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Mao, Pisith (Kyushu University) | Saisho, Tsuyoshi (Kyushu University) | Sasaoka, Takashi (Kyushu University) | Shimada, Hideki (Kyushu University) | Hamanaka, Akihiro (Kyushu University) | Wahyudi, Sugeng (Kyushu University) | Oya, Jiro (MM Nagata Coal Tech Co., Ltd.) | Naung, Naung (Kyushu University)
The ideal mindset of coal mine industries is to extract the maximum amount of coal possible from the coal seam resource. However, there is an absolute limitation when it comes to coal excavation depending on geological condition and the adopted mining method of each mine. As a result, there must be some remain coal thickness left. This can be beneficial for coal bed that is surrounded by weaker dominant rock as the remained coal can help improve the stability of any opening structure during the mining development and excavation. This research seeks to identify the optimum remain coal thickness (RCT) above and below the excavation in order to maximize the stability of the gate-entry and investigate appropriate support for gate-entry. With this in mind, a trial panel of an Indonesian coal mine, which is located in East Kalimantan, is selected as the research study area. This mine situated in weak geological condition, which is common for coal resource in this region. This paper use FLAC3D for numerical simulation. Preliminary result, show that the reduction of displacement on top and bottom of the gate-entry does not increase much when the RCT is left more than 1 m on both the gate roof and floor. This can be a great indicator for optimum thickness for remain coal. The outcome also shows that steel arch SS540 with 1 m spacing is appropriated for adopting in this trail panel gate support system. The result from this research is essential for developing mine design in this region as well as other coal resources that have a similar condition. This knowledge also allows mine design to have a better support system optimization compare to previous work, which did not consider the effect of RCT.
Indonesia hosts an abundant portion of thick coal deposit, which is usually found in weak geological condition (Sasaoka et al., 2015). This weak geological condition has led to the limitation of excavation into a certain height (Ozfirat et al., 2005). As a result, some of coal thickness remains on top and bottom of the excavation. This can be beneficial for coal bed that is surrounded by weaker dominant rock as the harder remained coal can help improving the stability of any opening structure during the mining development and excavation.
Submarine hydrothermal ore-deposits are known to be rich in metal resources and are to be found abundant around the Japanese islands. In recent years, several field studies had been carried out and a lot of data on chemical and physical properties of geological samples (ore-deposits, rocks, sediments) have been gathered especially for hydrothermal fields in the Okinawa Trough. However, the mechanism of formation and accumulation of these deposits is not yet clearly understood. In this study, we investigated hydrothermal fluid flow in combination with chemical reactions of a simplified model (2-dimensional radial model) representing hydrothermal activity around a vent fluid conduit beneath the seafloor. The numerical code TOUGHREACT V3.0 - OMP, which is for coupled non-isothermal multiphase fluid flow and geochemical reactive transport was employed. Almost all model parameters are chosen based on available results of geophysical and geochemical surveys of the Iheya hydrothermal fields in the Okinawa Trough. Therefore, the geological structures were set as having diverse permeability, which reflects alternating pumiceous volcaniclastics layer and hemipelagic sediment layer. Chemical reactions including precipitation of minerals (anhydrite, quartz and sphalerite) caused by mixing of hydrothermal fluid and seawater-derived fluid and/or cooling was considered in this setting. Following two features were clarified: First, high velocity venting hydrothermal fluid ascends to the seafloor through the fluid conduit at the center of the model, whereas nearby cold water percolates downward from the seafloor and convection occurs. Second, among the alternating layer structure, preferential horizontal flow is obvious for layers with high permeability, which resulted in primary sulfide precipitation with a lateral extend. These results are likely to be consistent to recent field studies during scientific drilling into the submarine hydrothermal fields.
Submarine hydrothermal ore-deposits are known to be rich in metal resources and are to be found abundant around the Japanese islands. In recent years, a lot of data on chemical and physical properties of submarine hydrothermal ore-deposits in the Okinawa Trough have been gathered due to several field surveys.
