Gob-side Entry Research Articles

Deformation mechanism and control technology of gob-side entry retaining with roadside backfilling: a numerical analysis and field investigation

The technology of gob-side entry retaining (GER) has the advantages in terms of higher resource recovery rate and lower drivage ratio. In this study, the GER implementation in N1217 panel in Ningtiaota Coal Mine, to verify the adaptability of the gob-side entry retaining with roadside backfilling, the FLAC3D numerical model was established, the stress evolution law and plastic zone distribution of the roadway surrounding rock were analyzed, the deformation characteristics of the roadway during the mining period were revealed, the roadway surrounding rock control technology was proposed, and the development of roof cracks was analyzed. The numerical results show that during the mining of the working face, the roadside backfill body and gangue are jointly loaded, the peak stress of the surrounding rock is transferred from the mining side to the solid coal side, the plastic zone of the roof and the solid coal side increases significantly, and the tensile and shear mixed failure occurs. Based on the evolution characteristics of the stress and plastic zone of the surrounding rock during the mining period of the working face, a collaborative control technology of the surrounding rock based on gangue retaining bracket + roadside backfill + bolt (cable) is proposed, and the borehole peep shows that the roadway is affected by roof fracture rotation and subsidence, which leads to the development of roadway overburden cracks and failures to the depth. The monitoring results indicate that the control measures are highly effective, with minimal roadway convergence observed and stable bolt (cable) supporting forces recorded. Additionally, hydraulic support resistance monitoring confirms that the roadway remains stable. It can ensure the safe mining of the working face of the Ningtiaota coal mine and other similar roadways.

Optimization of small coal pillar width and control measures in gob-side entry excavation of thick coal seams

This study introduces an innovative optimized bolting support system specifically tailored for gob-side entry excavation in thick coal seams at a coal mine in southwestern Shandong, China. Employing theoretical analysis, numerical simulation, and field measurements, the research focuses on examining the failure characteristics of surrounding rock during gob-side entry excavation. The key innovation lies in the development of a 5-meter optimal coal pillar width, ensuring balanced stress distribution and structural integrity. Additionally, a lag time of at least 46 days between gob-side entry excavation and the upper working face retreat is recommended to mitigate roof subsidence and surrounding rock deformation. The optimized bolting support system, featuring increased bolt pretension, utilization of high-strength steel strips, and reinforcement of weak points, effectively reduces deformation of the roadway surrounding rock, meeting support requirements for normal production. This novel approach successfully addresses the support challenges in thick coal seam gob-side entry excavation, enhancing mining safety and resource recovery rates.

Review on Engineering Application Status of Gob-Side Entry Retaining Technology in China

Gob-side entry retaining (GSER) technology has been widely used in underground coal mines. However, the applicable conditions of GSER technology in practical engineering still need further clarification to prevent the safety hazards and significant economic losses caused by its failure. In this study, 587 application cases of GSER in China from 2000 to 2024 were collected, and the relevant data, such as geological conditions and key technical parameters of GSER projects and their impact on engineering practices, were systematically analyzed. Considering the technical characteristics and the developing status of GSER technology, the current status of the application of GSER engineering in the mining areas of China was obtained, and then the applicable geological conditions and optimal technical parameters for the effective implementation of GSER technology were identified. Additionally, the existing technical challenges and further prospects of GSER technology were illustrated. This study provides a reference for reasonable applications and further research of GSER technology.

Failure mechanism of severe deformation in gob-side entry rib and unloading-supporting coupling control technology

