Study On Static And Dynamic Characteristics Of Improved Silty Clay In Seasonal Frozen Area

Approximately half of the Chinese territory is in seasonal frozen area.Silty clay is widely distributed in the seasonal frozen area.However,in silty clay subgrade in seasonal frozen area,uneven settlement,soil uplift and even pulping occur due to frost heave and thaw settlement of subgrade soil.At the same time,the subgrade soil will bear dynamic loads such as vehicle loads for a long time during its service,which is easy to cause the decline of the strength,stiffness and stability of the subgrade soil,which affects the long-term service performance and driving safety of the road.Therefore,cement is used in this paper to improve silty clay in seasonal frozen area.Basic physical and mechanical property parameters are measured by geotechnical foundation experiment on soil samples.Then the unconfined compressive strength obtained from the unconfined compression test is used as the index to evaluate the improvement effect of cement.Finally,through the analysis of the results of dynamic triaxial test,combined with theoretical analysis,the influence of different freeze-thaw cycles,different confining pressures and different cement content on the soil dynamic characteristics is explored.The main research contents and results are as follows:(1)The unconfined compressive strength tests of the improved soil is carried out.The effects of the modifier content and curing period on the unconfined compressive strength of silty clay are explored,and the optimal content is determined.The concept of failure absorption energy density is introduced,and the improvement effect of silty clay is evaluated from the perspective of energy analysis.By analysing the soil microscopic images,the improvement mechanism of the modifiers on the soil is discussed.The results show that with increasing cement content,the unconfined compressive strength and failure absorption energy density of the improved soil continuously increase.Considering the soil strength and energy absorption,the optimal cement content is 4%.(2)A series of dynamic triaxial tests are carried out on soil samples of pure soil and improved soil using dynamic triaxial system and constant stress amplitude loading.The experimental results show that the elastic modulus and cumulative plastic strain tend to be stable after 9 freeze-thaw cycles.Both dynamic elastic modulus and cumulative plastic strain are sensitive to low confining pressure.At the initial stage of dynamic loading,the elastic modulus has an obvious downward trend,and then increases and tends to be stable.At the initial stage of cyclic loading,the cumulative plastic deformation of soil samples increases rapidly,and then slows down gradually with the increase of vibration times and strain variables.Finally,the cumulative plastic strain curve tends to be gentle and has a slight increase.(3)The results of dynamic triaxial test are fitted,and the formula of cumulative plastic strain varying with vibration frequency under different freeze-thaw cycles,confining pressures and cement content is obtained.The fitting effect is good.The elastic modulus model of freezethaw cycles,confining pressure,cement content and vibration is obtained.(4)In order to study the changes of dynamic elastic modulus and cumulative plastic strain under the interaction of different factors,SPSS is used to analyze the significance of the combined effects of different factors.It is found that both elastic modulus and cumulative plastic strain are most significantly influenced by vibration and cement content.However,the interaction between the number of freeze-thaw cycles and cement content has no significant effect on the elastic modulus.