Compound Roof Research Articles

Case Study on Pre-Splitting Blasting Reasonable Parameters of Goaf-Side Entry Retained by Roof Cutting for Hard Main Roof

The key parameters of pressure relief pre-splitting blasting technology (PRPBT) contribute to the implementation effect of goaf-side entry by roof cutting (GSERC). This study is an attempt to design the key parameters including the roof cutting height, the roof cutting angle, the spacing between blasting boreholes, the charge structure and the sealing length by using theoretical analysis, numerical simulation and field implementation. The basic quality index of the main roof is 666.27, and combined with the peeping observation result, the main roof belongs to the category of a hard main roof. Different from a weakened roof and a compound roof, the unreasonable parameters of the PRPBT for the hard main roof lead to three problems including an insufficient pre-splitting blasting effect, roof suspension in the goaf and serious damage to the rock mass for the roof cutting rib. The PRPBT effect is closely related to key parameters, including the roof cutting parameters and the pre-splitting blasting parameters. Hence, to solve those three problems, a new design strategy was proposed based on the optimized directions of increasing the roof cutting height, decreasing the spacing between the blasting boreholes, changing the charge structure and adjusting the sealing length. According to the results of the theoretical calculation, numerical simulation and in situ measurement, the roof cutting height, the roof cutting angle, the spaced distance between the blasting boreholes, the charge structure and the sealing length were determined as 10 m, 15°, 500 mm, 4 + 4 + 3 + 3 + 2 and 2.4 m, respectively. The fissure rate was proposed to assess the developed effect of different pre-splitting blasting schemes. The proposed design strategy achieved a better effect of pre-splitting blasting for the entry, and eliminated the roof suspension of the hard main roof in the goaf. The design strategy in this study could contribute to other similar coal mines under the condition of a hard main roof.

Stability mechanism and control technology of large inclined working face roof in large-scale caving area

Abstract Based on the compound roof in the 211 112 working face of mine no. 2 in the Xinji area and various newly emerging geological conditions such as crack development in coal seams and major slopes, the roof of the severely sloped working face was studied focusing on the stress, strain and fracture features, along with the mechanism of rib spalling in the coal wall and the grouting strengthening technology. According to the analysis, the pre-loaded pressure on the working face tended to be redistributed with the development of the coal roof caving zone, which resulted in new stress concentration in the coal wall before the caving zone. Compared with the stress before rib spalling, stress decreased with the increased depth of rib spalling, which caused a slightly lower risk of rib spalling. Based on the analysis, an inorganic grouting reinforcement with a water-solid ratio of 3:1 was adopted to meet the needs of filling-body strength, which reduced operation time and increased economic benefits. The work ensures the safe and efficient mining of the composite roof face with a large inclination angle of Xinji No. 2 Mine and offers a reference for the mining coal seams under similar conditions.

Study on the controller factors associated with roof falling and ribs spalling in deep mine with great mining height and compound roof

To analyze the controllable factors associated with roof fall and rib spalling during the mining process in a deep well with a great mining height and compound roof, and to resolve such issues during the mining process, a mechanical model for describing the deflection of a compound roof was established based on the beam theory for an elastic foundation. The maximum deflection position of a compound roof and the associated depth of the rib spalling were further calculated and determined in this study. Based on the depth of the rib spalling, we determined the force distribution of spalling coal from the mine wall. By combining the force distribution with the safety margin, we established a critical failure equation of the coal wall and further calculated the height of the spalling coal. The human factors used to control the rib spalling issue were also analyzed based on these results. Furthermore, taking the mining conditions of the Pingdingshan No. 11 coal mine as the engineering background, we simulated the mining process on the working face (Ji16-17-24030) using FLAC3D numerical modeling software and an orthogonal array testing strategy. By conducting a range analysis on the simulation results, we determined the sensitivity of each main controllable factor to a roof fall and rib spalling in the working face. The results show that the comprehensive sensitivities of the main controllable factors to roof fall and rib spalling follow the order of cohesion > support strength > mining height > distance to face > lateral force. In addition, the maximum deformation of the coal wall decreases by 0.682 mm with every 1 MPa increase in the cohesion strength of the coal body.

