Mine Roof Research Articles

Comparative Analysis of Overburden Strata Movement in Fully Mechanized Top Coal Caving Mining in Entire (Sub) Layer of Ultra Thick Seam

Reasonable determination of entire layer or sublayer mining method is the key factor of safe and efficient mechanized caving mining of 14.0～28.0m ultra thick seam , numerical simulation on the entire (sub) layer coal caving mining by the FLAC3D , studying the stress and displacement variation of overburden strata , combining the underground pressure theory , comparative analysis on the calculation results . The results show that entire (sub) layer mining roof stress , movement contours are presented in a semi-elliptical arch morphology , indicating the existence of a high arch structure overburden formations , mining process appears roof tensile destruction , but the entire layer caving tensile stress intensity is lower than sublayer caving . When advancing the same distance , entire layer caving puts a greater impact on the overburden strata than the sublayer caving , has some features such as big range of influence and extent , small roof pressure , lead abutment pressure forward from grand , short time of achieving full extraction , etc.

Research Review and Advance on Shallow Buried Coal Seam Mining Pressure

In order to research the law of mine pressure and roof control in shallow buried coal seam, based on a comprehensive summary of mine pressure theory, technology application, engineering practice, summarized research results and status, analyzed research shortage, proposed research proposals. The results show that:1“short masonry beam” and “step beam” structure mechanical model and “key stratum in shallow seam theory” has provided theory basis for coal seam roof control shallow guidance. 2Rock and soil (bedrock and alluvium) coupling mechanism, loose layer dynamic structure theory," coal mining, water retention, ecology conservation, subsidence control" optimized portfolio on management theory and technical system of is the required research direction. 3Sichuan, Yunnan, Guizhou, representative of southwest mountainous shallow buried coal seam mining pressure research is conducive to development of mining pressure theory system.

Design of the Roof Support with Strait-Line Mechanism

One of the most important aspects of machine designing is to balance between the economic requirements and the safety ones. Taking into account these requirements it was conducted the design work to elaborate the new concept of the mining roof support that fulfil them. The mining roof support is a mining equipment that has the most influence on the safety of work in deep coal mines and on the productivity of deep mines. Moreover the hydraulic roof support generally accounts for over 50% of the total value of a coal mining and excavating system. It is consider not only with the complexity of the roof support but also with the accepted direction of the development of mining supports. Generally designers elaborate heavier constructions with prof of larger diameters and loads. In this way the support system must be prepare not only to withdraw the rock mass forces but also the forces generated by its hydraulic system. These prerequisites underlie the new project of a roof support. This project bases also on many Polish patents concerning the mechanical devices and hydraulic equipment of a mining roof support. The main idea of the work was to elaborate the scheme of a support that will be compatible with the system of loads generating by the rock mass and by the conditions of work in a deep mine. As a result it was proposed the concept of a hydraulic roof support equipped with four props that work only in a vertical position. To realize that task it was proposed the special designed strait-line mechanism protected by Polish patent. This mechanism is supported by gas springs with low resistance. These springs help to eliminate horizontal forces loaded the construction. It has been also designed special flexible roof part (also patented) that allows to eliminate the horizontal component of roof rock loads. The hydraulic system is equipped with gas dampers that compensate dynamic loads during bumps in longwalls. The design of the dampers is also patented. In the result of design process the new concept of the roof support have been elaborated. One prototype has been manufactured. According to analysis it is about half the weight of standard roof support and the cost of it reaches the 50% of a standard support. It should be the optimal proposal for the European mining industry.