Naung, Naung (Kyushu University / Mining Enterprise / Ministry of Natural Resources and Environmental Conservation) | Shimada, Hideki (Kyushu University) | Sasaoka, Takashi (Kyushu University) | Hamanaka, Akihiro (Kyushu University) | Wahyudi, Sugeng (Kyushu University) | Mao, Pisith (Kyushu University)
This study describes the importance on the evaluation of rock mass condition before mining and probability of failure during mining under slope surface in shallow depth. It is well known that several factors can affect the stability of underground openings such as the quality of rock mass, the in-situ stress, the depth below the surface and opening geometry. In addition to those parameters, if underground mining is conducted near the slope surface, the influence of slope surface should be taken into account during any mining activities. Consequently, stability analysis has been conducted for three different conditions including the evaluation on the strength of rock mass in the sloping surface, assessment on the stability of stope mining near the slope surface, and instability of stope in the nearground region in various mine condition. The preliminary results show the instability of rock mass near to slope surface is more severe than that of the rock mass far from the slope surface, therefore large instabilities of rock mass near the slope surface are experienced. In addition, the occurrence of failure zones of stope mining in the near-ground region under slope surface become more pronounced in weaker geological condition and higher stress ratio. All the investigations for these analyses are conducted by means of 3D finite difference software using FLAC3D.
Stope mining is the most common mining method adopted in underground metal mines of Myanmar. However, the assessments on the stability of stope still remain quite limited in those mining industries. Currently, most of the underground metal mines are being mined-out or still mining at shallow ground part. Moreover, there are not so many recorded data regarding rock mass failures cases in underground mining due to cut and fill stoping methods in Myanmar. Hence, the study on the stability of underground mines in shallow part become one of the important issues to mitigate the unpredictable nature of rock failures. Two forms of instability are readily observed around underground openings: (1) structurally controlled gravity-driven processes (2) stress-induced failure or yielding (Martin et al. 2003). In many pieces of literatures, some instability indicators are usually defined in terms of failure zones, stress condition, displacement and extent of yield zones (Abdellah et al. 2018) (Karian 2016) (Purwanto et al. 2013). In this study, the evaluation on rock mass condition and mining under the sloping surface are described by the occurrence of natural and mining-induced differential stress and failure zones affected to mining activities. Considering the importance stability of underground mining under slope surface, some investigations on the characteristics of rock mass and mining condition are carried out at Modi Taung gold mine, one of the largest underground gold mines in Myanmar.
Block toppling is one of the typical failure types of the rock slopes caused by overturning of the slender, layered rock blocks on the slope under gravitational or seismic conditions. For the stability assessment against the block toppling, limit equilibrium methods are conventionally used. However, in case of the earthquakes, rocking vibration of each rock mass, and the interaction among them may affect the stability of the whole slope. Thus, to evaluate the seismic safety of the toppling slopes, it is appropriate to use a numerical method that can incorporate the above mentioned phenomena precisely.
In this study, the discontinuous deformation analysis (DDA) is focused as a method to simulate rocking motion of the rock mass during the earthquakes. Since DDA is an implicit type numerical method for discontinua, robust computation of the discontinuous behaviors of jointed rock masses is possible. In the past studies, however, it was pointed out that decision of appropriate numerical parameters in DDA to reproduce the rocking motion with high accuracy is difficult. Therefore, the purpose of this study is to reveal the cause of the accuracy degradation of DDA in rocking motion analysis, and to propose an improvement scheme of the DDA for the rocking motion analysis.
The reason of the accuracy degradation in DDA is discussed based on the fundamental rocking problem. From the simulated results with the conventional DDA, it is found that the contact treatment by applying the constraint condition on the normal gap, so-called non-penetration condition, induces unnatural vibration of the contact point after the collision and loses the accuracy. Based on this insight, the new method is developed formulating the contact with zero gap rate condition to avoid the vibration of the contact point. In addition, to satisfy this constraint condition strictly, Augmented Lagrangian method (ALM) is also introduced instead of the conventional penalty method. The new DDA is applied to the fundamental rocking analysis, and showed good agreement with the solution of the rocking theory.
Infrastructure development in urban areas has progressed rapidly, and the demand for construction of pipes for electricity, gas, water supply and sewerage, etc. is increasing. In the urban construction of pipe, the non-open cut method is generally used to prevent traffic disturbance, building influence, noise and vibration, one of which is a Shield method. Shield method is a construction method that rotates the cutter head at the tip of the shield machine, excavates the ground, and constructs an underground pipe ditch.
In recent years, construction condition of Shield method is diversified such as long distance, great depth, high water pressure and gravel ground, etc. Bit wear is a factor affecting workability and economic efficiency in Shield method, and the various investigations have been discussed so far, but the quantitative guidelines on bit wear prediction have not been established because the wear factor is complicated in the gravel ground. This study was conducted in order to obtain fundamental knowledge for predicting bit wear in gravel ground.
