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By J. R. Stoltz

To date, there has been limited formal research dealing with the use of Mobile Roof Supports (MRS) for pillar recovery. This paper, which is a portion of a larger project, presents convergence data from 4 different mine case studies. MULSIM was used to create a numerical model. The resulting information from this model was then compared to the actual measured values. MULSIM was also employed to analyze the industry-accepted pillar/barrier layout for mining underground reserves with the Joy Highwall Mining System. This layout was examined for both a low cover and a high cover extreme,

Jan 1, 1999

By R. Fraher

Hazard analysis utilizes interaction mechanisms in combination with geologic, structural and mining conditions to delineate areas of potential damage in seams subject to interaction. Using characterizations of conditions peculiar to multi-seam mining, such as innerburden thickness, geology and structures, initial interaction contour maps can be constructed. Geologic hazard analysis is then carried out on roof, pillar and floor conditions in the affected seam using lower seam rock properties and layout geometries in the overlying seam. Either safety factors or damage ratings can then be developed representing degree of hazard in the lower seam. The final hazard map shows both the aerial extent and magnitude of potential damage from interaction.

Jan 1, 1992

By M. W. Fabjanczyk

Cement and resin encapsulated tendons are widely used in the stabilisation of mine roadways. One of the main factors in controlling the efficiency of the reinforcement is the ability of the tendon to generate load in response to rock deformation. The analysis of field data from instrumented reinforcing tendons complimented with extensive laboratory investigations have more accurately defined the mechanisms by which load generation occurs. The role of reinforcing tendon profiles, hole geometry and encapsulation medium properties in controlling the reinforcement stiffness and capacity are discussed. The results of the investigation have implications in both the design of rock reinforcing systems and the optimisation of encapsulation mediums and tendons.

Jan 1, 1992

One of the most important parameters in rock/resin/bolt load transfer mechanism is the surface property of the bolt. Although there are various bolt surface configurations available in the market, very little work is reported on the bolt/resin interface failure mechanism. This paper examines the behaviour of bolt surface roughness under constant normal stiffness conditions which is considered as being a realistic way of evaluating bolt surface roughness. A series of shear tests have been conducted on the flattened bolt surface to study the shear behaviour of bolt/resin interface. Based on the experimental results, a mathematical model has been developed to predict the shear resistance of the bolt/resin interface at various normal stress levels for the bolt types used in the study.

Jan 1, 1999

By Y. Luo

This paper presents a number of mathematical models for predicting the different phases of the complete surface subsidence process associated with underground longwall mining. A computer program developed based on the mathematical models is briefly introduced.

Jan 1, 1992

By Andre Zingano

An underground mine using room and pillar and retreat mining methods was developed during the 1950?s. In 2009 an open cast mine was opened in the same reserve with the objective of mining five coal seams including the one previously mined. Recently, a series of slope failures were detected at the open cast mine. The surface mine map was overlain on the underground mine map, and it was observed that the slope failures were located above a retreat mined area where the overburden had caved and the ground subsided. The deformation and displacement attributable to subsidence caused a loss of strength in the overburden strata. The objective of this paper is to study the causes of slope sliding (or failure) due to the ground subsidence of rock layers above oldmined out areas. A map was created to overlay the two mines -- the abandoned underground mine and the active surface mining. Two- and three-dimension numerical modeling was conducted to simulate the slope behavior and to verify whether the mine subsidence was the cause of slope instability. This study indicated that the subsided rock layers were the cause of slope instability and sliding.

Jan 1, 2013

By G. Herget

To improve quality control of roof conditions, a program was carried out at Elliot Lake uranium nines in Ontario, Canada to test a portable TV camera system. This camera has a 29 mm diameter probe and is capable of identifying crock locations, crack width and approximate dip direction. The extent of fractures to the roof was checked with the aid of a vacuum system by placing packers in various boreholes and checking for communication. The removal of some rock bolts indicated an increase in fracture extent.

Jan 1, 1982

By Zhanjing Yu

Longwall ground behavior in the Illinois Coal Basin was studied in the past (1, 2, 3). Most of the past studies, however, were concentrated on either surface subsidence or underground structural behavior. In this study, both surface and in-mine ground behaviors are considered, which include: 1) stress and deformation characteristics in the chain pillars; 2) roof and floor deformations; 3) surface subsidence characteristics, including time effect; 4) relationship between the surface subsidence and underground strata behavior; and 5) the ultimate hearing capacity underneath the chain pillars. Field measurements and tests were conducted and the data were analyzed using both analytical and statistical methods. The findings in this study can he used by mine operators in the Illinois Coal Basin for longwall ground control planning and design.

