Dr. Md. Rafiqul Islam (Rafiq) Assistant Professor Department of Petroleum & Mining Engineering Shahjalal University of Science & Technology Sylhet-3114, Bangladesh
EDUCATION • PhD in Mining (specialty in Rock Mechanics with mining geo-environment): 2009, Faculty of Engineering and Science, University of the Ryukyus, Japan • M. Sc (Structural Geology & Global Tectonics): 2006, Department of Physics & Earth Sciences, University of the Ryukyus, Japan • M. Sc (Engineering Geology): 1995, Department of Geology & Mining, University of Rajshahi, Bangladesh • B.Sc (Hons.): 1994, Department of Geology & Mining, University of Rajshahi, Bangladesh
WORKING EXPERIENCES: • 2004-2009: Academic & industrial (mining) researches with numerical modeling/simulation based on Boundary Element Method (BEM), and Finite Element Method (FEM) • 2001-2004: Assistant Mine Geologist, Barapukuria Coal Mining Development Project, Bangladesh.
TRAININGS: • 2011 (May 23-27): 'Sustainable Operation of Seismographic Network and Earthquake Studies in Bangladesh'. Department of Geology, University of Dhaka, Sponsored by the United States Agency for International Development (USAID), the United States National Science Foundation (NSF), and Columbia University, New York, USA • 2004 (April–October): "Underground Coal Mining in Bangladesh with special reference to Barapukuria Coal Mine" under China University of Mining & Technology (CUMT). • 2001(October)–2002(February): "Coal Mining Geology & Computer Modeling" under International Mining Consultant (IMC) Group, United Kingdom.
AWARD: • 2009: President's Honorary Award, University of the Ryukyus, Japan
SCHOLARSHIPS: • 2006-2009: Scholarship of Japanese Government (Monbukagakusho) • 2004-2006: Scholarship of Japanese Government (Monbukagakusho) • 1994-1995: Scholarship/grant of Faculty of Life & Earth Science, University of Rajshahi, Bangladesh • 1986-1987: Scholarship of Haji Mohammed Mohshin's Fund, Rajshahi Education Board, Bangladesh
RESEARCH INTERESTS: • 2D & 3D Boundary Element Method (BEM) modeling of mining excavation, • Geological & Hydrogeological impacts of underground and open pit mining, • Analysis of mining-induced fault reactivation, • Opencast mining and its impact on environment, • Coal Bed Methane (CBM) Resource, • Underground Coal Gasification (UCG) technology • Seam gas emission analysis of underground mining, • Stress state around underground mining roadway with water inflow, • Geochemical analysis of dyke, coal, and coal fly ash, • 2D & 3D Finite Element Method (FEM) simulation of the Earth's tectonic structures, like faults, and subduction zones, • Engineering Geology, • Urban Geology, and • Geo-environmental hazards assessments of ungerground and open pit mining.
PROFESSIONAL MEMBERSHIP: • American Association of Petroleum Geologist (AAPG) • American Geophysical Union (AGU) • The Geological Society of America (GSA) • World Coal Institute (WCI) • Bangladesh Geological Society (BGS)
PEER REVIEWER: • International Journal of Coal Geology, ELSEVIER • Journal of Mountain Science, SPRINGER • Journal of Geology and Mining Research (JGMR)
Abstract: In this paper, deformation and stress characteristics in the upper crust of the fold-and-thrust belt in the Colombian Eastern Cordillera were investigated by numerical analysis. The structural trend of Colombian Eastern Cordillera has long been considered a possible example of a true contraction orogen. Here we examine the issue of the convergent displacement along an elastic structural body that controls present-day deformation in this Cordillera. Modeling results are presented in terms of three parameters: (1) distributions, orientations, and magnitudes of principal stresses; (2) maximum shear stress (Taumax ) contour; and (3) proximity to failure of elements within faults. Mohr-Coulomb failure criteria with bulk rock properties are applied to analyze the faults. The model shows extensional stresses in the crust at shallow crustal levels (from surface to about 6 km) despite overall contraction, and contraction at depth is confirmed. Measurement results indicate that, for homogeneous crustal thickening, extensional stresses are concentrated in the Servita half-gaben and Bucaramanga fault systems, where the vertical thrust faults and thickening processes are located. Our two-dimensional (2D) modeling results emphasize that extensional stresses are still active along the vertical to sub-vertical fault system in the fold-and-thrust belt of the Colombian Eastern Cordillera.
