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By Zhengdong Liu, Kaizhong Zhang, Zhaonan Jiang, Yuanping Cheng, Biao Hu, Qingquan Liu, Ranpeng Wang

"Major coal mining areas in eastern China have entered into the deep mining state. Gas pre-drainage, which has been successful at shallower depths, is not suitable at greater depths because of complex conditions. Coal permeability, which is closely related to the damage behavior of coal, is the most important parameter in determining gas migration and gas drainage in a coal seam. To achieve an optimal gas drainage design in a deep mining state, the damage and permeability evolutions of coal should be further studied. The progressive failure process of coal has been analyzed by conducting a series of triaxial loading and unloading tests. The development of coal fractures has been successfully quantified, and the corresponding characteristic stress points have been obtained by using Martin’s fracture model and the stress-strain curve. Coal will produce plastic deformation, and its permeability will rapidly increase when the stress level reaches damage expansion stress. INTRODUCTION Coal mine methane (CMM) is a general term for all methane released during and after mining operations. CMM is both a potentially valuable energy and a serious hazard in active coal mines. Degassing coal seams is important for mitigating this hazard and results in the beneficial recovery of a cleanburning, low-carbon fuel resource (Karacan, Ruiz, Cotè, and Phipps, 2011). The permeability of coal is a key parameter in determining CMM production, coalbed methane (CBM) production, CO2-enhanced coalbed methane (CO2-ECBM) production, and CO2 storage in coal seam reservoirs (Connell, Lu, and Pan, 2010; Chen et al., 2011; Perera, Ranjith, and Choi, 2013). Significant research has been condcuted to the study of the evolution of coal permeability. These studies revealed that coal permeability evolution is controlled by the competing influences of effective stress and sorption-induced coal deformation. Chen et al. (2011) investigated the influence of an effective stress coefficient and sorption-induced strain on the evolution of coal permeability. Robertson and his team (Robertson, 2005; Robertson and Christiansen, 2005) measured sorption-induced matrix strain and permeability changes with regard to CO2, CH4, and N2. They found that the compressibility is not constant in a natural coal sample. Karacan (2007) conducted a series of experimental tests to study the swelling-induced volumetric strains internal to a stressed coal associated with CO2 sorption. Liu et al. (2016) investigated the effects of matrix swelling area propagation on the permeability evolution by using both natural and reconstituted samples. Many coal permeability models have been developed to describe the permeability evolution under uniaxial loading, biaxial strain, hydrostatic confining pressure, triaxial strain, and triaxial stress. Recently, some analytical permeability models have been developed to describe the anisotropic permeability behavior (Palmer, 2009; Pan and Connell, 2011; Robertson and Christiansen, 2005; Wang, Zang, Wang, and Zhou, 2014; Chen, Pan, Liu, and Connell, 2012)."

Jan 1, 2017

By Ed Van Eeckhout

As part of a U.S. Bureau of Mines-sponsored project on the utilization of "stiff' backflll to minimize potential rock burst hazards, a finite element study was undertaken to predict stresses and displacements around a stope mined up from the 5400 level of the Sunshine mine, Kellogg, Idaho. This stope was to be backfilled using a high-modulus fill. In preparation for that configuration, certain instrumentation was installed near the 5400 level to monitor stress changes. Due to untenable economics, only 2 cuts of the stope were ever made. This paper presents the results of the instrument readings taken during the first cut and compares them with the numerical predictions, as well as presents the modeling results of closure and fill stresses in the stope if it had been mined.

