Modeling Of 3D Complex Soil Electromagnetic Properties And GPR Signal Analysis

Along with changes in the global climate,regional rainstorms or droughts often occur.In the process of alternating rainfall and drought,due to the difference in water shrinkage and stress conditions of various particle components in the soil,the process of dispersion and integration between the particles will occur,and a regular soil fissure zone will be formed on the macro.Soil fissure zones can cause many disasters.For example,the integrity of the slope is extensively destroyed by the fracture zone,which weakens the cementation between the soil particles,and eventually causes disasters and accidents such as slope instability and collapse.In agriculture,water and fertilizer will penetrate rapidly along the fracture zone,greatly increasing the depth and efficiency of infiltration.Finally,the water nutrients in the soil will accelerate into the deep layer of the soil,reducing the utilization efficiency of water and fertilizer by plant roots.In terms of the environment,the soil fissure zone exacerbates the degree of infiltration of pollutants and deepens the process of groundwater pollution.Therefore,studying the structure of soil fissure zone is of great significance for predicting landslide caused by rainfall,improving agricultural water and fertilizer utilization and environmental protection.This paper first introduces the connotation and genesis of soil fissures and fracture zones,and then describes the methods and principles of four kinds of fracture zone modeling,such as spatial splitting,discrete network,variogram and fractal feature iteration.Comparing the advantages and disadvantages of the four modeling methods,the fractal feature iterative method is simple and easy to operate,only need to control the fractal dimension and the iterative termination condition,and the fractal process fits the process of soil fissure generation,and also in the actual soil microscopic morphology.Strong self-similarity and fractal dimension,so the shape of the fracture zone can be simulated more simply and quickly.Combined with the generalized principle of energy minimum,this paper extends the Koch fractal curve from two-dimensional plane to three-dimensional space,then uses the three-dimensional Koch curve to model the fracture zone skeleton and uses matrix transformation to control the position and shape of the fracture zone.After modeling the fracture zone skeleton,the Bruggeman equivalent medium method is used to give the skeleton size and attribute values,which makes the simple points and straight lines expand into spatial form and has physical meaning.In the modeling of soil background,the ellipsoid hybrid autocorrelation function random medium model of small-scale non-uniformity is introduced.Then the theory and method of Markov chain model are introduced,and the Markov chain method is extended to three-dimensional space.In order to verify the correctness of the Markov chain modeling method,a three-dimensional experimental model was established using the stochastic equivalent medium method and Markov property test was carried out.Then the three-dimensional Markov chain method was used to calculate the transition probability matrix and then simulated.The comparison results showed the simulated results.Similar to the original model.In terms of numerical calculation,this paper introduces the time domain finite difference method,PML boundary absorption condition and numerical stability condition of ground penetrating radar(GPR)forward calculation.Then a three-layer model of surface soil-wet clay-bedrock was established.The soil background was established by three-dimensional Markov chain method.The three-dimensional Koch fractal curve and Bruggeman equivalent method were used to establish the fracture zone with different water content in the wet clay layer.The GPR forward calculations were carried out for the comprehensive model with different water contents,and the influence of the water content in the fracture on the waveform of the forward performance was studied.Then the time-frequency characteristic analysis is carried out,and the numerically calculated response is subjected to S-transformation(ST)to study the influence of water content on the timefrequency characteristic signal of the fracture band response.The results show that the difference between the equivalent dielectric constant of the fracture and the background is larger.The more obvious the response.Finally,the fracture zone and the depth of the interface in the response are quantitatively calculated,and the error with the model is small.Comprehensive analysis of this hybrid modeling,response calculation and timefrequency analysis method for the detection of water-bearing fracture zones in soil.Based on the measured data of ground penetrating radar in Fuyu city's soil,a complex soil model with fracture zone was established by using Markov chain and three-dimensional Koch curve.The main characteristics of the model were compared with the response of the measured response and the water content of different fracture zones.After the results were S-transformed,the fracture zone moisture content in the measured data was compared and estimated.