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.
ABSTRACT: In the deep underground environment, with the high temperature and high confining pressure, the characteristics of hard rock, such as granite, will transform from brittleness to plasticity. Also, the mechanical behaviors and constitutive relations of the rock have great variation. For the rock under cyclic loading, its inner cracks are extended by stages, and the failing process is affected by cracks spatial distributions, mechanics behaviors and loading situations, which make the study more complex. In this paper, the triaxial compression test and Acoustic Emission (AE) monitoring test were used to analyze the failing mechanism of rocks. Also, the AE characteristics and their corresponding stress in each stage of failing process were described, so as to indicate the strength envelope of crack initiation, crack damage strength, peak strength and residential strength. At last, the relationship between AE characteristics and rock failing was obtained.
With the exploitations increasing by steps, the shallow resources are exhausted gradually in China, so many open-pit mines have to be faced with deep excavations. In this deep underground environment, with the high temperature and high confining pressure, the characteristics of hard rock, such as granite, will transform from brittleness to plasticity. A large number of scholars in the word have done a lot of researches on the failure mechanism of rocks at present. Xie et al. (2011) researched on the energy analysis for damage and catastrophic failure of rocks. Molladavoodi and Mortazavi (2011) analyzed the failure mechanism of brittle rocks with a damage based numerical method. Nicksiar and Martin (2012) gave a method to determine crack initiation in compression tests on low-porosity rocks. Ghazvinian et al. (2012) studied the failure mechanism of planar non-persistent open joints with PFC2D. Erarslan and Williams (2012) expounded the mechanism of rock fatigue damage in terms of fracturing modes. Peng et al. (2014) raised an empirical failure criterion for intact rocks. Although huge efforts have been done and mass information has been obtained on the failing mechanism of rocks under single loading, in order to acquire the particular failing mechanism of host rock, which is usually under complex loading environment, such as cyclic loading and confining pressure, the researches of rocks under cyclic loading are quite necessary.
ABSTRACT: Assessment of landslide hazard often requires a good knowledge of the landslide characteristics. To investigate the dynamic runout process of the landslide across 3D terrain, a three-dimensional model using spring-deformable-block model is proposed. On the assumption that the motion form of landslides is continuous and variable, the sliding body is divided into lots of columns. The model is based on a stability analysis of landslides and allows taking the deformation of sliding body into account. Considering the force and moment equilibrium of deformable columns and the principle of conservation of energy, a three-dimensional sliding body is simplified by a series of deformable blocks with different dimensions. According to the accumulation and the release of the deformation, the sliding body acceleration, velocity and displacement formulas are established. Correlating well with the discrete element method, the present results are satisfactory in describing the dynamic process of landslides and predicting the impact areas of the post-failure sliding body. Finally, the present model is applied to analyze the sliding time, the maximum velocity and displacement of the sliding body of Jiweishan landslide in Wulong, Chongqing Southern China. By comparing with existing numerical results, the model shows good agreement with the previous ones.
Landslides which defined as the movement of a mass of rock, debris or soil down a slope are characterized by long-runout displacements and high velocity (Cruden 1991). Even far away from the origin location of the slope, significant destruction still can be brought by rapid landslides through the sliding path. However, sometimes their potential for destruction can't be practically reduced by reinforcement of the source area (Hungr 1995). Prediction of post-failure motion is needed in the hazard assessment as an important part in case that a potential source of a landslide is detected. Therefore, engineering risk analysis emerged, especially the runout analysis which is applied to estimate the potential hazard area (Hungr 1995). In order to design protective measures, run out parameters such as the maximum displacement reached, the landslide velocity, and the distribution of the deposits should be determined through quantitative method during the runout analysis.
Tang, G. Y. (China JK Institute of Engineering Investigation and Design, Xi'an) | Liu, Z. H. (China JK Institute of Engineering Investigation and Design, Xi'an) | Zheng, J. G. (China JK Institute of Engineering Investigation and Design, Xi'an)
ABSTRACT: Coral reef calcareous rock, deposits in neritic environment, is widespread in tropical ocean area. It possesses special structure and engineering characteristics due to the sedimentary environment and short depositional history. This paper, on the basis of an actual project in East Java, discusses the basic engineering properties of coral reef rock. By way of electronic microscope scanning and mineral analysis, the results indicate that weak diagenesis of calcareous rock results in its large porosity and loose structure and, further, controls the mechanics behavior of the rock. Moreover, indoor tests and in-situ tests also show that the rock is the very soft type: its SPT blow count presents the feature of non-normal distribution with wide range of fluctuation. Besides, shear wave travels in reef rock much more slowly than it does in ordinary rocks, and the ratio of elastic wave speed and shear wave speed close to 2.0, all the phenomena showing the typical loose structure of this rock. Given plenty pores, water pressure test in borehole suggests high permeability and good connectivity of the calcareous rock, and its hydrogeological characteristics also differ greatly from that of other rocks.
Coral reef, deposit with rich calcium and insoluble carbonate material, is a type of calcareous rock developed mainly in tropical ocean environment under the biological (reef, seaweed, shellfish and other ocean species) formation and geological formation. It is widely distributed in the tropical waters between 30° south latitude and 30° north latitude.
Reef calcareous rock is formed after the reef deposits have gone through years of physical and chemical actions. Majority of it belongs to modem marine biogenic carbonate rock, with short depositional history, unique development environment and special material composition. Mineral composition of the rock includes mainly aragonite and calcite, and the rock mass structure retains the original skeleton of the biological pore. Characterized by high porosity, fragility, loose structure, easy cementation, and poor hardness, its engineering mechanics properties thus differ greatly from other terrestrial or marine sediments, making it a special type of rock and soil mass, whose special mechanic behavior and engineering properties deserve further studies when constructions are conducted in such calcareous rock area (Xu 1989, Zhao et al. 1997, Sun et al. 1999, Wang et al. 2008).
