Soft Roof Research Articles

Mechanics Model of Floor Heave: Case Study on Thin Coal Seam with Soft Roof and Floor

The fully mechanized caving roadway’s floor heave has a significant impact on the stability of the narrow coal pillars, the filling body next to the roadway, as well as the entire roadway. Significant floor heave necessitates extensive maintenance and rebuilding work, which has a negative impact on the mine’s regular operations. The costs of sustaining and maintaining the roads are significantly increased by production. In this study, a mechanical model of the floor heave of the road along the goaf is established using the Winker elastic foundation theory model. The mechanical model of the floor heave of the roadway is confirmed when combined with engineering cases. The findings of the study indicate that there is almost no deformation of the side floor of the roadside support and the solid coal. The floor deformation of the roadway area exhibits non-positive symmetry and a “parabolic” characteristic. Roadway width, burial depth, and roadway floor heave all have linearly positive correlations, but elastic modulus of the floor, burial depth, and highway floor heave all have negatively exponential correlations. The maximum deformation of the floor heave, which has a maximum value of 628 mm, is close to the side of the roadway support body; the theoretical model’s maximum value for the floor heave after 100 days of actual deformation monitoring is 645 mm. Between the maximum value and the maximum value as measured, there is a 2.6% error. The paper has important guiding significance for explaining the mechanism of floor heave in goaf roadway and controlling the deformation of the roadway floor.

Experimental Study on the Damage and Crack Evolution Characteristics of TS-RCR Structural Bodies under Cyclic Loading and Unloading

Four representative TS-RCR (three-soft rock-coal-rock) structural bodies were selected according to the lithofacies analysis of coal measures in the Xiangshui Coal Mine, Guizhou, China, to analyze the mechanical properties, internal structure damage characteristics, and crack evolution law of the TS-RCR structural body composed of a soft roof, a soft floor, and soft coal seams. The mechanical model of the TS-RCR structural body was proposed. (1) The stress-strain curves of TS-RCR structures with different lithologies under cyclic loading and unloading show a change rule of sparsity, density, and sparsity with the increased cycles. The deformation of TS-RCR structures under cyclic loading and unloading can be divided into four stages. When the height ratio of the TS-RCR structural body was the same, the higher the strength of the upper and lower rocks, the more cycles the TS-RCR structural body had, and the denser the cyclic loading and unloading curve. On the contrary, the fewer cycles the TS-RCR structural body had, the sparser the cyclic loading and unloading curve. (2) The T2 (transverse relaxation time) spectrum curves of the structural bodies were monitored at about 1 and 10 ms, and two obvious peaks were detected, indicating micropores and mesopores with a large volume in the structural body. Signal intensity increased at the relaxation time of 1 ms, decreased at 10–100 ms, and increased slightly at 100–1000 ms. The pore structure of the structural body with different lithologies changed significantly with the increased cycle number. (3) The damage and failure process of the structural body was roughly divided into three periods according to the time-history analysis of acoustic-emission AF (the ratio of acoustic-emission ringing count to duration) of the structural body: the active period with a relatively low AF value (AF < 60 kHz) in the 1st-2nd cycles; the rising period with a relatively stable increase of the AF value in the 3rd-4th cycles; and the explosive period with a relatively high AF value (AF ≥ 60 kHz) in the 5th cycles. According to the relationship between the RA (the ratio of the rise time to the amplitude of the acoustic-emission-detection wave) value and time, the evolution law of the RA value and AF value of structures with different lithologies is similar in different periods under cyclic loading and unloading.

Study on the Parameters of Strengthening Soft Surrounding Rock by Electric Pulse Grouting in the Mining Face

As an effective measure for the rapid fracturing of coal and rock, electric pulse fracture technology has been successfully applied in oil extraction and natural gas discharge. Using the electric pulse fracture mechanism, this technology can be applied to grouting reinforcement to improve the infiltration efficiency of grouting. In this study, we used a numerical simulation method to establish numerical models with different electric pulse peak pressures, different grouting times and different drilling spacing conditions Through numerical simulation studies, we found that the influence range of grouting reinforcement grows with the increased maximum pressure generated by the electrical pulse. The most economical and reasonable electric pulse parameter setting is 5 MPa for static grouting pressure and 100 MPa for peak electric pulse pressure. The best grouting time to keep pressure in the borehole is determined as 9 h, and the best borehole interval is 10 m. In addition, through the treatment of the soft roof of the Caojiashan coal mine, we also found that the reinforcement sample within the grouting reinforcement range had a compressive strength of more than 1.1 MPa; after each grouting reinforcement was completed, the hydraulic bracket could advance 12 m each time, which shows that the electric pulse grouting reinforcement technology has an obvious effect on the treatment of soft roof slab.