Jan 1, 1984

By Zbigniew Lubosik, Andrzej Walentek, Stanislaw Prusek, Aleksander Wrana

"The Carboniferous coal measures, mined across Europe including the major European underground coal mining countries of Poland, UK, Germany, and Czech Republic, suffer from increasing extraction depth. This results in major geomechanics problems associated with ground control and support design.With production being concentrated into ever fewer high performance longwalls, located at greater and greater depth, pressure to ensure the roadways’ functionality (required dimensions) continues to increase. Mining in deeper and more highly stressed mining environments creates several problems. The high stress and deterioration in geological and mining conditions in many cases causes problems with gateroads maintenance (due to excess convergence). That leads to costly production gaps, longwall slowing, transport problems, an increase in the methane hazard and in the general health and safety of the workforce, and deterioration in climatic conditions with major economic risk associated with interruption of the revenue stream. Time—and thus production—delays due to maintenance often result from insufficient geological and geotechnical data acquisition and misinterpretation combined with inadequate support for the type of rock mass.longwall face on the gateroad stability (described by the gateroad convergence, support load, and shape and height of the fractured zone around the longwall gateroad) are presented. The investigations were carried out in the longwall panel with roof caving located at the great depth, in conditions of the Upper Silesian Coal Basin in Poland.The measurement results showed that the gateroad fractures in roof strata began to occur at the distance of about 1000 m ahead of the face. Additionally, the load on support and gateroad convergence increased as the longwall face got closer.It is very important for coal mining research institutes and mine operators to investigate and develop practical solutions and apply innovative support technologies at a great depth (particularly for reinforcement and stabilization of roadways and other openings).Underground measurements of stability conditions around the gateroad is of great importance to mining practice, especially in planning and designing supports for longwall gateroads.The influence of the front abutment pressure results in an increase of support load, gateroad convergence, and shape of fractured rock zone."

Jan 1, 2015

By Jinwang Zhang, Zhaohui Wang, Jiachen Wang

"Thick coal seams (seam height larger than 3.5 m) account for a large portion of the proven coal reserves of China, and underground thick coal seam mining provides about 50% of the Chinese annual coal production. Such seams are mainly mined using the longwall top-coal caving (LTCC) method. For safe and successful mining, a number of analyses on the stability of surrounding rocks in the LTCC face area have been extensively performed, and certain research achievements have been made. This paper introduces the main findings on rock pressure occurrence in the LTCC face during the last few decades and presents face and roof stability control techniques. INTRODUCTIONUnderground thick coal seams in China provide 1.8 billion tons of coal every year, which accounts for approximately 50% of the total Chinese annual coal production and 25% of the world, indicating that thick coal seams stand an important position in Chinese coal mining industry (Wang, 2005). Before the 1980s, thick coal seams were mined mainly by using the multiple-slice mining method. With the improvement of mining techniques and equipment in last two decades, longwall top-coal caving (LTCC) and high-seam, single-cut longwall are employed for thick coal seam extraction, offering advantages over multiple slicing from entry excavation and production perspectives (Wang, 2013).. The primary author of this paper introduced the most popular thick coal seam mining methods in China at the 30th ICGCM (Wang, 2015). This paper presents the stability of surrounding rocks in face area and ground control techniques for mining thick coal seams. For traditional longwall faces (seam height less than 3.5 m), the well-developed VoussoirVoussoir beam theory has been successfully used to analyze the movement of overlaying strata, which indicates that ground control techniques have become mature for this mining system. In such faces, the four-leg support with loading capacity of 4000–8000 kN is considered adequate for safe and successful mining. These faces normally have an annual yield of 1–2 million tons (Wang, 2007). For thick coal seams, however, the traditional support becomes inadequate and the ground control problem change to be more difficult and complex. Thus, development of large-scale mining equipment and ground control techniques for enlarged mined-out space and entries have been recognized as the most basic technical problems in mining thick coal seams."

Jan 1, 2017

By John C. Stankus

From research started six years ago, a new design criteria has been developed for mine roof bolt systems This design criteria precisely and quantitatively determines parameters such as bolt length, installed tension, and spacing that will produce the Optimum Beaming Effect (OBE) OBE, a new roof control term, is defined as the roof beam that has no separation above and within the bolted range with the shortest bolt passible Utilization of this design criteria has shown that in many cases shorter roof bolts with higher installed tension can produce a much stronger beaming effect (Stankus, 1995) This paper will first present a brief deception of how the design criteria was formulated From there, actual case studies where the design criteria was utilized will be discussed In conclusion, current and future research efforts will be presented

