 amounts to 119 mm, with the grid bearing ν = ,050 The changes mean hourly coordinates Panonica in the period differences (m) 496 0,000-0,050-0,100-0, dx dy dh Figure 3.4 The change of coordinates of the Pannonica monitoring station for the period March 2014 January 2016 The vector of the Pannonica station position change for the period March 2014 January 2016 is shown in figure 3.5 (bold arrow). Figure 3.5 shows the movements of points determined by means of classical methods for the period Vertical shifts/subsidence are presented with the hypsometric scale of colours. Horizontal movements are shown as vectors. Graphic scale for vectors refers to horizontal shifts in the period , for which the max. horizontal displacement amounts to 6.7 m. The scale of the Pannonica station shift is 20 times larger than the extent of shift points from the period of exploitation. In addition to the points with known displacement, exploitation wells are presented as well. Wells symbol sizes are proportional to the total production of individual wells. Some streets/buildings, as well as artificial lakes built after 2006 are presented for the purpose of orientation datum

9 TS 5 GNSS and Indoor Navigation Figure 3.5 Movement of the ground surface and Panonica monitoring station 4. Conclusion The analysis of data for the continuous monitoring of the monitoring station Tušanj collected in the period from 2012 to 2016 indicates a satisfactory accuracy of the positioning of the Tušanj monitoring station, since the deviations from the mean value have the character of random sizes and do not exceed 5 mm. The differences between the initial and the last specified coordinates are within the specified interval, and it can be concluded that the Tušanj station is stable. A trend of changes for both the coordinates x, y and the height has been established for the Pannonica station. The intensity of the horizontal displacement changes periodically, while the direction is continuously changing from the southwest (220 ) to the south (190 ). Hence, it can be concluded that this technology is suitable for monitoring the ground movement, and for monitoring the behaviour of objects in the zone of influence of mining operations. It is known that at the site of the underground coal mining, daily shift points can range up to several centimetres in the active phase of the process of moving. The speed of the mass movement of active slides can also be sub-decimetre, so the achieved accuracy of the continuous monitoring is acceptable. Based on the experiences gathered in the work on the project, it can be concluded that continuous monitoring can yield further information about 497

10 SIG 2016 International Symposium on Engineering Geodesy, May 2016, Varaždin, Croatia the process of ground surface movement, as shown on the example of the Pannonica station. References Čeliković, R.; Dervišević, R.; Sijerčić, I.; Salihović, R.; Mancini, F.; Stecchi, F. (2010). Ground surface movements in the area of salt exploitation in Tuzla (Bosnia and Herzegovina), XIX Congress of the Carpatian Balkan Geological Association, Proceeding, Vol 1, Thessaloniki Greece, pp Čeliković, R. (2006). Pomjeranje površine terena tokom početne faze obustave eksploatacije tuzlanskog sonog ležišta metodom nekontrolisanog izluživanja, Međunarodna konferencija Trendovi u savremenom rudarstvu, Monografija zbornika radova, Tuzla. Čeliković, R.; Imamović, E.; Salihović, R.; Sušić, A. (2014). Prostorno-vremenska analiza vertikalnih pomjeranja terena u Tuzli za period , Naučnostručni simpozijum GEO-EXPO 2014, Mostar, pp Imamović, E.; Imamović, A.; Čeliković, R. (2015). Stabilnost terena i građevinsko zemljište na području grada Tuzla, Treći međunarodni naučni skup, Katastrofe-prevencija i saniranje posljedica, Europski univerzitet Brčko Distrikt, Brčko. Mancini, F.; Stecchi, F.; Zanni, M.; Gabianelli, G. (2008). Monitoring ground subsidence induced by salt mining in the city Tuzla (Bosnia and Hercegovina), Environmental Geology Journal, Special Issue. 58, pp Soklić, I. (1964.). Postnak i struktura tuzlanskog basena, Geološki glasnik br.10, Sarajevo. Zuber, R.; Efendić, M. (1975). Ispitivanje deformacija terena u gradu Tuzli geodetskim metodama, Simpozij o zaštiti čovjekove sredine od posljedica podzemne eksploatacije mineralnih sirovina, zbornik radova, Tuzla, pp URL 1: Leica GNSS Spider i Leica GNSS QC, ( ) 498

11 TS 5 GNSS and Indoor Navigation Kontinuirano GNSS praćenje pomaka u zoni utjecaja eksploatacije tuzlanskoga solnog ležišta Sažetak. Pomaci stijenskog masiva i površine terena u zoni rudarskih radova stvara rizik od nastanka materijalnih šteta ponekad i s katastrofalnim posljedicama. Zbog mogućih negativnih posljedica, za ove procese se uspostavlja monitoring, a osnovni segment je geodetski monitoring. Drastičan primjer utjecaja podzemne eksploatacije je na području urbanog dijela Tuzle. U cilju praćenja utjecaja eksploatacije na površinu terena i objekte obavljena su, počevši od godine, periodična geodetska mjerenja. Pored periodičnih mjerenja, od godine izvodi se i kontinuirana GNSS mjerenja na dvije lokacije (lokaciji iznad jame Tušanj, a od i na lokaciji Panonika). Kontinuirani monitoring u zoni utjecaja rudarskih radova mogao bi pružiti novu kvalitetu u sprečavanju posljedica rudarske aktivnosti. Budući da, do sada, ova metoda nije korištena za praćenje pomaka terena u zoni utjecaja eksploatacije tuzlanskog solnog ležišta, dan je kratak prikaz rezultata analize podataka prikupljenih u procesu kontinuiranog praćenja. Za sagledavanje problema utjecaja eksploatacije tuzlanskog solnog ležišta dane su osnovne informacije i o pomacima registriranim periodičnim geodetskim mjerenjima tijekom eksploatacije ležišta. Cilj rada je, kroz analizu do sada prikupljenih podataka kontinuiranog monitoringa površine terena u zoni utjecaja eksploatacije tuzlanskog solnog ležišta, prikazati mogućnosti/prednosti ove tehnologije vezano za primjenu u praćenju posljedica rudarske aktivnosti. Ključne riječi: eksploatacija, GNSS, monitoring, pomaci, referentna stanica. *professional paper 499