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By Tobias U. Papst

The German Ruhrgebiet is slowly transitioning into a post-mining state. It has been subjected to industrial-grade hard coal mining operations for more than 150 years. Due to a political decision, German hard coal mining will come to an end in 2018. By then the surface will have subsided up to 20 meters. After all mining activities in the area have ended, there will be no need to maintain the current mine water level. Accordingly, the company operating the last remaining coal mines has decided to let the water level rise to an as yet undetermined level. Alongside other issues that may be caused by rising groundwater levels, the protection of the area?s drinking water supply is of utmost importance. This notion is also represented by European and German law. The primary intent of the applicable laws is to protect the health of the citizenship. This means protecting ground water that may be used by humans from being contaminated by the mine water. This paper outlines the consequences of European and German legislature on mining aftercare using the example of one of Europe?s largest agglomerations.

Jan 1, 2014

By WenFeng Li

Comparing to the coal seams in Eastern China, the coal seams in Western China usually have better geological conditions. Therefore, changes in the conventional gateroads layout are required for the Western longwalls. A case study based on a Western coal mine (LiMin) was presented to discuss the feasibility of an innovative gateroads layout. Based on the geological conditions, a 5m wide pillar between the adjacent two longwall panels, 09112 and 09113, was proposed in order to increase the recovery rate. More importantly, the entry supporting strategy of panel 09113 headgate needed to be determined and verified carefully since only 5m wide pillar was left to separate the entry from the panel 09112 gob. Three strategies with different supporting intensities in the panel 09113 headgate were evaluated by numerical modeling. The model outputs indicated that roof and rib boltings plus single hydraulic props were essential to maintain the gateroads stable. Field observation showed that under the proposed entry supporting strategy, the total roof-tofloor and rib-to-rib convergences were only 360mm and 460mm, respectively, during the service life of the panel 09113 headgate, which indicated that the innovative gateroad layout proposed in this paper is suitable for longwalls with similar geological conditions in Western China.

Jan 1, 2013

By Zhikai Wang, Wensheng Lyu, Peng Yang

"To better understand the mechanical behavior of the compression deformation of backfill under high stresses corresponding to large depths, consolidation compression tests were performed for cemented tailings backfill with a cement-sand ration of 1:10 and 30% water under confined conditions. After applying different loading stress functions from 0.5 MPa to 32 MPa, the final axial deformation of the test specimen of backfill was obtained, and the micromorphology of backfill was studied before and after consolidation by scanning electron microscopy. Additionally, fitting analysis was performed for backfill confined compression deformation data and device model constitutive equations by the minimum square law. The constitutive model was revised according to the analysis results. The research results indicate that, as the load increases, the void ratio e obeys the functional relationship e=alnt + b (where a and b are fitting constants and t is compression time). Under the high-stress conditions of confinement, the constitutive model of backfill consolidation and creep can be used to describe the creep behavior of the backfill. Under high-stress conditions, after the consolidation of the confined backfill, the space between the tailing particles diminishes, the particles becomes more compact, and particle slippage occurs. INTRODUCTION With the depletion of shallow mineral resources, the mining industry has gradually shifted to deep mining (Zhang, Li, An, and Huang, 2010). Furthermore, with the continuous introduction of sustainable development policies regarding development and utilization of mineral resources, the mining industry must protect the limited available land and make full use of mineral resources as much as possible (Sijing, 1994; Zhihua, 2009). Backfill mining technology offers an unparalleled advantage in fully recovering mineral resources, controlling pressures, and improving environmental protection. As a result, this method has been widely used in various countries in the world (Burd, 2002; Benzaazoua, et al., 2008). Of the underground mines in the world, 45% of the large and medium-sized non-ferrous-metal mines and 37% of the gold mines use backfilling (Fuhrman, et al., 2014; Khaldoun, Ouadif, Baba, and Bahi, 2016). In addition, 45% of underground non-ferrous-metal mines and 37% of the gold mines use the filling method (Mchaina, Januszewski, and Hallam, 2001). According to incomplete statistics, more than 80 metal mines operate at a depth of more than 1 km; the depths of several typical deep mines are shown in Figure 1 (Burd, 2002; Fall, et al., 2009)."

