Shortwall Mining Research Articles

Anchorage performance of large-diameter FRP bolts and their application in large deformation roadway

In underground coal mines, fibre reinforced polymer (FRP) bolt is ideal for mined rib reinforcements as it can prevent gas explosions caused by shearer frictional spark. With increasing mining depth, small diameter FRP bolts used in shallow underground mining cannot fulfil the rib support requirements. Under the engineering background of deep underground shortwall mining in Wudong coal mine, this paper systematically studies Φ27 mm FRP bolt support for large deformation coal rib. Specimens with a fan-shaped cross-section were used to enable the tensile testing of the bolt rod, the measured average tensile strength of the studied FRP bolt was (486.1 ± 9.6) MPa with a maximum elongation of 5.7%±0.6%. The shear strength of the bolt was measured as approximately 258 MPa using a self-made double shear testing apparatus. Based on the equivalent radial stiffness principle, a laboratory short encapsulation pullout test (SEPT) method for rib bolting has been developed undertaken consideration of the mechanical properties of the coal seam. Results showed that the average peak anchorage forces of the Φ27 mm FRP bolt and Φ20 mm steel rebar bolt were 108.4 and 66.4 kN, respectively, which were agreed with the theoretical calculations and field measurements. Based on theoretical analysis of the loading states of the bolt under site conditions, bolting method of full-length resin grouting was adopted to offset the weaknesses of the FRP bolt. Numerical method was employed to compare the bolting effect using Φ27 mm FRP bolts and steel rebar bolts. Large diameter FRP bolting was determined as the optimum rib support scheme to increase the productivity of the coal mine and to enhance the ground control capability for +425 level mining roadways. This study provides the laboratory testing design and theoretical prediction of large diameter FRP bolts used for rib support in large deformation roadways.

Application of Pedrail Powered Support on Strata Control in Short-Wall Coal Mining

In this study, the role of the pedrail powered (PP) support produced in China in the Wongawilli short-wall mining was explored, and the process from its import and introduction to its localization and use effect were detailed. The influences of the gob side and the solid-coal side on the pillar pressure were numerically simulated by exploring the working resistance of PP support at different locations and under different widths of pillar between mining caves (PMC) of the same branch lane during mining and investigating the pressure distribution and variations of each single pillar. The main influencing factors and their relationships with the working resistance were derived accordingly. Finally, key processing technologies to solve the problem of PP support crushing in the crushed zone were analyzed. The results suggest that the rated working resistance of PP support satisfies the requirement for use, and the roof of the branch lane behind the cutting roof line does not collapse, which ensures the safety of short-wall mining. The gob-side pressure is notably higher than the solid-coal-side pressure. When the PP support undergoes a support crushing accident, it can be pulled out by jointly adopting four key technologies, i.e., reinforced support to the roof, reinforcing rib support and ground bolt support for caving gangue piles, roof and loose body reinforcement by grouting, and traction by a prop-pulling winch.

Effect of mining parameters on surface deformation and coal pillar stability under customized shortwall mining of deep extra-thick coal seams

Underestimation of customized shortwall mining parameters of deep extra-thick coal seams (namely, mining height, mining width, and pillar width) may result in coal pillar instability, surface subsidence, and mining structure failure, while their overestimation would cause a waste of coal resources. This study proposes a new method for optimizing these parameters, whose main purpose is to achieve the maximum coal recovery rate while satisfying surface deformation and coal pillar stability requirements. A case study of an extra-thick coal seam in Eastern China with one km-overburden depth and a thickness of 10 m was analyzed. First, a new method for predicting surface deformation under deep customized shortwall mining based on surface deformation data from fully caving mining was proposed. The variation pattern of the extreme values of surface deformation parameters (including surface subsidence, tilt, curvature, and horizontal strain) versus the area-based recovery rate and mining width was analyzed. After that, the evolution law of the surface deformation with the changing mining height and area-based recovery rate was simulated using the FLAC3D software. The maximum recovery rate and the corresponding mining height, the area-based recovery rate were preliminarily determined, while the surface deformation fell within the allowable range. Simulations of evolutions of the plastic zone width, elastic core ratio, and vertical stress of coal pillars with varying coal pillar width under the maximum recovery rate were performed. The optimal mining scheme had a mining height of 10, a mining width of 100, a coal pillar width of 122 m. It ensured the coal pillar’s long-term stability with the surface deformation within the allowable range and achieved the maximum coal recovery rate of 45%. These findings are considered instrumental in the customized shortwall mining of extra-thick coal seams under buildings, in particular, under Eastern China mining and geological conditions.

