Roof Support Research Articles

A method for calculating loads on roof support in mines

The author proposes an approach to the stress–strain analysis of mine support with regard to all displacements of the stope boundary until it makes contact with the support using the stiffness matrix of intact rock mass. Modeling of the void formation and of the joint deformation of the support and adjacent rock mass uses iterative procedures from the methods of initial stresses and initial strains. The support load algorithm and software package are developed.

Изменение горного давления при отработке пласта угля длинным очистным забоем

Development of the geomechanical processes is of great importance for human activity in the underground conditions. Coal mining is accompanied by displacement of the enclosing rocks, which requires a special approach to study of the geomechanical processes. In particular, this is due to an increase in the productivity of the excavation sections. Increase in the volume of the second working, the length of the longwalls and the size of the extraction pillars will transform all the geomechanical processes occurring in the face. Modern coal mining technologies are associated with certain specific features of the displacement of enclosing rocks, which necessitate the development of new approaches to the study of the geomechanical processes. The intensification of work inevitably leads to a change in the geomechanical environment in the vicinity of the face. The article discusses the methods and means of studying the process of rocks displacement as a result of construction of the mine workings. For example, a site is selected at the mine named after S.M. Kirov, long-face No. 24-62. Depth to the developed seam is from 476 to 520 m from the installation chamber. Average thickness of the seam is 2.5 m, length of the face is 300 m, length of the pillar is 2500 m. The average rate of advance is 10 m / day. Based on the monitoring of the rock pressure indicators on the mechanized support section, the wave-like nature of the rock pressure distribution in a long-face during mining of the extraction pillar was determined. The surface of the pressure domes was rebuilt using the Surfer software product, which allowed to track the processes in the face part of the longwall. Data on the pressure in the roof supports were used. In the calculations, the average rock density was assumed to be 2.5 m3/t. Since the surface of the pressure vaults makes it possible to judge the processes in the bottomhole of the mined seam, the height of the random collapse zone is determined from the pressure readings in the support struts. It is the one which presses on the powered support. Repetitive areas of the increased rock pressure were noted approximately every 200–250 m. Profiles of the surface of pressure arches along the length and in the long-face building cross are given. Considering the processes of structuring the rock mass, an algorithm for finding the height of the pressure arch was developed, which ensures a satisfactory convergence with the actual data.

Thermal Behavior and Stress Response of Steel-concrete Structures under Solar Radiation

Steel-concrete structures are widely used because of their large space and strong plasticity, but the long construction period, complex splicing process and other factors will make the main body of the structure directly exposed to solar radiation, resulting in temperature changes on the surface of steel structure and concrete structure. In order to obtain the stress changes of steel-concrete structures under solar radiation, two kinds of steel-concrete structures with different support forms were simulated. Under three temperature gradients, the thermal behavior and mechanical properties of two kinds of steel-concrete structures composed of upper steel roof and lower concrete support were analyzed. The results show that there is a linear relationship between the thermal behavior and stress response of steel-concrete structure and the daily temperature difference caused by solar radiation. Under the action of thermal effect, the stress difference between the lower steel frame of the full support structure and the lower steel frame of the support structure on both sides is about 10.7%.

Rock Mass–Multifunction Mobile Roof Support Interaction in Mining

Rock Mass–Multifunction Mobile Roof Support Interaction in Mining

Assessment of instability initiation in exposed salt rock roofs

Stability of rocks is the main requirement for the safe operation of mines. For this purpose, certain measures are applied for the protection and support of underground openings, including roof support design and roof arrangement in the most stable rocks. Stability assessment of underground excavations is largely related to their roof stability. Determination of possible instability conditions in mine roofs governs the choice of support system design and parameters of mine excavations. The Upper Kama Potash Salt Deposit represents a stratified layer of solid salt rocks. Roof instability develops as stratification and roof collapse. The Mohr–Coulomb criterion of coherent rocks is currently used to estimate parameters of a possible damage zone in the exposed roof. This criterion allows evaluating shear plane angles in roof rocks and, as a result, finding parameters of the possible collapse zone. The experience of mining operations in the Upper Kama deposit shows different failure conditions as against the Mohr–Coulomb criterion as the stress state is scarcely included in the criterion used. This study is an attempt to assess parameters of rock exposures by solving a Lame problem in terms of a single mine excavation. The analytical results were compared with the parameters obtained from the plane elasticity solutions by the finite element method. Based on the implemented studies, an engineering approach is developed for the assessment of anticipated instability parameters in exposed roofs in horizontal excavations driven in salt rocks.