Jan 1, 2017

By Ben Mirabile

Over the past three decades, the U.S. coal mining industry has widely used cable supports to supplement traditional primary bolting systems, especially in difficult ground conditions. However, increased mining activity in adverse conditions has underscored the limited effectiveness of the non-tensioned, partially grouted cable supports used to supplement primary bolts. Roof failures in conditions such as corrosive environments, highly laminated strata, low overburden depth and water intrusion have demonstrated that the need for cable technology has reached beyond the traditional non-tensioned, partially-grouted cable tendon. Furthermore, declining market conditions and increased competition for coal customers has demanded that new cable bolt technology be costeffective and readily adaptable to the mining cycle. Jennmar Corporation has developed several cable bolt technologies that can be used as stand-alone solutions or in concert with one another to mitigate adverse conditions. These technologies include rapid tensioning of cable supports, structural surface control and polyurethane injection. The case studies presented in this paper use one or more of these technologies to address adverse mining conditions or special ground control problems.

Jan 1, 2013

By David R. Burkhard

"Comparative roof beam performance, as measured by delamination within the bolted horizon, was used to evaluate two types of roof bolt drill hole geometries in a development setting. Short encapsulation pull tests had demonstrated a higher grip factor in drill holes featuring helical grooves in the side walls in comparison to drill holes featuring continuous smooth to slightly rough walls. The study incorporated the two geometries during development mining in which fully grouted mechanically anchored bolts were installed as primary roof support.bolts were installed as primary roof support.The study site, in an entry adjacent to a longwall panel, was instrumented with extensometers and data collected during longwall retreat. Statistical analysis was conducted to validate null and alternative hypotheses used to compare drill hole geometries. Analysis yielded no statistically significant difference between drill hole geometries. Inspection of the data does reveal less delamination within the smooth walled site in comparison to the site containing grooved hole geometry.INTRODUCTIONFrom their introduction as a means of ground control over sixty years ago, roof bolts today are the primary mechanism of roof support utilized throughout mining. Whether through suspension, keying, or beam building, roof bolts are employed to reinforce the inherent strength of the strata comprising the immediate roof with the goal of creating a competent bolted horizon of sufficient load bearing capacity to be self-supporting for a given mine's design life, stress regime, and geomechanical properties.For grouted bolts in sedimentary strata, axial loading due to vertical rock movement and bending due to horizontal rock movement are the principal means of loading (Signer, 2000). Regardless of the type of bolt and extent of grouting employed, the success of any roof bolting design is determined, to a large extent, by the effectiveness of load transfer between the rock, grout, and bolt.At San Juan Mine, an underground longwall mine located in the northwestern corner of New Mexico, a number of different roof bolt types, grades, and lengths have been used over the years in an effort to optimize primary roof support. One common denominator shared throughout has been the use of full length grout. Load transfer for full length grout is achieved primarily through mechanical bonding between the grout and rock. It is this interaction that is the focus of the study described in this paper. The study assessed and compared two types of bolt hole geometries employed during gate road development at San Juan. Underground instrumentation and evaluation of the bolted roof provided the means of assessment and comparison."

