| Intelligent compaction(IC)technology is widely used in subgrade construction,and its development has brought great convenience for high-speed railway construction.With the wide application of IC,It is found that moisture content affects the accuracy of intelligent compaction,so the introduction of real-time moisture content test is of great value to improve the accuracy of intelligent compaction test.However,there is still a lack of relevant continuous testing theory and method.Resistivity method is considered to be an effective solution,but it is not clear about the testing depth of moisture content in layered subgrade or the functional relationship between resistivity and moisture content when considering stress field.Therefore,this paper uses the numerical calculation method to analyze the influence depth of electric field when considering the influence of stress field and water separation field by simulating the water content test model under the coupling effect of water force electric field.The coupling mechanism of water field,stress field and electric field in the continuous compaction process of subgrade is studied,which is intended to provide effective theoretical support for IC moisture content test.The main research contents and achievements are as follows.(1)Through the establishment of a three-dimensional model,the influence of electrode length,spacing,upper layer thickness,upper and lower layer resistivity,reflection coefficient and contact resistance between electrode and soil on apparent resistivity is explored.The results show that when the h/L of symmetrical four electrode method is greater than 0.8,the apparent resistivity can basically reflect the resistivity of upper soil,that is,the maximum effective influence depth of current is 0.8Lwhen the current electrode spacing l device is used to test layered soil,which provides theoretical support for accurate analysis of subgrade water content distribution.(2)Based on the control equations of solid mechanics module and groundwater flow module in COMSOL and the control equations of electric field applicable to layered soil,the mechanism of two-way coupling of two fields is expounded and the basic equations of two-way coupling are proposed.By modifying the constitutive equation of physical field in the module,the water field and stress field are coupled bidirectionally and unidirectionally with the electric field.(3)Based on the control equations of solid mechanics module and groundwater flow module in COMSOL and the control equations of electric field applicable to layered soil,the mechanism of two-way coupling of two fields is expounded and the basic equations of two-way coupling are proposed.By changing the function relation of source term Qm in water field to couple the influence of stress field,the influence of water field is coupled by subtracting pore water pressure from three normal stress calculation formulas in solid mechanics module,so as to achieve the bidirectional coupling of water field and stress field.The influence of water field and stress field on electric field test is realized by changing the resistivity relation of material properties in electric field module.(4)The resistivity method was used to analyze the roadbed filler samples after the external load was stabilized.In order to explore the problem of the apparent resistivity characterizing the moisture content distribution in the roadbed compaction process,the roadbed compaction process test under the multi-field coupling action was established.model.By analyzing the changes of subgrade porosity,water content and apparent resistivity changes,the results show that the change of filling resistivity-water contentporosity in the subgrade compaction process conforms to the binary linear regression function.This model provides theoretical support for measuring the distribution of water content of subgrade using resistivity in the process of subgrade dynamic compaction,and lays a theoretical basis for the development of IC water content test. |
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