矿山压力下对煤层底板破坏深度的理论分析和数值模拟研究外文文献翻译

英文原文Theoretical analysis and Numerical Simulation Study on failure depth of coal seams floor caused by mining under pressureShuancheng Gu Ang Li School of Architecture and Civil Engineering Xian University of Science and Technology Xian 710054,China Jianhuan Wang School of Chemistry and Chemical Engineering Southeast University Nanjing 210096,China Abstract: With mining depth increased, most coal mine will face high pressure groundwater threat. Bearing mining has already became a coal mining method universally employed in deep mine of China, one of key problems in coal mining above confined aquifer is how to determine the depth of destroyed floor due to mining influence ,but the conventional method of mining failure depth from coal seam floor in coal mining above confined aquifer possesses high cost and study cycle long and other shortcomings. In the paper ,taking mining No.5 Coal Seam of Cheng-He Mining Area as an example ,this paper analyzes a method which combines the numerical simulation with theoretical calculation is brought forward, while the testing data are compared with those from the in situ measurement, drawing detailed reliable actual information can ensure safety in mining, it can be dynamically reproduced that the development and failure process of the whole floor strata during mining advance .The numerical simulation results educes the 1213m failure depth of the coal seam floor of mining working face, meanwhile, the results may be used to guide practice with similar water prevention work of a working face of bearing mining and design of the water control method, and also provide scientific basis. Key words: coal seam floor； failure depth of coal floor； theoretical analysis； numerical simulation I. INTRODUCTION Chinas coal reserves are very abundant, coal is also a very wide range, but several hundred million tons of coal reserves of coal mine water at the bottom of the Ordovician limestone aquifer confined there, so mine in the mining process, often be subjected to threat by the Ordovician confined water inrush. Mining coal in the mine floor and the floor with pressurized water pressure under the influence of the interaction, will form a seam from top to bottom floor rock formation mining water flowing fractured zone, The effective impermeable layer protection zone and conduction band of water pressure rise zone. The impermeable layer of seam floor resistivity water capacity depends on the effective resistivity water capacity of impermeable protective layer, impermeable layer of protection is only effective in order to effectively ward off the threat of confined water. Coal seam floor mining failure is due to the impact of mining disturbance, the original ground stress equilibrium is broken, re-distribution of ground stress .in the ground stress to reach a new equilibrium, there must be the release of strain energy, so that mining water flowing fractured rock zone Structure change. Therefore, the resistivity water capacity of mining water flowing fractured rock zone is weak, can be regarded as non-water-blocking capacity of rock. Confined water from the mining point of view of safety, the correct evaluation of mining water flowing fractured zone of the actual thickness, that is, the floor-broken depth to accurately determine the bottom impermeable layer of water blocking the effective protection capabilities. Shows the floor-broken depth prediction and control of water inrush is important in decision-making. The present study mining bearing mining coal seam floor-broken depth, mainly by comprehensive observation site (drilling injection pressure water test method, ground penetrating radar and ultrasonic detection method)1-2, similar elastic material model simulation and photo elastic experiment techniques mine the floor-broken depth. These methods are either the high cost or long cycle； either too simplistic test conditions, it is difficult in the bearing mining floor-broken depth application .To compensate for this deficiency, in this paper Cheng-He Mining Area No.5 seam mining face engineering background, application of rock failure process flow-stress coupling analysis system (RFPA2D-flow)3-6, from the perspective of fluid-solid coupling simulations analysis in high-confined water in mining, the coal seam floor strata failure process and floor-broken depth, to explore the basic law of coal seam floor-broken depth development. II. MINING FACE HYDROGEOLOGY CONDITIONS Cheng-He mining area No.5 seam mining under pressure face is located northern four mining area of mine field, north and south sides are solid areas, within No.5 seam, buried depth of 270340m, the average buried depth of 300m, No.5 seam average thickness of 4.2m. Mechanized mining using long-wall mining machine, all falling for management across the roof. No.5 seam elevation of the face below the static water level Ordovician +375m, the confined mining areas, the main factors for the water-filled No.5 coal floor the following Taiyuan group of sandstone or K2 limestone fissures confined water and coal base Ordovician limestone .Impermeable layer in the bottom mining face of the Ordovician limestone water pressure is 0.851.35MPa, in most cases is 1.2MPa. Taiyuan group sandstone aquifer and the limestone aquifer K2 for the same aquifer, its water is mainly affected by the bottom of the Ordovician water supply, water content of the medium. Second Feng-feng coal group of the Ordovician basement thick layer of limestone karst fissures and caves in partcular development, which contains very rich confined water, as the highly water aquifers, is the safety of mining coal in this area of the main confined aquifer, water-filled channel complex, heterogeneous nature of water is the No.5 coal seam overlying the main threat in Cheng-He mining area. III. THEORETICAL MODEL According to different theoretical assumptions and the strength of rock mass