Li, C. H. (State Key Laboratory of Ministry of Education for High-Efficiency and Safety of Metal Mines, China) | Qin, R. N. (University of Science and Technology Beijing) | Ma, H. T. (China Academy of Safety Science and Technology Beijing) | Wang, Y. H. (China Academy of Safety Science and Technology Beijing)
ABSTRACT: Aiming at the structure of goaf roof supported by a large number of irregular pillars, Voronoi diagram can calculate the order of pillars failure fast and easily, but the influence of pillar height, the pillar adhesion, different thickness of overlying strata on the strength of ore pillar have not been considered. In this paper, the stability of pillar is analyzed by using fuzzy set theory and improved the Voronoi algorithm. Taking Xianglushan tungsten mine as an example, stability of the mined out area is calculated. The simulation results show the accuracy and rationality of this method, that can achieve the goal of optimal design and ensure the maximum in mining mineral resources on the premise of safety.
The exploitation of mineral resources will leave plenty of goaf. As time elapse, the mined-out areas subject to the overall collapse due to the weathering and rheological factors (Wang et al. 2011, Wang et al. 201 0). There are many large scale goaf collapse reports at domestic and abroad (Caquot & Kerisel 1948). Because of the complicity of geological condition, and improper design and management, lot of the pillars with irregular shape and distribution remained in mined out area in China. For example, Guangxi HepuHengdagypsum mine, Gansu Changba Lead-zinc Mine, Tangling Shizishan copper mine, Henan Luanchuan molybdenum deposit, Yunnan Lanping lead-zinc mine (Ma & Xie 2013), etc. The mined-out areas deteriorate mining conditions, bring the serious effect on mine production and safety.
There are many scholars have studied the largescale mining dynamic disaster caused by pillar instability. Ma Hai-tao (Ma 2007) established stope numerical model by means of the finite difference method to research stress and strain of mined-out area. Zipf R.K. Jr. (Zipf 1996) used boundary element method to simulate continuous collapse. In addition, in order to analyze large-scale goaf collapse, Ma Hai-tao (Ma & Xie 2013) also proposed a simplified Voronoi area average method to analyze pillar stress.
Jiang, H. (University of Science and Technology Beijing) | Ji, H. G. (University of Science and Technology Beijing) | You, S. (University of Science and Technology Beijing) | Tian, X. L. (University of Science and Technology Beijing)
ABSTRACT: Rock burst is one of the Dynamic disasters in coal mining and other deep underground engineering as well as a hot-spot topic which the rock force field focus on widely. Along with the increasing depth of coal mining, the frequency and harmfulness of rock burst is increasingly serious, it has become a major technical problem to be solved in mines of our country. The paper treated the situation of rock burst when coal roadway tunneling in YANBEI colliery as the engineering background, based on the event data collected and sorted of real-time monitoring on microseismic and rock burst, to conclude the characteristics of spatial distribution under rock burst, analyzing the correlation between rock burst and microseismic, concluded the correlation between their distributions. To evaluate the impact factors of position and magnitude of rock burst, distinguishing the type of rock burst in this field is the bottom board of tunnel with stress. It has important engineering value on the studying and predicting of the mechanism about rock burst.
With the increasing demand for mineral resources, human are constantly looking for the mineral resources which in the deep of Earth, the deep resource exploitation has been becoming a trend of mining development. Mining depth is increasing under this trend. Under a certain high stress condition in the deep, the rock which is surround roadway, gob and pillar is easy induced unstable failure occurs, the rock burst. It usually refers to the elastic energy in the rock under the disturbance release instantaneously, generating the mine dynamic phenomena, often accompanied by a loud noise, rock burst and other phenomena (Qi & Chen 2003). Rock burst is one kind of rock dynamic disasters all around the world, it is the most serious disaster in coal mine. It tends to cause deformation of the mining face, the destruction of equipments, and result in casualties, even when serious cause surface subsidence and local earthquakes. In the long-term study on the earthquake, seismologists have accumulated a wealth of experience and made many valuable results, particularly the geophysical methods including microseismic monitoring, positioning, etc., all the results are valuable assets during the study of rock burst (Zhao & Tang 2005). In this paper, according to the existing data about microseismic and rock burst events of the 250204 face of Yanbei mine, finding the positions of microseismic and shocks, summarizing the events’ distribution rule under different locations and magnitude.
ABSTRACT: There is a large burning area in Xinjiang Laojunmiao open pit coal mine. To ensure the slope safety, characteristics of surrounding rock after baked and burnt were understood through the geological investigations and the rock mechanics tests. The typical profiles of burning area were selected according to the engineering geological characteristics. The safety factors of the profiles in the different final slope angles and the different states were computed through the limit equilibrium method, then the stabilities were analyzed to determine the reasonable final slope angle. The results show that strengths of burnt rock decrease compared with original rock. When the final slope angle of Laojunmiao mine is 36°, the slope safety can be ensured.
