Frost Heave Classification of Railway Subgrade Filling Material and the Design of Anti-Freezing Layer

There are serious frost heave diseases on the surface layer of railway subgrade in permafrost regions of China and there are no corresponding standards for frost heave classification of railway subgrade filling material in China.The characteristics of subgrade frost heave,the factors influencing subgrade frost heave,and the problems in the treatment of frost heave diseases are analyzed.On this basis,frost heave classification of railway subgrade filling material is presented and subgrade anti-freezing layer is suggested to be built in permafrost regions by borrowing domestic and foreign ideas of frost heave classifications for foundation soil,according to the characteristics of railway subgrade filling material classification,the limit depth of frost heave and the criterion of maintenance for railway track.The new frost heave classification for subgrade filling material is divided into two levels,which are frost heave sensitivity and frost heave rate,according to such indexes as fine granule contents of soil,pre-freeze water content in soil and frost heave depth.Non-frost-heave soil such as sand with fine granule content less than 5%,gravel with fine granule content less than 15% and crushed rock can be used to build the anti-freezing layer of subgrade.The thickness of the anti-freezing layer will be decided by the standard frost depth of subgrade,the running speed and the loading capacity of train.