Unit weight patterns of overlying rocks above commercial-value salt strata in the Upper Kama deposit

Stability of rocks is the main requirement for the safe operation of mines. For this purpose, certain measures are applied for the protection and support of underground openings, including roof support design and roof arrangement in the most stable rocks. Stability assessment of underground excavations is largely related to their roof stability. Determination of possible instability conditions in mine roofs governs the choice of support system design and parameters of mine excavations. The Upper Kama Potash Salt Deposit represents a stratified layer of solid salt rocks. Roof instability develops as stratification and roof collapse. The Mohr–Coulomb criterion of coherent rocks is currently used to estimate parameters of a possible damage zone in the exposed roof. This criterion allows evaluating shear plane angles in roof rocks and, as a result, finding parameters of the possible collapse zone. The experience of mining operations in the Upper Kama deposit shows different failure conditions as against the Mohr–Coulomb criterion as the stress state is scarcely included in the criterion used. This study is an attempt to assess parameters of rock exposures by solving a Lame problem in terms of a single mine excavation. The analytical results were compared with the parameters obtained from the plane elasticity solutions by the finite element method. Based on the implemented studies, an engineering approach is developed for the assessment of anticipated instability parameters in exposed roofs in horizontal excavations driven in salt rocks.

Cooperative Control Mechanism of Long Flexible Bolts and Blasting Pressure Relief in Hard Roof Roadways of Extra-Thick Coal Seams: A Case Study

The higher strength of a hard roof leads to higher coal pressure during coal mining, especially under extra-thick coal seam conditions. This study addresses the hard roof control problem for extra-thick coal seams using the air return roadway 4106 (AR 4106) of the Wenjiapo Coal Mine as a case study. A new surrounding rock control strategy is proposed, which mainly includes 44 m deep-hole pre-splitting blasting for stress releasing and flexible 4-m-long bolt for roof supporting. Based on the new support scheme, field tests were performed. The results show that roadway support failure in traditional scenarios is caused by insufficient bolt length and extensive rotary subsidence of the long cantilever beam of the hard roof. In the new proposed scheme, flexible 4-m-long bolts are shown to effectively restrain the initial expansion deformation of the top coal. The deflection of the rock beam anchored by the roof foundation are improved. Deep-hole pre-splitting blasting effectively reduces the cantilever distance of the “block B” of the voussoir beam structure. The stress environment of the roadway surrounding rock is optimized and anchorage structure damage is inhibited. The results provide insights regarding the safe control of roadway roofs under extra-thick coal seam conditions.

Study on Dynamic Evolution of Roof Crack and Support Timing of Secondary Tunneling for Large Section Open-Off Cut in Deep Mines

The stability of large section open-off cut in deep mines (LODM) is the key factor affecting the normal equipment installation and safe mining in fully mechanized top-coal caving face. The mechanical model shows that the deflection of the roof of the LODM is proportional to the cubic of span. In this paper, UDEC Trigon model is established, and the parameters of different coal measures strata are modified in detail. The evolution law, failure mode, and damage degree of roof cracks in secondary tunneling are studied, and the roof support effect is analyzed. The numerical simulation results show that the process of roof crack evolution after the primary excavation section and the second excavation section can be divided into three stages according to microseismic activities, and the reasonable supporting time can control the propagation of roof microcracks and reduce the development height of macrocracks. The rock bridge existing in the roof rock stratum after the combined support of long and short anchor cables can effectively limit the formation of macrocracks and their interaction; especially the key support in the interface area can reduce the development height of roof cracks in secondary tunneling and weaken the damage degree of roof rock stratum in the LODM. The field test shows that the moved volume of rib-to-rib and roof-to-floor of the LODM is stable at about 350 mm and 550 mm, respectively. The numerical simulation in this paper is helpful to understand the failure mode of roof in LODM with large mining height and provides a method for the design of its control technologies.

