Stopping Line Research Articles

Research on process parameter optimization of irregular coal face.

Based on the engineering background of 1353 working face in Daizhuang Coalmine, the paper identifies three primary issues with the working face mining process: conventional pressure relief means are limited, risk of impact and the length of working face changes, It also proposes comprehensive control measures to improve the blasting roof cutting scheme, optimize mining speed and the location of the stopping line. The three improvement measures mentioned above are simulated numerically, and the effects of the drilling and blasting plan, mining speed, and stopping line location on stress distribution are determined. The results show that by implementing the three improvement measures, the stress variation interval can be efficiently controlled and the working face's production safety can be increased. Finally, it is determined that the 1353 working face of Daizhuang Coalmine adopts the pressure relief method of drilling on one side and cutting the roof 20m deep on the other side, and the mining speed of the working face is 3m/day and the length of the stopping line is 85m. Based on the on-site monitoring results, the implementation of comprehensive treatment measures can effectively improve the surrounding rock state of 1353 working face, which has certain guiding significance for the mining of irregular working face.

Study on roadway layout and surrounding rock control of isolated island panel

During the re-mining of historical residual coal resources, the stress environment is complex, the surrounding rock conditions are bad, the mining roadway is significantly affected by ground pressure, the layout is difficult, and the safety is poor. Taking the recovery of isolated island coal pillar in 4# coal seam as the research background, based on the difference in the distribution morphology of the goaf on both sides of the isolated island coal pillar, the stress and failure law of the isolated island panel boundary are studied by numerical simulation method. (1) The peak stress difference of multiple goaf boundaries on both sides of the isolated island coal pillar is between 0.18 and 4.51 MPa. The peak stress is affected by the change of the length of the roof “cantilever beam” at the stopping line of the goaf, so that the peak stress of the goaf boundary is periodic. (2) The high stress is mainly concentrated in the center of the pillar. The peak stress at the end of each pillar is 35–40 MPa. The coal pillar bears high stress, and the stress zone of the original rock moves to the end of the coal pillar. (3) There is a plastic zone of 8–20 m at the corner of the end of each coal pillar. On the basis of the stress zone and failure zone distribution of the goaf boundary on both sides of the isolated island panel, the roadway layout of the isolated island panel is determined, that is, the air-return roadway of the isolated island panel is arranged at random, and the width of the isolated island coal pillar d1 is selected as 10 m. The transport roadway is arranged straight, and the transport roadway of the isolated island panel is in the width section area of the goaf X4103. The width d1 of the isolated island coal pillar is selected to be 8 m, and the length d5–d7 of the mining roadway layout in the width of the coal pillar is 24 m. The roadway of isolated island panel is divided into 4 areas for support control, and the drilling pressure relief technology is proposed for high stress roadway. Through the field monitoring data, it can be seen that the mining roadway can meet the requirements of isolated island coal pillar recovery, which provides reference for the layout and control of abandoned coal roadway in this mine and other mines.

Study on stress evolution law of upper coal seam in long‐distance advance mining of lower coal seam

AbstractWith the shift of coal resources to deep mining, the occurrence of long‐distance coal seams has increased, and protective layer mining is facing new challenges. This paper attempts to explain the stress evolution law of the upper coal group in the long‐distance mining of the lower coal group in Pingdingshan No. 8 Coal Mine. A simulation model of advance mining of lower‐group coal long‐distance was established. The stress evolution law of the upper coal seam under the influence of advanced mining disturbance of the lower coal seam is studied. The following conclusions were obtained: The advance mining of the lower coal group had a positive or negative impact on the stress distribution of the upper coal seam group. With the recovery of the lower coal group of the F‐21030 working face, the overburden of the F‐21030 goaf finally formed a “Y” type pressure relief area. The pressure relief effect of the E‐21070 working face near the stopping line was obvious. The coal seam of Group E was divided into three areas affected by the advance mining of the lower coal seam. The maximum pressure relief value was 6.6% lower than the initial stress. According to the simulation results, the E‐21070 working face was divided into three regions, namely, the pressure relief region, the stress increase region, and the original stress region. According to the field drainage results of pressure relief gas, the extraction curve could be divided into three parts, namely, the stable area, pressure relief area, and stress recovery area. The maximum pure gas drainage volume could reach seven to eight times of the original area. The pressure relief extraction effect was remarkable, and the optimal extraction range was 22–210 m behind the coal face of the group.

