Experimental Study And Application Of Foam Concrete For Gas Extraction Borehole In Soft Coal Seams

With the increasing depth of coal mining,the increase of in-situ stress and the decrease of coal seam permeability,gas disasters are becoming more and more serious.This poses a serious threat to coal mine safety production.Gas extraction is an effective treatment to control and prevent the gas problem.However,frequent drilling borehole circle coal body collapse and deformation after the drilling borehole forming in soft coal seam,under the influence of the factors such as in-situ stress and disturbance action.which seriously affects the effect of gas extraction.To prevent the borehole collapse in the fracture zone of stress concentration area and in the plastic zone under the influence of creep deformation in the soft coal seam,this paper proposed a new method to prevent drilling borehole collapse by using high strength and permeability foam concrete to support drilling boreholes with risk of borehole collapse.The main contents of paper are as following:(1)The mechanism of foam formation and the process of pores formation in foamed concrete was studied.And chemical foaming method was selected as the foaming method for this test by laboratory physics experiment,hydrogen peroxide as the foaming agent.(2)The single factor and multi-factor orthogonal experiment was conducted to select 12 sets of different mix ratios,and the compressive strength and permeability of the foam concrete under different mix ratios were tested by universal tester and permeability testing system.The performance change of foam concrete under different mix ratios was studied by Origin and Image Pro Plus.The optimum mix ratio with good compressive strength and permeability was finally determined.(3)The data of the bedding boreholes collapse in S5101 air return way from June to September were collected by the field test to plot the curve graph of average borehole collapse distance by Origin software.Analyzed the general rules of boreholes collapse and designed some targeted field test schemes.(4)A set of key attachment of foam concrete borehole grouting equipment is designed and produced,including casing pipe,sack and grouting pipe and so on.(5)By measuring and analyzing negative pressure attenuation,extraction mixing amount,gas concentration and extraction amount of 5 sets of boreholes control groups,the field application effect of the foam concrete with drilling boreholes is inspected.The results of this study reveal that the foam concrete for gas extraction borehole has good permeability,and can effectively support the fracture zone and plastic zone of the stress concentration zone in the borehole.It is feasible to provide support for drilling holes by using borehole foam concrete in soft coal seam,which has practical application value for the coal seam tend to occurred borehole collapse,especially the soft coal seam with high gas content.The foam concrete for gas extraction borehole has good permeability,and can effectively support the fracture zone and plastic zone of the stress concentration zone in the borehole,aiming at the soft coal seam prone to hole collapse,especially the high gas soft coal seam.