Mine Pressure Research Articles

Study on Control Technology for Working Faces Passing through Long-Span Abandoned Roadways

The width of an abandoned roadway has a great influence on the roof stability of the working face. According to the coal seam conditions of the 30106 working face in the Sanyuan Shiku mine, the advance of a working face through an abandoned roadway was studied by using theoretical analysis, similar material simulation, numerical simulation, and field testing to determine the law of stope roof fracture migration, the stress distribution characteristics, and the variation in support resistance. Several conclusions are drawn: (1) The roof of the overlying strata is fractured at the edge of the abandoned roadway in front of the coal pillar and rotates downward due to the run-through of the plastic zone between the working face and abandoned roadway. (2) The hydraulic support working resistance gradually increases with decreasing coal pillar width between the working face and abandoned roadway, and the working resistance of the support tends to peak when the plastic zone extends to the coal, resulting in 3~4 times the normal recovery. Leakage occurred in front of the support in the caving zone. (3) The analysis of the relationship between the support and surrounding rock with the mechanical model for calculating the support load allows the derivation of the support working resistance formula for a working face passing through an abandoned roadway. (4) When the working face is excavated to expose the abandoned roadway, the shrinkage of the front column of the hydraulic support is significantly greater than that of the back column, and the stability is greatly reduced. This problem can be effectively solved when the uniaxial compressive strength of the backfill ≥2 MPa. (5) The engineering practice showed that the danger of leakage and roof fracture impact load was eliminated with the mining pressure reduction after reinforcement measures were taken in the abandoned roadway. The working face passed the abandoned roadway safely, providing the theoretical basis and guidance for coal remining under similar conditions.

Effects of Ground Fracturing with Horizontal Fracture Plane on Rock Breakage Characteristics and Mine Pressure Control

Ground fracturing is a new and effective method for controlling high-level hard roofs. In underground coal-seam mining, the maximum principal stress is horizontal stress, along with the direction of hydraulic fracture propagation. In this study, the control mechanism of the horizontal fracture plane formed by ground fracturing on the strata breaking span was analyzed theoretically, and the effect of the horizontal fracture plane on the structural characteristics, stress distribution, and impact effect of the high-level thick and hard strata (hereinafter referred to as THS) were numerically investigated. To verify the results, the 8218 working face in the Tashan coal mine of the Datong mining area was selected as a case study. The fractured stratum was 20 m thick and was separated vertically from the coal seam by 110 m. After ground fracturing, the extension range of the fracture plane was 216 m in length and 30–100 m in width, covering the working face. In situ monitoring of the mine pressure revealed that the bearing strength of the supports in the working face was weakened by the ground fracturing, and that the roadway deformation was significantly reduced, indicating that ground-fracturing technology plays an important role in controlling high-level THS and improving the mining environment of the working face.

Pressure Distribution and Deformation Control of Gob-Side Entry Retaining Formed by Roof Cutting Influenced by Abandoned Roadways

To explore the influence of abandoned roadways on the technology of gob side entry retaining formed by roof cutting and pressure release, theoretical analyses, numerical simulations, and field engineering experiments are adopted to study the mining pressure distribution law, plastic zone evolution characteristics and surrounding rock control measures when the working face crosses an abandoned roadway. Mining to the vicinity of the abandoned roadway is equivalent to the process of recovering coal pillars. During the mining process, the width of the coal pillar decreases. Under the influence of mining pressure, the coal pillar will gradually lose its bearing capacity. The overburden rock gravity originally borne by the coal pillar will transfer to the retaining roadway and the coal seam in front of the abandoned roadway. Therefore, it is necessary to strengthen the support of the retaining roadway to prevent large deformations due to the sudden increase in pressure. Within 20 m near the abandoned roadway, based on the original NPR constant resistance large deformation cable (CRLD cable) support scheme, the second row of the CRLD cables is densely arranged, and the cable spacing is encrypted from 2400 to 800 mm. The successful application of these research results in actual engineering applications can provide a useful reference for working faces under similar geological condition.