Jan 1, 1997

By Phil R. Ames, Anil K. Ray, Murali M. Gadde, John A. Rusnak

"Many factors can be responsible for coal mine roof falls including, mining geometry, stress conditions and local geology. In the Illinois Basin coal mines, roof instability is commonly attributed to the low strength of the immediate roof, which is also moisture sensitive. Recently, in order to understand the mechanisms of roof instability, numerical modeling has often been the preferred ground control analysis tool. Since roof materials can exhibit significant spatial variability, such modeling results may not represent every section of the mine. At the same time, it is not feasible to carry out numerical modeling for the full range of geological and mining conditions possible at a mine. Operationally, it is more convenient and highly practical to have a simple map that depicts the expected roof conditions, determined through either complex numerical models or simple empirical analysis throughout the reserve area. In this paper, a case history is presented that shows how a combination of simple empirical analyses of geologic data and past ground control experiences at a mine can be synthesized into a roof stability map, which can then be used to forecast future ground conditions. The usefulness of such a roof stability map will be examined in terms of the predicted and actual ground conditions encountered over a period of more than a year after the map was created.INTRODUCTIONA roof fall, which can result in fatalities and lost work time, is considered to be one of the most severe ground control hazards in underground coal mines. In general, there are many factors responsible for roof falls, including mining geometry, stress conditions and local geology. In the Illinois Basin, roof falls are commonly attributed to the weak nature of immediate roof rocks, and some superficial falls may be initiated due to moisture sensitivity. Some unstable areas also occur when the immediate roof is highly laminated.Numerical modeling is a useful tool used to understand the mechanism of a roof fall by incorporating site-specific parameters. In the past, numerical modeling has been used to explain the mechanism of roof falls as well as simulate· roof falls and cutter behavior, but such work had been strictly site-specific (Gadde and Peng, 2005; Ray, 2009). Because of the restrictions imposed by the input parameters, numerical modeling results cannot represent the entire mine. In the real world, mining conditions vary from place to place, and even in a single panel, modeling results valid at one site may not apply at another nearby site. At the same time, due to the lack of input data pertaining to rock characteristics and in-situ stress variations, it is not practical to carry out numerical modeling for each local area of the entire mine site. In addition to these difficulties, mine operators prefer simple tools to understand the ground conditions at their mine sites. One simple and commonsense based tool is the roof stability map. A stability map not only synthesizes the geologic and stress analysis data empirically, but it can also be used to predict future ground control issues at that mine. Because of this practical appeal, stability maps are more likely to gain mine operators' acceptance and be used in their planning operations. In this paper, a case study is presented on the development of a 'Roof Stability Map' that was principally used for roof fall prediction for a mine in the Illinois Basin."

Jan 1, 2010

By Ximeng Li

The entries that are subjected to dynamic pressure are much more difficult to maintain due to repeated disturbance. A case study of an entry stress distribution was performed using the FLAC3D program. By analyzing the distribution of stress field around the entries, this paper provides guidelines for entry support design in the lower (#16) seam subjected to the repeated disturbance from longwall mining in the immediate overlying (#17) seam, 72ft (22 m) above. The results showed that there was stress superposition inside the barrier pillar in the lower seam, 15ft (5m) to 45ft (15m) deep, during development. The influence zone of the front abutment pressure in the upper (#16) seam was about 100ft (30m) outby the faceline. The stress-relieved zone was from 0 to 100ft (30m) inby the face. The area further inby the face (i.e., 230 ft (70 m) inby the face) was within the gob compaction zone. Along the face advancing direction, the affected zones of the entries in the lower (#17) seam that were subjected to the dynamic pressure from longwall mining of the immediate overlying seam could be divided into four stages: pillar development stress stage, front abutment pressure stage, unstable gob stage, and stable gob stage. Those entries within an area from 100ft (30m) outby to 100ft (30m) to 230ft (70m) inby the faceline should be reinforced with special supports. The numerical modelling matched the monitoring results well.