Jan 1, 2016

By Shengliyang Yang, Jinghu Yang, Jiachen Wang, Xiaomeng Li

"Safe and efficient mining of extremely inclined thick coal seams less than 20m thick is one of the new challenges in China coal industry. In recent years, the extremely inclined thick coal seams have been encountered in some old mines and western China, and currently the top coal caving longwall mining method has been successfully applied to this kind of coal seams. Accordingly, this paper studies the roof movement and its impact on shield supports of top-coal caving longwall mining in extremely inclined thick coal seams. The structure of main roof before failure was simulated by the fix-ended beam, and provided the solutions for determination of maximum compressive stress of the bottom beam end and maximum tensile stress of the top beam end. The failure mode on the upper end of working face is mainly a combination of compression and shearing, while that for the bottom end is tension and shearing. Roof fracture begins at the upper end of working and propagates downward. The shape of collapsed roof strata can be described as parabolic and divided into three segments from top to bottom, including no filling, uneven filling and densely filling segments. The roof loading conditions of no filling segment is more likely to have dynamic burst impacts.INTRODUCTIONExtremely inclined thick coal seam refers to that the dip angle of coal seam is greater than 45° and the thickness is greater than 3.5m (Wang and Zhang, 2015a; Wang and Zhang, 2015b; Wang, 2005; Xie, Gao, and Shangguan, 2005; Wu, et al., 2014; Deng and Wang, 2014; He, et al., 2015). This type of coal seams can be divided into three categories: 1. The extremely inclined thick coal seam, of which the thickness is less than 5m and the dip angle is less than 60°, is usually mined by fully-mechanized longwall mining method. 2. The extremely inclined thick coal seam, of which the thickness is 5 m-20m, is usually mined by top coal caving longwall method. And 3. When the thickness of extremely inclined thick coal seam is greater than 20m, it is mined by the horizontal section top coal caving longwall method. For example, the average angle ofWudong coal mine in Xinjiang province is 45°, and the thickness is 27m. Wudong coal mine is applying the horizontal section top coal caving longwall mining, producing 3 million tons annually per working face (Figure 1)."

Jan 1, 2016

By Chris Strawson

Moranbah North is a modern longwall operation mining premium coking coal in the Northern Bowen Basin, Central Queensland. Australia Moranbah North Coal (MNC) is owned and operated by Anglo Coal Australia. Extracting approximately 4.5m of the Goonyella Middle seam using a single longwall, the mine produces 5 to 6 Mt per annum. The weak coal (4.5 MPa), low strength laminated immediate roof, and strong upper roof sandstones, make operation of the longwall at depths in excess of 250m geotechnically challenging. In the past, there have been a number of production delays due to geotechnical issues. Roof instability resulted in a long stoppage on Longwall 105, and the eventual relocation of the face further outbye in the block. (Figure 1). When mining commenced in LW106, there was a requirement for uninterrupted production, particularly in the more demanding inbye area of the panel. Following discussions with a number of Geotechnical experts, it was decided to narrow the face, and test the theories of reduced face weighting due to spanning of the goaf across the panel. A new on line chock monitoring system, and microseismic monitoring was installed in order to characterise the difference in the rockmass response, as the panel width changed from 175m, to 265m, and then 300m. The nature of the goaf formation and impacts on face loading and production are discussed, having the unique opportunity of three different face widths within the same area.

Jan 1, 2007

By Uwe Wyink, Guenther Thiele, Isabel Gollnick, Klaus Thyrock

"The application of a thin spray on liner was implemented in longwall T-junction sections in 2009 for the first time. The development of the material and the application is based on a technical cooperation between RAG Deutsche Steinkohle AG and BASF Corporation. The report gives an overview of the first trials. The underground test occurred in a seam with a height of 1.5 m (5 ft) in a depth of 1,100 m (3,609 ft). The roadway is dual-use entry and the roof strata is composed of shale and sandy clay. In some sections geological faults impact the surrounding strata. The poor conditions induce separating and loosening of roof rock. Several remedial actions have to be implemented for decreasing deformations at the face entrance.The application of thin spray on liner (TSL) provides simplification and cost reduction of supporting work at longwall T-junction. The installation of TSL to avoid roof and coal fall operations for lagging are omitted.INTRODUCTIONFor safe operation of face retreat in dual-use roadways, the processes of securing and stabilizing the face end area are very important in order to minimize deformation and stress. Avoiding roof and coal fall are the main concerns for safe operation. For that reason different methods of reinforcement are tested in underground operation. In this paper the application of TSL is presented.The specifications of TSL are described, followed by the case study results. The underground study is located in one mine of RAG Deutsche Steinkohle. The extraction of the hard coal in this mine is characterized by great depth and high stress. There are poor geological and geotechnical conditions. The roadway used for the underground application was headed with the support system combination type A, which will be described later in the paper. After the first face retreat, deformation of steel arch support and bagging destroyed the roadway, so for the second face retreat remedial actions had to be undertaken. For this a new system of reinforcement, simplifying the supporting work at the longwall T-junction was tested. The reinforcement consisted of different parts that are described in the following report. Furthermore two different versions were applied. One method is the operation with TSL and the other one is the use of concrete for sealing. Both methods are compared in the text."

