Gob-side Roadway Research Articles

Study on overburden rock structure characteristics and surrounding rock control technology of island working face

Based on the background of ZF2822 island working face in Xiagou Coal Mine, the characteristics of overburden fracture structure and surrounding rock control technology of island working face are explored by means of theoretical analysis, numerical simulation and field measurement. The results show that the ten morphological structures of the main roof fracture can be divided into four typical symmetrical structures and six asymmetric structures. According to the stress calculation formula of the key block B to the coal pillar, the stress characteristics of the 10 structures are classified and the risk classification is carried out. Four typical structures (a), (b), (c) and (d) were constructed to simulate the stress and strain characteristics of surrounding rock. The overlying strata subsidence displacement values of (a), (b), (c) and (d) at the roadway are 1.75 m, 1.5 m, 0.8 m and 0.6 m respectively, and the maximum stresses are 26.6 MPa, 19.5 MPa, 15.5 MPa and 10.0 MPa respectively, (a) > (b) > (c) > (d). Therefore, the surrounding rock control technology of gob-side roadway in island working face is put forward, the fracture structure of basic roof is determined and the reasonable applicable type of gob-side roadway is selected. The results after pressure relief show that the average daily microseismic energy of ZF2822 working face after pressure relief is 0.87 × 104 J, which is about 42.38% lower than that of April. The average stress is 1.13 MPa lower than that of the mining before the pressure relief area, and the decrease is 22.42%. It shows that the pressure relief has played a very good effect and provides a reference for the same type of mine.

Analysing the application of a flexible formwork pre-cast wall driving roadway along goaf in a large mining height face

The technology of building a retaining roadway along goaf or a protecting roadway with a small coal pillar has been developed and applied for many years, and a satisfactory supporting effect has been obtained in medium–thick coal seam and thin coal seam mining. However, the gob-side roadway or small coal pillar mining in a thick coal seam is still subjected to technical problems occasioned by factors such as high roadway, high support pressure beside roadway, and waste of coal resources. To solve these problems, the author proposes an innovative technology of coal-free mining: the technology of driving roadway along goaf with a flexible formwork pre-cast wall. The article utilizes the 3503 and 3505 working faces of Wangzhuang Coal Industry Group as the research background, and comprehensively introduces the principle of the technology and the overburden rock movement law. Through theoretical calculations and numerical simulations, the support resistance and support parameters of flexible formwork pre-cast walls have been determined and successfully performed in industrial practice. The results indicate that the combination of the flexible mould pre-cast wall coal pillar-free mining technology and roof cutting process is more conducive to the maintenance of the roadway in the lower working face, and effectively reduces the stress and deformation of the surrounding rock. The roof and floor of the drivage roadway move, and the deformation of the two sides is small; furthermore, the overall roadway retention effect is satisfactory, which meets the requirements of mining in the lower working face. The coal pillar pertaining to the 20 m section of the 5 m high mining height face was recovered for Wangzhuang Coal Mine, and the recovery rate of the coal resources and the driving speed of the roadway were improved. The proposed method can be popularised and applied in this mine and even in the mining of 15# large-height coal seams in the two cities.

Deformation mechanism and control technology of gob-side roadway with continuous mining and continuous backfilling: a case study

Gob-side roadways are excavations created during the mining process, serving to alleviate mining-induced stress. Previous studies have predominantly focused on the caving method, neglecting the examination of failure mechanisms in gob-side roadway associated with continuous mining and continuous backfilling (CMCB). In this study, focusing on Sima Coal Mine, we employed numerical simulation method to thoroughly investigate the full-cycle stress evolution patterns of the gob-side roadway. The numerical simulation results reveal that during the upper working face mining period, severe stress concentration phenomena occur within the coal pillars, with peak stresses reaching 36.0 MPa. Throughout the mining period of next working face, as the CMCB process progressed, the coal inside the working face was gradually replaced by the filling body, forming various coal pillars with decreasing widths. The alternant load between the coal pillar and filling body led to the gradual increase of the internal stress of the coal pillar, with the peak stress reaching 45.0 MPa. To mitigate stress concentration in the surrounding rock of the roadways, this study proposes a control methodology that incorporates "directional control of hydraulic fracturing slots" in conjunction with "reinforcement support of coal pillars" and "temporary support of single hydraulic props" as core components. Industrial experiments were conducted to validate the efficacy of the proposed control techniques. Field monitoring results demonstrate significant improvements in the stress environment, effectively mitigating deformation of roadway.