Abstract: A 2D finite element (FE) model incorporating elastic mechanical properties is used in this study to examine the stress field within the fold-and-thrust belt of the Patagonian orocline of the southernmost Andes. We focused here on the extensional strain regime across the southernmost Andes, although the area is located within the contractional orogenic belt of the southernmost South American plate. The calculated results show extension in the crust at shallow crustal level (from surface to 7 km depth), in spite of overall contraction and contraction at depth, is confirmed. Mohr-Coulomb failure criterion with bulk rock properties were applied to analyse faults. The stress field at any point of the model was assumed to be comprised of gravitational and tectonic components. The tectonic component is assumed to act entirely in the horizontal plane in the far-field and at the modelâs southern boundary. The extensional deformation was distributed in and around vertical fault systems. Modeling results are presented in terms of two parameters, (1) distributions, orientations, and magnitudes of principal stresses (Ï1 and Ï3), (2) failure of the elements within the model layers. Results show that failures are concentrated within all major basement faults. Results of failure of elements within layers 4, and 6, show good consistency with most of the basement thrust faults developed within the Patagonian orocline.
Abstract: With an area of 5.16 km2, the Barapukuria coal deposit is one of the five largest Gondwana coal basins in Bangladesh, and is located in the north west of the country close to the towns of Dinajpur and Saidpur. The existence of the basin was initially indicated by a negative gravity anomaly in oil and gas exploration. Exploration for the deposit was commenced by the Geological Survey of Bangladesh (GSB), with seven surface boreholes that confirmed the existence of a significant coal deposit.
The deposit occurs as an asymmetrical synclinal structure with an axis striking approximately N-S. The deposit is limited to the east by a large normal fault which has displaced Archaean metamorphics against the Gondwana sediments.
The coal-bearing sediments are comprised of Gondwana Permian age, sandstones, siltstones, subordinate carbonaceous shales, and six correlated coal seams. The Gondwana sediments are unconformably overlain by Tertiary and Quaternary deposits, against which the coal seams are successively subcropped to the west.
Within the structural limits of the basin, approximately 377 Mt coal in-situ has been quantified in the six coal seams that range in depth from 118 to 518 m below surface. Due to the synclinal nature of the deposit, the upper coal seams, designated I to V, occur over diminishing areal extent with decreasing depth. The principal seam of interest is the lowermost Seam VI, with a variable thickness across the deposit from 22 m in the northern part of the deposit to more than 42 m in the southern and eastern areas.
Development of the Barapukuria Mine, the countryâs first coal mine, commenced in 1996 with the construction of two vertical shafts. Coal production from Seam VI began in 2005 and continues at the present time.
Seam VI coal is high volatile B bituminous rank. About 34 Mt of coal has been estimated as recoverable resources, utilising descensional multi-slice longwall mining.
The mine design and development have been severely constrained by adverse seam gradients and the presence of the overlying water-bearing Tertiary Dupi Tila sediments. The potential of coal bed methane extraction has been investigated as an alternative to underground mining. The study considers the Barapukuria deposit in terms of its geological structure, geothermal gradient, and the rank, porosity and permeability of the coal seams as determined by several phases of exploration of the area.
The methane content of the bituminous coal at Barapukuria varies within the range 6.51-12.68 m3/t, representing a potential resource of more than 5 Gm3 of gas.
Abstract: This paper deals with the geochemistry and techno-environmental issues related to mining and uses of the Barapukuria coal. It attempts to provide guidance for the mechanical and electrical engineers for designing more efficient boilers, environmental scientists to make plans towards reducing pollution.
Maceral analyses indicate that Barapukuria coal is enriched in inertinite and has maximum strength and stability for producing coking coal. Higher content of inertinite implies potential dust hazards during mining operation. Further, high content of silicon and alumina in the coal means grater possibility of generating reflective surface layers of ash on the boiler during it operation. The low sulphur content of the Barapukuria coal is considered favourable for coking behaviour and implies low acid rain hazard during ignition. Minor amount of chlorine in the coal may cause boiler corrosion and fouling of very low intensity. Owing to the presence of numerous calcareous bands in the coal seam, new minerals may form through coal combustion.