Jan 1, 1994

By B. Singh

The use of wire ropes has already been tried in a few countries for roof support In mines. But the use of scrap wire ropes, as a method of support on extensive scale has not been reported from anywhere except India. Extensive trials using freshly discarded wire ropes for roof support were undertaken both in the laboratory and field. In laboratory, model beams supported with different reinforcing techniques were tested to evaluate their comparative load bearing capacity vis-a-vis reinforcing factor. Among all the tests, the model supported with wire rope system at 60° angle in combination with two supplementary vertical bolts offered the best result 1.e. about 95% reinforcement. It also accepted post fracture loading of the beam. In statical analysis too, the best result could be obtained with the rope installed across the gallery at 60° angle. All these findings are in conformity with the field observations obtained during roof stitching practices in coal mines. Of late, roof stitching, an effective and economical method of roof support developed at CMRS, India in 1972, found wide application in over 200 coal mines. In this method, a freshly discarded wire rope is grouted across a gallery in two inclined drill holes supplemented with two middle vertical roof bolts at every 1.0 to 1.2 m interval along the gallery. It is tensioned against the roof using wooden sleepers and thus, the whole system functions like a roof truss.

Jan 1, 1990

By Kot F. Unrug

Since the introduction of longwall systems, the prediction of roof behavior and support requirements have become the major issue referring directly to safety as well as productivity. In more recent times, and especially in the USA where longwalls are exclusively equipped with costly hydraulic self- propelled support systems, a decision whether a longwall is applicable in a given condition, and when so, what kind of equipment should be selected, is of primary importance. There are numerous examples where lack of experience, and subsequently wrong selection of supports or winning machines, resulted in considerable losses. It should be emphasized that careful studies of prevailing geological and mining conditions, especially in a new area, are required to assure a successful operation. An evaluation of the conditions can be carried out in different ways utilizing such methods as: - Theoretical approach. applicable when geological conditions comply with the theoretical assumptions. - Empirical relationship which gives satisfactory results where the coefficients could be adequately determined. - Structural geological studies which must be undertaken in all cases, since the frequency of fractures and their orientation have a prevailing influence on roof behavior. - Scale model study on equivalent material for determination of failure conditions in the roof and mechanism of movement (flow) of broken rock matter. Coefficients for empirical formulas can be determined by these types of studies, as can boundary limits for mathematical modeling. - Mathematical modeling, e.g., finite element analysis. - Measurements and observations taken underground during the development period end utilization of experience for previous longwall panels in the area. Usually it is the most practical method where mining and geological conditions are comparable. An application of me or more of the above approaches remains to be a matter of judgement for particular conditions, however, the utilization of a practical experience, when available, is usually the safest way for planning a successful longwall operation.

Jan 1, 1982

Numerical simulation for microseismicity due to mining at one of the collieries in Australia was carried out and the results were compared to the observed microscismicity. 3-D Stress analysis showed stress concentration on the edges of the mined areas and on the coal pillars- The stress concentration ahead of the coal face was biased to the tailgate. This is similar to the observed distribution of microseismic events. Stress reduction above and below the mined area was seen. Tensile stress was observed mainly above the mined area. It was realized that compressive failure due to nearly vertical maximum principal stress and nearly horizontal minimum principal stress in retreat direction (NS) might occur ahead of the face. Tensile failure due to nearly vertical minimum principal stress above the mined area was expected. Compressive failure due to nearly horizontal maximum principal stress in EW direction and nearly vertical minimum principal stress above and below the mined area were also expected.

Jan 1, 2001

By Michael Kelly

Longwall mining is the principal method of underground coal mining in Australia, with 70 million tonnes being produced by longwall mines in 1999. However, the mechanisms that control longwall geomechanics are still not clearly understood resulting in stoppages costing several hundred million dollars per annum The CSIRO has been investigating longwall geomechanics with consultant groups and minesites through several ACARP supported projects since 1994. The research has aimed to improve longwall support design and control methods by defining strata failure mechanisms and their occurrence about underground extraction panels, It also aimed to develop better predictive tools bur a broad range of underground environments. As a result of site studies at more than 8 locations some of the aspects that have been touted to control longwall geomechanics, especially from a 3D aspect are highlighted. These aspects include stress controls, geometry, faulting, depth. longwall width and changes in lithology.

