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With the Longzhong Water Conservation and Ecological Water Supply and Storage Reservoir Project (Upper Yellow River) as the engineering background, this study selected sulfate sandy soil from Jingtai County (Baiyin City, Gansu Province, the project area) as the test soil to explore the effects of moisture content and salt content on the frost heave characteristics of sulfate sandy soil in seasonal frozen soil areas, and to avoid engineering problems caused by its frost heave deformation. Indoor freeze–thaw experiments and data analysis were conducted; water and salt content gradients were set in line with the actual engineering conditions, and indoor unidirectional freezing frost heave tests were carried out to simulate the natural freeze–thaw environment. The test results show that temperature is a key factor regulating soil frost heave: the frost heave rate varies in an “S-shaped” pattern with decreasing temperature (slightly decreasing at 10~0 °C, increasing rapidly at 0~−10 °C with the most significant growth at 0~−5 °C, and stabilizing below −10 °C). Under constant compaction, the frost heave rate increases parabolically with moisture content (the growth rate slows down after 15% and stabilizes at 17%) and linearly with salt content (with a small increment). Based on the test data, a frost heave rate prediction model considering moisture content and salt content was established; the correlation between the calculated values of the model and the measured values is strong (R2 > 0.92), which can provide a reference for predicting the frost heave rate of such sulfate sandy soil. The key conclusions are as follows: The frost heave of the soil is dominated by temperature and moisture content (the effect of salt content is secondary); the temperature range of 0~−5 °C is the critical period for engineering frost heave prevention. This study provides technical support for the frost heave prevention design of the Longzhong Reservoir and similar engineering projects in seasonal frozen soil areas of Northwest China.

Spring snowmelt has a significant impact on the hydrological cycle in seasonally frozen soil areas. However, scholars hold differing, and even opposing, views on the role of snowmelt during the thawing period in groundwater recharge. To explore the potential recharge effects of spring snowmelt on groundwater in seasonal frozen soil areas, this study investigated the vadose zone dynamics controlled by soil freeze–thaw processes and snowmelt infiltration in the Northeast of China for 194 days from 31 October 2020 to 12 May 2021. Responses of groundwater level and soil moisture to snowmelt infiltration show that most snowmelt was infiltrated under the site despite the ground being frozen. During the unstable thawing period, surface snow had already melted, and preferential flow in frozen soil enabled the recharge groundwater by snowmelt (rainfall), resulting in a significant rise in groundwater levels within a short time. The calculated and simulated snowmelt (rainfall) infiltration coefficient revealed that during the spring snowmelt period, the recharge capacity of snowmelt or rainfall to groundwater at the site is 3.2 times during the stable thawing period and 4.5 times during the non-freezing period.

The effect of spring snowmelt infiltration in a seasonal soil frost area on groundwater recharge was evaluated by systematically monitoring meteorological factors, soil temperature and humidity, groundwater table and temperature, electrical conductivity, and the value of δ 18 O in a small field site over a 2-year period. The variation of soil temperature and humidity, groundwater table during the freezing period, and the snowmelt period respectively, as well as their correspondence to the relevant environmental factors, and the influencing factors of the permeability of frozen layer were analyzed. The results showed that the evaluation of precipitation infiltration in seasonal soil frost areas should be divided into three stages: a non-freezing period, a freezing period, and a snowmelt period. Snow is the main form of precipitation during the freezing period, and groundwater cannot be recharged. During the snowmelt period of spring, the snow cover that accumulated during the freezing period infiltrates together with rainfall and has a significant effect on groundwater recharge. The general precipitation infiltration process occurs after the frozen soil thaws completely. These research results can improve the accuracy of groundwater recharge calculations for snowmelt infiltration in the seasonal soil frost area of Northeast China and provide a scientific basis for the evaluation and management of regional water resources.

The freezing and thawing of roadbed soils in seasonal frozen zones can cause uneven settlement and other road problems, which puts road operation at risk. This paper focuses on the rapid construction of expressways and analyzes the effects of using fly ash and cement as modifiers on the physical properties and chemical composition of subgrade soil. The study found that cement admixtures can improve soil mechanical attributes and frost resistance, while also increasing the degree of fly ash hydration. And the freeze-thaw cycle process can enhance the mechanical characteristics of soils with higher cement admixture content. This is due to the development of hydrates in cement fly ash-enhanced soils during freeze?thaw cycles, resulting in a denser interior structure. The use of neural network prediction analysis showed that using ANN4-10-3 to forecast soil mechanical property parameters can produce superior results. Therefore, it is recommended to use cement fly ash-enhanced soil for roadbed construction in seasonal freezing areas, and neural network can be used to predict soil mechanical parameters.

