Roof Support Research Articles

Tests of Geometry of the Powered Roof Support Section

A powered roof support is a basic protection mean for longwall excavations in which highly efficient mining is carried out. The support operates properly when its individual sections are spragged correctly in a working and their operating parameters meet specific requirements. The geometry of the section, and in particular, the correct position of the floor base and the canopy, have a significant impact on the parameters and effectiveness of its work. Disturbances in this area, in many cases, are the cause of damage and improper operation of the support. Therefore, a new method of testing the position of the section in a longwall was developed based on an analysis of its geometry. The basis of this method are inclinometers (angle sensors) mounted on the main structural elements of the section. Recorded values of the angles of inclination of these elements and the developed analytical models are used to determine the positioning of the section in a longwall. The main purpose of the research was to develop a method that would allow, in the simplest possible way, the analysis of section geometry in real conditions. A simplified analytical model was used to determine the actual geometry of the section. It was used then as a basis of an analysis of possible states of the position of the section in the mining wall, including the surrounding rock mass. The results were applied during tests of the section carried out in a testing station and in real (underground) conditions. The developed measuring system helped to determine selected geometrical parameters of the section during these tests. The purpose of the research was to verify the developed model and demonstrate that the geometry of the section has a significant impact on its uneven loading. The obtained results, especially from underground tests, confirmed that during operation the support sections are twisted, which may cause overloading of their construction and disturbance of the operation process. The developed method of testing the geometry of the section is a new approach to analyzing the work of the powered roof support operating in variable mining and geological conditions. The developed method of testing the position of the section based on the angle of inclination of its individual elements is undoubtedly a new approach to this research area. The results obtained should be successfully used in practice to optimize the support section and when selecting support for specific working conditions.

The design of a laboratory apparatus to simulate the dust generated by longwall shield advances

A laboratory apparatus (shield dust simulator) was designed and constructed to simulate the dust generated during the advance of longwall hydraulic roof supports, or shields. The objective of the study was to develop a tool that could be used to test the hypothesis that foam applied to a mine roof prior to a shield advance could be used to reduce the respirable dust generated during shield advances. This paper will outline the design parameters for the development of the system, as well as describe baseline testing of coal and limestone dust. Results show that the average instantaneous respirable dust concentrated during simulated shield advance. Confidence intervals were calculated from the instantaneous respirable dust data to determine the repeatability of the data produced by the device.

Hydrodynamic Cause Analysis for Roof Damage on Water Storage Tank

Abstract The causes of roof damage found on a large-scale water storage tank were investigated using hydrodynamic analysis. All operation and weather data, such as temperature inside and outside of the storage tank, atmospheric pressure, water level according to time, condensed water check inside pipelines, snowfall, and wind speed, were precisely reviewed. Four potential scenarios were postulated to estimate the vacuum pressure, presumed to be a direct cause of the roof damage to the storage tank. In the scenarios, an energy equation with a friction loss for pipelines and fittings was adopted to compute the pressure differences between the inlet and outlet of the ventilation and overflow pipes. A timewise pressure drop for the condition of fully clogged connected lines during a discharge operation was also carried out. A sequence solution for the unsteady Bernoulli equation to represent the dynamic motion of a water column inside a loop seal was successfully derived. This can predict the vacuum pressure limit inside the storage tank required to drain out the water from the loop seal. The predicted vacuum pressure was compared with the vacuum pressure required to cause the buckling phenomena at the roof support structures. In-depth analysis of each scenario showed that the roof damage of the storage tank developed when the vacuum pressure reached over the estimated vacuum pressure limit. To prevent further roof damage, including the storage tank of the same design at other plant, change of the layout of the air ventilation line was recommended.

Components of an innovative electro-control system for undeground mining – analysis

Abstract In the era of Industry 4.0, coal companies began to reach for new innovative technologies that increase work safety and their possible use affects the economic improvement of companies. One of them is to equip a powered roof support section with an electrohydraulic control system with a monitoring system that tracks operating parameters. The development of a monitoring system for a powered roof support is a key investment in new longwall complexes. It allows rapid diagnostics of status of the support. Currently used system designed to control the powered roof support are based on blocks of manually controlled distributors. The pilot control is currently the leading control that properly functions in all conditions, allowing to adapt to the requirements resulting from the construction of the section. A number of tests and analyses must be conducted prior to introducing the new control based on an innovative approach into operation. The basic research has focused on identifying the user interface that will potentially be the solution for the entire system. The user has defined how the driver should look like and how it will be operated and maintained. The results of the first series of tests on the elements of an innovative electronic control system of the powered roof support enabled to develop a prototype version. The assumptions for the system were verified during the conducted development studies. The article presents preliminary results of development research for devices included in the innovative control system of the powered roof support.

