Research On Stiffness Characteristics Of Heavy Haul Railway Subgrade By Wetting Process

Heavy haul railway transportation is one of the main channels for bulk cargo transportation in China.During operation,the heavy haul railway subgrade will be subjected to the long-term cyclic load of the heavy haul train.In addition,under rainfall,freezing and thawing,and other seasonal changes,the water body will be immersed in the subgrade.Under the combined effect of cyclic load and water immersion of the train,the roadbed soil will be easily softened.With the continuous impact of the train on the softened parts,the softening range is further expanded,which seriously affects the smoothness of the train tracks and threatens driving safety.This article takes heavy haul railway subgrade as the research object,and designs a dynamic triaxial test under the stress combination sequence and a dynamic triaxial test considering water intrusion.The main innovations and conclusions are as follows:(1)The stiffness of the soil has a strong stress dependence,which is mainly determined by the confining pressure and the deviatoric stress.When changing only a single variable,the dynamic resilient modulus decreases with increasing dynamic stress amplitude,and increases with increasing confining pressure.In addition,for soils with different moisture content and dry density,soils with larger dry density have larger dynamic resilient modulus,and soils with larger water content have smaller dynamic resilient modulus.(2)According to different influencing factors,different dynamic resilient modulus estimation models can be established.Based on the dynamic triaxial test data under the stress combination sequence in this paper,three composite models of dynamic resilient modulus were fitted,and good fitting results were obtained.Through model comparison and selection,it is found that the Ni model has a better fitting effect under multiple sequences.It can be used to estimate the dynamic resilient modulus of heavy haul railway subgrades to evaluate the performance of low liquid limit clay subgrades.(3)The dynamic resilient modulus showed a rapid increase in the first 100 cycles of loading during the dynamic stabilization phase,and then gradually stabilized.The larger the compaction coefficient of the soil sample,the higher the stable value of the dynamic resilient modulus at this stage.The smaller the moisture content of the soil sample,the lower the corresponding stable value of the dynamic resilient modulus.(4)The hysteresis curve obviously dumped with the progress of the soaking process,indicating that the soil had undergone stiffness softening.During the dumping of the hysteretic curve,the slope of the hysteretic curve of the soil with a compaction coefficient of 0.96 is significantly greater than that of the other two compaction coefficient soils.For soils with compaction coefficients of 0.9 and 0.93,respectively,after the number of loadings in the dynamic humidification stage exceeds 10 000 times,the slope difference of the hysteresis curve gradually becomes apparent.(5)The dynamic resilient modulus attenuated during the dynamic humidification phase,and the dynamic resilient modulus of the soils with compaction coefficients of 0.9,0.93,and 0.96 decreased by 22%,32%,and 42%,respectively.Although the degree of attenuation of the soil with the compaction coefficient of 0.96 is the largest,the dynamic resilient modulus after attenuation is still significantly higher than that of the other two types of compaction coefficients;while the soil with the compaction coefficient of 0.93,The stable value of the dynamic resilient modulus in the stable stage is greater than that of the soil with a compaction coefficient of 0.9,but during the decay process after immersion in water,the dynamic resilient modulus is gradually lower than that of the soil with a compaction coefficient of 0.9.(6)Aiming at the attenuation law of the dynamic resilient modulus in the dynamic humidification stage considering the immersion,a softening index of the soil was constructed based on the dynamic resilient modulus,and a soil stiffness softening model was established based on this.After verification,the model can well predict the stiffness of the soil.