Due to the dry climate and shallow coal seam in Xinjiang, coal-field fire are very serious. According to statistics (Cai & Wei 2008), there are currently 50 coal-field fire areas in Xinjiang, and the total area is about 570m2, which lead to the loss of more than 15 million t coal. A large burning area is formed after the coal spontaneous combustion, causing a serious impact on safety production of mine. Many scholars have studied the coal spontaneous combustion, burning area and burnt rock and achieved certain results. Ide et al. (2011) delineated the range of coal fires in underground area by magnetic method, and the geomagnetic characteristics were studied and reported. Heffern & Coates (2004) made a detailed study on distribution and cause of the geologic history coal fires in the Powder River Basin of the United States and used a variety of dating methods to date burnt rocks. Hoffman et al. (2004) used differential interferometric synthetic aperture radar to detect the coal fires in northern China. Christian et al. (2009) detected the range of coalfield fires using thermal infrared remote sensing technique. Voigt et al. (2004) conducted a survey to detected and analyzed coal seam fires in north China using integrating satellite remote sensing techniques.
Li, C. H. (State Key Laboratory of Ministry of Education for High-Efficiency and Safety of Metal Mines, Beijing) | Peng, J. W. (University of Science and Technology Beijing) | Zhao, K. (Jiang xi University of Science and Technology, Ganzhou)
ABSTRACT: Applying finite different method FLAC and neural network to back-analysis the displacement of tunnel, the testing samples based on orthogonal test design and FLAC numerical simulation are used to constitute mapping of rock parameter and rock displacement, then the modulus of elasticity and lateral pressure coefficient of surrounding rock were obtained by the mapping from the measurement data. The accuracy of inverse parameters is checked by FLAC. The result shows that optimal solution of parameter can be reached from the displacement back analysis. The results can be feedback for the design of tunnel and also applied to the informative tunnel construction.
The complicated geotechnical condition makes some difficulties in determination of physical and mechanical parameters of rock mass. By the finite element and boundary element methods, the obtained mechanical parameters and initial geostress usually deviate from actual values. Therefore, back-analysis methods have been proposed in which the easiest, available and precise testing parameter is displacement in extremely complex rock and soil mass. The required parameters could be solved accurately by the back-analysis method based on the displacement monitoring (Zhu & Guo 2006, Lv & Jiang 1998). In this paper, the method of displacement back-analysis combining neural network with FLAC3D is studied, and a practical solution has been established. In practice, it enables the displacement back-analysis used for this kind of surrounding rock, and the mechanical parameters and initial geostress could be obtained.
PARAMETERS AND MODEL OF TUNNEL
On the issue of modeling, the closer to the objective reality in the employed mechanics model, the more number of parameters needed to be back-analyzed. However, the objects of study are rock and soil mass which are not homogeneous at all, it is a composite geologic body including joint, crack and faults.
ABSTRACT: This article aims at more accurately studying an equivalent applying way of blasting load by numerical simulation method. Based on the theory of strength reduction, slope stability is analyzed. It can produce special blasting load when open-pit is mining, and made more able to simulate the actual blast load equivalent loading. The equivalent applying way of blasting load first analyze the characteristics of open-pit blasting load, it rings to pass from the explosion source to the surrounding, If the blasting load can equivalently load into the crushing outside the district boundary, so that it is more consistent with the actual hole blasting; The way uses FLAC3D to establish the open pit slope numerical model, and then analyzed using finite difference method under blasting dynamic loading the dynamic response characteristics of slope, then calculated using strength reduction pit slope seismic safety factor. And finally with the past will be the equivalent of blasting vibration is applied to the model boundary manner comparative, verification by the equivalent method is applied to blasting in the slope stability analysis under dynamic loading, the feasibility and rationality.
Since the 20th century, the ore proportion of both domestic and overseas open-pit mining is considerable in ore yield. For our country (Liu 1995), metal mine open-pit mining of iron ore accounts for about 80%-90%, non-ferrous metals accounts for about 40%-50%, and chemical materials accounts for 70%, building materials accounts for 100%, proportion of open-pit coal mining has been about 5%. In recent years, some large open-pit mine areas have set up, which suggests that the development potential of coal mining in future is very huge. Since the 1990s to the beginning of this century, with the development and utilization of resources, deep sunken open pit mine has become the trend of the open-pit mine in the world, and the resulting high steep open pit slope stability problem has been closely watched. With the rapid development of science, technology, economy, the excavation blasting technology is widely applied in open pit mining. But because of its complexity and moments in blasting, it is difficult to study its mechanism and function feature. At present, the problem of slope stability under blasting load research has aroused many scholars attention.