The fracturing models of hard roofs and spatiotemporal law of mining-induced stress in a top coal caving face with an extra-thick coal seam

Hard roof fracturing characteristics and mining-induced stress behaviors can be studied to ensure production safety in top coal caving face. Field tests were conducted at top coal caving face No. 8309 in the Tongxin mine of the Datong Coal Mining Group in China. The monitoring results indicated two modes of periodic weighting: short weighting steps with low intensity and long weighting steps with high intensity. According to three periodic weighting phenomena, three models of hard roof fracturing were proposed based on the cantilever-voussoir beam compound structure. And the equations of the working resistance for long/high periodic weighting were derived. Furthermore, a difference in the pressure changes among the front leg, back leg and front beam of the supports was observed, and the back leg pressure significantly increased during periodic weighting. The change in the single prop pressure was divided into a slow growth stage and a rapid growth stage. And the front abutment pressure fluctuated with the periodic instability of the roof compound structure. Moreover, the fracturing of the roof above the stope resulted in roadway deformation. The instability of the cantilever-voussoir beam structure also intensified the roadway deformation. Finally, a support-surrounding rock mechanical model was established considering the behavior of an elastic cantilever beam. The required work resistance considering the bearing capacity of top coal were discussed, providing a basis for reasonable support selection. These research results can provide references for mining pressure and stratum movement control.

Nonlinear Creep Model of Deep Gangue Backfilling Material and Time-Dependent Characteristics of Roof Deformation in Backfilling Mining

With the gradual increase in mining depth of coal resource exploitation, deep backfilling mining has effectively solved the impact of strong deep mine pressure and strong mining disturbances. However, after deep backfilling mining, the backfilling material is subjected to high stress for a long time, and its viscoelasticity has a significant impact on the roof control effect. This paper uses a large-scale bulk confinement test device to analyze the viscoelastic properties of gangue, establishes a high-precision fractional viscoelastic creep model, and identifies the gangue parameters. The established fractional viscoelastic model was used as the foundation model of the beam, and the roof model based on the fractional viscoelastic foundation was solved. The top deformation characteristics of elastic foundation and fractional foundation were compared and analyzed, and the time effect, viscoelastic effect, and order effect of the fractional order viscoelastic foundation beam were discussed. The results show that the viscosity of gangue increased under the action of deep high stress. As time increased, the roof deformation also increased. In order to more effectively control the long-term deformation of the roof, the viscosity coefficient of the backfilling material should be greater than 20 MPa. This research provides relevant guidance for the requirements of backfilling materials for deep backfilling mining and the prediction of long-term dynamic deformation of the roof in underground excavations.

Research on and Application of Roof Management Technology in 8.8m Ultra-high Fully Mechanized Mining Face

Aiming at the problems of high mining intensity and difficult roof management in a fully mechanized mining face with an ultra-high mining height of 8.8m, this article predicts the pressure parameters and rules of the working face based on the roof management technology of the 12402 fully mechanized mining face in Shangwan Coal Mine. The selection of the working surface bracket and the on-site roof safety management system are explained and analyzed. The results show that the analogy method can be used to predict the mining pressure parameters and rules of the working face to meet the needs of the application of large mining heights; the conventional techniques such as forced caving, “Scraped roof support moving method” and “Advanced drawing support method” are still effective under the condition of 8.8m mining height. The roof safety management system formed during construction guarantees the safe and efficient production of the ultra-high mining height working face, and provides a reference for the popularization of the mining technology of ultra-high mining height.

Mechanical Model of the Initial Leg Pressure Increment of the Shield and Its Application to Monitor Roof Load in Longwall Panels

The shield pressure cannot always be used to represent the upper load of longwall panels, since its value is steady or even decreases by the yielding action. However, the leg pressure increment of the shield (LPIS) at the initial stage is not influenced by yielding and could therefore be an important factor to judge the state of overlying loads. In this study, a mechanical model is established to analyze the relationship between the overlying loads of the main roof and LPIS after cutting. There is a linear positive correlation between leg pressure increment and overlying loads and a second-order relationship between leg pressure increment and length of main roof cantilever in the proposed model. Therefore, it can be used to determine the magnitude of roof weighting strength in different periods as well as the length of the main roof cantilever in a period. Finally, the mine pressure difference between the period of fully mechanized mining and the period of fully mechanized caving mining in the MinDong-1 coal mine serves to verify the rationality of the proposed model.

