Roof Support Research Articles

Characteristics and control methods of uneven deformation and failure of mining roadway roof in intelligent transportation system

An intelligent transportation system is an important part of the smart city. The roof control of (MR) in safe and efficient mining of coal mine is analyzed and studied to solve the obstacles to the development of wireless intelligent sensors in the intelligent transportation system. The idea of controlling roadway deformation by using the deformation and development of plastic zone has been innovatively put forward. Based on the butterfly-shaped plastic zone theory of surrounding rock of MR and the countermeasures of asymmetric roof support, Fast Lagrangian Analysis of Continua (FLAC3D) software is used to construct the numerical model of uneven deformation and failure of roof, and the uneven failure of surrounding rock of MR in Lijiatun Coal Mine is analyzed. The uneven distribution characteristics of MR under dynamic influence conditions show that after the mining effect, the roadway surrounding rock will produce large deviatoric stress, and the direction of the maximum principal stress will tilt to one side of the working face, to maximize the plasticity of one side of the roadway roof. Especially after secondary mining, the maximum position of plastic failure on the side of the roadway roof is more obvious, accompanied by the uneven failure of the roof. On this basis, the asymmetric support strategy of the roadway roof is proposed to strengthen the roof on the side with serious deformation. The maximum uneven expansion of the plastic zone after reinforcement occurs in the 11,209 working face 200m, not more than 45mm. This reinforcement scheme reduces the uneven deformation of the roof. The new technology clears the obstacles for the development of wireless intelligent sensors and lays a good foundation for the rapid development of smart cities.

Development of a biopolymer modified geopolymer based cementitious material for enhancement of pumpable roof support

Development of a biopolymer modified geopolymer based cementitious material for enhancement of pumpable roof support

The Investigation of Strata Control for Ultrasoft Coal Seam Mining

Strata control of ultrasoft coal seam has been a critical problem for mining and geotechnical engineers in years. In this paper, the No. 66207 longwall panel at Xinzhuangzi coal mine, Anhui, China, was used as an example for study. A systematic approach using laboratory testing, numerical simulation, and field validation was implemented to investigate the influences of roadway layout and presplit blasting on mechanical properties of surrounding rock. Based on the results, an inward-stagger roadway layout with presplit blasting on roof was proposed for the regional strata control. The investigation on the relationship between angle of repose of ultrasoft coal and water content showed that the angle of repose first increased then decreased with increasing water content. The peak value was observed at 17.659% water content, suggesting water injection into ultrasoft coal seam can improve the coal mechanical properties and rib stability. The “high resistance, integral beam, two-stage rib+roof support system” was design to replace the traditional equipment, which can support the ultrasoft coal seam. The combination of this system and proposed “difference stepping” mining technique was capable of preventing roof and rib from failure, as well as mitigating the rockfall during moving hydraulic support. Based on the field validation, it was found that the stress concentration coefficient was relatively low during mining process. This was able to effectively manage the mining-induced stress while improving the productivity three times than without the technique. There was also no failure event observed during mining, such that the safety of mine workers was improved significantly.

Practical aspects of induced structurization of rock mass

Ground control is connected with monitoring of deformations of enclosing rock mass in the course of mining for ensuring stability of underground openings. One of the negative consequences of redistribution of rock pressure in an extraction panel during mining operations is swelling of floor rocks. The present article considers mining conditions of coal seams using the features of formation and development of nonlinear structurization of rock mass during longwall advance, earlier revealed at the Institute of Coal. The calculation basis is the developed parametrical model of geomechanical processes in rock mass during mining using the longwall top coal caving method. The rock mass is considered at the first approximation as a uniform isotropic medium without regard to mechanical properties of rocks. The model rock mass is presented as a set of manmade geomechanical layers. Their formation begins from a coal seam being mined and develops with the longwall advance with regard to elastic energy of rock mass. In the manmade change of external conditions, the rock mass rebates its energy potential via arching and movement. The bodies of “arches of movement” tend to paraboloids in shape. Formation of such shapes corresponds to the concept of minimum energy spend for the creation of a new surface under uniaxial unloading. The height of the arches-paraboloids is equal to the thickness of geomechanical layers at different scales of the structural hierarchy of rock mass. The horizontal dimension of the archesparaboloids is divisible by a longwall length. It is possible to detect sites of increased rock pressure applied to the boundaries and roof support of underground openings by means of geometrical overlapping of circles having diameters equal to the basal parts of displacement arches with load-bearing edges. Integration of the displacement arches of the adjacent extraction panels leads to connection of their mined-out areas and to gas cross-flow between them. The cardinally new approach to understanding geomechanical processes in rock mass can allow predicting adverse phenomena of rock pressure and the increased methane emission during high-rate longwalling.

