Roof Support Research Articles

Comparison of steel and fiber-reinforced polymer rebars for mining applications: A numerical approach

Underground mines offer various non-favourable environmental conditions, one among them is the presence of corrosive elements which are not suitable for conventional materials such as steel. This problem can be avoided to a certain extent by using glass reinforced polymer (GRP) rebars. GRP rebars show high tenacity and excellent corrosion resistance compared to conventional steel which extends these materials application to constructions roofing supporting and columns. Thus this paper aims to carry out a comparative study of between steel and GRP rebars strength under tensile, compressive and bending forces using LS-DYNA. Numerical analysis results showed that the stresses generated under tensile and compressive loading are 25% and 37.25% higher for GRP rebars when compared to steel but within the safe limits. Similarly, deformation under tensile and compressive loading for GRP rebar is 62.16% and 87.12% higher compared to steel, respectively. However, load carrying capacity of GRP rebar of GRP rebar is the almost same as steel. Since both the materials showed no sign of damage under 40 kN, thus GRP rebar could be used as a replacement material instead of steel in roof supporting and column in mines.

Roadway Surrounding Rock under Multi‐Coal‐Seam Mining: Deviatoric Stress Evolution and Control Technology

Multi‐coal‐seam mining creates surrounding rock control difficulties, because the mining of a coal face in one seam can affect coal faces in another. We examine the effects of multi‐coal‐seam mining on the evolution of the deviatoric stress distribution and plastic zone in the roadway surrounding rock. In particular, we use numerical simulation, theoretical calculation, drilling detection, and mine pressure observation to study the distribution and evolution characteristics of deviatoric stress on Tailgate 8709 in No. 11 coal seam in Jinhuagong mine when the N8707 and N8709 coal faces in No. 7‐4 coal seam and the N8707 and N8709 coal faces in No. 11 coal seam are mined. The evolution laws of deviatoric stress and the plastic zone of roadway surrounding rock in the advance and behind sections of the coal face are studied, and a corresponding control technology is proposed. The results show that the peak value of deviatoric stress increases with the advance of the coal face, and the positions of the peak value of deviatoric stress and the plastic zone become deeper. The deflection angle of the peak stress after mining at each coal face and the characteristics of the peak zone of deviatoric stress and the plastic zone of the roadway surrounding rock under the disturbance of multi‐coal‐seam mining are determined. In conclusion, the damage range in the roadway roof in the solid‐coal side and coal pillar is large and must be controlled. A combined support technology based on high‐strength and high pretension anchor cables and truss anchor cables is proposed; long anchor cables are used to strengthen the support of the roadway roof in the solid‐coal side and coal pillar. The accuracy of the calculated plastic zone range and the reliability of the combined support technology are verified through drilling detection and mine pressure observation on site. This research can provide a point of reference for roadway surrounding rock control under similar conditions.

Study on Deformation Mechanism and Supporting Countermeasures of Compound Roofs in Loose and Weak Coal Roadways

This paper considers the 333 return airway of the Gaokeng Coal Mine to analyze the deformation characteristics and failure mechanism of the surrounding rock of the composite roof for a loose and weak coal roadway. The reasons for the large deformation are explored and the superiority of the prestressed truss and anchor rope is compared to ordinary anchor cables from the perspective of mechanics to propose a targeted coal roadway support method. Sinking of the composite roof in the coal roadway is accompanied with a release and transfer of the surrounding rock stress. The pressure of the composite roof transfers to the roadway sides and intensifies the fracture process of the coal body. As a result, the ability to support the composite roof is weakened, and it further bends and sinks to form a vicious cycle that repeats itself. Therefore, the support of the composite roof in the coal roadway should consider the roof, roadway sides, and floor as a single unit to achieve the support goal of reinforcing the roadway sides and roof. Based on the above analysis, a comprehensive control technology with a truss and anchor rope is proposed as the main body and a bolt + anchor cable + metal network as the auxiliary. This technology can improve the integral bearing capacity of the composite roof, strengthen the roadway side structures, and reinforce the roadway sides and roof. Numerical simulation and field application results show that the support scheme can effectively realize safe control of the composite roof in coal roadways.