Prevention Technology for Strong Mine Pressure Disaster in the Hard-Roof Large-Mining-Height Working Face

The movement and destruction of the hard roof in a stope is an important reason for the occurrence of strong ground pressure disasters at the working face. Considering Tongxin Coal Mine as the engineering background, the stress distribution law of the surrounding rock and the overburden rock damage characteristics of a large-mining-height working face under the hard roof were investigated. To solve the problem whereby the stope’s hard roof is difficult to collapse, the hard rock key stratum of the roof was hydraulically fractured to weaken the mechanical properties of the roof rock stratum. Additionally, microseismic monitoring technology was used to monitor the cracking effect of the rock stratum. The theoretical calculation and numerical simulation results reveal that, after hydraulic fracturing, a crack with a more consistent trend formed inside the hard rock stratum and a large area of the rock stratum was damaged. According to the monitoring results of the stope stress after hydraulic fracturing, the law governing the occurrence of the leading bearing pressure was in effect. In contrast, the influence range and peak strength of the leading bearing pressure were considerably reduced at the working face after hydraulic fracturing. After performing hydraulic fracturing on the roof of the working face, the bearing pressure of the working face can satisfy the production requirements better. Finally, the results obtained through this study can be used as a reference for determining the width of coal pillars under similar mining conditions.

Study on the Regularity of Ore Pressure in Overburden Hard Rock Working Face of Overburden Mining on Reverse Faults

In order to study the mining pressure on the upper coal seam in the fault, the working pressure of the working face with a hard rock roof is based on the production geological conditions of the 3301 working face of Yiqiao Coal Mine. Use flac numerical simulation software to establish a three-dimensional numerical calculation model of mining face, and study the distribution characteristics of mining plastic area, the advance support pressure and elastic strain energy density. And the change curve is treated by origin software fitting function. In the end, it was found that the total volume of the plastic zone and the propulsive distance of the working face showed an exponential function. Before and after the "first square", the total volume of the plastic zone increased more significantly, and the hard roof failure was mainly bending failures; There is a logarithmic function between the advance support pressure and the advancing distance of the working face. The range of 5–14 m in front of the coal wall is a region where the pressure increases sharply. The elastic strain energy density appears relatively high. During the mining process, the advance support of the roadway should be strengthened, and the key monitoring should be carried out. If necessary, corresponding pressure relief measures should be taken to ensure the safe production of the working face.

Geomechanics model test research on automatically formed roadway by roof cutting and pressure releasing

The N00 mining technology is a new coal mining method of automatically formed roadway (AFR). The roadway is created by roof cutting and pressure releasing (RCPR). Compared with the traditionally longwall method, this new technology does not require excavating mining roadways and reserving protective coal pillars (no-pillar). In order to make an in-depth study on the law of the mining pressure behavior, the first working face of N00 mining technology around the world is taken as the engineering background in this manuscript. A three-dimensional geomechanics model test system is independently developed for the N00 mining technology and the model test is carried out. Combined with numerical comparative analysis, the law of surrounding rocks stress evolution and overlying strata movement of AFR is obtained. The variation law of roof and floor convergence deformation of AFR has obvious zoning characteristics, which can be divided into four significant stages. These stages are the pressure releasing stage, the dynamic pressure deformation rising stage, the dynamic pressure deformation stabilizing stage, and the compaction stabilisation stage, respectively. The overload test results indicate that the key damaged parts are the shoulder corner of solid coal side, and the gangue rib of AFR. The research results can be used as a reference for theoretical research, engineering design and field application of the N00 technology.

