Highwall Stability Research Articles

Analysis of Fault’s Effect on the Highwall Stability of Medapalli Open Pit Coal Mine

Analysis of Fault’s Effect on the Highwall Stability of Medapalli Open Pit Coal Mine

Simulation Research for the Influence of Mining Sequence on Coal Pillar Stability under Highwall Mining Method

Highwall mining, which is referred to the technique of extracting coal from the bottom of an exposed highwall, features safety, efficiency, and economy. According to existing highwall mining methods, the mining sequence has a great influence on highwall stability. Based on a highwall mining project in Australia, this study adopted the FLAC3D numerical simulation method to investigate the stability of coal pillars with different mining sequences. The results show that different mining sequences of boreholes exert a great effect on highwall stability. Compared with sequential mining, the skip mining method achieves higher speed of highwall stabilization and smaller plastic zone of coal pillar with its maximum strength decreasing by 12%. By adjusting the mining sequence scientifically, the coal pillar failure and roof collapse caused by the deviation of mining angle can be avoided. The results may provide a new angle for the studies on the coal pillar layout and stability design in highwall mining.

Understanding the connection between blasting and highwall stability

Surface mines continue to implement highwalls for several reasons, such as increasing recovery, improving margins, and justifying higher stripping ratios. Highwall stability is a complex issue that is dependent upon a variety of mining and geologic factors, and a safe design is necessary for a successful surface operation. To improve highwall stability, it is important to understand the connection between local geology and blasting. Explosives are employed throughout the mining industry for primary rock breakage. There are a number of controlled blasting techniques that can be implemented to improve highwall stability. These include line drilling, smooth wall blasting, trim blasting, buffer blasting, air decking, and presplitting. Each of these techniques have associated advantages and disadvantages. Understanding local geology is necessary for selecting the appropriate controlled blasting technique. Furthermore, understanding the limitations and conditions for successful implementation of each technique is necessary. A discussion of the impact of geologic conditions on highwall stability is provided. Additionally, discussion is provided for the successful incorporation of the controlled blasting techniques listed above, and the associated mining and geologic factors that influence the selection and design of controlled blasting plans. Finally, a new methodology is proposed.

Highwall mining of thick, steeply dipping coal–a case study in geotechnical design and recovery optimization

Highwall mining of thick (up to 30.48 m) steeply dipping (20° or more) coal seams provides many challenges, both geotechnically and operationally, as seam dips near or in excess of highwall mining machine capabilities are encountered. Maximizing coal recovery while maintaining highwall stability requires innovative techniques with regard to web and barrier pillar layout, depth of penetration, and choice of mining horizon within the seam. Stability of highwall mining slopes, openings, and pillarsare typically analyzed using the ARMPS-HWM program, as well as LAMODEL, UDEC and Slope-W modeling. Highwall stability can be maintained, and highwall mining production optimized by applying design criteria in creative ways, including alternating miner penetration depths and initiating mining of thick seams toward the bottom of the seam. Highwall mining of thick, steeply dipping coal requires careful planning and execution, including close cooperation between geotechnical design engineers, the mining company, and the highwall mining contractor. This paper describes the application of creative design techniques to a specific pit arrangement at the Westmoreland Kemmerer Mine, Kemmerer, Wyoming. Highwall mining was accomplished by UGM ADDCAR Systems, LLC on a contract basis.

The influence of the unsaturated soil zone on 2-D and 3-D slope stability analyses