Jan 1, 2000

By E. Yasar

This paper describes the use of the sand and plaster physical modelling technique to investigate the deformation around mine roadways using a variety of support methods in a particular form of stress field. The characteristics and conditions of coal measures rock were considered prior to the preparation of the models and the insertion of support The investigation has clearly shown how floor lift, roof failure and sidewall movements of mine roadways in laminated weak rock conditions gradually develops as a result of the increase in the stress and, also, how it is related to the level of support used.

Jan 1, 1995

By Daniel W. H. Su

Underground roof geology reconnaissance is being conducted by CONSOL Inc. to enhance mine productivity. Often, roof instability within mine entries is the consequence of highly variable geology that cannot always be detected from information provided by widely-spaced surface core holes. Utilizing a combination of roof drilling data, geophysical logs, and borehole camera and fiberscope observations, roof geology mapping is conducted within longwall development entries in areas of specific concern prior to commencement of longwall mining, Depending on the uniformity of the site-specific roof geology, data point spacing along the longwall development generally ranges from one to five crosscuts. Surface core hole data are correlated with the roof geology mapped underground to validate the underground observations. Detailed roof geology maps can then be produced to enable ground control engineers and mine management to select cost-effective ground control techniques. However, this procedure is not necessary or useful in all situations and it is employed only when there is strong geologic evidence to justify a closer inspection.

Jan 1, 1999

By Satyendra K. Singh

If the extraction is beneath massive roof strata, the roof tends to 'bridge' across large spans without failing, the caving behaviour is complex and irregular. Understandably, these give rise to many geotechnical problems with safety implications and involving sometime huge direct and indirect costs. Only two important problems, 'feather-edging' in pillar mining and `severe periodic weighting' in longwalling, are discussed in this paper in the background of geomechanics investigations in Australia at Blue Mountain Colliery and in South Bulga Colliery respectively. `Feather edging'- a major source of injury and fatal accidents in Australia and South Africa in such situations, refers to a phenomenon where the roof, at the goat edge, falls as a thin wafer of rock often suddenly, over-riding conventional timber breakerlines. The results of the first comprehensive, monitored trial in an Australian pillar extraction coal mine, suggests how the roof falls into feather-edging caving (generally) because of multiple shear-planes (interpreted) and how it may be alleviated. Because of complex fracturing behaviour of massive roof strata, periodic weighting at a longwall face is certain to manifest itself as 'yielding supports', heavy conditions', rapid convergence and in the worst case, as a cause of face stoppage. After briefly discussing the programme of instrumentation (in a chain-pillar and over the would-be goal) and results, this paper attempts to improve mechanistic understanding of the related geotechnical issues associated with the weighting behaviour and aims at establishing a 'threshold' value of weighting severity index (suggesting intensity of periodic weighting) with an objective to optimise operational controls before mining through potential (future) weighting areas.

Jan 1, 2000

By Robert M. Cox

The successful application of the science of rock mechanics to the practical problems of coal mine design requires the acquisition and reduction to useable form of large amounts of field and laboratory data, and the construction and analyses of numerous geostructural models containing a wide variety of geometric and physical strength variables. Typically, the rime constraints placed on a new mine design project coupled with the inherent complexities of a good rock mechanics study combine to limit the applications of rock mechanics to the most rudimentary level. To facilitate a better application of rock mechanics to mine design problems, an interactive software package has been developed for use on a graphic mini-computer system that serves to aid the engineer in the timely and efficient analyses of rock mechanics data and geostructural models. The first phase of the rock mechanics package solicits the input of the raw geologic and rock strength data, analyzes and arranges this data in a logical manner, produces complete listings and statisitical summaries of the various rock properties, and stores the data on magnetic tapes and disks to serve as a future Rock Mechanics Data Base. The second phase of the software package provides for the analyses of a variety of geostructural models using a wide variety of geometric variables coupled with the rock strength data stored in the Rock Mechanics Data Base. This software package allows for the evaluation of numerous geostructural mine models for the design and selection of mine roof support and pillar systems (see Table l).