Given the problem of the solid coal side produces strong mine pressure in the stage of strong mining and lagging dynamic pressure in the gob-side entry retaining (GER). Using the W3233 ventilation roadway in the West-Third mining area as a case study, the research employs numerical simulation, field observation, and engineering analogy. Key findings include: (1) The optimal plan reduces maximum stress on the coal side and shifts it inward, primarily by severing the main roof and alleviating the gangue wall load, offering limited pressure relief on the solid coal rib. (2) When hole-creating depth is too close to the solid coal rib (b = 6 m), it compromises integrity. If the depth exceeds the stress maximum region (b = 10 m), it fails to effectively sever the peak stress area. However, a depth within the stress maximum region (b = 8 m) effectively absorbs and transfers stress, with a buffer area of approximately 3.7 m from the external support area. (3) The length of the hole (l = 2, 4, 6 m) directly affects deformation absorption and pressure relief, while longitudinal row spacing (s = 2.7, 3.6, 4.5 m) has an inverse effect. For optimal results, a hole length of 4 m and a row spacing of 3.6 m are recommended. (4) After 150 days, the new bag pressure regulating system maintains about 40 % of the absorbable deformation space in the LPRH, confirming simulation results. Observations show that external support forces remain stable at around 250 kN, and coal rib displacement is controlled within 350 mm, over 65 % less than similar GER sections with comparable geological conditions. This research introduces a novel technology and methodology for managing large deformations of the solid coal rib in gob-side dynamic pressure roadways, providing significant reference value.

Research on the evolution law and control technology of deviatoric stress in the surrounding rock of gob-side entry retaining

Gob-side entry retaining (GER) play a crucial role in enhancing coal recovery, improving roadway stress conditions, and ensuring safe and efficient mining operations. This study focuses on investigating the stability characteristics of surrounding rock using flexible formwork concrete (FFC) along the headgate of 3405 panel. According to the fracture pattern of roof, a mechanical model of GER was developed. This study derived expressions for the support resistance of the filling body and determined its optimal bearing capacity. A FLAC3D numerical model was employed to simulate the GER process, segmented into early, middle, and late stages. Simulation results demonstrate a progression in peak deviatoric stress and extent of plastic zones in the surrounding rock. This evolution includes an initial minor increase (early stage), followed by rapid escalation (middle stage), and eventual stabilization (late stage). The middle stage emerges as critical, characterized by pronounced mining-induced stress effects on the roof. During this phase, significant changes are observed in deviatoric stress curves, with plastic zones rapidly migrating deeper into the rock mass. Practical implementation of the findings revealed a maximum deformation of the filling body of only 198 mm, affirming the feasibility of employing FFC in GER. This research provides valuable insights into managing stability concerns in GER thereby enhancing safety and operational efficiency in coal mining under similar conditions.

Study of the Constraint Pillar Test and the Application in Gob-Side Entry Retaining

Firmly, the bearing capacity test of 1:1 equal ratio pillar under different constraint forms and different filling medium conditions was carried out. The results show that the binding pillar-forming effect is relatively good. The constraint ability of unconstrained, metal mesh, polyester mesh, hooked iron flat-hoop bushing, bellows, and spiral iron pipe is enhanced, in turn, and the carrying capacity is improved successfully. The homogeneity of high-water materials is better than concrete, and they have better compressibility, but their carrying capacity is relatively weak. The carrying capacity of concrete pillars is generously higher than that of high-water materials, but the compressibility is poor. Second, the migration characteristics of the surrounding rock structure of the gob-side entry retaining and the rule of side support are analyzed, the requirements of the side support are pointed out, and the side-support technology of the binding pillar is proposed. Taking Hijiata Mine’s 50108 working face gob-side entry retaining as an example, the bellows pump-filled concrete pillar is used as the side support body, supplemented by handling steel mesh and air-duct cloth, and toughness material is sprayed between the pillars to seal the goaf, meeting the requirements of side support and road stability. The pillar has the characteristics of high early strength, strong final consolidation carrying capacity, good crimping effect, high mechanism degree, fast construction speed, less concrete consumption, low comprehensive cost, etc., and it has a good application prospect in the gob-side entry retaining or rapid advanced working face.

Control Study on Surrounding Rock of Gob-Side Entry Retaining below near Distance Goaf

Control Study on Surrounding Rock of Gob-Side Entry Retaining below near Distance Goaf

Numerical Simulation and Engineering Application of Synergistic Support Effect of Bolt–Mesh–Cable Support in Gob-Side Entry of Deep Soft Coal Seam

Numerical Simulation and Engineering Application of Synergistic Support Effect of Bolt–Mesh–Cable Support in Gob-Side Entry of Deep Soft Coal Seam

Research on Key Roof-Cutting Parameters for Surrounding Rock Stability Control in Gob-Side Entry Retention without Coal Pillars in Karst Mountainous Area