It is commonly understood that a 2-D slope stability analysis will provide a lower factor of safety than a 3-D slope stability analysis. The difference in the calculated factors of safety between a 2-D and a 3-D analysis is generally less than 15% for simple slope geometries. Most past comparative studies between 2-D and 3-D stability analyses have ignored the effect of negative pore-water pressures (i.e., matric suctions) in the soil zone above the groundwater table. In this paper, a comparison is made between 2-D and 3-D slope stability analyses on soil slopes where a portion of the soil profile has matric suctions. The factors of safety on simple geometry slopes and complex geometry slopes (i.e., slopes which have two intersecting slope surfaces), are investigated for a range of shear strength parameters and groundwater conditions. For simple slopes with a low slope angle, the difference in factor of safety between a 2-D and a 3-D slope stability analysis, (i.e., ΔFs/Fs2-D), generally ranges from 9% to 16% when ϕb is equal to 15°. The value of ΔFs/Fs2-D for a steep, simple slope is generally larger than for a low angle, simple slope. When ϕb is 15°, the values of ΔFs/Fs2-D for the simple, steep slope generally range from 12 to 18%. The difference between a 2-D and a 3-D stability analysis was most pronounced for concave geometries where a portion of the soil profile contained unsaturated soils. The values of ΔFs/Fs2-D for corner angle concave slopes with angles ranging between 180 to 270° can be as large as 20 to 59% when ϕb is equal to 15°. Two case histories, (i.e., the highwall stability failure at the Poplar River coal mine and the Kettleman Hills landfill slope failure), were used to illustrate the effect of the unsaturated zone on changes in the factors of safety.

Applying real time seismic monitoring technology for slope stability assessment—An Indian opencast coal mine perspective

This paper outlines the results obtained from real time microseismic monitoring of an opencast coal mine in South India. The objective of the study is to investigate the stress changes within the rockmass along the slope due to underground mine development operation and their impact on the stability of the highwall slope. The installed microseismic systems recorded the seismic triggerings down to −2 moment magnitude. In general, most of the events recorded during the monitoring period are weak in seismic energy. The study adopts a simple and more reliable tool to characterize the seismically active zone for assessing the stability of the highwall in real time. The impact of underground working on the slope is studied on the basis of the seismic event impact contours and seismic clusters. During the monitoring period, it is observed that the intensity of the overall microseismic activity along the slope due to the mine development operations did not cause any adverse impact on the highwall stability.

Successful Repair of a Subtotal Rupture of Distal Tracheobronchial Tree With Complete Abridgment of the Right Bronchus in a 4-Year-Old Child

Accurate diagnosis of tracheobronchial injuries in children is difficult due to the paucity of clinical presentation and the variety of clinical symptoms. They are potentially life threatening in blunt chest trauma. We report here on a clinical case of a boy who was injured during outdoor activity. We describe intraoperative findings of the massive tracheobronchial lesion and its successful repair using a pericardial patch technique and postoperative recovery. Such a serious tracheobronchial injury with a positive outcome has not been reported so far. Clinical and technical steps are described and discussed.

Ground control for highwall mining in the United States

Highwall mining is an important coal mining method in the USA and may account for approximately 4% of total USA coal production. Highwall stability is the major ground-control-related safety concern in highwall mining. Engineering away the safety risk by decreasing the highwall slope angle may be the best solution to the hazard posed by vertical joints in highwalls. The Mine Safety and Health Administration (MSHA) requires a ground control plan that usually specifies the hole width, maximum hole depth, maximum overburden depth, seam thickness, web pillar width, barrier pillar width and number of holes between barriers. Design charts for these parameters are given. Web pillars containing pre-existing auger holes are analysed and a design chart for estimating their minimum width is also presented. Close-proximity multiple-split highwall mining, which caused several serious highwall failures, is analysed and recommendations are made. Finally, this study examined records from 5289 highwall miner holes with a total completed hole length of 780 300 m to understand the reasons for early pull out. Average loss was almost 20% of planned hole length, and only 35% of the holes reached the planned depth.

Highwall Stability due to Punch Mining at Opencut Coal Mines

Conventional highwall mining extracts coal with an auger machine or a continuous miner from exposed seams at the base of opencut or strip operations. However, under poor strata and high stress conditions, highwall mining cannot be conducted due to pillar and roof failures. In such cases, punch highwall mining is more effective than the conventional highwall mining. This paper describes conventional highwall mining and punch highwall mining systems and discusses the stability of the highwall due to punch highwall mining at opencut coal mines.