Roof fracture and front abutment stress evolution of large mining height coal face with weak overburden under goaf

The mining pressure evolution of large mining height coal face with weak overburden under goaf is complicated, significantly influencing mining safety. This study uses the actual geological conditions of the II3 coal seam in Lingdong Coal Mine as research background. First, we combine the key layer theory and roof and floor lithology, the middle sandstone strata are determined as key strata. The fracture thin plate model for weak overburden with large mining height is established, considering elastic-plastic theory. We then obtain the calculation formula of key strata initial fracture span lo, periodic fracture span l0, and front abutment stress. Second, the roof fracture and front abutment stress evolution during lower coal mining are obtained using the FLAC3D numerical simulation method. As the coal face advances, the immediate roof continues to collapse, and periodic fracture subsidence occurs. The coal face periodically appears, causing the phenomenon of roof subsidence acceleration, serious coal wall spalling, increasing pillar stress, and roof-stepped subsidence. The numerical simulation results show that the initial fracture span is approximately 25 m, and the stress of the key strata is approximately 12.5 MPa. The roof weighting span of the first cycle is approximately 2.39 m, the front abutment stress peak is approximately 14.33 MPa, and the influence range of the front abutment stress is approximately 17.50 m. Finally, comparing the numerical simulation results with the theoretical results shows that the evolution is similar, verifying the correctness of the mechanical model. The research results can predict the periodic weighting of overburden and provide a reference for the design of roof mining pressure control for large mining height coal face with weak overburden of lower coal seam.

Surrounding rock control technology for the fault passing of mining face by removing gangue in advance from excavation roadways

This study presents a new technology for passing through faults quickly by removing gangue in advance from driving roadways of working faces; this technology has the advantages of short moving time and good coal quality during fault passing. However, in practice, driving roadways are affected by mining pressure during the driving and mining period; thus, roadway support is difficult. This study aims to develop appropriate support for driving roadways, not only to ensure the stability of the roadway and satisfy the space requirements for the working face when it passes through the fault but also to reduce the strength of the rock pillars in the roadway. In this manner, the shearer can directly reduce the working strength during the period of fault passing. In this study, UDEC numerical simulation software is used to explore the size of rock pillars and the parameters of bolt support. In addition, the supporting effect of ordinary, high-strength prestressed, and high-strength prestressed yielding bolts is compared. On the basis of the simulation results, a reasonable control scheme of surrounding rock in advanced driving roadways is proposed. Moreover, the successful application of the technology in field practice shows the remarkable effect of this scheme on the surrounding rock control when passing faults. Thus, this study provides some references for surrounding rock control during the fault passing of the mining face.

Vegetation misclassification compromises conservation of biodiversity and ecosystem services in Atlantic Forest ironstone outcrops

A recent state provision allows quarzitic campo rupestre (QCR) set-asides as in-kind compensation for ironstone campo rupestre (ICR) suppression in the Atlantic Forest, which induces out-of-kind compensation. However, the recently published state provision defines no clear parameters to demonstrate “ecological equivalence” as an in-kind compensation. We evaluated whether there is ecological equivalence between and ICR and QCR in the Brazilian Atlantic Forest. We show marked geological, pedological, floristic, structural, and functional differences between ICR and QCR. There is evidence that the new compensation rules only partially offset loss of biodiversity and ecosystem services hosted by ICR, determining limited effectiveness of the legislation for ICR conservation in the Atlantic Forest. We conclude that the development of clear compensation parameters based on scientific evidence and quantitative indicators is a priority gap for the conservation of ICR under increasing mining pressure.

Research and Application of Roof Cutting and Pressure Release Technology of Retracement Roadway in Large Height Mining Working Face

In this paper, according to problems of large deformation, high stress and strong disturbance exist in the retracement roadway during the equipment withdrawal of 18,205 large height mining working face in Xiegou mine. The method of roof cutting and pressure release by deep-hole blasting is put forward. Based on the analysis of the characteristics of different roof cutting depth on the stress and deformation of surrounding rock of the retracement roadway by using Phase numerical simulation software, the optimum roof cutting depth suitable for safe retracting of working face is obtained. The support scheme of retracement roadway of the working face and its cross area with the mining gateway is put forward and realize the safely equipment retreat of the working face. The research results show that the stress of surrounding rock and the development depth of plastic zone as well as the displacement of roof, floor and left side of the retracement roadway are effectively reduced after roof cutting, and the larger of the roof cutting depth, the more obvious the pressure release effect will be. The optimal roof cutting position of the working face is calculated and the monitoring results of mine pressure show that the deformation of the retracement roadway and the cross area of the roadway after cutting off the roof and unloading is small, and the support scheme could effectively control the destruction of the surrounding rock of the retracement roadway.