Research on the Deformation and Failure Characteristics and Control Technology of Mining Area Rises under the Influence of Mining Stress

Affected by mining stress, roadways surrounding rock face problems such as serious deformation and failure and difficult support. In this study, with the II2 mining area rise in Taoyuan Coal Mine taken as the engineering background, the evolution laws of stress, deformation and plastic zone area of the mining area rises during the advance process of the working face were explored with the aid of FLAC3D software. The results suggested that the stress, deformation and plastic zone area of the surrounding rock increase significantly when the distance between the working face and the track rise is less than 20 m. Based on this finding, it was further determined that the stopping line of the II8222 working face should be at least 20 m away from the track rise. Furthermore, in accordance with the deformation and failure characteristics of surrounding rock under the influence of mining stress, this paper conducted a simulation on four support schemes of mining area rises, and quantitatively analyzed the mechanical response of a roadway surrounding rock under these support schemes. The simulation results revealed that the support scheme of “bolt-mesh-spray-cable + grouting bolt” can effectively deal with the influence of mining stress on the working face. Meanwhile, an engineering application was carried out. By monitoring the surface displacement of the surrounding rock, it was found that the deformation of the roadway surrounding rock was effectively controlled, and a remarkable support effect was achieved. In short, the proposed support scheme greatly improved the stability and safety of surrounding rock in the mining area rise under the influence of mining stress.

Reasonable location of stopping line in close-distance underlying coal seam and partition support of large cross-section roadway

Close-distance coal seams are widely distributed over China, and the coal pillars left by the overlying coal seams affect the retracement channel of the underlying coal seam in the stopping stage. Based on the engineering background of close-distance seam mining in a coal mine, the reasonable position of the underlying coal seam's stopping line and the support method of the large section roadway during stopping are investigated using field measurements, similar simulation experiments, and numerical simulations. There are three types of location relationships between the stopping line of the underlying coal seam and the stopping line of the overlying coal seam: "externally staggered with the upper stopping line" (ESUL, stops mining under the overlying goaf), "overlapped with upper stopping line" (OUL), and "internally staggered with the upper stopping line" (ISUL, ISUL-SD for shorter internal staggered distances, ISUL-LD for longer ones). There are different stress arch structures in the overlying strata of the above three positions, and the stress arch evolution process exists in the process of ESUL → OUL → ISUL-SD → ISUL-LD: a front and rear double stress arch structure → the front arch gradually decreases → the front arch dies out, and the double arch synthesizes the single arch → the single-arch range expands → the nested double arch. The relationship between the stress arch structure and the position of the stopping line is evaluated as follows: (1) ESUL: the stress concentration in the roof plate of the retracement channel of the underlying coal seam is the highest, because the overburden block of the extensive collapse zone acts directly on the roof plate of the retracement channel, resulting in relative difficulties in roof support. (2) OUL: although the retracement channel roof pressure is minimal, the overlying rock structure has the potential for rotation or slippage instability. (3) ISUL-SD: the pressure on the roof of the retracement channel is small and the overburden structure is stable, which is conducive to the safe retraction of the support and not limited by the width of the end-mining coal pillar. (4) ISUL-LD: it is basically the same as the condition of stopping under the non-goaf; however, it has a limitation on the width of the end-mining coal pillar. The location of the stopping line is selected as ISUL-SD, and the retraction process of the self-excavating retraction channel was adopted. A partition asymmetric support scheme which is proven by field practice is proposed, through a comprehensive analysis of the pre-stress field simulation of the support scheme, based on the different control requirements of the roof above the support and the roof of the retracement channel in the stopping area. This method realizes safe and smooth withdrawal of the support.

