Research On The Strength Properties And Microscopic Characteristics Of Saline Soil In Area Of Zhenlai In Jilin Province

Saline soil is widely distributed in China,especially in the western region of Jilin.In west Jilin some engineering construction projects need to be built on the saline soil foundation.But the frost heave,dissolve trapped,salt expansion and many other bad engineering geological properties of saline soil have a great influence on engineering properties.In this paper,the 40 cm layer of saline soil in Zhenlai area of Jilin Province was used as the main research object,and the basic properties and strength characteristics of saline soil were studied experimentally.Combined with the micro test results,the influence mechanism of saline soil strength was analyzed.The main contents and achievements of this paper are as follows:?1?Through a field investigation and field sampling of typical areas of saline soil in Zhenlai County,Jilin Province,and then conducted a series of laboratory tests,it can be concluded that: from the material composition point of view,the granule compositions of soil samples in research area are mainly powder and clay and other fine particles,accounting for about 93%,so it is light silty clay.From the point of physical and chemical properties,the soil sample in research area is low liquid limit silty clay soil.Through testing the soluble salt content,the total salt content of saline soil is 0.4515%.Among the components,the cation is mainly Na⁺ and the anion are mainly HCO₃^-,Cl^-and SO₄^2-.Depending on the classification standard of salinization type,the salinization type of soil sample is named carbonate type.From the point of mechanical properties,the compressibility of undisturbed soil in the study area is 0.36 MPa-1,compression modulus is 5.05 MPa,so it belongs to the medium compressibility soil,and the shear strength of soil is not very great.The compressive strength decreases with the increase of soil shear strength after remodeling.The optimal moisture content of soil in the study area obtained by compaction test is 20%.This lays the foundation for the next study of the strength characteristics of saline soil.?2?In order to study the compressive properties of saline soil,three influencing factors of water content,salt content and compaction were selected,and the unidirectional high pressure consolidation test of saline soil in the study area was carried out.Select compression coefficient as a measure of saline soil compressibility and the experiment showed that: under the same salt rate and compaction degree,the compressibility of soil increases with the increase of water content,but the compressibility of soil is very low in the vicinity of optimal moisture content.Under the same moisture content and compaction degree,with the increase of salt content,the compressibility of soil reduces at first and next start to increases,and begins to increase at the salt content of salt saturation.Under the same moisture content and salt content,the compressibility of the saline soil decreases with the increase of the compaction degree.?3?In order to study the shear strength characteristics of the saline soil,three axis unconsolidated undrained shear tests with different moisture content,salt content and compaction degree were designed.Select shearing strength index to analyze the shear strength of saline soil,and the experimental results showed that: the stress-strain curve of saline soil is basically strain hardening type.Under the same salt content and degree of compaction condition,soil cohesion C and internal friction angle?decreased gradually with the increase of moisture content,but after the moisture content is more than 22%,the internal friction angle reduced greatly.Under the condition of the same moisture content and degree of compaction,the soil cohesion C decreases with the increase of salt content,and it is minimized and begins to increase when the salt content is 1.5%.Internal friction angle?decreases with the increase of salt content.Under the same moisture content and salt content,the soil cohesion C showed a trend of increase with the increase of degree of compaction.And with the increase of the degree of compaction,the growth rate of the cohesion increased gradually.Internal friction angle?is gradually increasing with the increase of degree of compaction,but the growth rate is not very great.?4?Microscopic study on soil samples with different moisture content,salt content and compaction after remodeling is carried out by mercury penetration experiment.The resuls show that the porosity is gradually increasing with the increase of moisture content of soil.With the increase of salt content,when the salt content is less than 1.5%,the porosity increases gradually,and decreases after the salt content is more than 1.5%.With the increase of degree of compaction,soil porosity is also gradually reduced.Under different conditions,the distribution of pores is dominated by small pores.With the change of water content,salt content and compaction degree,the distribution of pores has changed accordingly.?5?Scanning electron microscopy experiments were carried out on remolded soil with different water content and salt content and the qualitative analysis of the obtained image found that: the structure of the soil is mainly agglomerated structure and many illite with montmorillonite mixed layer mineral were observed.With the increase of water content,the agglomeration of the particles increases.With the increase of the salt content,the needle-like sodium bicarbonate crystals can be observed in the soil.?6?The image of the scanning electron microscope was processed by IPP software,and the data were quantitatively analyzed.The abundance,the equivalent diameter and the fractal dimension of the pore and structural unit are analyzed and studied,and the results showed that: under different moisture content and salt content,the shape of the pores and structural elements in the soil is mainly elliptical,and it is lack of nearly round and rectangular;with the increase of water content,the fractal dimension of pore and structural element gradually increased,but with the increase of salt content,it is decreasing gradually,and the fractal dimension of the pore in the soil is higher than that of the structural element.?7?The mechanism of the influence of the water content,the salt content and the compaction degree on the strength of the saline soil was analyzed by combining the macroscopic and microscopic test results.There are many factors influencing the strength of saline soil.In this paper,the effects of water content,salt content and compaction degree on soil strength are discussed.The compressive index of the soil,the compressive index of the soil,the change of the cohesion and the internal friction angle of the soil with the change of the influencing factors,shows that the compressive amount of the soil increases or decreases,The ability to increase or decrease.And in the microscopic view is the performance of the particles in the soil between the thickness of the water film,soil pore volume and the connection between the particles changes,and then the compression index and shear strength index impact.