Experimental Study On Mechanical Characteristics Of Subgrade Filling Of Shen-Shuo Railway Under Freeze-thaw Cycles

The Shenshuo heavy-duty railway is located in the seasonal frozen soil area in northern China.Subject to seasonal freezing and thawing cycles,and heavy-duty train loads,the roadbed is prone to freezing damage,such as uneven frost heaving,thawing and pumping of the subgrade,which seriously threatens driving safety.Therefore,it provides theoretical basis of treating the roadbed disease and ensuring train driving safety to study the mechanical properties and freeze-thaw cycles of subgrade fillings under heavy load.This paper studies the Shenshuo railway subgrade filling(low liquid limit silt)and its improved filler.Based on the results of indoor triaxial test,the static and dynamic strength characteristics of the subgrade filler and its modified filler are analyzed.On this basis,the finite element calculation of the deformation of the subgrade in the seasonal frozen soil area under heavy-duty train loads is carried out.The main research results include the following aspects:(1)Through the on-the-spot investigation,the characteristics and the causes of the freezing damage of the Shenshuo railway subgrade are summarized.Causes are analyzed from the aspects of soil quality,moisture and temperature.Through experiments,the basic physical properties of the Shenshuo railway subgrade fill are determined,and the subgrade filler is named as low liquid limit silt.(2)The static triaxial test results of the subgrade filling show that the stress-strain relationship of the soil changes from softening to hardening with the increase of confining pressure.When the confining pressure is the same,the higher the water content,the higher the shear strength.Smaller,as the confining pressure increases,its strength gradually increases.After the freeze-thaw cycle,the strength of the soil showed a gradual decrease,but its strength gradually stabilized after 5 cycles of freezing and thawing.(3)The results of dynamic triaxial test of subgrade filling show that the damping ratio and equivalent shear modulus of the fine-grained soil decrease with the increase of dynamic stress and tend to be stable under normal temperature conditions.The stability values are about 0.4.and 150MPa,but the number of dynamic loads has little effect on it.After the freeze-thaw cycles,the dynamic cohesion of the soil decreased by about 10%and the internal friction angle increased slightly,but the equivalent shear modulus decreased.(4)After the low liquid limit silt was mixed with TGH curing agent,the results of static and dynamic triaxial tests showed that the static and dynamic strength of TGH curing agent improved soil significantly improved;the optimal blending ratio of TGH curing agent was 2%.At this time,the static strength of the improved soil is increased by about 40%,and the equivalent shear modulus is increased by 30%,but the relative change in the damping ratio is small.(5)By summarizing the dynamic constitutive model established by domestic and foreign scholars,based upon the experimental results,the dynamic characteristics of the Shenshuo railway subgrade and its modified filler apply to Hardin-Drnevich model and Davidenkov model.(6)It is verified that the modified subgrade filler has improved characteristics,by analyzing the results of subgrade deformation under different working conditions using finite element theory.