Study On Influencing Factors And Prediction Of Unfrozen Water Content In Saline Soil In Western Jilin Province

In the west of Jilin province,there is a large area of carbonate saline soil.Due to the influence of the climate environment,and soil material composition,and so on,it also has the characteristics of typical the dispersive soil and the seasonal frozen soil,so its engineering geological properties are relatively complicated.In the freezing process of the soil,the moisture in the soil will move to the freezing direction,on the one hand,it will lead to the frost heaving of the soil,which will cause engineering problems such as channel and slope instability in the irrigation project;On the other hand,the water in the soil has carried salt to the surface and accumulated,increasing the degree of salinization,which has led to agro-ecological problems such as grassland and cultivated land degradation,and engineering problems such as road boiling and civil engineering corrosion.The above problems are closely related to the unfrozen water content.In the freezing process of the soil,the amount of the unfrozen water content determines the amount of water migration in the frozen soil.The amount of frost heave a of frozen soil and the degree of salinization are directly affected by the amount of water migration.The unfrozen water content of saline soil in Western Jilin Province is the core and foundation of the soil frost heave Mechanism and water salt transport mechanism.Therefore,it is necessary to conduct necessary research on the unfrozen water content of saline soil in western Jilin.In this paper,the carbonated soil in Zhenlai and Nong'an research areas is selected as the research object.With the support of the Key Project of International(Regional)Cooperation and Communication of the National Natural Science Foundation of China(No.41820104001),the State Key Program of the National Natural Science Foundation of China(No.41430642),and the Special Fund for Major Scientific Instruments of the National Natural Science Foundation of China(No.41627801),combined with field surveys and the previous results of the research group.Firstly,the material composition,physical and chemical properties,and pore structure characteristics of the soil samples were studied using indoor tests and other methods.After analysis,the soil in the study area is mainly composed of clay particles and silt particles,and the content of clay particles is less than that of silt particles;The mineral composition of the soil is dominated by primary minerals,and the proportion of illite/smectite mixed layer mineral and illite in the clay minerals of Zhenlai soil is the highest,and and Nong'an clay minerals have the highest relative content of illite;The water and salt content shows different change rules in different seasons;Because of the soil is carbonated saline soil,the content of sodium ions in the soil is the highest;The p H of the soil is slightly higher than 7,which is alkaline soil;In the pore structure of soil,medium and large pores are the main ones,and the proportion of micro and small pores is also relatively large.Secondly,the laboratory freezing temperature test of saline soil samples from Zhenlai research area and Nong'an research area was carried out by applying the "integrated freezing and thawing test box for rock and soil in super cold environment" independently developed.Before the test,the water content,salt content,and degree of compaction were designed as the test conditions for the freezing temperature test,and the type of salt added in soil samples is bicarbonate.After testing,the freezing temperature of soil samples in the study area was obtained.The analysis of the test results showed that,the freezing temperature of saline soil in the study area is mainly affected by water content and salt content,and the degree of compaction has almost no effect on freezing temperature.The freezing temperature is positively correlated with the moisture content,the higher the moisture content is,the higher the soil freezing temperature is,and vice versa;The salt content has an inhibitory effect on the freezing of the soil.The greater the salt content is,the lower the freezing temperature of the soil is,and the harder the soil is to freeze,and vice versa.Thirdly,based on different initial water content,different salt content and different temperature,the unfrozen water content of saline soil in Zhenlai and Nong'an research areas was studied.The suitable moisture content and salt content of the test soil were designed in advance,combined with the nuclear magnetic resonance test equipment,the soil was tested,and the unfrozen water content of the soil in the study area at different temperature points was obtained.The test results were compared with the results predicted by the thermometry method.The thermometry method is suitable for studying the change of the unfrozen water content after the initial freezing of the soil.The nuclear magnetic resonance test can obtain a complete curve of the unfrozen water content with temperature.Fourthly,the influence factors of the unfrozen water content were discussed and analyzed.By comparing and analyzing the freezing change curves of unfrozen water content,it is found that,temperature,initial water content,salt content,and freeze-thaw cycles all had a certain impact on the change of unfrozen water content in soil.The unfrozen water content is very sensitive to temperature changes.The higher the temperature is,the higher the unfrozen water content of the soil is,and vice versa.The greater the water content is,the greater the unfrozen water content of the soil is at the same temperature.The presence of the salt inhibited the freezing of soil,resulting in the higher the salt content,the higher the unfrozen water content,and the lower the temperature when the unfrozen water content tends to be stable.In the process of freezing and thawing,there is an obvious hysteresis phenomenon in the unfrozen water content of the soil.The unfrozen water content of the sample is different between the freezing process and the thawing process.The unfrozen water content of samples in the freezing process is always greater than that in the thawing process.In addition,for saline soil under any conditions,even if the temperature is reduced to-20 ?,there is still unfrozen water in the soil,and the variation range of unfrozen water content is basically stable.Finally,based on the back propagation neural network(BPNN),the adaptive fuzzy neural inference system(ANFIS)and the support vector machine(SVM)theorys,a prediction model for the unfrozen water content of saline soil in Zhenlai and Nong'an research areas was established.The results of NMR test were as the the data samples,80% of the datas were used as the training samples of the models,and 20% of the datas were the test samples of the models.The initial moisture content,salt content and temperature of the soil were selected as the input variables of the models,and the unfrozen water content is taken as the output variables of the models.Combining BPNN theory,ANFIS theory and SVM theory to establish a prediction model for soil unfrozen water content in the study area.Statistical parameters were used to evaluate the predictive ability of the models,and five-fold cross-validation was used to evaluate the usability of the three models.Through comparison,it is found that the ANFIS model and the BPNN model can be used to predict the unfrozen water content of the saline soil in the Zhenlai study area and the Nong'an study area in the west of Jilin.Through these studies,it will help to enrich the theory of salinization in Western Jilin Province,and provide theoretical basis for the restoration of ecological environment,agricultural cultivated land and the smooth development of engineering construction.