Application Research of Ground Pressure Coupling Monitoring Network for Deep Mining in Sanshandao Gold Mine

Transcription

1 Application Research of Ground Pressure Coupling Monitoring Network for Deep Mining in Sanshandao Gold Mine, Dong JI,, Chao PENG,, Liang ZHAO,, Jiaxuan HUANG,, *Corresponding Author Fenhua REN School of Civil and Environmental Engineering, University of Science and Technology Beijing, Beijing 8, China; Key Laboratory of High-efficient Mining and Safety of Metal Mines, Beijing 8, China; Abstract Aiming at the problem of surrounding rock stability and ground pressure induced by deep mining in Sanshandao Gold Mine, coupling monitoring network composed of convergence monitoring section, rock deep displacement monitoring section and stress monitoring section is arranged, combined with the tunnel monitoring theory and project actual conditions; satisfactory data are obtained through long-term monitoring work and practical application. On the basis of monitoring results, activity law of ground pressure is well studied. Achieved results reveal the deformation and stress change of surrounding rock cased by backfill mining are relatively small; The coupling monitoring network is engineering practicable, which meets the needs of rock stability prediction of Sanshandao Gold Mine during its deep producing period. Keywords: Coupling Monitoring Network, Forecast of Surrounding Rock stability, Activity Law of Ground Pressure, Deep Mining, Application Research. Introduction Underground mining operation is carried out in rock mass, the excavation of stope and roadway lead surrounding rock to unbalance status. The released stress redistribution within a limited range and local stress concentration will induce rock displacement and deformation, even failure at worse []. Furthermore, ground pressure problems such as roadway floor heave, rib spalling, roof fall and stope collapse will be cased []. Series of ground pressure problems become more and more outstanding and directly threat mining safety with the enlargement of goaf area and increase of mining depth []. The rocks are usually complex and nonlinear in mechanics form and constitutive model as a research object when we face with mining engineering. Meanwhile, satisfactory quantitative calculation results of rock stability are not available at present owing to special construction method and load form. Therefore, implementation of site monitoring is the only way to predict and forecast mining ground pressure. Related researchs show monitoring method is an important part of ground pressure study and offers a reference to engineering design and scientific construction []. The monitoring methods and monitoring content according to mining ground pressure should be decided combined with the actual situation. Common monitoring means used in site are displacement monitoring, deformation monitoring, stress monitoring, acoustic emission monitoring and so on. Only one or two of above methods are finally applied in site due to actual restriction []. However, real situation of ground pressure appearance is difficult to acknowledge through single monitoring information []. Mining monitoring research of special geological conditions at great depth is barely reported both in China and abroad [7]. Coupling monitoring network composed of convergence monitoring section, rock deep displacement monitoring section and stress monitoring section is arranged rely on research project Study on rock mechanics and rock stratum control technology in Sanshandao Gold mine. Massive data are obtained through long-term monitoring work. Ground pressure activity rule during the deep mining process is studied though detailed monitoring data analysis. The achieved results have certain directive significance for ground pressure controlling and ensuring the safety deep mining of Sanshandao Gold Mine. International Journal of Digital Content Technology and its Applications(JDCTA) Volume7,Number7,April doi:./jdcta.vol7.issue

2 . Engineering background Sanshandao gold mine characterized with trackless mining equipment application and highest degree of mechanization in China, is a main mine of Shandong gold group. The mining area consists of directly under area, Xinli area and Pinglidian area. The gold mine is located km far from the north of Laizhou city and has an excellent geographical position in Shandong Province. North and west of mine area is in close proximity to Bohai sea, the southeast is joined with land. Its gold deposit located in the northwest of Jiaodong Peninsula. The tectonic position of gold mine lies in the southern margin of the North China Jiaobei uplift, where is south of Longkou rift basin and Bohai depression, north of Jiaolai depression in Jiaobei terrane, east of Yishu fault zone and west of Muping-Jimo tectonic melange belt[8]. The gold mine has entered deep mining stage and the mining depth will exceed m. Increase of mining depth intensifies ground pressure problems. Accidents induced by ground pressure, such as roadway floor heave, roof fall, rib spalling and collapse, are more and more common. Especially, a significant phenomenon of ground pressure, rockburst, appeared in the excavation process below - m level. Meanwhile, the gold mine now is in the period of production capacity expansion and devote to the ore daily output target of tons. This production plan will not only enhance the strength of stope mining, but also demand a better stability of stope and roadway. As the increase of mining depth, in-situ stress and water pressure, how to solve the stability problem of surrounding rock in deep mining is an important prerequisite to ensure high-efficient mining and safety. Ground pressure monitoring, including stress, displacement, deformation, seepage and so on, should be carried out in the mining process to assure scientific design and safe construction. Combined with actual situation, the roadway and stope can be optimally designed on the basis of theory studies and large amount of monitoring data. The objective of safety production in Sanshandao Gold Mine will be finally achieved.. Principle of coupling monitoring network.. Principle of surrounding rock convergence monitoring The common displacement monitoring work for roadway surface contains convergence of two sides, floor subsidence monitoring and floor heave measurements. Roadway surface displacement relates to many factors, such as in-situ stress, excavation method, shape and size of roadway, support technique, construction quality and affect of other excavation projects in vicinity. Consequently, the occurrence and development of surrounding rock deformation is a very complex process, which synthetically reflect all the influence factors mentioned above. According to the information provided by surrounding rock deformation, the following content will be well studied and evaluation of surrounding rock stability can be effectively guided: amount and change rate of roadway relative displacement; relationships between the deformation, position of mining work face and time of support construction[9]. A A A' B C h H D E B B' O C' X B' X C'XC C X B Figure. Wiring method and principle of surrounding rock convergence monitoring 99

