Theoretical And Experimental Study On The Resistivity Method In Testing Unfrozen Water Content Of Frozen Soil

The unfrozen water content of frozen soil is a key physical quantity that affects the design,construction and service characteristics of engineering in cold region.How to accurately and efficiently determine the content of unfrozen water in frozen soil is one of the key scientific problems to be solved in cold region.To solve the above problems,a new method for testing unfrozen water content based on the change of frozen soil resistivity is proposed in this paper.The main contents include:1.The theory of "pore passage weakening effect"is proposed to explain the change of permafrost conductivity characteristics,and the theoretical model for testing the content of unfrozen water is deduced;2.Verify the rationality of the theoretical model based on NMR technology and resistivity testing equipment;3.Extended the theoretical model,proposed a method to quickly calibrate the theoretical test model and carried out experimental verification.The research content of this paper provides a new idea for the analysis of permafrost conductivity characteristics and a new method for the measurement of unfrozen water content in cold region engineering.In view of the existing research on permafrost conductivity mechanism and permafrost resistivity affected by liquid water related theoretical research lack of problems,the "pore channel weakening effect" theory to explain the permafrost conductivity mechanism.In addition,it was found that the loss of liquid water in the soil in any form would affect the electrical conductivity of the soil.The general law of water evaporation in soil under drying condition is summarized.It is found that the physical process of liquid water drying evaporation in conventional soil is similar to the physical process of unfrozen water phase turning into ice in frozen soil.In view of the problem that the soil resistivity model does not consider the influence of the change of unfrozen water content on the soil resistivity,this paper firstly considers the change rule of soil resistivity under the successively frozen state of free water and combined water in the unfrozen water of frozen soil,and deduces the resistance expression of micro-element representing four different unfrozen water content.Considering the general law of soil freezing process,including the comprehensive influence of water ice phase change and water transfer,the method of stratified integration of macroscopic frozen soil resistivity in different freezing stages is proposed.Based on the derived theoretical model of unfrozen water content and the related research results of previous scholars on the conductivity characteristics of soil,water and ice,a theoretical model to express the correlation between unfrozen water content and resistivity of frozen soil by power function is proposedValidation works were carried out by using NMR and resistivity testing device were tested for large,medium and small three kinds of different particle size of the soil,it is concluded that the clay,silt and sand not frozen water with conductive particles in the threshold of directional mobile channel are 17%,14%and 13%respectively,which is not frozen water content is lower than the threshold,the conductive channel of soil weakening change,in turn,affects the frozen soil resistivity,the test results verify the validity of the theoretical modelIn order to expand the theoretical model for more efficient application and field test,the correlation between the resistivity of soil in the drying state and the content of liquid water was proposed to characterize the correlation between the resistivity in the frozen state and the unfrozen water.Selection for large,medium and small three kinds of different size of clay,silt and sand,to carry out the drying conditions of soil resistivity and the relationship between residual water content determination,and compared the drying and freezing liquid water content in the two soils change on the influence of soil resistivity,the results found that clay and silt contrast result has higher anastomotic,sandy soil test data comparison show the certain error.