The shield machine has the cutter head with bits as shown in Fig.1, and the ground is excavated by rotating the cutter head and pushing it by thrust jacks. However, the bit wear during cutting operation is inevitable. As the bit wear has an obvious impact on the construction progress and cost, such as lowering of drivage efficiency, increasing the frequency of bit replacement, etc (H. Shimada et al, 1989). Therefore, the prediction of cutter bit wear in advance is important. However, there is few research on the characteristics of bit wear in gravel ground and the prediction method of the bit wear in theoretically and quantitatively.
From above point of view, this paper discusses the effects of characteristics of gravel and the gravel content on the characteristics of bit wear in gravel ground based on the results of a series of laboratory tests for the simulated sample of the gravel ground in order to develop the prediction method of bit wear for excavation in gravel ground.
Maehara, Kazuki (Kyushu University) | Shimada, Hideki (Kyushu University) | Sasaoka, Takashi (Kyushu University) | Hamanaka, Akihiro (Kyushu University) | Matsumoto, Fumihiko (Alpha Civil Engineering Co., Ltd.) | Morita, Tomo (Alpha Civil Engineering Co., Ltd.)
In recent years, the underground space has overcrowded with the overcrowding of urban areas. Therefore, the adjacent construction of underground structures is increasing. In such a construction, an influence of the construction of a new structure on the existing structure has to be considered. In order to minimize the influence on such existing structures, application of the underpinning method is expected. The underpinning method is a construction method that attempts to reduce the influence on the existing structures by excavating the ground around existing structures with constructing, rebuilding, and reinforcing new foundations. This study focuses on the underpinning method using pipe jacking. In order to ensure the effectiveness of the underpinning method, 3D finite element analysis was carried out. In particular, four major considerable factors were discussed: the influence of pipe presence, comparison of using conventional underpinning and pipe jacking, the influence of the distance between the pipes and new structure, the influence of pipe length. Based on the numerical results, it is possible to reduce the vertical displacement on the existing structure by using the underpinning method using pipe jacking. Additionally, the underpinning method using pipe jacking is effective to reduce the displacement over a wide range compared with the conventional underpinning method. Furthermore, the influence on the existing structure and the surrounding ground can be minimized by adopting the proper distance of pipe length and the space between the pipes and the new structure.
In recent years, overcrowding has occurred due to the factors such as population increase in urban areas. Various structures are complicated in the underground space and the underground space is overcrowded along with the overcrowding of urban areas. Therefore, adjacent constructions of underground structures are increasing in the underground space of urban areas. Adjacent construction of the underground structure is the construction such as adding an underground tunnel to the surroundings of the drainage pipeline. In adjoining constructions of such underground structures, it is a problem that the influence on existing structures becomes particularly large when constructing new structures. Application of the underpinning method is expected as a construction method to reduce the influence on existing structures. Recently construction methods such as cutting edge jacking method, and shielding method are mainly applied when constructing an underground structure. (Matsumoto et al., 2015) These construction methods are required to occupy a wide range of construction area, long construction period and high cost, so it is difficult to apply those construction methods in urban areas. Therefore, pipe jacking method which is non-cutting technique is required as an effective construction method in urban areas (Japan Tunneling Association, 1997). For the above reasons, construction of the underpinning method using the pipe jacking method is expected for adjoining construction of underground structure.
Sawayama, Kazuki (Kyushu University) | Ishibashi, Takuya (National Institute of Advanced Industrial Science and Technology) | Jiang, Fei (Yamaguchi University / Kyushu University) | Tsuji, Takeshi (Kyushu University) | Fujimitsu, Ysuhiro (Kyushu University)
Hydraulic and mechanical behaviors of the geothermal reservoirs or the seismic faults are strongly controlled by the characteristics of rock fractures. To monitor and predict the hydraulic-mechanical coupling within the crust, geophysical explorations potentially are the powerful tools. However, there is few established rock physical model to link the hydraulic properties of fracture to the resistivity or elastic wave velocity. For our better interpretation of the exploration data, detailed investigation linking hydraulic properties to the mechanical/electric properties for the fractured rocks is required. Therefore, we explore the link by coupling the laboratory experiments and digital rock modeling on the fractures with different aperture distributions. We conduct the fluid-flow experiments and the numerical modeling on granite fractures. In our modeling, we first digitalized the real granite fractures by 0.1 mm grid system. Then, under the same condition with experiments, we calculate the fluid flow (Lattice Boltzmann Method) and resistivity/elastic wave velocity (finite-element method). Laboratory experiments show that fracture permeability decreases with increasing pressure, and this relationship could be reproduced in our modeling study. We further determine the aperture distributions based on the permeability matching approach. As a result, we successfully constrain the variation of permeability, resistivity and elastic wave velocity as well as fracture stiffness of the rock fracture against the pressure build-up; changes of permeability and resistivity are controlled by connection or disconnection of fluid-flow pathway whereas velocity and fracture stiffness are not. Our results suggest that the evolutions of permeability and flow area associated with aperture closure of fracture can be modeled by the changes of resistivity or fracture stiffness regardless of the roughness of the fracture.
