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By Xianming Zhou

Mining economics is such that too conservative in safety will result in a considerable penalty in mining cost. However, initial planning and design of a mining project often must be done without complete information. The assurance of economical and safe mining is thus difficult. This study is focused on the improvement of the mine design associated with Zhaoyuan Gold Mine in P.R. China as more information becomes available. Attention is given to the selection of backfill structures. Based on a proposed practical finite element model, a design, which is believed to be not only reliable but also cost-effective, is recommended for further mining operations in this mine.

Jan 1, 1989

By Stephen Tadolini

A unique circumstance created by monitoring a pre-driven longwall recovery room permitted measuring the stresses of a coal pillar throughout its entire life cycle in less than a week. A fender pillar, created in approximately the middle of a longwall panel at a depth of 650 ft, transformed from a solid barrier pillar - to a yielding pillar - to a residual pillar as 3 ft slices were methodically removed with the longwall shearer. The complete transformation, or life cycle, took place in less than 12 hours. The stresses were quickly transferred from the pillar onto the standing pumpable concrete supports and into the outby pillars. Roof to floor closure measurements, combined with the timing of the pillar behavior, provides a detailed look at the uncontrollable convergence of underground mine openings. Pillars remain the most important form of ?primary support? and understanding these life cycles is vital for safe and efficient mine design, in both room and pillar and longwall panel extractions.

Jan 1, 2007

By Robert J. Coutts, Dan A. Payne

"The Broadmeadow mine is a punch longwall mine owned and operated by BHP Billiton Mitsubishi Alliance (BMA) in the Bowen Basin of Queensland, Australia. In 1999, an exploratory adit was driven as part of the feasibility study for the establishment of the mine. Subsequent development of the mine in 2004 started some distance away from the initial test adit. Ten years later, the trial adit would be used as the headgate of the 5'h longwall panel. However, multiple roof falls had occurred in a heavily jointed area over a distance of 1, 000 ft (300 m) during the past 10 years. Due to the immediate coal roof, low stress environment and time, some of these falls had progressed to 38 ft (11.5 m) above the mining floor. As a result of the extensive work involved and safety implications of trying to recover the roof falls conventionally, a strategy was developed to fill these roof falls with a cement based product from the surface, down boreholes, and redrive the roadways through the consolidated roof fall material. This paper describes the process of rehabilitating these roadways, the results when the roadway was redriven and the headgate performance as the longwall mined through the area.INTRODUCTIONBMA operates 7 open cut and 2 underground mines in the Bowen Basin of Queensland, Australia producing over 50 mt per year of high quality coking coal. As a result, BMA has established over 150 miles (250 km) of open cut highwall.Broadmeadow Mine is a punch longwall mine located 22 miles (35 km) north of Moranbah in Queensland, Australia on the western limb of the Bowen Basin Coal Measures (Figure 1). Broadmeadow Mine commenced development in 2004 and began longwall operations in 2005. Broadmeadow is currently completing the fifth longwall panel and produces over 4 Mt per year of high quality coking coal. Mining is undertaken in the Goonyella Middle Seam, which is 21 to 25 ft (6.5 to 7.5 m) thick in the current mining area.The mine layout required the use of an old exploratory gateroad as the headgate of its 5th longwall. This gateroad had experienced numerous large roof falls and required extensive rehabilitation."

Jan 1, 2010

By Chris Mark

Successful longwall mining requires a stable tailgate entry. Gate entry performance is influenced by a number of geotechnical and design factors, including: - Pillar size and pillar loading; - Roof quality; - Floor quality; - Entry width; and, - Artificial support (primary and secondary). This paper describes a comprehensive, practical, design methodology, based on statistical analysis of a nationwide data base of longwall ground control experience. Geotechnical surveys were conducted at 44 U.S. longwall mines, and underground observations of site geology, entry conditions, and support design were recorded at each mine. The observations were combined with discussions with mine personnel to identify 69 longwall gate entry designs as satisfactory, unsatisfactory, or borderline. Only conventional longwall designs, in which the pillars are expected to carry the full abutment loads, were included in the data base. Designs which employed yield pillars only were excluded. The case histories were characterized using five descriptive parameters. Pillar design was described by the Analysis of Longwall Pillar Stability Factor (ALPS SF). A major new contribution is the Coal Mine Roof Rating (CMRR), a rock mass classification system that quantifies the structural competence of bolted mine roof. Other quantitative measures were developed for primary support, secondary support, and entry width. Multivariate statistical analyses indicated that in 84% of the case histories the tailgate performance could be correctly predicted using just ALPS and the CMRR. Most of the misclassified cases fell within a very narrow borderline region. The analyses also confirmed that primary support and gate entry width are essential elements in successful gate entry design. The relative importance of the floor and of secondary support could not be determined from the data. Based on these results, a simple equation was developed to guide the design of longwall pillars and gate entries: ALPS SF,, = 1.76 - 0.014 CMRR Where: ALPS SF, = ALPS SF suggested for design. Guidelines for entry width and primary support density, as related to the CMRR, are also provided.