Jan 1, 1982

By Jesse L. Craft

Field investigation of surface subsidence events associated with both active and abandoned underground coal mines in the United States has established criteria that enable the prediction and classification of mine-related subsidence. The key was establishing the role of geology in all types of subsidence and the recognition of beam subsidence in specific geologic settings. The classification is based on overburden thickness, variations in stratigraphy, topography and mine plan. Types of subsidence are Pit, Room, Sag, and Beam. Pit subsidence is associated with three geologic settings: shale overburden, seasonally wet unconsolidated overburden, and perched water table in unconsolidated overburden. Room subsidence occurs where the roof across the width of the room fails to the surface and a shallow depression develops. Sag subsidence develops where the pillars are failing in conjunction with roof failure. Overburden thickness is generally greater than 150 feet. Beam subsidence can occur in all terrains. It is associated with retreat mining and room and pillar mining where pillar crushing or pillar compression has taken place and barriers are left inplace. They occur as beam arch or one-sided beam subsidence. Beam arch failure occurs where mining has taken place on both sides of a coal barrier. One-sided beam failure is associated with retreat mining moving from a barrier towards the entry in hilly topography. This type of subsidence occurs where a hard, thick, rock unit is acting as a bridge supporting the overburden and outcrops on the hill side.

Jan 1, 1992

By I. Sedat Buyuksagis, Jamal Rostami, Ali Naeimipour

"Improving the safety of underground openings and optimizing ground support systems requires reliable ground characterization. This includes understanding the joints, discontinuities, and rock strength. Joint information can be obtained from borehole cameras, but measuring in-situ rock strength is very difficult. Use of borehole probes can be an ideal and efficient way to meet this requirement. This paper discusses the development of the Rock Strength Borehole Probe (RSBP) and presents the preliminary laboratory/field test. This device can be an accurate, flexible, quick, non-disruptive, and cost-effective alternative to estimate the rock strength inside boreholes in underground mines and tunnels. In addition, the scratch testing procedure in the laboratory by means of a newly developed miniature linear cutting machine is explained. Based on the results of these tests, two equations are developed to estimate the uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of the sedimentary/metamorphic rocks. These equations, are based on testing 27 different sedimentary, igneous, and metamorphic rocks by full-scale scratch tests, including the cutting tests by a miniature disc. The results show a good correlation between the normal force and the compressive strength of sedimentary rock if the depth of the scratch is known. No significant correlation was observed for igneous rocks, due to the impacts of grain size.INTRODUCTIONEstimated rock mass properties are essential input for geomechanical studies and stability analysis for any structure constructed in or with rock. The availability of geological information is the crucial component of rock mass classification. One of the important parameters in evaluating rock mass properties is the intact rock strength. This parameter is usually measured by testing the core samples, obtained from exploration boreholes. These samples are subsequently tested in geomechanics laboratories. The test results offer limited information about the rock at the few boring locations despite all the efforts and costs. In addition, these results may not necessarily be representative of the behavior of the rock in the field as the test cannot provide the insitu condition of the ground."

Jan 1, 2016

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 Timothy Batchler

"Pumpable roof supports are currently being used to provide a safe working environment for longwall mining. Because different pumpable supports are visually similar and installed fundamentally in the same manner as other supports, there is a tendency to believe they all perform the same way. However, there are several design parameters that can affect their performance, including the cementitious material properties and the bag construction practices that influence the degree of confinement provided. A full understanding of the impact of these design parameters is necessary to optimize the support application and to provide a foundation for making further improvements in the support performance.This paper evaluates the impact of various support design parameters by examining full-scale performance tests conducted using the National Institute for Occupational Safety and Health (NIOSH) Mine Roof Simulator (MRS) as part of manufactures' developmental and quality control testing. These tests were analyzed to identify correlations between the support design parameters and the resulting performance. Based on more than 160 tests over 7 years, quantifiable patterns were examined to assess the correlation between the support dimensions, cementitious material type, wire pitch, and single-wall vs dual-walled bag designs to the support capacity, stiffuess, load shedding events, and yield characteristics.INTRODUCTIONDeveloped in the 1990s, the first major use of pumpable supports systems in U.S. longwall operations was in the support of bleeder entries (Barczak, Tadolini, 2008). Since then, they have been utilized as yieldable concrete supports to provide a safe working environment for longwall mining gateroads, bleeders, and emergency escapeways while also maintaining adequate ventilation pathways. The basic structure of pumpable roof supports has remained unchanged over the years. Formed in place with a twopart fast-setting grout, the support material can be pumped into a containment bag from several thousand feet away often through surface boreholes. The containment bag then acts as a form to fill the support and provides confinement to the grout during loading and after failure. Pumpable roof supports provide full contact with the mine roof and floor, which eliminates the need for secondary material to establish proper roof contact (see Figure 1). They provide a high peak load capacity and a sustained, confinement controlled yield behavior while maintaining stable ground conditions, which is essential to underground mining operations."

Jan 1, 2016