Experimental Study On The Mechanical Properties And Numerical Simulation Of The Lime Modified Silty Clay Under The Freeze-thaw Cycle

Based on the engineering background of a silty clay in Hunan province highway roadbed,silty clay as the research object,freeze-thaw cycles,the dosage of lime and confining pressure as the main variables,by combining the theoretical analysis and laboratory soil test,the different mechanical properties change rule of the lime improved soil sample is studied through the freeze-thaw cycling test and triaxial compression test to analyze the mechanical behavior of lime-modified silty clay under different freezing-thawing cycles,such as stress-strain relationship,stress-strain hysteresis characteristic,elastic modulus,strength and shear strength index,and the optimal amount of engineering ash was determined.Finally,combined with the results of laboratory tests,a numerical model was established by FLAC^3D5.0 to analyze the effect of freeze-thaw on the deformation of the modified subgrade.The main work contents and conclusions of this paper are as follows:?1?By laboratory geotechnical tests,the physical and mechanical indexes of silty clay were measured,and the proportion of lime content in the soil was determined,and the optimal water content of silty clay and modified silty clay with different limes was measured,and the static and dynamic characteristics of soil samples were studied by compaction under the optimal water content.The results showed that the stress-strain curves of both silty clay and lime modified silty clay showed strain hardening.The cohesion of soil samples increases gradually with the increase of confining pressure,and the cohesion of soil samples first increases and then decreases with the increase of lime content,and the internal friction angle fluctuated within a certain range.Under the action of dynamic load,the axial strain of silty clay is close to 6%after 2000 times of vibrations,while the axial strain of lime modified soil is less than 2%.With the increase of confining pressure,the hysteretic loop is closer to the vertical axis,and the resistance to deformation is gradually enhanced,and the lime improved effect is obvious.?2?The triaxial compression test was carried out under different freezing-thawing cycles for the samples of silty clay and different amounts of lime to obtain the variation rules of mechanical properties such as stress-strain relationship,modulus,strength and shear strength index of the samples under different amounts of lime and freezing-thawing cycles.The results showed that the strength deterioration degree of the samples decreased with the increase of lime content under the freezing-thawing effect,and the decrease amplitude gradually decreased.As the number of freezing-thawing increases,the resistance to deformation of silty clay and lime modified silty clay decreases.The cohesive force first decreases and then gradually stabilizes.The internal friction angle fluctuates within a certain range,and the elastic modulus first decreases and then increases.Under the same freezing-thawing cycle,with the increase of lime content,the sample cohesion first increases and then decreases,and the internal friction angle and elastic modulus basically show an increasing trend.Lime can effectively improve the ability of silty clay to resist deformation and improve the stability of silty clay subgrade to resist freezing and thawing.Finally,9%was determined as the optimal lime content.?3?The strain field of roadbed after freezing-thawing was simulated and analyzed by FLAC^3D.The results show that the settlement and lateral displacement of the lime modified soil filler roadbed are small and meet the quality engineering requirements.Freezing-thawing has a deterioration effect on the roadbed,and the settlement and lateral displacement of the roadbed increase first and then decrease with the increase of freezing-thawing times.After more than 9 freezing-thawing times,the settlement and lateral displacement of the roadbed basically tend to be stable.