Temporary mechanized gate roof support in the YapiTec mine

For more than sixty years in all the world are trials of gateroad temporary mechanized roof supports in mechanized development operation have been conducted unsuccessfully. A case study - temporary mechanized gateroad roof support implemented in one of the entrances/drifts development in the turkish coal mine Yapi Tec Maden from the construction to 12-month practical experiences in practical use as described in the article. The review of gateroad roof support for different purposes is presented in article as a background or circumstances for the described case study. The YapiTec trial of the company own temporary mechanized gateroad roof support is discussed in comparison with second mechanized gateroad face without temporary mechanized roof support and same mining conditions during comparable time.

Analysis of the impact of mining and geological conditions in longwalls on the introduction of pressure monitoring for powered roof supports

Polska Grupa Górnicza has analysed the longwalls in its mines where powered roof supports should be subject to pressure monitoring. The main goal was to increase the safety of people working in the longwall. The scope also included the economic improvement of active longwalls in terms of stoppages caused by roof fall or possible tremors. The analysis, carried out in this regard, allowed strategic longwalls to be selected from the individual mines of Polska Grupa Górnicza. The paper describes mining and geological conditions in the longwalls, where monitoring is carried out, with particular attention paid to potential tremors. The paper discusses the scope and use of powered roof supports in longwalls. The research team selected the pressure monitoring system as the most important parameter of work of the powered roof support. The paper also presents the results of an analysis carried out on the implementation of the system. A survey was conducted among the employees regarding the relevance of the monitoring system. The analyses results were used to recommend the directions of further actions related to a development of the system for monitoring the supporting parameters of the powered roof support systems.

EKSPLORASI ETNOMATEMATIKA NGADHU DAN BHAGA DALAM KAITANNYA DENGAN PEMBELAJARAN MATEMATIKA PADA MASYARAKAT DESA UBEDOLUMOLO KABUPATEN NGADA

This study aims to determine: (1) to identify the structure of ngadhu and bhaga in Ubedoulumolo Village of Ngada District. (2) Explain the relation of ngadhu and bhaga to mathematics learning in school. The research method used is qualitative with an ethnographic approach. The subjects of this study consisted of three informants (pengu chief, and traditional elders of pengu and gelo tribe). Using observation and interview techniques, supported by documentation, and using qualitative descriptive analysis. The results of the study showed ngadhu and bhaga has related to mathematics, that is the geometry concept. The geometry concept found in ngadhu is: (1) pole ngadhu (made of sebu tree) in the form of a tube; (2) base of ngadhu is composed of a stone in a circle; (3) the roof of ngadhu (material of reeds and palm fibre) in the shape of a cone; (4) bhenga (2 roof support posts) in the form of a beam; (5) mangu (NOK pole) shaped beam; (6) sobhe (head ngadhu made of bamboo) shaped tube; (7) paja (roof truss of bamboo) formed triangle, rectangles, trapezoid. The geometry concept in the bhaga building are: (1) bhaga in the form of the beam; (2) roof (made of reeds) in the shape of a trapezoid and triangular prism; (3) pole shape of beams and tubes; (4) Ube (wall made of plank wood fai) shape of the rectangle; (5) Dawu (arranged boards) with carvings in the form of circles and triangle; (6) Soku bhotha and soku wi’i ( as a roof truss made of bamboo) shape tube rectangle, square and triangle. Geometry forms that exist in the ngadhu and bhaga in the Ubedolumolo Village are lines, angles, triangle, square, rectangle, trapezoid, circle, beam. Tube, cone and triangular prism.

Anti-Fatigue Design for Powered Roof Supports

A powered roof support is defined a set of support sections arranged next to each other, which creates space for mining and transportation machines and also for staff. The housing protects the newly discovered ceiling by moving a distance equal to the width of the mining body. The powered roof supports (PRS) must keep roof in variable cycle loads in mine and then it can lead to a complex combination of physical occurrences and changes in the construction. Micro-damages arising as a result of cyclical loads gradually develop and accumulate, leading to fatigue cracking. This paper presents an approach for the complexity of powered roof supports design taking into account fatigue life. In the work there can also be found some information on existing notches and how they are taken into account in the calculation. The main purpose of the work was to develop such an anti-fatigue design methodology to make calculations using the elastic model, and then at critical points apply the local elastic-plastic model methods using the Neuber model. Next there were adopted the appropriate fatigue criteria to determine fatigue life wall housing. To obtain the final form of the algorithm in this paper there are different fatigue tests presented, including: tests of wall casings with strain gauges and numerical analyzes using finite element method. Based on the tested main subassemblies of the PRS, the most effective method was defined taking into account the average values of cycle amplitudes, and the next step determined the degree of damage for all load supports. The results from experiments allow determining durability of critical places for the main subassemblies of the PRS and determining the most stressed components. Due to the shortage of systematic procedures and guidelines for the strength calculations of PRS enclosure which would take into account fatigue life, the proposed method meets the expectations of a correct and full recognition of static and fatigue strength analyzes...

