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Analysis and control on anomaly water inrush in roof of fully-mechanized mining field
Mining Science and Technology (China) 21 (2011) 89e92
Contents lists available at ScienceDirect
Mining Science and Technology (China) journal homepage: www.elsevier.com/locate/mstc
Analysis and control on anomaly water inrush in roof of fully-mechanized mining field Peng Linjun a, b, c, *, Yang Xiaojie a, c, Sun Xiaoming a, c a
School of Mechanics and Civil Engineering, China University of Mining & Technology, Beijing 100083, China Academician Pioneering Park, Dalian University, Dalian 116622, China c State Key Laboratory of Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Beijing 100083, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 May 2010 Accepted 15 July 2010
Caving of mine roofs from water inrush due to anomalous pressure is one of the major disasters and accidents that can occur in mines during production. Roof water inrush can trigger a wide range of roof collapse, causing major accidents from breaking roof supports while caving. These failures flood wells and do a great deal of damage to mines and endanger mine safety. Our objective is to analyze the anomalies of water inrush crushing the support at the #6301 working face in the Jisan Coal Mine of the Yanzhou Mining Group. Through information of water inrush to the roof, damage caused by tectonic movements, information on the damage caused by roof collapse and the theory about the distribution of pressure in mine abutments, we advice adjusting the length of the working face and the position of open-off cut relatively to the rich water area. In the case of anomalous roof pressure we should develop a state equation to estimate preventive measures with “transferring rock beam” theory. Simultaneously, we improve the capacity of drainage equipment and ensured adequate water retention at the storehouse. These are all major technologies to ensure the control and prevention against accidents caused by anomalous water inrush in roofs, thus ensuring safety in the production process of a coal mine. Copyright Ó 2011, China University of Mining & Technology. All rights reserved.
Keywords: Roof Water inrush pressure Anomaly Analysis Control
1. Introduction Both domestic and foreign investigators pay considerable attention to coal mine pressure anomalies and obtained various results. However, because of the complexity of anomalous pressure, as well as the mutability of surrounding rock conditions caused by caving, a number of difficulties are encountered in building an exact and systematic mathematical mechanical model. Furthermore, because geological conditions differ considerably in various parts of a coalfield and the reality is very complex, we must therefore adopt a number of different measures and methods to predict and monitor geological conditions, given that many methods have their own limitations. The process of calculation for the support of the surrounding rock summarizes this mechanism, thus perfecting the method of forecasting and monitoring, forming a feasible and efficient system for safety in production, ensuring security and efficiency at coal mining faces. Coal mine pressure anomalies, showing up in fully-mechanized caving fields, as dynamic phenomena interfering with safe production in coal mines, refer to anomalous rock pressure occurring under special conditions. When
* Corresponding author. Tel.: þ86 13898401666. E-mail address: [email protected] (P. Linjun).
the mechanical balance is broken in a coal (rock) body around a coal mining field, it usually shows up as damage to the support system, as a crushed or sinking roof level or as severe spalling, before the occurrence of risky leaks and ultimately coal and gas outbursts. When rock pressure appears as anomalies, it often results in damage to equipment, significant loss of coal resources and forming simultaneously significant security risks, which in coal mines may lead to devastating consequences. In recent years, a large number of mine pressure anomalies occurred in fully-mechanized caving mines in China’s Yanzhou and Xuzhou mining areas, causing considerable economic losses to coal companies. Therefore, further systematic study of the structure and movement of the overlying rock in fully-mechanized caving mines, may reveal the behavior of mine pressure anomalies, discover the conditions under which these anomalies occur, find methods to forecast and prevent them, in order to achieve safety and efficient production [1e4].
