| This paper studies the evolution of karst aquifer system in the case of rainfall infiltration using the finite difference numerical simulation techniques, as well as the impact of different rainfall to the development of karst aquifer system. In summing up the previous research on the karst aquifer system to build a conceptual model, the range of assumption model in the study area is a complete 2200mⅹ800m carbonate rock, the left vertical boundary and the right vertical boundary and the bottom boundary of the model is impermeable boundary, the top boundary of the model is rainfall infiltration boundary, and assume the rainfall infiltration coefficient is 0.3, in the middle of the model is a surface of river, the head is 600 m. In order to make the model to be more straight and reliable, using the Monte-Carle method to generates two random fractures to represent the actual rock fissures, for the large-scale faults directly enter the coordinates of the original crack and crevice width and other parameters. When the model numerical calculate, it is assumed that the fracture in this model is two-dimensional smooth parallel plates, the movement of water in the fracture obey the cubic law, and according to the results of previous experiments, when Re> 500 cubic law is corrected, then Cracks in the network nodes to establish the flow of water balance principle of linear algebraic equations, and solving equations using iterative method. When the head value is obtained for each node in the fracture network karst aquifer system, assuming that in a time step in the karst aquifer system the head of fracture network nodes is stable, which can be the basis of experimentally derived carbonate Palmer karst erosion empirical formula to solve the karst aquifer system of fissures dissolution rate, and after a certain period of time the new fissure gap width after the dissolution step. When Obtains the new fracture aperture, the head can be re-calculated, and in turn to calculate the dissolution rate of fractures. In addition, compared the numerical solution with the theoretical solution, the results proved the reliability of the program.This study simulates the differences corrosion phenomena due to uneven fissures in karst aquifer system, the simulation results of the model reproduce the self-evolution of karst aquifer system at different stages, and gives quantitative data in dissolution process of the two karst springs exposed to the model’s right boundary and the evolution of the aqueous medium. After 10,000 years of erosion, the rate of flow from springs increased from an initial 0.45 ml / s to 9e3 ml / s at 6100 year, and after 6100 year the spring drainad, the 2nd springs flow from the initial 0.33 ml / s increased to 2.6e5 ml / s at 10000 year, the average fracture width is increased from 0.1mm at 0 year to 0.813 mm at 10000 year. During the simulation, found that the participation is positively correlated with the maturity rate and evolution rate of karst aquifer system, the dissolution of karst aquifer system mainly occurs around in the sources and sinks of the water table, it is not developed in the deep of karst aquifer system, and the dissolution rate of different group fractures in different parts of the karst aquifer system is different, this is mainly made by the media field and the hydraulic gradient and atmospheric precipitation and other factors. |
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