The differential distribution of original rock stress and stress concentration caused by the variation in coal seam depth in karst topography are critical factors influencing the selection of roof-cutting parameters. Based on this, this study explores a method to determine reasonable roof-cutting parameters by incorporating the characteristics of coal seam depth variation in karst mountainous areas. A mechanical model of the cantilever beam structure for roof cutting in gob-side entry retention (GSER) is constructed, and the critical values and reasonable ranges of roof-cutting height and angle under different burial depths are derived. Furthermore, the displacement and stress evolution characteristics of surrounding rocks in gob-side entry retention under different coal seam burial depths, roof-cutting heights, and roof-cutting angles within the reasonable range of roof-cutting parameters are analyzed. The results show that there is a positive correlation between roof-cutting height and tensile stress in the uncut portion of the main roof, while roof-cutting angle and coal seam depth are negatively correlated with tensile stress. From the perspective of impact, roof-cutting height has a greater impact than roof-cutting angle, followed by coal seam depth. As for the distribution characteristics of the reasonable roof-cutting parameter range, the fan-shaped area of reasonable roof-cutting parameters gradually decreases with increasing coal seam depth. Taking the geological conditions of Anshun Coal Mine as an example, when the burial depth increases from 350 m to 550 m, adjusting the roof-cutting height to 6 m, 7 m, and 8 m, respectively, and setting the roof-cutting angle at 10° can effectively achieve the stability of the surrounding rock in the GSER. The research findings can provide a scientific basis and engineering references for selecting roof-cutting parameters in mines with similar geological conditions.

Research on the technology of uniformly injecting nitrogen into the porous long pipes in the gob of the gob-side entry retaining mining mode with roof cutting and pressure relief

The implementation of the Gob-Side Entry Retaining Mining Mode with Roof Cutting and Pressure Relief (GERRCPR) results in the gob connecting to the retaining roadway, creating an open space that causes significant air leakage and increases the risk of spontaneous combustion. A study was conducted during the implementation of the GERRCPR in the Xiaonan Coal Mine N1-1502 working face to investigate spontaneous combustion characteristics, along with fire prevention and extinguishing measures. To analyze gob airflow, Computational Fluid Dynamics (CFD) was employed to collect data on airflow conditions, O2 concentration, and temperature. Based on this, this study focuses on exploring the effects of nitrogen injection treatment under various rates and positions to optimize parameters for buried pipe nitrogen injection. Results indicated that within the GERRCPR, air leakage in the gob increased, leading to an increase in O2 concentration, expansion of the oxidation zone, and an elevated risk of spontaneous combustion. Air leakage primarily occurred from the retaining roadway and the working face near the intake-air roadway, peaking at a retaining roadway length of 500 m, with a flow rate of 226 m3/min. Following nitrogen injection treatment, the oxidation zone was significantly reduced, with optimal treatment achieved at a nitrogen injection depth of 70 m and a rate of 600 m3/h. Field monitoring data showed that the inertization measure of using porous long pipes, a nitrogen injection spacing of 30 m, and a nitrogen injection rate of 600 m3/h significantly decreased the O2 concentration within the gob. This reduction meets safety production requirements and outperforms the effectiveness of traditional buried-pipe nitrogen injection methods, thereby validating the simulation accuracy. Understanding the laws governing spontaneous coal combustion in the GERRCPR and enacting preventive measures for nitrogen injection can improve safety standards in mining operations. This proactive approach can effectively prevent spontaneous coal combustion accidents, resulting in substantial social benefits.

Quantitative Research on Roof Deformation and Temporary Support Stiffness in Deep-Mine Gob-Side Entry Retaining by Roof Cutting

The important technical process to ensure the success of gob-side entry retaining by roof cutting (GERRC) was the advanced pre-splitting blasting to cut off the mechanical connection between the roadway and working face roof. The whole-cycle roof structure evolution and stress characteristics of GERRC were analyzed. The factors affecting the roof deformation of GERRC were analyzed, and the quantitative relationship between the roof deformation of GERRC and the support stiffness was determined. The results showed that the temporary support stiffness was higher, the support position to the side of the roof cutting was closer, and the roof subsidence deformation of GERRC was smaller. It is proposed to use a single support mass with a high stiffness to control the deformation of the roof, but it also made the support mass and roof elastic potential energy aggregate. To fully utilize the matching of the support stiffness and roof subsidence, improve the stability, and control the subsidence deformation of the roof in GERRC, double-row stacking supports were adopted in the inclination of GERRC, which were used to increase the stiffness of the support system.