Determination and quality classification of rock mass of the Diatomite mine, Algeria

Reserch relaevance. Most ground movements are generally due to rock instability, this natural phenomenon poses a risk to humanity. The properties of the rock mass directly influence the type of movement especially in underground structures. Research aim. Our goal is to characterize and classify the rock mass of diatomite from the sig mine using geomechanical classification systems such as the RQD and RMR in order to determine the quality of the rocks in the sig mine Western Algeria from the determination of the physical and mechanical properties. Methodology. In this article, the characterization analysis of the diatomite rock mass of the sig mine was carried out. First, determinations of the physical properties and carried out the triaxial test to determine the mechanical properties (young’s modulus, the friction angle, the dilatancy angle, the cohesion, the poisson’s ratio). Secondly to classify the deposit and give a recommendation to avoid stability problems. Research results. The results from physical and mechanical analyzes, it can be said that the nature of the rock present in the diatomite (underground mine) does not have enough resistance. Conclusion. Our study definitively proves that the rock mass of sig diatomite is of very low quality and it will be very dangerous for the underground mining work of the mine especially in places where the mineralized layer is very deep. And we suggest to replace the mining technique room and pillar currently used in the diatomite mine and put another mining method which includes roof support system to ensure the safety both of the miners and the equipment.

Computational Fluid Dynamics Simulations for Investigation of the Damage Causes in Safety Elements of Powered Roof Supports—A Case Study

The paper describes a case study of the safety hydraulic system damage in the working of a longwall in a Polish coal mine. The safety elements are a component of the powered roof supports which secure the shield against damage during rock burst incidents. The damage event, which occurred in the hydraulic system during the mining process, caused the uncontrolled lowering of the powered roof support height during the mining process. The uncontrolled lowering of a shield may cause the danger of the loss of the stability along the longwall working in the form of a rock burst and collapses and may represent a serious and immediate danger to the safety and health of employees. Based on the results of the computational fluid dynamics methods (CFD) analysis of the safety elements in the hydraulic system of longwall 2-leg shield, the causes of damage were diagnosed and presented. The CFD and the strength analysis by the finite element method (FEM) were used for numerical modeling. The diagrams and maps of changes of parameters having an impact on the damage mechanism in safety elements of the hydraulic leg were developed based on the results of model tests. The forecasted values of stress distributions in the safety system of the hydraulic leg have made it possible to identify the reasons of the damage causes, verified by real observations.

Investigation of the suitable dimensions for hydraulic prop support of self-advancing hydraulic roof support in underground mining at Quang Ninh coal basin in Viet Nam

According to the study, the authors have calculated and determined the reasonable size of hydraulic prop support of self-advancing hydraulic roof support, used in underground coal mining in the Quang Ninh area. The study took into account various factors that are related to the geological conditions of the mine areas, the manufacturing materials, and mining technology. The results obtained from the study can be reasonably applied to calculate the suitable size of the hydraulic prop support based on the durability and stability required for coal mines with similar geological conditions as the Quang Ninh mines. The study was carried out with the aim of improving the efficiency of using hydraulic prop support and reducing product costs. In addition, the research results can be the basis for calculating other types of hydraulic prop support used as a reference for manufacturing other underground coal mining supports at Quang Ninh coal basin.

