The distribution of freezing and thawing within rock masses is time varying (day to day or season to season) and controls the effectiveness of the frost cracking processes from the surface until various depths. These processes are major contributors to the development of rock instabilities. By altering the thermal regime of rockwalls, global warming could have a major impact on rockfall dynamic by the end of the 21st century. This study seeks to improve our understanding of the influence of this warming on (i) the distribution of freezing and thawing within rock masses, (ii) the effectiveness of frost cracking and (iii) the frequency and magnitude of rockfalls. Thermistor sensors inserted in a 5.5-m horizontal borehole and a weather station were installed on a vertical rockwall located in the northern Gasp & eacute; Peninsula (Canada). This instrumentation was used to calculate the surface energy balance of the rockwall and to measure and model its thermal regime at depth over a period of 28 months. Combining locally recorded historical air temperature data with simulated future data (scenarios RCP4.5 and RCP8.5) made it possible to extend the rockwall thermal regime model over the period 1950-2100. The effectiveness of frost cracking over this 150-year period has been quantified using a thermomechanical model. Depending on the scenario, warming of 3.3 degrees C to 6.2 degrees C is expected on the northern Gasp & eacute; Peninsula by the end of the 21st century. This rapid warming is likely to decrease the maximum depth reaches by the seasonal frost by 1-2 m and shorten its duration by 1-3 months. The frequency of freeze-thaw cycles could increase twelvefold in January. Frost cracking effectiveness should intensify around 70 cm in depth and disappear beyond that (RCP4.5) or diminish starting at 10 cm in depth (RCP8.5). In areas subject to seasonal freeze-thaw cycles, decimetric rockfall frequency could grow considerably in winter but be significantly reduced in fall and spring. Furthermore, frost cracking would cease contributing to the development of larger magnitude instabilities. Depending on the scenario, warming of 3.3 degrees C (RCP4.5) to 6.2 degrees C (RCP8.5) is expected on the northern Gasp & eacute; Peninsula by the end of the 21st century. By altering the thermal regime of rockwalls, the global warming could have a major impact on rockfall dynamic. In regions subject to seasonal freeze-thaw cycles, small magnitude rockfall frequency could grow considerably in winter but be significantly reduced in fall and spring. Frost weathering would cease contributing to the development of larger magnitude instabilities. image

In order to investigate the freezing damage problem of berms of earth-rock dams in cold regions, an earth-rock dam in a cold region was selected as the research object in this study. A finite element model, considering the effect of thermo-hydro-mechanical coupling, has been developed to solve the problem by combining the characteristics of the earth-rock dam. The whole process of freezing damage of berms under the influence of the reservoir level and the water migration of the dam filling was investigated, and the laws in temperature, humidity and displacement of earth-rock dams were analyzed. The calculated displacement field was then compared with the measured frozen deformation data to validate the results of the finite element simulation. The results showed that the freezing influence range of the dam slope was about 2 m, the range of temperature influence on the dam slope mainly depended on the depth of freezing, and the temperature change in the shallow range (0-2 m) of the dam slope was influenced by the outside air temperature. Also, the internal temperature of the dam body was small relative to the shallow dam slope, and there was a certain hysteresis. In addition, the effect of negative temperature was such that the shallow pore water phase of the dam slope turned into ice, manifesting macroscopically as a reduction in unfrozen water content. Water phase change, water migration from the dam filling to the dam slope, and the movement of the ice peak towards the dam body were found to be the main causes of berm freezing and expansion damage. The calculated amount expansion (due to freezing) of the dam slope was found to be in the range of 20-30 cm with a maximum value of 36 cm, which was consistent with the measured results. It was also found that the freezing and expansion damage of the berm is mainly caused by the joint action of freezing and expansion of the soil and rock mixture such as gravel bedding and dam filling, as well as the ice thrust force. It is expected that the results of this research can provide a basis for the design of berms of earth-rock dams in cold regions.

Frost damage significantly reduces global wheat production. Temperature development in wheat crops is a complex and dynamic process. During frost events, a vertical temperature gradient develops from soil to canopy due to the heat loss from the soil and canopy boundary. Understanding these temperature gradients is essential for improving frost management strategies in wheat crops. We hypothesise that the relationship between the temperatures of the canopy, plant and ground can be an early indicator of frost. We collected infrared thermal (IRT) images from field-grown wheat crops and extracted the temperatures from the canopy, plant and ground layers. We analysed these temperatures and applied four machine learning (ML) models to detect coldness scales leading to frost nights with different degrees of severity. We implemented a gated recurrent unit, convolutional neural network, random forest and support vector machines to evaluate the classification. Our study shows that in these three layers, temperatures have a relationship that can be used to determine frost early. The patterns of these three temperatures on a frost night differ from a cold no-frost winter night. On a no-frost night we observed that the canopy is the coldest, plant is warm, and the soil is warmest, and these three temperatures did not converge. On the other hand, on a frost night, before the frost event, the canopy and plant temperatures converged as the cold air penetrated through the canopy. These patterns in temperature distribution were translated into an ML problem to detect frost early. We classified coldness scales based on the temperatures conducive to frost formation of a certain severity degree. Our results show that the ML models can determine the coldness scales automatically with 93%-98% accuracy across the four models. The study presents a strong foundation for the development of early frost detection systems.

The risk of frost damage to building materials is strongly dependent on the water content, particularly when the water content is high. Therefore, to understand the moisture behavior of materials with high water content is essential to predict the frost damage risks of buildings. While little liquid water transfer takes place over the capillary saturation under unfrozen conditions, the pressure drop of the unfrozen water contained in the frozen domain (cryosuction) may be a strong driving force for water transfer during the freezing processes. Therefore, in this study, we investigated water transfer in a building material over capillary saturation during freezing through a one-dimensional freezing experiment using the gamma-ray attenuation method and hygrothermal simulations. In the experiment, an aerated concrete specimen, with a water content greater than the capillary saturation, was subjected to a temperature gradient by cooling the specimen bottom to the freezing temperature. The results show that significant water transfer occurred even in the capillary-saturated material during freezing and thawing. Water moved to the cold side in the material and the most significant water accumulation was observed at a position where the temperature was close to 0 degrees C. The hygrothermal simulation, including the freezing processes, confirmed that cryosuction was a dominant driving force of water movement and accumulation in the material compared with other driving forces, such as gravity and temperature gradient. Moreover, mechanism of the water accumulation at a position where the temperature was close to 0 degrees C was discussed from the perspective of water chemical potential distribution and water conductivity of the material. The findings of this study will help develop a more reliable model for evaluating moisture damage risks by considering the hygrothermal behaviors of building envelopes.