Research on the mechanism and control of roof deformation in gob-side entry retaining of close-distance coal seams

Multiple mining operations in close-distance coal seams (CDCSs) can reduce the integrity and bearing capacity of the surrounding rock, leading to roof fracturing and widespread subsidence in gob-side entry retaining (GER). This highlights the critical need for research on roof control technology. For this purpose, adopting the panel of the Xinchazhuang Coal Mine (the distance between two coal seams is 7.3 m) as the engineering background, a theoretical model of GER of CDCSs was established on the basis of the surrounding rock structure and roof rock movement characteristics, and the roof failure deformation mechanism was examined. The roof failure deformation encompasses two parts: rotational sinking of roof rock blocks and roof separation deformation. To achieve roof control, a strategy involving optimized roof cutting and higher preload cables was suggested. The impacts of key roof control parameters on roadway deformation were examined and compared by numerical simulation studies. The findings showed that optimized roof cutting resulted in a 21.1 % reduction in the roof stress, whereas the use of roof cables with higher preload levels resulted in a 55.1 % decrease in roadway deformation, effectively mitigating rotational sinking and roof separation deformation. The field tests demonstrated that the optimized scheme facilitated roof integrity preservation, and the maximum deformation of the roof reached 98 mm, a decrease of 68.5 % on average from that in the original scheme. These research results could provide a reference for roof support in CDCSs roadways under similar geological conditions.

Non-pillar mining of upper coal seam layers with double-roadway driving using a flexible-formwork pre-cast partition wall

Abstract When mining layered coal seams, three-soft coal seams, high-gas coal seams, or hard-roof coal seams with the application of gob-side entry retention technology, various practical problems that seriously threaten construction safety arise, such as roadway deformation, shear failure of the roadway supporting body, and air leakage in the goaf. To effectively address these issues, in this work, a novel, pillar-free, coal mining technique based on a flexible-formwork pre-cast partition wall was proposed and applied to a case study: working face 2301 (upper) at Yuecheng Coal Mine, China. The principles of the technique and the characteristics of the movement in the surrounding rock were comprehensively examined. Through theoretical analysis and numerical simulation, the support parameters of the roadway and flexible-formwork pre-cast partition wall were determined and applied in the case study. From our analysis, it was demonstrated that the parameters of the flexible-formwork pre-cast partition wall and roadway support are reasonably designed, achieving effective roadway retention. Combined with a top cutting and pressure relief process, the roadway deformation can be eventually stabilised with the mining of the working face and does not affect the subsequent use of the roadway. From the acquired data, a good agreement between the field real-time measurements and the numerical simulation software measurements was found, which is helpful for the analysis of technological perspectives of the proposed framework. The introduced technology can effectively solve the technical problems existing in the traditional gob-side entry retention. It can not only realize non-pillar mining, but also double-roadway driving without coal pillars in 2301 working face can be achieved, which significantly improves the technical and economic index of the mine.

Classification of Composite Hazards of Gas and Coal Spontaneous Combustion in Gob

ABSTRACT To prevent the occurrence of gas and coal spontaneous combustion composite disasters in gob areas during coal mining, this study considers the gob area of the Longfeng Coal Mine as the experimental background. By analyzing the pressure values of the hydraulic props in the isolation wall, the composition of gases in the gob area, and the low-temperature oxidation characteristics of coal, it was found that the pressure values of the hydraulic props were correlated with the concentration of gases in the gob area, temperature, and the g-factor and free radical concentration of coal. The absolute values of the correlation coefficients were ranked as T > O2 > CH4 > CO2 > g-values > Ng > N2, and all correlation coefficients were greater than 0.85. When the isolation wall was located in the stress concentration area, the wall deformed and cracked, leading to frequent gas exchange between the gob-side entry retaining (GSER) and the gob area, which increased the risk of gas and coal spontaneous combustion composite disasters in the gob area. According to the safety risk level, the areas adjacent to the gob area were divided into high-risk areas (0 ~ 100 m, 300 ~ 600 m, 700 ~ 900 m, 1050 ~ 1200 m), moderate risk areas (200 ~ 300 m, 900 ~ 1050 m), general risk areas (600 ~ 700 m), and low-risk areas (100 ~ 200 m), the positions at 500 ~ 550 m and 700 ~ 750 m were located in the gas and coal spontaneous combustion composite disaster area. The study suggests that for high-risk areas, the injection amount of fire extinguishing materials should be increased to strengthen safety assurance, whereas for low-risk areas, the injection can be moderately adjusted and reduced to achieve the optimal balance between economic benefits and safety benefits.