Jan 1, 2010

By Joseph C. Zelanko

Cable bolt support techniques. including hardware and anchorage systems, continue to evolve to meet U.S. mining requirements. For cable support systems to be successfully implemented into new ground control areas, the mechanics of this support and the potential range of performance need to be better understood. To contribute to this understanding, a series of 36 pull tests were performed on 10 ft long cable bolts using various combinations of hole diameters, resin formulations, anchor types, and with and without resin dams. These tests provided insight as to the influence of these four parameters on cable system performance. Performance was assessed in terms of support capacity (maximum load attained in a pull test), system stiffness (assessed from two intervals of load-deformation), and from the general load-deformation response. Three characteristic load-deformation responses were observed. An Analysis of Variance identified a number of main effects and interactions of significance to support capacity and stiffness. The factorial experiment performed in this study provides insight to the effects of several design parameters associated with resin-anchored cable bolts.

Jan 1, 1995

By Tristan H. Jones

Rib-related accidents in underground coal mines continue to cause injuries and take lives at a rate of 1.3 fatalities per year for the last 17 years. Prevention of these accidents cannot simply be a matter of installing more rib support, though the eventual final solution will undoubtedly include that component. Ultimately, rib safety will be brought about through an understanding of the causes and mechanisms that cause rib fatalities, and by fine-tuning mining methods and procedures that are currently in place. This paper investigates the factors likely to be most influential in the occurrence of rib fatalities. A careful analysis has been conducted of the rib fatality reports documented by the Mine Safety and Health Administration between 1996 and 2013. The primary outcome is the determination of the relative impact of each type of rib fatality factor and a better understanding of the impact each factor has. Among the rib fatality factors considered, the influence of rib profileis considered for the first time. Mining height, rib stratigraphy, mining cycle, and the standing position of a miner next to a pillar are also considered. Questions are also raised about the current interpretation of rib fatalities due to mining depth, with the indication being that mines operating at the greatest depths may actually have the most respectable rib fatality record among all mining depths. Additionally, a new method of considering rib exposure is developed. Based on the results, recommendations are made for future work. By gaining a better understanding of how particular factors contribute to rib fatalities as opposed to rib failure or stability, it is hoped that future efforts can be more precisely directed towards the desired outcome of fatality reduction.

Jan 1, 2014

By Eugene D. Krupa

Mine 33 of Beth Energy has serious and complex roof cutter problems causing delay of the advance rate of both the entry development and longwall face retreat. The cost of maintaining these entries is very high due to the requirement of wry heavy artificial supports. It was suspected that this problem was caused by multiple factors including high in-situ horizontal stresses and weak roof in the problem areas. In order to alleviate the problem, proper design of panel entry and roof reinforcement were considered. This paper presents the results of extensive measurements in experimental panel entries of Mine 33 in order to assess the performance of the designed structure and roof support system during the entry development and longwall retreat. An experimental panel entry has been designed and implemented. The designed parameters were varied seeking for the most ideal parameters which provide stable roadways. Changing these parameters accompanied instrumentation of roof, floor, and pillars. Typical instrumentation, including stress meters, convergence measurement stations, and borehole borescope were utilued. Gnensive monitoring of the behavior of the designed structure and support system led to the development of a complete stress-deformation history of the roadway and an ideal roof reinforcement, support system, which reduced the cost of entry development by less than a third of the previous method.

Jan 1, 1990

By Yongping Wu

Roadway deformation and stress migration occur with uncertainty and randomness because of geology, tunneling and mining influence. In order to study the surrounding rock deformation and failure mechanisms in three-dimensional stress state, an air return roadway of Yuanyang Lake mine of Shenhua Ningxia Coal Industry Group Co., Ltd. was chosen as a research object. The three-dimensional model was a designed and completed experiment with a dynamic-static coupling load. The model was loaded by hydraulic cylinder, simulating the in-situ rock stress field and the induced stress field of surrounding rock. The deformation monitoring system of the roadway model was constituted by optical total stations, borehole observation instruments, acoustic emission monitoring, and stress sensors. A wealth of data was obtained through an omni observation of surface displacement, characteristics of stress distribution, and deformation and failure of surrounding model material. By acoustic-optic-electric methods, a real-time testing on physical, mechanical, and damage parameters was realized through the experimental process. The results showed that the data of deformation and failure obtained from the deformation monitoring system of the roadway were authentic, which has great significance for warning and forecasting safety hazards of surrounding rock in coal mines.

