Numerical Simulation Of Soil Resistivity Test On The Influence Of Different Electrode Arrangements

The resistivity method has the advantages of convenience,continuity,rapidity and nondestructiveness,and can effectively reflect the geological and environmental anomalies of geotechnical engineering.Resistivity is often used to evaluate the physical properties of soil in the field of geotechnical engineering.In some studies of resistivity test by combining geotechnical test instruments,due to the complexity of the structure of the geotechnical test device,it is impossible to directly carry out the resistivity standard test.It is often necessary to use different electrode shapes and layouts according to the actual test conditions,and this resistivity can only be called apparent resistivity.The value is different from the actual true resistivity,and the soil parameters cannot be directly quantitatively evaluated.Therefore,the quantitative relationship between the apparent resistivity and the true resistivity of the soil has become a key link in the resistivity evaluation of the physical properties of the soil and its variation.In this thesis,in order to focus on the influence of electrode arrangement on apparent resistivity and avoid the interference of anisotropic soil structure parameters on electric field,the soil is idealized as homogeneous material,and the copper rod electrode is selected to carry out numerical simulation of apparent resistivity of soil under different electrode arrangements.The quantitative conversion relationship between apparent resistivity and actual true resistivity of soil is explored,and the verification analysis is carried out in combination with electrical measurement test,so as to promote the application of nonstandard resistivity test method.The main research contents and conclusions are as follows :(1)The finite element analysis process of soil electric field and the apparent resistivity calculation method of finite element model under the specific electrode arrangement of constant current field are given,and the influence of electrode size on the apparent resistivity of soil is analyzed.(2)With the help of COMSOL Multiphysics finite element software,the numerical simulation of apparent resistivity of soil under different electrode arrangements is carried out.The results show that when the length-width ratio of soil model size and the length-width ratio of different soil model sizes are fixed,the apparent resistivity and true resistivity of soil under symmetrical arrangement and unilateral arrangement of electrodes show a linear relationship.The apparent resistivity decreases with the increase of electrode spacing.With the increase of positive electrode position,the apparent resistivity decreases first and then increases,and the change of the middle position is relatively small.(3)According to the numerical simulation results of soil apparent resistivity under different electrode arrangements,the quantitative conversion relationship between soil apparent resistivity and true resistivity is obtained.By analyzing the influence of electrode coupling effect and edge effect on apparent resistivity,the electrode arrangement range that is not affected by these two effects is given.The basic linear function relationship between true resistivity and apparent resistivity is used as the main formula,and the explicit prediction formula of soil true resistivity is established.(4)The apparent resistivity test of Na Cl salt solution and saturated sand under different electrode arrangements was carried out.The test results were compared with the formula calculation results.At the same time,the apparent resistivity test values were substituted into the true resistivity explicit prediction formula to analyze the true resistivity prediction error rate.The results show that the variation law of apparent resistivity test results is consistent with that of formula calculation results,and the prediction accuracy of true resistivity is high,but the overall prediction error rate of saturated sand true resistivity is larger than that of salt solution.It shows that the idea of establishing the explicit prediction formula of soil true resistivity is reasonable,which can provide a concise and clear method for the prediction and transformation of apparent resistivity value to true resistivity value in the field of soil parameter evaluation of geotechnical engineering.