Arch. Min. Sci., Vol. 61 (2016), No 1, p. 157168 Electronic version (in color) of this paper is available: http://mining.archives.pl DOI 10.1515/amsc-2016-0012 KRZYSZTOF TAJDU* ANALIZA PRZEMIESZCZE POZIOMYCH POMIERZONYCH NAD EKSPLOATACJ CIANY 537 POKLADU GIRONDELLE 5 KOPALNI BW FRIEDRICH HEINRICH-RHEINLAND The article presents an analysis of the horizontal land surface displacements taking place as an effect of coal exploitation on the Girondelle 5 seam in the Friedrich Heinrich-Rheinland mine in Germany. The paper presents changes in displacement vectors measured on the surface following the progress of the exploitation face and an analysis of horizontal displacement measurements assuming that their magnitude is proportional to the profile of subsidence trough slope. Then, the values of horizontal displacement coefficient B are assessed for selected longitudinal and transversal calculation cross-sections of longwall No. 537. Keywords: horizontal displacements, surface deformations, mining exploitation, horizontal displacement coefficient Artykul przedstawia analiz przebiegu przemieszcze poziomych powierzchni terenu powstalych w wyniku eksploatacji górniczej kopalni Niemieckiej Friedrich Heinrich-Rheinland w pokladzie Girondelle 5. Autor przedstawil zarówno zmiany wektorów przemieszcze powierzchni terenu wraz z postpem frontu eksploatacji, jak równie analiz pomiarów przemieszcze poziomych zakladajc, e ich wielko jest proporcjonalna do nachylenia profilu niecki osiadania. Nastpnie dla okrelonych przekrojów obliczeniowych wzdlu oraz w poprzek analizowanej ciany 537 oszacowano wartoci wspólczynnika przemieszcze poziomych B. Slowa kluczowe: przemieszczenia poziome, deformacja powierzchni, wplyw eksploatacji na powierzchni, wspólczynnik przemieszcze B STRATA MECHANICS RESEARCH INSTITUTE OF THE POLISH ACADEMY OF SCIENSES, UL. REYMONTA 27, 30-059 KRAKOW, POLAND 1. Introduction Due to the protection of surface constructions, underground mines are carrying out regular measurements of land surface subsidence caused by the mining exploitation. Only some of the mines however do carry out measurements of horizontal displacements due to the significant complexity of this type of observations. Developments in the GPS technology over the last decade allowed larger scale measurement of surface horizontal displacements. These observations demonstrate that horizontal displacement values are low in areas located at the boundary of the exploitation subsidence trough, increasing towards the edge of the exploitation field and decreasing again near the central point of exploitation field. In the centre of the subsidence trough, horizontal displacement of land surface is equal to zero. Comparing the maximum values measured of horizontal displacements umax with the maximum values of subsidence wmax, it has been found that their ratio ranges within: 0.24 umax wmax 0.58 (1) and depends on a variety of factors, including among other things the geological structure of the overlying rock formations, depth of mining exploitation, number of previously exploited seams and longwalls, exploitation methods, size of the panel field, etc. The majority of these quotients fit a narrower range of 0.3 to 0.35. Several publications (Popiolek & Ostrowski, 1978; Bialek, 2010; Tajdu, 2015, 2013 and others) have presented attempts to determine distribution of surface horizontal displacements caused by underground mining activity based on the Avershin hypothesis, assuming a linear relationship between the value of horizontal displacement and slope. This publication presents further distribution analysis of the surface horizontal displacements. The study was performed in relation with mining exploitation of longwall No. 537 at the Girondelle 5 level (seam) of the Friedrich Heinrich-Rheinland coal mine in Germany. 