Mechanical Test On Salinized Silty Soil Of Binhe Subgrade

This paper is in the research background of the uneven settlement,swelling,cracking and other problems for Binhe subgrade in somewhere.Through a series of mechanical test on the salinized silty soil of its subgrade,it is hoped that the local understanding of the engineering properties of salinized silty soil can be improved,and the experimental basis can be laid for the study of the causes of pavement diseases and the later treatment.Taking consolidation pressure,drainage condition,loading mode and salt condition as the experimental variables,the basic physical properties test,triaxial compression test and cyclic load test were carried out,and the mechanical properties were researched.In addition,the effects of salt on mechanical properties of silt were compared in detail.The main test results are summarized as follows:(1)Study on basic physical properties,conservation and preparation of soil samples.Through the test,the optimum moisture content determination,liquid plastic limit,particle size distribution analysis and determination of salt content,it is concluded that the optimal moisture content of the salinized silty soil of Binhe subgrade is 22.1%,the maximum dry density is 1.58g/cm,the liquid limit is 27.58%,the plastic limit is 20.13%,the particle content greater than 0.075mm accounts for 14.0%of the total weight,the particle content less than 0.005mm accounts for 7.1%of the total weight,and the salt content is 2.93%.Therefore,Binhe subgrade saline silt belongs to medium chlorine saline silt.In the curing process of soil sample,the target moisture content of soil sample is configured with deionized anaerobic water based on the optimal moisture content obtained from the test on the basis of air drying,crushing and screening.In the remolding process,stratified compaction is adopted,and the contact surface of each layer is fully shaved to ensure the consistency of the sample.(2)Tri-axial consolidated undrained shear test and tri-axial consolidated drained shear test.Some phenomena were found after sorting out the triaxial compression test data,the consolidated undrained stress-strain curves of salinized silty soil and salt-washed silty soil show strain hardening type,while the pore water pressure first increases and then decreases.However,in the consolidated drained test,the stress-strain curves all belong to the slightly softening type,and the volume variables also show obvious peaks.Under the same condition,with the increase of consolidation pressure,the deviatoric stress corresponding to the same strain increases,and the pore pressure or volume strain also increases.According to the triaxial compression test,compared with salinized silty soil,the strength of salt-washed silty soil is slightly lower and the dilatancy trend is obviously weakened.(3)Cyclic triaxial test.It can be seen from the cyclic load test results of salinized silty soil and salt-washed silty soil that with the increase of consolidation pressure,the anti-deformation ability and dynamic elastic modulus of the sample are also increased.When the consolidation pressure is the same and the dynamic stress amplitude is different,with the increase of the dynamic stress amplitude,the vibration number required for the specimen to be destroyed is less,and the pore water pressure also increases faster.By comparing the cyclic load tests under different salinity conditions,it can be concluded that under the same test conditions,the required vibration number of the salt-washed silty soil sample when it reaches a certain strain or pore pressure is obviously higher than salinized silty soil.The dynamic elastic modulus of salt-washed silty soil is smaller than that of salinized silty soil when the strain is small,with the increase of strain,the dynamic elastic modulus of salt-washed silt is gradually larger than that of salinized silty soil,but its damping ratio is less than salinized silty soil.It can be seen that consolidation pressure,dynamic stress amplitude and salt all have a significant impact on the strength of silt.The increase of consolidation pressure is helpful to increase the shear strength and dynamic elastic modulus of the soil,reduce the energy dissipation of the soil,and make the stress wave more easily spread in the soil,thus strengthening the strength of the soil.However,the increase of dynamic stress amplitude will make the soil more prone to deformation,and the pore water pressure in the soil will be more difficult to dissipate,accelerating the liquefaction of the soil and making the soil more prone to failure.The increase of salt content reduces the dynamic elastic modulus of soil,and at the same time makes soil more prone to dilatancy and water absorption,aggravating the development of strain and pore water pressure.