Study On Pressure-relief In The Remote Lower Protective Layer And Instability Of Surface Borehole Under Mining

Huainan mining area is a typical representative of high gas concentration and complex geological condition mining area. The method surface boreholes extracting gas from pressure-relieved seam have succeeded in several coal mines. Taking the Ding-ji and Gu-qiao coal mine as the survey object, combining theoretical analysis, numerical experiment with engineering practice, this paper studied the pressure-relief deformation law of the coal and rock mass using the remote lower protective seam exploitation method, and the stability analysis of the surface borehole, special reinforcement measures and the three-dimension extraction engineering practice with pressure-relieved seam surface extracting boreholes and surface extracting boreholes. Using the software FLAC3 D, this paper simulated and analyzed the exploitation pressure-relief deformation laws of the protected 13-1 coal seam and the coal and rock mass above theremote lower protective 11-2 coal seam, the permeability evolutionary law of the protected seam. This paper also simulated and analyzedthe compression and shear failure responding mechanism of the surface borehole casing cementing deformation. Taking coal seam strike as infinite radius, building a model along the coal seam inclination, this paper simulated deformation law of the surface boreholein different locations in the advancing process of the working face, revealed the failure characteristics of the boreholes under the effect of the extraction, chosed the reasonable locations of the surface borehole and adopted the G-glass oilwell cementing method to avoid the casing fracture.Engineering practice in thesurvey region showed that, three-dimensional gas extractionmethod used in Gu-qiao and Ding-ji coal mine,such as surfaceborehole,high pumping lane in underground working face,strike borehole,goaf pipe laying,bedding borehole and boreholesthough seams from bottom pumping lane, madethe gas extraction rate in the working face reach 47.8 ~ 87.5%. Surface boreholes gas extraction effect evaluation method in Huainan Mining area is raised.Through the evaluation criteria it is successful in Ding-ji surfaceboreholes, while it is a failure in Gu-qiao surface boreholes. It is suggested to use the G-class oilwell cementing method to improve the stability of surface boreholesin Gu-qiao coal mine.