Analysis of coal crack and permeability characteristics slotted by water jet and the effect on gas outburst
Abstract
Water jet slotting technology is an effective method of increasing coal permeability, improving gas extraction quantity and prevention mine gas dynamic disaster, and the designs of the slot parameter and layout are the key factors. We investigated the mechanical properties of slot samples and acoustic emission characteristics in different slotting numbers and angles by uniaxial loading tests. Texts indicated that, the coal strength was weakened by slotting and reduced significantly with increasing slotting numbers, and the coal was damaged easier when the slot plane was perpendicular to the axial stress. Meanwhile, exampled of Guhanshan coal mine 1603 working face, we analyzed the evolution of the coal fracture, stress and porosity when the slots were at the same level and at the different levels by numerical simulation of Particle Flow PFC2D. The results showed that, to the sample of slots at the same level, the area around the slot was damaged significantly, and the stress concentration was distributed between the adjacent slots, which was easily induced coal and gas dynamic risk. However, the stress and crack fields were distributed uniformly when the slots were at the different levels, the stress was decreased significantly and the porosity of coal was 1.5 times high than the original value.References
Huang B.X., Liu C.Y., Fu J.H., Guan H. (2011). Hydraulic fracturing after water pressure control blasting for increased fracturing. International Journal of Rock Mechanics and Mining Science. Volume 48, No.6, pp. 976-983.
Shen C.M., Lin B.Q., Meng F.W., Zhang Q.Z., Yang W., Zhang L.J. (2012). Induced drill-spray during hydraulic slotting of a coal seam and its influence on gas extraction. International Journal of Mining Science & Technology. Volume 22, pp. 785-791.
Li X.H., Wang J.S., Lu Y.Y., Yang L., Kang H.M., Sun J.J. (2000). Experimental investigation of hard rock cutting with collimated abrasive water jets. International Journal of Rock Mechanics and Mining Science. Volume 37, No.7, pp. 1143-1148,.
Lu Y.Y., Liu Y., Li X.H., Kang Y. (2010). A new method of drilling long boreholes in low permeability coal by improving its permeability. International Journal of Coal Geology. Volume 84, No. 2, pp. 94-102.
Lu T.K., Yu H., Zhou T.Y., Mao J.S., Guo B.H. (2009). Improvement of methane drainage in high gassy coal seam using waterjet technique. International Journal of Coal Geology. Volume 79, No. 1-2, pp. 40-48.
Lu T.K., Zhao Z.J., Hu H.F. (2011). Improving the gate road development rate and reducing outburst occurrences using the waterjet technique in high gas content outburst-prone soft coal seam. International Journal of Rock Mechanics and Mining Science. Volume 48, No.8, pp. 1271-1282.
Cundall P.A.,PFC2D user's manual (Version 3.1) (2004). Minnesota: Itasca Consulting Group Inc.: 15p.
