Study On Influence Of Improved Surface Layer Of High-Speed Railway Subgrade On The Subgrade And Dynamic Responses Of The Track

Most region of northeast China belongs to seasonal frozen soil zone. Though the total length of railway line in this area is relatively longer than other areas of China, the lines there are aged, what’s more, the large population put more pressure on it, more and more high speed-railways are in needed. In the past 3 years, many problems occurred in Harbin-Dalian high-speed railway due to temperature changes, such as frost heave in subgrade, inducing a deformation of 5mm to 20mm. In order to eliminate failures induced by subgrade deformation, the practice of adding cement in grading crushed stones of highways is introduced to the subgrade of high-speed railway. A phase based transient heat transfer model is introduced. The deformation of subgrade is calculated in the model, and the result is then introduced into the next model as an initial condition. In the next deformation-train coupling model, the dynamic responses of the train, the track and the surface layer of subgrade are computed. In the last model, a fatigue formula of semi-rigid base is used, the fatigue lives of different conditions are evaluated. By the results of the 3 models, we can evaluate the effects of different cement proportions in subgrade. The contents and its results are as follows:(1) Based on the software ANSYS and its subroutine usermat, the paper studied the frozen depth, heat affect area and subgrade deformation in different subgrades in the condition of freeze-cycling load, the results shows that, the frozen depth and heat affect area decreases as more cement is added, when the cement proportion is larger than 3%, the decreasing magnitude decreases. With the cement proportion rises from 0 to 5%, the wavelength are 15.7m、18.6m、22.3m、26.2m,and wave amplitude are 10.17mm、 7.59mm..6.08mm、4.99mm respectively; as no deformation is allow to excess the limit of 5mm, the cement is sposed to be 5%.(2) Based on the deformation-train coupling model and 3 different speeds of 200km/h、250km/h、300km/h, the dynamic responses of the train, the track and the surface layer of subgrade are calculated. In a certain speed, all the indexes of show a decrease in a certain amount with the cement rises from 0 to 5% in the surface layer of subgrade, which means the cement added is helpful to the operation; when the cement mass is fixed, with the train speed rises from 200km/h to 300km/h, the derailment, the load resuction rate and most dynamic responses increase. The results means that a higher train speed may means a harm to the operation of the track; the maximum derailment and load reduction rate is 0.347 and 0.325 respectively, after improved with cement of 5% proportion, they decreased in 34.8% and 34.7% respectively.(3) Based on the deformation caused by temperature changes, a statics model of subgrade is built to obtain the maximum bending stress exerted, the maximum stress is then introduced into a fatigue formula for semi-rigid materials, in the last step, the result is transferred by an equivalent axle formula to estimate the fatigue life of the subgrade. It shows that the cement is helpful to the fatigue life of the subgrade in seasonal frozen regions, when the cement varies from 3% to 5%, the fatigue life increases in an amazing magnitude of 36%-48%. In conclusion,5% proportion of cement is recommended.