Study on Deformation and Supporting Measures of Mining Roadway with Compound Roof

Study on Deformation and Supporting Measures of Mining Roadway with Compound Roof

Similar Simulation Test of Overlying Rock Failure and Crack Evolution in Fully Mechanized Caving Face with Compound Roof

Similar Simulation Test of Overlying Rock Failure and Crack Evolution in Fully Mechanized Caving Face with Compound Roof

Research on Plastic Zone Evolution Law of Surrounding Rock of Gob-Side Entry Retaining under Typical Roof Conditions in Deep Mine

To solve the control problem of the surrounding rock of gob-side entry retaining under typical roof conditions in deep mines, we conduct theoretical analysis, numerical simulation, and actual measurements. Starting from the plastic zone of the surrounding rock, the serious damage area, the degree and scope of damage, and the dynamic evolution process of the surrounding rock of the gob-side entry retaining are systematically analyzed under four typical roof conditions in deep mines; the expansion and evolution laws of the plastic zone of the surrounding rock are expounded; and a key control technology is proposed. The results indicate that (1) the plastic failure of surrounding rock was concentrated mainly on the coal side and on the floor, especially in the filling body. The plastic zone of the surrounding rock of the gob-side entry retaining with the thick immediate roof was widely distributed and deep, but the plastic failure of the filling body was not obvious. The plastic failure of the surrounding rock of the gob-side entry retaining with the compound roof was mainly concentrated on the roof, filling body, and floor of the filling area. (2) According to the typical roof conditions of the deep gob-side entry retaining, the order of the degree of damage to the surrounding rock was as follows: thick immediate roof, compound roof, thin immediate roof, and thick-hard roof. (3) A “multisupport structure” control system is proposed for the gob-side entry retaining in a deep mine, including measures for enhancing the bearing performance of the anchorage system, increasing the strength of the cataclastic coal-rock mass, enhancing the bearing capacity of the filling body, and increasing the bearing capacity on the tunnel side. The proposed technology was applied to the deep gob-side entry retaining project in the east area of Panyi Mine, and it effectively fulfilled the reuse requirements of gob-side entry retaining in deep mines.

Deformation Mechanism and Stability Control of Roadway Surrounding Rock with Compound Roof: Research and Applications

In view of problems with roadways with a compound roof, such as the occurrence of instability in the roof strata, ease of separation of the layer caving, difficulty of maintenance, and poor safety, we established a mechanical calculation model of a roadway with compound roof using the elastic mechanics theory, taking the stability control of a roadway with compound roof at a coal mine in Guizhou Province, China as the research background, and based on the actual characteristics of the coal seam and the roof and floor slate. Expressions of the separation layer and instability limit load of compound roof were derived, and the calculation and verification were carried out in combination with the actual conditions. By means of numerical simulation, the distribution and evolution laws of stress, displacement and plastic zone of roadways with a compound roof were studied, and the deformation characteristics and instability mechanism of roadways with a compound roof were revealed: (1) in early stage deformation of roadway, the amount is large, the speed is fast, and the scale is wide; (2) compound roofs are vulnerable to abscission and instability, the bearing capacity of the two sides is low due to softness and cracking, the shear failure of side angles and vertex angles weakens the strength of surrounding rock, and the self-bearing capacity of surrounding rock is low; (3) the bolt and anchor bear relatively large tensile force, and the support structure is easy to be broken up. On this basis, the stability control principle of a roadway with compound roof tunnel was put forward: fast and timely support; high-strength bolt strong support; improving the stability of the roof and the bearing capacity of the two sides; restraining the shear failure of the key bearing parts such as the side angles and the bottom angles, and targeted stability control technology for roadways with a compound roof was developed. The field industrial test showed that the deformation of this roadway with a compound roof was effectively controlled and the overall stability of the roadway was effectively improved. The results of this study could provide useful reference for a roadway with a compound roof under similar conditions.

