| Guizhou Province,as a large coal producing province in Southwest China,plays an important role in the development and utilization of coal resources in China,so it is a significant work to ensure its safety in production.Currently,the developing system of roadway in many coal mines in Qianbei mining area of Guizhou Province is arranged in the carbonate strata adjacent to the coal seam,which can effectively avoid the shortages of roof support,roadway maintenance,gas outburst and other unfavorable factors for construction safety caused by arranging excavation roadway in the coal seam strata.And this is a more reasonable and feasible roadway layout method.However,due to the wide distribution and heterogeneity of karst in carbonate strata,once it forms a hydraulic connection with water-conducting structures,it will become a major hidden danger of water inrush in excavation roadway.Nowadays,when the roadways are arranged in the extremely developed karst limestone in the northern Guizhou mining area,there is almost no research on the water inrush mechanism from karst water-conducting fault.Therefore,under the special mining layout mode of Qianbei mining area,the research on water inrush and thickness for preventing water inrush from fault has practical significance for revealing the mechanism of fault water inrush disaster and mine water disaster prevention.In this study,by taking the water inrush accident from fault occurred in the process of coal mine roadway excavation in Qianbei mining area as a research object and based on the regional geological background,theoretical analysis,numerical simulation,multiple regression and other methods,the evolution characteristics of water inrush disaster of karst water-conducting fault under the effect of fluid-solid coupling in the process of roadway excavation were analyzed,and the changing laws of physical fields of stress,displacement,seepage and so on in surrounding rocks were also revealed.Besides,the influence of different factors on the thickness for preventing water inrush from faults was concluded and the prediction model of the thickness for preventing water inrush was constructed.Achievements in this study are as follows:(1)The geological environment of water inrush disaster from fault studied in this paper is mainly composed of two parts.One is that its own characteristics as a tensile fault create good geological conditions for the occurrence and migration of groundwater,and also favorable conditions for groundwater's supply and storage as well as karst development;Secondly,the karst around fault are well developed,which makes it able to receive various sources and forms of supply,and this is a favorable external condition for the occurrence and migration of groundwater.Due to the characteristics of water conductivity and abundance of the target fault,once the water-rich fracture zone of the water-conducting fault is exposed in the panel of roadway excavation,water inrush disaster will easily occur.(2)By adopting the numerical simulation software,the catastrophic process of water inrush from karst water-conducting fault in excavation roadway under the effect of fluid-solid coupling is presented.By analyzing the evolution law of multi physical fields in water-resisting surrounding rock and in fault fracture zone's surrounding rock,the catastrophic mechanism of water inrush from fault is revealed.Research results show that when there is a karst water-conducting fault in front of the excavation panel,the water inrush process of the fault has relatively obvious characteristics of stages,precursors and multi physical fields under the disturbance of roadway excavation.And the water inrush stages can be divided into four statuses: "stable status ","developing status","mutation status" and "post stable status".The precursory characteristics of water inrush are as follows: with the roadway excavating,before the water inrush is induced by the breaking of the water-resisting rock between the roadway and the fault,the stress value of the surrounding rock increases slightly and then decreases rapidly,and the stress concentration area of the front section of the roadway is gradually connected with the stress concentration area of the fault,and the plastic damage of the surrounding rock between the roadway and the fault is gradually developed and connected with each other.The vertical displacement of the roof and floor increases to the maximum value in different directions.And the pore water pressure of the surrounding rock decreases gradually in the process of approaching the fault.When water inrush occurs,the pore water pressure of the surrounding rock in the fault fracture zone decreases sharply.In addition,each physical field presents certain characteristics in the process of water inrush,such as the stress redistribution around the roadway affected by excavation.Specifically,the unloading of the surrounding rock of the roof and floor forms a stress reduction area,and the surrounding rock at both ends forms a stress concentration area.Moreover,when the excavation is close to the fault,the stress concentration of the front end of the excavation is easy to be superimposed with the stress concentration of the fault fracture zone,resulting in the increase of the stress concentration,which makes the surrounding rock near the fault more prone to instability.Besides,the negative displacement of surrounding rock of roadway roof and positive displacement of surrounding rock of roadway floor are produced.At the same time,the "shielding" effect of the fault makes the rock near the roadway more sensitive to excavation disturbance than the one near the other side,while the deformation and failure of the rock far away from the excavation panel has obvious hysteresis,and the sensitivity of each field of the surrounding rock to excavation disturbance can be arranged as: pore water pressure field > stress field > vertical displacement field.(3)The analysis of the non-linear seepage process of water inrush from karst water-conducting fault in excavation roadway shows that the flow of water in excavation roadway is mainly divided into Brinkman non-linear seepage in fault fracture zone and surrounding rock fracture zone(water inrush channel),and Navier Stokes seepage in excavation roadway.The variation of water pressure is characterized by continuous decrease along the process.When water inrush occurs,the velocity increases from the top of fault fracture zone to the entrance of water inrush channel.The velocity of Brinkman fluid in water inrush channel further increases,and the velocity increases to the maximum near the junction of Brinkman flow and Navier Stokes flow.(4)Based on the developing mode of excavation roadway in Yulongshan formation limestone aquifer in northern Guizhou mining area,considering the influence of the dip angle of fault,the height of roadway section,the water pressure of fault,the depth of roadway and the grade of surrounding rock on the thickness for preventing water inrush from fault in excavation roadway,orthogonal experiment is designed,and the prediction model of thickness for preventing water inrush is obtained by numerical simulation and multiple linear regression.Results show that the order of influencing factors is as follows: the water pressure of fault> the grade of surrounding rock > the depth of roadway > the height of roadway section> the dip angle of fault.Specifically,the grade of surrounding rock,the water pressure of fault and the depth of roadway have significant influence on the thickness for preventing water inrush.And the thickness for preventing water inrush decreases with the increase of the dip angle of fault,decreases with the increase of the height of roadway section,increases with the increase of the water pressure of fault,increases with the increase of the depth of roadway,and decreases with the increase of the grade of surrounding rock.Compared with the standard,the prediction model of the thickness for preventing water inrush obtained by numerical simulation and multiple linear regression has higher accuracy and certain superiority. |
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