Vast deserts and sandy lands in the mid-latitudes cover an area of 17.64 x 106 km2, with 6.98 x 106 km2 experiencing seasonal frozen soil (SFG). Freeze-thaw cycles of SFG significantly influence local surface processes in deserts, impacting meteorological disasters such as infrastructure failures and sandstorms. This study investigates the freeze-thaw dynamics of SFG in crescent dunes from three deserts in northern China: the Tengger Desert, Mu Us Sandy Land, and Ulan Buh Desert, over the period from 2019 to 2024.Freezing occurs from November to January, followed by thawing from January to March. The thawing rate (2.72 cm/day) was 1.8 times higher than the freezing rate (1.48 cm/day). The maximum seasonal freezing depth (MSFD) exceeded 0.80 mat all dune slopes, with depths surpassing 1.10 mat the leeward slope and lower slope positions. Soil moisture content, ranging from 1 % to 1.6 %, is critical for freezing, and this threshold varies depending on the dune's mechanical composition. The hardness of frozen desert soil is primarily controlled by moisture, along with temperature and particle size.Temperature initiates freezing, while moisture and particle size control the resulting hardness.These findings shed light on the seasonal freeze-thaw processes in desert soils and have practical implications for agricultural management, engineering design, and environmental hazard mitigation in arid regions.

On July 20, 2024, a rainfall-induced, group-occurring debris flow event occurred in the Malie Valley, southwestern China. This study systematically investigated the damage and rainfall-triggering conditions of the debris flow event using remote sensing data, field surveys, and satellite-based rainfall measurements. Debris flows were commonly initiated by mobilizing widespread shallow landslides on steep slopes. Among them, the Lannisanwan (LNSW) debris flow was the most extensive and destructive, and its impact was amplified due to several factors, such as steep terrain gradient, high channel sinuosity index, and significant accumulation of loose material. The LNSW debris flow reached a velocity of 5.29 m/s and a peak discharge of 2,304.30 m3/s at the catchment outlet. Furthermore, the convergence of debris flows from tributaries exacerbated the hazards alongside the main valley channel. Though the event was triggered by the short-duration night rainfall, with a peak intensity of 25.44 mm/h, antecedent rainfall played a critical role. Rainfall analysis revealed that the 3-day antecedent effective rainfall total was as high as 108.75 mm, 4 to 20 times greater than those of past heavy rainfall events in the area. This study emphasizes the importance of antecedent rainfall preceding intense rainfall on landslide-type debris flows and highlights the aggravating effects of group-occurring and night-occurring on the magnitude and consequences of debris flows.

Southwest China was affected by two extreme droughts in the autumn to spring of 2012-2013 and the winter to summer of 2020-2021. These droughts caused water depletion, crop damage, and socio-economic disruption. However, little is known about the accurate representation of the two drought events and the responses of vegetation to the droughts. We used multiple vegetation indices and multi-source climate data to quantify the spatiotemporal variations of the two events. We assessed the different responses of vegetation greenness in Southwest China to the two drought events to determine the underlying mechanisms. Vegetation greenness in Southwest China showed different responses to the two events due to differences in the early hydrothermal conditions. The 2012-2013 autumn-spring drought suppressed vegetation growth in Southwest China, with a total decrease of 0.17 (31.7 %) in the normalized difference vegetation index relative to the baseline conditions in the early stage of the drought. The decrease in precipitation and soil water depletion in late summer 2012 aggravated the decrease in vegetation greenness from winter 2012 to spring 2013. By contrast, during the winter-summer drought in 2020-2021, there was an increase of 0.22 (52.3 %) in the normalized difference vegetation index in January-March 2021 relative to the baseline conditions. Adequate precipitation and soil water in the late summer to autumn of 2020 compensated for water loss due to the extreme drought, and, concurrently, more downward solar radiation and warmer conditions linked to less cloudiness contributed to vegetation greening in spring 2021. These results show that early hydrothermal conditions have a vital role in the different responses of vegetation greenness to extreme drought events. These results will help in water management and ecosystem protection in the current background of more frequent extreme weather and climate events resulting from the global climate crisis.

