Study On The Relationship Between Void Property And Permeability Of Karst Aquifer Medium In Jinan

Void structures such as pores,fissures,pipelines and karst caves constitute the underground water-bearing system.The movement of groundwater in the water medium has diversity.The heterogeneity of karst development and the degree of high dispersion make groundwater seepage more complex.Groundwater seepage is mainly reflected in permeability.Therefore,the study of the influence of void structure in water-bearing medium on permeability can better study groundwater movement in karst areas.Taking Jinan karst water-bearing medium as the main research object,on the basis of reading domestic and foreign literatures and obtaining geological and hydrogeological conditions of the research area,this paper analyzes the structural characteristics of karst development in the research area by using methods such as field geological survey,hydrogeological drilling,CT scanning,three-dimensional reconstruction of digital cores,seepage simulation,mercury injection experiment,fuzzy analysis,etc.After processing CT scanning images for void structure extraction and mesh dissection,The seepage simulation under different void types and different pressure differences is carried out,and the hydraulic parameters and permeability of karst water medium are studied in combination with the data obtained from indoor seepage tests and mercury injection tests.The static factors and dynamic factors are combined to evaluate the permeability in the study area by using fuzzy evaluation method,which provides scientific guidance for spring conservation and has certain theoretical and practical significance.Through the above analysis and research,this paper mainly draws the following conclusions:(1)Through hydrogeological drilling and statistical analysis of original hydrogeological data,it can be obtained that the karst development in the study area is mainly composed of dissolved pores,fractures,dissolved caves,and pipelines.Karst development is characterized by vertical and horizontal zoning.The vertical surface karst is poorly developed.The shallower 60 meters are mainly Ordovician YeliFormation and Liangjiashan Formation.The karst development is between 10.92%-16.15%.The 60-160 m area is mainly the Cambrian Fengshan Formation,with karst development between 17.31% and 17.46%.The development of Ordovician karst from the surface to 40 m horizontally is mainly distributed near the discharge area of the four spring Groups in Jinan,mainly in the area of Jingshi Road.The 100-150 m Cambrian Fengshan Formation water medium karst development has a wide distribution range.(2)Through 3D reconstruction and mercury intrusion experiments,the average surface porosity is slightly smaller than the porosity in the 3D form.The error of the two porosities is less than 1.03%.The first and second members of Majiagou Formation,Liangjiashan Formation and Yeli Formation of Ordovician porosity is about 6.45%,and the porosity of the Cambrian Fengshan Formation is about 0.88%.The pores of 0.2-2mm in the pore structure account for 91.2% of the total number of pores,and pores with a diameter greater than 10 mm only occupy 0.2% of the total number of pores.(3)Through the statistical analysis of hydraulic parameters such as inclination angle,tortuosity,opening degree and roughness of the fracture structure in the study area.The Ordovician Yeli Formation and Liangjiashan Formation stratigraphic fracture development rate is 6.2%,the fracture opening is between 0.22-2.13 cm,and the surface fracture rate is mostly less than 5%,about 0.33-4.01%,concentrated in1-3%,The fissure direction is roughly the same as the groundwater flow direction in the study area,and the fissure roughness is relatively small,about 0.16 mm.(4)Three-dimensional models of pores and fissures are constructed to simulate seepage.The permeability differences of hydraulic parameters of media under different pressure difference seepage conditions are discussed,and the pressure field,velocity field distribution and permeability parameters are obtained.With the increase of pressure difference in seepage simulation,the range of fluid pressure field and velocity field gradually expands,with strong non-uniformity.Along the direction of fluid penetration,the overall velocity and pressure of the fluid tend to decrease,but pressure and velocity It is completely and evenly reduced,and the specific fluctuationis affected by the internal karst development structure.Take the Ordovician Majiagou Formation,Yeli Formation and Liangjiashan Formation as examples.The porosity in the pore structure has a certain effect on permeability,and the pore throat radius and pore connectivity have a greater influence on the permeability than the porosity.When the fracture is unblocked and the fluid flow direction is consistent with the extension direction of the fracture surface,under the uniform pressure difference,the system permeability basically remains unchanged with the change of fracture inclination and strike,and the fracture opening,roughness and length are the main factors affecting the permeability.(5)Through indoor high-pressure infiltration experiments,seepage models of pore structure,flow rate and time of fracture structure,hydraulic gradient are established.Under a single pressure,the flow rate tends to decay from large to small,and the flow rate within the pore structure fluctuates greatly.In the process of multi-group pressure infiltration,fracture flow and pore flow conform to non-linear flow laws,and the relationship between flow rate and hydraulic gradient is well fitted with power function.(6)Fuzzy evaluation method is used to quantitatively judge the permeability of the karst water-bearing system,and all indexes of static parameters and dynamic parameters of the karst water-bearing system are comprehensively considered,which are divided into poor karst fissure undeveloped permeability,normal seepage and possible dominant seepage with good karst development degree.It is calculated that the existence of better seepage conditions in the discharge area may have dominant seepage channels.Using fuzzy evaluation method to determine the dominant seepage channel in the runoff area of the karst water system,which has practical significance in accordance with the tracer test results.