Simulated Experimental Study On Gas Pressure Sensing Testing In Coal Seam

As an assistant decision-making tool for gas outburst prediction,the reliability of indicators is determined by the quantity,scope and representativeness of experimental data,and the critical value of outburst has not been well determined theoretically,which is easily influenced by human factors,and the reliability of prediction results is not high.Traditional prediction methods mainly determine whether there is outburst danger based on outburst parameters,mainly including: tile.The reliability of prediction results is high due to the pressure,gas content,coal seam firmness coefficient and initial velocity of gas emission.However,the existing methods of gas pressure measurement are prominent,the selection of sealing methods is difficult,the implementation process is cumbersome and the period of pressure measurement is long.In this paper,a gas sensor pressure measuring device for coal seam in Wangjialing Mine is studied.A gas sensor is placed at the bit end.The idea of reverse sealing,real-time pressure measuring,compact drilling and dynamic pressure measuring is put forward.Firstly,the process of coal accumulation and compaction in boreholes is studied by stress analysis of coal caved in boreholes,combining rock mechanics and elastic-plastic mechanics,and the feasibility of self-closure of boreholes is theoretically analyzed.Then the conditions of borehole instability are analyzed from four aspects: mechanism of borehole instability and instability characteristics,deformation and failure characteristics and multi-stress coupling.It is concluded that the factors affecting borehole instability are coal cohesion,fluid pressure in coal seam,coal burial depth,internal friction angle and borehole diameter.Secondly,the basic parameters of No.2 coal seam in Wangjialing Coal Mine are collected,and FLAC3 D numerical simulation is used to study the relationship nephogram of vertical displacement,vertical stress distribution,plastic zone distribution and compaction stress distribution of surrounding rock under different borehole diameters.From the nephogram,when borehole diameter is 65 mm,the borehole instability-self-closure effect is the best.By establishing the steady flow equation of the pressure chamber,the relationship between the equilibrium time of the chamber and the volume of the chamber is obtained.The optimum volume of the pressure chamber of the sensor pressure measuring device is determined to be 0.141 m3.Under this condition,the equilibrium time of the chamber is about 2.3 hours.Finally,according to the theoretical research of the sensor pressure measuring device,through designing the instruments needed for the experiment and simulating the gas pressure measurement,the experiments of different drill pipe diameters and the self-closing effect of drilling holes are carried out in the laboratory.The experimental results further prove the correctness of the theory and preliminarily study the physical objects of the gas sensor pressure measuring device.This paper provides a theoretical basis for the research of gas sensing pressure measuring device,and has a certain scientific value and practical significance for reducing the cost of borehole sealing,improving the efficiency of borehole sealing and realizing remote sensing pressure measurement.