Research On The Prediction Method Of Water Inflow Of Exposed Karst Water-filled Deposits

Mine flooding is a major hydrogeological problem which affects the safety of mining.It is difficult to describe the water inflow precisely due to the heterogeneous development of karstification,which makes the hydrogeological conditions of karst-filled water deposits complicated.The traditional prediction methods of water inflow are mainly based on some empirical formulates,which have some limitations,and the accuracy is relatively poor.So that it is an important task to predict water inflow accurately for the geologists.Conduit flow and fracture flow are the major water flow of the karst fracture and cave water-filled deposit,which exposed on the surface.The movement of groundwater in karst conduit is turbulence,which does not follow Darcy's law and it is difficult to predict the water inflow.In this paper,it proposes a new model to calculate the water inflow of this kind of deposit based on the theory of water balance and the mechanical energy balance.While,fracture flow is the main kind of water flow of the karst fracture water-filled deposit,the anisotropic of the rock mass is obvious that the recharge of groundwater to the tunnel is controlled by direction.The theory of permeability tensor is taken as a guide to construct tunnel drainage model for the water inflow prediction of the karst fracture water-filled deposit which exposed on the surface.The above models have been tested in Gejiu Gaosong mine in the southeast of Yunnan Province and Huize lead-zinc mine in the northeast of Yunnan Province to verify the correctness and accuracy respectively.The main research contents of this paper are as follows:(1)Conduit flow and fracture flow composed the main kind of groundwater flow of the karst fracture and cave water-filled deposit which exposed on the surface.Due to the heterogeneity and the anisotropy of the karstic aquifer,the connectivity of karst which formed in different periods is relatively weak that may form a number of discontinuous water tables.The result of which impact the groundwater drainage scheme of the mine.In this paper,the "reservoir model" is constructed based on the theory of water balance and the mechanical energy balance,which only take the recharge and discharge of the reservoir into consideration.The karstic aquifer or karst zone is generalized as a reservoir,through analyzing the communication between different reservoirs to predict the water inflow of the tunnels which located in different reservoirs.Rainfall data constitutes the recharge of the reservoir,which exposed on the surface.While discharge is the drainage of the mineral tunnel.If there is a lower reservoir,it accept the recharge from the upper reservoir because of the energy difference of water table.Combined with the hydrogeological conditions of mine and the historical data of mine drainage,Gaofengshan ore field and Damalu ore field of Gejiu Gaosong mine in Yunnan province calculates the water inflow by double-layer reservoir model and single-layer reservoir model respectively,and the results are in good fittings.(2)The anisotropy of the karst aquifer is obvious for the karst fracture water-filled deposit.Because of the anisotropy of the karst aquifer,the recharge of tunnels which located in different directions or different strata are not like the same.Based on the the theory of permeability tensor,the "tunnel drainage model" is established on the view of microcosmic and macroscopic.In the model,the per meter section of the tunnel is taken as the object into research,the water inflow of the whole tunnel is predicted by the integral calculation of the water inflow in different directions and lengths.This model is validated in Huize lead-zinc mine in the northeast of Yunnan Province,and the fitting result is good.(3)The permeability tensor is a major factor for the "tunnel drainage model",which is usually obtained by field fracture measurement or pumping test.The statistics of the field survey shows that the directions and shapes of morphological characteristics of the surface karst depressions,the cone of depression formed by pumping test and the permeability tensor ellipsoid of the macro karst fractures which formed in the same period are similar to each of them.Thus,if the pumping test is unavailable to be taken,the permeability tensor of the karst aquifer could be obtain through analyze the statistics of the karst depressions and the calculation of karst fractures in the study area.It is concluded that the karstification affects the filling condition and the amount of water inflow directly.For the mine area,the groundwater flow of which are mainly of conduit flow and fracture flow,the water inflow could be predicted by using the"reservoir model" through analyze the characteristic of the karst development.For karst fracture water-filled deposit,the water inflow could be calculated through analyze the permeability tensor of the rock mass and the geometric properties of the tunnel,such as the direction,length,section size,etc..In a word,it is important to choose suitable model to predict the water inflow of the mine,which could provide some reference for the safety of mining.