Failure Characteristics and Cooperative Control Strategies for Gob-Side Entry Driving near an Advancing Working Face: A Case Study

Gob-side entry driving near an advancing working face can improve the recovery rate of coal resources and keep the balance between mining and development. However, the large displacement of the gob-side entry caused by the mining dynamics of abutment pressure challenges the safety and processes of coal mining. This article takes the 15102 tailentry of Xizhang Coal Mine in Changzhi City, Shanxi Province, as an example to study the stability of the coal pillar and the failure characteristics of the surrounding rock and proposes cooperative control strategies of surrounding rock stability. Field tests indicated that when the coal pillar width was 15 m, the displacements of the entry floor, roof, coal pillar side, and solid coal side were 1121 mm, 601 mm, 783 mm, and 237 mm, respectively. A meticulously validated numerical model, incorporating a double-yield model for the gob materials and calibrated parameters, was developed to investigate the stress changes and yield zone distribution across the coal pillar with different sizes. The results of the simulation indicate that the influence range of the dynamic abutment pressure caused by mining in the upper section of gob-side entry driving is 30 m ahead and 70 m behind. When the coal pillar width increases from 7 m to 20 m, the internal stress of the coal pillar increases continuously, while the internal stress of the solid coal decreases continuously. It is estimated that the reasonable coal pillar width should be 7 m, which is subjected to a lower load. The cooperative control strategies comprising a narrow coal pillar, hydraulic fracturing roof cutting for pressure relief, and entry dynamic support were proposed and applied in the 15103 tailentry. The final displacements of the floor, roof, coal pillar side, and solid coal side were 66.01%, 62.06%, 61.05%, and 63.30% lower than that of the 15102 tailentry in the same period, respectively, which effectively controlled the stability of surrounding rock. In addition, this finding for the gob-side entry driving near an advancing working face in this study can potentially be applied to other similar projects.

Ground response and failure mechanism of gob-side entry by roof cutting with hard main roof

Ground response and failure mechanism of gob-side entry by roof cutting with hard main roof

Floor Heave Control in Gob-Side Entry Retaining by Pillarless Coal Mining with Anti-Shear Pile Technology

The severe floor heave in gob-side entry retaining is the major restriction factor of the wide application of pillarless mining thin coal seams. Reinforcement and stress-relief floor heave control methods are the most promising. However, in practice, floor restoration is widely used. Therefore, floor heave control technology in gob-side entry retaining needs to be improved. This study proposes anti-shear pile technology to control floor heave in gob-side entry retaining. The research was mainly carried out by numerical simulation. It was found that the transformation of high vertical stresses in the entry floor underneath the filling wall and coal seam body into horizontal stresses starts the floor heave process. The vertical dilatancy of rocks under the roadway span and their subsequent unloading lead to the delamination of the floor strata and uplift of the entry contour. In this paper, the best pile installation scheme was found. It is a 2pile 5+2 scheme with the installation of two piles, each 2 m long. After that, it was shown that filling piles are more than 3.3 times cheaper than comparable analogs, and pile installation is less labor-intensive. The implementation of the proposed floor heave control method leads to a reduction in heaving by 2.47 times.