A wireless pressure parameters visualization system of a powered roof support on the example of Polish mines

A wireless pressure parameters visualization system of a powered roof support on the example of Polish mines

Preliminary results of tests on nitrogen cushion for combating fire hazard in longwalls rich in methane

Ventilation hazard is the most dangerous phenomena occurring in the hard coal extraction process. This particularly applies to endogenous fire hazard. In order to reduce it, it is necessary to improve the effectiveness of preventive measures. Hence this paper presents new solutions that substantially improve fire prevention effectiveness. The main idea is to develop and create an additional nitrogen cushion in the zone behind the powered roof support operating in a longwall face. The solution is based on installations for inerting of goafs and sections of the powered roof support. The nitrogen cushion restricts the access of air and oxygen to the area of goafs and limits the possibility of fire. Practical application of the developed solution allowed for effective reduction of fire hazard in conditions of a very high tendency of coal to self-ignite at short incubation period. This, in turn, enables safe exploitation and decommissioning of the longwall. Undoubtedly, the solution presented and the results obtained constitute a new approach to preventive actions in mines. It is the result of the work of theoretical and practical researchers. The solution is a combination of the potential of these two environments. The developed solution should find wide range of applications in the areas where endogenous fire and methane hazards occur.

РАЗУПРОЧНЕНИЕ КРОВЛИ НА МОЩНЫХ ПОЛОГИХ ПЛАСТАХ УГЛЯ ПУТЁМ ПРИМЕНЕНИЯ ТЕХНОЛОГИИ ИХ ОТРАБОТКИ СЛОЯМИ ПО ПОЧВЕ

Heavy rock falls of coal roof cause increased pressure load on powered roof support systems during the mining of first layers in seams III and IV-V of Tomusinsky coal field. Moreover, the complex morphology of the seam creates additional difficulties in downward working of seam layers. All these factors call for validation of thick flat-lying coal seams mining methods that involve longwall face layered floor mining as an alternative to any kind of artificially induced weakening of coal roof.

Power generating units for a powered roof support complex

The degree of utilisation of machinery and equipment is an important factor influencing the volume of daily output of an underground hard coal mine. Consequently, it also affects the efficiency and economic performance of an underground mining plant. The main task of a new pumping station is to ensure safety and continuity of the operation process in both active and new longwalls in the future. The article presents a modern and innovative pumping station that meets the assumptions of Industry 4.0. The power units supplying a longwall complex included in the central pumping station were selected so as to minimise the number of failures. The interruptions in the technological process of coal mining related to the lack or insufficient pressure of the working medium in the supply bus of the powered roof support are caused by inadequate type of hydraulic pumps. The paper presents a developed concept of an innovative central hydraulic pumping station feeding a longwall complex based on a powered roof support. The presented implementation—starting from the concept through design and implementation—has contributed to the improvement of working conditions and safety.

A case study on the efficacy of different roof bolting schemes in Lhoist North America’s Crab Orchard Mine

Roof bolting has long been used in underground mines across the world to provide ground support. Modern roof bolts are cheap and easy to install with the use of specialized machines as a part of the production cycle. Lhoist North America’s Crab Orchard Mine is an underground room and pillar limestone mine that uses mechanically anchored roof bolts for ground support. The mine currently employs two different roof bolting patterns: a standard 1.5 × 1.5 m pattern, and another 0.8 × 0.8 m pattern for use in areas with particularly hazardous roof conditions. The purpose of this study is to evaluate the relative effectiveness of each bolting pattern. A series of numerical models were created using RocScience’s RS2. The models were based on a symmetrical section of the mine at its deepest point, and were modeled using generalized Hoek-Brown failure criterion along with a discrete fracture network. A series of sensitivity analyses were performed on the models by varying parameters such as joint friction angle, crack persistence, joint randomization, and tensile strength of the limestone. Based on the results of the original models and sensitivity analyses, it appeared that the standard bolting pattern provided sufficient roof support capacity under almost all the expected conditions at the mine, since safety factors below the design value of 1.5 were only found for individual bolts in a few of the worst test cases considered. These results can help improve the mine’s productivity and reduce operating costs without compromising safety.

A contribution to the design of powered roof support for operations in a rockburst-hazardous environment

A contribution to the design of powered roof support for operations in a rockburst-hazardous environment

