Abutment Pressure Research Articles

Analysis of insidious fault activation and water inrush from the mining floor

Based on the stress field distribution rule of the mining floor under abutment pressure, we have established a simplified mechanical model, which contains multiple factors relating to activation and evolution of insidious water-conductive faults. The influence of normal and shear stresses on fault activation and effective shear stress distribution in the fault plane was acquired under mining conditions. Using fracture mechanics theory to calculate the stress intensity factor of an insidious fault front, we have derived the criterion for main fault activation. Results indicate that during the whole working face advance, transpressions are exerted on fault planes twice successively in opposite directions. In most cases, the second transpression is more likely to lead to fault activation. Activation is influenced by many factors, predominant among which are: burial depth of the insidious fault, friction angle of the fault plane, face advance direction and pore water pressure. Steep fault planes are more easily activated to induce a sustained water inrush in the face.

Study on the Abutment Pressure and Advanced Support of Driving Roadway along Goaf of Isolated Mining Face

WuTongZhuang No.182309 mining face is an isolated mining face. The abutment pressure is big and roadway deformation is severe due to driving roadway along goaf with short pillar remained. In view of these problems, taking WuTongZhuang No.182309 mining face as project background, the law of the abutment stress distribution was analyzed by use of numerical simulation software FLAC3D and field measurement study. The results showed that the influence scope of the lead abutment pressure was about 55m , the peak value was about 6m ahead of the mining face and the stress concentration factor is 3.3.Based on the above study results, a scheme of advanced support was proposed which effectively controlled the roadway deformation and ensured the safety production of the mining face.

Strata behavior investigation for high-intensity mining in the water-rich coal seam

This paper describes a specific case of mining in a water-rich coal seam in western China. Water inrushes, roof caving and other disasters induced by intensive mining operation could pose great threats to the safety of coal mines. The strata behavior during the high-intensity extraction in the water-rich coal seam is analyzed by employing the numerical simulation method and in situ monitoring. The results show that about 10m ahead of the workface, the front abutment pressure peaks is at 34.13MPa, while the peak of the side abutment pressure is located about 8m away from the gateway with the value of 12.41MPa; the height of the fracture zone, the first weighting step and the cycle weighting step are calculated to be 45, 50 and 20.8m, respectively; pressure distribution in the workface is characterized by that the vertical pressure in the center occurs earlier and is stronger than those on both ends. Then, the results above are verified by in situ measurement, which may provide a basis for safe mining under similar conditions.

Hybrid assessment of pre-blasting weakening to horizontal section top coal caving (HSTCC) in steep and thick seams

Horizontal section top-coal (HSTCC) caving offers a powerful method to efficiently excavate rude coal in steep and thick seams, and pre-blasting weakening has a profound effect on pursuing great production, high efficiency and good benefit under particular conditions like a small-scale working face with large-scale sectional caving height. +564-level HSTCC working face in B3–6 coal seams of Jiangou Colliery in Urumqi was taken as study case for in situ industrial experiment. Total thickness of seams in the study case is about 50.0m and average angel here is over 83°. In the industrial experiments, at first we adopted continuous charge machine and emulsion matrix explosive to substitute for traditional blasting schemes for specific geological settings in the study case. Hybrid analyses and assessments with blasting crack propagation analysis, abutment pressure monitoring prediction and economical benefit assessment were attributed to be able to attest pre-blasting weakening effects practically. Meanwhile crack propagation analysis after pre-blasting weakening showed that in all triple monitoring bore holes rock masses of top-coal would be fallen into three stages from the bottom up: fracture zone, plastic zone and elastic zone generally, and fracture toughness respectively in correspondent zones was calculated by the analytical formula: 0.5616–0.8806, 0.6403–0.9541 and 0.7535–1.1900MPam1/2 after pre-blasting weakening. Pressure monitoring prediction and economical benefit assessment also indicated that it was necessary to introduce the pre-blasting weakening with predominant blasting scheme from both views. For excavation in extremely steep and thick coal seams, relevant results would be a useful tool to study the mechanism of pre-blasting weakening both qualitatively and quantitatively.