Self-bearing Characteristics and Control Strategy of a Cataclastic Regenerated Rock Mass in a Roadway Roof with Top Remains: A Case Study

A roadway roof has compound and cataclastic features when tunneling a roadway under a gob with top remains in downward mining. To identify the self-bearing characteristics and to develop a control strategy for a regenerated roadway roof with top remains (RRRTR), mechanical and numerical models of a RRRTR were built on the basis of a structural model of a compound and cataclastic roof. Through a theoretical analysis and numerical simulations, the formation and instability criterion of a three-hinged arch in a RRRTR were analyzed. Meanwhile, the self-bearing characteristics of a RRRTR with various crack spacing values in the top remains were studied. On this basis, a bolt-net-belt (BNB) support scenario was proposed to control the RRRTR and an on-site roof subsidence monitoring task was conducted. The theoretical and numerical analyses both indicate that a three-hinged arch exists in the roadway top remains, and it has a certain bearing capacity. The compressive failure of the hinge points is an instability trigger of a three-hinged arch that would trigger the entire failure of the RRRTR. The crack spacing values of the top remains influenced the formation and bearing capacity of the three-hinged arch. The three-hinged arch is easier to establish and has a better bearing effect when the top remains have a larger crack spacing value. The BNB support scenario could not only control the roof subsidence but also facilitate the potential self-bearing capability of the RRRTR.

Evaluation of the Mechanical Instability of Mining Roadway Overburden: Research and Applications

Under the superposed action of the primary rock stress and the mining stress, the compound roof of a roadway will have irregular plastic failure zone with greater depth, resulting in a wide range of non-uniform deformations and roof failures. Mastering the deformation and failure characteristics of this roof is essentially to recognize the development of the plastic zone of a compound roof. In this paper, the on-site roof detection method is mainly adopted to arrange a large number of boreholes for visualization and the deep displacement monitoring with the high-density points. Combined with numerical simulations, the rupture development characteristics and deformation mechanisms of the compound roof are revealed. The results show that the magnitude and direction of the principal stress of surrounding rock in a mining roadway are constantly changing, and the penetrating phenomenon will occur during the plastic zone expansion process. The order of the compound roof rupture as follows: shallow strata plastic failure, deep strata penetrating plastic failure and middle strata rupture. Severe roof deformation is mainly caused by plastic failure, and the strong deformation pressure caused by deep strata penetration plastic failure can easily lead to tensile failure and rupture in the middle strata. According to the plastic zone penetration development of the compound roof, the hierarchical support design led by the long-extension bolt is carried out on the test roadway. The monitoring results show that the roof is controlled well. The research results can provide a reference for the control of compound roofs in mining roadways.

Mechanism and Control Methods of Roof Deformations in Gob-Side Entry Retention by Roof Cutting Under Medium-Thick Coal Seams

In order to ensure the successful implementation of gob-side entry retention by roof cutting under medium-thickness coal seams and compound roof conditions in Guandi Coal Mine, a mechanical model was established to analyze the factors affecting the roof deformation, and the roof fracturing height and roof fracturing direction were researched by way of numerical simulation and field experiments. The theoretical analysis and numerical simulation showed that the rotation angle of the upper main roof is the main factor leading to roof deformation, that increasing the support strength in the roadway cannot reduce the roof deformation, and that the roof deformation can be effectively controlled by increasing the roof fracturing height and the fracturing direction. The results confirmed that the roof fracturing height was 7 m, the roof fracturing direction was 15°, and the charging structure was 3 + 3 + 2 + 1. The roof was strengthened using a constant resistance and large deformation anchor, a single hydraulic prop reinforcement support in the lane, and a U-shaped steel retaining gangue support. The retained entry was stable at 200 m behind the working face and can meet the demands of reuse for the next mining face.

Deformation mechanism and optimum design for large cross-sectional longwall installation roadway under compound roof

Both the deformation characters and the failure mode of the large cross-sectional longwall installation roadway under compound roof are becoming an emergent issue than ever before due to the rapid development of modern mining equipment. Various engineering applications have revealed that the insufficient design and inappropriate support technology are the main reasons for the fatal accidents associated with the sudden roof fall attributed to the separation of the overlying compound strata. The present research work, therefore, starts with a case study using the conventional support technology in order to demonstrate the importance of this issue followed by a summarization of the typical failure mode of the longwall installation roadway under compound strata with varied thicknesses. Then a simplified theoretical model is proposed and set up aiming at a better understanding of the distribution of the elastic-plastic zones as well as the effects of different caving procedures. The finite element analysis software program FLAC3D is adopted to evaluate the effect of the caving method and the reinforcement provided by an additional support. Then a case study conducted at a typical coal mine with compound roof condition is presented to verify the advantages of the proposed design. The results obtained show that the optimized design presented in this research work is effective to control the deformation of the surrounding rock, particularly in terms of separation of the overlying compound strata.