2. Coal seam conditions and structure of overlying rock The Jisan Coal Mine is located in a suburb of Jining city, where the mining area is about 110 km2. Geological reserves of 880 million tons, industrial reserves of 800 million tons, and recoverable reserves of 530 million tons have been confirmed. The #3 coal layer
1674-5264/$ e see front matter Copyright Ó 2011, China University of Mining & Technology. All rights reserved. doi:10.1016/j.mstc.2010.12.010
90
P. Linjun et al. / Mining Science and Technology (China) 21 (2011) 89e92
has 400 million tons of coal, accounting for 75.5% of recoverable reserves. These coal strata are part of the Permian Shanxi Formation and the Carboniferous Taiyuan, with eight layers of locally accessible coal and an average thickness of 10.44 m. The major recoverable coal is found in the 3up, 3down layer with an average thickness of 6.21 m. The geological condition of the mining area is a simple middle structure. The main northesouth normal fault is apparently regular, with most of the east rising and the west falling. Also, there are faults showing the development of eastewest with the east and southeast dipping gently, generally at slopes less than 5 , and gentle changes in their wrinkly trend. Deeper dips toward the west and southwest have slopes between 5 and 9 . The mine is expected to discharge 516 m3/h of coal water. The key layer, affecting anomalies in water inrush from the roof in the working faces, is the following layer of the second rock beam, i.e. M5 siltstone, 6.5 m thick, and a detailed roof rock structure is shown in Table 1 [5,6]. Fig. 1. #6301 working face flooding accident.
3. Analysis of roof water inrush pressure causing anomalous crushing supports The main reasons for the five water inrush accidents which flooded the #6301 working face of Jisan are twofold: 1) the overlying stratum contains water; according to drilling data from the surface and audio-frequency electrical penetration at this working face, there are four water-rich areas above the face, located at both ends and the middle. Moreover, water-rich Jurassic strata are found at 193 m above the roof of 3down coal seam. 2) Large area of main roof caving, break lines extending to overlying aquifers, as well as faults in the working face; with the initial face exposed, water is showing up along the fault plane; with working face advancing, the exposed fault length also increases, resulting in a continuously increasing water inrush [7e10]. Therefore, the break lines communicate faults to the water-rich fault zones as shown in Fig. 1.
3.2. Conditions of occurrence of roof water inrush anomalies crushing supports 1) With progressive face advance, the overlying rock layer is in communication with the water-rich sandstone layer which causes increase in the thickness of simultaneously moving main roof, decrease in main roof span length, and increase in roof pressure; 2) The depth of roof break lines from the front wall increases, causing decrease in the thickness of immediate roof; 3) The immediate roof is thin which increases the roofefloor convergence; 4) The main roof is, in general, very thick, and it is easy to form a large cantilever beam space, causing an impact on the main roof dynamic pressure when roof caving [13]. 3.3. Structural model of roof water inrush caused by anomalies
3.1. Reasons of roof water inrush anomalies crushing support 1) The support force resisting pressure is insufficient against roof convergence (support is working under a given deformation status). 2) Pressure on the roof rock beams is excessive; support load bearing capacity cannot meet the conditions to main roof convergence (to the given deformation status), i.e., roof convergence exceeds the maximum value of nominal yield of support [11,12].
。。。。 11.20 。。。 4.20 。。 3.80 M5 。。。。 6.50
kkk
7.06
DhA ¼
[K $SA CE
Roof structure
Thickness (m)
Step
(1) (2)
C0 C
639
M4 。。 10.00 。。 。。 M3 。。。。 9.00 。。。。 M2 。。 19.00 。。 。。 。。 M1 7.00 M
where
SA ¼ h MZ ðKA 1Þ hd
Table 1 Profile of cave mining face of a stope roof. No. Lithology Thickness Depth (m) of layer (m)
1) In a “given deformation” condition, the roof convergence is determined by the position of a free-falling rock beam contacting the floor in the gob shown in Fig. 2, i.e., DhT ¼ DhA
Following layer Support layer
The second rock beam
16.5
60 20
Following layer Support layer
The first rock beam
28.0
82 27
Immediate roof 685
7.0 Fig. 2. Structural model of a water inrush accident of a fully-mechanized caving mine.
P. Linjun et al. / Mining Science and Technology (China) 21 (2011) 89e92
91
The lower limit of support capacity:
PT ¼ hf gf þ mz gz ¼ 4 1:4 þ 8 2:5 ¼ 25:6 T=m3
(4)
The upper limit of support capacity:
PT ¼ A þ k0
DhA m C g ¼ A þ k0 ¼ A þ E E E ¼ 133 T=m3 DhEzmin 2lk
(5)
The lower limit of support resistance: Fig. 3. Forecasting graph of possible permeability.