Roof weighting and support of a largely mined shallow coal seam

To study roof weighting and the support of a largely mined shallow coal seam, the hydraulic support resistances in both small and large periodic weightings were derived by different theoretical formulae. Support working resistances of the 12,401 mining face in small and large periodic weighting were 10,442 and 17,064 kN, which represented a loading-increase coefficient of up to 1.64. Mining cracks were formed up to land surface and were visible to the naked eye, and numerical simulation of roof stratum structure by 3DEC has been proven to be realistic. A 1.2-MPa supporting intensity represented a critical threshold for effectively reducing horizontal displacement and inhibiting rib spalling using FLAC3D. Hydraulic fracturing and micro-seismic monitoring were used to ensure the safety of the 12,401 mining face. These findings can explain the mechanism of mining a shallow coal seam for effective prevention and controlled design. The results show high accuracy and are consistent with reality.

Synthesis of a CKD modified fly ash based geopolymer cementitious material for enhancing pumpable roof support

Synthesis of a CKD modified fly ash based geopolymer cementitious material for enhancing pumpable roof support

Study on mechanism of end face roof leaks based on stope roof structure movement under repeated mining

In view of the problem that the broken stope roof under repeated mining is prone to end face roof leaks, this paper’s research background is the close distance coal seams mining of a mine in Guizhou province, China. The impact of stope roof structure movement on the immediate roof was elucidated from the analysis of stope roof structure movement under repeated mining employing a combination method of field measurement, physical simulation, theoretical analysis, and numerical simulation. As a result, the mechanism of end face roof leaks under repeated mining is investigated, and the corresponding control measures are proposed. The results show that the cantilever beam structure instability of the stope roof under repeated mining is an important reason for the end face roof leaks and support crushing accident. The fracture forms of cantilever beam structure are divided into direct fracture and hinged structure fracture. The direct fracture is affected by the support working resistance. The cantilever beam hinged structure is divided into sliding and rotational instability. The periodic weighting interval is small and the fracture degree is large under repeated mining, which leads to the sliding instability. It is concluded that reasonable support working resistance is the important reason to keep the cantilever beam structure stability. Therefore, the stope roof leakage control countermeasures under repeated mining are proposed. The UDEC numerical simulation is used to verify the above analysis again, so as to provide the basis for the end face roof leaks prevention and control under repeated mining.

Stress–strain behavior of rock mass around the roadway with roof support of rock fall-hazardous zones by the phenolic resin fill

The authors discuss roadway heading and support in unstable rock mass. The stress–strain analysis is performed for rocks and mine support system when voids generated by rock falls in roof and sidewalls of a roadway are filled with phenolic resin. The change in the stresses when the zone of rock fall-hazardous zone in the roadway roof grows in height is shown.

Efficiency evaluation of roof rock control in conveyor drift 555 in Chertinskaya-Koksovaya Mine

The depth of coal mining in Kuzbass reaches 600 m and more. The geological, geomechanical and gas-dynamic conditions of mining persistently complicate. In this respect, it is required to undertake additional geomechanical research of rock masses in order to select the most effective approach to ground control. Deeper level mining induces higher stresses in enclosing rocks and at the boundaries of roadways. This article describes the studies into the geomechanical processes outside and inside the zone of roof rock destressing in conveyor drift 555 in Chertinskaya-Koksovaya Mine, and the determined values of horizontal and vertical displacements in rocks. As the face of conveyor drift 555 was advanced, intense displacements took place in the roof, floor and sidewall rocks of the roadway, which greatly affected its operating conditions. The implemented work package included geomechanical and geophysical research, in situ measurements, adjustment of the behavior and structure of enclosing rocks, as well as development of roof control and validation of the selected parameters with due regard to the actual condition of rock mass, which enabled reduction in the adjacent rock mass movements, improved serviceability of roof support and preserved the roadway cross-section. The dipole electromagnetic sounding of the floor rocks susceptible to swelling determines the destressing depth; the product of the floor destress depth and the rock expansibility allows evaluating potential displacement of the floor rocks. The roof rock destressing made it possible to reduce displacements in the roof from 607 to 58–0 mm, which ensured maintenance-free support of the roadway. The studies proved the main roof rock destressing efficiency at the selected parameters, which ensured sufficient operating conditions in the drift for the whole service life.