Mechanical properties of fractured geological formations and fluid-flow in that are of interest in a number of contexts such as 1) developing and monitoring fractured reservoir (e.g., geothermal, shale and groundwater) and 2) elucidating the mechanism of earthquake (e.g., fault-valve model; Sibson, 1992). Although permeability is often discussed for evaluating the potential of reservoir exploration or reoccurrence of the earthquake triggered by pore pressure build-up, local behavior of fluid-flow (e.g., fluid-flow pathway) within fractures is also important because it controls preferential-flow and total thermal response in geothermal area (e.g., Hawkins et al., 2018). To monitor and predict these hydraulic properties and hydraulic-mechanical coupling within the crust, geophysical explorations potentially are the powerful tools. In geothermal fields, the change of resistivity or velocity associated with the hydraulic stimulation, earthquake and geothermal fluid production was detected (e.g., Peacock et al., 2012; Taira et al., 2018). Although these geophysical monitorings could detect the change of reservoir condition, quantitative interpretations about the injected water distribution, permeability enhancement associated with aperture changes of fracture have not been evaluated yet. To monitor these fluid-flow behaviors from the geophysical explorations, we should investigate the basic relationships between the hydraulic (permeability and fluid-flow pathway), electric (resistivity) and mechanical (elastic wave velocity and fracture stiffness) properties of rocks.
Hamanaka, A. (Kyushu University) | Su, F. Q. (Henan Polytechnic University) | Itakura, K. (Muroran Institute of Technology) | Takahashi, K. (Muroran Institute of Technology) | Kodama, J. (Hokkaido University) | Deguchi, G. (Underground Resources Innovation Networks, NPO)
Underground coal gasification (UCG) is a technique to recover coal energy by the in-situ conversion of coal into gaseous products. In this study, an application of co-axial UCG system with a horizontal well is discussed by means of the model UCG experiment with a large-scale simulated coal seam which the size is 550 × 600 × 2,740 mm. A horizontal well which has 45 mm diameter is used as an injection/production well. The effect of injection rate is evaluated by using the results of gas compositions, temperature profile, and acoustic emission monitoring. During the experiment, the changes of temperature field and product gas compositions were observed by changing the position of an injection pipe, meaning that it is possible to control gasification area and the quality of product gas by controlling the injection position. Additionally, the increase of injection rate attribute to improve the calorific value of product gas while the higher flow rate may cause to move the gasification area rapidly when the coal with higher ash is gasified.
Underground coal gasification (UCG) is a technique to extract energy from coal in the form of heat energy and combustible gases through the chemical reactions in the underground gasifier. This technique enables to utilize coal resources that remain unrecoverable in underground due to either technological or economic reasons. We are developing a co-axial UCG system that is compact, safe, and highly efficient. The co-axial UCG system uses only well drilling and a double pipe. Gasification agents are injected from the inner pipe to expand the combustion zone. The production gas is recovered from the outer pipe. Until now, various UCG model experiments have been carried out to develop the co-axial UCG system (Hamanaka et al., 2016; Su et al., 2018; Su et al., 2017). However, the recovered energy from the coal is relatively low because the gasification area in a co-axial system is limited around a well. In order to improve the total efficiency of gasification process, an application of co-axial UCG system with a horizontal well is suggested (Fig. 1). Additionally, the range of the gasification area and the quality of product gas are affected by the quality of coal and the injection conditions (Bhutto et al., 2013: Kacur et al., 2014; Stanczyk et al., 2011). Considering those backgrounds, this study investigates the effects of the quality of coal and the injection conditions on the range of the gasification area and the quality of product gas by means of the model UCG experiment with a horizontal well.
In Japan, a bench cut method is mainly applied for limestone quarries. As most of the mines are located in the mountain regions and steep slope mountains, the shaft and the underground opening for installation of facilities such as crushing equipment are applied in order to provide workability and economic efficiency for transportation and crushing ores. However, as the mining operation proceeds, the level of the pit will be down and the distance between the mining area which is the bottom of the pit and the opening for underground facilities such as crushing equipment become to be short. In order to maintain the safe mining operation and the stability of the underground opening, the appropriate distance between them has to be maintained. Therefore, in order to develop the guidelines for safety distance between the mining area and the underground opening for installation of facilities such as crushing equipment under different rock mass conditions in a limestone quarry, a series of numerical simulations are conducted by means of finite differential code “FLAC3D”.