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.
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.
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.
ABSTRACT: Concrete socket is considered as a functional structure to improve the displacement and stress distribution, and enhance the stability of high arch dam and abutment, especially when geological condition of such large rock engineering is defective, but lack of particular clear mechanism description. The evaluation of concrete socket effect in this paper, resulting from numerical simulation for Baihetan arch dam is based on a particular nonlinear finite element method, in which Deformation Reinforcement Theory (DRT) is applied. The mechanism of action is clarified generally from two perspectives: the first one contains conventional parameters such as displacement, stress and volume of plastic zone; from the second one, Plastic Complementary Energy (PCE) of such as left bank, right bank and dam, is adopted to quantify the structure stability, and unbalance force is considered as measurement of local area failure, in a sense of characterizing the distance of local stress state beyond the yield surface during the overloading process. It is suggested that evaluation based on deformation reinforcement theory can also be a reliable reference of high arch dam design and construction.
Chinese history of high arch dam construction has lasted for more than 30 years, during which Ertan arch dam was completed and has been under normal operation so far, in addition, many other 300m level high arch dams such as Xiaowan, Xiluodu and Laxiwa are also under construction. Due to their unfavorable geological condition of the dam foundation and asymmetry of both sides of abutment, concrete socket is always designed to enhance dam body and adapt to adverse topographical and geological condition of foundation. In order to reduce the load on abutment rock mass and improve state of stress and strain of dam, the concrete socket located in riverbed or abutment is particularly assumed to be applicable, especially where geological condition of lower part of foundation is poorer than the upper part. It is clearly informed that concrete socket is set in international finished dam cases like Vaiont arch dam in Italy and Enguli arch dam in Georgia, and proposed dam case like Jingpin-1 high arch dam and Baihetan arch dam in China.
ABSTRACT: By means of introducing strength reduction method and gravity increase method to particle flow code, the stability of the jointed rock slope is analyzed. In the analysis, rock is described by the particles and their contacts, and joints by the smooth joint model. Meanwhile, there is no longer need predefined constitutive relation or presupposing sliding surface. After strength reducing or increasing gravity, the fractures generate, propagate, and coalesce along the contacts with minimum tensile or minimum shear strength, forming the final sliding surface. Comparing with traditional limit equilibrium method, the result of particle flow code is more reliable in obtaining the safety factor and has more advantages in determining the sliding surface. It will provide a new approach for the stability analysis of jointed rock slope.
After repeated geological action, rock mass in slope primarily composes of rock and structural surface. The structural surface can divide into bedding plane, joint, crack and fault fracture zone, due to its structure, occurrence, and characteristics (Chen 2005). The rock mass is cut into structures with different sizes, shapes for the presence of structural surfaces, as a result, it exhibits discontinuity. What's more, the rock strength is always determined by the structural surfaces because of their extremely low strength properties. Specially, joint is one of the important structural surfaces.
The main methods analyzing slope stability are traditional Limit Equilibrium Method (LEM), Finite Element Method (FEM), Discrete Element Method (DEM), etc. LEM is mainly applied to homogeneous slopes (Bishop 1955). This method requires pre-defined sliding surface shape and location with artificially, and it does not consider the relationship of sticks' stress and strain. FEM has considered the stress and strain relationship, and can qualitative evaluate the slope stability according to nodes' displacement and plastic strain zone. In recent years, Zheng & Zhao (2004) incorporated strength reduction method and gravity increase method into FEM, which not only calculated the safety factor, but also showed the sliding surface corresponding to the minimum safety factor.
Zhu, Q. J. (University of Science and Technology Beijing) | Jiang, F. X. (Guizhou Coal Mine Design and Research Institute, Guiyang) | Yu, Z. X. (Guizhou Mine Safety Scientific Research Institute, Guiyang) | Han, Z. L. (University of Science and Technology Beijing) | Li, S. Q. (China Academy of Safety Science and Technology, Beijing) | Zhang, P. X. (Guizhou Coal Mine Design and Research Institute, Guiyang)
ABSTRACT: Microseismic monitoring involves the geophones placement within the rock mass of a mine to record its micro seismic activity. Prior to reducing the number of records required for the post processing and proving the hypocenter and automatic location, a microseismic waveforms classification technique using Hidden Markov Model has been studied in this article. Four different kind of microseismic signals were considered as most representative of coal mines in our study, including blasting, random noise, electromagnetic interference and rock fracture signals. Using the MATLAB module, feature extraction process was applied to obtain the MFCC characteristic of each kind of signal. The features were performed to reduce the number of them using an optimization process, and normalized to generate a feature vector at last. Then a Hidden Markov Model was implemented as a classifier to develop mining microseismic waveforms automatic classification system. And the EM method was applied to optimize the initial parameters. Our method was tested and verified on a dataset from Shandong province, provided by Longgu coal mine. The result indicates that the event classification method presented in this paper was precise and automatic. The described methodology can be used to classify more seismic signals to improve the study of the activity of this coal mine or to extend the study to other active mines.
Classification of microseismic waveforms is the important basis to improve the rate and accuracy about the microseismic location. Through identify the effective mining microseismic events accurately and effectively, we can eliminate a lot of useless background noise and mechanical vibration interference waveforms, and transmission signal interference in the process. This is the important foundation for the automatic location.