Abstract: The present paper deals with the geologic factors relating to water inrush hazard which affect the development of the Barapukuria coal mine. The Barapukuria coal basin is an intracratonic half-graben basin criss-crossed by normal extensional faults. The coal bearing Permian Barapukuria Formation of Gondwana Group forms a plunging syncline that sub-crops below the Plio-Pleistocene Dupi Tila Formation. Two major faults of extensional character, Fa and Fb, are major controlling factors for water inrush prone nature of the coal field. The groundwater from the overlying Upper Dupi Tila (UDT) aquifer frequently enters into the coal-bearing Barapukuria Formation through diverse faults and joints and often flood the mine tunnels. Although dewatering has been practiced to mitigate water inrush hazard, over inflow rate in pre-mining juncture of coal face implies that the coal mine may suffer from severe water inrush where large-scale cavity are generated during coal extraction. Moreover, shallow-focus (<33 km) earthquakes close to the study area may induce water inrush if the aforesaid structures are rifted due to seismic activity.
The frequent occurrence of faults and fissures within the Gondwana rocks and their connection to the overlying Upper Dupi Tila aquifer have made the mine vulnerable to water inrush hazard.
Abstract: The Phulbari coal deposit is one of the largest coal reserves in NW Bangladesh. The country requires exploring this resource to overcome the present energy crisis. Two types of mining methods-open-pit and underground, might be considered for the exploration of coal worldwide. However, depths of the coal seam, geological, and hydrogeological circumstances of the Phulbari area vigorously disfavor open-pit mining. In this article, geology and hydrogeology of the area have been reviewed first, and then Boundary Element Method (BEM) numerical modeling has been applied to recognize in situ stress state around the proposed open pit mine of the Phulbari coal deposit. The modeling result reveals that the tensional rock failure state would be created around the proposed open-pit excavation. The major focus of the article is to explain the geological and hydrogeological problems linked to the in situ stress state of the surroundings open-pit dimension and how long distance the groundwater table would be affected because of the mine dewatering.
Abstract: The Patagonian Andes Orocline is located along the precisely active margin of southernmost South America. The area is very close to the convergence boundary of the South America and Antarctic plates. As a consequence, far field tectonic stress field is highly effective to the fold-and-thrust belt structures of the Patagonian Orocline. Only along this part of the Andes a maximum of 600 km and a minimum of 300 km shortening was calculated. This large-scale horizontal shortening indicates a fresh tectonics activity and due to its main events of compressive deformation numerous basement faults developed (Kraemer, 2003). Owing to large extent and relatively uniform tectonism along southernmost Andes, it is reasonable to suspect that the broad-scale compressional tectonic stresses induced by Antarctic plate may be useful for inferring the relative importance that cause regional faulting and crustal deformation.
One of the most important problems in the Neotectonic of the Patagonian Orcline is how the far field tectonic stress is accommodated in each major basement faults across the region. The main objective of this presentation is to emphasize a linearly plane-strain numerical model which predicts the state of stress and deformation pattern in and around major basement faults of the Patagonian Orocline. To realize the stress distribution around the basement faults a 2D finite element (FE) model incorporating elastic mechanical properties is used. The stress field at any point of the model is assumed to be comprised of gravitational and tectonic components. The tectonic component is assumed to act entirely in the horizontal plane in the far-field and at the model southern boundary. Modeling results are presented in terms four parameters, i. e. (i) distributions, orientations, and magnitudes of principal stresses (Ï1 and Ï3), (ii) displacement vector, (iii) strain distribution, and (iv) maximum shear stress (Tau-max ) contour line within the model. Calculated results show that high stresses are concentrated at the initial bottom positions of all basement faults, which are finally propagated up to two-thirds height (thickness) of the model. Results of failure of elements within layers 4, and 6, show a good consistency with most of the basement thrust faults developed within the Patagonian Orocline.