Key Technologies and Application Test of an Innovative Noncoal Pillar Mining Approach: A Case Study

The waste of coal resources, a complicated production process and slow mining speed seriously restrict the rapid development of longwall mining. To achieve effective mining, an innovative noncoal pillar mining approach (i.e., Gob-side Entry Retaining by Roof Cutting (GERRC)) was introduced. The mechanism of the GERRC approach and its three key technologies (i.e., roof support technology, directional presplit cumulative blasting technology and surrounding rock control technology) were studied by theoretical analysis, numerical simulation, laboratory and field experiments. The new approach was finally tested under medium-thick coal seam and compound roof conditions. The results show that the directional presplit cumulative blasting technology can effectively control the damage evolution in the roof rock, maintain the integrity of the entry roof and contribute the gob roof to the cave in time. The support technologies in different roof movement stages can control the entry surroundings, and the final section of the retained entry met the safety production requirements. The test results suggested that the proposed approach for coal effective mining is feasible, and the introduced key technologies and design methods potentially produce reasonable values for applications of pillarless mining in similar projects.

Mine Strata Pressure Characteristics and Mechanisms in Gob-Side Entry Retention by Roof Cutting under Medium-Thick Coal Seam and Compound Roof Conditions

Coal is among the most important energy sources, and gob-side entry retention by roof cutting (GERRC) is an innovative non-pillar mining technique that can effectively increase coal recovery rates and avoid coal wastage. To investigate the characteristics of mine strata pressure using the GERRC technique, a field case study under conditions involving a medium-thick coal seam and a compound roof was performed, and the mine strata behavior mechanisms were studied by theoretical analysis. Field monitoring shows that the distributions of the weighting step and strength along the longwall working face are asymmetrical. The periodic weighting length on the entry retaining side is longer than that on the other sides of the longwall working face, and the average increase is appropriately 4 m. Compared to the other sides of the longwall, on the entry retaining side, the periodic weighting strength is weaker, the average pressure is reduced by 2.1 MPa, and the peak pressure is reduced by 10.2 MPa. The lateral distance affected by roof cutting along the longwall is approximately 29.75 m, and the closer to the cutting slit, the more significant the roof cutting effect is. The retained entry becomes stable when it is more than 230 m behind the mining face, and the final cross section of the retained entry can meet the reuse demand of the next mining face. Theoretical analysis shows that the roof pressure mechanism in GERRC can be explained using cantilever beam theory. Within the area affected by roof cutting, the thickness of the immediate roof increases, and the suspension plate length of the roof immediately behind the longwall decreases. Then, the gangue pile in the goaf behind the longwall formed by the immediate roof’s collapse and expansion can support the main roof and other overlying strata much better. Therefore, the rotational breaking angle of the main roof is smaller, the periodic weighting step strength increases, and the periodic weighting decreases. According to the structural state of the surrounding rocks during the entire entry retaining process, the retained entry can be divided into coal support, dynamic pressure and stable entry areas.

Research into stope roof control of compound roof by solid backfilling mining

Based on the analysis of the failure characteristics and backfilling effect of the compound roof at 1801 backfilling workface in Taiyuan coal mine, China, we propose a method of controlling the pre-subsidence of a compound roof by using pre-stressed bolts to improve the backfilling ratio of the workface so as to maintain the global stability of the stope roof. In addition, PHASE simulation software was employed to analyze the influence law of pre-stressing force, length, and interval on roof subsidence at the workface. On the basis of the numerical simulation results, a model for calculating the pre-stressing force and length of the bolts, the interval between the bolts, as well as roof subsidence at the workface, was established by using SPSS regression analysis software. Moreover, the research results were applied successfully to the 1801 filling workface. According to the monitoring data of roof closure, it was found that the final subsidence value for the goaf roof was 350mm and the filling ratio at the workface was 86%, which could fully meet the demand for safety production at the workface. The safe and effective control of the stope roof was therefore realized, which achieves the goal of safe and efficient backfilling mining under a compound roof.