Stress distribution of mine roof with the boundary element method

Mine roof, is a stiff rock strata, located on the top of coal seam, which can prevent the deformation and control the stability of coal roadway after the coal roadway is tunneled, so mine roof is one of the most important structures in coal mining engineering. In this paper, mine roof is treated as elastic plate, which is studied thoroughly at the theoretical level. Based on the mechanical models of plane and stress analysis for elastic roof, using the boundary integral equation which is obtained by the natural boundary reduction, this paper obtains stress functions of elastic half roof, as well as the analytical and numerical solutions to the each stress field functions. We also analyze the rules of different stress distributions for roof under a concentrated force and a uniform distribution load, the results of calculation show uniformity of the stress distribution. In order to research the mine roof deformation law, Mohr–Coulomb model is established to describe the deformation behavior of roof surrounding rock, FLAC3D is also used to simulate the deformation of roof after the coal roadway is tunneled under different length of coal roadway excavation. The comparison result between BEM solution and FLAC3D simulation shows advantages to solve the problem by boundary element method, and numerical simulation proves the deformation behavior of roof is influenced by the length of coal roadway excavation.

Stress Distribution Characteristics in Rock Surrounding Heading Face and its Relationship with Temporary Supporting

To solve the problem of underground tunneling face from the empty top, using FLAC3D analysis software, surrounding rock stability for coal roadway 2-1121 of Ganhe Coal Mine are analyzed in numerical calculation. (1) During the tunneling, distance drivage face head-on 0.5-1m at the roof of roadway deformation and destruction features are more obvious, the two sides of roadway are even more significant. (2) Ganhe Coal Mine roof deformation has been established with different empty the experience formula of the zenith distance, obtained Ganhe underground tunneling face reasonable empty zenith distance is 3.5m. (3) Temporary support can obviously reduce roof deformation, reduce thickness of plastic zone of the top, to improve the stability of surrounding rock tunneling faces.

Simulation of roof shear failure in coal mine roadways using an innovative UDEC Trigon approach

Shear failure is a common failure mechanism in underground coal mine roadways. This paper presents an innovative numerical approach to simulate shear failure of a coal mine roadway roof. The distinct element code, UDEC, incorporating a proposed Trigon logic is employed for the study. Using this approach, shear failure in the mine roof characterized by fractured initiation and propagation is successfully captured. The results suggest that shear failure of the roadway roof initiates at the roadway corners and then progressively propagates deeper into the roof, finally forming a large scale roof failure. The numerical results confirmed the time sequence of marked microseismic activity, significant stress changes and accelerated displacement during the process of a roof fall. The effect of rock bolting in the control of roof shear failure in a roadway is evaluated using the UDEC Trigon approach. It is found that the installation of rock bolts constrains rock dilation, reduces failure of rock bridges and maintains rock strength thereby leading to a significant decrease in roof sag.

Comparing the reinforcement capacity of welded steel mesh and a thin spray-on liner using large scale laboratory tests

Steel mesh is used as a passive skin confinement medium to supplement the active support provided by rock bolts for roof and rib control in underground coal mines. Thin spray-on liners (TSL) are believed to have the potential to take the place of steel mesh as the skin confinement medium in underground mines. To confirm this belief, large scale laboratory experiments were conducted to compare the behaviour of welded steel mesh and a TSL, when used in conjunction with rock bolts, in reinforcing strata with weak bedding planes and strata prone to guttering, two common rock conditions which exist in coal mines. It was found that while the peak load taken by the simulated rock mass with weak bedding planes acting as the control sample (no skin confinement) was 2494kN, the corresponding value of the sample with 5mm thick TSL reinforcement reached 2856kN. The peak load of the steel mesh reinforced sample was only 2321kN, but this was attributed to the fact that one of the rock bolts broke during the test. The TSL reinforced sample had a similar post-yield behaviour as the steel mesh reinforced one. The results of the large scale guttering test indicated that a TSL is better than steel mesh in restricting rock movement and thus inhibiting the formation of gutters in the roof.

Piezoelectric Self-Excited System in Mining Roof Anchor Stress Change Measurement

The paper presents the application of a new type of a measurement system called Self-excited Acoustical System (SAS). It was applied for stress change monitoring of anchors which are used to secure roofs and walls in mines and in hollowed tunnels. The knowledge about the state of anchors can indirectly indicate the state of rock masses which is crucial for mining safety. One of the main problems so far has been reliable sensor mounting, especially in difficult mining conditions. The SAS system overcomes this problem because it can be mounted easily at the anchors end or even on the anchors flange. The laboratory tests were conducted on a hydraulic tensile testing machine. The mining roof anchor was placed in the machine and then stretched. The changes of the resonance frequency caused by the increase of the tensile strength were observed during the research.