Influence of Key Strata on the Gas Downward Leakage Law in Dual-System of Coal Seam

In Datong mining area, CO and other harmful gases were discharged from the gob in the Jurassic overburden strata to the panel of Carboniferous coal seam. To this end, panel 8309 of Tongxin coal mine in Datong mining area was taken as the engineering background; the change law of CO concentration in the upper corner of the panel and the law of mining pressure were studied through field measurement, and the influence of periodic movement of key strata on the downward leakage law of harmful gases was analyzed. In this paper, the fracture law of the key strata and fracture development characteristics of overburden strata were further studied by the similar simulation test, and the influence of the periodic movement of the key strata on the pathway formation of gas downward leakage was analyzed. The results show that the main cause of harmful gas downward leakage in the Jurassic gob is through the fracture produced by the fracture of the higher key strata. If the higher key strata fractures in the coal mining in the Carboniferous system, through fracture connecting the Jurassic gob above the open-off cut and the upper part of the panel are formed, and effective pathways for gas downward leakage are generated. The fracture and rotation of the higher key strata are accompanied by the formation and disappearance of the effective pathway for gas downward leakage above the panel. Then the periodic change of harmful gas discharging to the panel is caused and consistent with the law of mining pressure.

Mechanical Analysis of Mining Stress Transfer on Isolated Island Face in Extra-Thick Fully Mechanized Top-Coal Caving Mining

The mining spatial structure of isolated island face in extra-thick fully mechanized top-coal caving mining is unique, which leads to a complex mining stress distribution and serious safety hazards. In this study, combined with a specific engineering example, the mining stress distribution characteristics of isolated island face are expounded, and a bearing structural mechanical model of the continuous beam of overlying strata is established using elastic–plastic mechanics theory. The mechanical equations of the mining stress distribution and failure depth of coal–rock mass are then obtained. Comparison of theoretical calculation results with numerical simulation and field measurement results shows basically consistent stress distribution characteristics. The derived mechanical equations can provide an estimation method for the analysis of mining dynamics on isolated island face in extra-thick fully mechanized top-coal caving mining. The following conclusions are acquired. The coal–rock mass should bear not only the lateral mining superposition influence but also the advance mining influence in front of the coal wall, so the isolated island face is in the complex environment of multiple mining stress superposition. In the mining process, the maximum advance mining stress concentration factor is 4.0–6.0 and is located at the upper and lower ends of the isolated island face. The lateral mining failure depth of the coal wall of the isolated island face increases by 2.0–5.0 m under the influence of advance mining. Therefore, compared with the nonisolated island face, the mining pressure appearance is intense. The mining influence in the range of 20–30 m of the upper and lower ends is intense, and the mining stress in this area is characterized by “cone distribution.” This zone is an important hidden danger area with coal–rock mass mining instability on isolated island face, which requires special attention to avoid mining disasters. According to the analysis of the influencing mining factors and laws of isolated island face, it is concluded that the longer the isolated island face size is, the closer the goaf size on both sides of the isolated island face is, the smaller the coal seam buried depth is, the better the mechanical conditions of coal and rock medium are, and the smaller the mining height of coal seam is, the more favorable the safe mining of isolated island face is.

Experimental Study on Overburden Deformation Evolution under Mining Effect Based on Fiber Bragg Grating Sensing Technology

In order to study the regularity of overburden deformation and mining pressure changes in the stope. Take the geological conditions of Hanglaiwan coal mine in Yushen mining area as the background, a 3000 mm×1340 mm×200 mm physical similar material model was established in laboratory. Eight fiber Bragg grating sensors were embedded in the model, used to monitor the movement and deformation of the overburden key stratum and the change of mining abutment pressure in real time and then to determine the influencing factors and strain transfer coefficients of the fiber grating through theoretical analysis and calibration experiments. The results show the following. (1) The changes in value, position, and shape of the strain can reflect the dynamic evolution process of bending deformation, breaking, and rotation of the key strata. When the key layer breaks for the first time, the strain curve shows a peak shape; when the key layer breaks periodically, the strain curve of the fiber grating sensor showed a plateau shape for a period of time. (2) The strain curve has a good corresponding relationship with the change in supporting pressure. When the strain curve of the fiber Bragg grating sensor was at the trough stage, the abutment pressure was at the peak stage, with the increase of sensor buried height, and the supporting pressure and the strain value had a linear relationship within the range of the advanced abutment pressure. The conclusion shows that the fiber Bragg grating sensor monitoring technology has good effect on the internal strain and key supporting pressure monitoring of the overburden in the model test; it provides new monitoring methods and means for the model tests.