Failure Mechanism and Stability Control of Soft Roof in Advance Support Section of Mining Face

There is a great risk of roof falls in the advance support section of the mining face (ASSoMF), and it is difficult to control the roof. Based on the soft roof of Lijiahao coal mine, this paper studies the stress distribution of the ASSoMF and the space-time evolution of the surrounding rock plastic zone by using theoretical analysis and numerical simulation, and reveals its failure mechanism. Based on the control effect of support resistance on plastic zone, it is proposed that the advance support should mainly adapt to the roadway deformation. Advance equipment without repeated support for mechanized movement has been developed, and the support timing analysis and strength check have been carried out. Results show that the roadway at ASSoMF is in a non-uniform stress field, the confining pressure ratio reaches 1.5~7, and the surrounding rock forms asymmetric failure; the principal stress direction deflects, the angle between it and the vertical direction is about 10°~25°, and the plastic zone of the surrounding rock also rotates to the roadway roof. The proposed equipment can adapt to the characteristics of an unsymmetrical large deformation of a soft roof, and can effectively bear the roof load and maintain the stability of the roadway.

Mining-Induced Stress and Ground Pressure Behavior Characteristics in Mining a Thick Coal Seam With Hard Roofs

The hard roof of coal mines has the characteristics of high hardness, good integrity, and large layer thickness, which leads to many ground control problems. To reveal the influence of a hard roof structure on the stress performance and coal pillar stability during mining operations, the 8,104 and 8,105 working faces in the Tongxin coal mine were considered as the research object to analyze the stress behavior during the working face advance. Numerical simulation software FLAC3D was used to establish the numerical model of the longwall face under hard roof conditions. The stress distribution laws and coal pillar stability under different roof strengths were analyzed so as to explain the impacts of the hard roof on the stress distribution at the working face. The results show that during the second face proceeding, the influence zone of the front abutment pressure under hard roof conditions is 6 m wider than that under soft roof conditions, and the bearing stress at the working face is 10.4 MPa higher. At the mining position, the plastic zone of the pillar under hard roof conditions is 11 m wider than that under soft roof conditions, and the peak vertical stress is 5.13 MPa higher than that under soft roof conditions. At 25 m ahead of the working face, the plastic zone of the pillar under hard roof conditions is 6 m wider than that under soft roof conditions, and the peak vertical stress is 24.84 MPa higher than that under soft roof conditions. Additional overburden pressure produced by the uncaved hard roof increased pillar stress and plastic zones. Therefore, the hard roof is the main cause of strong ground pressure behavior in the Tongxin coal mine. Aiming at the strong mine pressure behavior, it is suggested to adopt the pre-splitting technology to reduce the influence of the hard roof on mine pressure.

RESEARCH OF INNOVATIVE MECHANISMS CREATION OF MODERN BUILDING MATERIALS FOR IMPROVEMENT OF PRODUCTION PROCESSES

Purpose. To reveal the mechanism of formation of contact zones and purposeful choice of mastic composition and its substantiation on the basis of revealing of regularities of interrelations "mastic composition – waterproofing resource". Methodology. The sequence of changes in the technical condition of roofing materials, which varies from normal without damage to emergency with intermediate satisfactory and unsuitable for normal operation depending on the specific damage and leakage of the roof affects the definition of conventional material resources, means and methods of arrangement and arrangements. roofs, as well as the mechanism and kinetics of loss of serviceability are a key factor in improving the whole set of measures aimed at making technology competitive. Results. Technologies of repair of point and local damages in the form of cracks, breaks, exfoliations which are carried out by cutting and the subsequent gluing of pieces of cloths on the prepared sites with filling, allow to receive short-term results. Elimination of continuous surface damage by applying an additional layer of rolled or mastic material is associated with the inevitable preservation in the lower layers of the causes of premature loss of operational functions of the coating. The results provide an opportunity to perform non-dismantling repair and restoration work using purposefully proposed repair composition with the minimum possible cost of resources and a high degree of mechanization. The developed technology is based on the ability of the used repair composition to impregnate and saturate the adjacent surfaces with ingredients that can eliminate damage of a certain type and return the coating or protective layer of the initial waterproofing potential and strengthen it. Originality. Substantiation of possibilities of use of the residual waterproofing resource of the existing soft roof by its saturation with ingredients of the offered repair composition. Practical value. It is possible to effectively use, restore and enhance the residual waterproofing potential of bitumen-roofing roof by pneumatic spraying repair composition of the developed composition.