failure criteria used for calculating the floor-broken depth of coal seam floor mining face theory, in turn, can predict water inrush.Now more commonly used criteria for the four theoretical calculations were: (a)fracture mechanics and the Mohr-Coulomb failure criteria；(b)elasticity and Mohr-Coulomb failure criteria；(c)elasticity and the Griffith failure criteria；(d)plasticity theory and Mohr-Coulomb failure criterion. The specific conditions under 24508 mining face, through the actual floor rock mass stress field distribution law and propagation features of the research, combined with Mohr-Coulomb failure criterion of rock and rock mass strength theory of plasticity to calculate the plastic floor-broken depth of rock more in line with the actual floor failure site law,so choose the fourth Mohr-Coulomb plasticity theory and failure criteria as Cheng-He Mining Area depth of broken floor rock No.5 seam mining face theoretical model. Figure 1. The schematic diagram of the maximum floor-broken depthcalculation under the limit state1 -coal abutment pressure zone； -gob pressure zone； -floor plastic failure zone； 2 I-preharvest advance pressure compression section； II-postharvest pressure relief expansion section； III-postharvest pressure compression-stable section；4-preharvest primary rock stress section Working face in advancing the process, the coal seam floor along the coal seam strike can be divided into two strata due to the influence of mining is divided into three stages: preharvest advance pressure compression section(I)；postharvest pressure relief expansion section(II)； postharvest pressure compression-stable section(III). The three stages of coal mining strata process is mobile and dynamic process, with the working face forward and repeated .It is because of the existence of such a dynamic process makes the rock within a certain range of the bottom edge of the coal, when the effect of abutment pressure on it reaches or exceeds a critical value, the rock will undergo plastic deformation, the formation of plastic zone；When the abutment pressure can lead to complete destruction of part of the biggest load of rock, the abutment pressure bearing rock surrounding the plastic zone will be connected into one, resulting in gob area floor heave, plastic deformation that has occurred will move the gob area floor rock movement, and the formation will form a continuous slip-line field, and the rock that do not form plastic failure will present a slip surface. At this point, the destruction of floor rock within the sliding interface will be the most serious ,shown in Fig. 1. After the coal mining, rock floor will occur slide, the plastic zone boundary slip line fed in Figure 1 below .Damage zone consists of three parts: active limit area abf and passive limit area acd, the slip line of the straight line formed by the two groups； squeeze transition zone abec, its slip-line of a group formed by a logarithmic spiral ,another group of radiation from a starting point .In Figure 1, plastic zone by the formation and development can be seen, after the coal seam recovery, the floor rock during the gob area will produce abutment pressure when the rock abutment pressure area (abf in Figure 1), the stress exceeds the ultimate strength, the rock will occur plastic deformation, This part of the rock mass is compressed in the vertical direction, in the horizontal direction will result in expansion of rock .Between the expansive rock extrusion transition zone within the rock mass (the logarithmic spiral abec in Figure 1), while the stress transfer to the area. Transition region of the rock continue to squeeze the passive region (acd in Figure 1), because the passive region has free face in the gob area, and its collapse on the role of stress than the original rock stress is lower, so the transition zone and passive zone in the active zone of rock transfered the force will expand inside the gob area, resulting in gob area floor rock heave, which is mined under pressure floor water invasion prone to reason in the gob area. An analytical method for the floor plastic zone that built on the basis of slip-line field theory limit state, based on rock plastic strength theory and rock Mohr-Coulomb failure criterion to determine the geometry of the limit plastic zone in figure 1, which reached the maximum failure depth inside the floor limit plastic zone under the abutment pressure of the coal edge. In abf In aeg However As inThe above equation shows that the floor-broken depth with different angle changes, When , we can find the maximum depth of floor-broken zone, is thus calculated: Substitution of (3) and r1 of (1) shift formula (2),where the maximum depth of floor-broken zone is: Where, -the width of the coal seam plastic zone(m)；- floor rock weighted average internal friction angle(). Calculated by the above floor-broken depth of coal seam floor rock, you need to substitute the plastic zone width of the coal edge, through on-site installation within the borehole stress sensor of the coal internal the measured value can be obtained. According to Cheng-He Mining Area No.5 seam mining face has carried on the floor and coal seam core field sampling 7 (Fig. 2), and indoor rock mechanics experimental results (Fig. 3), using rock mass strength discounted method, calculated the physics mechanics parameters of floor rock result is ； the plastic zone width of the coal edge measured by the on-site available:during the first weighting the result is ；During the periodic weighting the result is .Figure 2. floor Strata field drilling core diagramFigure 3. floor and coal seam core laboratory test diagramFinally, The ,and substituted into (4) draw and .Through the above calculation, we can see Cheng-He Mining Area No.5 seam mining face to first weighting period and periodic weighting period, within the floor strata the maximum failure depth caused by the impact of mining is between 