Traditional landslide early-warning systems usually focus on displacement, rainfall, and stress, neglecting temperature effects. Rock deformation and failure processes are fundamentally characterized by energy dissipation, which can manifest through thermal changes. It is essential to explore whether temperature response inside landslides could help predict instability. This study investigates a representative landslide in southeastern Jilin Province, which has repeatedly experienced intense disturbances due to consecutive typhoon events. By employing a comprehensive multi-source monitoring strategy, including digital elevation model differencing (DoD), underground instrumentation, and detailed field surveys, we tracked temperature fluctuations, internal deformation, and surface displacement of the landslide. Our findings demonstrate that exceptionally intense rainfall events, occurring approximately once every sixty years, nearly reactivated landslides previously considered stable. Reactivated landslides exhibited accelerated movement, presenting severe hazards to infrastructure and nearby communities. Significantly, temperature within the landslide mass displayed distinctive fluctuation patterns at the onset of instability: Sharp Peak & Gentle Slope (SPGS) and Roller-Coaster (RC). These thermal signatures correlated strongly with rainfall intensity and deformation rates. To explain these observations, we propose two theoretical frameworks: the ambient heat-driven SPGS fluctuation patterns and the spontaneous heat-driven RC fluctuation patterns. The coupled temperature-accumulated rainfall-rainfall intensity analyses showed that: Temperature data can establish joint thresholds for cumulative rainfall and rainfall intensity. Further validation of the SPGS fluctuation patterns is essential for practical application in rainfall-induced landslide early-warning systems. Further research and validation efforts are essential to conclusively determine the predictive value and reliability of temperature changes induced by rainfall in forecasting landslide initiation. Highlights Exploring the impact of extreme rainfall events brought by continuous typhoons on FS landslide evolution. The correlation between temperature-deformation response within the FS landslide mass and rainfall was established. Introduced a novel differential display method to reveal more details.

Under global warming, the permafrost-underlain headwater catchments of the Tibetan Plateau have undergone extensive permafrost degradation and changes in precipitation characteristics, which may substantially alter the riverine suspended sediment and riverine solute fluxes. However, these fluxes and their influencing factors in such catchments are poorly understood. We studied the suspended sediment and solute fluxes in a permafrost-underlain headwater catchment on the northeastern Tibetan Plateau, based on comprehensive measurements of various water types in spring and summer in 2017. The daily flux of suspended sediment in spring was close to that in summer, but heavy rainfall events following a relatively long dry period made the largest contribution to the suspended sediment fluxes in summer. The riverine solute flux (in tons) was 12.6% and 27.8% of the suspended sediment flux (in tons) in spring and summer, indicating the dominating role of physical weathering in total material exportation. The snowmelt mobilized more suspended sediment fluxes and fewer solutes fluxes than summer rain, which may be due to the meltwater erosion and freeze–thaw processes in spring and the thicker thawed soil layer and better vegetation coverage in summer, and the longer contact time between the soil pore water and the soil and rock minerals after the thawing of frozen soil. The input of snowmelt driven by higher air temperatures in spring and the direct input of rainfall in summer would both act to dilute the stream water; however, the supra-permafrost water, with high solute contents, recharged the adjacent streamflow as frozen soil seeps and thus moderated the decrease in the riverine solute content during heavy snowmelt or rainfall events. With the permafrost degradation under future global warming, the solute fluxes in permafrost-underlain headwater catchments may increase, but the suspended sediment flux in spring may decrease due to the expansion of discontinuous permafrost areas and active layer thickness.

Soil slope in seasonal frozen area subject to rainfall or freezing and thawing cycles, the shear strength of soil damage and lead to landslide hazard. In order to predict the landslide hazard through monitoring the soil slope stability real-time, the soil slope stability evaluation system is established. The Neural Network Algorithm can simulate elastic-plastic finite element method well, and using Genetic Algorithm to search cohesion(c) and internal friction angel(φ) which meet the accuracy requirements. And the intelligent parameter inversion model of soil shear strength (c, φ) based on displacement is established. So, the slope stability can be evaluated real –time based on displacement monitor. Application of this method in actual project shows that this method is accurate and effective.

A 9-yr study (1983-1991) was carried out in Thjórsárver, central highland of Iceland, to investigate the seasonal and annual dynamics of frozen ground and explore the relationship with environmental factors. The presence/absence of frozen ground and active layer thickness were recorded three times over the growing season (4-7 July, 1-4 August, and 20-24 August) at 51 permanent points in different plant communities and on 12 palsas. There were large annual fluctuations in the proportion of frozen ground, varying from about 20-100% in 4-7 July and from 0-50% in 20-24 August. The incidence of frozen ground in early summer was related to conditions in the previous early winter. The combination of a wet (high water availability) and mild weather (allowing percolation) in September to November may maximize soil moisture content at the onset of winter, facilitating frost penetration through higher conductivity of wet rather than dry soil, and lead to widespread frozen ground in early July. In contrast to frozen ground, active layer depth showed very little annual variation. This indicates that much of the frozen ground melts from below. Widespread frozen ground in early August was primarily associated with a dry July although a correlation with cold weather in July was also found. Both indicate the importance of water in melting seasonally frozen ground, probably by heat transported by flowing groundwater. The wide annual variation in frozen ground incidence in late August supports earlier notions about the marginal nature of permafrost in Iceland. The results indicate that changes in the amount and seasonal pattern of precipitation may be more important than summer temperatures in influencing the aggradation and degradation of permafrost in the central highland of Iceland.