RT ¼ PT ST ¼ 26 7:5 ¼ 1950KN
(6)
The upper limit of support resistance: 2) Relationship between roof water inrush and movement of overlying rock strata In a case of a given open-off cut position and the length of the working face, the broken rock strata may reach to rock aquifer, especially water-rich region, with progressive face advance [14e17]. When the aquifer is parallel to the seam, as in Fig. 3, the possibility of flooding and related parameters of the model can be determined. Where L is the advance step at the working face; Lo length of working face; LB water-rich area in rock stratum of water open-off cut location; LR center of breaking rocks (breaking arch) cut from the bottom position; h height of broken rock stratum; H height of water in rock stratum; and B width of water-rich zone. 3.4. Support conditions in #6301 working face and the actual effects of roof control during flood According to the analysis of the first roof water inrush accident, the pressure crushed the support of the #6301 working face, when it advanced 613 m, increased the volume of the water at the face to 50 m3/h, flooding the coal mine and the gob area. With the working advancing, a big bang above the face was heard (the sound of main roof breaking) and the volume of water at the face increased to 327 m3/h, with a maximum volume of 350 m3/h. This caused some of the temporary electrical stations to be inundated and work at the face was forced to stop. The roof suddenly broke and sunk, the supports of #11-67 were crushed at the face. When water suddenly flooded the working face and the amount of water increased considerably, the capacity of the pump of the integrated drainage system was insufficient, resulting in an amount of water 2 m deep at the face. At the start, large volumes of water were discharged in the roadway. Slurry water, coal and other debris flooded into airtight wall, closed the outlet, and appeared dangerous situation due to high water pressure. Peak discharge lasted five days, the water inflow continued for seven days, and the entire water gushing process lasted 41 days. The position of water inflow is at the location of main roof periodic caving. In a given geo-mining condition in this case, structural parameters are calculated by using structural mechanic models to assess the support requirement in the following. When the mining depth is about 700 m, the coal seam is 7 m, the length of the working face 200 m and after 200 m advance, the front distance of SM is about 20 m. From Eq. (3), we have the following results: [18e20] The breaking distance from the front wall of face at the lower rock beam is:
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2SM mE CE gE 2 20 19 2:8 2:5 ¼ 3:2M ¼ S0 ¼ 3 2:5 685 kgH
(3)
RT ¼ PT ST ¼ 133 7:5 ¼ 9975KN
(7)
Under conditions of roof water inrush when the working face is stop, the largest roof convergence (hd ¼ 0)
DhA ¼
ð[ac þ S0 ÞSA ð5 þ 3:2Þ4:2 ¼ 1:23M ¼ 28 C
(8)
The current support working resistance is RT ¼ 6200 kN, maximum convergence is 3max ¼ 1000 mm. Obviously, the support resistance (RT ¼ 6200 kN) is less than the “given deformation” of the maximum resistance force (RT ¼ 9975 kN) required. As a result, the support system will work in a state of “given deformation”. If there is no floor coal left (hd ¼ 0) or no measures are taken to speed up the face advance, collapse of the face supports will occur and result in more serious flooding hazard. If the advance of face is fast, i.e., let S0 ¼ 0, the convergence of face is controlled in the range of DhA ¼ 0.8M, collapse of the face supports can be avoided as long as the cutting height is adequate. 4. Conclusions The anomalous pressure in the working face and water inrush occurred, caused by geological factors first, the overburden aquifer is the main factor. Strengthening of forecast technology and accurate prediction of the “two zone” developed height is needed. According to a detailed hydro-geological report, a degree of communication between a working face and the amount of water in rock layers needs to be determined. We can draw the following conclusions: 1) Before main roof periodic caving occurs, begin using no top coal caving advance method, until the main roof caving in order to make sure that the main roof has enough cushions to reduce the height of the ultimate convergence. 2) Before main roof caving, ensure the largest cutting height. Support must be maintained as long as possible at a high level collapse of the face supports in order to maintain the maximum leg convergence to reduce the possibility of support closure. 3) In a case of given length of the face, the scope of the overlying strata, including the thickness of both the immediate and the main roof as well as the height of the permeable fracture zone. The span of main fall and periodic caving location may fall into the fractured zone of the aquifer under the action of gravity. 4) Information on the distribution of the abutment pressure focused on the width caused by “internal stress field” around the walls of the working face. 5) Reasonable selection and transformation of support. In order to prevent the collapse of supports due to roof caving, we can select proper support and increase the caliber of safety valves to adjust the rapid yield valve requirement for safe working of the support.