The Zhongning Grottoes, China, are one of the most important Tang Dynasty cultural sites on the Silk Road and contain numerous historical clay sculptures. Under the influence of human activities and natural weathering, the sculptures have experienced various types of damage, most significantly the extensive shedding of the outer fine clay layer, which plays a crucial role in maintaining the sculptures' overall structure. In this study, the mixture of soil, sand, and cotton fiber that was most suitable for restoring this layer was determined. The mechanical properties of fine clay layers with different sand and fiber contents were studied by shrinkage tests and soil beam bending tests. The main results were as follows: for a low sand content (0-45%), the tensile strength increased slightly with increasing fiber content. For a high sand content (>45%), the tensile strength decreased with increasing fiber content. The best effect was obtained for sand and fiber contents of 30-45% and 1-2%, respectively. The results provide a scientific basis for the restoration of clay sculptures in the Zhongning Grottoes.

This paper investigates the spatiotemporal dynamics and their changes of the southern limit of latitudinal permafrost (SLLP) and the lower limit of mountain permafrost (LLMP) in Northeast China, emphasizing the roles of climate change and human activities. Permafrost in this region is primarily distributed in the northern parts of the Da and Xiao Xing'anling mountain ranges and in the upper parts of the Changbai Mountains and at the summits of the Huanggangliang Mountains in the southern part of the Da Xing'anling Mountain Range. Permafrost degradation, ongoing since at least the local Holocene Megathermal Period (8.5-6.0 ka BP), has intermittently reversed during cooler climatic intervals but continues to exert significant impacts on regional environments, infrastructure stability, and carbon storage. Notably, the northward retreats of the SLLP since the mid-19th century underscore the sustained nature of this degradation, especially in southern patchy permafrost zones increasingly sensitive to warming and anthropogenic influences. LLMP variability is similarly shaped by a combination of climatic, hydrometeorological, ecological, and topographic factors. The distributions of SLLP and LLMP are further complicated by the presence of relict and sporadic permafrost, as well as the hydrothermal effects of vegetation and snow cover. Addressing the challenges of mapping and modeling boreal permafrost in Northeast China requires comprehensive field investigations, long-term in situ monitoring via station networks, and advanced numerical modeling. Emerging technologies, including satellite and airborne remote sensing (RS), geographic information systems (GIS), unmanned aerial vehicles (UAVs), surface geophysical methods, and big data analytics, offer new possibilities for enhancing permafrost monitoring and mapping. Integrating these tools with conventional field studies can significantly improve our understanding of permafrost dynamics. Continued efforts in monitoring, technological innovation, multidisciplinary collaboration, and international cooperation are essential to meet the challenges posed by permafrost degradation in a changing climate.

In subsurface projects where the host rock is of low permeability, fractures play an important role in fluid circulation. Both the geometrical and mechanical properties of the fracture are relevant to the permeability of the fracture. To evaluate this relationship, we numerically generated self-affine fractures reproducing the scaling relationship of the power spectral density (PSD) of the measured fracture surfaces. The fractures were then subjected to a uniform and stepwise increase in normal stress. A fast Fourier transform (FFT)-based elastic contact model was used to simulate the fracture closure. The evolution of fracture contact area, fracture closure, and fracture normal stiffness were determined throughout the whole process. In addition, the fracture permeability at each step was calculated by the local cubic law (LCL). The influences of roughness exponent and correlation length on the fracture hydraulic and mechanical behaviors were investigated. Based on the power law of normal stiffness versus normal stress, the corrected cubic law and the linear relationship between fracture closure and mechanical aperture were obtained from numerical modeling of a set of fractures. Then, we derived a fracture normal stiffness-permeability equation which incorporates fracture geometric parameters such as the root-mean-square (RMS), roughness exponent, and correlation length, which can describe the fracture flow under an effective medium regime and a percolation regime. Finally, we interpreted the flow transition behavior from the effective medium regime to the percolation regime during fracture closure with the established stiffness-permeability function. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The soil packing, influenced by variations in grain size and the gradation pattern within the soil matrix, plays a crucial role in constituting the mechanical properties of sandy soils. However, previous modeling approaches have overlooked incorporating the full range of representative parameters to accurately predict the soaked California bearing ratio (CBRs) of sandy soils by precisely articulating soil packing in the modeling framework. This study presents an innovative artificial intelligence (AI)-based approach for modeling the CBRs of sandy soils, considering grain size variability meticulously. By synthesizing extensive data from multiple sources, i.e. extensive tailored testing program undertaking multiple tests and extant literature, various modeling techniques including genetic expression programming (GEP), multi-expression programming (MEP), support vector machine (SVM), and multi-linear regression (MLR) are utilized to develop models. The research explores two modeling strategies, namely simplified and composite, with the former incorporating only sieve analysis test parameters, while the latter includes compaction test parameters alongside sieve analysis data. The models' performance is assessed using statistical key performance indicators (KPIs). Results indicate that genetic AI-based algorithms, particularly GEP, outperform SVM and conventional regression techniques, effectively capturing complex relationships between input parameters and CBRs. Additionally, the study reveals insights into model performance concerning the number of input parameters, with GEP consistently outperforming other models. External validation and Taylor diagram analysis demonstrate the GEP models' superiority over existing literature models on an independent dataset from the literature. Parametric and sensitivity analyses highlight the intricate relationships between grain sizes and CBRs, further emphasizing GEP's efficacy in modeling such complexities. This study contributes to enhancing CBRs modeling accuracy for sandy soils, crucial for pertinent infrastructure design and construction rapidly and cost-effectively. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Earthen sites, such as the Great Wall of China, are important elements of cultural heritage, but are at high risk of erosion due to environmental changes. In this study, unmanned aerial vehicle low-altitude oblique photography was used to assess the erosion of the Ming Great Wall in Gansu Province. The erosion characteristics (height, depth, area, and ratio) were quantified using a 3D point-cloud model. Combined with onsite sampling and analysis, the deterioration distribution was examined, and the progression of damage summarised using historical images. The degree of erosion in the rammed earth Great Wall was linked to the soluble salt content in the soil. The degree of deterioration of the walls indicates a significantly larger hollowing area on the southern side than on the northern side, and a slightly larger area on the western side than on the eastern side. This paper addresses the challenges of assessing and quantifying erosion development in specific segments and provides a risk assessment of erosion at any point in each segment. It also provides a valuable reference and scientific support for the protection and restoration projects of the Great Wall during the Ming period.