Jan 1, 2013

By Gennaro G. Marino

As part of the development of a shopping center in West Virginia, a significant bench had to be cut into a mountainside that was over 700 ft. high. As a result, a steeply stepped, over 400-ft.- high wall was created. The high wall exposed old abandoned room-and-pillar coal workings at the toe of the cut. Because of exposure to the elements, the mine openings began to severely deteriorate with significant potential of undermining of the rock cut face and causing a large rock fall(s). Exacerbating this wall problem was a set of fairly planar sub-parallel and sub-vertical joints creating, in essence, thin rock slabs. Also present were stress relief fractures that were observed in the exposed pillars. Given the proximity of the project building to this high rock face, mitigation of the rock fall potential was deemed necessary. In order to prevent continued damage and deterioration of these exposed mine entries, the rubblized openings were filled with bulkhead grout and pressure injected with grout. The total amount of grout installed in these openings was about 3,945 CY. Also, a rock drape was attached to the entire face to mitigate small rock falls from natural causes. There also existed another level of mining below the ground surface and under an existing building at a depth of about 160 ft. Under a portion of the building, the pillars in these old works were second mined, and the building seemed to have been already affected by limited subsidence above this area. Also, calculated pillar safety factors in this high extraction section of the mine were too low. Consequently, these old works were stabilized by saturation grouting. An indication of overall roof distress was the significant fracturing encountered in the bedrock overburden during the drilling of the injection holes and the volume of grout placed in these holes. The total grout installed in the high extraction section of the lower mine was about 6,660 CY. This paper describes the investigation and the grouting techniques employed at the rock cut face and under the existing building to mitigate continued damage to avoid future subsidence problems at the face and the building premises.

Jan 1, 2013

By Heather E. Lawson

Recent field data providing measured pillar loading from a deep western mine revealed that an increased load transfer distance existed compared to expected values (Larson et al., 2012). Additionally, recent work by Tulu and Heasley (2012) has shown that the abutment angle in deep longwall mines can be significantly reduced as the depth of mining increases. The load transfer distance and abutment angle are both used as parameters to estimate pillar loading in longwall design. To investigate the potential implications of these observations on pillar loading in deep longwall mines, a parametric study using ALPS loading estimation procedures was performed. A supplemental study was conducted using LaModel to further investigate pillar loading at the tailgate. The study found that the abutment angle is particularly important for panels with supercritical geometries. As panels reach a subcritical geometry with increasing depth, the primary influence of the abutment angle is reduced and matched by other factors, including load transfer distance for tailgate loading. An extended load transfer distance was shown to potentially reduce loading on pillars adjacent to the longwall as the loading is spread over a larger area. The results of these studies indicate a need for further field verification and research toward regional geologic influences on pillar loading and how these may impact ground stability.

Jan 1, 2013

By Shuren Wang, Wenbing Guo, Paul C. Hagan, Yanhai Zhao

"The overlying strata is often destroyed in large scale during shallow coal seam mining, and the sliding instability of the caved roof seriously threatens the safety of the mining field. The typical shallow coal mining in Shendong Mining Area in China was used as engineering background; the load distribution characteristics of the overlying strata were analyzed based on the monitoring data of the support resistance. Through theoretical analysis and numerical simulation, the formation and changing process of the pressure-arch in the overlying strata were studied, and the instability mechanism of the overlying strata was revealed by focusing on the accumulation and release law of the elastic energy in the pressure-arch. The results show that the continuous pressure-arch was formed when the horizontal stress exceeded the primary vertical stress of the mining field, and the elastic energy of the roof was released by the mining unloading effect. The elastic energy was accumulated in the pressure-arch, and the energy arrived the highest at the front arch foot. The accumulated energy at the arch foot was released by coal mining, and the shear zone could be formed. Therefore, the sliding of the caved zone along the shear zone induced strong roof weighting. The concentrated stress and the released energy during each mining increased with the panel advancing, and the height of the shear zone also increased. The conclusions obtained in the study are of important theoretical value to direct similar engineering practice.INTRODUCTIONThe instability of overlying strata during shallow coal mining, such as the large-scale roof falling and step-like ground subsidence, is a key problem that can restrict the safety mining in the mines (Ju and Xu, 2015). The self-bearing structure of the pressure-arch can form in the overlying strata after coal mining, and this structure can support the load of the upper strata and soil layer, so the weighting intensity of the panel is determined by the caved rock in the unloading zone under the inner boundary of the pressure-arch. A large amount of elastic energy is accumulated in the pressure-arch under the concentrated stress, and the released energy for mining is the internal cause of rock failure (Wang et al., 2017). It is an important problem to reveal the distribution characteristics of the stress and energy fields in the mine and to analyze the stability of the overlying strata during shallow coal mining based on the evolution characteristics of the pressure-arch."