Abstract: Knowledge of understanding the mining-induced state of stress around large underground excavations at the Barapukuria mine site is a very important factor. The field of rock stress in coal basins is not uniform because rock stress is affected by some geological factors. The most common geological factors are surface topography, geological structures, especially major boundary faults, some igneous dykes, and lithological characteristics of the basin. There are other two factors causing stress in rock mass, of which one is the gravitational stress resulting from the weight of the rock themselves and the other is tectonic stress induced by the activity of the earth crust. A number of in-situ measured rock stresses show that mining-induced stress is commonly higher when it is induced by gravitational stress. In the case of Barapukuria, mining tunnels are highly affected by gravitational stress. The stress distribution has a major influence on the bulk volume permeability of the fractured and disturbed zone. The stress and fracture zones created by the extraction and caving process in the vicinity of high-production retreat longwall faces strongly influence the emission of gas into the mine workings. The changes in permeability upon longwall extraction promote the release and enhanced flow of strata gases from seams above and below the extraction horizon into the waste and mine workings. It has recently been studied that maximum percent of the methane entering a longwall district may come from adjacent seams. As a consequence of longwall coal mining, the gas permeability of the rock strata are substantially increased by the development and dilation of joints, bedding planes and mining-induced fractures. The opening of fractures due to the mining disturbance is also responsible for the release of methane gas adsorbed within adjacent coal seams by increasing the exposed surface area of the coal. The zone of newly caved waste immediately behind the supports forms a region of relatively low stress. This low loading allows for a penetration of the ventilation air from the face travel-way into the caved waste. This ventilation air flow leakage keeps the fringe of any strata gases present back into the waste and flushes the waste gases to the return gate of the face. To understand the nature of gas flow around a longwall panel, there is a need to characterize the potential role of predominant fracture flow paths to the emission of gases through a fractured/permeable region. In this case, numerical modeling techniques are required to more accurately simulate the large-scale deformation around underground excavations, which define the potential flow paths of strata gases. In the present century, the most useful way to encourage profound conceptual understanding of the stress field is through the investigation of computer programming based numerical modeling methods. In this study, first we used a numerical âBoundary Finite Element Methodâ to realize the state of stress around the 1110 Belt Gate tunnel, and second, we emphasized on surrounding geologic structures which show the potential implications for the occurrence of gas emission. The modeling provide information on: (i) the presence of numerous fractures/deformation within coal strata that act as gas pathways, (ii) the horizons within the roof (about 7-15m thick) and floor (about 22m) of coal seam VI which were potential gas sources, and (iii) on the changing of height of roof caving of the Igneous Dyke that affects the increased strata stress condition to the roof.
Abstract: Coal deposits are one of the most important energy resources in Bangladesh and because of countryâs limited natural gas resources coal production is essential for the economic development of the country. In near future, Bangladesh desires to continue to rely on coal from the discovered coal basins including Barapukuria, Phulbari, Dighipara, Khalaspir, Nawabgonj, Dangapara etc in the northwest part of the country for covering utmost percent of its energy. Conversely, the first coal mining operation from the Barapukuria Coal Basin, one of the foremost coal fields in the northwest Bangladesh, is susceptible by a major complexity such as occurrence of gas emission from1110working panel. Barapukuria coal basin consists of a self-contained half-faulted graben-controlled sedimentary basin of Gondwana (Permian) age resting unconformably on an ancient denuded Archaean (Precambrian) surface â the Basement Complex. Sedimentation of this relatively thick sequence was probably assisted by subsidence occurring along the down-thrown (western) side of a major North-South fault in the Archaean basement â the âEastern Boundary Faultâ. The general tectonic structure of the coal basin is an asymmetrical syncline trending along NN-W and dislocated by abundant faults (Fig.1). Barapukuria coal deposits, multi-layered with high thickness (36m) of mineable coal seam VI, complicated tectonic structures including 37 major faults, soaring intensity of fractures (7-10 per meter), joints (2-3 per meter), recurrent detected and undetected bedding faults (throw 1-3m) within and above coal seam as well as existence of an igneous dyke, imply high gas emission tendency and outburst-prone zones. From physical analyses it was observed that the coal is extremely brittle and granular with low specific gravity, vitreous to sub-vitreous luster. Deficiency of ductile coal laminations inside the strata at roof and floor of the 1110 working panel indicate high tendency of fractures propagation by mining activity and large-scale deformation