Theory and Application of Gob-Side Entry Retaining in Thick Three-Soft Coal Seam

With the characteristic of less roadway excavation and high resource recovery, gob-side entry retaining (GER) technology is a safe and efficient green mining technology. Many experts and scholars have done extensive research on its principle and application. However, GERs are rarely used in thick soft coal seams. In this paper, based on the geological conditions of a coal mine in China, we propose a novelty approach of GER in thick three-soft coal seam (it means a single seam with a soft roof and a soft floor). The engineering scheme includes roadway expansion, large section roadway support, cutting roof to relieve pressure, and road-inside backfill body construction. The established mechanical and numerical calculation models effectively guide the engineering practice. Field observations showed that all the processes met the requirements of field production. The research results could provide theoretical guidance for the application of GER under similar geological conditions.

TO THE QUESTION OF INSPECTION AND EXAMINATION OF SOFT ROOFS

Problem statement. The discrepancy between the requirements for soft roofs and their actual condition is gradually increasing, especially in conditions of significant restrictions on the funds allocated for their maintenance and repair. Under these conditions, organizations repairing and restoring roofs reimburse the cost of repairing or installing new ones using lower quality materials, reducing the number of layers of both the main roll carpet, which is laid, and the details of combining the roof with protruding elements on the floor (parapets, lanterns). structures, ventilation shafts, etc.). From these positions, the generalization of the experience of examinations and the improvement of the methodology for verifying the effectiveness of the use of funds provided for the installation or repair of roofs, is a very important task today. Purpose of the article. Recommendations for improving the quality of examinations performed on the inspection of commissioned soft roofs, and the procedure for determining whether they comply with the requirements of current regulatory and technical documentation. Conclusion. Determining the quality and checking the effectiveness of the use of funds provided for the construction, reconstruction and repair of soft roofs in our country in order to improve their condition at the moment is still a very important issue. The training of specialists in matters related to the repair and operation of roofs at the current level has shortcomings. The current regulatory and technical documentation in the field of repair, reconstruction and operation of modern roofs does not contain sufficient information, taking into account modern technologies of their device. For qualitative, operative and objective assessment of quality of inspected soft roofs and definition of cost of volumes, actually executed works on construction, reconstruction and repair it is necessary to equip all interested participants with the modern devices allowing to improve quality of performed examinations considerably.

Analysis on the Regular of Underground Pressure in Large Dip Angle Coal Seam with Soft Roof and Floor

The dip angle of coal seam in Guanyinshan coal mine is between 32° and 39° and the first mining area is X11 and X12. According to the caving degree of the immediate roof in the gob, the intensity of pressure of the main roof is analyzed, and the dynamic load coefficient of the main roof is small. The three-dimensional simulation software FLAC is used to calculate the distance of initial caving and distance of initial pressure of working face. The initial caving distance of the immediate roof at each part of the working face is about 4 m, and the initial pressure distance of main roof is about 20 m on average. This paper analyzes the caving of the main roof: when the distance of initial pressure is 20 m, the caving height of the main roof is about 4 m; when it is pushed to 30 m, the caving height of the main roof is about 10 m; with the continuous mining of the working face, the caving height of the main roof is also increasing, when it is pushed to 90 m, the caving height of the main roof reaches 18 m. Through the analysis of the regular of underground pressure in large dip angle soft roof and floor coal seam mining, it can guide the production.

Experimental and numerical investigation of energy dissipation of roadways with thick soft roofs in underground coal mines

AbstractThe roadway deformation process is closely associated with the accumulation and dissipation of energy. Understanding the characteristics of energy dissipation in surrounding rock is critical to revealing the development process and the disaster mechanisms of the roof accidents in underground coal mines. This paper presents a triaxial compression experiment to analyze energy characteristics of mudstone taken from Huangyanhui Coal Mine. A numerical study is performed to study the energy distribution under different roof strengths. The results suggest that the instability of the roadway is an irreversible energy dissipation process with high nonlinearity and complexity. The roadway support principle, based on the energy balance theory, is proposed to explain the energy distribution. The safety control of roadways with thick and soft roofs should consider the following three aspects: (a) optimize the layout of the roadway, avoid placing it in the stress concentration zone, and reduce the strain energy of the surrounding rock accumulation from the source; (b) improve the ability of the supporting structure to adapt to the deformation of the surrounding rock and avoid the failure of the supporting structure because of excessive force; and (c) set weak structures in the surrounding rock, that dissipate part of the energy, thus reducing the load acting on the support. The results of field application monitoring show that roadway severe deformation was effectively controlled using pressure relief boreholes (PRB), and the average floor heave speed of the roadway decreased from the original 2.0 to 0.98 mm/d. Therefore, PRB provides a new approach for roadway control.