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P. Linjun et al. / Mining Science and Technology (China) 21 (2011) 89e92
In short, scientific management, overall arrangements, organizing highly efficient production and accelerating the speed of face advance are required. Rock strata failure and movement needs a time period, we can accelerate face advance where pressure anomalies may appear, then the roof falls may occur in the gob to avoid occurrence of pressure anomalies. Acknowledgments This research is sponsored by the National Natural Science Foundation of China (No. 50874021), the Program for New Century Excellent Talents in University (No. NCET-08-0833), and the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT0656) of the Ministry of Education of China. We thank the Jisan Coal Mine of the Yanzhou Coal Mine Group for providing a good research environment for this project, and we thank the groups of researchers for their hard work. References [1] Miao XX, Li SC, Chen ZQ. Bifurcation and catastrophe of seepage flow system in broken rock. Journal of China University of Mining and Technology 2009;19 (1):1e7 [in Chinese]. [2] He MC, Xie HP, Peng SP. Study on rock mechanics in deep mining engineering. Chinese Journal of Rock Mechanics and Engineering 2005;24(16):2803e13 [in Chinese]. [3] Wang EY, Liu XF. Study of electromagnetic characteristics of stress distribution and sudden changes in the mining of gob-surrounded coal face. Journal of China University of Mining and Technology 2008;18(1):1e5 [in Chinese]. [4] Jiang FX. Ground pressure and strata control. Beijing: Mine Industry Press; 2004 [in Chinese]. [5] Song ZQ, Yang ZF, Peng LJ. The study of the foundation of dynamic information of the forecast and control of serious disasters. Beijing: Mine Industry Press; 2003 [in Chinese].
[6] Zhou RB, Cheng BF, Ye GJ, Wu Q. Time effect of water busting in fault rupture zone. Journal of Engineering Geology 2000;8(4):411e5 [in Chinese]. [7] Yang XJ, Deng FH. Response of carrying capacity of piles induced by adjacent metro tunneling. Journal of China University of Mining and Technology 2009;19(2):176e81 [in Chinese]. [8] Gao YF, Zhang QS. Mine rock mechanics. Xuzhou: China University of Mining and Technology Publishing House; 2000 [in Chinese]. [9] He MC, Cao XL, Xie Q, Yang JH, Qi P, Yang Q, et al. Principles and technology for stepwise utilization of resources for mitigating deep mine heat hazards. Journal of China University of Mining and Technology 2010;20(1):20e7 [in Chinese]. [10] Zhu XS. The application of engineering geophysics in the remediation of water inrush in fractured zone. Express in Formation of Mining Industry 2004;11: 5le3 [in Chinese]. [11] Li SC. Nonlinear dynamical study on non-darcy flow in broken rock. Dissertation. Xuzhou: China University of Mining & Technology; 2006 [in Chinese]. [12] Sun XM, He MC. Numerical simulation research on coupling support theory of roadway within soft rock at depth. Journal of China University of Mining and Technology 2005;34(2):166e9 [in Chinese]. [13] Guo ZB, Guo PY, Huang MH, Liu YG. Stability control of gate groups in deep wells. Journal of China University of Mining and Technology 2009;19 (2):155e60 [in Chinese]. [14] Yin LM. Forecast and control of the abnormity rule of the full-mechanized stope pressure. Shandong University of Technology; 2005 [in Chinese]. [15] Liu HZ, Han BP. Vertical variation of trace elements and its relation to the water-bearing capacity of Ordovician strata, in Datun coal field. Mining Science and Technology 2009;19(2):166e9 [in Chinese]. [16] He MC, Gong WL, Li DJ, Zhai HM. Physical modeling of failure process of the excavation in horizontal strata based on ir thermography. Journal of China University of Mining and Technology 2009;19(6) [in Chinese]. [17] Miao XX, Li SC, Huang XW. Experimental study of seepage properties of nondarcy flow in granular gangues. Journal of China University of Mining and Technology 2006;16(2):105e9 [in Chinese]. [18] Wu H, Fang Q, Zhang YD, Lu YS, Liu JC. Mechanism of anomalous low friction phenomenon in deep block rock mass. Journal of China University of Mining and Technology 2009;19(4):409e19. [19] Zhang XL, Zhang ZW, Peng SP. Application of the theory of quantification in identifying gushing water sources of coal mines. Journal of China University of Mining and Technology 2003;13(3):251e4. [20] Chen ZH, Xie HP, Wang JC. Numerical simulation on three dimensional deformation and failure of top coal caving. Chinese Journal of Rock Mechanics and Engineering 2002;21(3):309e13 [in Chinese].