1113m. IV. NUMERICAL SIMULATION ANALYSIS The failure process of water-inrush from coal floor and the hydraulic fracturing mechanism is same, both are considered the seepage-stress coupling mechanism. With respect to the numerical model of mechanism study of water inrush, the critical issue is building a description of rock mass permeability after rupture of the mutation and the equation of water hydraulic tracking transfer law, so as to distinguish different hydraulic mechanisms of the water insulation unit and water conductivity unit, but also can give out a correct interpretation of rock fracturing about evolution process how to turn the impermeable layer into a underground watercourse layer.This paper applied rock failure process seepage-stress coupling analysis system (RFPA2D-flow), besides, the paper also simulated and analysed the whole process of the floor impermeable layer broken water-inrush from the seepage-stress coupling angle8-10. A. Numerical Model According to Cheng-He mining area No.5 Coal Seam geological conditions, a simplified mathematical model length of the coupling is 260m, height of 200m, within the range of the calculation model these rocks of similar physical properties will be simplified,the whole numerical calculation model will simplify 15-story structure body of coal-series strata to be studied. Based on test report on rock-mechanics index, numerical model of the rock material groups in accordance with the sequence from upper to lower, the specific calculation parameters listed in Table 1. Through excavation by steps this time example is used to simulate the floor by the impact of mining, the specific numerical simulation model shown in Figure 2. By the geological model, the number of units is 260200, a total of 52,000 units. Limited by the capacity model, the top of the model added overburden layer, its thickness is 50m, while overburden layer bulk density is about 4.5 times that of the loose weathered layer, equivalent to the 225m thickness of overburden layer under the normal bulk density. The rock only bear gravity stress and water pressure, the geological model of the example shown in Fig. 4. Figure 4. Mechanics model of numeral simulationThe boundary conditions of geological model: Selected to limit the horizontal displacement on both sides of the sliding bearing, which can move vertically. The bottom of the model limits the vertical displacement of the sliding bearing, the two corner points of bottom and sides are to limit the fixed support of horizontal and vertical displacement； Set the 120m high constant water head boundary to simulate confined hydraulic for ordovician limestone water (Its value is 1.2MPa).The model uses step excavation to simulate the impact of mining: including the first step is deadweight calculation process, the second step starts excavation from 65m, each step is 5.4m, a total of 35 steps are excavated, accumulative excavation length is 189m. TABLE I. ROCK MECHANICS PARAMETERS FOR NUMERICAL MODELB. Analysis of numerical simulation resultsWhen coal seam didnt mine, the sole rock strata was whole to be pressed, the distribution type of internal stress is uniform and gentle .As the coal seam mined, rock stress balance is damaged, the internal stress of the floor is redistributed ,the seam floor rock bears abutment pressure of the working face roof, it makes the floor occurrence displacement-deformation of dynamic change, resulting in destruction of post-harvest floor. In this paper, bottom of the excavation is a step-wise, the excavation of the floor of numerical simulation damage by the mining process is a step-wise, a total of 35 times excavation, each excavation is 5.4m, the excavation of coal accompanies progressive failure of rock stratum ,the focus of this numerical simulation is to analyze the floor strata progressive failure characteristics during the working face advancing, and to analyse floor strata failure depth during the periodic weighting and first weighting of the overlying strata .This paper is mainly analyzed from three aspects for the failure of floor strata, including floor pressure distribution, floor failure development process and the depth of destroyed floor. (1) Floor pressure distribution From the previous theoretical analysis shows that a floor of rock deformation and failure in the mining process from initiation-development-formation and the whole process of change reflects the floor rock is a whole dynamic process of the moving and changes, the paper is from RFPA2D-flow experimental analysis angle of numerical simulation of a more comprehensive to study on coal seam mining under the combined effects of the mine pressure and water pressure.Along the coal seam strike by the influence of mining coal floor has the following three stages, respectively forpreharvest advance pressure compression section, postharvest pressure relief expansion section and postharvest pressure compression-stable section, with the face constantly promote these three stages repeated. On the Basis of the impact of features, along the coal seam, according to the different positions of the impact of mining the floor strata will be divided into three stages, namely preharvest advance pressure compression section (I), postharvest pressure relief expansion section (II) and postharvest pressure compression-stable section (III). Along the forward direction, bearing pressure distribution of the coal seam floor strata shown in Fig. 5 the pressure decreased area in the figure is regarded as the gob area. Figure 5. Floor strata pressure distribution(2) Floor failure development process By the numerical simulation analysis shows that the seam floor strata experienced development and damage evolution can be divided into two stages in the working face advancing. a) Stage of first weighting With the stope face advancing to 10.8m (step 3), in the horizontal seam at the bottom of the increased stress on the t