Monitoring of the Mining Powered Roof Support Geometry

Monitoring of the Mining Powered Roof Support Geometry

Research and Application of Low Density Roof Support Technology of Rapid Excavation for Coal Roadway

The mismatch of speed of mining and excavating is the main contradiction of high efficiency production in China, improving the excavating speed of coal roadway is an effective way to solve the problem. According to the engineering geological conditions of the main haulage roadway 21205 in Hulusu Coal Mine, the technical problems existing in the original support scheme were analyzed, increased the excavating speed of roadway through improve support efficiency of single bolt and reducing density of bolt, a rapid excavation technology based on anchoring method of critical high efficiency and low density on roof of coal roadway was proposed. The influence of different bolt length and different pre-tightening force on the stability of roadway roof was studied by FLAC3D simulation, the results showed: (1) increasing the length and pre-tightening force can control the development of the roof vertical strain with a certain range; (2) as the length of bolt increases, the compressive stress zone of the rock layer between the two bolts increases and the compressive stress in the rock layer area of the anchorage section tends to increase; (3) with the increase of pre-tightening force, the effective, compressive stress zones between the two bolts overlap with each other, forming a whole, and the compressive stress values in the near zero stress zone increase. Decided the scheme that, bolt length is 4 m, pre-tightening force is 200 kN, and the support density is 0.5 root/m2, industrial experiments were carried out. The mine pressure monitoring showed that the roof of the roadway has almost no ionosphere, and the deep ionosphere was well controlled. The monthly excavating progress of the roadway was increased from 520 to 825 m, with a rise of 58.7%, the technical and economical effects were significant. It was proved that the scheme is in line with the actual. It can provide reference for roadway rapid excavating support technology for similar conditions.

Longwall model for feedback control of powered roof support

Longwall model for feedback control of powered roof support

Optimization of an intrinsically safe solenoid valve and the static and dynamic characteristics

© 2019 IOS Press and the authors. All rights reserved. The solenoid valve used on the hydraulic roof support in the coal mine is an intrinsically safe solenoid. It requires the solenoid valve to achieve large electromagnetic force at low current. The load can not be driven if the current is too low, while a large temperature rise and energy loss would occur in the form of heat if the current is too high. In order to solve this contradictory problem, the load force of the solenoid valve was analyzed first. Then the ANSYS models of the solenoid were established to carry out the simulation jobs. The effects of the three parameters, the sleeve length, the seat length and the boss height, on the electromagnetic forces and magnetic fields were researched so as to optimize the three parameters. The static and dynamic characteristics of the optimized solenoid valve were also studied. An experimental setup was established to verify the simulation results finally. Results show that the simulation values are in good agreement with the experimental values. The peak value of starting current and holding current is small and the solenoid responses rapidly. This study proves the accuracy and reliability of the simulation models and the methods. It also provides valuable references for the design and optimization of the intrinsically safe solenoid valve.

The effect of burnt rock on inclined shaft in shallow coal seam and its control technology

AbstractBurnt rock is a geo‐material widely existed in many countries. After the rock mass is burned, the fracture is developed, the structure is destroyed, the integrity and strength are reduced, and a good water storage space is formed in suitable hydration conditions. In this paper, the roof fall characteristics and failure mechanism of inclined shaft in shallow water‐rich burnt rock area (SWRBRA) are analyzed using theoretical analysis, numerical simulation, and field measurement. It is revealed that the main factors causing the instability of surrounding rock on inclined shaft in SWRBRA are the deterioration of structure and integrity after rock mass is burnt, the weakening of surrounding rock strength under the action of fissure water, and the lagging support method. Therefore, the key measure to control the stability of surrounding rock in SWRBRA is to block cracks to eliminate the weakening effect of water and advance reinforcement to improve the surrounding rock strength. Through the comprehensive technologies such as rear roadway reinforcement, filling, and rebuilding artificial false roof and pipe shed advanced support, the effective restoration of the roof fall area in SWRBRA is realized. The surrounding rock fractures were closed, the strength of surrounding rock is improved by means of grouting reinforcement, and the stability control of surrounding rock of inclined shaft in SWRBRA is achieved.

Influence of canopy ratio of powered roof support on longwall working stability – A case study

The case study describes longwall coal seam A in a hard coal mine, where longwall coal face stability loss and periodic roof fall occurrences had been registered. The authors have attempted to explain the situation based on in-situ measurements and observations of the longwall working as well as numerical simulation. The calculations included several parameters, such as powered roof support geometry in the form of the canopy ratio, which is a factor that influences load distribution along the canopy. Numerical simulations were realized based on a rock mass model representing realistic mining and geological conditions at a depth of 600 m below surface for coal seam A. Numerical model assumptions are described, while the obtained results were compared with the in-situ measurements. The conclusions drawn from this work can complement engineering knowledge utilized at the stage of powered roof support construction and selection in order to improve both personnel safety and longwall working stability, and to achieve better extraction.