Contents lists available at ScienceDirect
Mining Science and Technology (China) journal homepage: www.elsevier.com/locate/mstc
Analysis and control on anomaly water inrush in roof of fully-mechanized mining field Peng Linjun a, b, c, *, Yang Xiaojie a, c, Sun Xiaoming a, c a
School of Mechanics and Civil Engineering, China University of Mining & Technology, Beijing 100083, China Academician Pioneering Park, Dalian University, Dalian 116622, China c State Key Laboratory of Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Beijing 100083, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 May 2010 Accepted 15 July 2010
Caving of mine roofs from water inrush due to anomalous pressure is one of the major disasters and accidents that can occur in mines during production. Roof water inrush can trigger a wide range of roof collapse, causing major accidents from breaking roof supports while caving. These failures flood wells and do a great deal of damage to mines and endanger mine safety. Our objective is to analyze the anomalies of water inrush crushing the support at the #6301 working face in the Jisan Coal Mine of the Yanzhou Mining Group. Through information of water inrush to the roof, damage caused by tectonic movements, information on the damage caused by roof collapse and the theory about the distribution of pressure in mine abutments, we advice adjusting the length of the working face and the position of open-off cut relatively to the rich water area. In the case of anomalous roof pressure we should develop a state equation to estimate preventive measures with “transferring rock beam” theory. Simultaneously, we improve the capacity of drainage equipment and ensured adequate water retention at the storehouse. These are all major technologies to ensure the control and prevention against accidents caused by anomalous water inrush in roofs, thus ensuring safety in the production process of a coal mine. Copyright Ó 2011, China University of Mining & Technology. All rights reserved.
Keywords: Roof Water inrush pressure Anomaly Analysis Control
1. Introduction Both domestic and foreign investigators pay considerable attention to coal mine pressure anomalies and obtained various results. However, because of the complexity of anomalous pressure, as well as the mutability of surrounding rock conditions caused by caving, a number of difficulties are encountered in building an exact and systematic mathematical mechanical model. Furthermore, because geological conditions differ considerably in various parts of a coalfield and the reality is very complex, we must therefore adopt a number of different measures and methods to predict and monitor geological conditions, given that many methods have their own limitations. The process of calculation for the support of the surrounding rock summarizes this mechanism, thus perfecting the method of forecasting and monitoring, forming a feasible and efficient system for safety in production, ensuring security and efficiency at coal mining faces. Coal mine pressure anomalies, showing up in fully-mechanized caving fields, as dynamic phenomena interfering with safe production in coal mines, refer to anomalous rock pressure occurring under special conditions. When
* Corresponding author. Tel.: þ86 13898401666. E-mail address: [email protected] (P. Linjun).
the mechanical balance is broken in a coal (rock) body around a coal mining field, it usually shows up as damage to the support system, as a crushed or sinking roof level or as severe spalling, before the occurrence of risky leaks and ultimately coal and gas outbursts. When rock pressure appears as anomalies, it often results in damage to equipment, significant loss of coal resources and forming simultaneously significant security risks, which in coal mines may lead to devastating consequences. In recent years, a large number of mine pressure anomalies occurred in fully-mechanized caving mines in China’s Yanzhou and Xuzhou mining areas, causing considerable economic losses to coal companies. Therefore, further systematic study of the structure and movement of the overlying rock in fully-mechanized caving mines, may reveal the behavior of mine pressure anomalies, discover the conditions under which these anomalies occur, find methods to forecast and prevent them, in order to achieve safety and efficient production [1e4].