especially caving of roof around underground excavations, which define the potential flow paths of strata gases through a fractured/permeable region. Outsized thickness of coal (ranges from 7m to 15m) rest over the roof and more than 22m lay down on the floor of 1110 panel acts as a gas bearing pathway due to relaxation of strata connecting to insufficient ventilation. From, mechanical characteristics of coal it was found that Youngâs Modulus ranges from 3201 MN/m2 to 3239 MN/m2 with a Poisonâs ratio of 0.1919 to 0.2705 specify a low degree of elasticity with a tendency for caving to occur. This type of caving, as formed in 1110 Track Gate and Belt Gate roadway throughout crossing over an igneous Dyke (Fig.2), act as a gas generating chamber. A large roof fall occurred and thousands tones of overburden rocks and coal partings associated with minor quantity of water were released from the roof and created an undetectable volume of caving at position 271.5 to 274.00m in the 1110 Belt Gate. Our rationalization is that this immeasurable size of caving acts as gas generating chamber under insufficient ventilation air. Initially slow oxidation, in existence of water, occurred on exposures at low temperature which cause evolution of heat, gasses and moisture. As a result, the temperature of the coal raised, the rate of coal oxidation increased and outsized quantity of methane (CH4), CO2 and CO formed and influx at 1110 panel occurred through relaxed, brittle, faulted and fractured seam rest over the roof and floor under insufficient ventilation and low atmospheric pressure conditions. Considering aforementioned circumstances, it may be concluded that tectonic structures particularly 37 detected faults with numerous undetected faults, joints and fractures in side of coal seam VI, geotechnical factors and insufficient mine ventilation system directly influenced for the occurrences of gas emission at 1110 working panel of Barapukuria Coal Mine. Finally, 2D or 3D Finite Element numerical simulation of underground caving and fractures that act a gas chamber and flow paths respectively due to the mining disturbance is required for controlling the occurrence of gas emission at 1110 working panel of Barapukuria Coal Mine.
Abstract: Rajshahi is one of the fast expanding cities in Bangladesh where population is increasing terribly day by day. Urban population of the city was 56885 in 1961, 294056 in 1991 and more than 699700 in 2001. Rapid intensifying rate of population creating tremendous pressure on urban land and many ground-breaking areas in and around of the city are going to be residential to resolve habitation problems for city dwellers. But, in most of the vicinity, development is going on excluding careful investigation of subsoil and geo-environmental hazardous impacts. One of the most important factors that have to be measured in urban development is the suitability of subsoil and rocks for foundation. Additionally, information on groundwater conditions will be required for the design of foundation. Haphazard development of the regions for residential and industrial purposes is no longer socially acceptable, since, without careful investigation and planning, serious environmental problems, which can be avoided, might arise in future. Considering aforementioned state of affairs, in this paper, initially a comprehensive study on geotechnical properties of subsoil, as received from assorted engineering boreholes (up to 15m in depth) at dissimilar locations inside of Rajshahi City, has been carried out and a profile typeâs zonation map has been prepared based on prime subsoil characteristics. Afterward, a geological map, based on remote sensing (SPOT) image, has been prepared to ascertain a relationship among visual interpretation of outer surface, geotechnical properties of subsoil and different geo-environmental hazardous impacts to provide better outlook for prospective urbanization of Rajshahi City. Finally, geotechnical, geological, and geo-environmental aspects imply that the areas towards the east, northeast and north from the present city center are good for prospect urbanization.
Abstract: Rajshahi, one of the fast expanding cities in Bangladesh, is located at the northwestern part of the country and stands on the northern floodplain of the river Ganges. This study focused the area of suitability for urbanization of Rajshahi city and its adjoining areas considering engineering geological characteristics of subsoil. Geological and geo-environmental aspects have been considered as another two important basis to evaluate this research. Over all geomorphic features of the area have been divided into seven geologic units, which have been grouped into seven engineering geologic units based on their physical properties and geo-technical behaviors. Subsoil characteristics of the study area are mainly clay dominant and cohesive. Consistency limits, low shear strength, low SPT (Standard Penetration Test) resistance, moderate to high co-efficient of compressibility and low to moderate gross bearing capacity indicate that the near surface sediments are medium suitable for the construction of shallow foundations. Geo-environmental hazards, like- river-bank erosion, dust storm, flooding, water logging, expansive soils and potential land subsidence etc. hampering socio-economic development, have also been considered to assess the suitability for urbanization. Finally, it has been suggested that the area towards the east, northeast and north from the present city center are found suitable for future urbanization and planning.