Study on Overlying Strata Motion Rule of Shortwall Mining Face of Shallow Seam with Simulation Experiment

Taking Shendong mining area as a research object, the roof strata moving law in the shallow buried deep thin bedrock was studied with 3D simulation experiment. The results showed that the surface displacement and roof pressure decrease little, and the roof does not appear the phenomenon of full thickness cutting. As the advancing distance of the working face increases, the displacement of the surface and roof increases. The old roof breaking is not easy to form a hinge structure, the roof when the pressure of mine pressure appearance is very intense.

Modeling geomechanical processes in underground longwall and shortwall mining of thick coal seams with elements of robotization

A variant of the technological scheme for thick layer mining with top coal caving and pre-destruction of coal by means of advanced parallel chambers is proposed. Based on the results of numerical modeling, the optimum dimensions are justified for chambers, interchamber coal pillars as well as crown pillar between the chambers and immediate roof rocks. It has been proved that after the advanced chambers are made, the strength roof coal is reduced by a factor of 2 to 2.5, and therefore the conditions are created for uniform coal caving without dilution. A variant of the technology of unmanned coal mining in the chambers is proposed.

Applicability of the shortwall mining methods in Rembas mine pits

In the Rembas mine pits, the coal exploitation lasts for more than one century. During this period, most of coal reserves have been mined, so there is a need for introduction the new and modern technical solutions, which will enable rationalization of exploitation, higher productivity, safety on operations and better operation conditions with lower investments. In the Rembas mine pits for coal exploitation, the low-productive pillar mining methods are used. During the eighties of the last century in some pits, the mechanized longwall mining method was applied, but the expensive equipment and complex natural-geological conditions in the area Resava-Moravian coal basin restrict application of this metod. Bad financial situation, as well as the increasingly difficult operation conditions of exploitation, indicate a need to apply some of the methods which would be technically justified, and whose cost of exploitation would be proportional to the possibilities of mine. In this paper, the possibilities for application the shortwall mining methods are considered with their advantages compared to the previously applied mining methods in the Rembas mine.

Numerical Estimation of Suitable Distance between Two Adjacent Panels’ Working Faces in Shortwall Mining

AbstractDetermining a suitable distance between two adjacent panels’ working faces (DBTF) is an important issue that should be considered in underground mining methods. A suitable DBTF causes a decrease in stresses on the pillar, reduces the width of the pillar, and controls the ground subsidence. The main purpose of this study was to determine the suitable DBTF in shortwall mining of the Tabas central coal mine. For this purpose, at the beginning, an algorithm is presented for numerical modeling. In this algorithm, front abutment stresses first and then side abutment stresses are evaluated on the chain pillar. Numerical modeling is performed by finite-difference method software in different distances of P5 and P6 panels’ working faces (5–45 m). The result of this research shows that the front abutment stress on the chain pillars is not different for a distance of 25 m or more. Moreover, by increasing the distance up to 25 m, the side abutment stress in the vicinity of the P5 panel face is decreased on th...