A Step-by-Step Procedure for Tests and Assessment of the Automatic Operation of a Powered Roof Support

A powered longwall mining system comprises three basic machines: a shearer, a scraper (longwall) conveyor, and a powered roof support. The powered roof support as a component of a longwall complex has two functions. It protects the working from roof rocks that fall to the area where the machines and people work and transports the machines and devices in the longwall as the mining operation proceeds further into the seam by means of hydraulic actuators that are adequately connected to the powered support. The actuators are controlled by a hydraulic or electro-hydraulic system. The tests and analyses presented in the developed procedure are oriented towards the possibility of introducing automatic control, without the participation of an operator. This is important for the exploitation of seams that are deposited at great depths. The primary objective was to develop a comprehensive methodology for testing and evaluating the possibility of using the system under operating conditions. The conclusions based on the analysis presented are a valuable source of information for the designers in terms of increasing the efficiency of the operation of the system and improving occupational safety. The authors have proposed a procedure for testing and evaluation to introduce an automatic control system into the operating conditions. The procedure combines four areas. Tests and analyses were carried out in order to determine the extent to which the system could be potentially used in the future. The presented solution includes certification and executive documentation.

Enhancement of rock bolt performance through “active” ground control

The research has proved that rock mass stability can be ensured using steel resin rock bolting including rods, fast-setting resin capsules, bearing plates, strapping and tension nuts. Interaction of these structural components with roof rocks and sidewalls involves obligatory displacement of rocks. The article presents the studies into applicability of steel resin rock bolting in difficult geological conditions in coal mines in Kuzbass. The steel resin rock bolting is considered in this case as the method of ‘active’ ground control. The ‘active’ ground control consists in the capacity of steel resin rock bolts to alter main strength characteristics of rocks, to increase their resistance and stability, and, thereby, to ensure efficiency of roof support. It is found that horizontal and vertical stresses in underground excavations depend on the mining depth. It is proved that rock bolts installed in the roof rocks can prevent or confine rock fracture.

Disaster Control of Roof Falling in Deep Coal Mine Roadway Subjected to High Abutment Pressure

The roof falling accident is a serious threat to the lives of miners in deep coal mining, especially when the coal mine is more than 1000 meters deep. In regard to the 5306 coalface in the Tangkou coal mine, Shandong, China, the depth of coal seam is 992.8 m and the stress concentration coefficient of the roadway surrounding rock is 3.33. This leads to a serious deformation of the roadway roof, thereby producing a high risk of the roof falling disaster. In this pursuit, based on the mechanical analysis of roadway roof subjected to a high abutment pressure, the mathematical expressions of the setting load and movable column length of supports were introduced. Furthermore, the stability control mechanism of the roadway roof was analyzed and the optimized support parameters of supports are provided. The results showed that the longtime effective support of the roadway roof required the strength and deformation coupling of supports and anchored surrounding rock. The support length of the belt roadway should be at least 57.7 m, with 0-30 m away from the coalface supported by hydraulic supports and 32-57.7 m supported by single props. In addition, the maximum setting load and movable column length of hydraulic supports were 21.67 MPa and 280.3 mm and 12.44 MPa and 177.1 mm for single props, respectively. By applying the optimized support parameters of supports to the belt roadway of the 5306 coalface, the effective control of the roadway roof and the disaster control of roof falling were realized.

Analysis of Roof Failure at the Intersections on a Coal Mining

The objective of this paper is to understand the behavior of the roof and the cause of roof failure of a coal mining. Eleven roof falls occurred in the mine section in sequence. All the roof falls were surveyed, and the geological features were determined which include rock type, mechanical properties, and thickness. The immediate roof thickness was interpolated to determine the cause of the roof failures which was the inappropriate roof support where the immediate roof is thicker. The average thickness of the immediate roof was determined by the drilling log in 1.2 m (3.9 ft.). The roof support was design based on the average thickness, and the bolt length is 1.5 m (4.9 ft.) in suspension. The challenge was to estimate where the immediate roof gets thicker and to design the support considered to maintain the regular bolt length. This is because the cost and productivity of support operation could increase if the bolt length changes as the roof thickness changes. The idea was to adjust the support for beam building with a fully grouted bolt and rearrange the bolt geometry to keep the roof stable. It means, with the same bolt length the type of roof support would change from suspension to beam building depending on when the roof gets thicker. Two empirical approaches were considered to design the roof support: 1) CMRR and 2) RMR. The entry width is 5 m and the roof support was designed with four bolts per row. Where the roof support must change to beam building, the number of bolts per row changes to five or six. The results of the design and application on underground showed that the approach keeps stable.

Rock Mass-Multifunction Mobile Roof Support Interaction in Mining

Rock Mass-Multifunction Mobile Roof Support Interaction in Mining