Study on the Ground Fissure Development Law of Coal Mining Based on UAV Photogrammetry and the Particle Flow Theory

Ground fissures caused by underground coal seam mining easily result in secondary geological disasters and destroy the ecological environment, which seriously impacts the production and life of mining areas and residents. The traditional monitoring methods, such as manual measurement and satellite monitoring, have their disadvantages. Therefore, it is urgent to develop a large-scale monitoring technology for ground fissures and study its development law. In this article, we analyzed the distribution characteristics of ground fissures based on the low-altitude UAV remote sensing images and combined them with field investigation as validation. Moreover, we introduced the particle flow theory to study the development law and formation mechanism of ground fissures. This article takes the 8092 working face of a mine in Ordos City as the study area. The results showed that the accuracy rate of ground fissures based on the visual interpretation of UAV images was 95%. The ground fissures were mainly distributed near the stopping line and the groove of the working face. The plane forms of ground fissures were mainly two types: the linear type and arc type, and the location relationship can be divided into the parallel type and bifurcation type. The types of ground fissures were the tensile type and step type. Whether the upper and lower parts of the key strata were broken simultaneously is the root cause of tensile ground fissures and step ground fissures. The stability of the overlying strata had a significant influence on the change of abutment pressure above the goaf. The process of surface movement and deformation can be divided into three stages: tensile failure of the slope bottom, traction failure of the slope body, and sliding failure of the slope top. In addition, the zero point of the surface horizontal movement value and the maximum surface subsidence were not in the center of the goaf. Due to the horizontal slip of the downhill direction in the horizontal movement on the surface, the value of the downhill direction subsidence was zero. However, the value of the horizontal movement was not zero, and there was even a large horizontal movement. In conclusion, the research results can provide a useful reference for the rapid monitoring of large-scale geological disasters caused by underground coal seam mining and the application of the particle flow theory.

Effect of Strong Mining on the Fracture Evolution Law of Trick Rise in the Mining Field and Its Control Technology

This study investigates the law of stress field and fracture field of the surrounding rock at the trick rise of the mining area affected by strong mining. It is found that as the working face continues to approach, large-scale cracks occur in the surrounding rock on the track rise. In particular, when the working face crosses the track rise, the equivalent stress τ oct concentration area expands, gradually intersecting with the surrounding rock concentration area of the roadway. It indicates that the working face advancement caused a dramatic change in the stress field of the roadway envelope, which will have an immediate adverse effect on the track rise. With comprehensive support costs, economic efficiency, and other factors, the working face will no longer cross the track rise, and the stopping line is roughly controlled at -20 m so that the track rise can serve other working faces for a long time. The reinforcement support scheme of “anchor mesh spray + grouting anchor” is proposed for the key areas such as arch shoulder. Through the analysis of the field monitoring of the roadway surface displacement, the deformation of the roadway surrounding rock showed a change trend of increasing first and then stabilizing with time, which indicates that the support effect was good and greatly improved the stability and safety of the roadway.

Structural Characteristics of Regenerated Roof and Distribution Law of Overburden Porosity in Downward Mining of a Bifurcated Coal Seam

During downward mining of a bifurcated coal seam, the roof of the lower coal seam is relatively broken and difficult to control due to the mining influence of the upper coal seam. Roof accidents occur frequently during mining of the lower coal seam, reducing mining efficiency. How to ensure safe and efficient mining of the lower coal seam is a significant issue. In this paper, overlying strata migration and fracture characteristics of the lower coal seam, the structure and stability of the regenerated roof, and porosity and permeability characteristics of the overlying strata under the mining influence of the upper coal seam are studied by using similar simulation tests. Results show that the overburden structure of the lower coal seam is altered due to the mining influence of the upper coal seam, and the regenerated roof of the lower coal seam is divided into three structural types from top to bottom, namely: intact rock mass+block fracture rock mass+loose rock mass (type I structure); intact rock mass+block fracture rock mass+loose rock mass+cataclastic rock mass (type II structure); and intact rock mass+block fracture rock mass+loose rock mass+cataclastic rock mass+slab-rent rock mass (type III structure). The stability of each type of rock mass structure is evaluated, and the stability of three types of rock mass structures is III > II > I. The overburden porosity and slurry permeability coefficient are relatively large at the cutting hole and stopping line. The porosity of the caving zone within 70 m of the cut hole and stopping line is greater than 5%, and the permeability coefficient is greater than 0.1 m/s. Based on differences in the surrounding rock porosity and permeability characteristics, the grouting difficulty of overburden is divided into three types of areas: extremely easy grouting areas, easy grouting areas, and difficult grouting areas. The results of this paper can provide reference for the stability evaluation of the regenerated roof and the selection of grouting treatment parameters for the broken roof under similar conditions.