Parameters and surrounding rock control of gob-side driving under double key stratum after roof cutting

Taking the return-airway 4204 with roof cutting in Longquan Coal Mine as the engineering background, roof structure, key parameters, and deviatoric stress evolution were studied. Conclusion: The Key Stratum within a 4–8 times mining height is considered as Near Key Stratum. Cutting the roof makes it possible to form a cantilever structure of the Key Stratum on the solid coal side, which is more conducive to the stability of gob-side roadway. During cutting angle of 90–55°, the deviatoric stress increases linearly, and the increase rate is coal pillar > solid coal > roof > floor. While cutting length from 0 to 35 m, the deviatoric stress decreases linearly, and the decreasing range: coal pillar > solid coal > roof > floor. When coal pillar width is from 30 to 4 m, the deviatoric stress of left side and floor presents a “single peak” distribution. The deviatoric stress of coal pillar changes from an asymmetric “double peak” to a bell-shaped distribution, and the deviatoric stress of roof changes from a “single peak” to an asymmetric “double peak” distribution. Under same coal pillar width, the deviatoric stress of left, coal pillar and roof after roof cutting decreases most obviously, followed by the floor. Finally, the coal pillar width is 8 m, the cutting angle is 75°, the cutting length is 20 m, and the hole spacing is 1.0 m. The support scheme is bolt + metal mesh + steel belt + anchor cable combined support. The stable period of roadway is about 10 days.

Strong strata behavior mechanism and roof cutting control of small pillar gob-side roadway in extra-thick coal seam

Strong strata behavior mechanism and roof cutting control of small pillar gob-side roadway in extra-thick coal seam

Combined blasting for protection of gob-side roadway with thick and hard roof

The deformation control of surrounding rock in gob−side roadway with thick and hard roof poses a significant challenge to the safety and efficiency of coal mining. To address this issue, a novel approach combining directional and non-directional blasting techniques, known as combined blasting, was proposed. This study focuses on the experimental investigation of the proposed method in the 122108 working face in Caojiatan Coal Mine as the engineering background. The initial phase of the study involves physical model experiments to reveal the underlying mechanisms of combined blasting for protecting gob-side roadway with thick and hard roof. The results demonstrate that this approach effectively accelerates the collapse of thick and hard roofs, enhances the fragmentation and expansion coefficient of gangue, facilitates the filling of the goaf with gangue, and provides support to the overlying strata, thus reducing the subsidence of the overlying strata above the goaf. Additionally, the method involves cutting the main roof into shorter beams to decrease the stress and disrupt stress transmission pathways. Subsequent numerical simulations were conducted to corroborate the findings of the physical model experiments, thus validating the accuracy of the experimental results. Furthermore, field engineering experiments were performed, affirming the efficacy of the combined blasting method in mitigating the deformation of surrounding rock and achieving the desired protection of the gob-side roadway.

Experimental and numerical investigations of goaf roof failure and bulking characteristics based on gob-side entry retaining by roof cutting

The stability control of gob-side entry retaining (GSER) has consistently been an important topic of interest within the field of no-pillar mining. This paper presents a novel discontinuous similar material for conducting physical model experiments, in conjunction with discrete element numerical simulation, to investigate the goaf roof failure and bulking characteristics based on gob-side entry retaining by roof cutting. The results indicate that the application of roof cutting technology (RCT) can significantly expand the failure range of the goaf roof vicinity to the roof cutting line. This expansion leads to a 20% increase in the volume of broken roof rock, which in turn facilitates the formation of effective support and stress compensation for the overlying strata, and the possibility of failure and displacement in the overlying strata is reduced. RCT can decrease the length of the cantilever beam located on the gob-side roadway, which is beneficial for maintaining the stability of the roadway. This paper presents a rational approach for determining an appropriate roof cutting height and angle. The in-situ application results show that the deformation of the surrounding rock of GSER by RCT is small, indicating a high level of integrity, fully meeting the requirements of serving the production of the subsequent working face. This paper serves as a reference for future research on the stability control of gob-side roadways based on GSER approach.

