Expansion Characteristics Analysis Of Expansive Soil Based On Nuclear Magnetic Resonance Technology

Infrastructure in areas with expansive soil has been plagued by the impact of expansive soil disasters,and its governance is particularly difficult,with repeated disasters occurring.Therefore,research on the expansive characteristics of expansive soil is particularly important.This article takes the expansive soil in Ningming,Guangxi as the research object,and conducts a series of studies on expansive force and expansive deformation of expansive soil with different initial water content and dry density.Combined with the results of nuclear magnetic resonance and scanning electron microscopy micro-experiments,the impact of initial water content on the expansive characteristics of expansive soil was explored.The main research results obtained in this article are as follows:（1）In the nuclear magnetic resonance experiment,the signal-to-noise ratio（SNR）values obtained after testing are all greater than 10 d B,indicating that the external noise impact on the instrument is small,and the experimental results are reliable.That is,nuclear magnetic resonance technology is an important tool for studying soil.Based on the nuclear magnetic resonance technology,it was found that the optimal relaxation time of the expansive soil is the largest,followed by kaolin and the smallest for red clay.The initial water content and dry density have little effect on the optimal relaxation time of red clay and expansive soil,while they have a certain impact on the optimal relaxation time of kaolin.At the same dry density,with the increase of initial water content,the laminar structure of the soil samples at low dry density becomes smaller and produces pores,while the stacked structure of high dry density becomes thicker and the bent laminar structure almost disappears.For soil samples with low dry density,the initial water content has a greater impact on the pore size of large pores,while for soil samples with high dry density,the initial water content has a greater impact on the pore size of small pores.（2）The expansion force experiment shows that under low dry density conditions,the variation of expansion force is not significant with different water content,and the rate of increase in expansion force is slow;with the increase of dry density,the rate of change in expansion force increases.Based on the microstructure of expansive soil obtained by nuclear magnetic resonance technology after the completion of expansion force experiment,it was found that with the increase of water content,the range of T₂distribution curve increases,which is due to the compression of montmorillonite particles and the decrease of interlayer spacing,resulting in a larger range of water distribution;with the increase of dry density,the T₂distribution curve moves to the right,and the movement of the T₂distribution curve becomes more obvious with the increase of dry density,and the distribution range of the curve becomes larger.Mercury intrusion results show that dry density has no effect on pore position,while the variation of water content in soil affects the size of pore size.（3）Under the condition of the same initial dry density,the dry density during stable expansion deformation decreases with increasing initial water content,and the amplitude of the decrease in stable dry density becomes smaller with increasing water content.At the same time,under the condition of the same initial water content and dry density,the stable dry density of the soil sample decreases more in the initial stage,and the decrease in amplitude becomes slower in the later stage.When the soil moisture content is less than 10%,the expansion deformation law is similar but the results are not significant.Based on the T₂distribution curve obtained by nuclear magnetic resonance,it can be seen that under the same dry density and vertical load,with increasing initial water content,the volume of small pores in the soil increases and the volume of large pores decreases.Based on the analysis of the microscopic experimental results on the macroscopic experiment,it can be concluded that during soil deformation,pore water first decreases from the water in the large pores,and at the same time,the peak area decreases with increasing initial water content.