Jan 1, 2013

By Anthony T. Iannacchione

The Solar No. 7 and Solar No. 10 mines were designed to prevent mine waters from directly discharging to the surface. In January of 2004, a discharge occurred as the Solar No. 7 mine was in its final stage of flooding through a barrier averaging 456-ft in width over a 1,600-ft length (No. 1). Another barrier (No. 2) was designed to protect four municipal water wells operating 1,800- ft away and producing from within or slightly below the Upper Kittanning coalbed from the adjacent Solar No. 7 and No. 10 mine pools. These two barriers were selected for this study because of varied mine layouts, mining methods, and geology factors affecting their performance. Analysis was aided by the collection and georeferencing of 6-month mining maps from the Pennsylvania Department of Environmental Protection (PA DEP). A structure contour map of the Upper Kittanning coalbed was constructed from mine map elevation points. These data and 2-ft surface contour maps were used to measure the precise location of the coal outcrop. The actual discharge point was as little as 425-ft away from a thinpillar section and 475-ft away from a pillar recovery section. The discharge point was found to be located slightly above the coal, indicating that the drainage path was at least partially through the strata directly above the Upper Kittanning coalbed. Hydraulic conductivities and potential discharge pathways are analyzed and discussed. The possible factors influencing the performance of the down-dip barriers at Solar No. 7 and Solar No. 10 are: a) the width of the barrier, b) the applied hydraulic gradient, c) the type of mining adjacent to the barrier, d) the overburden, e) the pattern and characteristics of fractures, and f) the quality of waters contained within the mine pools. This study, part of a larger effort funded by the Appalachian Research Initiative for Environmental Sciences (ARIES), is tasked to determine the key factors responsible for the successful design of down-dip coal barriers.

Jan 1, 2013

By David K. Ingram

The objective of this U.S. Bureau of Mines (USBM) investigation was to characterize overburden response due to longwall mining. Subsurface strata and surface deformations were monitored at two sites in southeastern Ohio. Site A included two adjacent longwall panels. Site B consisted of one longwall panel. Both sites had similar mine geometries and overburden thicknesses. The major difference between the two sites was the rock strata within the overburden. Multipoint borehole extensometers (MPBX) were employed to measure subsurface displacements. Survey monuments were installed above the centerline and profile of each panel to measure surface deformations. Subsidence of the surface was observed before and after movement was detected in the MPBX units. Initial and final displacement of the MPBX units occurred at the same time at both sites. No deformation was detected outside the panel area. The development of overburden deformation was different over each panel. The final subsurface failure characteristics also varied between panels.

Jan 1, 1994

By Mikko Ahola

This paper describes recent innovative analyses conducted by the Bureau of Mines to demonstrate the application of the boundary-element method in evaluating the effectiveness of caving chambers or sacrificial entries to relieve the stress conditions initiating cutter roof failure in underground coal mines. The analysis assumes that cutter roof failure results when the shear strength of the roof rock at an entry corner is exceeded by the applied shear stress. The applied shear stress is due to large differences between the horizontal and vertical in situ stresses known to exist in many coal mining districts experiencing cutter roof failure. The results of boundary-element analysis suggest that driving an arched lead entry in advance of adjacent rectangular entries and allowing it to cave significantly reduces the difference between the principal stresses at the corner of the rectangular entry, thereby lowering the maximum shear stress. Slippage of the immediate roof along horizontal bedding planes into the caved entry is shown to further reduce the stress conditions in adjacent entries. Practical applications of this stress control technique to longwall and room-and-pillar mining are discussed.