Jan 1, 2018

By Yanfa Gao

Abstract In order to control and reduce ground subsidence due to coal mining, and to protect building, railway and other surface construction, a new subsidence control method is proposed. Ground subsidence is reduced by grouting bed separations in overlying strata with fine-coal ash. Engineering application tests have been performed for 5 years in Tangshan Coal Mine. Kailuan Group Corporation. China. The technology has been applied to 4 fully mechanized sublevel caving mining faces. Its effect in reducing subsidence has been significant. The technology including grouting engineering design method and ground subsidence prediction theory is introduced in detail. Keywords: overlying strata separation, multi-layer grouting, subsidence control

Jan 1, 2002

By Pinnaduwa H. S. W. Kulatilake, Biao Shu

The intact rock properties and discontinuity properties for both Devonian Rodeo Creek (DRC) and Devonian Papovich (DP) rock formations that exist in the selected open-pit mine were determined from tests conducted on rock samples. Special survey equipment, which has a total station, laser scanner and a camera, was used to perform remote fracture mapping in the research area. From remote fracture mapping data, the fracture orientation, spacing and density were calculated using more refined procedures compared to what exist in the literature. Discontinuity orientation distributions obtained through remote fracture mapping agreed very well with the results of manual fracture mapping conducted by the mining company. The GSI rock quality system and Hoek-Brown failure criteria were used to estimate the rock mass properties combining the fracture mapping results with laboratory test results of intact rock samples. Fault properties and the DRC-DP contact properties were estimated based on the laboratory discontinuity test results. A geological model was built in a 3DEC model including all the major faults, DRC-DP contact and two stages of rock excavation. The built major discontinuity system of 44 faults in 3DEC with their real orientations, locations and three-dimensional extensions were validated successfully using the fault geometry data provided by the mining company using seven cross-sections. Numerical modeling was conducted to study the effect of boundary conditions and lateral stress ratio on the stability of the considered rock slope. For the considered section of the rock slope, the displacements obtained through stress boundary conditions seemed more realistic than those obtained through zero velocity boundary conditions (on all four lateral faces). Stable deformation distributions were obtained for k0 in the range of 0.4 to 0.7. Because the studied rock mass is quite stable, it seems that an appropriate range for k0 for this rock mass is between 0.4 and 0.7. The displacements occurred between July 2011 and July 2012 due to the nearby rock mass excavation that took place during the same period; they were compared between the field monitoring results available from the mining company and the predicted numerical modeling results and a good agreement was obtained. Overall, the successful simulation of the rock excavation during a certain time period indicated the possibility of using the procedure developed in this study to investigate rock slope stability with respect to expected future rock excavations in mine planning.

Jan 1, 2015

By Peng Cao, Jimin Su, Yang Li

"Abutment pressure distribution is different when a longwall panel is passing through the abandoned gateroads in a damaged coal seam. According to the geological conditon of panel E13103 in Cuijiazhai Coal Mine in China theoretical analysis and finite element numerical simulation were used to determine the front pressure distribution characteristics when the longwall face is 70 m, 50 m, 30 m, 20 m, 10 m, and 5 m from the abandoned gateroads. The research results show that the influence range of abutment pressure is 40 m to 45 m outby the face, and the peak value of front abutment pressure is related to the distance between the face and abandoned gateroads. When the distance between the longwall face and abandoned gateroads is reduced from 50 m to 10 m, the front abutment pressure peak value kept increasing.When the distance is 10 m, it has reached the maximum. The peak value is located in 5 to 6 m outby the faceline. When the distance between the longwall face and abandoned gateroads is reduced from10 m to 5 m, the front abutment pressure sharply decreases, the intact coal yields and is even in plastic state. The peak value transfers to the other side of the abandoned gateroads. The research results provide a theoretical basis for determining the advance support distance of two gateroads in the panel and the reinforcement for face stability when the longwall face is passing through the abandoned gateroads.INTRODUCTIONFront abutment pressure is the result of rearrangement of in situ rock stress caused by the mining (removal) of the coal seam. Research on the distribution character of face abutment pressure have significant importance in confirming the width of the coal pillar and the distance of advance support in roadways (Liu et al., 2011; Liu, Jiang, and Zhu, 2015). Currently, there is a lot of research on abutment pressure characteristics of traditional longwall coal faces, thick coal seam longwall faces, isolated faces, and extra wide face abutment pressure distribution (Xie et al., 2006). However, theoretical analysis and research on the distribution law of the fully mechanized coal face to abandoned gateroads are relatively less. Abandoned roadways are often from less mechanized or room and pillar mines. Due to the existence of these roadways pre-longwall mining, the in situ stress has already been redistributed around the roadway (Liu et al., 2007). Thus, when the longwall approaches and mines through the roadway, the abutment pressure distribution behaviour has different characteristics than those of traditional solid undisturbed coal. Especially when the face approaches the abandoned roadway, the understanding of face abutment pressure distribution has significant importance to the timing of support installation (Ren and Ning, 2014). This prevents the occurrence of a roof and rib failure ahead of and on the longwall and highly efficient advance of the longwall safely and productivity. This paper analyses the E13103 face of the Cuijiazhai Mine of Wenzhou Mining Co., Ltd of Kailuan Group, as the engineering case study, and uses FLAC3D numerical simulation software to conduct numerical simulated analysis on the abutment pressure distribution mechanism of longwall coal mining face."

