Rational Protection Range Of Lower Protective Layer And Application In Pressure-relief Gas Extraction

Exploitation of protective seam as a principal and effective measure for avoiding gas and coal outburst has received increasingly attention due to the severe degree of gas dynamic disaster. The present study utilizes fundamental theories such as elastic mechanics, percolation mechanics, rock mechanics, and the like to research on stress distribution, expanding deformation, the pressure-relief and protective range of protected seam, the law of pressure-relief gas flowing and the method of pressure-relief gas exploiting of upper coal and strata after the long distance protective seam exploited, using the following means: theoretical analysis, similar simulation, numerical value simulation and so forth. The results can provide the crucial reference for exploitation of protective seam as well as pressure-relief gas extraction.This dissertation analyzes the state bearing the force of upper coal-rock mass, yields the expressions of stress and squate with respect to the upper protected seam. Based on theoretical analysis, similar simulation, numerical value simulation and observation on the spot, the study concludes the laws of stress distribution and expanding deformation regarding the oblique working face of upper protected seam. The pressure-relief effect is obtained in the range of normal projection as regards the protected seam projecting roadway and wind roadway of protected seam's working face, stress in the central section of oblique working face with a dramatically decline and a little change in the two sides of coal pillar. Also, coal seam occurs in expanding deformation. In particular, the central section of working face deforms a lot and two sides relatively small. The relative pressure-relief guide line of coal mass between the completely pressure-relief boundary (i.e. certain boundary of pressure-relief angle) and the normal projection of pillar edge(called oblique extending area) satisfies the request of protective seam exploiting. The area The normal projection between pressure-relief boundary and edge of coal pillar. This demonstrates that the expanding area still lies in its protected range. The widths of working faces regarding protective seam and protected seam are the similar with each other, i.e. inclining pressure-relief the angle can occur in change from acute angle to right angle 90°.The paper presents the laws of stress change and expanding deformation with regard to the working face of upper protected seam, adopting simulation test, numerical value simulation and observation on the spot and so on. Along direction of working face, the area can be divided into four sections,namely original stress area, concentrated stress area, pressure-relief area and gradual resuming area. All the pressure-relief effect is obtained in the range of normal projection which the gob along working face of protective seam projects protected seam. In the protected seam with the range of 56°direction of pressure-relief angle, terrestrial stress falls and expanding deformation occurs to a great extent in coal. The terrestrial stress of coal mass, which is between the completely pressure-relief boundary (i.e. certain boundary of pressure-relief angle) and the normal projection of pillar edge(called oblique extending area), declines and coal seam occurs in expanding deformation The expanding deformation satisfies the technique guide line, that is, pressure-relief angle can give rise to about 90°from 56°.As for long distance protected seam, this study, associating with fracture development characteristics of long distance upper protected seam, surveys the characteristics of gas flowing and influx, and found the methods of pressure-relief gas extraction and relative parameters. Pressure-relief gas extraction of upper protected seam mainly involves two ways: extraction from the net-like floor roadway to penetrating borehole and drilling extraction on the floor. The current study carries out an application test on exploitation of long distance lower protective seam in PanSan Coal Mine, HuaiNan, reduces the gas content of upper protected seam, eradicates the disaster of outburst coal seams and realizes their exploitation safely and effectively. According to the results of examination, relative expanding deformation is 20.74‰, permeability coefficient is 2592 times, the rate of gas extraction reaches 62%, gas pressure falls from 4.1MPa to0.51MPa and gas content from 10m3/t to 3.8m3/t after the deformation stabilization of upper protected seam C13 in PanSan Coal Mine, HuaiNan. In addition, results have a reliability and rationality applying the ways of the theoretical analysis, similar simulation numerical value simulation, etc.