Jan 1, 1987

By Jiachen Wang

China is the largest coal producing country in the world. Coal is widely distributed in China and thus the mining conditions are complex and diverse. This paper summarizes the important achievements in the last 20 years in various mining methods including the extra thick seam with large mining height top coal caving, the thick seam with large mining height and top coal caving mining, the steep seam with top coal caving and fully-mechanized mining, the thin seam automated mining, and the backfill mining. At the same time, the rapid advance in the development of mining machinery and manufacturing has also contributed to the advancement of coal mining technology and the great improvement of coal mine safety. The future direction of China?s coal mining is to further improve mine safety as to improve the coal recovery rate, promote the pillar less mining technology, develop high-efficiency backfilling technology, develop steep seam high-efficiency mining technology for seams less than 10m thick, and high recovery mining techniques for extra thick seams, improve the reliability of mining equipment, and strengthen the protection and restoration of surface environments and water resources.

Jan 1, 2014

By Stephen C. Tadolini, John P. McDonnell

"High-strength cable bolts have been used for ground support in underground coal mines for many years. Cable bolts are routinely used as secondary ground support in numerous longwall gateroad support applications, areas that possibly experience the most severe conditions in current underground coal mining. Additionally, when mining ground conditions deteriorate, engineers oftentimes recommend cable supports as a principal solution because of the established credibility for successful ground control. Nevertheless, there is still a reluctance to utilize non-tensioned cable supports as an effective primary roof support alternative.This paper provides historical and recently documented examples of non-tensioned cable supports utilized as an effective primary ground support method in a western U.S. underground coal mine, and it will continue the technical discussion between the differences of various degrees of tension in cable supports with respect to ground behavior and reactions.INTRODUCTIONResin-grouted cable supports are widely used to support difficult ground conditions throughout the world. Through the use of innovative applications and configurations they have proven to be a major paradigm shift in roof support and ground control technology in the U.S. (Tadolini and Koch, 1993; McDonnell et al., 1995; Tadolini and Gallagher, 1994; Tadolini and Trackemas, 1994)Today, the basic cable bolt support consists of a high-strength steel cable installed in bore holes that range in diameter from 25 to 50 mm (1 to 2 in) depending on the strand size and drilling equipment. Cables are offered in both bright and galvanized, for corrosion protection, and range in capacity from about 30 to 60 tons. An example of a resin-grouted cable bolt and the key components is shown in Figure 1. The steel cables are flexible and the support length is not limited by the height of the opening. Lengths of up to 10 m (32 ft) have been supported with high pattern densities when standing supports were not operationally feasible. The most common lengths are 3 to 5 m (10 to 16 ft). An important physical characteristic is that PC-strand has an ASTM minimum elongation requirement of 4%. For comparison purposes, the ASTM 432-08 Standard Specifications for Roof and Rock Bolts and Accessories specifies elongation requirements for traditional roof bolts are a minimum of 12% for grade 40, 9% for grade 60, and 8% for grade 75 materials, respectively. Traditional roof bolts can stretch and elongate twice the length that cable bolts can, which makes design considerations challenging."

Jan 1, 2010

By Jimenez Leon, Christopher Newman, Boede Gabriel, Zacharias Agioutantis

"Ground movements due to longwall mining operations have the potential to damage the hydrological balance within as well as outside the mine permit area in the form of increased surface ponding and changes to hydrogeological properties. Recently, the Office of Surface Mining, Reclamation and Enforcement has completed a public comment period on a newly proposed rule for the protection of streams and groundwater from adverse impacts of surface and underground mining operations (80 FR 44435). With increased community and regulatory focus on mining operations and their potential to adversely affect streams and groundwater, there is now a greater need for better prediction of the possible effects mining has on both surface and sub surface bodies of water.As mining induced stress and strain within the overburden is correlated to changes in the hydrogeological properties of rock and soil, this paper investigates the evaluation of the hydrogeological system within the vicinity of an underground mining operation based on strain VALUES (calculated through a surface deformation prediction model. Through accurate modeling of the pre- and post-mining hydrogeological system, industry personnel can better depict mining induced effects on ground water flows through the overburden material aiding in the optimization underground extraction sequences while maintaining the integrity of surface and subsurface bodies of water.INTRODUCTIONThe utilization of high-recovery underground mining methods, such as longwall or high-extraction room-and-pillar operations, have the potential to cause adverse impacts to both surface and subsurface bodies of water as strata movement and deformations propagate from the mined seam through the overburden to the surface (Peng, 2008).Previous research has indicated that mining induced strains are the most damaging to surface streams (Singh, 1992) as well as greatly affecting the integrity of subsurface bodies of water and groundwater flow conditions (Booth, 1986). On the surface, adverse effects to the stream can occur due to the development of either tensile or compressive strain in the stream bed. The development of tensile cracks along the bedrock allows for a potential loss of stream flow through developed fissures. In fact, water flow in the Cataract River of Australia ceased in 1994 as a result of mining-induced strains from longwall operations in the Bulli seam 430 meters (1320 feet) below the river gorge (McNally and Evans, 2007). On the other hand, the development of compressive strains within the rock layers can cause rupturing or buckling of the stream bed, blocking stream flow and/or diverting flow into the fractures at the base (Iannacchione et al, 2010). While these localized fractures can contribute to the loss of stream flows, given time, damaged streams have the ability to self-heal through the regeneration of near-surface aquifers as well as the sealing of mining-induced fractures with rock debris, gravel, sand, clay or other soil particles carried from upstream sources and deposited in the river bed (Waddington and Kay, 2002)."