3 In fact, the roadway convergence monitoring section is equal to the measurement of relative displacement between roadway two sides, roof and floor. The most frequent wiring way in the monitoring called double triangle arrangement is presented in Fig.. Deformation situation of roadway two sides will be studied through the measurement results of line and DE, and relative deformation between roof and floor can be obtained based on the results of line,, AD and AE. The peripheral displacement of surrounding rock, is an integration of various points strain of a linear length in a certain range of rock. Rock displacement is a macroscopic physical quantity with larger magnitude compared to strain, which can be obtained by convergence gauge. With the help of convergence gauge, the displacement amount of two fixed points in its attachment direction is measurable. Furthermore, deformation situation of the roadway is understood. The closed triangular analytical algorithm method is usually used in the displacement calculation of each measuring point. To facilitate the calculation process, assumptions in analysis are put forward as follows: () Surrounding rock deformation appeared in the cross-section vertical to axis of the roadway. () Measuring vertex A is in the vicinity of the roadway centerline, only vertical displacement is considered, Ax. () Measuring point on two sides of roadway B and C are at a same level, vertical displacement of two points is ignored, By Cy. The assumption applies to point D and E. Length of initial baseline is respectively defined as L, L, L, L AD, L AE and L DE,and baseline length at any one time: L ' ', L B ' C ', L ' ', L AD ' ', L AE ' ' and L D' E '. As Fig. shows, AO, O is the foot drop. The initial distance from foot drop O to each point is H, X B and X C. The following equations are solved through Pythagorean theorem: X B L L L () L L L L X L X () C B L H L X L X () B C In same way, the distance from O to each point at anytime H, X B ' and X C ' will be obtained. Finally, the displacement of each monitoring point is as below: A H h, B XB XB ', C XC XC'... Principle of displacement monitoring in rock formation deep On purpose of exploring the stability state of deep surrounding rock, deep research on movement of top rock and relationships between rock deformation, site and activity rules of ground pressure should be performed. The content of this study not only includes relative displacement measurement of roadway surface, but also observation of deformation and damage in deep rock stratum []. The observation of deep rock stratum is normally accomplished by drilling construction in which multiple measuring points are installed. Equipment and system arranged in the drilling are named drilling displacement gauge, set of several stations is referred to as multi-point displacement gauge. The multi-point displacement gauge used in this monitoring is anchoring type. Displacement of different depths in rock internal is surveyed and relations between deformation and depth is studied rely on this special gauge. As what Figure (a) displays, the gauge is made up by four parts: steel claw, inner tube, measurement wire and disc. Steel claw plays a role in fixing the gauge. One end of the wire used for measurement is fixed in the gauge, opposite end extends to drilling orifice. In this monitoring plan, gauges (#, #, #, #) are installed in the drilling of roadway roof centre. The specific set form 99