Estimating mechanical rock mass parameters relating to the Three Gorges Project permanent shiplock using an intelligent displacement back analysis method

Establishing the mechanical rock mass parameters is one of the important tasks for the highwall stability analysis of the permanent shiplock at the Three Gorges Project in China. Existing back analysis methods are not sufficient to provide the necessary accuracy and to recognize non-linear relations. The new displacement back analysis method proposed in this paper is a combination of a neural network, an evolutionary calculation, and numerical analysis techniques. The non-linear relation involving displacement and mechanical parameters is adequately recognized by the neural network techniques. The neural networks learn using an evolutionary technique, with samples created by orthogonal design and tested with new cases given by event design. With the neural network model established, the mechanical parameters are recognized using a genetic algorithm over a large search space in the global range. The predicted displacement occurring for each excavation step from January 1998 to the end of excavation and their cumulative values for 5 later excavation steps are closely characterized by the new analysis technique.

Progrssive failure analysis of windrow induced slope movements at the syncrude limited mine site

Abstract The presence of Marine Sediments below the operating bench in the Syncrude Canada Limited oil sand mine (NE Alberta, Canada) has negatively affected dragline mining operation. Any material that exhibits strain softening behaviour is prone to progressive failure. The Marine Clays at the Syncrude site exhibit distinct strain softening behaviour and numerous windrow-induced failures have occurred along these layers. Some of these failures have resulted in highwall failures but no highwall failures have been reported in the absence of windrow or dragline loads. Therefore, the possibility of progressive failure of an idealized highwall due to external soil loading (windrows) was of interest to study. Elastoplastic finite element analyses were carried out to investigate the influence of several variables (oilsand stiffness, shear strength parameters of marine clay, pore water pressure coefficients, depth of embedment of clay layer, insitu stress field, windrow construction mode etc.) on highwall stability, and enable us to develop a better understanding of the progressive failure mechanism. The results of the numerical analysis revealed that windrow construction results in undrained loading of the clay layer and can induce progressive failure along the brittle marine clay layers. The progressive failure process is amenable to analysis by the finite element method. The analysis indicated the importance of identifying the location and the strength properties of any weak inclusion in an otherwise strong material.

Three-dimensional modelling of highwall stability : M. S. Craig, in: Applications of computers and operations research in the minerals industries. Conference, Brisbane, 1995, ed ANON (AusIMM), 1995, pp 515–520

Three-dimensional modelling of highwall stability : M. S. Craig, in: Applications of computers and operations research in the minerals industries. Conference, Brisbane, 1995, ed ANON (AusIMM), 1995, pp 515–520

Sedimentology and its applications within the UK opencast coal mining industry

Abstract The opencast coal industry seeks to identify and extract near-surface coal reserves. Within the UK Pennine Basin, most coal deposits suitable for opencast exploitation range from middle Westphalian A to lower Westphalian C in age. These deposits dominantly accumulated in an upper delta plain setting in which subsidence rates and depositional setting formed the primary controls on the initial distribution, thickness and quality of coal reserves. Hence an appreciation and analysis of the sedimentary setting and controls on sedimentation are important in the delineation of potential areas of thick, persistent coals. The calculations of in situ coal reserves and coal to overburden ratios are important objectives during exploration for prospective opencast coal sites. Coal reserves are detrimentally affected by early, depositionally related factors such as as wash-outs, seam splits, channel bank collapse and compaction faults. The thickness and type of interseam sedimentary rock (overburden) is directly related to the original despositional environment and the nature of the overburden can change substantially across the working area of an opencast site, reflecting sedimentary facies variations. The various sedimentary facies have unique characteristics and adversely influence mining in a variety of ways, including highwall stability problems, seam gradient changes, groundwater problems, interseam interval variations and facies-specific discontinuities. Many of these problems are related to the presence of palaeochannels. Palaeochannels occur at different scales and contain a variety of fills, and their identification is an important aspect of site exploration. Sedimentary facies mapping, incorporating facies analysis, the construction of isopach maps and palaeocurrent studies can play an important part in an opencast exploration programme. Facies maps have many applications which may be invaluable in site planning, including the delineation of areas of sedimentary disturbance, improved understanding of seam thickness and quality variations, and changes in the interseam strata.