Jan 1, 2018

By Mingju Liu

In this research, we measured fractal characteristics of over ten typical outburst areas on different scales and related them to their outburst proneness, in attempts to provide new methods for outburst prediction. It was shown that both faults and folds follow the power law on coal basin scale, mine scale or mining district scale, whichever it is. Fractal dimensions are appropriate indices to describe geological structures quantitatively. Preliminary relationships have been established between outburst proneness and fractal dimension. Comparisons have been made among fractal characteristics and degrees of outburst proneness on all three scales. The results indicate that multi-scale assessment of outburst proneness can be made based on fractal measurements independently or supplemented by other assessment methods.

Jan 1, 2000

By Zhang Hongzhen

The fast convergence of boundary is a major problem of probability integral method, especially for the prediction of mining under thick alluvium, abandoned mine goaf, etc. To solve this problem and improve the accuracy of probability integral method, a modified model is constructed for surface movement and deformation based on theoretical analysis. In which, three weighted values i.e. 1, -1/t1, 1/t2 are set for the mining movement and deformation of three different major influence radius i.e. r1, R1, R2, respectively, then the parameters are selected as following: (1) Parameters are inversed based on the observation data, in which the subsidence factor q, deviation of inflection point s, displacement factor b are considered as generic parameters, the tangent of major influence angle tanß is modified as tanß2, that is the major influence radius r is modified as r2. (2) Inversion parameters of tangent of major influenceangle tanß or major influence radius r, based on the observation station edge data which beyond major influenc eradius distance from work-face mining boundary. The inversed tanß and r will be used as tangent of major influence angle tanß1 and major influence radius r1, respectively. (3) Other relevant parameters i.e. t1, t2, R1, R2, are calculated with the algorithm of this paper. A comparison experiment between the traditional and modified models has been conducted using the observation data from a observation station, the results show that in its central area, 58.6 percent of observation points accuracy is improved and 36.6 percent is decreased, while in its edge area, 61.5 percent is improved and 15.4 percent is decreased, totally, 68.6 percent is improved and 30 percent is decreased. Therefore, we can draw the conclusion that our modified model can improve the prediction predication accuracy, in particular, the boundary region.

Jan 1, 2014

By Pinnaduwa H. S. W. Kulatilake

To exploit an underground mine effectively and safely, it is important to have a good understanding of the geotechnical behavior of the rockmass surrounding the underground mine excavation. The aim of this study was to investigate, at the threedimensional level, the geotechnical behavior around a tunnel excavated in a metal mine in China. A three-dimensional numerical model was built by using the 3DEC software package to simulate a tunnel excavation under a high in situ stress condition and by relying on the information available on lithology, geological structures, in situ stress measurements, physical and mechanical properties of intact rock, discontinuities, and interfaces between different rocks. The authors also investigated the effect of the discontinuity network, possible intact rock and discontinuity parameter variability, representation of rock masses as discontinuum or equivalent continuum material and rock support system on the deformation, and stability around the tunnel. A very good agreement was obtained between the collected field deformation monitoring results and the results of the conducted numerical stress analyses with appropriate geomechanical property values.