Analysis of the Influence of Dynamic Load on the Work Parameters of a Powered Roof Support’s Hydraulic Leg

One of the basic tasks of powered roof support is to protect the longwall excavation against deformation of the rock mass during the underground exploitation of hard coal. The behavior of the rock mass during mining is difficult to predict. Therefore, the loads acting on the support are diverse in terms of nature, direction and force. The dynamic load resulting from rock bursts, relaxation and tremors may lead to particularly dangerous consequences involving the functionality of the workings and the safety of the crew. The powered roof support will function properly only if the elements dynamically loaded are under control at the moment of impact. The article presents the results of tests of the basic powered roof support’s element − a hydraulic leg impacted by dynamic load. The source of the load was a free falling impact mass dropped from a certain height. The tests covered the actual hydraulic leg with all hydraulic equipment used in the powered roof support. During the tests, the original measurement-recording system developed by the authors was used, in which, among others, a high-speed dynamic camera was used to record movements of the leg’s elements. The original research methodology developed together with the measurement system enabled the registration of many parameters of the leg’s work under dynamic load. In particular, this applies to time series of pressure in the leg and the value of its withdrawal depending on the energy of the impact. The individual phases of the leg’s work were also registered, including the opening and closing of the safety valve protecting the leg against overloading. The obtained results broaden knowledge in the field of hydraulic legs used in the mining support under dynamic load. At the same time, they are a valuable source of information for mine maintenance services and should be applied to the design process, selection and operation of a powered roof support in dynamic conditions. The subject of the article fits in with the philosophy of sustainable development, especially in the field of full use of options of the support and ensuring safe and environmentally friendly mining processes.

Magnetic-and-powder Method in Diagnostics of Welded Joints in Powered Roof Supports

A possibility of diagnosing the welded joints in the components of powered roof supports used in longwall panels of hard coal mines is analysed. It was found that the magnetic-and-powder method is most useful for that purpose. Devices which facilitate assessment of technical condition of welded joints in canopies and bases are discussed. Design and principles of operation of welded joints liquid detector adapted for operation in industrial conditions are presented. Two ideas of a magnetic inductor for technical diagnosis of powered roof support components by the magnetic-and-powder method is discussed.

Research and Application of Support Technology for Re-mining Roadway in Goaf Under Regenerated Roof in Thick Coal Seam

Aiming at the problem of roadway support in the re-mining of residual coal in the goaf under the condition of regenerated roof in thick seam, this paper takes 6F301 re-mining face in Taiping Coal Mine as the background, combines with the roadway layout of the re-mining face, uses 3DEC simulation software to study the movement law of overlying rock in the re-mining face, and designs and studies the support scheme of the re-mining roadway according to the movement law of overlying rock. The results show that the shotcrete + steel roof support scheme can improve the strength parameters of surrounding rock, improve the stress state of surrounding rock and limit the yield failure of surrounding rock. The measured results show that the maximum relative displacement of roof and floor and two sides of roadway is 97 mm and 105 mm respectively, which effectively controls the deformation of surrounding rock strata with good supporting effect. Through on-site industrial test and application, it can effectively improve the average recovery rate of coal resources, improve the economic efficiency of coal mining, reduce the comprehensive cost of coal mining in coal mining enterprises, and has very important engineering application and research value.

Dendrochronology at the Mission San Xavier del Bac convento (Tucson, Arizona, USA)

The Spanish Colonial Mission San Xavier del Bac near Tucson, Arizona has been studied extensively for its contribution to the origin and development of Tucson as an urban center. While the general timeline of construction is understood from historical documentation, suggestions of timber reuse from earlier structures (Fontana, 2015) have not been scientifically evaluated. Three vigas (horizontal roof support timbers) and an internal wall beam were sampled for tree-ring analysis and compared to tree-ring chronologies from the nearby Santa Rita, Catalina, and Rincon mountain ranges. Dates for the timbers suggest that timber reuse from earlier structures is not supported in the case of one room, the convento. Additionally, chronologies from the Santa Rita, Catalina, and Rincon ranges do cross-date with these and other historic materials from downtown Tucson, demonstrating potential for dating of local structures from the same period.