Numerical Simulation on the Effect of Compound Roof Separation Position on Bolting Performance

Prestress is a key parameter in bolting, while the cohesive force of layers in the compound roof strata is low and prone to separation, causing the prestress proliferation very poor. With the method of numerical simulation analysis,the location of separation in compound roof to affect the performance of bolting support was researched. It is concluded the roof separation in the edge of anchorage zone, the prestress field superpose, but is away from the deep surrounding rock and shows poor stability,however the role of cable can make up for the defect of rockbolts support. It has been found the highly prestressed strength bolting system adapts to the compound roof.

Characterization and Evaluation of Sheet Molding Compound Roof Tiles

The characteristics of sheet molding compound (SMC) roof tiles are: lightness, high strength, high stiffness, and corrosion resistance. This paper describes a trial production of SMC roof tiles in a composite manufacturing industry in Tangerang, Indonesia. The SMC roof tiles samples were then characterized and evaluated to determine the mechanical properties of the material and the performance of the roof structure. Mechanical properties of the material, i.e. the tensile strength and the elastic modulus, were obtained from the tensile test. Evaluation of the SMC roof tiles as a roof structure was carried out by static loads testing of the roof structure model. The tensile test according to ASTM D638: 2003 shows that the tensile strength and the elastic modulus of the SMC material are 30 ± 3MPa and 10 ± 1GPa, respectively. Failure of the SMC roof tiles as a roof structure when loaded by static load of cylindrical steel loads due to crack occurred at 94 kgs load.

The Application of High Strength Anchor about Compound Roof Support about in Guantun Coal Mine

50101 working face roof is typical compound roof in Guantun coal mine. Gateway design uses anchor-net + anchor rope supporting method. Sinking large roof abscission layer,the maximum abscission reached 450 ~ 500 mm Within one month after the construction .Anchor cable faults is frequently. In order to solve the above problem, We proposed to anchor cable φ15.24 mm changed toφ21.60 cable and Mining steel i-beam changed to W steel band . We can improve the support strength of anchor cable. With new support mode, We successfully make the roof abscission layer of subsidence and anchor cable fracture rate decline .

Study on the Supporting and Repairing Technologies for Difficult Roadways with Large Deformation in Coal Mines

It is essential to research into the supporting and repairing technologies for ensuring the difficult roadways safety. Based on the widely field investigation including the surrounding environments and supporting technologies of the rock and coal roadways with large deformation, such as in Tangkou, Liuzhuang, Huajiahu, Xinzhi coal mine, etc, the preliminary combining supporting styles and the corresponding effect for the rock roadways are analyzed and concluded. The corresponding supporting technologies for the difficult roadways, such as the roadways with large cross section, soft surrounding rock, intensively dynamic pressure, compound roof, high ground stress, water seepage in the roof or two sides and the influence of the roadways nearby, are studied theoretically and also concluded. Finally, some subsidiary contents are brought forward to control the roadway deformation, which include concrete parameters, the quality of supporting materials, the building of monitoring system.

Study on Roadway Parameters of Broken Compound Roof of Gently Inclined Thick Coal Seam

This paper through investigation of the geological conditions of Da’ Anshan's coal mine, according to the special of the broken compound roof on inclined thick coal seam, select the anchor suspension theory and composite beam theory, design the roadway support's anchor parameters, and apply the finite element software ADINA carry out simulation analysis, through the contrast of analysis and engineering data, proved that the design of support parameters is reasonably and practicable. The research has practical value and can guide similar projects.

A Research into Extra-thick compound mudstone roof roadway failure mechanism and security control

Using roof accident cases, this paper analyzes the characteristics of extra-thick compound mudstone roof surrounding rock in the laboratory, and then it studies the failure characteristics and instability mechanism of the roof through numerical simulation, together with field measurement of the digging roadway surrounding rock deformation and bolt support load. The results show that roadway support structure is rational and four solutions are proposed for reinforcing surrounding rock timely, enlarging anchorage range, improving the support stiffness of lower rock stratum, and disposing the bolt and anchor cable along the cracks to improve the intensity at the top right angles of the roadway. This study might provide scientific basis for the similar compound roof roadway support in the future.