The moisture accumulation and freezing damage of coarse-grained fill (CGF) in high-speed railway (HSR) subgrades have been widely concerned. Based on the newly developed water-vapor-heat-mechanical coupling test apparatus, a series of soil column tests were carried out to investigate the frost heave mechanism of CGF. The results indicate that the liquid water in CGF is discontinuous and difficult to migrate to the freezing front. The primary mechanism of moisture accumulation and frost heave in CGF is vapor migration and phase transition. With increasing freeze-thaw cycles, both vapor migration and frost heave reduce. The thaw settlement of the CGF is less than the frost heave, so there is a net upward deformation in each cycle. Furthermore, the fine particle content has a prominent effect on the heat transfer and frost heave of the CGF compared to the fine particle type. Even under the condition of vapor replenishment, controlling the content of fine particles is still an important way to inhibit frost heave. Moreover, after reducing the maximum particle size of CGF, the frost heave of the sample increases. Nuclear magnetic resonance (NMR) test results show that CGF is dominated by large pores, and the freeze-thaw cycle further promote the development of large pores, providing a good channel for the migration of vapor. In conclusion, the frost heave development caused by vapor migration is slow and continuous, posing a non-negligible risk to HSR subgrades during long-term service.

It is essential to investigate soil hydro-thermal behavior to reduce the potential damage to geotechnical constructions caused by varying climatic conditions. In this work, an in-situ monitoring station was built on a clay slope with high groundwater table, situated in Yixing, China. Ten SMT-100 sensors were instrumented on the site to record the evolutions of soil temperature and volumetric water content at various depths. Meteorological information, including relative humidity, air temperature, rainfall, wind speed and solar radiation, and slope runoff was collected. A numerical investigation was also conducted to analyze the variations of soil hydrothermal response to the recorded climatic conditions by combing coupled hydro-thermal model and soilatmosphere interaction model. The profiles of soil temperature and volumetric water content suggest that the diurnal changes are limited to depths <40 cm, and the seasonal changes are usually approaching a location deeper than 120 cm. Soil heterogeneity can affect its hydro-thermal response, e.g., higher volumetric water content was observed at the points with lower dry density, which is mainly related to soil water retention capacity. However, appropriate theoretical models to consider soil heterogeneity in the description of soil hydrothermal properties need to be further investigated.

The long-term stability of water ice at cold traps depends on subsurface temperature and regolith thermophysical properties. Based on Chang'E-2 microwave radiometer data, we have inverted attenuation coefficient, thermal gradient and instantaneous temperature profiles at permanently shaded craters (Cabeus, Haworth and Shoemaker) on the Moon's south pole. The nonuniformity of the inverted attenuation coefficient within the craters reflects the inhomogeneous thermophysical properties of regolith. In addition, thermal gradient decreased significantly from the crater walls to the bottoms, which may be caused by scattered sunlight, internal heat flux and earthshine effect. Considering continuous supplement of water ice (with volumetric fraction 0-10%) at cold traps, it changes subsurface thermophysical properties but has little effect on thermal gradient. We also assumed that abundant ice (10%) mixed with regolith, the inversion results showed that the maximum difference of diurnal temperatures between wet and dry regolith were no more than 0.5 K. That is, the effect of water ice on subsurface thermal behavior can be neglected. (c) 2016 Elsevier Ltd. All rights reserved.