Study on the Overburden Failure Law of High-Intensity Mining in Gully Areas With Exposed Bedrock

Most hilly areas are dotted with gullies, some of which contain plenty of water, especially in rainy seasons. Once surface water penetrates the underground working face, it will lead to an increased water inflow of the working face. Even worse, it may induce water and sand burst accidents. To prevent geological disasters such as water and sand burst and ensure the safe production in coal mines, it is necessary to reveal the development law of “two zones” in the overburden caused by shallow-seam fully mechanized top coal caving high-intensity mining in hilly areas with exposed bedrock and timely grasp the communication between the water-flowing fractured zone (WFFZ) and the water in surface gullies. In this study, the working face P2 of the exposed bedrock surface in the Coal Mine DN is taken as the research object. First, the characteristics of overburden movement and the law of exposed bedrock surface movement in areas with exposed bedrock were investigated through similar simulation. Meanwhile, the temporal–spatial evolution of overburden movement caused by shallow-seam fully mechanized top coal caving high-intensity mining was clarified, and the mode of overburden movement was revealed. Moreover, the reason why the water inflow of the underground working face increases suddenly was theoretically explained. The following conclusions were drawn: Under shallow-seam fully mechanized top coal caving high-intensity mining, the WFFZ of the working face P2 is directly connected to the exposed bedrock surface, and the movement of the overburden is subject to the typical “two-zone” mode. The development height of the WFFZ is greater than the value in the traditional “three-zone” mode calculated according to the empirical formulas. The ratio of the WFFZ height to the mining thickness is 43.75. Under the “two-zone” mode, a water-flowing channel exists in the overburden near the open-off cut and the stopping line. When the surface water source is in the right position, the water inflow of the underground working face will increase suddenly.

A mathematical assessment of the efficiency of quarantining and contact tracing in curbing the COVID-19 epidemic

In our model of the COVID-19 epidemic, infected individuals can be of four types, according whether they are asymptomatic (A) or symptomatic (I), and use a contact tracing mobile phone application (Y ) or not (N). We denote by R0 the average number of secondary infections from a random infected individual. We investigate the effect of non-digital interventions (voluntary isolation upon symptom onset, quarantining private contacts) and of digital interventions (contact tracing thanks to the app), depending on the willingness to quarantine, parameterized by four cooperating probabilities. For a given ‘effective’ R0 obtained with non-digital interventions, we use non-negative matrix theory and stopping line techniques to characterize mathematically the minimal fraction y0 of app users needed to curb the epidemic, i.e., for the epidemic to die out with probability 1. We show that under a wide range of scenarios, the threshold y0 as a function of R0 rises steeply from 0 at R0 = 1 to prohibitively large values (of the order of 60−70% up) whenever R0 is above 1.3. Our results show that moderate rates of adoption of a contact tracing app can reduce R0 but are by no means sufficient to reduce it below 1 unless it is already very close to 1 thanks to non-digital interventions.