Hu, J. J. (Beijing University of Science and Technology) | Yu, B. (Beijing General Research Institute of Mining and Metallurgy) | Zheng, L. (Beijing General Research Institute of Mining and Metallurgy) | Wu, P. (Beijing General Research Institute of Mining and Metallurgy)
ABSTRACT: For reducing boulder yield in bench blasting of an open pit mine, rock breaking mechanism in rock blasting is applied, while engineering geological survey, numerical simulation analysis and on-site tests are utilized. Through alteration of charge structure, detonate direction and adjustment of blasting sequence, fragmentation is obviously improved and the cost for secondary blasting, shoveling and loading are all reduced.
It is an important topic to lower boulder yield in drilling and blasting in mine. Rock blastability comprehensively reflects its own physical-mechanical properties as well as explosive and blasting process; natural rock mass contains numerous faults, joints, fractures and other structural surfaces, thus its strengthen depends on rock strength and strength of structural surface and is mainly controlled by the latter in more conditions. Therefore, most of fracture planes of rock are generated along structural surface inside the rock mass.
Structural surface imposes stress concentration, reflection enhancement of stress wave, energy absorption, energy release, pitching-in, change of break line, etc. on blasting effect. It is commonly wished to search for the most proper explosive and blasting parameters under set ore rock properties in mine production, thus to reach the composition featuring the lowest total mining production cost. Therefore, the method for lowering boulder yield in blasting for fracture-developed mine is directly associated with economic and safety benefit of mine.
Yu, W. J. (Hunan University of Science and Technology, Xiangtan) | Du, S. H. (Hunan University of Science and Technology, Xiangtan) | Feng, T. (Hunan University of Science and Technology, Xiangtan) | Wang, W. J. (Hunan University of Science and Technology, Xiangtan)
ABSTRACT: There were many small and medium coal mines in South China, and its geological conditions was very complex, so it could often found that there have large deformations during application in these coal mines and become very difficult to support. In view of the roadway deformation and control issues under complicated geological conditions, several mining area, such as Qujiang Coal Mine and Baise coal mines, geological conditions, roadway deformation characteristics of coal mines and outstanding problems of roadway support after in South China were summarized; and a series of field investigations, industrial test and supporting design research were carried out. According to the deformation characteristics of roadway surrounding rock in typical mines, industrial test of control technologies in high stress and large deformation rock, small coal pillar roadway and soft inflating half coal roadway were respectively illustrated. This study could provide theoretical and practical support in control technology for the same kind roadway, and it was of great significance to promote the development of science and technology of coal mines in South China.
Compared to large coal mines in North mine, the supporting technology of soft rock roadway in South mine in china was relatively backward, and it was mainly include the following aspects: the design was not reasonable, supporting form was simple, the strength of supporting materials was low and the construction quality was poor. Moreover, all of these did not get enough attention of scientific research for a long time. In recent years, Hunan University of Science and Technology had temped up with many coal mines comprehensively, inventing the “pre-stressing force and large stiffness truss cable beam“ as the comprehensive control core measures, and the high resistance to pressure release and high strength supporting technology with high strength bolt, strong anchor, and grouting. These techniques were used in the field, and its effect was obvious. The results can provide theoretical and practical support in control technology for the same kind of roadway, and it was of great significance to promote the development of science and technology of coal mines in South China.
ABSTRACT: In order to achieve the purpose of early warning, a scientific and reasonable evaluation system of early warning is required to be established. Based on multi-source information obtained by monitoring surrounding rocks, this paper proposes three parameters as early warning indicators, namely, rock displacement, deformation rate and acceleration for deformation. First, it made a quantitative analysis and evaluation of the monitoring data, and used a variety of data smoothing methods or wavelet analysis for the diagnosing of monitoring data to determine the criteria for the safety of surrounding rocks. Then, it gave a consideration to the genetic mechanism of rock deformation and combined it with mathematical and statistical methods to establish a forecast model of monitoring data, thereby getting a system for monitoring, warning and evaluating the ground pressure. It has extremely important theoretical and practical significance for correctly predicting rock failure, effectively preventing accidents, and successfully warning accidents.
Currently, the warning reference for rock safety mainly includes the permissible ultimate displacement, displacement rate, displacement acceleration, deformation ratio and other judging bench marks. It's hard to use only one single index as a reference to judge the safety of surrounding rock and supporting structure. Sometimes the peripheral displacement goes beyond the reference value of displacement control, but no damage occurs to the supporting structure; sometimes the deformation rate is large, but still far less than the reference value of surrounding displacement control, and no structural damage has occurred; sometimes the rock deformation has not yet reached the reference value of displacement control, but the supporting structure has became instable. Within a certain period of time, the damage of rock will accelerate the destruction (Lian 2012).