Currently, more than 200 limestone mines are in operation in Japan. A bench cut method is mainly applied for limestone quarries of the open-pit mine. In general, the limestone ore excavated from a limestone quarry at a high elevation is introduced into the shaft to achieve efficient transportation by utilizing the gravity. After that, the ore is crushed by the underground crusher and transported by the belt conveyor to the facility of processing at the foot. As most of the mines are located in the mountain regions with a steep slope, the shaft and the underground opening for installation of facilities such as crushing equipment are applied in order to provide workability and economic efficiency for the transportation and crushing ores. However, the stability of the shaft and the underground opening is suspected when the rock mass conditions are poor due to the existence of a fractured zone. In addition to that, as the mining operation proceeds, the distance between the surface and the underground opening becomes to be short with the down of the level of the pit. In order to maintain the stability of the underground opening, the appropriate distance between them has to be maintained. However, there are few studies about the influence of the rock mass conditions especially fractured zone and the mining operation on the stability of the underground opening. Therefore, in order to discuss the safety distance between the surface and the underground opening for installation of facilities such as crushing equipment under different rock mass conditions in a limestone quarry, a series of numerical simulations are conducted by means of finite differential code “FLAC3D”.
SweWIN, Thant (Kyushu University) | Shimada, Hideki (Kyushu University) | Hamanaka, Akihiro (Kyushu University) | Sasaoka, Takashi (Kyushu University) | Wahyudi, Sugeng (Kyushu University) | Yamasaki, Hiroto (Kyushu University) | Matsumoto, Shinji (Geological Survey of Japan) | Tun, Myo Min (Yadanabon University)
Kyaukpahto gold mine located in the Kawlin Township, Sagaing Region of Myanmar is the first open pit and the largest gold mine of Myanmar. As the gold is exploited by open-pit mining, a large amount of waste rocks are disposed at waste dumps near the mine site. The metal sulfides such as pyrite, arsenopyrite, and chalcopyrite in the waste rocks are exposed to the surface, favoring the oxidation of these metal sulfides and generating acidic water. There is a possibility of AMD generation in the open pit and at the low grade ore dump. This work focuses on assessment of the potential acid-forming waste rocks and characterization of these waste rocks in Kyaukpahto gold mine. Waste rocks and water samples were taken from the open pit, low grade ore dump, and waste dumps and subjected to various tests and analyses such as NAG test, Paste pH test, Paste EC test, ANC test, XRF, XRD, and ICP-MS analyses. Based on the results of the chemical tests and analyses, waste rock samples collected from open pit and low grade ore dump are identified as PAF rocks which particularly concerned with the potential generation of acidic mine water. Two-step batch leaching test indicated that low pH value (pH 4) and elution of metal ions such as As, Al, Fe, Cu, Zn, and SO42− were observed with the high concentration from the samples. Elution of As is higher than other metal ions and this elution process will take place over a longer period than other metal ions. Thus, it is very critical to take appropriate measures against generation of AMD, such as controls on sulfides oxidation, and reduction of metals elution.
Acid mine drainage (AMD) which is also known as acid rock drainage (ARD), causes environmental problems that affect many countries with historic or current mining activities. AMD is resulted from the exposure of sulfide ores and minerals to water and oxygen. When the ore is exposed to generate AMD, sulfate and heavy metals such as iron, copper, lead, nickel, manganese, cadmium, aluminium and zinc are also released to contaminate into that water (Moodley et al., 2017). Acidic, metals-rich waters may also form in spoil heaps, waste rocks and mine tailings, essentially by the same biologically reactions as in mine adits, shafts, pit-walls and pit-floors. Due to the more disaggregated (and more concentrated, in the case of tailings) nature of the acid-generating minerals in these waste materials, AMD that flows from them may be more aggressive than that discharges from the mine itself. Another important consideration is that it poses the potential long-term pollution problem as the production of AMD may continue for several years after mines was closed and tailing dams was decommissioned. (Johnson & Hallberg, 2005). The most common acid-generating sulfide minerals are enlisted as pyrite/marcasite (FeS2), pyrrhotite (FeS), chalcopyrite (CuFeS2) and arsenopyrite (FeAsS). In general, pyrite, the most common sulfide mineral of waste rocks and typical of many oxidation processes during weathering, is oxidized in accordance with the following reactions (Sengupta, 1993):