Study on the mechanism of coal pillar instability in coal seam sections containing gangue

The tail entry of the Shanxi Mine No. 10103 working face is a gob-side roadway featuring a 25 m protective coal pillar that contains double-strata gangue. This composition poses a risk of instability and failure, which can endanger personnel safety and mining efficiency. To address this issue, a mechanical model of coal pillars containing gangue was constructed, and a combination of discrete element modeling and engineering monitoring was utilized to reveal the failure mechanism and influencing factors of such coal pillars. The study offers a sound theoretical foundation for the support of coal pillars in gob-side roadways. Through an examination of the friction coefficient (f) of the coal gangue interface in relation to the Barton peak shear strength (τmax), it was determined that coal pillars containing gangue are susceptible to slip instability failure at the coal gangue interface when the normal stress (σR) reaches 20 MPa. The stability of coal pillars containing gangue was further analyzed using discrete element numerical simulation software, which identified key factors such as gangue hardness, thickness, location, and number of strata. Utilizing the outcomes of discrete element simulation, the FLAC-PFC coupling model was formulated to meticulously scrutinize the temporal and spatial progression of the deformation of the surrounding rock, as well as the features of its deformation and failure. As a result of this research, the implementation of the grouting cable + through layer bolt anchoring technique is proposed, wherein the bolt is inclined on both sides to traverse through the coal seam and gangue, thereby stabilizing the interface between the two.

Comparison of large deformation failure control method in a deep gob-side roadway: A theoretical analysis and field investigation

Comparison of large deformation failure control method in a deep gob-side roadway: A theoretical analysis and field investigation

Failure mechanism of gob-side roadway in deep coal mining in the Xinjie mining area: Theoretical analysis and numerical simulation

Failure mechanism of gob-side roadway in deep coal mining in the Xinjie mining area: Theoretical analysis and numerical simulation

Dynamic Response Analysis of Roadway Surrounding Rock Induced by Dynamic Load under the Action of Hard and Thick Rock Stratum

In the process of coal seam mining, there are often hard thick key layers in the overlying strata. Due to the high strength and good integrity of the hard thick key layer, after the hard thick key layer is broken, the overlying strata will collapse and lose stability in a large area, which is very easy to induce dynamic disasters such as rock burst, mine earthquake, coal wall caving, and roof slab caving. Aiming at the hard and thick key layer overlying the working face, the dynamic response of the mine under the strong mine earthquake induced by the breaking of the main key layer of high-level magmatic rock is numerically simulated and analyzed by using FLAC2D numerical simulation software, and the variation laws of the stress field, displacement field, and velocity field of the coal seam roadway under different boundary conditions and different focal heights are studied. The research shows that the roof of solid coal roadway is prone to vibration in a small range, and the displacement increases and decreases with the disturbance. The displacement of the floor and two sides of the solid coal roadway and the top floor and two sides of the roadway along the goaf continues to increase in the initial stage of the disturbance, and the displacement will remain stable with the continuation of the disturbance. The displacement of both sides and roof and floor of gob roadway can reach stability in the later stage of disturbance, and with the increase of the number of adjacent goaf, the longer it takes for the displacement of surrounding rock to reach stability. When the focal height is lower than 90 m, the variation of surrounding rock response increases sharply with the decrease of focal height. When a strong earthquake occurs in the low rock stratum, the impact damage of roadway surrounding rock is almost inevitable. The influence degree of strong earthquake on the stability of roadway surrounding rock is arranged as follows: gob-side roadway (mined out on one side) > solid coal roadway (mined out on both sides) > solid coal roadway (mined out on one side). The evolution process also shows that the working face boundary conditions have an important influence on the energy propagation of mine earthquake. With the increase of the number of adjacent goafs, the faster the energy attenuation rate of mine earthquake propagation is. The research results have important reference significance for the safe mining of working face under similar geological conditions.

