The Prediction Of Mine Inflowfrom Open-pit To Underground Mining In Yanqianshan Iron Ore Mine

Yanqianshan Iron Mine was set up in 1960. In order to satisfy the economic demandand simultaneously meetthe safety requirements.The mining method of Yanqianshan Iron Mine was transformed from open-pit tounderground mining in 2012. With further mining operation and underground roadway excavation, the influence of tunnel gushing water on engineering operationis increasing. Throughdatacollection, hydrogeologicalinvestigation, exploration, and theanalysisofhydrochemistry, this paper makes a thorough analysis of the hydrogeologicalcondition of the Yanqianshan Iron Mine,finds out the fault structures which havemuchinfluenceongroundwatermovementandevaluatesthe hydraulic connection of groundwater. Based on the aforesaid and alsoonVisualMODFLOW,thispaperbuildsahighly reliable 3D groundwater simulationmodel of the study area. By the numerical analysis,the underground flow field was analyzed, and the source of tunnel gushing waterwas revealed.The model also predicted the water inflow valueunder future mining. All the results can provide the basis and reference for waterproof and drainagemeasuresof mine water disaster. The main conclusions are as follows:(1) The main aquifers of the study area are the Quaternaryporous aquifer which is around the stope, and the fracture aquifer of basement rock. Phyllite and quartzite are regarded as relatively impermeable layers. They restrict the flow of groundwater.And the analysis mentioned above areverified by using RQD method. The hydraulic conductivity of fault F19 and fault Fm-1 which cut the fracture aquifer areof good value. This two faults strongly control the enrichment and movement of groundwater.(2)Meteoric water is the main source of groundwater in the study area. Some of it infiltrates intoQuaternary aquifer and becomes pore water whilst some of it infiltrates intothe basement rock through the cracksand becomes fissure water. The pore water in Quaternaryaquifer has hydraulic connection between the fissure water in the fracture aquifer of basement rock and the relatively impermeable layer to various degrees. This degree is mainly controlled by the development level of structural fracture and the property of filling material of the fault. Mining and underground roadway excavation can cause water-guiding cracks to appear. These cracks increase the connectivity betweendifferent groundwater bodies.(3)Running the 3D groundwater simulationmodel of the study area,the underground flowfield after underground roadway excavation can be estimated.Itisrevealedthatgroundwater level falls significantly near the undergroundroadway. By adding particles into the model to finding out the source of tunnel gushingwater, the numericalresult confirms the theoretical analysis. The water in the tunnel which is around or in thefracture aquifer mainly comes from the water in this aquifer. However, the tunnel which is in the relative impermeable layers and far from the aquifer(especially the one at the periphery oftunnels) can be seen as a preponderance flow path in the layer. The ground water in the relative impermeable layers willinflow into thetunnelconstantly. Groundwater level becomes stable after simulating 5 years, and the result shows that the tunnel discharge is 81016m3/d. It is suggested that the prevention measures for tunnel gushing water should included ground prevention measures and underground prevention systems.Tunnel gushing water is discharged to the surface through the step-by-step drainage system, and it can be integrated used after proper treatment.