Jan 1, 2013

By Wenbing Guo, Yi Tan, Erhu Bai

"It is important to study the mining technology under structures for raising the coal resources recovery ratio. Based on the geological and mining conditions, the top coal caving harmonic mining technique in thick coal seam beneath the earth dam was put forward and studied. The 5 factors such as the panel mining direction, panel size, panel location, panel mining sequence and panel advance velocity were taken into account in this technique. The dam movement and deformation were predicted after the thick coal seam mining and the effects of mining on the dam were studied. By setting up the surveying stations on the dam, the movement and deformation of the dam were observed during mining. By taking some protective measures on the dam, the top coal caving mining technique in thick coal seam beneath the earth dam was carried out successfully. The study demonstrates that harmonic mining in thick coal seam is feasible under the dam. The safety of the earth dam after mining was ensured and the coal resources recovery ratio was improved.The surface movement and deformation caused by coal mining not only influence the ecology environment in the mining area, but damage the surface structures such as buildings, railroads, highways, water bodies and damsr1-31_ The movement of strata and surface caused by mining had disturbed various aspects of industrial and agriculture productions in the mining arear41. The earth dam is a very important water retaining structures, so it must makes sure the safety of dam if mining under it. Therefore, to study the effect of mining on dam and control measures to ensure safety of mining under the dam are important factors for improving the mining recovery ratio, reliving the mining continuity, preventing or reducing damage to the dam.By means of the harmonic mining technologyrs1, theoretical analysis and field observation, the mining method under an earth dam and the mining influences were studied and analyzed in this paper. The mining of a thick coal seam under the dam was carried out safely and successfully."

Jan 1, 2016

By Liang Dong, Jinxuan Liu, Biao Qiu, Jing Chai

"The Cenozoic unconsolidated strata in the east area of China are composed of clay, sandy clay, fine sand, hardpan, etc. Numerous shafts of the coal mines in these areas have been damaged in various degrees since 1987. The main reason for this disaster is the vertical additional stress on shaft caused by the subsidence of the thick unconsolidated strata. In order to monitor the subsidence deformation of the unconsolidated strata, a sensing network system with multiplexed Fiber Bragg Grating (FBG) for monitoring settlement deformation of the unconsolidated strata in deep borehole is proposed. The field monitoring results show that, soil layers settle or expand with decrease or increase in ground water levels. The thick hardpan generates the main compressive deformation. This FBG strain monitoring method can take place of traditional ground water measuring method. This system is stable and reliable, and the monitoring results can show the subsidence deformation of different layers, which has significance for the predictive maintenance of the shafts.INTRODUCTIONSince 1980s, a specific geologic hazard has occurred frequently on the coal mine shafts in eastern China: non-mining-induced shaft deformation, involving up to 100 shafts located in Jiangsu, Shandong, Anhui and Herran province, distributed in Xuzhou, Datun, Huainan, Huaibei, Yanzhou and Yongxia coal fields. This kind of geologic hazard can lead to shaft wall deformation, water infiltration, cage stuck, water-sand burst or shutting down of coal mines, which seriously risks the coal mines. Zhangshuanglou coal mine, Haizi coal mine and Linhuan coal mine shut down for 2-8 months due to this hazard (Chen, 1997; Cui, 1998). The main reason for this geologic hazard is the subsidence of the super thick unconsolidated strata (Liu et al., 2007; Xu et al., 2006).An innovative structure health ·monitoring and damage estimation method has been developed in recent years, i.e., optical fiber smart material and structure (Nobuo, 2002; Wang et al., 2000). A Fiber Bragg grating (FBG) sensor is a device that can transfer the change of the measured strain or temperature to the change of Bragg wavelength. One of the most important applications of FBG sensors is to monitor the internal stress and strain distribution of material and structure (Philipp et al., 2000; Ansari et al., 1998). Compared to traditional electrical sensors, FBG sensors have many advantages; they are adaptable to harsh environments, abrasion resistant, immune to electrical magnetism (EM) interference, safe and reliable. They also offer integrated sensing and transmission on a single fiber, have simple structure and are convenient to use, which satisfies the requirements of long distance, distributional and long term use in monitoring mining and geotechnical engineering structure. Due to such advantages, the FBG sensor has already been applied in petroleum engineering (Kersey, 2000), rock mechanics testing (Cornelia et al., 2003; Yang et al., 2007; Wei et al., 2008), physical simulation experiments (Chai et al., 2007; Chai et al., 2006; Zhu et al., 2008; Li et al., 2008; Chang et al., 2008), strain sensor (Li et al., 2007; Chai et al., 2008) and construction structure damage diagnosis (Dong et al., 2004; Kerrouche et al., 2008; Whitten et al., 2001)."