Stability and Control of Retracement Channels in Thin Seam Working Faces with Soft Roof

To reduce the risk of roof falling and rib spalling during equipment retracement in thin coal seam faces with soft roofs, the 25070 working face of Xuehu Coal Mine was taken as the research object, and theoretical analysis, numerical simulation, and field practice methods were used. Under different space relationships between retracement channels and main roof fracture, the load of hydraulic supports was quantitatively analyzed. The relationship between the working resistance of the hydraulic support and the sinking rotation angle of the immediate roof was analyzed, and a reasonable time for the arrangement of the retracement channel was determined. The sublevel excavation technology and the combined support technology of roof anchor cables and coal rib anchors were proposed. The field application shows that the falling height and rate of movable prop of the hydraulic supports, working resistance of the hydraulic supports, and the roof subsidence all meet the requirements of safety production during the terminal mining period, and the surrounding rock control effect of retracement channel was determined to be good. The safe and efficient mining of the coal mine is ensured, and the research results can provide guidance for similar working faces.

Organizational-and-technological solutions for waterproofing joints of highly prefabricated coating panels

This paper describes the technology and organization of the production of works on waterproofing the joints of highly prefabricated coating panels on a soft roof. The process of manufacturing waterproofing works can be divided into three stages - preparatory, main and final ones. Each stage has its own technological features and rules for performing work. The quality of execution of each stage affects the quality of work as a whole, ultimately providing the necessary reliability and strength of the coating.

Exploration the Causes of Emergency Leaks of a Soft Polyurea Roof

Exploration the Causes of Emergency Leaks of a Soft Polyurea Roof

Analysis of the Causes of PVC Membrane Defects that Caused Soft Roof Leaks

Analysis of the Causes of PVC Membrane Defects that Caused Soft Roof Leaks

Numerical simulation and control of a rockburst induced by main roof fracture in a deep coal seam

ABSTRACT In view of the engineering problem whereby the main roof fracture of deep coal seam still induces frequent rockburst after soft direct roof buffering, a UDEC numerical model was established based on the actual geological conditions of a mine, and the influences of the length of hanging roof and periodic weighting step on the stress in front of coal wall were discussed. The dangerous area at most risk of rockburst in the working face was monitored by using core-drilling, the risk of a rockburst was predicted by classification, and countermeasures were taken against all levels of rockburst. The results show that the longer the hanging roof length, the higher the stress in front of coal body; However, when the coal body changes from an elastic state of stress to a plastic state of stress, the stress will suddenly decrease, the range of variation of stress under static load is larger than that under dynamic load, which indicates that shock wave attenuates the stress in front of the coal body. The larger the periodic weighting step distance, the higher the stress in front of coal body, and the greater the increase of stress. However, compared with the attenuation effect of dynamic load, when increasing the hanging roof distance, the attenuation effect of dynamic load under the condition of increasing the periodic weighting step distance is greater. Dynamic load or static load will increase the stress in front of coal wall, which will lead to a rockburst. The techniques of large-diameter borehole pressure relief, coal seam water injection, and pressure relief blasting can be used to control the high-stress area monitored, ensuring the safe mining of the working face, so that coal resources can be extracted efficiently, and the rate of utilization of coal resources can be improved.

DETERMINATION OF THE COMPETITIVE DIRECTION OF RESTORATION OF OPERATIONAL SUITABILITY OF SOFT ROOFS

Purpose. The reorientation of roofing work from new construction to repair area without significant transformation of conventional technological solutions and the lack of sufficient mechanization have led to the need for a radical improvement of the multifaceted roof repair measures. Methodology. The sequence of change in the technical condition of roofing roofs, which changes from normal without damage to emergency with intermediate satisfactory and unusable for normal operation depending on the specific damage and the flow of the roof affects the determination of conventional material resources, tools and methods of reclamation roofs, as well as the mechanism and kinetics of the loss of serviceability are the key factors for improving the entire set of measures emit provide competitive technology. Findings. The technologies of repair of point and local damages in the form of cracks, breaks, exfoliations, which are performed by cutting and subsequent gluing of pieces of cloths on the prepared areas with putty, allow to obtain short-term results. The elimination of continuous surface damage by applying an additional layer of rolled or mastic material is associated with the inevitable preservation in the lower layers of the causes of premature loss of operational functions by the coating. The results provide an opportunity to perform dismantled repair and restoration work using a purposefully proposed repair composition with the lowest possible cost of resources and a high degree of mechanization. The technology developed is based on the ability of the repair composition used to impregnate and saturate adjacent surfaces with ingredients capable of eliminating damage to a particular species and returning the initial waterproofing potential to the coating or protective layers and enhancing it. Originality. Substantiation of the possibilities of using the residual waterproofing resource of the existing soft roof with its saturation with the ingredients of the proposed repair composition. Practical value. It is possible to effectively use, restore and enhance the residual waterproofing potential of the bitumen-roofing material by pneumatic spraying of the repair composition of the developed composition.