Strata behavior and control strategy of backfilling collaborate with caving fully-mechanized mining

Abstract This article analyzes the technical difficulties in full-section backfill mining and briefly introduces the technical principle and advantages of backfilling combined with caving fully mechanized mining (BCCFM). To reveal the strata behavior law of the BCCFM workface, this work establishes a three-dimensional numerical model and designs a simulation method by dynamically updating the modulus parameter of the filling body. By the analysis of numerical simulation, the following conclusions about strata behavior of the BCCFM workface were drawn. (1) The strata behavior of the BCCFM workface shows significant nonsymmetrical characteristics, and the pressure in the caving section is higher than that in the backfilling section. φ has the greatest influence on the backfilling section and the least influence on the caving section. C has a significant influence on the range of abutment pressure in the backfilling section. (2) There exits the transition area with strong mine pressure of the BCCFM workface. φ and C have significant effect on the degree of pressure concentration but little effect on the influence range of strong mine pressure in the transition area. (3) Under different conditions, the influence range of strong mine pressure is all less than 6 m. This article puts forward a control strategy of mine pressure in the transition area, which is appropriately improving the strength of the transition hydraulic support within the influence range (6 m) in the transition area according to the pressure concentration coefficient. The field measurement value of Ji15-31010 workface was consistent with numerical simulation, which verifies the reliability of control strategy of the BCCFM workface.

Field experiment on directional roof presplitting for pressure relief of retained roadways

Roadway failure control in modern longwall mining has been universally difficult and needs to be resolved. To address the failure of retained roadways in longwall mining, in this study, a novel approach of directional roof presplitting (DRP) is introduced and examined through a field experiment. The DRP method utilizes the mine pressure effect and broken expansion nature of rock to achieve the active pressure relief of retained roadways. Directional tensile blasting presplits the trial roadway roof by forming a smooth fracture surface in the roof. After mining, the gob roof within the presplitting height caves in under the mine pressure and subsequently expands to fill the gob to counter the mine pressure. A field test was conducted, and a comprehensive monitoring scheme and a system were designed to study the DRP effect. The results indicated that, the trial roadway roof can be directionally cut apart under the guidance of the charge test and with the help of the established theoretical model for hole distance; after blasting, the roof could maintain its reliability, even though the working face approached. After mining, the retained roadway with DRP exhibited good pressure relief. Roof integrity was guaranteed; furthermore, roadway convergence significantly decreased, and sidewall stability on the pillar side was improved because the high pressure transferred to a farther position. In addition, DRP reduced the scope and degree of the lead abutment pressure and the periodic weighting loads on the working face. This study provides an effective and practical way to control retained roadways and potentially discusses a new approach for utilizing the geomechanical characteristics to prevent and control the mine pressure disasters.

Mine Pressure Prediction Study Based on Fuzzy Cognitive Maps

The study on the prediction of mine pressure, while exploiting in coal mine, is a critical and technical guarantee for coal mine safety and production. In this paper, primarily due to the actual demand for the prediction of mine pressure, a practical prediction model Mine Pressure Prediction (MPP) was proposed based on fuzzy cognitive maps (FCMs). The Real Coded Genetic Algorithm (RCGA) was proposed to solve the problem by introducing the weight regularization and dropout regularization. A numerical example involving in-situ monitoring data is studied. Mean Square Error (MSE) and fitness function were used to evaluate the applicability of MPP model which is trained by RCGA, Regularization Genetic Algorithm (RGA) and Weight and Dropout RGA optimization algorithms. The numerical results demonstrate that the proposed Weight and Dropout RGA is better than the other two algorithms, and realizing the requirement for prediction of mine pressure in the coal mine production.