Restructuring of mines: technological and economical aspects

The present paper covers technological changes in the coal mining process. Coal is the main domestic energy resource in Ukraine. In this context such issues as upgrading of conventional technologies and introduction of innovative developments need early solution. Technology is a driving force of strategic development of enterprises in all industries, including the mining.Technological aspects and their interrelation with competitiveness were explored and substantiated by I. Ansoff, who also identified three possible variability levels of technology: 'stable', 'productive' and 'changeable'.'Stable' technology is virtually unchangeable throughout the life cycle of demand. It is intrinsic to coal production as coal has been mined for centuries and in spite of changes in mining techniques, the demand for it is high enough. This technology originated approximately in the late 18th century when the first mines appeared in the Donets Basin.'Productive' technology means the traditional one within which various innovations are introduced. In the early development period of the mining industry only pillar mining was used. Two new directions were subsequently developed: shortwall and longwall mining. Winning mechanization in European countries was achieved through development of longwall machines. The USA preferred shortwall mining of coal seams.The above mining alternatives were examined at Donbas mines, the results compared by such parameters as the number of workers and their labor capacity.The necessity of introduction and further improvement of 'manless' mining flow diagrams was substantiated. Some methods for roadway maintenance without repairs were described. The measures required for roadway maintenance without repairs under different conditions can be divided into a number of groups: ways of roadway protection, use of supports with improved yielding, an increased cross-sectional area and longitudinal section of workings during driving, reinforcement of seam bearing rock, application of mine overhead carriers.'Changeable' technology comprises such unconventional techniques as underground gasification, hydrogenization and hydraulic coal mining by boreholes as well as ancillary recovery of methane gas.

Совершенствование селективной выемки калийных пластов короткими очистными забоями с частичной закладкой выработанных камер

Совершенствование селективной выемки калийных пластов короткими очистными забоями с частичной закладкой выработанных камер

Research of Large-Area Hard Roof Caving Prevention and Control System in Shortwall Mining Face

In the mining process, if the roof is very hard, it will hang in a large area in the gob. The hanging roof may cave suddenly, which will crash the mining face and generate hurricanes so as to cause casualties and equipment damage. The hard roof control technology has mainly been used in the longwall mining face in coal mines for a long time, and made little use in shortwall mining face. The factors of roof caving is analyzed in shortwall mining area, which mainly consists of the coal pillar size and layout, the length of coal face, roof thickness and strength, the overburden load, the supporting conditions of roof and so on and the relationship of the factor and the limit caving area is studied. And then a new integrated control technology system is put forward, which includes: support and isolation by coal pillars, roof caving pressure relief, monitoring and early warning of roof fall, gob sealing by the stopping walls, and the principle of different technology and the parameter selection method is claimed. This technology is applied in Shangwan Mine of Shendong Group in China and the results shows that the hard roof caves naturally in small area, the hidden danger of large-area roof caving is eliminated completely, so the coal production is guaranteed to be safe.

Water inrush and environmental impact of shallow seam mining

Shallow seam mining is very common in China for enhancing coal recovery. However, this may cause a series of severe problems in environment and mining safety in some cases, because the alluvium aquifers are directly above the shallow coal seams. Some typical water and sand inrush incidents resulting from shallow mining in China are analyzed. Based on in-situ observation, the mining-induced strata failures are investigated. The height of the fractured zone decreases as the size of the outcrop pillar or mining depth decreases. The spatial distributions of the failure zones in the shallow mining have specific features compared to the deep mining. These provide an advantageous condition for the shallow mining under alluvial aquifers. Optimal designs for outcrop pillar sizes are also given in different hydrogeological conditions for environment friendly and production-safe mining at shallow depths. According to in-situ mining experiments in several coalfields, technical measures for shallow mining are presented. These primarily include the lift mining for thick seams and reduction of the thickness of extraction in the first lift, short-wall mining, and detection of faults and other potential hazards prior to mining.

Investigations of water inrushes from aquifers under coal seams

In many coal mines, limestone-confined aquifers underlie coal seams. During coal extraction from these mines, water inrushes occur frequently with disastrous consequences. This paper introduces the hydrogeological conditions of the coal mines and the potential water inrush disasters from aquifers under coal seams. It then presents the water inrush mechanism. The main factors which control water inrushes include strata pressure, mining size, geologic structures and the water pressure in the underlying aquifer. Analysis shows that reduction of confinement due to mining is the major cause of the water-conducting failure in the floor strata. The depth of the failure zone is strongly dependent on the mining width. This paper also presents field observation results of the water-conducting failure in the floor strata, and applies the finite element method coupled with stress-dependent permeability to analyze hydraulic conductivity enhancement due to coal extraction. Finally, theoretical and empirical methods to predict water inrushes are given, and technical measures for improving mine design and safety for coal extraction over aquifers are presented. These measures include fault and fracture grouting and mining method modification such as changing long-wall to short-wall mining.

