Study On Frost Heaving And Thawing Settlement Characteristics Of Swamp Turfy Soil In Dunhua,Jilin Province

Turfy soil is a type of humus soil with exceptive engineering geological characteristics,such as high moisture content and organic matter content,high compressibility and high porosity ratio.It often exists in special marsh environment,which plays an significant role in adjusting the ecological balance of the surrounding environment.It is widely distributed in northeast China,Qinghai-Tibet Plateau,Western Sichuan Ruoergai Plateau and the lower-middle Yangtze River and other low-lying areas with vegetation development and perennial water accumulation.When turfy soil is distributed in seasonal freezing area,frost heaving and thawing subsidence will occur,which will lead to road damage,subgrade softening,reducing the highway carrying capacity and other engineering problems.In the last few years,national economic construction is developing rapidly,highway and railway construction is also developing,so it is inevitable that many new line projects pass through the seasonal frozen swamp turfy soil distribution area.In order to protect swamp turfy soil wetland and reduce the occurrence of engineering problems,it is necessary to explore the characteristics of frost heaving and thawing settlement of turfy soil,and provide a theoretical basis for engineering architectural design.Based on the National Natural Science Foundation of China project"Study on frost heaving mechanism of swamp turfy soil in the seasonal frozen region",this paper takes typical swamp turfy soil in Dunhua region of Jilin Province as the subject investigated.Firstly,the basic physical and chemical indexes of turfy soil are determined by conventional geotechnical tests.Four influencing factors including natural water content,dry density,organic matter content and decomposition degree were selected to conduct frost heaving and thawing settlement experiments on turfy soil under closed conditions at different freezing temperatures.A prediction model of frost heaving and thawing settlement of turfy soil based on ELM was established,and the conclusions were as follows:（1）According to Pearson correlation analysis,there was a significant linear correlation among moisture content,dry density,organic matter content and decomposition degree of turfy soil.Percentage of moisture was negatively correlated with dry density,but is directly proportional to organic matter content and decomposition degree.The dry density is inversely proportional to both the organic matter content and the decomposition degree.The organic matter content and decomposition degree were positively correlated.（2）There is a great difference between the moisture content and dry density of turfy soil at different depths,and the frost heave force is proportional to both moisture content and dry density,but the frost heave force will not be obvious when the dry density is too small.When the dry density of 0-0.4m soil sample is less than0.41g/cm~3,there is almost no frost heave force.With the increase of depth,moisture content increases gradually,dry density decreases gradually,and the limit value of no obvious frost heave force decreases gradually.When the dry density of turfy soil is lower than 0.25 g/cm~3at the depth of 0.8-1.6m,no obvious frost heave force occurs.（3）Turfy soil belongs to strong frost heaving soil,and the frost heaving rate has a significant proportional relationship with thawing settling coefficient.The effect of water content and decomposition degree on frost heaving rate and thawing settlement coefficient is the same,and is proportional to each other.They are both increase first and then decrease with the increase of organic matter content.In addition,the higher moisture content,the higher the unfrozen water content,the lower the temperature of frost heaving.The higher dry density is,the smaller porosity is,the higher the frost heaving rate is,and the lower the temperature required for freezing is.As for the thawing settlement coefficient,the dry density increases,which is gradually decreased first and then increased,that is,there is a critical dry density value that minimizes the thawing settlement coefficient of turfy soil.（4）The prediction models of frost heaving and thawing settlement of turfy soil based on ELM were constructed and tested respectively.The deviation between the predicted values and the measured values obtained by the model was small,and the overall fitting degree was good,which could be applied to the preliminary prediction of frost heaving and thawing settlement characteristics of turfy soil subgrade engineering in seasonal freezing region,providing some reference for practical engineering.