Li, S. G. (Xi' an University of Science and Technology) | Ding, Y. (Xi' an University of Science and Technology) | An, Z. F. (Xi' an University of Science and Technology) | Li, H. T. (Xi' an University of Science and Technology) | Wei, X. W. (Xi' an University of Science and Technology)
ABSTRACT: Under the conditions of repeated mining in multiple coal seams, overlying strata experience repeated pressure relief, and the fracture paths are different from that formed in single coal seam mining. The movement of overlying strata, the fracture distribution and evolution, and the shape were investigated by physical tests and theoretic analysis. The results demonstrate that a mobilized elliptic parabolic zone would be formed if the bed-separated fissures and broken fissures are connected in the process of the overlying strata movement. Compacted area gives shrinkage effect with subareas further developing, and fracture of the overlying strata undergoes five stages, i.e. fracture initiation, expansion, compaction, expansion again and compaction again. Equations on voids and permeability in overlying caved rock, residual expansion coefficient, gob depth and the strata movement were established when composite gob becomes basically stable, which can be used to analysis the expanding characteristics of strata and the gap seepage characteristics of composite gob under the condition of repeated mining. At last, a mathematical model of the elliptic parabolic zone in overlying strata is derived, which provides a theoretical basis for determining the location of drilling hole for gas extraction.
Cracks in coal seam and rocks are the main channel of infiltration and fluid migration caused by overlying strata regularly cave, rupture and sink with the mining face advance (Qian & Miao 1996). Bai (1990) and Palchik V (2003) agree that there exist three different mobile belt above longwall mining gobs (caving zone, fracture zone, bending subsidence zone); Liu (1981), Qian (1983) established theoretical system of “Horizontal Three Area“ and “Vertical Three Regions“ on the basis of overburden failure and conductivity fracture distribution characteristics. Through experimental and theoretical research. Qian (1998 & 1997) put forward the theory of “O“ ring. Yuan (2004 & 2008) put forward the concept of “roof annular crack circle“. Lin (2007) called it a “recurrent“ ringand and Li (1990 & 2000 & 2011) described it as “mining fissure elliptic paraboloid zone“ and covered “mining fissure rounded rectangle ladder“. Xie (2008) described it as an “arch“ cap. The above researches reveal the evolution law of fracture zone in single coal seam mining, and form a more completely theoretical system which is playing an important role in guiding simultaneous extracting of coal and methane.
Sun, Z. G. (Chongqing Research Institute) | Li, S. G. (China Coal Research Institute, Beijing) | Li, L. H. (Chahasu Coal Mine, Investment Inner Mongolia Energy Co. Ltd., China Electric Power Construction and Investment) | Tian, L. T. (Chahasu Coal Mine, Investment Inner Mongolia Energy Co. Ltd., China Electric Power Construction and Investment)
ABSTRACT: In light of the coal roadway deformation in soft rock conditions under dynamic pressure influence, this research was made on the governance practices in No. 3101 working face, combined theories and computer numerical simulation, the floor heave and spalling mechanism under the influence of multiple mining activities were analyzed and a rational pillar size was calculated and bolt-cable coupling improvement support projects were designed on the basis of the original support plan. The study result shows that it was expansion-flexural composite of floor heave and rib spalling affected by coal pillar size. It can effectively control the volume expansion at the roadway bottom plastic zone and reduce the impact of the surrounding rock pressure of two sides on the floor by increasing coal pillar size to 25 m and using “add floor rock bolt and increase support density in two sides of roadway and enlarge anchor length“ comprehensive reinforced support means.
For a long time, the problem of soft rock roadway supporting is always one of the major technical hurdle which seriously influence the coal production safety in China coal mines (He & Sun 2004, Qian & Shi 2003). Influenced by soft rock and engineering stress disturbed, there were large-scale rib spalling and floor heave issues during mining in No. 3101 work face, and they are seriously restricting the safety production of coal mine (as shown in Fig. 1). In allusion to the problems mentioned above, the deformation mechanism of soft coal roadway was analyzed and an improved roadway support design scheme was proposed by combining the theories and computer numerical simulation.
2 ENGINEERING GENERAL SITUATION
The No. 3101 long-wall fully-mechanized working face with large mining height is the first mining face in Chahasu coal mine, its buried depth is 398.8 m and the thickness is 6.45 m. Structures in zonation are simple and dip angle of coal seam is 1~3°. The roof rock was composed of mudstones, sandy-mudstones and medium grain sandstones. Among them, the medium grain sandstone is the main roof and its thickness is about 12.55~24.85 m. The immediate floor of coal seam is carbon mudstone with a thickness of 0.85~1.8 m, the main floor is consisted of coarse-grained sandstones and its thickness is 5.35-14.18 m.