Jan 1, 2016

By Boqiang Wu, Ganggang Xu, Xiaodong Wang, Hai Wang, Shibin Zhu

"Using a paste-like slurry as a filling from the ground surface to the goaf, artificial pillars can be built in the cavity goaf to support the goaf roof to prevent roof collapse and ground subsidence. If the accumulation laws of paste-like slurry are known well, the filling technology can be optimized. The laws can establish the foundation for finding out the best methods for building artificial pillars and filling technology. In order to understand the accumulation laws of paste-like slurry in the cavity goaf, Aeolian sand with wide distribution in northwestern China was selected as aggregate, and Portland cement was used as cementitious material to prepare a paste-like slurry. A test model of the cavity goaf was built to simulate the filling process by pump from the ground surface to the goaf to study accumulation laws of the paste-like slurry. The results show that the whole process of expansion and accumulation of the paste-like slurry could be divided into stages: free expansion, fill tightening expansion, and stable expansion. The angle of repose of the accumulation body of the paste-like slurry is constant in the stage of stable expansion, and it is the final angle of repose of the accumulation body. The angle of repose of the accumulation body is highly relevant to the slump of the paste-like slurry, and it is unrelated to the distance between the floor and roof. Under certain conditions of the cavity goaf, reducing the slump of paste-like slurry is one of the effective ways to obtain cost-effective pillars.INTRODUCTIONA large number of cavity goafs of coal mines were left in northwestern China; they were formed in the mining process by room-pillar or strip mining. Safety coal pillars were used to support the roof to keep long-term stability in the goaf, so the ground subsidence was not obvious (Fu, Deng, and Zhang, 2011; Xie, 2014). With gradual weathering, destruction of coal pillars, or additional load from ground surface buildings and structures, there could be a risk of instantaneous collapse of the roof in the goaf. This would affect the safety of existing structures on the ground and adjacent mines (Qu et al., 2017; Li, Xiang, and Jia, 2011; Tan, Guo, and Zhao, 2016; Tan et al., 2017). For disaster prevention of the falling cavity goaf, the current common practice is full filling (Hu et al., 2008; Liu, Zhu, and Huang, 2015; Pan and Wu, 2010). However, for buildings and structures with lower deformation requirements, full filling is excessive. For example, it is acceptable for goaf treatment under general roads and industrial sites to control the maximum deformation and keep the deformation continuous (Liu, 2011; Liu, 2012)."

Jan 1, 2018

By S. F. Smith

Following a roof beam collapse on a major production district at the British Steel Corporation's Dragonby Iron Ore Mine, Scunthorpe, South Humberside, UK, rock mechanics investigations were undertaken in this room and pillar operation to assess the stability of workings throughout all the underground mine area. Over a four year period room convergence and roof sag were monitored in different mining areas and various junction configurations in order to assess and compare the relative movement of the strata resulting from mining activities, where varying rock bolt lengths and patterns have been utilised. The paper, after shortly describing geological aspects and mining methods, presents the research procedure adopted together with the instrumentation employed and discusses the results obtained during these investigations.

Jan 1, 1995