2. Coal seam conditions and structure of overlying rock The Jisan Coal Mine is located in a suburb of Jining city, where the mining area is about 110 km2. Geological reserves of 880 million tons, industrial reserves of 800 million tons, and recoverable reserves of 530 million tons have been confirmed. The #3 coal layer
1674-5264/$ e see front matter Copyright Ó 2011, China University of Mining & Technology. All rights reserved. doi:10.1016/j.mstc.2010.12.010
90
P. Linjun et al. / Mining Science and Technology (China) 21 (2011) 89e92
has 400 million tons of coal, accounting for 75.5% of recoverable reserves. These coal strata are part of the Permian Shanxi Formation and the Carboniferous Taiyuan, with eight layers of locally accessible coal and an average thickness of 10.44 m. The major recoverable coal is found in the 3up, 3down layer with an average thickness of 6.21 m. The geological condition of the mining area is a simple middle structure. The main northesouth normal fault is apparently regular, with most of the east rising and the west falling. Also, there are faults showing the development of eastewest with the east and southeast dipping gently, generally at slopes less than 5 , and gentle changes in their wrinkly trend. Deeper dips toward the west and southwest have slopes between 5 and 9 . The mine is expected to discharge 516 m3/h of coal water. The key layer, affecting anomalies in water inrush from the roof in the working faces, is the following layer of the second rock beam, i.e. M5 siltstone, 6.5 m thick, and a detailed roof rock structure is shown in Table 1 [5,6]. Fig. 1. #6301 working face flooding accident.
3. Analysis of roof water inrush pressure causing anomalous crushing supports The main reasons for the five water inrush accidents which flooded the #6301 working face of Jisan are twofold: 1) the overlying stratum contains water; according to drilling data from the surface and audio-frequency electrical penetration at this working face, there are four water-rich areas above the face, located at both ends and the middle. Moreover, water-rich Jurassic strata are found at 193 m above the roof of 3down coal seam. 2) Large area of main roof caving, break lines extending to overlying aquifers, as well as faults in the working face; with the initial face exposed, water is showing up along the fault plane; with working face advancing, the exposed fault length also increases, resulting in a continuously increasing water inrush [7e10]. Therefore, the break lines communicate faults to the water-rich fault zones as shown in Fig. 1.
3.2. Conditions of occurrence of roof water inrush anomalies crushing supports 1) With progressive face advance, the overlying rock layer is in communication with the water-rich sandstone layer which causes increase in the thickness of simultaneously moving main roof, decrease in main roof span length, and increase in roof pressure; 2) The depth of roof break lines from the front wall increases, causing decrease in the thickness of immediate roof; 3) The immediate roof is thin which increases the roofefloor convergence; 4) The main roof is, in general, very thick, and it is easy to form a large cantilever beam space, causing an impact on the main roof dynamic pressure when roof caving [13]. 3.3. Structural model of roof water inrush caused by anomalies
3.1. Reasons of roof water inrush anomalies crushing support 1) The support force resisting pressure is insufficient against roof convergence (support is working under a given deformation status). 2) Pressure on the roof rock beams is excessive; support load bearing capacity cannot meet the conditions to main roof convergence (to the given deformation status), i.e., roof convergence exceeds the maximum value of nominal yield of support [11,12].
。。。。 11.20 。。。 4.20 。。 3.80 M5 。。。。 6.50
kkk
7.06
DhA ¼
[K $SA CE
Roof structure
Thickness (m)
Step
(1) (2)
C0 C
639
M4 。。 10.00 。。 。。 M3 。。。。 9.00 。。。。 M2 。。 19.00 。。 。。 。。 M1 7.00 M
where
SA ¼ h MZ ðKA 1Þ hd
Table 1 Profile of cave mining face of a stope roof. No. Lithology Thickness Depth (m) of layer (m)
1) In a “given deformation” condition, the roof convergence is determined by the position of a free-falling rock beam contacting the floor in the gob shown in Fig. 2, i.e., DhT ¼ DhA
Following layer Support layer
The second rock beam
16.5
60 20
Following layer Support layer
The first rock beam
28.0
82 27
Immediate roof 685
7.0 Fig. 2. Structural model of a water inrush accident of a fully-mechanized caving mine.
P. Linjun et al. / Mining Science and Technology (China) 21 (2011) 89e92
91
The lower limit of support capacity:
PT ¼ hf gf þ mz gz ¼ 4 1:4 þ 8 2:5 ¼ 25:6 T=m3
(4)
The upper limit of support capacity:
PT ¼ A þ k0
DhA m C g ¼ A þ k0 ¼ A þ E E E ¼ 133 T=m3 DhEzmin 2lk
(5)
The lower limit of support resistance: Fig. 3. Forecasting graph of possible permeability.