Implementation of non-standard tests at powered roof support testing stands in KOMAG

Examples of broadening the scope of application of the unique test stands, originally dedicated to conducting functionality, kinematic and strength tests of powered roof support. Test cycle of bridge bearings load capacity is discussed. The obtained results were used during the certification process of the bearings. The method of testing the strength of welded rails as well as the tests procedure and the results of stiffness tests of the folding metal scaffoldings is given.

Research on Stress Distribution and Safe Mining of Lower Layer Working Face Based on Resource Integration

The use of small face mining mode in the upper stratification of Qudi Coal Mine leads to the imbalance of mining succession, in order to improve coal recovery rate and utilization rate, solve the problem of over-limit gas overrun, in the context of resource integration, combine two adjacent working face goafs into one large working face, ensure safe and efficient recovery of the remaining 24m coal pillar, through numerical simulation and on-site measurement, the variation law of stress in lower layer is studied. The results show: ZYP3200/17/28 hydraulic support can fully meet the roof support. Residual gas content and the gas-concentration in air-return laneway indicate that the 31012 mining face has eliminated the outstanding danger, safe, efficient and green mining has been realized.

Innovative technologies for thick coal seam mining on the basis of powered roof support with controlled coal discharge

A new trend for designing powered supports for thick coal seam mining with controlled coal discharge is substantiated. Numerical modeling for gravity flow of disintegrated rocks and the flow interaction with the support section is performed. A test bench is developed, and the laboratory studies into coal discharge process are carried out.

Investigation of coal discharge modes on brassboards of powered roof support unit

Physical and analytical modeling of caved top coal discharge by adjustable feeders on armored face conveyor during underground mining of thick flat seams has been performed. The process of top coal caving is studied using laboratory installation with the feeders operating in wave and areal modes. Based on 3D discrete element method (DEM), gravity flow of coal and its interaction with the powered roof support unit is modeled numerically.

The impact of selected structural and operational factors on load bearing capacity of the powered roof support

This paper presents a short analysis of the state of knowledge regarding the selection criteria of the powered roof support unit parameters for specific geological and mining conditions. The study exhibited that the theoretical models and selection methods applied so far do not allow to determine the impact of structural and operational factors on the load bearing capacity of the powered roof support unit. The authors have proposed a research procedure which uses the developed load model of the powered roof support unit in the longwall heading, allowing the prediction of roof stability conditions by determining convergence of the heading for given parameters of the support unit or selection of technical parameters and initial load bearing capacity to achieve the planned convergence of the heading. Thanks to this method it is possible to determine the characteristic relating the load bearing capacity of support unit with the convergence of the heading, the measure of which is the inclination angle of the roof part of rock mass, and further analysis of the impact of structural and operational factors on the load bearing capacity of the support unit.

The stability and roof-support optimization of roadways passing through unfavorable geological bodies using advanced detection and monitoring methods, among others, in the Sanmenxia Bauxite Mine in China’s Henan Province

The safety and stability of roadways is greatly influenced by the complex geological conditions present in the Sanmenxia Bauxite Mine, Henan Province, China. In this study, based on data from field survey, advanced detection methods, numerical studies, and monitoring studies, we have adopted the method of steel fiber-reinforced shotcrete to improve the excavation rate of roadways and guarantee the safety of the tunnel when it passes through unfavorable geological bodies, such as shale rocks and broken argillaceous limestone. Field surveys showed that the stability of roof rocks is the major problem faced by engineers; however, tunnel construction using cast-in-situ concrete, which is the method currently applied, costs too much time, resulting in an excavation rate that is too slow to meet the requirements of the Sanmenxia Bauxite Mine. Here, we propose an optimized scheme which, when combined with numerical simulations and data from advanced detection techniques and field monitoring surveys, can improve the efficiency of roadway roof support. During the implementation of the new scheme, the geological anomalies ahead of the working face were detected in advance. It is assumed that the supporting effect of the steel fiber-reinforced shotcrete is equivalent to that of the cast-in-situ concrete as long as a certain thickness is reached. Moreover, the steel fiber-reinforced shotcrete has better mechanical properties than cast-in-situ concrete and achieves a better combination effect with surrounding rock masses. Based on geological conditions and numerical results, the shotcrete should be thickest in the middle area along the roadway axis passing through the unfavorable geological bodies, and gradually become less thick from the middle to both ends. Field tests were carried out to verify the effectiveness of the scheme. The monitoring results show that the roadway passing through broken argillaceous limestone was stable after being supported by shotcrete (at least 80 mm); its thickness should reach at least about 120 mm when passing through shale rock mass. The results indicate that the use of steel fiber-reinforced shotcrete can considerably shorten the construction time compared with cast-in-situ concrete support. The scheme has proved to be a feasible, economical, and time-saving method for underground excavation in the Sanmenxia Bauxite Mine.