Jan 1, 1993

By Yi You

A research has been conducted to study the long-term subsidence and its possible effects on surface structures In this research, the surface movements in areas when potential for developing long-term subsidence is high have been monitored over an extended period of time Long-term subsidence data have also been collected from other sources The avail- able data from this on-going research have been analyzed and the results is presented in this paper.

Jan 1, 1997

By Robert Trueman

This paper details the results of an assessment aimed at understanding the shield loading mechanisms associated with strata-related issues on a longwall face. Shield load cycle analysis theories developed by the authors were used to quantify the interaction between the shields and strata. Shield pressure data was back-analyzed using a version of the Longwall Visual Analysis (LVA) software that has been extended to enable efficient load cycle analysis to be undertaken. The software outputs enabled the shield strata interactions to be characterized. The results of the analyses indicated that the major cause of the roof falls was high-level periodic weighting, resulting in periodic shield overload. Exploration borehole data was analysed to identify and characterize the overburden unit that was the likely cause of the shield overloading.

Jan 1, 2011

By D. Minney

The quality of resin used in South African collieries is currently controlled according to South African Bureau of Standards, "SABS-1534:2002". It has however been found that resin which passed the SABS tests failed in underground short encapsulation pull tests. An investigation was therefore conducted to determine the characteristics of resins that are currently being used in collieries. A series of in situ short encapsulated pull tests was conducted to determine the effect of expired resin on support performance. The results showed that the longer the time after the expiry date the poorer the resin performance. A series of resin-torque tests has been performed using Anglo Coal's testing facility. The following parameters were investigated on different resins: Spinning speed, Mixing time, and Setting time. An attempt was also made to develop a new quality control procedure for resin. This procedure enables mining personnel to make sure that the quality of resin can provide the required support performance. The effect of spinning speed on resin performance was also investigated. The results showed the resin gelling times of resin decreases as the spinning speed increases. It is found that over-spinning with slow speed roofbolters may result in decreased bond strengths. It was found that a 30-second resin (10-second spin, 30-second hold) should never be spun more than 20 seconds, even with very slow roofbolters (100 rpm).

Jan 1, 2005

By John Popovich

The MICON RokLok binder system including component and consolidation processes and safety and its first aide are described. The implementation procedures and selection of injection parameters are discussed. Finally a case example of recovering a 30-ft. long roof fall in mainline haulage entry is used to illustrate the economic potential of preventive measures by RokLok injection.

Jan 1, 2001

By Charles Steed

The design of pillars in room and pillar operations is always a compromise between factor of safety and ore recovery. In actively mined and accessed areas the stability of pillars must be sufficient to support the roof, providing safe working conditions for men and equipment, while optimizing ore recovery. As a reserve is mined out, and if conditions are favourable, pillars are often removed to increase recovery. Considerations for pillar removal include value of the ore, the effect on immediate and overall mine stability and the safety of the mining operations as well as the consequence of disruption of overlying strata and surface infrastructure as the support of the pillars are removed. Many parameters influence pillar strength and the contribution of the pillar to ground support. These include seam height, seam depth, seam inclination, room span, quality of rock, time, etc.. Empirical, analytical and numerical modeling methods are commonly used to optimize pillar sizing and placement and predict influence of pillar extraction or reduction on ground stability. Practical examples for pillar design and optimization in low seam gypsum mining operations and optimizing sequencing of pillar extraction in thick seam metal mining operations are outlined.

Jan 1, 2003

By Don Kay

A two year study into the effects of coal mining induced subsidence on cliff lines was undertaken by the Department of Mineral Resources with the support of a grant under the National Energy Research, Development and Demonstration Program. A new monitoring technique, using an Electronic Distance Meter and acrylic reflectors attached to the cliffs, provided safety for the surveyors and extensive and accurate three dimensional displacement data on the movement of the cliffs as they were being undermined. The study report included many graphs showing the measured vertical and horizontal displacements, differential subsidence, tilts and strains and included analysis of these movements with various parameters, such as, seam thickness, depth of cover and distances between the reflectors, longwall face and the edge of the chain pillar. Some of these graphs are presented in this paper and could be used, with caution, to predict subsidence movements around other cliff lines, after allowing for differences in geology and mining layout. A mechanism is suggested as an explanation for the observed high horizontal movements around the cliff lines. Sixteen percent of the overall lengths of cliffs that were undermined during the monitoring study fell and the contributions of various factors that appeared to influence the cliff falls are discussed. It is concluded that no single factor dominated as the major cause of the cliff falls and, often, many factors combined to cause cliff face instability.

