Water migration and deformation during freeze-thaw of crushed rock layer in Chinese high-speed railway subgrade: Large scale experiments

Abstract

The water migration and deformation of soil induced by freeze-thaw cycle is a significant issue which influences the stability of subgrade in Chinese high-speed railway. Soil column studies under controlled laboratory settings can help understand the thermal-hydrodynamics of the crushed rock layer. In this study, four large-scale subgrade models with different initial soil moisture contents, fine contents were subjected to freeze-thaw action by bringing the soil surfaces exposed to air temperature fluctuating between −15 and 15°C. The results show that soil moisture migration occurs in both frozen and unfrozen soils during the freeze-thaw cycle. The freezing-induced soil water distribution is affected by fines content and loading conditions. Crushed rock with 50% fines content produced visual deformation, and the maximum amount of frost heave was 12.1 mm under external loading, comparable with the results from the previous field investigation. The unfrozen water content of fills decreases gradually with the depression of soil temperature. Some liquid water remained unfrozen at the end of the freezing period with residual unfrozen water content between 0.07 m3 m−3 and 0.10 m3 m−3, and continuing to exist even at −8.7°C. The frozen soil contains more volumetric water content at the same minus soil temperature, resulting in a hysteresis loop-like behavior in the soil characteristics curve. The results of this study will help in understanding, and finally forecasting, the deformation of subgrade in Chinese high-speed railway.