Study On Mechanical Properties Of Lignin-lime Modified Silty Soil Under Dry And Wet Cycles

Subgrade is an important part of railway engineering,it repeatedly bears train loads and alternating wet and dry loads during its design life,which will lead to the decline of mechanical properties of subgrade fillers and even cause subgrade instability damage.Therefore,it is necessary to have a thorough understanding of the mechanical behavior of subgrade fillers under cyclic loads and alternating wet and dry loads.In this paper,lignin and lime were used as curing agents to improve the Yellow River alluvial silty soil.The effects of dry and wet cycles on the compressive strength and shear strength of improved silty soil were studied by unconfined compressive strength test and static triaxial test;the dynamic triaxial apparatus was used to reveal the effects of the number of dry and wet cycles,vibration frequency and confining pressure on the dynamic characteristics of the improved silty soil;scanning electron microscopy,energy dispersive spectrometer and IPP image processing were used to investigate the improvement mechanism of lignin-lime improved silty soil and the influence mechanism of dry and wet circulation on improved silty soil.The main conclusions of the study are as follows:(1)The compressive strength of 6% lignin+3% lime modified silty soil increased first and then decrease with the increase of the number of dry and wet cycles,dry and wet cycle tend to stabilize after 4 times,and the effect of resisting dry and wet cycles is better;the compressive strength of 9% lignin+3% lime modified silty soil are gradually reduced under the wet and dry cycles,compared with 6% lignin+3% lime modified silty soil,the effect of anti-dry and wet cycle is slightly worse.(2)The cohesion of 6% lignin+3% lime modified silty soil and 9% lignin+3% lime modified silty soil is similar to that of compressive strength with the number of dry-wet cycles;the dry-wet cycle has little effect on the internal friction angle of the two types of modified silt.(3)6% lignin+3% lime modified silty soil experienced a decrease in cycle ductility after 1dry and wet cycle,the dynamic elastic modulus increased,the damping ratio decreased,and then the number of dry and wet cycles continued to increase,the soil cyclic ductility increased,and the dynamic elastic modulus decrease,the damping ratio increases;different from 6%lignin+3% lime modified silty soil,9% lignin + 3% lime modified silt did not show a decrease in cyclic ductility,an increase in dynamic elastic modulus,and a decrease in damping ratio during the dry-wet cycle.(4)With the increase of confining pressure and frequency,the ability of 6% lignin+3%lime modified silty soil to resist deformation increases,the dynamic elastic modulus increases,the cyclic ductility decreases.As the confining pressure increases,the damping ratio of the modified silt decreases.When the vibration frequency is 3 Hz,the damping ratio of the modified silt is the largest.(5)Scanning electron microscopy and IPP image analysis show that the incorporation of lignin-lime cause the pores of the alluvial silt of the Yellow River to decrease and the compactness to increase.The lignin-lime modified silt after one dry and wet cycle has the smallest ratio of pores to particles and the densest soil.