Jan 1, 1992

By D. Su

This paper presents the details and results of a preliminary investigation into the response of borehole pressure cells (BPCs) in soft coal. Two parallel approaches, laboratory calibration and nonlinear finite element simulation, were adopted for deter- mining the BPC K-factor, which was defined as the ratio of cell pressure change to the corresponding change in external pressure. Results from both the laboratory calibration and the nonlinear finite element simulation revealed a nonlinear response of cell internal fluid pressure to external loading. The K-fact& also is shown to increase with increasing setting pressure and decreasing medium modulus. -Depending on the setting pressure, the K-factor for coal having a Young's modulus of 1.6 x lo5 psi ranges from nearly 1.2 at 2,000 psi of external pressure to 1.485 at 8,400 psi of external pressure. The improved under- standing of BPC behavior leads to the more accurate calculation of BPC K-factor in coal which significantly improves the correlation between pillar pressures measured in underground coal mines and those predicted by nonlinear finite element simulations of these pillars.

Jan 1, 1990

By Christopher Mark

Mines with exceptionally low-strength roof (UCS <3,500 psi and CMRR <40) are much more likely to struggle with roof falls than other mines. Weak-roof is a particular problem for many room and pillar mines in the Midwestern and Northern Appalachian coal basins. Traditional roof support techniques are often not up to the challenge at these operations. This paper focuses on two mines, one operating in the Upper Freeport seam and the other in the Herrin No. 6 seam. Together, the two mines had more than 300 roof falls during a recent 5 year period. Each has experimented with a variety of roof bolt types and lengths, and with different supplemental supports. Detailed statistical analysis was conducted to determine which support combinations have proven to be most effective. Geology, horizontal stress, and time are also important at both mines. Successful control techniques have included; ? Identifying particularly troublesome lithologic roof units; ? Installing longer and stronger roof bolts; ? Installing supplemental support in intersections, and; ? Limiting the duration that a panel remains open. The lessons learned from these mines, and others like them, could help improve ground control safety for the entire U.S. mining industry.

Jan 1, 2004

By Clifford J. Roblee

In this paper, various seismic indicators are evaluated for ability to discern fractures induced into a rock mass by blasting. This is accomplished by presenting results from in situ crosshole seismic studies performed prior to and after a sequence of controlled blasts within limestone and dolomite rock near Austin, TX. Indicators investigated are compression (P-) and shear (S-) wave travel times, first peak and maximum amplitudes, first arrival rise rate, and the linear spectrum of the received signal. Compression wave travel time yielded the most consistent results, while the various amplitude indicators yielded the poorest results for the equipment configuration utilized. In addition, this study documents magnitudes of change in seismic measurements which occurred following blasting. Both P- and S-wave travel times exhibited a wide range of variation due to blasting. Near blast centers below the surficial fractured rock, velocity decreases of about 10% were noted, significantly less than the 50% decrease observed for previously fractured near-surface rock through which the explosive energy was vented. Signal amplitude measurements also varied in magnitude but were less consistent.

Jan 1, 1989

By Gustavo Herrera Rico

As part of a general effort to increase safety, efficiency, and profitability of its mining operations, MICARE personnel with the support of NorWest Mine Services, Inc. determined that the key to improving development mining was the implementation of roof bolting as the means of primary roof support for both main entry and longwall gate road development. Until mid-1994, MICARE had relied exclusively upon primary roof support systems composed of heavy steel beams and wooden posts. Support systems were designed, implemented, and evaluated that were successful in controlling the mine roof under extreme geological conditions. This paper describes the geological challenges, support selection criteria, and presents the instrumentation and &apos;mine measurements made to assess the bolting performance during the development and retreat mining process of longwall mining.

Jan 1, 1997

By Robert C. Garson

The Mine Roof Simulator at the DOE&apos;S Mining Equipment Test Facility is described. Its use in the research and development on the behavior and response of longwall roof supports to simulated mine environment is investigated. Advanced technology analysis methods such as finite element modeling, strain gage instrumentation, and photoelastic techniques are investigated for application in roof support design two case studies are presented of test data and results.

Jan 1, 1982

By André C. Zingano

The coal pillars in room-and-pillar mining method are subjected to vertical stress due to overburden rock mass and horizontal stress relieve due to entries excavation around them. Some coal mining companies are applying rock bolts and steel straps to improve the pillar strength, consequently to reducing the pillar size and increasing coal recovery. This kind of approach deserves some discussion, whether it is pillar reinforcement or just rib support. The efficiency of pillar reinforcement (or rib support) is directly related to the initial load capacity of coal pillar, the type of excavation, and the width to high ratio of the pillar. The objective of this paper is to understand the mechanism of pillar reinforcement (or rib support) using rock bolts and steel straps on pillar ribs. Numerical simulation taking into account the relations listed above. The results showed that the increase of coal pillar strength is very short, and there is no influence on improvement of load capacity of pillar. However, the rib support avoids block falling, rib failure, and displacement, reducing the pillar failure propagation into the pillar center. Keywords: coal, pillar reinforcement, room and pillar.