Technologies of mine roof support using cable bolters: Experience and prospects

The modern mines in Russia and in the near abroad target themselves at effective mechanization and higher production output through modernization of manufacturing capabilities. Currently mining is carried out at great depths and in wider roadways using large-size self-propelling machinery. The geological conditions complicate with growing depth of mining, which impedes operations as a rule. At the present day, mine support systems for great depths include heavy steel support, which calls for essential physical and technical resources. Thus, it is required to improve methods of mine support and to expand application ranges of rock bolting. As a case-study of Maisky Mine, the authors discuss applicability of RANK 2 AK series cable bolting using a cable bolter and with anchorage using chemical ampules and injection syringe. The two-level support design, using a cable bolt anchored using a chemical ampule, with individual supporting components such as a plate or a pickup without complete fill of a hole, is the most effective method of mine roof support. Moreover, it enables safe and efficient operations at intersections in the mine, or in wide roadways, with no blocking the ways for personnel or for rock haulage by large-size self-propelling machines.

Early-age hydration characteristics of modified coal gasification slag-cement-aeolian sand paste backfill

A clear understanding of the hydration characteristics of cemented paste backfill (CPB) is helpful to analyze the reasons for the defects of low strength, large deformation and high cost in the early curing period of CPB. This is conducive to realizing the sustainable utilization of solid waste. In this paper, the hydration exothermic characteristics of MGCAPB slurry was tested. Moreover, uniaxial compressive strength(UCS) tests were carried out on the MGCAPB with curing times of 3 and 28 d. In addition, microstructure tests such as TG-DTG and SEM were performed on the MGCAPB with curing time of 3d. The hydration exothermic characteristics of MGCAPB were emphatically studied, the hydration kinetic parameters of MGCAPB were analyzed exclusively by using Krstulović-Dabić model. In addition, the mechanical properties and microscopic characteristics of MGCAPB were studied. The results shows that the hydration kinetic process of MGCAPB slurry can be described by nucleation and crystal growth (NG), phase boundary reaction (I) and diffusion (D). All the formulations of MGCAPB went through the NG-I-D stage. The process of hydration reaction was controlled by NG at the initial hydration stage, and gradually changed to process I and process D with the increase of hydration degree. Compared to the Control group, The α1 of the MGCAPB activated by the activator was high, indicating that the NG process changed to the I process only when the hydration degree was high, which was related to the effective water-cement ratio of the slurry and nucleation effect. In addition, according to the requirement(3d ≥ 0.5 MPa and 28d ≥ 1.0 MPa) that CPB can provide good roof support in a typical underground mine. In this experiment, the mechanical propertiesof all formulations met the requirements, except for the 3d UCS of the Control group(0.37 MPa) and the C-C1(0.46 MPa). Finally, TG-DTG and SEM were used to analyze the microstructures of MGCAPB with activator type and dosage. The research results can provide a new approach for intensive and comprehensive utilization of solid waste resources.

A method of straightening armoured face conveyor based on space kinematics of reserve pushing mechanism

The straightness control of armoured face conveyor is one of the key problems in longwall mining. Aiming at the problems of less sensing information and low accuracy of straightening of armoured face conveyor, a method of straightening based on the movement laws of reverse floating connection mechanism and deep learning trajectory is proposed in VR (Virtual Reality) environment. Firstly, the spatial kinematic model of the reverse floating connection mechanism of roof support and armoured face conveyor are established with knowledge of the industrial robot, the movement laws are obtained. Secondly, SL-LSTM (Single Layer Long Short Term Memory) prediction model is established by sensitivity analysis method after super parameters are selected, and by considering the influence of sensor error and fluctuation of coal floor, the establishment method of date sets and thought of trajectory prediction are put forward. Thirdly, according to requirements for straightness of fully mechanized working face and data availability, the correction model of prediction trajectory and the trajectory-attitude transformation model are established. Finally, based on the obtained armoured face conveyor trajectory, the relative position between a roof support and the corresponding middle trough is determined after timely advancing of roof support, and then the straightening process of armoured face conveyor is realized after precise pushing of the roof support. The straightness error of the straightening method proposed in this paper is within ±0.14 cm and the straightening effect is better by experiment verification.