Mechanism and Control Technology of Rockburst Induced by Thick Hard Roof and Residual Coal Pillar: A Case Study

Rockburst caused by the fracture of thick hard roof and the instantaneous instability of residual coal pillar seriously jeopardize the deep coal mining safety. This study takes Boertai Coal Mine, Shendong, China, as the engineering background, in which dynamic instability mechanisms of the gob-side roadway surrounding rock are analyzed by integrating field research, theoretical analysis, and numerical simulation. The results show that the overlying residual coal pillar, side abutment pressures, and front abutment pressures together induce high static stresses in the surrounding rock of the gob side roadway, with peak values exceeding the in situ stress by one order of magnitude. High stresses accumulated in the goaf-side roadway surrounding rock can easily induce dynamic disaster. With the working face advanced, overburdens are caved in succession, resulting in a continuously decreasing of the overlying residual coal pillar width, once the working face entered the influence area of the residual coal pillar. As the morphology of abutment pressure in the residual coal pillar changes from “unimodal distribution” to “bimodal distribution,” the residual coal pillar gradually changes from elastic state to plastic state. When the width of the overlying residual coal pillar is less than the critical width, the thick hard roof and residual coal pillar structure (THRRCPS) lose stability suddenly, resulting in strong dynamic load on the surrounding rock of gob-side roadway. In order to prevent the rockburst of the gob-side roadway under the influence of THRRCPS, regional and local prevention measures are adopted to mitigate the accumulation of stress in the thick hard roof and gob-side roadway surrounding rock by hydraulic fracturing technology and large diameter pressure relief drilling hole.

Research on Deformation and Failure Law of the Gob-Side Roadway in Close Extra-Thick Coal Seams

To reveal the deformation and failure law of the gob-side roadway (GSR) and the main influencing factors in close extra-thick coal seams, the research methods of field monitoring, theoretical analysis, and numerical simulation are adopted in this paper. Field monitoring data shows that microseismic events occur and accumulate frequently in the surrounding rock and some overlying key layers of the GSR. Large deformation is experienced in the middle part of roadway near the solid coal side, the middle and upper parts of the roadway near the coal pillar side, and the roadway floor. The overlying strata of the GSR are fractured to form a composite structure as “low-level cantilever beam and high-level masonry beam”. The coal pillar is squeezed and effected by the composite beam structure and the rotation moment M, causing serious bulge in middle and upper part of the coal pillar side. The stability of the solid coal side of the roadway is affected by the stress transferred from gangue contact point. Numerical simulation shows that the immediate roof and key layer breakage are induced by the mining of the 30,501 working face. Shear and tension failures happen in the GSR due to overburden subsidence and rotary extrusion. The stress and displacement at the middle and upper of the roadway on the coal pillar side are larger than the other area. Compared with the solid coal side, the coal on the coal pillar side is obviously more fractured, with a lower bearing capacity. The peak stress in the coal pillar shows up 2 m away from the roadway, which is close to the length of bolt support. The mining-induced stress and the stress transferred from gangue contact point are the direct reasons for solid coal bulge beside the roadway. The peak stress on the solid coal side is located 7 m away from the roadway, at the gangue contact point where overburden fractures. The overburden strata loads and the transferred stress near the gangue contact point are transferred from the sides to the roadway floor. Their coupling effect with the in situ horizontal stress acts as the force source for the plastic floor heave.