Evaluation of directional drilling implication of double layered pipe umbrella system for the coal mine roof support with composite material and beam element methods using FLAC 3D

This study demonstrates possible scenarios of double-layered umbrella pipe system installed over a longwall take down room in a western coal mine, where holes are drilled and cased from an adjacent entry in advance of undermining. Finite difference analysis in FLAC 3D with strain hardening gob model is used because this method is a complex and rigorous way for solving boundary value problems, such stress and strain in a continuum and at an excavation boundary due to undermining. Support system was simulated with two different methods: composite material method and beam element method. We realized that the composite material method is very conservative compared to beam element method. Thus, in the rest of the simulation, we used the beam element method to investigate the effect of different angles of umbrella pipes on the roof support. To validate the modeling results, we compare the numeral modeling results with empirical formula widely used in subsidence calculation. Also, this computer simulation compared displacement of roof between in the presence and absence of this pipe umbrella support system. In this paper, we demonstrated that a relative stiffness increase ∼185% for a reinforced zone can decrease the displacement ∼ 12.5 cm (∼ 5 in.) in the longwall recovery room roof based on results from the equivalent stiffness method. This reduction is a substantial amount, which could be really beneficial to mine operators during mining processes.

Design of Coal mining Roof Pressure Monitoring System Based on Labview

In order to monitor the press of mining roof in combined face, the paper design a coal mining roof pressure monitoring system. The system includes roof pressure testing device, intelligent portable data acquisition meter and upper lever computer monitoring and processing system. Roof pressure testing device is mainly testing the pressure of mining roof and transmitting pressure data to intelligent portable data acquisition meter by infrared communication technology within the allotted time. Intelligent portable data acquisition meter can also transmit pressure data to upper lever computer monitoring and processing system for further analysis and storage. Test results indicate that the system can achieve long-term continuous monitoring to roof pressure and provide the reference frame about roof control through the analysis of the monitoring results.

Practical strength criterion for coal mine roof support design in laminated soft rocks

The stone roofs of coal mine roadways typically comprise low strength, thinly bedded and closely jointed mudstones, siltstones and sandstones. A practical strength criterion for use in currently available numerical codes should include consideration of the pronounced transverse isotropy introduced by the bedding and the tensile strength should be set to zero. The compressive strength is then the greater of either the damage/brittle criterion implemented as cohesion = UCS/6 and a friction angle of 0° or a purely frictional component with a friction angle of 33°. This criterion can be used to estimate the maximum height of a roof fall in bedded sedimentary rocks similar to coal measures.

Virtual Analysis of the Mining Support under Loads of the Roof

The paper presents the results of virtual analysis of the stability of mining roof supports loaded by the roof rocks. The hydraulic roof support generally accounts for over 50% of the total value of a coal mining and excavating system. Many reports show that in some conditions roof supports behave differently than foreseen. To explain this phenomena the investigations basing on the virtual model were done [1,2]. This phenomena is very dangerous for miners because this behaviour of a mining roof support may cause dangerous accidents in coal mines. In the investigation process some questions have been asked. Firstly what type of a mining support is more liable to this behaviour. Secondly what work conditions are the most dangerous. To analyse this phenomena it was used models of two types of a mining support. One with two props and one with four ones. Results show that that the problem of plunged of roof parts of a support in the coal bed is consider with the construction of the support. The most dangerous is the roof support with two props. The consequences of this results are the recommendations to use rather supports with four props then two.

Fracturing of an Euler–Bernoulli beam in coal mine pillar extraction

The paper models the first stage of the process of pillar extraction in a coal mine. The problem of understanding how a coal mine roof collapses after secondary cutting of the supporting pillars to create small supporting snooks is considered. The fracture of the roof is considered when a set of snooks have failed and the roof must support itself between two pillars. Models that account for the relative importance of the overburden weight on the roof and the compressive stresses in the roof are examined using a simple strut and beam theory.