4 is presented in Figure (b). Relative displacement in monitoring process was obtained by subtraction of initial measurement value and observation reading value. # # # # (a) Structure diagram of displacement gauge (b) Set position of the gauges Introduction for structure diagram (a): - steel claw, - inner tube, - measurement wire, - disc Figure. Structure diagram and arrangement of multi-point displacement gauge.. Principle of rock stress monitoring Deformation, displacement and destruction of surrounding rock are action results of interaction between rock internal stress. The stress state in rock interior, of which composes gravity stress of overlying strata, tectonic stress and hydraulic pressure, is very complex. The status of redistributed stress after roadway excavation is closely related to physical and mechanical properties of rock and mining technology. The borehole stress monitoring is a measurement aiming at stress field change of rock internal stress caused by mining disturbance. As an indispensable means to study ground pressure activity law, stress monitoring research plays on important role in evaluating rock stability and guiding scientific supporting design []. ZLGH-type drilling stress tester and GSJ-A-type vibration string data memory are applied to field monitoring work (Fig. ). With high accuracy, strong adaptability and simple operation, they have been wildly used for surrounding rock stress monitoring in recent years. Figure. Picture of ZLGH-type drilling stress tester and GSJ-A-type vibration string data memory used in the monitoring ZLGH type drilling stress tester is a kind of vibrating wire sensor. According to Monitoring requirement, it can be installed to any position of the drilling within a certain distance. The stress tester is usually used combined with GSJ-A-type data memory, and measuring direction of stress can be 99

5 Application Research of Ground Pressure Coupling Monitoring Network for Deep Mining in Sanshandao Gold Mine freely selected. Stress value F is calculated by GSJ-A data memory on the basis of measured frequency value f: F Af ( f ) Bf ( f) () Where A and B are parameters of the sensor, f is initial frequency value when F=. Rock stress value can be directly measured in the monitoring process. The main technical indicators of drilling stress tester are presented in Table.. Table. Main technical indicators of ZLGH-type drilling stress tester Range Accuracy Repeatability Resolution External diameter Mpa.%FS.%FS.%FS mm. Selection and arrangement of monitoring points Among the production levels of Sanshandao Gold Mine, -m level has a representative significance. Under of the production level, alternate room-and-pillar mining with ascending backfill method is used in # stope, # stope and # stope. The mining process is divide into two steps: first step mining and second step mining. Ming and filling construction are carried out alternately. This mining meanings with low blasting cost substantially enhances production efficiency, however total costs are relatively high. In summary, this method not merely meets the production target proposed, but also fits the wide application prospect of deep mining. Therefore, the points of coupling monitoring are arranged in -m level with wide application meaning of mining technology. point, 7 point 8, 风 point 97, 北 风 联.. 结 束 point 7, point, 7 Multi-point displacement mointoring point 7, point (9, 7) Stress monitoring point (9, 77) point, 7 point, 77 (a) Monitoring points in south of -m level (b) Monitoring points in north of -m level Figure. Arrangement of monitoring points in -m level of Sanshandao Gold Mine 99

6 Eight convergence monitoring sections, Eight stress monitoring sections and one multi-point displacement monitoring section is arranged in -m level of Sanshandao Gold Mine after on-site survey. The sections of convergence monitoring and stress monitoring are distributed equally along the haulage roadway, while multi-point displacement monitoring section is installed in a key location where stopes are intensive (Coordinates: 7, ). The following factors are fully taken into consider when choosing the site of monitoring points: prevention of air duct and water pipe, keeping clear in a section between two measuring points, avoid the influence on daily production induced by drilling and install. Specifically, only survey line, and are reserved in convergence monitoring owing to wide existence of line pipe.. Process and analysis of monitoring data.. Analysis results of convergence monitoring data The period of convergence monitoring is May to October, totally 7 days in year. The monitoring data of 8 points at depth m are received times in a Monday times frequency. On the basis of monitoring results, line curves of relative displacement with time are drawn. Four monitoring curves with typical representative significance are shown in Figure Relative displacement (mm) (a) Monitoring curves of No. point Relative displacement (mm) Relative displacement (mm) (b) Monitoring curves of No. point Relative displacement (mm) (c) Monitoring curves of No. point (d) Monitoring curves of No.8 point Figure. The representative part of roadway convergence monitoring curves The following laws can be revealed through analysis of each convergence monitoring curve: () The deformation amount of No.8 points is 8. mm, more than any other points during the monitoring period. Maximum and minimum of deformation rate are respectively.8mm/d and.mm/d, which fit the fact of roadways are basically stable for a long time after excavation. () The horizontal deformation () amounts of No. and No.7 points are relatively less owing to the stress release cased by stope mining nearby. () Generally, the deformation phenomenon of monitoring points No. to No.8 north of F fault is more significant than points No. to No. south of the fault. Rock stability north of F fault is comparatively poor, to which enough attention should be attached in supporting design. 99