Modeling Drivers’ Stopping Behaviors during Yellow Intervals at Intersections considering Group Heterogeneity

Stopping behavior during yellow intervals is one of the critical driver behaviors correlated with intersection safety. As the main index of stopping behavior, stopping time is typically described by Accelerated Failure Time (AFT) model. In this study, the comparison of survival curves of stopping time confirms the existence of group specific effects on drivers. However, the AFT model is developed based on the homogeneity assumption. To overcome this drawback, shared frailty survival models are developed for stopping time analysis, which consider the group heterogeneity of drivers. The results show that log-logistic based frailty model with age as a grouping variable has the best goodness of fit and prediction accuracy. Analysis of the models’ parameters indicates that phone status, maximum deceleration, vehicles’ speed, and the distance to stopping line at the onset of the yellow signal have significant impacts on stopping time. Additionally, heterogeneity analysis illustrates that young, middle-aged, and female drivers are more likely to brake harshly and stop past the stop line, which may block the intersection. Furthermore, drivers, who are more familiar with traffic environments, are more possible to make reasonable stopping decisions approaching intersections. The results can be utilized by traffic authorities to implement road safety strategies, which will help reduce traffic incidents caused by improper stopping behavior at intersections.

Are helmeted cyclists taking more risk at signalized intersections?

Objective The aim of the present study was to investigate the relationship between bicycle helmet use and safety behavior at signalized intersections. Two hypotheses were investigated: The first states that bicycle helmet use leads to risker behavior because of the increased sense of protection (risk compensation), the other states that helmeted cyclists have a general inclination toward safer behavior (safety package) and that helmet use is one of several behaviors for improving safety. Method Based on video recordings of 1031 cyclists at 12 signalized intersections in Denmark, two indicators of risky behavior were compared between helmeted and unhelmeted cyclists: Speed and time after the onset of yellow at which the cyclists crossed the stop line. Linear regression models were developed with gender, type of bicycle, and intersection characteristics as predictor variables, in addition to helmet use. Results Helmeted and unhelmeted cyclists do not differ in how many seconds after the onset of yellow they cross the stopping line. This is consistent with the absence of both risk compensation and safety package, alternatively with a general inclination of helmeted cyclists toward safer behavior which is about offset by risk compensation. Helmeted cyclists had higher speed on average, which indicates that risk compensation may occur. However, the higher speed may also be due to the generally better fitness of helmeted cyclists which is likely to result from larger cycling volumes. Moreover, the effect of helmet use on speed may be overestimated because of a lack of control for potential confounding variables. The results show further that, regardless of helmet use, before-red (lights on a separate bicycle signal shift to red before the main signal) is related to later crossings of the stop lane after the onset of yellow and that cyclists stop earlier on average at intersections with right-turn signals. Conclusions The results do not provide support for the position that promoting or mandating bicycle helmet use will have adverse safety effects because of more risky behavior among helmeted cyclists.

Research on the temporal-spatial evolution of ground pressure at short-distance coal seams

To study the temporal-spatial evolution of ground pressure at short-distance coal seams, this paper studied the displacement law of overlying strata and the temporal-spatial evolution of ground stress by analog simulation experiments. The results show when the upper coal seam is mined, overlying strata of the stope form three zones: the caved zone, the fractured zone and the bending subsidence zone. The caved zone which subsided in the largest quantity showed an irregular subsidence curve. The fractured zone where the maximum subsidence amounts are basically located in the middle of the goaf had approximately parabolic subsidence curves. The bending subsidence zone underwent the least subsidence as it was controlled by the key layer. In the coal mining process, stress concentrated in front of both the opening-off cut and the working face. When the working face advanced to 150 m, bearing stress of the opening-off cut and the working face was up to 20 MPa, with a stress concentration coefficient of 1.98. When the lower coal seam was mined, the immediate roof kept caving as the mining proceeded, with no obvious initial weighting or periodic weighting in the main roof. Only the roof stress within the mining area demonstrated greater fluctuations as the mining moved on. Pressures at the opening-off cut and the stopping line remained high in the whole process, so it is suggested to pay special attention to pressure detection during the first cut and make sure the roof is well supported for the mining of lower coal seam.