Understanding the volume change behavior of deep-water sediments is essential for the safety design of deep-water engineering structures. In this study, the volume change behaviors of marine sediments from the South China Sea were studied through oedometer and isotropic compression tests. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests have been conducted to investigate the microstructure evolution of two types of sediments under loads. The experimental results showed that the structural anisotropy of intact specimens is more pronounced in oedometer tests with the increase of stress, however, depolarization occurs in the isotropic consolidation test. The volume change after yield in the oedometer and isotropic consolidation tests comes from inter-aggregate pore variations associated with the adjustment of the soil fabric. The reconstituted specimen presents a more uniform distribution of pores than that of the intact specimen, and the macropores are more easily compressed for the reconstituted specimen than those of the intact specimen. With increasing stress, the oedometer compression and isotropic consolidation curves of intact specimens gradually approach those of the reconstituted specimen. The deformation mechanism under high stresses is that soil particles are reoriented and the variation of micropores.

The seepage of groundwater and the strain-softening of rock mass in a submarine tunnel expand the plastic region of rock, thereby affecting its overall stability. It is therefore essential to study the stress and strain fields in the rocks surrounding the submarine tunnel by considering the coupled effect of strainsoftening and seepage. However, the evolution equation for the hydro-mechanical parameters in the existing fully coupled solution is a uniform equation that is unable to reproduce the characteristics of rock mass in practice. In this study, an updated numerical procedure for the submarine tunnel is derived by coupling strain-softening and seepage effect based on the experimental results. According to the hydro-mechanical coupling theory, the hydro-mechanical parameters such as elastic modulus, Poisson's ratio, Biot's coefficient and permeability coefficient of rocks are characterized by the fitting equations derived from the experimental data. Then, the updated numerical procedure is deduced with the governing equations, boundary conditions, seepage equations and fitting equations. The updated numerical procedure is verified accurately compared with the previous analytical solution. By utilizing the updated numerical procedure, the characteristics of stress field and the influences of initial pore water pressure, Biot's coefficient, and permeability coefficient on the stress, displacement and water-inflow of the surrounding rocks are discussed. Regardless of the variations in hydro-mechanical parameters, the stress distribution has a similar trend. The initial permeability coefficient exerts the most significant influence on the stress field. With the increases in initial pore water pressure and Biot's coefficient, the plastic region expands, and the water-inflow and displacement increase accordingly. Given the fact that the stability of the tunnel is more sensitive to the seepage force controlled by the hydraulic parameters, it is suggested to dewater the ground above the submarine tunnel to control the initial pore water pressure. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).