2. Description of the mining and geological situation of the Friedrich Heinrich-Rheinland mine in the region of longwall panel No. 537 The analysis of horizontal surface displacements and distribution of the B coefficient was carried out based on the example of the BW Friedrich Heinrich-Rheinland (DMT) coal mine. In 1998, the mine has initiated exploitation of longwall No. 537 (seam Girondelle 5) located at an average depth of 925 m. The exploitation ended in 1999. The length of the exploited longwall was 430 m with a panel run of 2003 m (Fig. 1). The inclination of the seam was from 3° to 4° in the longwall panel run direction. Longwall No. 537 was designed as a high yield wall generating approximately 1300-1400 tons of coal per meter of extraction progress. Thickness of longwall No. 537 was not constant, in first phase of the exploitation it ranged from 2.5 m to 2.7 m and increased to 3.1 m in phase second (Fig. 2). The average thickness was 2.77 m. Fig. 1. Mining situation of the Girondelle 5 mining level Fig. 2. Changes in longwall No. 537 thickness The exploitation rate in longwall No. 537 varied, decreasing with increasing thickness of the coal seam and occurrence of sandstone veins (Fig. 3). The average exploitation rate was v = 4.60 m/day, yielding 6 000 to 6 500 Mg/day exploitation from the longwall. Fig. 3. Daily longwall 537 exploitation velocity From 1988 to 1997, the seam Girondelle 5 was exploited in 8 longwalls, located in the area of longwall No. 537, using both pneumatic stowing and caving systems. The types of extraction and exploitation parameters are shown in Table 1. TABLE 1 Characteristics of the longwalls in the extraction area (Hegemann, 2003) Longwall no. Date started Date finished Thickness Extraction Longwall Longwall Method of [m] rate [m/day] length [m] panel run [m] filling the void Stowing Caving Longwalls no. from 531 to 536, and 543, 553 ran in the East-West direction and longwall No. 537 was exploited in the opposite direction. After completion of works in longwall No. 537, exploitation started in adjacent longwall No. 538 with a thickness of 2.6 m, length of 429 m and 943 m run. The longwall equipment and infrastructure systems were installed and exploitation began in 2000 (ending in 2001). Ten seams were exploited above Girondelle 5 in previous years. In five of them the panels were backfilled (stowed) and the rest were carried out with caving. In general, all these coal seams had an average thickness of 1.2 m and mining works started at the beginning of the 20th century (1914) and ended 15 years before initiation of extraction works in longwall No. 531 on the Girondelle 5 seam (1973). The lowest level exploited in the previous years (Präsident) was located approximately 450 m-550 m above Girondelle 5, and its exploitation ended 19 years before commencement of works in longwall No. 531. The rock mass structure in the mining operations area is diversified. It includes, among others, quaternary layers (thickness of 20 m) over layers of tertiary and carbonaceous formations characterized by alternating layers of sandstone, shale and sandy schist with veins of coal. The boundary line between the quaternary, tertiary and carbon formations runs at a depth of approximately 180-200 m. In the carbonaceous formations down to a depth of 1320 m the shale with coal veins accounted for about 30%, along with 40% of sandy schist and 30% of sandstone. In general, the carbonaceous deposit layers can be classified as high strength formations. The above structure was determined by borehole drilling (Fig. 5). 3. Measurements of surface deformations caused by exploitation of longwall No. 537 The mine has established a surface measurement network composed of a number of dispersed survey points (Fig. 4). Measurements were performed using the GPS method, guaranteeing an accuracy of less than 5 mm (Sroka et al., 2000). The initial measurement (No. 0) was made on 29.01.1998 and longwall extraction began on 24.02.98. Figure 4 shows a diagram of the longwall with locations of the extraction face for the survey measurements (from p.0 to p.27). The vertical and horizontal displacement measurements were made in in dispersed surface points. Exploitation of the longwall ended on 16.12.1999. Fig. 4. Diagram of longwall No. 537 exploitation progress with measurement points Values and distribution of subsidence (Fig. 5) and horizontal displacements in the x (Fig. 6a) and y (Fig. 6b) coordinates were obtained by measurement. The values presented in the figures correspond to the measurements taken on 04.05.2000, so four and half month after exploitation ends. Fig. 5. Maps