Numerical simulation on stress evolution and deformation of overlying coal seam in lower protective layer mining

Protective layer mining (PLM) is one of the most effective regional measures against gas outburst, and the most preferred technique to prevent and control gas outburst. This paper attempts to disclose the effect of close-range PLM in Hezhuang Coal mine, Western Henan Coalfield. Firstly, coal seam I7 was selected as the lower protective layer, and coal seam II1 was taken as the overlying coal seam. Considering the situation of actual production, a simulation model for lower PLM was established on Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D). The established model was adopted to simulate the mining of the working face 11030# of the lower protective layer (I7) at the mining depth of 50, 100, 200 and 250 m, respectively. Through the simulation, the authors summarized the laws of stress evolution and deformation of the working face 11030# of the overlying coal seam (II1) in the upper part of the stope. The research results are as follows: After the lower PLM, the stress distribution of 11030# II1 in the strike direction can be divided into three parts from the open-off cut to the stopping line: original stress zone, pressure relief zone and stress concentration zone; the stress distribution of 11030# II1 in the dip direction can also be divided into the three parts from the top to the bottom. However, the stress distribution in the dip direction is less uniform than that in the strike direction. Meanwhile, the 11030# II1 had an unobvious deformation in the original stress zone, compressive deformation in the stress concentration zone, and expansive deformation in the pressure relief zone; the maximum expansive deformation was observed in the middle of the pressure relief zone. The research results lay the theoretical basis for engineering application of lower PLM.

Stress Evolution Law of Coal and Rock Mass Affected by Mining before and after Dydraulic Fracturing

Stress concentration of coal and rock mass is the intrinsic cause of rock burst, the dynamic evolution law of coal seam stress and roof rock stress during the advancing process of mining face is obtained by using the coal seam stress monitoring system and the developed surrounding rock stress monitoring system, In this paper, the stress variation law of coal and rock mass during mining and the correlation between them are analyzed in detail. In order to reduce the danger of rock burst caused by stress concentration, hydraulic fracturing measures of roof strata were adopted in the field, and the stress changes of coal and rock mass before and after hydraulic fracturing were compared and analyzed. The results of the inspection show: The vertical stress gradient is linearly correlated with the trend of coal seam stress. The influence of mining on the stress of rock seam is earlier than that of coal seam, but the influence of mining disturbance on the stress of coal seam is higher than that of rock seam; The increase amplitude of vertical normal stress of roof strata under mining disturbance is obviously higher than that of two horizontal stresses; the stress value of coal and rock strata decreases after hydraulic fracturing, and the decrease amplitude of stress in coal seam is larger than that of rock strata after hydraulic fracturing. The peak stress of coal seam moves toward stopping line than that before hydraulic fracturing. Field application shows that the stress evolution information of coal seam can provide the corresponding basis for anti-scouring measures and ensure the safe and efficient production of working face.

Safe Braking Distance at Signalized Intersection

Signalised intersection is an area where most of the drivers having dilemma in making decision to either pass through the intersection or stop when the light turns to yellow. During this phase, a sudden deceleration and incorrect estimate of intersection clearance time cause rear-end collision, severe right-angle crash and left-turn head-on collision. Therefore, the aim of this study was to determine the safe braking distance at signalised intersection by using the concept of stopping sight distance, so that a set of road marking and road sign can be proposed to help the driver in making decision within the dilemma zone. Samples of vehicle’s approaching speed were collected at a signalised intersection within the Ipoh-Lumut Highway in Perak Tengah. Statistical analysis showed that the observed 15th and 85th percentile speed at the intersection were 66.2km/h and 88.5km/h, with a mean and standard deviation of 77.5km/h and 9.99km/h. Goodness-of-fit tests showed that the distribution of the approaching speed at the intersection was normally distributed with a probability of 14.4%. It was concluded that safe braking distance from the stopping line of the signalised intersection is between 97m for lower speed limit to 152m for the upper speed limit.

