To systematically investigate the short-term consequences of sudden temperature fluctuations and address the challenges of frost damage in extreme environments, this study examined tunnel entrances in the Northeast China. Laboratory freeze-thaw/freezing tests and multi-field coupling simulations were conducted to assess the response of tunnel linings and adjacent rock in cold regions. This study reveals, for the first time, the spatial and temporal migration pattern of 'low temperature at the foot of the arch–high temperature at the arch', providing a reference for the anti-freezing design of tunnels in cold regions. The main conclusions are as follows: (1) High water content and repeated freeze-thaw cycles significantly affect the soil's stress-strain curves, hardening them under increasing confining pressure while accelerating soil strength degradation. Before the freeze-thaw cycle, a 3% increase in water content reduces the modulus of elasticity by approximately 40%. After 10 freeze-thaw cycles, the modulus reduction escalates to 33%–63%, with soil specimens exhibiting the most significant degradation at the optimal water content. (2) During the freezing process, the soil's stress-strain curves exhibit softening features, with failure strength and cohesion increasing nonlinearly as temperature decreases. The internal friction angle reveals no clear pattern, and the failure mode tends toward brittleness. (3) A sudden temperature decrease results in the lowest temperature at the arch foot of the secondary lining, while the highest is at the primary support's vault. After a sudden temperature increase, the lowest temperature shifts to the primary support's arch foot, while the highest shifts to the secondary lining's vault. Temperature changes in the surrounding rock are most pronounced within 0.5 m outside the lining. (4) Sudden temperature fluctuations induce short-term irreversible vertical displacement at the ground surface, expansion of horizontal clearance after temperature decrease, and convergence after the temperature increase. The vault and invert undergo cyclical uplift and settlement due to freezing and thawing. A temperature decrease of 20 °C leads to the maximum freeze-heave stress. Stress distribution in the lining shows tensile stress at the sidewalls (473 kPa) and compressive stress at the arch foot (1,005 kPa). Both values are below the material's strength limits, indicating structural safety under freeze-heave stress alone.
Frost heave phenomenon poses significant geohazard, threatening the safety of the infrastructure in cold regions as a result of freezing-thawing cycles. This threat the destabilizes the environment and complicates further construction. The paper aims to evaluate the uneven displacement associated with frost heave, focusing on the thermo-mechanical interactions that govern embankment stability and the potential benefits of the New Geocell Soil (NGCS) system. Field experiments were conducted to monitor thermal penetration, and microstructural analyses were performed to assess soil composition changes in response to thermal cycles. It is significantly correlated with the displacement, suggesting that temperature characteristics can be employed in assessments. The New Geocell soil system has been introduced to mitigate thermal effects and uneven frost heave. The identified alterations highlight essential weak zones for mechanical response evaluation at the top layer, with a significant increase in frost heave within the range of −2 °C to −1 °C. This complicates traditional evaluation models and necessitates a deeper understanding of thermo-mechanical properties. The results indicate that frost heave below 1 mm showed substantial improvement when reinforced with NGCS. The embankment is strengthened before the New Geocell system fails. The study presents a reliable strategy with soil pressure decrease in the range of 0–250 kPa. The frost front is diminished and it further indicates that New Geocell reinforcement can adapt to migration of thermal response.
Petroleum extraction and transportation in cold regions often result in leakage accidents, which can cause severe environmental pollution. The prevalent freeze-thaw cycles in these areas significantly influence the migration and dispersion of petroleum. Therefore, understanding these processes is essential for effective environmental protection. The experimental results indicate that capillary action, liquid pressure, and particle adsorption primarily influence petroleum migration in the unfrozen zone. Under freeze-thaw cycles, proper temperature gradients facilitate petroleum migration from unfrozen to frozen zone, while extreme temperature gradients impede this migration. The migration processes of water and petroleum are interdependent and mutually restrictive. An increase in initial moisture content promotes petroleum migration. However, when the moisture content exceeds a certain threshold, a significant amount of pore water (or ice) occupies the pore space, which hinders petroleum migration. Additionally, as the number of freeze-thaw cycles increases, the capability of petroleum to migrate into the frozen zone significantly improves. These findings provide experimental methods and scientific evidence for further exploration of petroleum migration mechanisms in cold regions and the development of effective soil contamination remediation strategies.