A Novel Method of Combined Deep Hole Blasting for Gob-Side Roadway Protection

A Novel Method of Combined Deep Hole Blasting for Gob-Side Roadway Protection

Research on Deformation and Failure Control Technology of a Gob-Side Roadway in Close Extra-Thick Coal Seams

Close extra-thick coal seams are subject to the broken overburden of mined coal seams, and the deformation and damage of the roadways is serious, which affects the safe operation of the mine. To reduce the deformation and damage of the roadways, this paper studied the deformation and damage law of the gob-side roadway in close extra-thick coal seams through numerical simulation and field monitoring, compared and analyzed the deformation and damage characteristics of the roadway under different reinforcement support methods, determined the optimal reinforcement support method, and carried out field verification. The obtained results indicated that the deformation and damage of the gob-side roadway showed asymmetric characteristics. The large deformation of the coal body in the deep part of the roadway wall is an important reason for the continuous occurrence of roadway wall heave in the coal pillar. Under the action of unbalanced support pressure, the floor is subject to the coupling effect of horizontal extrusion pressure and vertical stress that cause extrusion mobility floor heave. The horizontal and vertical displacement of the coal pillar side of the roadway under different support methods is much larger than that of the solid coal side. Increasing the anchor cable length and fan-shaped arrangement can improve the support effect. Grouting at the coal pillar side can significantly improve the bearing capacity and stability of the coal pillar. The effect of floor grouting is much better than the anchor cable in controlling the floor heave. The integrated reinforcement method of anchor cable + coal pillar side grouting + floor grouting has the best effect with the least horizontal and vertical deformation. The research results are of great significance for ensuring the stability of similarly endowed roadways.

Research on the Key Technology of Gob-Side Entry Retaining by Roof Cutting for Thick and Hard Sandstone Roofs

In order to ensure the application of gob-side entry retaining by roof cutting for thick and hard sandstone roofs, the key technology of pre-split blasting was studied. The LS-DYNA was used to analyze the blasting effect of the energy-gathering pipe. Using the methods of theoretical analysis and numerical simulation, it was determined that the optimal cutting height was 16 m and the optimal cutting angle was 15°. The effect of pressure relief by roof cutting was verified by FLAC3D. It is proposed to use deep-hole loosening blasting to solve the problem of the sandstone with a thick hard roof being difficult to collapse. A group of loose blasting holes was designed to be arranged every 20 m in the gob-side roadway. The depth of the #1 blasthole was 47 m, and the angle to the horizontal direction was 20°; the depth of the #2 blasthole was 65 m, and the angle to the horizontal direction was 15°. A field test was carried out in the 7135 ventilation roadway of Qidong Coal Mine China. The on-site peeping results showed that the blasting with the energy-gathering pipe had a good effect of directional slitting. After deep-hole loosening blasting, the thick hard sandstone roof collapsed and filled the gob in time. The monitoring curves of the hydraulic support showed that the hydraulic support resistance of the working face in the side with roof cutting was much smaller than that of the side without roof cutting, and the effect of pressure relief by roof cutting was good.

Efficient Excavation and Support Cooperation Technology for Surrounding Rock of Deep Buried Long-Distance and Large Section Gob-Side Roadway: A Case Study

The gob-side roadway technology is widely used in coal mining in China, as it can improves the recovery rate of coal resources and alleviate the shortage of mining replacement. However, it is still difficult to control the stability of surrounding rock in gob-side roadway under deeper mining depth and more complex stress environment. With the auxiliary transportation roadway 30207 (ATR 30207) of the Muduchaideng Coal Mine as engineering background, this paper introduces the engineering case of gob-side roadway characterized by deep buried, long-distance, and large section. Through comprehensive methods, we studied and put forward the efficient excavation-support cooperation technology for surrounding rock of gob-side roadway. The research shows that the head-on cutting of gob-side roadway causes the stress to transfer and gradually adjust in the heading face to form a steady-state advanced abutment stress field. The coupling effect of the advanced abutment stress and the lateral abutment stress of goaf are the main reasons for repeated hole collapse of anchor cable drilling in solid coal rib, development and expansion of the roof separation fracture, and the low excavation speed. Supposed that upon the heading face support is completed, the next excavation-support cycle is quickly started during the early stage of stress adjustment, and the time effect can be fully utilized to alleviate the disturbance intensity of the advanced abutment stress in the heading face, as well as reduce the damage of rock mass. This paper puts forward the time-effect collaborative control countermeasures of the roof and rib in gob-side roadway of “hole collapse anchor cable of solid coal rib lag construction and waits for pressure relief and rapid excavation-support cycle in the heading face.” Engineering practice shows that the mine pressure behavior of roadway roof and solid coal rib is effectively controlled, and the roadway forming speed is greatly improved, which can provide reference for the efficient excavation-support design of gob-side roadway under the conditions of deep buried, long-distance, and large section in similar deep mines.