Sequential analysis and design of fixed-precision sampling of Lake Kariba fishes using Taylor’s power law

Taylor’s power law (TPL), which states that the variance of abundance is a power function of mean abundance, has been used to design sampling of agricultural pests and fish species. We show that TPL holds for means and variances of abundance of accumulated fish samples in the fished and unfished areas separately of Lake Kariba (between Zambia and Zimbabwe), measuring abundance indices by number and weight separately. We use TPL parameters estimated from sequentially accumulated samples to update a stopping line of fixed precision 0.1 after each new sample from a sampling day. In these Lake Kariba data, depending on the sampling area and abundance measure, our updated stopping-line method requires 21% to 41% of the number of sampling days and 19% to 40% of the number of samples that are planned a priori and performed under systematic sampling. Our novel method yields mean abundance estimates similar to those from systematic sampling and provides a conservative approach to reaching a fixed sampling precision level with reduced sampling labor and time. Using mixed-effect modeling for cumulative means and variances with either number or weight from both fished and unfished areas, we find that fishing increases the slope of TPL. This study provides the conceptual framework and an empirical case study for implementing a sequential sampling method for fish assemblages of an inland lake. The possible limitations and applications of our method for sampling in other environments are discussed.

Method to Calculate Working Surface Abutment Pressure Based on Key Strata Theory

Overburden key strata (KS) have a significant influence on abutment pressure distribution. However, current calculation methods for working surface abutment pressure do not consider the influence of the overburden KS. This study uses KS theory to analyze the overburden load transferred to coal‐rock masses on both sides of the stope through fractured blocks in different layers of the KS in the fissure zone and KS in different layers of the curve subsidence zone. Using Winkler’s elastic foundation beam theory, we consider the fissure zone KS on the coal mass side and the curve subsidence zone KS as many elastic foundation beams interact with each other. A method to calculate the abutment pressure of the coal mass and the goaf was then established, considering the influence of the overburden KS. The abutment pressure distribution of working surface 207 after mining was then calculated using our method, based on mining conditions present in the Tingnan coal mine. The calculated results were verified using measurements from borehole stress meters and microseismic monitoring systems, as well as numerical simulations. In addition, the calculation results were used to determine a reasonable position for the stopping line and remaining width of the roadway’s protection coal pillar in working surface 207. The results of this study can be used to calculate the abutment pressure distribution of the working surface under a variety of overburden KS conditions. The results can also provide guidance for forecasting and preventing mine dynamic hazards, controlling the surrounding rock in mining roadways, determining reasonable widths for protection coal pillars, and designing the layout of mining roadways.

Surface subsidence characteristics of grout injection into overburden: case study of Yuandian No. 2 coalmine, China

A study on the surface subsidence characteristics is essential for evaluating the effects of subsidence control technologies and improving such technologies. One such technology is grout injection into overburden (GIO), which is used in coal mining areas. In the past, the subsidence reduction ratio—a single index—was often used to evaluate the final amount of subsidence control achieved by GIO; however, little research has been conducted on the dynamic process of surface subsidence. In this study, the surface subsidence characteristics of GIO on the side of a stopping line (SSL) of a longwall were examined through in situ monitoring, and the characteristics of areas with grouting were compared with those without. The final maximum subsidence, horizontal displacement, and subsidence rate decreased considerably (70.2, 80.4, and 77.5 %, respectively) with the use of GIO. However, 4.6 % of the mining height subsided at a certain surface point on the SSL before GIO controlled subsidence at that point. Compared with the duration of the active period without grouting, that with grouting and the corresponding subsidence decreased considerably (44.2 and 87.1 %, respectively). Generally, it is quite difficult to control the surface subsidence when GIO is implemented on the SSL of a longwall because the surface and subsurface are already affected by the coal extraction, without grouting on the side of the open-off cut. Thus, the success of GIO technology in the case study described in this paper demonstrates its effectiveness in controlling the surface subsidence in coal mining areas.

Numerical Simulation Study on Setting Stopping Line of Working Face in Shuguang Mine

The surrounding rock deformation of pedestrian roadway was serious under the influence of the working face. And it has affected the safety and normal use of roadway. To ensure the long-term stability of the pedestrian roadway surrounding rock and increase the coal recovery rate of working face, the paper studied the position of stopping line of 1203 working face by numerical simulation. The results show that setting 115m wide of security coal pillar between 1203 working face and pedestrian roadway that the area of stress concentration near the working face has less effect on the pedestrian roadway could better control the surrounding rock stability of the pedestrian roadway and meet the need of the long-term normal production use. It narrows the width of security coal pillar, increase the coal resources recovery rate and achieve the better economic benefits.