Study On Seepage Mechanism Of Heterogeneous Aquifer Based On Spatial Network Connectivity

The excavation of tunnels,underground engineering,mines and other engineering excavations often faces the problem of seepage in fissures,which is closely related to the seepage characteristics of the fluid in the fissures.The geometric parameters of the fissures are the controlling factors that determine the permeability of the engineering rock mass.The fracture network existing in the natural rock mass is intricate and complex.The fractures with different occurrences,different densities and other structural characteristics are not completely connected.The structural characteristics of the fractures directly affect the seepage behavior of the rock mass.Therefore,it is of great engineering significance and scientific value to preliminarily identify the connectivity of the fissures existing in the natural rock mass and explore the influence on the seepage mechanism of the rock mass.This paper first assumes that the fracture seepage is affected by the connectivity of the fracture network,establishes the relationship of the permeability coefficient based on the?theorem,and then uses indoor experiments and numerical simulations to verify how the connectivity is affected by these parameters.The main results of the research are as follows:(1)Using dimensional analysis and related theories,the main factors affecting the permeability coefficient(K_j)of the fracture model are summarized as fracture width(e),fracture intersection angle(?),fracture density(N),fracture trace length(l),and the kinematic viscosity Hysteresis coefficient(?),water bulk density(?),Then,based on the?theorem,the law of fracture seepage was obtained,and the relationship of permeability coefficient(K_j)of the fracture model was established.(2)In order to verify the rationality of the established permeability coefficient formula,the corresponding permeability coefficients under different fracture seepage models were measured by laboratory infiltration tests.According to the purpose of the test and the characteristics of the fractures,the test equipment is designed,and the indoor test models of different fracture seepage models are established,and the indoor tests of the hydraulic characteristics of different fracture structures are carried out.Tracer experiments on different fissure models show that the results of tracer tests are different in aquifer structures formed by different fissure combinations.The shape,peak concentration,peak time,and breakthrough time of the penetration curve of different aquifer structures under the same current All are different.The steady-state tests on different fracture models show that the flow state of the seepage flow in the fracture network is not only related to the fracture density,fracture orientation,and fracture inclination angle,but also has a relationship with the water inlet head of the fracture.By calculating the permeability coefficient,it can be known that the permeability coefficient of the fracture network has a positive correlation with the fracture density.The larger the fracture density,the larger the permeability coefficient;the positive correlation with the fracture direction,and the larger the fracture direction,the larger the permeability coefficient;The larger the fracture inclination angle is,the smaller the permeability coefficient is;there is a negative correlation with the fracture inlet water head.The larger the fracture inlet water head is,the smaller the permeability coefficient is.(3)Based on a large number of experimental data of measured water flow,the influence of different fracture models on rock seepage characteristics is analyzed,but the natural rock mass is a heterogeneous,discontinuous,and anisotropic network boundary.Considering the universality of the problem,this paper establishes a fracture network model with different parameters in MATLAB,and calculates the connectivity index of the fracture network model by designing an orthogonal test scheme,and studies the significance of the influence of fracture geometric parameters on the connectivity of the fracture network model.The influencing factors of the connectivity of the fracture network in the model are in order of trace length,density,inclination angle and tendency,and through multiple regression fitting method,the mutual relationship among the fracture trace length,fracture density,fracture inclination angle and fracture tendency Relationship and corresponding connectivity estimation model.