Experimental Study On Freezing Characteristics Of Subgrade Fillings Of High-speed Railway In Cold Regions

ABSTRACT:The service performance of high speed railway subgrade in cold regions is influenced by frost damages, which are caused by repeating freezing-thawing cycles. Thus, it is significant to study the freezing characteristics of filling and explore the mechanisms of frost damage for the design and service performance of high speed railway subgrade in cold regions. In this paper, firstly freezing properties of coarse&fine-grained soil were analyzed by conducting laboratory tests; secondly temperature and moisture fields of fine-grained soil were simulated through coupled hydro-thermal FEM theory and calculational results were compared with the experimental results; finally, based on existing research results, the service performance of high speed railway subgrade in cold regions was evaluated.The main conclusions are as follows:1. For the fine-grained soil used in lab tests, whose moisture content is18%, with the elapsing time of freezing going, its frost heave rate increases rapidly and then stays stable. The ultimate frost heave rate is5.39%. During the freezing process, the water migration occurs in the soil, and finally moisture content changes clearly at the cold side of samples as well as the freezing front.2. For coarse-grained soil whose maximum grain size is below20mm and fine-grained content is7.9%, when its moisture contents are9.5%,12%and14.5%respectively, the corresponding frost heave rates are0.72%,2.14%and4.14%respectively.3. The experiment results of filling collected from construction field indicate that the freezing heave rate is0.18%,0.66%,1.57%and2.14%when the fine-grained content is2.2%,10%,15%and20%respectively. Obvious moisture migration is observed in the tests of which the fine-grained content is2.2%,10%,15%and20%. And the average migration rate is1.53%,1.55%,1.60%, and1.63%respectively.4. Hydro-thermal coupling of freezing process of fine-grained soil is calculated by using FEM. The calculated results are in good agreement with the experimental data.5. According to the construction of embankment and engineering geological conditions of Harbin-Dalian High Speed Railway, indexes of service performance of embankment are determined and then the evaluation of service performance of embankment between Shenyang and Dalian is conducted by adopting multi-level grey theory. And the analysis shows truthfulness.