Numerical Study on the Influence of Altitude on Roof Temperature in Mine Fires

The temperature distribution of the roadway roof in a mine fire is closely related to the internal environment of the mine, which changes by the mine's altitude. In order to accurately reveal the distribution of roof temperature in mine fires at different elevations, altitude should be considered as avariable. Using FDS (Fire Dynamic Simulator), six fire sources of different scales are designed to simulate fire scenarios at five different altitudes from 0 to 4,000 m (equal diversion point). The roof temperature distribution along the longitudinal centerline of the tunnel is obtained. At the same time, the influence of high temperature on the roof support of the roadway is analyzed when the mine's altitude changes. The results show that when the fire heat release rate is relatively small, the combustion belongs to fuel-controlled combustion, and the roof temperature rises with altitude. As the heat release rate continues to increase, the roof temperature decreases with increasing altitude, which is mainly due to the low-oxygen environment in plateau areas. In addition, mine fires at normal altitudes (altitude <; 3,000 m) are less affected by altitude changes, and the roof temperature is always positively related to fire heat release rate. However, high altitude has an inhibitory effect on fire. In the initial stage of continuously expanding the heat release rate, There is still a positive correlation between the roof temperature and the heat release rate. When the heat release rate increases to 100 MW, the roof temperature distribution does not continue to increase. Instead, it remains stable, and the higher the altitude, the lower the stable value. Finally, based on the combination of dimensional analysis and dimensionless analysis, a correlation for predicting the longitudinal distribution of roof temperature in mine fires at different altitudes is established. The predicted data of this empirical model is highly consistent with the measured data.

Analysis of regenerated roof and instability support control countermeasures in a steeply dipping working face

Roof regeneration in coal mining occurs when the remaining bottom slice of thick coal is re-mined. In view of the challenges of roof fall and instability support of a regenerative roof in the mining of steeply dipping coal seams, combined with the geological and engineering conditions of the working face in the Panbei Coal Mine, the mechanism of the instability of the regenerative roof and support is studied, and control countermeasures are proposed. Based on the comprehensive combination of the measurement of the roof structure, physical simulation, numerical simulation, and theoretical analysis, the cementation and compaction degree of the regenerated roof were described. The caving and sliding law of the regenerated roof after bottom slice mining was explored, and the model of support dumping and sliding instability under the roof fall state was established. The results obtained yielded three main findings. Firstly, the compaction degree of the regenerative roof is higher than that of the middle part of the working face, and the compaction degree of the upper part of the working face is the smallest. Secondly, the overburden structure instability of the bottom slice underwent six stages. The fracture of the cantilever beam and the slippage of gangue are the reasons for the enhancement of the acoustic signal at each stage. Finally, the upper part of the stope was identified as the crucial zone in the prevention and control of the support instability. A moving method of metal mesh with pressure and roof scraping was developed, and the support anti-overturning and anti-skid jack was set up to effectively control the stability of the support and roof fall, for safe and efficient mining of a steeply dipping coal seam under a regenerative roof.

Design and Evaluation of the Roof Bolt Corrosion Test System in a Simulated Underground Coal Mine Environment

Corrosion of steel roof support systems can cause potential premature failure of the support, thus adversely affecting the excavation stability and rock-related safety. An in-house corrosion test system was designed and developed to test full-length roof bolts for material performance based on tensile load capacity and strength under different corrosive conditions found underground. The roof bolts tested are also used to identify the possible corrosion mechanisms that influenced the bolts’ performance over time. Initially, the most commonly used bolt material in the USA, the ASTM A615 grade 60 steel roof bolts, was tested with and without stresses in a simulated underground coal mining environment for approximately 6 months, and the results are discussed. Localized corrosion forms such as crevice and pitting were mainly observed after testing. The stressed and unstressed roof bolts with and without threads that were tested in alkaline coal mine corrosive environment for 6 months passed their load-bearing capacity as per ASTM F432 test standards. From the results, it is concluded that this test protocol could be applicable to test the material performance of different roof bolt metallurgies and coatings with desired modifications to the proposed methodology for the specific underground mine environment. This paper mainly discusses the test system and protocol and shortcomings of the system and makes recommendations based on the observations and results.

Sliding instability characteristics and re-stabilization mechanism of key stratum in thin-topsoil SCS mining: a computer-aided case study from the Niushan Coal Mine, China

Roof step subsidence and support crushing accidents caused by the sliding instability of fractured single key stratum often occur in shallow coal seam (SCS). For this reason, the exploration of fracture displacement laws and control mechanism of key stratum in thin-topsoil SCS is of great significance for both roof control and safety production. From this perspective, in this study, numerical simulation and theoretical analysis were conducted to establish a mechanical model of the key stratum structure after sliding instability in thin-topsoil SCS. Moreover, its instability characteristics and re-stabilization control mechanism were analyzed. The results revealed that the fractured key stratum block could reach re-stabilization without any support crushing after sliding instability in thin-topsoil SCS depending on the significant unloading effect of the topsoil. The mechanical model of the key stratum structure after sliding instability was also analyzed to obtain the criterion for the re-stabilization of the sliding instable rock block. The computational analysis corroborated that increasing the support intensity could promote the re-stabilization of fractured key stratum block after sliding instability, and the required support working resistance could be obtained for preventing support crushing incidents.