Evaluation of Aquifer Behavior and Characteristics in the Singrauli Coalfield, Central India

Hydrological investigations were conducted to determine the aquifer characteristics, recharge boundary location, and the amount of ground water which can be withdrawn safely in order to minimize potential ground–water contamination from open pit coal mining. Analysis of data obtained from bore holes drilled in the study area has revealed two aquifers: (1) an unconfined composed of medium–grained sandstone, and (2) confined composed of medium– to coarse–grained sandstone. A pumping test was conducted in Jayant block study area on the confined aquifer. Accordingly, the values for the transmissivity (T), storage coefficient (S), and hydraulic conductivity (k) obtained are 84.14 m2/day, 4.076 × 10-4, and 4.2 × 102 m /day, respectively. The results of the pumping tests indicated that a recharge boundary is located at a distance of 163 m. The recharge boundary was determined to be a stream trending N–S and situated at about 200 meters from the pumping well, closely corroborating the field situation with pump test data. From these studies it is concluded that water–supply wells should be completed in the confined aquifer. The impact of surface mining of coal on the ground–water system in Singrauli Coalfield, Central India has been investigated. Surface–water and hydrogeologic analyses were conducted in Jayant block. Field studies measured the infiltration characteristics of surface-mined land, determined surface–water runoff, and analyzed the hydrogeologic impacts of surface mining. This study provides the framework for three–dimensional analysis of such problems as the hydrogeology, risk of potential contamination, mine flooding, highwall stability, and reclaimed land surface.

Highwall Stability Analysis on a PC

Highwall Stability Analysis on a PC

Mineralogical and engineering index properties of the basal McMurray Formation clay shales

Analysis of 83 specimens of the basal McMurray Formation clay shales (basal clays) has revealed a novel clay mineralogical suite: the clays are illite–kaolinite clays, but vermiculite and mixed-layer clays are present in significant amounts. Index and engineering behavior are affected: high compressibilities, low residual angles of shearing resistance, and low permeabilities are characteristic; index properties, however, are typical of illite–kaolinite clays.Comparison of outcrop and borehole data reveal significant differences between the sample sources.The location of the basal clays at the base of future open pits has implications for oil-sand development with respect to highwall stability and tailings disposal structures.

Sedimentology, Petrology, and Geotectonic Properties of Athabasca Oil Sands, Alberta: ABSTRACT

The Athabasca oil sands deposit is not only one of the largest petroleum reservoirs in the world (870 billion bbl of oil in place), it is virtually the only supergiant oil accumulation that can be examined at outcrop. Sedimentologic and petrographic knowledge, gleaned both from the outcrop and from many subsurface cores, has direct and immediate implication for surface mining and in-situ reservoir engineering. Most of the Athabasca reserves are contained in the Lower Cretaceous McMurray Formation, a 40 to 100-m-thick sequence of uncemented quartz sandstones and associated shales, saturated with heavy oil in virtually all zones where there is significant primary porosity and permeability. Through most of the deposit region, sedimentation was dominated by fluvial and related depositional systems, culminating in the localized development of very large channels in which were deposited distinctive solitary sets of epsilon cross-strata up to 25 m thick. Insight into the characteristic facies patterns of the McMurray Formation sediments has important applications in surface mining; for projecting high-grade trends and locating prospective mine sites; for predicting variations in reservoir grade and designing mine layout accordingly; for identifying natural discontinuities (e.g., the sloping epsilon beds) that adversely affect pit high-wall stability; and for numerous other engineering uses. In the subsurface, detailed knowledge of the reservoir facies is of critical importance: in outlining the geometry of steam- or fire-flood patterns; in selecting zones which optimally may be treated with solvents, emulsifiers, or heat in order to establish inter-well communications; in identifying permeability barriers that can be exploited to cont in a given stimulation flood; and, given the current context of fledgling experimental technologies, in explaining what went wrong in specific pilot programs. End_of_Article - Last_Page 499------------