Rock permeability in displacement zones at coal deposits: A case study of underworked inundated mines

Rock displacement in some sites of coal mines is accompanied by changes in the permeability and fil� tering structure of the host rock massif. Transforma� tion of a massif resulting from the appearance of such hydrogeological channels significantly affects the con� ditions and environmental impact of mining; such a channel provides water flow through it and is called a “zone of water conducting displacement cracks” (ZWCDC). The maximal changes take place at the sites of a collapsed mine roof. The operational practice has revealed the ability to keep the minimal increment in through permeability of a dividing rock mass within the ZWCDC and to pre� serve the zones of minimal permeability values within the massif. These conclusions, supplemented with the studies of cracked structures based on equivalent material models, were also reported in [1] and became standard for Russian norms regarding the determination of coal extraction conditions near water objects.

Analysis of Unsafe Acts in Mine Roof Accident and Prevention Measures

According to the research of Heinrich, DuPont Company and U.S. National Security Council, more than 80% of accidents are caused by individuals’ unsafe acts. In order to eliminate unsafe acts causing mine roof accidents, 10 types of common unsafe acts were summarized and 4 kinds occur most frequently based on 40 typical roof accidents, these 4 kinds of common unsafe acts are not choose the right work methods(20%), not prevent unsafe acts of others(17.5%), not check the environment(15%), nobody observe roof while working(12.5%). And then, corresponding safe acts are given. Finally, 4 types of improving measures are proposed, they are unsafe acts demonstration via 3-D animation, virtual reality training, unsafe acts knowledge contest and pithy formula teaching.

A Middle Miocene carbonate embankment on an active volcanic slope: Ilhéu de Baixo, Madeira Archipelago, Eastern Atlantic

Carbonate factories on insular oceanic islands in active volcanic settings are poorly explored. This case study illuminates marginal limestone deposits on a steep volcanic flank and their recurring interruption by deposits linked to volcaniclastic processes. Historically known as Ilhéu da Cal (Lime Island), Ilhéu de Baixo was separated from Porto Santo, in the Madeira Archipelago, during the course of the Quaternary. Here, extensive mines were tunnelled in the Miocene carbonate strata for the production of slaked lime. Approximately 10 000 m3 of calcarenite (−1 to 1ø) was removed by hand labour from the Blandy Brothers mine at the south end of the islet. Investigations of two stratigraphic sections at opposite ends of the mine reveal that the quarried material represents an incipient carbonate ramp developed from east to west and embanked against the flank of a volcanic island. A petrographic analysis of limestones from the mine shows that coralline red algae from crushed rhodoliths account for 51% of all identifiable bioclasts. This material was transported shoreward and deposited on the ramp between normal wave base and storm wave base at moderate depths. The mine's roof rocks are formed by Surtseyan deposits from a subsequent volcanic eruption. Volcaniclastic density flows also are a prevalent factor interrupting renewed carbonate deposition. These flows arrived downslope from the north and gradually steepened the debris apron westwards. Slope instability is further shown by a coral rudstone density flow that followed from growth of a coral reef dominated by Pocillopora madreporacea (Lamarck), partial reef collapse, and transport from a more easterly direction into a fore-reef setting. The uppermost facies represents a soft bottom at moderate depths in a quiet, but shore-proximal setting. Application of this study to a broader understanding of the relationship between carbonate and volcaniclastic deposition on oceanic islands emphasizes the susceptibility of carbonates to dilution and complete removal by density flows of various kinds, in contrast to the potential for preservation beneath less-disruptive Surtseyan deposits. Copyright © 2013 John Wiley & Sons, Ltd.