Jan 1, 2006

By Hani S. Mitri

The behaviour of grouted cable bolts used for rock reinforcement as a means of ground control in hard rock mining is investigated. The study utilizes an analytical model which is based on the variational principle to calculate the shear bond stress distribution along the embedded length of cable bolt. In this paper, a comprehensive parametric study which covers both geometric and mechanical design parameters involved is presented. Special emphasis is placed on studying the characteristics of the grout model represented by Winkler springs. This involved varying the maximum shear strength of the grout, its residual strength and the slip occurring between the cable and the borehole wall.

Jan 1, 1990

By P. Palmer

Using 3D numerical modeling as a tool to predict rock behavior during mining extraction is still an uncommon practice at many underground operations. This paper will discuss how 3D numerical models were used to identify potential underground instability problems in the later stages of mining. Detailed modeling was then used to make modifications to the mine design in order to minimize the impact of the potential instability problems. This paper will also discusses how the back analysis of a previous underground collapse event at the same mine in a room and pillar area was used to identify the instability problems for a new orebody being developed deeper in the mine. A 3D numerical model was first created in the MAP3D software to determine the conditions of the pillars and the magnitude of the vertical displacement above the mining zone prior to the underground collapse. The results from the ground collapse model were then used as a threshold limit for predicting potential instabilities and developing a model for the new mining zone. sing the results from this analysis, mine management has been able to implement a much higher percentage recovery of the reserve in a new, high-grade area of the orebody while minimizing potential instabilities in the future.

Jan 1, 2005

By David A. Newman

Severe roof control problems have plagued a West Virginia underground mine since its initial development in the late 1970&apos;s. Adverse roof conditions in the Eastern portion of the reserve result from a combination of mining: - perpendicular to the major principal horizontal stress direction, - near lineament intersections, - in areas where the ratio of horizontal stress to vertical stress exceeds 2.00 to 4.00, and - where laminated strata are present in the immediate roof. The focus of this study is to identify the engineering (mine orientation, roof safety factor) and geological parameters (lineament and horizontal stress orientation, horizontal to vertical stress ratio, and immediate roof lithology) causing poor roof conditions and to quantify their influence on projected mining conditions in the Western portion of the reserve Rose diagrams were used to illustrate the correlation between the orientation of eight hundred thirty-six (836) roof falls with that of forty-four (44) lineaments and the principal horizontal stress Similarly a composite map was used to demonstrate the relationship between roof falls and the ratio of horizontal stress to vertical stress The immediate roof strata across the property were categorized as either laminated or non-laminated based upon a thorough examination of one hundred sixty-two core logs. The presence or absence of fireclay, a rider coal, and carbonaceous shale was also noted because of the historic correlation with poor roof conditions. Rock strength and physical property tests were conducted on selected immediate roof strata recovered from coreholes drilled along the mains projected to the Western portion of the reserve Potential roof control problems in the Western reserve were quantified based upon the correlations developed by analyzing engineering and geological data The main conclusion is that laminated roof strata, the rider seam, and its associated fireclay will have the greatest influence on mining conditions. Roof problems attributable to horizontal stresses will not be as severe in the West due to an increase in overburden depth and corresponding decrease in the stress ratio. Recommendations are provided for mining orientation, the layout of mains and submains, panel location, and roof support based on intended service life.

Jan 1, 1999

By Chris Kelly

The Monroe County Quarry is an open pit granite quarry located near the town of Bolingbroke. Monroe County. Georgia. The quarry has been in continuous operation for approximately 10 years. The quarry covers approximately 27 acres and has an annual production rate of 1.0 million tons. On the morning of April 26. 2000 a sudden rapid highwall failure occurred at the west end of the north wall of the quarry pit. The failure occurred approximately one hour after a three inch-wide crack was observed in an access road located at the crest of the highwall. No indications of failure had been observed prior to the development of the crack. The active mining area had been at the base of the failed area. The pit was successfully evacuated prior to the failure and there were no losses of either personnel or equipment. The amount of failed material was estimated to be in excess of two million tons. In order to ensure a safe working environment at the quarry a slope monitoring program was established in the area of the failure. The program consisted of using an EDM survey instrument to periodically measure the location of survey prisms installed at carious points on the north wall. The locations of the prisms were recorded over several months and changes in location were analyzed in order to identify and characterize the movement of the failed mass. The results of the analysis provided a basis for recommendations regarding access to various areas of the quarry. This paper discusses the factors contributing to the failure, the method of post-failure slope monitoring, anti the interpretation of the monitoring data.

Jan 1, 2002