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Frequent occurrence of landslides induced by rainfall or irrigation has seriously threatened the urban and rural development in the Loess Plateau, China. The increase in pore water pressure has been identified as a key factor for understanding wetting-induced loess slopes failures. However, experimental studies are limited regarding the increase in pore water pressure of the collapse loess from an initial negative value until failure occurs under constant total stress condition. An old landslide with progressive retreat development at an early stage of the construction of the Lvliang Airport was selected as a case study. Field surveys including exploration wells and boreholes revealed very fresh sliding shear planes and clearly visible cracks, suggesting the creeping movement of the old landslide. In case of heavy rain or long-term rainfall, this old landslide may be resurrected, threatening the stability of the airport site. To examine the mechanism of the failure induced by wetting for this unsaturated loess landslide, loess specimens were taken from the field, followed by performing a series of laboratory tests, including triaxial shear tests at constant matric suctions and wetting tests at constant deviator stresses. The test results revealed that the wetting-induced deformations of the loess included volume and shear deformations, reflecting compression and shearing behaviour induced by wetting. The failure behaviour of the loess along a wetting path was dependent on the stress level and the loss degree of matric suction as well as the hydro-mechanical path, and could be well described by the linear form of the Mohr-Coulomb strength theory. On this basis, the threshold value of the stress level was identified, which could be used to judge whether the wetting-induced failure of the loess occurs. The threshold value of matric suction at failure was also identified to analyse the loss degree of matric suction from stable conditions to failure. The mechanism of the failure of the soil due to wetting revealed from the present study could interpret the rainfall-induced landslide in unsaturated loess.

Underground coal mining often causes subsidence, goaf landslides, fissures, and even hazard chains, seriously damaging the ecological environment. To address the ecological vulnerability of mining areas is key to exploring the development characteristics and failure mechanisms of surface multi-hazards. Taking the Shuiliandong coal mine as an example, the mine deformation area was identified using differential interferometric synthetic aperture radar (D-InSAR) technology. We found that the spatial evolution of the deformation areas was controlled by the mining sequence. The impacts on the surface deformation and the mining-induced landslide were continuous and long term. Thus, the surface fissures and landslide were characterized using historical images. The fissures were clustered and short, and there was a negative exponential relationship between the length and the cumulative number of fissures. The fissure density decreased with increasing distance from the mine tunnel. In addition, the particle flow numerical simulation analysis method was used to simulate the subsidence-fissure-landslide hazard chain process. Three distinct stages were identified: initial stage, rapid development stage, and creep stage. The displacements at the different monitoring points exhibited a distinct S shape. The cumulative number of fissures developed same as the subsidence and landslide, exhibiting an S shape. The fissures played an important role in the hazard chain, accelerating the subsidence and landslide processes.

Fissured loess slopes along the railway in the Loess Plateau frequently suffer from disintegration disasters under the coupled effects of rainfall and train vibrations, causing soil collapse that covers tracks and severely threatens railway safety. To reveal the disaster mechanisms, this study conducted water-vibration coupled disintegration tests on fissured loess using the self-developed EDS-600 vibration disintegration apparatus, based on the measured dominant vibration frequencies (12–46 Hz) of the Lanzhou-Qinghai Railway. The influence patterns of vibration frequency ( f ) and fissure type ( t ) on disintegration rate ( S ), disintegration velocity ( V ), and disintegration velocity growth rate ( ) were systematically investigated, with scanning electron microscopy (SEM) employed to uncover microstructural evolution mechanisms. Results indicate that vibration frequency and fissure type significantly accelerate disintegration: V reaches its maximum at f  = 20 Hz, and under the same frequency, V increases with the growth of fissure-water contact area. Under two fissures and f  = 20 Hz, V increases by 225% compared to the without vibration and fissures scenario, with the value peaking at 137.23% and the synergistic effect index exceeding the single-factor superposition value by 45.99%. Microscopically, water-vibration coupling disrupts clay mineral cementation, reconstructs pore networks, and forms dominant seepage channels, leading to reduced interparticle bonding strength, heterogeneous water film distribution, and stress concentration, thereby inducing fractal propagation of secondary fissures and shortening moisture absorption and softening stages. Combined with unsaturated soil mechanics theory, the study reveals a cross-scale progressive failure mechanism involving simultaneous degradation of matric suction, cementation force, and macroscopic strength. A theoretical framework integrating vibration energy transfer, seepage migration, and structural damage is established, along with a quantitative relation linking vibration frequency, fissure parameters, and disintegration velocity. This provides multi-scale theoretical support for disaster prevention and control of railway slopes and foundations in loess regions.