Research on Stress Distribution Regularity and Support Optimization of an “Umbrella” Coal Pillar in a Gob-Side Roadway Based on Irregular Gob

Aiming at the phenomenon of a large amount of roof subsidence and rib caving in the gob-side roadway under the special “umbrella” coal pillar in isolated panel No. 325 of Yangcun Coal Mine, the stress distribution regularity of the gob-side roadway under a “umbrella” coal pillar was studied in detail by establishing mathematical models, theoretical analysis, and numerical simulations. The results show that the following: (1) The stress distribution regularity of the irregular coal pillar is actually the mechanical structure of irregular gob. (2) The abutment pressure of the gob is always distributed vertically along the edge of the gob. When the edge of the gob intersects diagonally with the gob roadway, the stress distribution of the surrounding rock of the roadway cannot be calculated only by the width of the coal pillar—the angle between the edge of the gob and the roadway should also be considered. (3) The abutment pressure at each cusp position in irregular gob extends in the opposite direction of the bisection cusp line, which may lead to peak stress concentration area in gob roadways with solid coal on both sides, and even roof caving and sidewall deviation disasters.

Determination of Narrow Coal Pillar Width and Roadway Surrounding Rock Support Technology in Gob Driving Roadway

In order to determine the rational width of coal pillars and study the surrounding rock control technology of gob side entry driving with a narrow coal pillar, this paper first calculates the width of narrow coal pillar according to limit equilibrium theory; after that, the lateral support pressure and plastic zone development of the goaf is analyzed by numerical simulation to determine the rational width of reserved coal pillar; finally, through the ring breaking deformation regulation of surrounding rock of the gob side entry, the deformation and failure characteristics of the gob-side roadway during excavation and the influence of mining on the deformation and failure of the gob-side roadway are analyzed. The research results show that, combined with theoretical analysis and numerical simulation, the width of narrow coal pillar is decided to be 10 m; the deformation of the coal pillar side of the gob side roadway is much bigger than the roof subsidence, the deformation of the solid coal wall and the floor deformation; after the bolt support design of the gob side roadway, the deformation and damage of the gob side roadway during the driving period is small; during mining, the deformation of the narrow coal pillar wall is the key factor to determine the stability of the gob roadway; under the bolt support scheme, the overall deformation and failure of surrounding rock of the goaf roadway is small, and the control effect of the surrounding rock of the goaf roadway is good.

Mechanism and Control of Rockburst Induced by Draining Spatial Islands and Squaring

A small-pillar gob-side roadway showed rockburst appearance during the mining of a gob-side working face located in the Shaanxi-Inner Mongolia mining area. This study examines the 2202 gob-side working face of a coal mine in Inner Mongolia as a case study. A stress evolution model was built for the static-stress spatial islands formed by drainage regions and goafs based on the spatial relationships between drainage regions and goafs. The average microseismic frequency and energy of the high-stress zone of spatial islands were at least 1.37 times of those of other zones, validating the presence of spatial islands. The dynamic and static load effects of working face squaring were obtained based on the evolution of the stope roof as well as changes in microseismic data. Microseismically active zones were advanced to 200 m–300 m on working faces. The rockbursts induced by high static loads and dynamic and static loads formed by spatial islands and squaring were calculated. According to calculation results, the critical stress concentration value under high static loads was 3.27; the critical static stress concentration value under dynamic and static loads was 1.81. The superposition of drainage boundary stress, goaf lateral stress, and lead stress might reach the critical stress concentration under dynamic load disturbances, causing rockbursts. A stress adjustment scheme was established, including overall hydraulic fracturing of the external roof of the drainage region, reduction of stoping speed, and pressure relief of large-diameter boreholes. The stress adjustment scheme was implemented on-site and supplemented by monitoring and early warning methods to safely advance by the first squaring region.