| China ranks third in the world in the proven geological reserves of coal,ranking first in the world in recent years in the exploitation of coal,accounting for about 3.5 billion tons of coal,which accounts for 60%of the energy structure.At the same time,China's coal seam is complex and special,restricted by mining technology,mine water accident seriously restricts the development of the coal industry.Ordovician limestone is the base of Carboniferous-Permian coalfield in North China.It has the distinct characteristics of high confined water level,large water volume and high water head pressure.There are a large number of karst fissures developed and many structures concealed.It is tens of meters from the floor of coal seam,which poses a great threat to mining face.Compared with other types of coal mine disasters,floor water inrush accident has great harmfulness and universality,once the occurrence of light flooding surface heavy flooding well,will cause a large number of personnel and property losses.There is a great demand for efficient and fast non-contact detection of floor damage depth and confined water conductivity elevation.Aiming at the problem of water inrush prevention in confined aquatic mining of Ordovician lime,this paper studies the geophysical detection and numerical simulation of floor failure and confined aquatic lift by means of theoretical analysis,field measurement,laboratory test,numerical simulation and engineering practice.The main results and conclusions of this paper are as follows:The response characteristics of elastic wave field and electromagnetic field of floor failure are studied,and the detection method of floor failure depth is selected accordingly.The study of elastic wave field response includes elastic wave equation,propagation characteristics of elastic wave in coal and rock media,the relationship between floor rock failure and elastic wave field response,and summarizes the time evolution law of acoustic wave velocity field and spatial evolution law of acoustic wave velocity field.The study of electromagnetic field response characteristics includes electromagnetic wave propagation characteristics,attenuation characteristics,principle of inter-hole radio wave perspective method and electromagnetic wave bottom plate exploration.Examples are given.The method of floor failure depth is selected,and its working principle is introduced in combination with single-hole acoustic velocity measurement and double-end sealing side leakage geological method.Based on the analysis of regional geology and hydrogeology,the depth and extent of floor failure are measured by single-hole acoustic wave test and double-end plugging method,and the detection results are analyzed.The distance between the bottom of the water-proof layer and the top of the Ordovician limestone in 3501 working face is very different,the shortest distance is only 20.1m,and the water-rich layer in the Ordovician limestone aquifer is not uniform.The analysis of acoustic test results includes the analysis of the relationship between working face propulsion and acoustic velocity,the analysis of the relationship between burial depth and acoustic wave.The acoustic wave waveform in the measuring area below 21 m remains unchanged,that is,the lower limit of damage of hole 2 of acoustic wave is 21m,and that of hole 3 and hole 4 of Tong The lower limit is 19 m and 16 m,respectively.According to the observation hole 1-8 of double-end plugging and leak detection geological method,the failure depth is 24,17,16,15,20,25 and 18 M.The vertical failure depth of the floor is estimated to be 6.0 m,and the failure zone shape map is drawn.Field measurement of confined aquifer elevation of Ordovician ash is carried out.Comparing with mine geological radar,mine electromagnetic wave perspective method and mine direct current resistivity method,high density resistivity method is selected to be used in this field measurement;according to the actual situation of 3501 working face,476 m long measuring lines are arranged in return air lane and transportation lane respectively,the maximum isolation coefficient N is 15,and 80 measuring points are set up.According to the above requirements,the temperature and nanometer quadrupole,dipole and differential measurement are carried out respectively.Based on the analysis of high-density resistivity imaging results of return air roadway and transport roadway in 3501 working face,the lithology of floor is divided into five electrical layers.From the upward development of low resistivity anomaly area,it can be inferred that the overburden interface of Ordovician limestone aquifer is about 30m away from the floor of coal seam.The mechanical parameters test of each stratum of floor,numerical simulation of floor failure in FLAC3D,safety evaluation of West Wing mining and engineering practice of trial mining are carried out.According to the test results of mechanical parameters of rock samples on the floor,the physical and mechanical parameters,permeability coefficient and porosity of each rock stratum are obtained as the basis of numerical simulation of floor failure in FLAC3D.Through the analysis of numerical simulation results,it is determined that the plastic failure depth of floor rock mass is 12.4m,and the bearing conductivity is 19.4m,which is consistent with the field measurement results;combining the method of water inrush coefficient and the method of water resistance coefficient,the plastic failure depth of floor rock mass is 12.4m and the bearing conductivity is 19.4m.Sectional safety evaluation is carried out on the West Wing of the mine field,and the above results are verified by the engineering practice of 3501 working face.The research results provide a basis for the application of elastic wave field detection,high-density resistivity detection,in-situ measurement of floor damage,confined water conduction of Ordovician lime,combined with mechanical parameters test and numerical simulation to evaluate the water inrush risk of confined water mining in Ordovician lime. |
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