Jan 1, 2010

By Hongwei Zhang, Sen Yang, Shimin Liu

"This laboratory study investigates the damage evolution of sandstone specimens under two types of cyclic loading conditions through monitoring and analyzing the variations of elastic moduli and ultrasonic velocities. We adopted the rigidity degradation method for evaluating the damage accumulation through the rock dynamic ultrasonic velocity measurements. Compared to the ultrasonic test, the method of rigidity degradation shows deficiencies in the detection of damage development. The cyclic loading within the elastic limit led to a stiffening trend for the loading process but a softening trend for unloading process. The method of rigidity degradation was unable to describe the damage accumulation in this situation, while P-wave velocity clearly reflected the damage development. Moreover, a simplified model is established for interpreting the behaviors of the modulus variations and ultrasonic velocity. The cyclic loading within elastic limit enhances the anisotropy of rock, which causes a denser packing pattern in the direction of axial stress. The persistent damage accumulation under the cycling with an increasing upper limit is the consequence of the tensile failure in the microstructure of sandstone. INTRODUCTION The damage accumulation due to dynamic (cyclic) loading is highly detrimental in many engineering structures, such as mine openings, petroleum and natural gas boreholes, tunnels, rock foundations, and underground chambers. The sources of cyclic or repetitive loadings can be roughly divided into two types: (1) periodic operation, including drilling, blasting, and mining; (2) random vibration, including earthquakes and traffic loads. The repetitive loading-unloading process opens and closes the micro-pores and micro-cracks within the rock, further inducing the growth of cracks. As expected, the accumulating damage becomes a potential factor to trigger the rapid and violent failures of large-scale engineering rock structure."

Jan 1, 2017

By Kudret Tutuk, Serkan Saydam, Sungsoon Mo

"This paper presents an overview of the floor heave management at the Glencore Bulga Underground Operations and investigates the contributing factors to the behaviour of the floor. The mine experienced a number of major floor heave events in gateroads on development. As the longwall face approached the roadways, the magnitude of floor heave frequently increased, while new floor heave also developed. Furthermore, severe floor heave events took place along the longwall face. The most observed failure mode was buckling. While regular floor measurements were conducted to better understand the nature of the phenomenon, and various measures were considered to control the deformation of floor, the mining height was increased for the predicted floor heave domains, which facilitated effective management of the floor issues. The experience in the mine indicates that mainly high horizontal stresses with greater depths of cover and certain types of floor lithology configuration are likely to contribute to the failures of floor strata.INTRODUCTIONThe Glencore Bulga Underground is located in the Southwest of Singleton in the Hunter Valley of New South Wales, Australia. Blakefield South, part of Bulga Underground, commenced longwall mining in 2010, extracting coal from the Blakefield seam, while the overlying longwall panels were previously mined from the Whybrow seam. The coal seam ranges from 4.5 m to 8.0 m thick with the mining heights varying from 2.9 m to 3.5 m. The longwall panels are 320 m and 400 m wide and up to 3.5 km long.The mine experienced a wide range of floor issues around longwall panels LW7 and LW8, both 400 m wide. For instance, the concrete floor in the travel road failed and lifted as the longwall retreated in close proximity as can be seen in Figure 1. Figure 2 shows the beam stage loader (BSL) buried into the lifted floor, and Figure 3 shows a timber prop distorted due to the movement of the floor. In addition, severe deformation of the floor along the longwall face impeded the longwall operation, as shown in Figure 4."

Jan 1, 2018