RT ¼ PT ST ¼ 26 7:5 ¼ 1950KN
(6)
The upper limit of support resistance: 2) Relationship between roof water inrush and movement of overlying rock strata In a case of a given open-off cut position and the length of the working face, the broken rock strata may reach to rock aquifer, especially water-rich region, with progressive face advance [14e17]. When the aquifer is parallel to the seam, as in Fig. 3, the possibility of flooding and related parameters of the model can be determined. Where L is the advance step at the working face; Lo length of working face; LB water-rich area in rock stratum of water open-off cut location; LR center of breaking rocks (breaking arch) cut from the bottom position; h height of broken rock stratum; H height of water in rock stratum; and B width of water-rich zone. 3.4. Support conditions in #6301 working face and the actual effects of roof control during flood According to the analysis of the first roof water inrush accident, the pressure crushed the support of the #6301 working face, when it advanced 613 m, increased the volume of the water at the face to 50 m3/h, flooding the coal mine and the gob area. With the working advancing, a big bang above the face was heard (the sound of main roof breaking) and the volume of water at the face increased to 327 m3/h, with a maximum volume of 350 m3/h. This caused some of the temporary electrical stations to be inundated and work at the face was forced to stop. The roof suddenly broke and sunk, the supports of #11-67 were crushed at the face. When water suddenly flooded the working face and the amount of water increased considerably, the capacity of the pump of the integrated drainage system was insufficient, resulting in an amount of water 2 m deep at the face. At the start, large volumes of water were discharged in the roadway. Slurry water, coal and other debris flooded into airtight wall, closed the outlet, and appeared dangerous situation due to high water pressure. Peak discharge lasted five days, the water inflow continued for seven days, and the entire water gushing process lasted 41 days. The position of water inflow is at the location of main roof periodic caving. In a given geo-mining condition in this case, structural parameters are calculated by using structural mechanic models to assess the support requirement in the following. When the mining depth is about 700 m, the coal seam is 7 m, the length of the working face 200 m and after 200 m advance, the front distance of SM is about 20 m. From Eq. (3), we have the following results: [18e20] The breaking distance from the front wall of face at the lower rock beam is:
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2SM mE CE gE 2 20 19 2:8 2:5 ¼ 3:2M ¼ S0 ¼ 3 2:5 685 kgH
(3)
RT ¼ PT ST ¼ 133 7:5 ¼ 9975KN
(7)
Under conditions of roof water inrush when the working face is stop, the largest roof convergence (hd ¼ 0)
DhA ¼
ð[ac þ S0 ÞSA ð5 þ 3:2Þ4:2 ¼ 1:23M ¼ 28 C
(8)
The current support working resistance is RT ¼ 6200 kN, maximum convergence is 3max ¼ 1000 mm. Obviously, the support resistance (RT ¼ 6200 kN) is less than the “given deformation” of the maximum resistance force (RT ¼ 9975 kN) required. As a result, the support system will work in a state of “given deformation”. If there is no floor coal left (hd ¼ 0) or no measures are taken to speed up the face advance, collapse of the face supports will occur and result in more serious flooding hazard. If the advance of face is fast, i.e., let S0 ¼ 0, the convergence of face is controlled in the range of DhA ¼ 0.8M, collapse of the face supports can be avoided as long as the cutting height is adequate. 4. Conclusions The anomalous pressure in the working face and water inrush occurred, caused by geological factors first, the overburden aquifer is the main factor. Strengthening of forecast technology and accurate prediction of the “two zone” developed height is needed. According to a detailed hydro-geological report, a degree of communication between a working face and the amount of water in rock layers needs to be determined. We can draw the following conclusions: 1) Before main roof periodic caving occurs, begin using no top coal caving advance method, until the main roof caving in order to make sure that the main roof has enough cushions to reduce the height of the ultimate convergence. 2) Before main roof caving, ensure the largest cutting height. Support must be maintained as long as possible at a high level collapse of the face supports in order to maintain the maximum leg convergence to reduce the possibility of support closure. 3) In a case of given length of the face, the scope of the overlying strata, including the thickness of both the immediate and the main roof as well as the height of the permeable fracture zone. The span of main fall and periodic caving location may fall into the fractured zone of the aquifer under the action of gravity. 4) Information on the distribution of the abutment pressure focused on the width caused by “internal stress field” around the walls of the working face. 5) Reasonable selection and transformation of support. In order to prevent the collapse of supports due to roof caving, we can select proper support and increase the caliber of safety valves to adjust the rapid yield valve requirement for safe working of the support.