Development of a Hydraulic System for the Automatic Expansion of Powered Roof Support

A mechanical support in a longwall complex requires proper supervision and control of operating parameters because it is responsible for the safety of machines and workers. Its main functions are to protect the excavation against the adverse effects of rock mass and to move it along with the operational progress of the shearer and the scraper conveyor. In the era of Industry 4.0 as well as green economy and sustainable development, the development of machines and devices included in the longwall complex is an important area of invention. When it comes to the mechanical support included in the longwall complex, the authors propose changes to the hydraulic control system. The main purpose of the work was to develop a system that can automatically expand the legs of the powered support. Tests were carried out under real conditions while equipping the support section with a prototypical hydraulic system and with a system monitoring the correct operation of the prototype. This article presents the development of a prototypical installation under real conditions for testing on a longwall. The innovative solution proposed by the authors consisted of introducing a prototypical double valve block into the hydraulic system of the housing, which enables the function of automatic section expansion. The authors proposed a solution aimed at shortening the work time of the powered-support-section operator. The research results made it possible to evaluate the usefulness of the proposed solution. This type of solution can be considered technical support in the process of coal mining in an underground mine. Analysis presented in this paper, along with results from research conducted and its conclusions, can be of practical help to enclosure users to improve reliability and achieve optimal performance.

Choice of powered roof support FAZOS-15/31-POz for Vang Danh hard coal mine

The article presents the choice of a Polish powered roof support from FAMUR Group forthe conditions of one of the hard coal mines in Vietnam. In the analytical calculations, the strengthand structural parameters of the rock mass from the Vang Danh mine region were adopted. Thelongwall face is 93 m long and the thickness of the coal layer is equal 3 m. For the needs of thechoice of support, the load of the longwall face determined and the capacity of the powered roofsupport were determined. On the basis of the permissible roof deflection method, the condition ofexcavation maintenance was characterized. In the calculations, it was assumed that the condition ofusing a powered roof support type FAZOS-15/31-POz, except in addition to complying of theworking range and permissible value of longwall face inclination, is to ensure proper roofmaintenance conditions, which are determined by the index of load capacity of the roof „g”.

Adaptable and energy-efficient powered roof support unit

Adaptable and energy-efficient powered roof support unit

Development of a charging system ensuring the load-carrying capacity for powered roof support

Development of a charging system ensuring the load-carrying capacity for powered roof support

Development of Roofing Tiles Support Made from Bituminous Plywood

Inthis study, a new design of roof support was investigated to improve the systemof roof coverings with roofing tiles. Usually, wood frames or slabs are oftenused as support for roofing tiles, which presents many disadvantages such asthe expensive cost of the slabs and sometimes inefficient Corresponding woodframes. The new design proposed in this study uses the technique of Kodjo Attipouwood frames, but by interposing between the frames and the roofing tiles, abarrier is made of bituminous plywood. The barrier is composed of plywood 1.22m in width, 2.44 m in length and 4 mm in thickness. The plywood is covered witha cloth of cotton fibers, impregnated in petroleum bitumen fluidized bykerosene. A test of permeability was conducted and has shown good results after3 weeks of imbibition in water. The new composite material obtained can thenserve as intermediate support in the system of roof coverings with roofingtiles and wood frames.

Discussion on Roof Support Technology of Underground Roadway Excavation in Coal Mine

Discussion on Roof Support Technology of Underground Roadway Excavation in Coal Mine

Analysis of the Results from In Situ Testing of a Sensor In-Stalled on a Powered Roof Support, Developed by KOMAG, Measuring the Tip to Face Distance

Mining in underground plants is associated with high risk. Improving work safety and increasing the productivity of longwall systems in the mining industry is a problem considering many criteria. Safety aspects concern both the crew and the machinery. The KOMAG Institute of Mining Technology designed and manufactured a geometry monitoring system based on inclinometers that meet the requirements of the ATEX directive. Monitoring of the roof support geometry is used for the prevention of loss of roof stability: roof fall or/and cave-in. The system was tested on a real object in real conditions.

Geometrical Tests of Powered Roof Support Positioning in a Longwall Complex

A powered roof support protects people and equipment in the longwall from potential dangerposed by the surrounding rock mass. The study to determine the position of the powered roof supportwas conducted in an active longwall. The research team made measurements of the geometric height ofthe powered roof support structure located in the longwall complex. The main objective of this studywas to determine the position of the powered roof support in actual underground conditions. Theanalysis of the results provided data on whether the assumed height of the longwall was maintainedduring operation of the complex.