Deformation and Failure Evolution Law and Support Optimization of Gob-Side Entry in Weakly Cemented Soft Rock under the Influence of Fault

Under the condition of weakly cemented soft rock in Western China, the surrounding rock deformation of gob-side entry is obvious, especially under the influence of fault, and the problem of surrounding rock control becomes increasingly prominent. To solve this issue, this paper firstly studied and obtained the evolution law of the ground pressure appearance of the gob-side entry in the fault area, then put forward the concept of surrounding rock control in the fault area of the gob-side entry, put forward a targeted pressure relief + increase preload + passive reinforcement parallel to the roadway surrounding rock strengthening control scheme, and carried out field applications. The results show that the roof subsidence and mining side heave of the roadway in the fault area increase significantly, accompanied by the characteristics of broken cables, the length of the broken cable is 0.2 m–0.6 m, and the breaking process is divided into multiple breaks. The stress evolution of gob-side entry in fault area presents a stage characteristic of “rapid growth-stable.” The surrounding rock control effect is improved under the bolt cable high pre-tightening support, and the roadway deformation is effectively controlled under the pressure relief + active + passive support, with a good application effect.

Influence of Sealing Wall Crack on Gas Migration in Working Face without Coal Pillar Under Gob Connectivity

ABSTRACT Aiming at the problem of gas control in the working face of gob-side entry retention, taking the 97,312 fully mechanized mining face of Shaft No. 2 in Sihe Coal Mine as the research object, combined with numerical simulation and field measurement, the influence of the sealing wall crack on the gas migration rule of the goaf under the state of the adjacent goaf connection is studied. The results show that the simulation results match those measured in the field. The established physical model and numerical simulation model of goaf can better simulate the 97,312 goaf gas migration law. Considering the connection between 97,312 goaf and 97,311 goaf and 97,310 goaf, compared with only considering the connection between 97,312 goaf and 97,311 goaf, the maximum gas concentration difference between 97,312 fully mechanized mining face and 97,224 lane gob-side entry retention is only 0.01%, and the gas concentration has no significant change. Therefore, only the connection of 97,312 goaf with 97,311 goaf is considered. It can meet the demand for research on gas migration law in 97,312 goaf. The connection between 97,312 goaf and 97,311 goaf can well reflect the study of gas migration law in 97,312 goaf. The tightness of the gob-side entry retention sealing wall directly affects the gas concentration in the gob-side entry retention. With the sealing wall’s porosity increasing, the gas concentration in the corner of the return air gradually decreases. In contrast, the gas concentration in gob-side entry retention gradually increases. In order to prevent the gas concentration in gob-side entry retention from exceeding the limit, the porosity of the sealing wall on the side of the gob-side entry retention should be lower than 10%.

Differential roof cutting for roadway support in dual gob-side entry retention on a single working face − Multilevel continuous anchor-grouting control technology: A case study

The coal pillar-free gob-side entry retention technology (GER), which enhances resource recovery rates and reduces the amount of tunnel excavation, has been applied in multiple mining areas in China. However, cases of implementing gob-side entry retention on both sides of a single working face are rare. The asynchronous extraction of long-distance working faces leads to significant differences in the stress environment of roadways on both sides, and uniform technical means are poorly adapted to the control of surrounding rock on both sides, affecting the safe and efficient production. This paper, taking the dual gob-side entry retention on both sides of the 61001 W working face with thick mudstone roofs in Zhao Guan Coal Mine, Shandong Province, as the engineering background, utilizes a combination of theoretical calculations, numerical simulations, and on-site detailed monitoring to analyze the uncoordinated deformation characteristics of the upper part bulging and the lower part concaving of the two roadways. It clarifies the differentiated spatiotemporal evolution law of the number of fractures and the development turning points at different depths of the surrounding rock of the two entries, revealing the differential deformation mechanism of the surrounding rock of the two entries caused by stress state and fracture development differences. A “cutting roof to relieve pressure-multilevel continuous anchor-grouting” combined control technology system is proposed. By cutting off the stress transmission of the roof through drilling and blasting, and then reconstructing the integrity of the surrounding rock and improving the rock strength with the help of anchor-grouting. With the application of this new technology, the deformation of the surrounding rocks of the two entries was reduced by more than 60 % and 29 %, respectively, and the maximum crack depth of the roof was controlled within 3 m, significantly enhancing the stability of the roadways. The research results of this paper provide a reference for the control of surrounding rock in gob-side entry retention under similar conditions.