Research on Development Characteristics of Micro-Fractures in a Soft Coal Seam Based on the Water-Injection Effect

The development characteristics of micro-fractures in the soft coal seam, which are often neglected in water-injection and exploitation of coalbed methane, are more complex compared to the hard coal seam. To investigate the influences of micro fractures on the water-injection effects in soft coal seams, our research took the dust control through water injection in a soft coal seam with soft roof and floor as the object. By using an optical microscope, a scanning electron microscope (SEM), and an X-ray diffractometer (XRD), the development characteristics of micro fractures in the soft coal seam were obtained. The relationship between the development characteristics of micro fractures and the wetting effect of the coal was analyzed by studying the change of water content in coal samples after water injection in the coal seam. The research results showed that micro fractures were well developed, the fractures had poor directivity and connectivity, and some fractures were filled with minerals. In addition, the fractures were mainly 0~10 im wide, and the linear density was more than 6 fractures per millimeter. Fracture width and linear density positively correlated with the water content of coal after water injection, while clay minerals in coal mass exhibited a negative correlation with the water content.

Gob-Side Entry Retained with Soft Roof, Floor, and Seam in Thin Coal Seams: A Case Study

Gob-side entry retained technology is of great significance to develop coal mining industry sustainably, which can improve the coal recovery rate by mining without the coal pillar. However, scholars and researchers pay little attention to the gob-side entry retained with soft roof, floor, and seam in thin coal seams. In this study, the difficulties and key points of surrounding rock control for gob-side entry retained with soft roof, floor, and seam in thin coal seams were firstly proposed. Secondly, the mechanical model of the interaction between the roadside backfill body and the roof for gob-side entry retained with soft roof, floor, and seam in thin coal seams was established, and the relevant parameters were designed. Finally, the above results were verified by the engineering practice of gob-side entry retained technology and the monitoring of mine pressure on the 1103 working face of the Heilong Coal Mine. Moreover, the effect factors of surrounding rock stability for gob-side entry retained with soft roof, floor, and seam in thin coal seams were discussed using the discrete element method. The results could provide guidance for gob-side entry retained with soft roof, floor, and seam in thin coal seams under similar geological conditions.

Deviatoric Stress Evolution Laws and Control in Surrounding Rock of Soft Coal and Soft Roof Roadway under Intense Mining Conditions

Aiming at the problem of large deformation and instability failure and its control of soft coal and soft roof roadway under intense mining, laboratory experiments, theoretical calculations, Flac3D numerical simulation, borehole peeping, and pressure observation were used to study the deflection characteristics of the deviatoric stress of the gas tailgate and the distribution and failure characteristics of the plastic zone in the mining face considering the strain softening characteristics of the roof and coal of roadway, and then the truss anchor cable‐control technology is proposed. The results show the following: (1) The intense mining influence on the working face will deflect the peak deviatoric stress zone (PDSZ) of the surrounding rock of the gas tailgate. The influence distance of PDSZ is about 20 m in advance and 60 m in lag; the PDSZ at the gob side of the roadway is located in the range of 3–5.5 m from the surface of the coal pillar, while the coal wall side is mainly located in the range of 3–4.5 m at the shoulder corner and bottom corner of the solid coal. (2) The intense mining in the working face caused the nonuniform expansion of the surrounding rock plastic area of the gas tailgate. The two shoulder angles of the roadway and the bottom of the coal pillar have the largest damage range, and the maximum damage location is the side angle of the coal pillar (5 m). Angle and bottom angle of coal pillar are the key points of support control. (3) The plastic failure line of the surrounding rock of the gas tailgate is always between the inner and outer contours of the PDSZ, and the rock mass in the PDSZ is in a stable and unstable transition state, so the range of anchor cable support should be cross plastic failure line. (4) The theoretical calculations and numerical simulation results agree well with the drilling peep results. Based on the deflection law of the PDSZ and the expansion characteristics of the plastic zone, a truss anchor cable supporting system with integrated locking and large‐scale support function is proposed to jointly control the roof and the two sides, which effectively solves the problem of weak surrounding rock roadway under severe mining deformation control problems realizing safety and efficient production in coal mines under intense mining.

膨胀型软岩顶板沿空巷道支护设计优化

膨胀型软岩顶板沿空巷道支护设计优化