Microseismic Monitoring and Numerical Simulation Research of Floor Failure Depth in Extra-Thick Coal Seam

Based on the condition of fully mechanized caving face in one mine, two methods of microseismic monitoring and numerical analysis were combined to study the evolution characteristics and development law of floor failure depth in extra-thick coal seam. Microseismic monitoring results show that the number of microseismic events partly reflects the influence of mining disturbance in the roof and floor rock mass. The distribution of microseismic events are intensive near the coal mining face, which show the floor rock mass is seriously damaged during the coal mining. The greatest floor failure depth estimated from mine microseismic monitoring is 31 meters. Numerical analysis indicate that the rock stress around the mine stope is redistributed during the coal mining, due to the effect of mining disturbance. The abutment pressure increases in front of the coal mining face and the stress reduces in the mined areas. The concentration and release of the stress makes contribution to the destroy of the floor rock. The maximum floor failure depth is up to 28 meters calculated from numerical simulation. The consistency of microseismic monitoring results and numerical analysis improve that it is effective and reliable to obtain floor failure depth and considerably possible to predict the water inrush using microseismic monitoring technology with its inherent ability to remotely monitor the progressive failure caused by mining. The research results have great popularization and application values for the similar mine.

Strata-pressure behavior of double-unit mining method combining fully-mechanized and mechanized coal face

Based on the engineering background of double-unit face mining under complicated geological conditions and the lagging fully-mechanized face surpassing the fore mechanized face of double-unit face in Zhou Yuanshan coal mine, strata-pressure behavior in the process was analyzed based on FLAC3D and on-site measurement. The results show that the stress concentration factor of superposition abutment pressure and the alternate distance of double-unit face are meeting gauss function, the relationship between the depth of stress concentration point and alternate distance also meets gaussian function. When the alternate distance is larger than 24 m, the superimposition of pilot support pressure in the double-unit face is weak. When the alternate distance is more than 12–15 m, the changes of the roof subsidence coefficient and the depth of stress concentration point are stabilized; when the alternate distance is 3–6 m, the fore working face end is in the greatest impact area of superposition abutment pressure, this area should be avoided in determining the reasonable alternate distance.

Relevance between abutment pressure and fractal dimension of crack network induced by mining

Based on the geological conditions of coal mining face No. 15-14120 at No. 8 mine of Pingdingshan coal mining group, the real-time evolution of coal-roof crack network with working face advancing was collected with the help of intrinsically safe borehole video instrument. And according to the geology of this working face, a discrete element model was calculated by UDEC. Combining in situ experimental data with numerical results, the relationship between the fractal dimension of boreholes’ wall and the distribution of advanced abutment pressure was studied under the condition of mining advance. The results show that the variation tendency of fractal dimension and the abutment pressure has the same characteristic value. The distance between working face and the peak value of the abutment pressure has a slight increasing trend with the advancing of mining-face. When the working face is set as the original point, the trend of fractal dimension from the far place to the origin can be divided into three phases: constant, steady increasing and constant. And the turning points of these phases are the max-influencing distance (50m) and peak value (15m) of abutment pressure.

Control Technology and Application for Surrounding Rock Deformation in T-Junction Area of Gob-Side Entry Retaining

On the bases of theoretic analysis, numerical simulation, and project practice, stress distribution of surrounding rock and movement characteristics of roof strata in T-junction area of gob-side entry were analyzed. Besides, control technology in T-junction area was proposed after indicating deformation characteristics of different stages in gob-side entry. Results show that there is an inclined block in T-junction area after fracture of main roof and the period when the block is tending to stability is a critical stage of pressure appearance for gob-side entry. Further, three stress zones: in-situ stress zone, abutment pressure zone and low stress zone appear in both strike and dip of mining panel and enhanced support of gob-side entry before excavation should keep away from the abutment pressure zone, which also indicates that deep bolting support can exert the bearing capacity of deep rock mass. Additionally, the whole procedure of surrounding rock deformation can be divided into four stages and deformation in gob-side entry is larger than that of entry excavation, which means that efficient support design should be taken into account. Ultimately, district control technologies for surrounding rock of gob-side entry in back zone, filling zone, and front zone are proposed and it showed a good adaption in project practice of coalmine.

Study on Support of Roadways in Fractured Rock Mass under Mining-Induced Stresses

One of the difficult issues in underground mining is the ground control of roadway subject to mining induced stresses. As a longwall face advances, the state of initial stresses dramatically changes. Accordingly, lateral abutment pressure forms on the pillar and frontal abutment pressure on the roof and lateral sides of the roadway. These pressures will lead to severe deformation and deterioration of the rock mass surrounding the entries. In this paper, a systemic study on this issue is proposed using the combination of numerical modeling and in-situ monitoring which was carried out at a coal mine in the Lu.An Group, China. The condition of stress redistribution caused by mining-induced stresses and the state of the surrounding rock mass of the roadway situated in front the work face are systematically investigated. Different patterns of support and reinforcement as well as their effects on the stability of the roadway are also presented.