Development of technology for withdrawal of the powered roof support from a row and its relocation from the liquidated longwall system

Directions in improvement of efficiency and safety of the used systems for relocation of powered roof supports from the liquidated longwall was indicated basing on a review of the current systems. Suggestion for the machines and devices used for mechanization of a powered roof support relocation from a row and its transportation in cross-cut entry is presented. The innovations consist in combination of two functions in one machine used for roof support reinstallation and its rotation as well as its safe and fast relocation to the main transportation roadway.

Comparative analysis of hydraulic power systems for a powered roof support aimed at obtaining optimal power parameters

Hydraulic power systems for powered roof supports, depending on the place of installation of hydraulic aggregates, can be divided into local and central systems. Central systems are gaining popularity and a number of their features are more advanced compared to the local system. However, it is widely believed that their main disadvantage is the necessity to install pipelines with larger lengths, which can have a significant impact on the obtained hydraulic power supply parameters by occurring pressure losses on the pipeline length. This paper discusses the impact of these parameters on the correct operation of the powered roof support section, which is connected with the uninterrupted continuity of the production cycle in a longwall.

A Cascaded Pushing Displacement Estimation Approach for Hydraulic Powered Roof Support based on Multi-Segmental Kalman Filter

To tackle the problem of non-reusability of the magnetostrictive displacement sensor which is embedded in a pushing hydraulic cylinder, and improve the accuracy of pushing displacement sensing for hydraulic powered roof support, the compact self-contained inertial sensor is utilized in pushing displacement measurement. The motion characteristics of pushing operation are re-considered, and multi-segmental Kalman filter (MS-KF) is proposed based on the motion characteristics. A cascaded framework is constructed for pushing displacement estimation, and key technologies such as orientation estimation, segmental recognition and MS-KF implementation are demonstrated. The experiment is elaborated and experimental results show that the proposed approach significantly reduces the cumulative error and proves to be practical and valuable.

Development and substantiation of parameters of multifunctional mobile roof support

The paper describes the technical parameters and requirements for the basic element of longwall systems for mining thick and steeply dipping seams and for extraction of coal from safety pillars. The proposed multifunctional mobile roof support ensures safe and efficient operation of mines in complicated geological conditions. The authors offer classification of the performance capabilities of the multifunctional mobile powered roof support.

Model tests of the effect of active roof support on the working stability of a longwall

Incorrect shield construction may result in a situation where the powered roof support does not sufficiently interact with rock mass. The properly interaction of powered support with the rock mass are one of the most important factors determining the condition in which the excavation fulfils its functions in the production process and ensures work safety for miners. The main symptoms of the loss of the stability of a longwall working are roof falls. The article discusses modelling of performance of different variants of shield designs (i.e., canopy ratio) during longwall coal mining. The results of multiple numerical simulations are presented in terms of the size of the fracture zone as a one of indicators of design performance. The fracture zone is identified in the numerical model as a results of rock mass displacement which reflects stability of a longwall working. The results of model tests demonstrate the influence of the shield capacity distribution (active roof support) on the stability conditions of a longwall working. The numerical solution demonstrates the dependence between the strength parameters of the rock mass and the active roof support along the length of the canopy.

Numerical study of the effect of console length of the main roof hanging on the geomechanical parameters of the mine face

This article presents the results of scientific research aimed at establishing the effect of console length of the main roof hanging above the gob on geomechanical parameters in the vicinity of the mining face. According to the results of numerical modeling of the stress-strain state of the rock massif, the nature of the distribution of vertical displacements and stresses in the vicinity of the face was established with a consistent increase in the console length of the hanging main roof, the dynamic loads on the roof support sections, the hydraulic props settlement, the inrush area of roof rocks and the coal sloughing from the seam surface in the face. The results of the conducted research allow the preventive measures to be developed, the implementation of which will ensure the stable and safe operation of the working faces during underground coal mining in difficult mining and geological conditions.

Studies of two-stage coal discharge with stepped-type powered roof support

The authors propose the powered roof support of the stepped type. Such design ensures safe and efficient mining, as well as complete extraction of coal from thick seams with coal discharge to the rear armored face conveyor. The paper describes physical simulation and numerical modeling of two-stage top coal discharge.