Analysis on Gas Geological Law of No.56 Coal Seam in Shengli Mine

Based on the analysis of geologic structure evolution and distribution characteristic in the Shengli Mine, which studied the influence that the mine geological structure, roof and floor lithologic of coal seam and elevation of seam floor, made on mine gas occurrence, combined with geological data and a large number of experimental data. Detailed elaboration about the situation in the Shengli Mine gas geology law, and prediction about gas emission and the dangerous of gas regional outburst. The results show that the gas content of the seam would be increases with the depth of the seam increases; There would be an abnormal phenomenon occurred at the geological fault about the gas occurrence, which is especially obvious in fault fracture zone.

Design of Intelligent Coal Mine Roof Online Monitoring System Based on CAN Bus

Design of Intelligent Coal Mine Roof Online Monitoring System Based on CAN Bus

Fracture aperture and fill characterization in a limestone quarry using GPR thin‐layer AVA analysis

The detection and characterization of fractures is important in many engineering practices e.g., rock fall assessment, quarry rock quality determination and mine roof and tunnel stability. Fractures may provide suitable contrasts in electrical properties for detection by GPR instruments. Their ability to reflect radar waves and the dependence of this reflectivity on fracture properties (aperture and fill) makes the GPR method a promising tool for rock fracture characterization. Doing so successfully requires quantification of the reflectivity, reflection coefficient, R, of individual fractures and its variation with incidence angle (AVA), or in practice, offset. Measuring the full AVA response using Common Mid Point (CMP) surveys enables simultaneous estimation of fracture aperture and fill permittivity, difficult to achieve with Common Offset (CO) profiling which does not evaluate angle dependence. This paper reports on AVA analysis carried out on CMP data acquired with 500 MHz antennae over Carboniferous Limestone with horizontal bedding plane fractures in Yorkshire, United Kingdom. Using the transverse electric (TE) polarization mode, data were collected at a sampling interval of 0.05 ns for offsets at 0.04 m steps from 0.37–16.05m.The recorded amplitude is related to the reflection coefficient but is also influenced by other factors we eliminated by making some simplifying assumptions and amplitude corrections. We assume frequency‐independent electrical properties, constant antenna coupling with the ground surface, constant losses associated with transmission losses through any interfaces above the target reflection for the range of offsets considered and a flat homogeneous surface over which measurements are made. Amplitudes were corrected for conductive attenuation, spherical spreading and antenna patterns, which we measured through transillumination surveys across limestone boulders and numerical modelling using the GprMax 3D modelling code. To constrain fracture aperture and fill permittivity, we use the least squares fit of normalized reflection coefficient curves to corrected CMP amplitudes. The analysis allowed characterization of the (bedding plane) fracture fill relative permittivity (~7.8) and aperture (~0.043 m, ~0.2 at 500 MHz). The values obtained are consistent with field observations of fracture fill, corresponding to a mixture of clays and calcite.

Numerical analysis and geotechnical assessment of mine scale model

Various numerical methods are available to model, simulate, analyse and interpret the results; however a major task is to select a reliable and intended tool to perform a realistic assessment of any problem. For a model to be a representative of the realistic mining scenario, a verified tool must be chosen to perform an assessment of mine roof support requirement and address the geotechnical risks associated with longwall mining. The dependable tools provide a safe working environment, increased production, efficient management of resources and reduce environmental impacts of mining. Although various methods, for example, analytical, experimental and empirical are being adopted in mining, in recent days numerical tools are becoming popular due to the advancement in computer hardware and numerical methods. Empirical rules based on past experiences do provide a general guide, however due to the heterogeneous nature of mine geology (i.e., none of the mine sites are identical), numerical simulations of mine site specific conditions would lend better insights into some underlying issues. The paper highlights the use of a continuum mechanics based tool in coal mining with a mine scale model. The continuum modelling can provide close to accurate stress fields and deformation. The paper describes the use of existing mine data to calibrate and validate the model parameters, which then are used to assess geotechnical issues related with installing a new high capacity longwall mine at the mine site. A variety of parameters, for example, chock convergences, caveability of overlying sandstones, abutment and vertical stresses have been estimated.