Numerical investigation on the assessment and mitigation of coal bump in an island longwall panel

This study presents a numerical investigation to assess the risk of coal bumps and produces a stress–relief technology using boreholes to mitigate risk during the extraction of an island longwall panel. Based on the geological condition in an island longwall panel in the Tangshan Coal Mine, Tangshan, China, a numerical FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) model was established to determine and to map the zones in the panel with a high risk for coal bumps. The results of the numerical modeling show that the roof deformation starts to occur at more than 30m ahead of the longwall face and the deformation starts to accelerate after a distance of 10m in front of the longwall face. Large and rapid roof deformation is considered to be an important precursor of coal bump occurrence during the extraction of an island longwall panel. Based on the numerical results, a stress–relief technology using boreholes, which was employed to release abutment pressure, was investigated through numerical methods. The modeled results suggest that the peak stress concentration could be released by drilling boreholes in the zones prone to coal bumps. The effectiveness of the stress release increased with the borehole length and decreased with the borehole spacing.

Numerical Analysis on Ground Pressure Feature in Fully Mechanized Coal Face

Base on the fully mechanized coal face of 8113 (1) in LaoYingSan mine, numerical analysis method was applied to analyze the ground pressure feature, FLAC software is carried out to set up numerical model, and offer numerical procedure. The mining abutment pressure distribute form and its partition in front of fully mechanized working face. All four different mining height (2.6m2.8m3.0m3.2m) was respectively calculated. In addition, the influence of mining speed to mining abutment pressure and intervals is analyzed, four different mining distance (20m30m40m50m) selected separately. Afterwards, the different solution analyzed respectively, these results show that the mining abutment pressure distribution form in front of fully mechanized working face essentially identical, they including the stress increasing zones, the stress decreasing zones and the initial rock stress stable field. The influence of mining pace to wall rock looseness range greater than mining height.

Research on Reasonable Position of Roadway for close Multi-Seam and its Application

The principle of roadway layout is in the low stress zone. Roadway will be difficult to support due to the lower seam face in the close multi-seam is affected by dynamic pressure of the upper seam face mining. The distribution of abutment pressure after the upper seam face mining were analyzed,concluded that: The layout of lower seam roadway should avoid the stress concentration area of residual coal pillar; Stress concentration of the coal pillar is related with mining order, and stress concentration degree is higher in the first mining side of the coal pillar; when the upper coal seam is gob, the layout of the roadway in the lower coal seam with the pattern of homodromous alternate interior layout will be easy to support.

Floor stress evolution laws and its effect on stability of floor roadway

According to the distribution of abutment stress in a stope, this research established the mechanical model of mining abutment pressure transmission in floor base on the theory of semi-infinite plate body in elasticity. This study takes the 762 working face of Haizi Coal Mine as a case in point, and analyzed the dynamic evolution law of seam floor stress during the mining process. With an organic combination of the mining floor stress and surrounding rock stress, the study obtained the change laws of the maximum principle stress and the minimum one for the floor roadway surrounding rock when mining the upper working face. Considering the non-constant pressure force state and the cracks revolution mechanisms of floor roadway surrounding rock, the research built the mechanical model of roadway stress. Simulation results verify the reliability of the above conclusions. Moreover, this model could provide the theoretical basis and technical support for controlling floor roadway surrounding rock.

Study on Distribution Laws of Abutment Pressure for Fully-Mechanized Top-Coal Caving Face in Deep and Large Mining Height

Based on the geologic and technology condition of 2301 fully-mechanized top-coal caving and large mining height face in Longgu colliery, the paper have comprehensive studied distribution laws of abutment pressure by theoretical analysis, FLAC3D numerical simulation and field measurement. The study draws the trend and inclination distribution range and value and concentration factor of the peak, which of these were impacted by mining height and depth and advance distance, and reveals distribution laws of abutment pressure with face advancing, and also pointed out that laws was in favor of top-coal caving, but not conductive to the prevention and treatment of the rib fall of coal wall; field measurement and numerical simulation and theoretical analysis results can be achieved mainly unified.