Abstract: According to World Coal Institute (WCI), coal is the major fuel used for generating electricity worldwide. Coal provides 26% of global primary energy needs and generates 41% of the world's electricity. Bangladesh is blessed with natural energy resources, especially coals in the northwest region and gas in eastern fold-and-thrust belt region. Natural gas is currently the major indigenous nonrenewable energy resource, which is going to be ended by 2020 if new gas field is not discovered in Bangladesh. The top five Gondwana coal basins of the country where the total in situ reserves over 4500 Mt coals are Jamajgonj, Khalaspir, Phulbari, Barapukuria, and Dighipara. Bangladesh desires to produce coal from the Gondwana coal deposits due to gradually demands of electricity and to safeguard the energy crises in 21th century. Barapukuria is the first and only coal mine in the country.
This dissertation connects the Boundary Element Method (BEM) and Finite Element Method (EFM) with its practical applications to recognize the some mining related geo-environmental hazards associated with the Gondwana Barapukuria Coal Basin of northwest Bangladesh. Several geo-environmental hazards, such as- (i) ground movement and water inrush/inflow, (ii) seam gas outburst (iii) mining-induced fault reactivation, and (iv) rock burst with major roof fall, have been recognized during mining operation which generate adverse impacts on the exploration and underground multi-slice longwall mining in the Barapukuria coal deposits. A summary and problems regarding the present research have been emphasized in the 1st chapter. In the 2nd chapter of this thesis, I discussed general geologic understanding of Bangladesh. In the 3rd chapter, geological, hydrogeological, geotechnical, and tectonic setting of the study area have been focused.
Chapter 4th highlights ground movement and water inrush/inflow hazards into the mine. This chapter deals with current coal mining operations under a mega-aquifer in NW Bangladesh, and presents a case study of underground mining in Barapukuria. The study uses numerical analyses to evaluate stress redistribution, strata failure, and water inflow enhancements that result from these coal extraction operations. A total of three models (A, B, and C) are presented in this study. Two-dimensional numerical modeling was performed to analyze the deformation and failure behavior of rock elements for two different models (A and B). For model A, we used an elastic finite element software package considering a Mohr-Coulomb failure criterion. For model B, we used boundary element method (BEM). The first two models were applied to determine the stress patterns. Model A provides the tectonic stress pattern of the basin, whereas model B represents the mining-induced stress field. The third model is a schematic model.
The results of model A show that tensional failure of rock elements is concentrated in the Gondwana coal sequences as well as within the Eastern Boundary Fault (EBF) and its surroundings. Failure occurs in the middle to lower part of the model, and the magnitude of tensional stress in the shallow part is much greater than in the deeper part. Contours of ï´max magnitudes are attributed to up-bending of the overburden, which would create numerous upward propagating fissures/fractures. The results of model B show that fracture propagation would be about 240 m upward for single-slice (height 3 m) mining extraction. From the contours of mean stress magnitudes, it is observed that the high range of fracture propagation increased upward for multi-slice extraction of coal. It is apparent from the fracture heights that large amounts of caving would occur towards the roof due to the multi-slice extraction of coal, and finally would be linked with the water-bearing Dupi Tila Formation. If this is happened, it would ultimately cause a major water inflow hazard in the mine.
Seam gas outburst related geo-hazards have been focused in the 5th chapter. In this case study, I use two-dimensional Boundary Element Method (BEM) numerical modeling to analyze the deformation and failure behavior of a coal seam and to understand the nature of gas flow into a roadway entering the Barapukuria coal mine in Bangladesh. The Barapukuria basin contains Permian-aged Gondwana coals with high volatile B bituminous rank. Three models (A, B, and C) are presented here. Model A assumes horseshoe-shaped geometry, model B assumes trapezoid-shaped geometry, and model C assumes horseshoe-shaped geometry coupled with a roof fall-induced cave generated by the break-up of rock materials along the vertical dimension of an igneous dyke. The simulation results show that there is little difference in strata deformation between models A and B. In model A, there is no horizontal tensional stress and the overall horizontal stress patterns are compressive, while the distribution and magnitude of vertical stress show higher tensional stresses on the immediate rib sides and floor. In model B, both horizontal and vertical stress distributions indicate low to medium tensional stresses on the immediate roof, floor, and rib sides, but compressive stresses are prominent toward the interior of the coal seam. Deformation vectors indicate that failure extends laterally to about 7.5 m around the excavation geometry.