of geodetic measurement results1 surface subsidence w [mm] -1 50 Fig. 6. Maps of geodetic measurement results : horizontal displacements in the x axis [mm], horizontal displacements in the y axis [mm] 1 The matching was done using the Kriging method in which appropriate weights are allocated to points located inside the estimation area (sample selection area). These weights are referred to as kriging coefficients (weights) and they are allocated in a way to minimise the average square estimation error (kriging variance) based on the linear behaviour of the variograph. Horizontal displacement u() distribution in directions parallel and perpendicular to the axis of longwall No. 537 are shown in Fig. 7. y' x' y' x' Fig. 7. Horizontal displacement isolines along the local coordinates system for the x' and y' axis, over the exploitation area of longwall No. 537. Subsequently, the distribution was analysed for the ratios of maximum horizontal displacements to maximum subsidence umax /wmax in particular points. Distribution of these values is shown in Figure 8. Fig. 8. Isolines of the ratio umax /wmax in particular measurement points over the exploitation area of longwall No. 537 (|umax|/wmax) = 0.2 for exploitation of longwall No. 537 are reached in the central part of the extraction area (according to previous Soviet studies (|umax|/wmax) = 0.3), moving away from As demonstrated by the analysis presented in Figure 8, the minimum values of ratio the edge, the value of the ratio increases up to values exceeding one. In some distance from the area of extraction, the value of horizontal displacement is more than two times greater than the value of subsidence. 4. Analysis of the value and distribution of the B coefficient for the exploited longwall No. 537 Eleven calculation cross-sections, perpendicular to the longwall's panel run, were prepared to support analysis of the B coefficient value distribution in the BW Friedrich Heinrich-Rheinland mine (Fig. 9). Fig. 9. Cross-sections (from 1 to 11) perpendicular to the panel run of longwall No. 537 with locations of measurement points Cross-sections from 1 to 11 are composed of over one hundred points, in which the values of horizontal and vertical displacements were estimated using the Kriging interpolation principle. A graph showing the values of horizontal displacements in the cross-section direction u() in function of the cross-section slope T() (angle corresponds to axis Y') was also prepared. Figures 10a and 10b show the example of horizontal displacement graphs for the cross-section plane u() in function of slope T() for cross sections No. 4 and 8 . Fig. 10. Graph of horizontal displacements on the cross-section plane u() in function of slope inclination T() for cross-sections No. 4 and 8 For the analysed cross-sections (1÷11), functional relationships between horizontal displacements and slope were determined using the linear regression method (Table 2). In the formulae presented, the values of horizontal displacements are given in mm and the slope in mm/m, which means that the value of parameter B is expressed in metres. TABLE 2 Linear regression matching formulae for cross sections perpendicular to the panel run of longwall No. 537 Number of section Cross Section no.1 Cross Section no.2 Cross Section no.3 Cross Section no.4 Cross Section no.5 Cross Section no.6 Cross Section no.7 Cross Section no.8 Cross Section no.9 Cross Section no.10 Cross Section no.11 Formula of linear regression U() = 175.7T 19.2 U() = 132.6T 74.0 U() = 158.7T 123.9 U() = 170.3T 150.2 U() = 152.8T 42.2 U() = 161.6T 18.8 U() = 192.0T 3.0 U() = 227.3T 45.0 U() = 226.2T 49.3 U() = 221.7T 46.5 U() = 186.6T 8.3 Matching R2 = 0.87 R2 = 0.76 R2 = 0.74 R2 = 0.78 R2 = 0.95 R2 = 0.96 R2 = 0.93 R2 = 0.90 R2 = 0.91 R2 = 0.96 R2 = 0.99 Analysis of the linear regression results for the eleven cross-sections (Table 2) indicates that in the first four cases, the matching is less than R2 = 0.9, and in the other cross-sections the linear regression matching is more accurate. These conclusions are further confirmed by summary analysing values for cross-sections from 1 to 5 (Fig. 11a) (to the mid-point of the longwall panel run) and for cross-sections from 6 to 11 (Fig. 11b). (c) Fig. 11. Linear regression matching graph for cumulative values of B in sections: from 1 to 5 and from 6 to 11 and (c) from 1 to 11 The following matching values were obtained for the above-mentioned summary crosssections: for cross-sections 1 to 6: U() = 148.5T 58.0, with R2 = 0.83, for cross-sections 6 to 11: U() = 197.1T 35.4, with R2 = 0.91. The following formula was obtained for all summary cross-sections, i.e. from 1 to 11: U() = 167.9T 52.9, with R2 = 0.86. The above formulae for matching linear regressions to the measurement results differ from the Avershin hypothesis by the value of the absolute term. In order to approximate these values to the solution presented by Avershin it has been assumed that the regression lines cross in the centre of the coordinate system (Table 3). TABLE 3 Matching formulae for linear regressions crossing in the centre of the coordinate system in cross-sections perpendicular to panel run of longwall No. 537 Number of section Cross Section no.1 Cross Section no.2 Cross Section no.3 Cross Section no.4 Cross Section no.5 Cross Section no.6 Cross Section no.7 Cross Section no.8 Cross Section no.9 Cross Section no.10 Cross Section no.11 Formula of linear regression U() = 174.1 · T U() = 129.0 · T U() = 138.6 · T U() = 171.0 · T U() = 151.3 · T U() = 161.2 · T U() = 191.4 · T U() = 227.4 · T U() = 225.1 · T U() = 219.7 · T U() = 188.8 · T Matching R2 = 0.86 R2 = 0.67 R2 = 0.57 R2 = 0.55 R2 = 0.92 R2 = 0.96 R2 = 0.92 R2 = 0.88 R2 = 0.88 R2 = 0.91 R2 = 0.98 The results of this matching are also presented for summary cross-sections: for summary cross-sections from 1 to 5: U() = 143.6 · T, where: R2 = 0.78, for summary cross-sections from 6 to 11: U() = 196.4 · T, where: R2 = 0.89, for summary cross-sections from 1 to 11: U() = 165.7 · T, where: R2 = 0.82. A standard deviation of the sample equal to S = 34.2 m was determined for the estimated values of the horizontal displacement coefficient B. This means that individual values of B were determined with an accuracy of 19%. The value of horizontal displacement coefficient can be also present as a function of depth (H) or radius of main influence (r) where: for summary cross-sections 1-5: B = 0,16H or B = 0,22r, for summary cross-sections 6-11: B = 0,21H or B = 0,30r, for summary cross-sections 1-11: B = 0,18H or B = 0,26r. 5. Conclusions Distribution analysis of the horizontal displacement coefficient B, carried out for the exploitation of longwall No. 537 on the Girondelle 5 seam of the Friedrich Heinrich-Rheinland coal mine has demonstrated that there is a proportional relation between the horizontal displacement vector and the slope of subsidence trough. This proportionality is noticeable in the case of cross-sections perpendicular to the excavation face. They indicate that the average displacement coefficient is B = 0.26r (where r is the radius of main influence range) or B = 0.18H. This value was obtained assuming that tan = 1.43, ( angle of main influences) as determined for the above-mentioned longwall in the publication by Ballhaus et al. (2000). The intermediate values of coefficient B for different cross-sections range between 0.20r and 0.35r (in the case of data meeting the R2 > 0.85 condition). The rock mass in the region of seam Girondelle 5 are consisting of mostly high strength formations (strong sandstones and sandy schist are almost 70% of whole overburden thickness). As a result of such rock mass conditions the value of angle of main influence (tan = 1.43) is low. The value of horizontal coefficient B is describe as a function of depth (H) or radius of main influence (r) (so the value of tan). The coefficient presented in formula B = ·H is strongly dependent on rock mass overburden properties. It is recommended to determine the value () from GSI rock mass classifications. The approximate value of coefficient B = 166 is close to the value of the boundary line between the quaternary, tertiary and carbonaceous layers. The project was financed from the means of National Science Center granted on the grounds of decision No. DEC 2011/01/D/ST8/07280
Archives of Mining Sciences – de Gruyter
Published: Apr 1, 2016
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