Strata Behaviors of Fully-Mechanized Sublevel Caving Face Based on Similar Simulation Test

in view of research situations of the fully mechanized sublevel caving, the similar simulation test model for fully mechanized sublevel caving was presented. During the top-coal caving process, variation of top-coal subsidence and abutment pressure were measured. Consequently, the ground pressure behavior of fully mechanized sublevel caving was analyzed. The following conclusions can be reached: (1) top coal subsidence experiences the process of slow increase, trend to aggressive and sharp increase; (2) undulate change as well as decay after reaching the peak of abutment pressure is appeared with the advance of working face, strata behaviors of main roof displays smoothly; (3) on account of cushion above hydraulic support, influence of dynamic load during periodic weighting such as rock burst can be eased and abutment pressure peak moves forward, consequently, strata behaviors in the working face presents smoothly.

Optimization Analysis of Pillar Position under Inclined Coal Seam Pillar

In order to get reasonable pillar position, this paper researched 20 m inclined pillar abutment pressure spread distribution rule on multiple inclined coal seam roof and floor, based on these lower coal seam have three pillar position can be determined, they were in the central or upside or downside. We are from three aspects to respectively analysis degree of pillar relief, pillars peak pressure concentration factor and pressure spread depth of the floor when pillar layout in different location. The results show that pillar abutment pressure concentration factor along the pillar normal and gravity synthesis direction spread, and with flat oval symmetrical decline distribution on roof and floor, also obtain the upper and lower pillar staggered arrangement is beneficial to the upper pillar pressure relief, at the same time, pillar itself abutment pressure peak coefficient is lower, floor propagation depth is smaller. In short, if the coal seam under inclined pillar want to layout pillars, upside better than downside, and downside is better than vertical, which the result has certain guiding significance for inclined coal seam of reasonable choice pillar position.

Effective Filling Rate in Filling Mining’s Influence on Overlying Strata’s Movement

Similarities and differences of overlying strata movement rule and abutment pressure distribution between filling stope and traditional strope was analysied guided by “practical mine pressure control theory ”. The admissible condition of strata’s depending from bending failure to caving was put forward, and caving zone’s height was analysied on the basis of this. Results showed that caving zone’s height and resistant force required by hydraulic pillar would decrease leapingly ,until the lowest strata transfer into the main roof, and when pressure was stable main roof’s maximum subsidence would become smaller. With the increase of the effective filling rate, filling body’s supporting degree to overlying would increase, when the filling rate reaches to a value, Coal wall’s edge would not appear the plastic zone, the abutment pressure curve is monotone decline with the peak near coal wall edge .

The Applied Research of Loose Blasting Technique in Managing Crushing Accident of Fully Mechanized Coal Mining Face

Support crushing accidents occur frequently in coal mines, which have a serious impact on their safety production. Usually people adopt the loose blasting technology for processing the pressing frame accidents, that is, using the detonative action generated by explosives to cause the rock mass particles vibration which would spread in the form of stress wave to crush the surrounding rock mass. After the release of the rock mass internal stress, the hydraulic support would make use of its own abutment pressure to prop up again the overlying rock and make it work normally. Based on the research of detonative action and making use of FLAC3D numerical simulation technology, this paper provides a theoretical basis as well as the experience for handling the pressing frame accidents by applying a dynamic load test to theoretically calculate the appropriate explosive amount.

The Zonal Disintegration Law within Coal in Front of Working Face in Deep Coal Mine

The mining coal in the front of long wall face consists of elastic zone, plastic zone and fracture zone. Based on the research of zonaldisintegration of surrounding rock mass in deep tunnel, the zonal disintegration phenomenon of deep coal mine was analyzed by using the theoretical analysis method. On the basis of the Griffith theory, the internal and external boundary formulas of fracture zone and the mechanical criteria of zonal disintegration were obtained. The research shows that the essence of zonal disintegration is the tensile failure and brittle tension crack failure under the abutment pressure, the main influence factors of the width variation of fracture zone are original rock stress and un-axial tensile strength of coal.

Measurement and Analysis for Gas Emission Characters in Fully Mechanized Caving Face

According to the practical condition of 3401 fully mechanized caving face in Dayang coal mine, the relationship between strata behaviors, mining technology and stope gas emission are analyzed through real-time monitoring of the support working resistance, advance abutment pressure and gas concentration of working face. It shows that the change of working face abutment pressure has an obvious effect on the regularity of coal face gas emission. The crest value of gas emission falls behind periodic weighting, the lagging time is about one day. Other factors, like coal production processes, daily coal output and advance speed also have close relationships with gas emission.