On the contrary, for model C, the distributions and magnitudes of horizontal and vertical stress show higher tensional stresses in both rib sides of the roof fall zone. The deformation around the dyke-induced perturbation zone affects a large volume of coal. The deformation vectors with high magnitudes are nearly horizontal and propagate laterally up to 30 m; whereas, lowâmagnitude deformation vectors extend about 25 m toward the roof and 20 m toward the floor. The vertical tensional displacement, which is concentrated in the floor and the left and right hand sides of the roof, propagates about 30 m on both sides and about 22 m in the floor. From these simulation results, it is thought that the extension of the dyke-induced perturbation zone toward the roof, floor, and rib sides of the entry roadway initially creates small tensional cracks that gradually grow into large-scale tensional features. These features could also be responsible for high concentrations of gas, which are emitted into the mine from fractured coals due to insufficient mine ventilation and low atmospheric pressure.
Mining-induced fault reactivation and its impacts on main conveyor belt roadway have been discussed in the 6th chapter. In this chapter, I use same methodology as previously mentioned and the study paper investigates the mining-induced reactivation of faults associated with the main Conveyor Belt Roadway (CBR) and safety of the mine. The stress characteristics and deformation around the faults were investigated by boundary element method (BEM) numerical modeling. The model consists of a simple geometry with two faults (Fb and Fb1) near the CBR and the surrounding rock strata. A Mohr-Coulomb failure criterion with bulk rock properties is applied to analyze the stability and safety around the fault zones, as well as for the entire mining operation. The simulation results illustrate that the mining-induced redistribution of stresses causes significant deformation within and around the two faults. The horizontal and vertical stresses influence the faults, and higher stresses are concentrated near the ends of the two faults. Higher vertical tensional stress is prominent at the upper end of fault Fb. High deviatoric stress values that concentrated at the ends of faults Fb and Fb1 indicate the tendency towards block failure around the fault zones. The deviatoric stress patterns imply that the reinforcement strength to support the roof of the roadway should be greater than 55 MPa along the fault core zone, and should be more than 20 MPa adjacent to the damage zone of the fault. Failure trajectories that extend towards the roof and left side of fault Fb indicate that mining-induced reactivation of faults is not sufficient to generate water inflow into the mine. However, if movement of strata occurs along the fault planes due to regional earthquakes, and if the faults intersect the overlying Lower Dupi Tila aquiclude, then liquefaction could occur along the fault zones and enhance water inflow into the mine. The study also reveals that the hydraulic gradient and the general direction of groundwater flow are almost at right angles with the trends of faults Fb and Fb1, which could act as barriers to groundwater flow into the mines.
In the 7th chapter, I preferred to rethink about coal bed methane (CBM) resource potential rather than underground mining of Barapukuria coal basin. The coal-bearing sediments are comprised of Gondwana Permian-age sandstones, siltstones, subordinate carbonaceous shales, and six correlated coal seams. Within the structural limits of the basin, approximately 377 Mt coal in-situ has been quantified in the six coal seams that range in depth from 118 to 518 m below surface. About 34 Mt of coal has been estimated as recoverable resources, utilising descensional multi-slice longwall mining. Rest of 343 Mt coal could be used for CBM. The potential of CBM extraction has been investigated as an alternative to underground mining. The study considers the Barapukuria deposit in terms of its geological structure, geothermal gradient, and the rank, porosity and permeability of the coal seams as determined by several phases of exploration of the area. All parameters show supportive of CBM. The methane content of the bituminous coal at Barapukuria varies within the range 6.51-12.68 m3/t, representing a potential resource of more than 5 Gm3 of gas.