7 .. Analysis results of monitoring for deep rock formation displacement When the roadway surrounding rock of multi-point displacement monitoring produce deformation, the position of observation points at different depths will also be changed. The relative displacement of observation points and drilling orifice can be measured with the help of high precision measuring scale. At last, absolute displacement of observation points will be calculated based on the monitoring data. Four observation points(no. to No.) are arranged in prepared drilling hole, as what Fig. shows. The distances between observation points(no. to No.) and orifice are m, 8m, m and 8m respectively. Sixteen groups data of multi-point displacement are obtained through monitoring work lasting days, from May 8 to August in year. The monitoring cures of displacement and time are drawn in Fig.. displacement(mm) 7 # measuring point # measuring point # measuring point # measuring point Time(day) Figure. Monitoring cures of multi-point displacement meter in rock formation deep The rock deformation state during the monitoring period can be divided into three stages by analysis of Fig.: stage, initial stage of the monitoring, the displacement of each measuring point increased rapidly. The rock mass this stage were under stress growth area owing to mining influence; stage, mid-term of the monitoring, backfill construction made stress redistribution of surrounding rock. The concentrated stress decreased and deformation speed slowed down as a result; stage, the displacement increased again because of new mining process. The displacement amount of No. and No. points is larger than No. and No. points. This suggests the surrounding rock at deep position is more stable. In addition, supporting design for surface surrounding rock should be paid special attention avoiding loose even damage. In one word, the mining influence on rock stability and ground pressure is not very obvious, and the corresponding rock deformation is acceptable... Analysis results of rock stress monitoring The rock stress monitoring work in year began at May 9, and ended at August, totally 98 days. Our group collected the monitoring data every five days and 9 groups of data were acquired. Line curves of relative stress with time are drawn after data arrangement, and part of the curves are shown in Fig. 7. As Fig.7 shows, the stress of No. monitoring point increased slowly and changed little in overall. This is due to the excavation effect of small chamber nearby. In the meantime, No. stope nearby was barely in production. Different from No. point, the mining construction had direct influence in the change of stress of No. monitoring point: the stress reduced at the beginning and increased later. The goaf was filled and filling body suffered load, this resulted in the reduction of stress at the beginning; New mining construction later led to stress concentration and increase. Stress situation of No. point is similar with No. point, also due to the effect of mining. The roadway excavation near No.8 monitoring point was implementing from south to north. As the embodiment of this construction influence, the rock stress increased fast in the early days, then tended to be stable when the construction is far away from measuring point position. 99

8 . Relative rock stress (MPa).8 Relative rock stress (MPa) (a) Monitoring curves of No. point.8 Relative rock stress (MPa) (b) Monitoring curves of No. point. Relative rock stress (MPa) (c) Monitoring curves of No. point (d) Monitoring curves of No.8 point Figure 7. The representative part of rock stress monitoring curves The mining method used in Sanshandao Gold mine is backfill method, and spacing distance between mining and filling is meters. As monitoring result indicates, when the stope is under mining, rock stress has a tendency of increase; the monitoring stress decreases while the filling construction is carried out. Although the variation tendency of rock stress during mining process is obvious, variation range is indistinctive and acceptable overall.. Conclusion In this study, coupling monitoring network consist of convergence monitoring section, rock deep displacement monitoring section and stress monitoring section is successfully implemented in Sanshandao Gold Mine, -m level. Based on long-term monitoring work and application research, the variation law of rock displacement and stress during the mining process is revealed, in the meantime, the stability of surrounding rock under backfill mining condition is discussed. The main conclusions in this paper have been summarized as follows: () The coupling monitoring network, composed of convergence monitoring section, rock deep displacement monitoring section and stress monitoring section, can effectively measure and learn of the changes of rock stress and deformation, both surface and internal. Stability state of roadway surrounding rock can be precisely evaluated in real time according to the monitoring results. () Stress and displacement change of surrounding rock cased by backfill mining method is relatively small, which has no serious influence in the deterioration of rock stability. However, support work should be taken into enough account in some areas where joint fissure primely developed (areas close to F fault, for example). In addition, the rock stability monitoring work should be enhanced in future with the increase of mining depth. () On the basis of original monitoring method, some other means, including acoustic emission realtime monitoring, loose circle testing and so on, can be introduced to the coupling monitoring network, which will improve the accuracy and reliability of monitoring result and offer a better guarantee for safety of Sanshandao Gold mine deep mining. 7. Acknowledgment This work is supported by national natural science foundation of China (No. )

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