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In short, scientific management, overall arrangements, organizing highly efficient production and accelerating the speed of face advance are required. Rock strata failure and movement needs a time period, we can accelerate face advance where pressure anomalies may appear, then the roof falls may occur in the gob to avoid occurrence of pressure anomalies. Acknowledgments This research is sponsored by the National Natural Science Foundation of China (No. 50874021), the Program for New Century Excellent Talents in University (No. NCET-08-0833), and the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT0656) of the Ministry of Education of China. We thank the Jisan Coal Mine of the Yanzhou Coal Mine Group for providing a good research environment for this project, and we thank the groups of researchers for their hard work. References [1] Miao XX, Li SC, Chen ZQ. Bifurcation and catastrophe of seepage flow system in broken rock. Journal of China University of Mining and Technology 2009;19 (1):1e7 [in Chinese]. [2] He MC, Xie HP, Peng SP. Study on rock mechanics in deep mining engineering. Chinese Journal of Rock Mechanics and Engineering 2005;24(16):2803e13 [in Chinese]. [3] Wang EY, Liu XF. Study of electromagnetic characteristics of stress distribution and sudden changes in the mining of gob-surrounded coal face. Journal of China University of Mining and Technology 2008;18(1):1e5 [in Chinese]. [4] Jiang FX. Ground pressure and strata control. Beijing: Mine Industry Press; 2004 [in Chinese]. [5] Song ZQ, Yang ZF, Peng LJ. The study of the foundation of dynamic information of the forecast and control of serious disasters. Beijing: Mine Industry Press; 2003 [in Chinese].
[6] Zhou RB, Cheng BF, Ye GJ, Wu Q. Time effect of water busting in fault rupture zone. Journal of Engineering Geology 2000;8(4):411e5 [in Chinese]. [7] Yang XJ, Deng FH. Response of carrying capacity of piles induced by adjacent metro tunneling. Journal of China University of Mining and Technology 2009;19(2):176e81 [in Chinese]. [8] Gao YF, Zhang QS. Mine rock mechanics. Xuzhou: China University of Mining and Technology Publishing House; 2000 [in Chinese]. [9] He MC, Cao XL, Xie Q, Yang JH, Qi P, Yang Q, et al. Principles and technology for stepwise utilization of resources for mitigating deep mine heat hazards. Journal of China University of Mining and Technology 2010;20(1):20e7 [in Chinese]. [10] Zhu XS. The application of engineering geophysics in the remediation of water inrush in fractured zone. Express in Formation of Mining Industry 2004;11: 5le3 [in Chinese]. [11] Li SC. Nonlinear dynamical study on non-darcy flow in broken rock. Dissertation. Xuzhou: China University of Mining & Technology; 2006 [in Chinese]. [12] Sun XM, He MC. Numerical simulation research on coupling support theory of roadway within soft rock at depth. Journal of China University of Mining and Technology 2005;34(2):166e9 [in Chinese]. [13] Guo ZB, Guo PY, Huang MH, Liu YG. Stability control of gate groups in deep wells. Journal of China University of Mining and Technology 2009;19 (2):155e60 [in Chinese]. [14] Yin LM. Forecast and control of the abnormity rule of the full-mechanized stope pressure. Shandong University of Technology; 2005 [in Chinese]. [15] Liu HZ, Han BP. Vertical variation of trace elements and its relation to the water-bearing capacity of Ordovician strata, in Datun coal field. Mining Science and Technology 2009;19(2):166e9 [in Chinese]. [16] He MC, Gong WL, Li DJ, Zhai HM. Physical modeling of failure process of the excavation in horizontal strata based on ir thermography. Journal of China University of Mining and Technology 2009;19(6) [in Chinese]. [17] Miao XX, Li SC, Huang XW. Experimental study of seepage properties of nondarcy flow in granular gangues. Journal of China University of Mining and Technology 2006;16(2):105e9 [in Chinese]. [18] Wu H, Fang Q, Zhang YD, Lu YS, Liu JC. Mechanism of anomalous low friction phenomenon in deep block rock mass. Journal of China University of Mining and Technology 2009;19(4):409e19. [19] Zhang XL, Zhang ZW, Peng SP. Application of the theory of quantification in identifying gushing water sources of coal mines. Journal of China University of Mining and Technology 2003;13(3):251e4. [20] Chen ZH, Xie HP, Wang JC. Numerical simulation on three dimensional deformation and failure of top coal caving. Chinese Journal of Rock Mechanics and Engineering 2002;21(3):309e13 [in Chinese].