Experimental Research On Pore Characteristics And Strength Characteristics Of Saline Soil In Area Of Qian'an

The western part of Jilin Province is a typical soda saline soil area in China,and it is also a seasonal frozen soil area.The hot summer,cold winter,climate change and special topography in this area will lead to the migration of water and salt in the soil,thus causing soil salinization disasters.In recent years,the degree of salinization in Western Jilin has been increasing,which has caused great harm to local irrigation projects,such as large deformation,low strength,poor stability and so on.Porosity of soil is an important factor affecting engineering properties such as soil moisture migration and slope stability.Deformation,permeability,slope stability and foundation bearing capacity of soil can be directly or indirectly expressed by soil porosity.It can be seen that the study of the pore characteristics of saline soil in Western Jilin Province and the variation of pore under different conditions can further explain the strength of the soil in this area from the micro-point of view.Therefore,this paper takes the saline soil in Qian'an area,a representative area of Western Jilin Province as the main research object.The basic properties,pore characteristics and strength characteristics of saline soil are studied experimentally,and the strength characteristics of saline soil are analyzed from the point of view of pore changes.The main contents of this paper are as follows:?1?By investigating the physical geography and climatic characteristics of the study area and analyzing the causes and distribution of the local saline soil,it can be seen that the formation of saline soil in the study area is the result of the interaction of natural factors such as special topography and climate conditions with human activities.?2?Field investigation and sampling were carried out to determine the basic properties of saline soils with different depths of 0⁸0 cm in Qian'an area.Natural density and water content increased with depth,and a turning point occurred at the depths of 30⁵0 cm.Through particle analysis experiments,the grain size components of soil samples with different depths are obtained.The content of silt is the highest,followed by clay,and the content of sand is the lowest.They are all silty clays.The mineral components are mainly primary minerals.The content of soluble salt in the sampling points ranged from 0.52%to 0.67%,and decreased with the increase of depth.Na⁺is the main cation,HCO₃^-is the main anion,and the saline soil type is medium carbonate saline soil.?3?Mercury intrusion tests were carried out on saline soils of 0⁸0 cm depth in the shallow surface of the study area,and the measured porosity increased with the increase of depth.The pore distribution of saline soil in the study area has fractal characteristics.The fractal dimension D of the pore decreases with the increase of depth,which indicates that the complexity of the pore decreases with the increase of depth.?4?According to the characteristics of soil under different natural conditions,soil samples with different water content,compactness and salt content and different freezing and thawing cycles were selected to conduct mercury injection experiments,and the pore characteristics of saline soil in Qian'an area under complex conditions were analyzed.The results show that:When the water content is low,the porosity decreases with the increase of water content;when the water content is high,the porosity increases with the increase of water content,and the water content at inflection point of different pore index changes is 22%.When the salt content is less than 1.5%,the porosity increases with the increase of salt content,and then decreases when the salt content is more than 1.5%.The turning point of pore characteristics is 1.5%salinity.With the increase of compactness,the porosity decreases gradually,the number of smaller pore increases,the number of larger pore decreases,and the fractal dimension D of pore increases with the increase of compactness.The change of pore characteristics is non-linear with the increase of freezing and thawing cycles.After the first freeze-thaw cycle,the indexes change significantly.The porosity increases greatly,while the fractal dimension D decreases greatly.Then the porosity increases and the fractal dimension decreases.After the tenth freezing and thawing cycles,the indexes tend to be stable.?5?The unconfined compression strength tests of the remolded soil samples under the above different conditions were carried out.With the increase of water content,the unconfined compression strength decreases gradually.When the water content is lower than 22%,the strength decreases slowly,and when the water content is higher than 22%,the strength decreases rapidly.When the salt content is less than1.5%,the unconfined compression strength gradually decreases with the increase of salt content.When the salt content is higher than 1.5%,the unconfined compression strength gradually increases with the increase of salt content.With the increase of freezing and thawing cycles,the unconfined compression strength decreases gradually until it stabilizes after 10 cycles.?6?From the point of view of pore,the change characteristics of mechanical strength of saline soil are analyzed.The change of strength and pore characteristics of saline soil is affected by many factors.Under different conditions,the change of unconfined compression strength with the change of porosity presents different rules.The influence factors of unconfined compression strength of saline soil are analyzed by grey correlation entropy.The results show that water content has the greatest influence on unconfined compression strength,followed by salt content,and the number of freezing and thawing cycles has the least influence on unconfined compression strength of saline soil.