Exploitation of developed coal mine pillars by shortwall mining—a case example

The shortwall mining technique is similar to longwall mining but with shorter face lengths, ranging between 40 and 90 m, with the aim of controlling the caving nature of the overlying upper strata, the load on support and the overall operation of the supports applied at the face. Field observations and three-dimensional numerical modelling studies have been conducted for the longwall panel extraction of the Passang seam at Balrampur Mine of SECL to understand the caving behavior of the overlying upper strata. A large area of the Passang seam adjacent to the longwall panels has already been developed via bord and pillar workings. In this paper, numerical modelling studies have been conducted to assess the cavability of the overlying strata of the Passang seam in the mine over developed bord and pillar workings along with the support requirement at the face and in the advance gallery. The caving nature of the overlying rocks characterized by the main fall is predicted for varying face lengths, strata condition and depths of cover. The support resistance required at the face, the load in the advance gallery and its optimal obliquity were estimated for faster exploitation of the developed pillars in the Balrampur mine by shortwall mining.

Shortwall mining of Trona using an advancing tailgate : Hynes, P W Min EngngV41, N11, Nov 1989, P1126–1131

Shortwall mining of Trona using an advancing tailgate : Hynes, P W Min EngngV41, N11, Nov 1989, P1126–1131

A case study on past shortwall mining methods and the risk of ground subsidence in the Lanarkshire Coalfield, Scotland

Abstract A site investigation involving archival research and a borehole drilling programme was carried out in order to assess the risk to surface stability from abandoned shallow shortwall mineworkings at a proposed housing development site located on the Lanarkshire Coalfield. Of the exploitable coal seams present below the site, the Ell coals were confirmed to be at shallow depth and were mined into the mid-1950’s from the adjacent Thankerton Colliery. The Ell coal in this part of the coalfield occurs in three distinct leaves, the uppermost of which crops through the site and was not mined. The investigation confirmed the extent of mining in the Mid and Lower Ell seams which were proved to be no more than 0.5 m apart with a combined unworked thickness of 1.5 to 1.9 m. The mine records indicate that the Mid and Lower Ell seams were mined by shortwall methods, individual panels having been worked from a network of main roadways or headings with subsidiary side or haulage roadways. Due to the thin partings between the seams, a method of mining each seam from common roadways extending to the full height of combined seams was used in addition to single seam workings of the thicker Mid Ell. From the abandonment information it has been deduced that mining involved the total extraction of the Mid Ell whilst maintaining the integrity of the roadways. Subsequently, the same roadways allowed access to the Lower Ell for extraction below the collapsed Mid Ell workings. The investigations recorded the shortwall panels to be largely consolidated but also noted that several panels had been undeveloped with respect to the lower seam and that some roadways were confined to the Mid Ell seam. The borehole investigation together with the use of down-the-hole closed circuit television (CCTV) also confirmed the presence of broken ground and open voids of 0.3 to 2.0 m height along former roadway alignments. A risk to surface stability was identified from these open voids and development constraints zones are discussed in relation to the likely mining methods. Seam depths, void heights, condition of roof strata and thickness of superficial cover are considered in the assessment of void migration mechanisms arising from such a past mining situation.

Ground movement and pressure changes associated with shortwall mining : Howell, R C; Wright, F D; Dearinger, J A In: Monograph 1 on Rock Mechanics Applications in Mining (New York: AIME, 1977), P40–45

Ground movement and pressure changes associated with shortwall mining : Howell, R C; Wright, F D; Dearinger, J A In: Monograph 1 on Rock Mechanics Applications in Mining (New York: AIME, 1977), P40–45