| Guizhou Province is rich in coal resources and is the largest coal production and transfer out province in the South.It plays a pivotal role in the energy balance in the South.Because of its location in the southwest karst development zone,the mine’s hydrogeological conditions are complex,and the mine water damage problem has not been solved well.At present,many coal mines in Qianbei mining area arrange the roadway of the development system in the Maokou limestone,which is more reasonable and feasible than the coal series stratum and the Changxing limestone stratum.However,the development of Maokou limestone karst is uneven,and in the case of karst development,this will become a major hidden danger of water inrush in the mine tunnel.At this stage,the research on the mechanism of karst water inrush in the mine tunnels in the southwest region is almost blank.Related research has important practical significance.In order to better understand the catastrophe evolution mechanism of water inrush of concealed karst caves during the tunneling process,this paper takes the water inrush accident which occurred in the excavation of a main roadway in a coal mine in Tongzi County as the research object,revealing the variation law and evolution mechanism of the stress field,displacement field and seepage field under the influence of disturbance during the excavation of the overlying concealed karst caves when tunneling based on regional hydrogeological conditions,fluid-solid coupling theory,and numerical simulation methods.The relevant research results in this paper can provide scientific basis for the monitoring and early warning of water inrush in concealed karst caves and roadway during coal mining.The research mainly gained the following knowledge:(1)The karst in the Qianbei mining area is developed on both surface and underground,and the individual shape is complex.The formation of karst is striped in the horizontal direction and delaminated in the vertical direction;karst water can be divided into karst hole-karst pore water,karst pore-karst cave water,karst cave-pipe water,with different occurrence states and hydrodynamic characteristics;the development of pores in each stratum is complex,with heterogeneity and inhomogeneity in vertical and horizontal directions.Therefore,the water abundance and water permeability of various strata are also complicated,and they also have heterogeneity and inhomogeneity in vertical and horizontal directions.(2)Based on the COMSOL Multiphysics numerical simulation software,a roadway excavation model for a water inrush mine is established,and analysis can be concluded as follows: With the excavation of the roadway,the stress value of the surrounding rock between the roadway and the concealed karst cave continuously increases and gradually connects before the water inrush caused by the breakage of the relative aquifuge between the roadway and the concealed cave.The plastic failure of the surrounding rock between the roadway and the concealed karst cave gradually develops and tends to approach each other.The pore water pressure of the surrounding rock increases when it approaches the concealed karst cave,and it decreases significantly when the water inrush occurs.(3)Based on COMSOL Multiphysics simulation of nonlinear seepage flow of concealed karst cave in mine,analysis shows: The flow of water in the concealed karst cave has undergone two physical transformation processes,which are Navier-Stokes seepage(in the karst cave)→ Brinkman nonlinear seepage(in the water inrush channel)→ Navier-Stokes seepage(in the roadway).When a water inrush occurs,the fluid velocity inside the karst cave close to the water inrush channel increases significantly,and the flow velocity of the Brinkman fluid in the water inrush channel is further increased.The flow velocity increases to the maximum near the boundary between the Brinkman flow and the roadway Navier-Stokes flow.The reason is that near the contact surface of the two watersheds,the water flows into the roadway under the energy difference,causing the energy in the vicinity to drop sharply and convert the energy into flow velocity.(4)Multi-field catastrophe simulations of mine water inrush under different geological conditions are conducted,and the effects of different karst cave sizes,karst cave water pressure,and the thickness of the aquifuge between the roadway and the cave on the stability of the surrounding rock of the roadway are studied.This paper sets up five sets of numerical simulation experiments for each factor,adopts the principle of "fixing two into one," and sets up a key monitoring point between the roadway and the karst cave.Simulation analysis shows: The stress at the monitoring point between the roadway and the karst cave will undergo four changes with the progress of the excavation,which are "steady state" → "germination state" → "abrupt state" → "post stable state";the degree of influence of each factor on the excavation of the roadway from the largest to the smallest is: the thickness of the aquifuge> the size of the cave> the water pressure of the cave;when the karst cave passes through the plastic zone of the roadway,the water inrush channel may not be formed immediately.When the pore water pressure values at the monitoring points show the largest decrease during the excavation process,it is judged that the water inrush comes to the most dangerous time.Before the water inrush,the vertical stress and displacement of the monitoring points increased briefly,and the increase in vertical stress was more obvious.(5)This paper uses scientific methods such as numerical simulation calculations and quantitative analysis to reveal the changes and evolution mechanisms of the stress field,displacement field,and seepage field under the influence of excavation disturbances in the overburden karst cave during the tunneling process,provides a scientific basis for the monitoring and early warning of water inrush in concealed karst caves and mine water inrush disasters during the process of coal mining,and has great significance for the safe production and construction in mine roadways. |
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