Study On Frost Heaving Characteristics Of Fine Frain Fulphuric Acid Saline Soil And Its Effect On Roadbed Deformation

With the rapid development of China’s economy and the gradual development of the western region,the construction of railway projects and other transportation infrastructure in the western region has ushered in a golden period of development.As the western region is located in the interior of the continent,the distribution of inland rivers and lake waves is more,and most of them are saltwater lakes,so the distribution area of the soil is relatively large in salt content,and most of them are saline soil.The physical and mechanical properties of saline soil are different from those of other soils,and their properties are more complex.The characteristics of saline soil are mainly the characteristics of salt frost heaving and dissolution.However,the salt frost heaving disease has caused a great impact on the safety of highway,railway subgrade and large building foundation,so it is necessary to study the salt frost heaving characteristics of frozen sulfuric acid saline soil.In order to study the deformation mechanism of sulfuric acid saline soil salt frost heaving,the construction of Railway Subgrade in Tieshan tin Hobson to the north area of Qinghai province is taken as the background.Based on the solute conservation and mass conservation laws of sulfuric acid saline soil,the influence mechanisms of temperature,sulfate content,water content and soil porosity on the frost heave of sulfuric acid saline soil were obtained.In order to further study the salt frost heaving characteristics of sulfuric acid saline soil and the contribution rate of salt heaving and frost heaving to the total deformation of soil in the process of salt frost heaving of sulfuric acid saline soil,DK35+150~DK36+750 sections of saline foundation soil samples were taken to prepare the soil samples needed for the test.Laboratory salt frost heave control group test and frozen soil triaxial test were carried out under the conditions of different temperature,sulfate content,water content and compaction degree.Combined with numerical analysis,the deformation of subgrade under natural conditions is simulated under the condition of original sulfuric acid soil and replacement of non-salt subgrade filler.The main research results are as follows.(1)Under the condition of 92% compaction degree and 16.8% optimal moisture content,the freezing temperature of fine-grained sulfate soil decreases with the increase of sodium sulfate content with the increase of salt content.With the decrease of temperature,the change trend of salt expansion rate is basically the same as that of salt frost expansion rate.When the freezing temperature is below-5 ℃,the salt expansion develops fastest,and the salt expansion rate increases little below-5 ℃.Temperature and sulfate content are the two main factors that affect the proportion of salt expansion.The lower the temperature is,the larger the proportion of salt expansion is;the higher the content of sodium sulfate is,the larger the proportion of salt expansion is.In addition,at the same temperature,with the increase of the degree of compaction,the coupling ratio and the proportion of salt heave increase.(2)Under the condition of 92% compaction degree and 1% sulfate content,the salt frost heave rate of fine-grained sulfate soil increases linearly with the increase of water content;the coupling rate of salt frost heave increases with the increase of water content,and the proportion of salt frost heave decreases with the increase of water content.Under the condition of 16.8% moisture content and 1% sulfate content,in the range of 82% ~ 92% compaction degree,the salt frost heave rate and salt heave rate of fine-grained sulfate soil show a nonlinear trend of slow growth rate and fast growth rate with the increase of compaction degree.When the degree of compaction is less than 87%,the growth rate is slow;when the degree of compaction is more than 92%,the growth rate is gradually accelerated.In addition,at the same temperature,with the increase of the degree of compaction,the coupling ratio and the proportion of salt heave increase.(3)Under the same temperature and other conditions,the triaxial compressive strength and elastic modulus of fine-grained sulphate salinized soil increase linearly with the increase of sulphate content in the range of 0.5% ~ 4% salt content.Under the condition of constant sulfate content,the triaxial compressive strength of soil sample increases nonlinearly with the decrease of temperature.When the temperature remains constant,the elastic modulus of frozen fine-grained sulphate salinized soil increases linearly with the increase of sulphate content.(4)With the same sulfate content,the water content increased from 10.5% to 16.8%,and the triaxial compressive strength and elastic modulus of the frozen fine sulfuric acid saline soil increased linearly.Under the condition of the same water content and 1% sulfate content,the triaxial compressive strength and elastic modulus of the frozen sulfuric acid saline soil increased linearly with the increase of the compaction degree between 82% and 92%.(5)The results of numerical analysis show that the subgrade under the condition of in-situ subgrade does not meet the basic requirements for the control of Subgrade Frost heave deformation,while the subgrade filled with replacement subgrade soil meets the requirements of post construction settlement of railway subgrade.Therefore,it is necessary to reduce the use of sulfuric acid saline soil as the soil for railway subgrade construction.