In the intricate and precise natural process of the hydrological cycle,precipitation plays a pivotal driving role as the core link in the mutual transformation between surface water and atmospheric water.From a hydrological perspective,precipitation is not only the most active input in the hydrological cycle but also the primary driving force behind watershed hydrological processes.Its spatiotemporal distribution characteristics directly influence the dynamic processes of hydrological elements such as surface runoff,infiltration,and evapotranspiration.Ac-curate precipitation data is crucial for advancing hydrological studies,supporting agricultural practices,improving flood prediction,enabling effective drought monitoring,and formulating strategies to adapt to climate change.However,the Loess Plateau region,with its complex terrain and strong spatial heterogeneity,Together with the sparse and unequal distribution of rainfall ground stations,makes large-scale and accurate studies on precipitation characteristics challenging.This study concentrated on the Loess Plateau,employing remote sensing and reanalysis datasets to derive spatially distributed precipitation data for the targeted area.A comparison was conducted among nine precipitation datasets against observed data to evaluate the feasibility of each product.Furthermore,the precipitation estimation capabilities of two mixing methodologies were analyzed.The analysis reveals that the GPM dataset delivers the most accurate outcomes,whereas both MERRA-2 and ERA5_Land consistently overestimate precipitation values.The incorporation of mixing techniques enhanced the precision of precipitation estimates;notably,the maximum R(Rmax)method produced interannual precipitation predictions with a maximum deviation of merely 10 mm from observed values,thus demonstrating its accuracy in interannual precipitation estimation within the Loess Plateau.Additionally,the Bayesian Model Averaging(BMA)method outperformed individual datasets in both spatial and temporal analyses.This method effectively estimates pre-cipitation in the Loess Plateau by transforming site-specific weight values into grid formats.According to BMA estimates,average annual rainfall from 2001 to 2018 was around 445.2 mm,with a linear annual increase of 2.79 mm throughout this timeframe.Understanding the spatial heterogeneity characteristics and dynamic vari-ation patterns of spatiotemporal precipitation is of significant theoretical and practical importance for formulating scientific soil and water conservation strategies and ecological restoration plans.In the Loess Plateau,a typical ecologically fragile region,precipitation,as a crucial hydro-meteorological element,directly influences the for-mation of surface runoff,the process of soil erosion,and the potential for vegetation recovery through its spatial and temporal distribution patterns.
In the northern Da Xing'anling Mountains of Northeast China, thermokarst lakes have undergone significant changes. These changes are particularly evident along the Highway X302, which stretches from Yakeshi in the south to Yitulihe in the north, across zones of discontinuous to patchy Xing'an permafrost (XAP). Thermokarst lakes are highly sensitive to both climate warming and human activities. However, changes in their areal extent and number over the past two decades remain unclear. To identify the drivers of thermokarst lake changes in the XAP region, this study analyzes the relationship among lake dynamics, climate change, and human activities. Rich data on lake changes were extracted using the modified normalized difference water index (MNDWI) from the Google Earth Engine (GEE) and verified against the Joint Research Centre (JRC) global surface water datasets. The results show a net increase in both the number and areal extent of thermokarst lakes along the Highway X302 from 2000 to 2020. Larger lakes (greater than 0.01 km2) expanded in surface area. Meanwhile, smaller lakes (less than 0.01 km2) increased in number. A bell-shaped trend was observed, with an initial increase in lake area followed by a decline around 2013. Before 2013, climate factors such as precipitation, air temperature, and potential evapotranspiration (PET) strongly influenced lake changes. After 2013, annual precipitation became the dominant driver of lake expansion. Human activities also contributed to changes in permafrost thermal regimes, further influencing lake dynamics. These findings provide valuable insights into the management of thermokarst lakes and wetlands in the region, and offer a reference for mitigating frost-related hazards along the Highway X302.
