Liquefaction Characteristic Test Of Salt Saturated Sand Soil And Its Subgrade Application

In recent years,China's northwest region has responded to the call of the national“One Belt,One Road”strategic project,and has built many large-scale railway and highway projects.However,due to the complicated geological conditions in the northwest region,many complicated technical problems have also been encountered in the construction of the project.For example,in the construction of railway subgrade in Xitieshan,Qinghai Province to the North Hobson Salt Lake Mine,due to the wide distribution of high-salt sandy soil in the area,the salt lake area has high water content and frequent rainfall,and some high-salt sands are located all the year round.The saturated state,combined with the region's seismic intensity of 8 degrees,and salt-saturated sand will produce liquefaction under the action of earthquake,which will lead to liquefaction of railway subgrade,lateral sliding of embankment,overall subsidence of roadbed,irregular track,etc.Security risks.To this end,the liquefaction characteristics of salt-saturated sand under earthquake action,the liquefaction mechanism of salt-saturated sand and ordinary saturated sand and the influencing factors were analyzed,and the liquefaction of saturated sand under different salt contents was compared.The mechanical parameters and the deformation law of salt-saturated sandy soil subgrade under earthquake action have far-reaching and realistic significance.Due to the differences in the types and properties of saline soils in different regions,the climatic conditions are also different,and the roadbed is affected by rainwater.Therefore,there is no comprehensive and systematic study on the liquefaction characteristics of saturated sand with salt.Based on the construction of the railway subgrade of the Xitieshan to North Hobson area in Qinghai Province,the high-salt saline soil saturated area adjacent to the salt lake in the area was selected for sampling,and the salt content of the soil sample was obtained through indoor basic geotechnical tests.Basic physical parameters such as optimal moisture content,maximum dry density,gradation curve,and remodeling of soil samples,and four saturated sands containing no salt,10%salt,20%salt,and 30%salt The liquefaction characteristics of the test soil samples were tested by GDS dynamic triaxial apparatus.The axial stress curves??_a-N?and axial strain curves??_d-N?of the four soils were obtained by indoor dynamic triaxial test.,shear stress-strain curve??-?_d?,excess pore pressure ratio curve?Y-N?,dynamic shear modulus change curve?G_d-?_d?,dynamic damping ratio characteristic curve?D-?_d?,and soil resistance Liquefaction CSR curve and verification of liquefaction of salt-saturated sand Judging criteria,finally combined with ANSYS numerical simulation software to simulate the mechanical properties and settlement laws of saturated sand railway subgrade under different salt contents under seismic loading.The main research contents and results are as follows:?1?This paper analyzes the liquefaction mechanism of salt-saturated sand,and points out the particularity of salt-saturated sand liquefaction,that is,the excessive water content under the action of seismic load will cause the salt-saturated sand to be dissolved and liquefied.The synergy.At the same time,the liquefaction criterion for saturated sand containing salt is to start liquefaction of salt-saturated sand when the standard ratio of excess pore water pressure is u_d/?₃=1 and the amplitude of bidirectional strain??_d?is 5%,and in subsequent tests.Verification of its rationality.?2?According to the basic parameters of the geotechnical test,the indoor test was designed,and the salt-saturated sand,10%,20%,and 30%were mixed with salt-saturated sand,and the indoor dynamic triaxial test was carried out.The cycle number of the soil sample increases with the dynamic load,the axial dynamic stress and the dynamic strain curve are obtained.As the salt content increases,the axial maximum stress value of the soil sample decreases.The axial strain of different salt-saturated sands increases with the increase of the number of load vibrations.It is also found that the liquefaction damage caused by salt-saturated sand is longer than that of salt-free saturated sand.?3?The comparison of the excess pore pressure ratio curves of the four soil samples increases with the increase of the number of vibrations.When the pore pressure ratio coefficient reaches 1,the axial double deformation?_d of the soil also reaches 5%.The axial stress?a also reaches the maximum value.At this time,the soil conforms to the liquefaction discrimination mechanism of the salt-saturated sand,indicating that the soil reaches the initial liquefaction state.?4?Analyze the shear stress-strain hysteresis curve of the specimen.As the number of vibrations of the load increases,the dynamic shear strain?_d gradually increases,and the dynamic stress amplitude also increases.When four different salt-saturated sands are at In the pre-liquefaction stage,the shear stress and strain curves are concentrated in a very small range of variation.With the increase of the number of vibrations,the shear stress of the salt-saturated sand reaches the initial value of liquefaction,and the soil cannot continue to withstand the impact of the vibration load.Liquefaction,the area of the hysteresis loop gradually began to increase.?5?At the initial stage of vibration load,the dynamic shear modulus changes little with the increase of shear strain.As the shear strain?_d increases,the decay rate of dynamic shear modulus G_d gradually increases.Slowly,when the dynamic shear strain value is greater than5%,the dynamic shear modulus change trend gradually becomes flat,and its value is asymptotic to zero.The damping ratios of the four saturated sands increase with the increase of the dynamic shear strain.By calculating the dynamic shear of four saturated soils,the soil liquefaction resistance curve should be obtained according to the CSR value.The liquefaction resistance is:10%salt saturated sand>20%salt saturated sand>30%salt saturated sand>Saturated sand without salt.?6?Constructing four kinds of saturated sand roadbed models with different salt contents after filling and filling,and applying concrete seismic three-way wave,it is found that the displacement settlement of salty saturated sand roadbed is much smaller,indicating salt-saturated sand roadbed.Better resistance to earthquakes.Comparing the shear stress of four saturated soils,the maximum stress in the four subgrades can not reach the shear stress during liquefaction,which indicates that the subgrade is effectively reduced after the replacement.