Lvliang airport is a typical loess filling engineering located in 20.5 km north of Lvliang City in Shanxi Province, China. By the end of March 2012, 14 fissures extending more than 7.5 m were observed in a loess-filled slope, of which the longest fissure is up to 82 m. Field monitoring and laboratory tests have been performed to investigate the slope failure modes. The test program includes wetting tests on unsaturated compacted samples and stress path tests on saturated samples. Field monitoring and observations show that differential settlement caused by non-homogeneity in compacted loess density might lead to the formation of fissures in the loess-filled slope. It was founded that the wetting deformation contributed to the development of differential settlement. Fissures are the essential factor for the loess-filled slope failure. Four deformation stages exhibit in the loess-filled slope prior final failure including development of the fissures, softening of the compacted loess, creeping of the slope leading edge and fissuring of the trailing edge and formation of the through-sliding surface. Development of the sliding surface mainly includes upward and downward expansion of the fissures. Upward expansion is a wetting failure process in loading condition, while downward expansion is a load-off wetting process. In addition, development of the sliding surface is accelerated by softening of the compacted soils as a result of water infiltration. Therefore, the key for taking countermeasures against filling landslides is to monitor and control the development of differential settlement and fissures in the slope shoulders. Digging out and extra-filling the fissures are an effective way for preventing these landslides.

The engineering importance of compacted loess is now much greater than that of intact loess because of the occurrence of a large number of loess fill slopes and foundations in the last few years. Molding water content (MWC) and degree of compaction (DOC) (or dry density) are two key factors that determine the structure of compacted soil. However, it is not clear how MWC affects the mechanical behavior of compacted loess. In this study, compacted loess specimens were prepared under various compaction conditions to have different MWCs (i.e., 14, 16, 18 and 22%) or DOCs (i.e., 85, 90 and 94%). Unconfined compression tests were performed on these specimens and their counterparts, the effects of MWC and DOC on the mechanical behavior of compacted loess under unconfined condition were interpreted with the assistance of the measured pore-size distribution curves (PSDs), soil–water retention curves (SWRCs) and computed structural parameters. The results show that both MWC and DOC significantly affect the strength-deformation characteristics of compacted loess. When DOC and initial water content are given, the larger the MWC, the larger the unconfined compressive strength (UCS), and the greater the ductility of specimen because of the more uniform distribution of pores and higher suction. At a given MWC, the greater the DOC, the larger the UCS, and the greater the initial stiffness of specimen because of the closer particle arrangement. The initial structural parameter reduces with DOC and increases with MWC, indicating that the soil strength is more susceptible to disturbance from loading or soaking when DOC is smaller or MWC is larger. Consequently, this leads to a higher structure potential for compacted loess. The relationship between the initial structural parameter and UCS is not unique, indicating that the structural difference caused by different particle arrangements may still exist upon soaking, while the UCS of compacted loess grows with the initial structural parameter.

The freeze–thaw cycles will lead to rock deterioration and pose a significant threat to engineering stability in cold regions. In this study, granite samples collected from the Luanshibao Landslide in the Eastern Tibetan Plateau were subjected to a maximum of 120 freeze–thaw cycles at two temperature paths (− 10–20 °C and − 20–20 °C). The Brazilian test, uniaxial and triaxial compression tests were carried out to evaluate the strength behavior of samples while the scanning electron microscopy tests to investigate microstructural changes. The correlation between strength be-havior and microstructural evolution of samples after freeze–thaw cycles was discussed. Results indicate that the uniaxial compressive strength, elastic modulus, tensile strength, and peak strength of samples decreased nonlinearly with freeze–thaw cycles. Besides, freeze–thaw cycles exhibit more pronounced effect on the strength of samples, compared to the temperature path. Based on the Mohr–Coulomb criterion, a joint strength expression was proposed for the tensile, compressive, and shear strengths of granite, which characterizes the influence of freeze–thaw cycles and strength paths on strength behavior of granite samples. SEM images revealed the freeze–thaw damage to the microstructure of granite and further the deterioration of the mechanical properties. The results of this study can provide a valuable reference for assessing the freeze–thaw strength of granite in the context of construction in highland areas, guiding the development of more resilient engineering practices and informing future research on the long-term durability of materials in extreme climates.

Loess is susceptible to large and sudden volume reduction induced by loading or wetting. The work in this paper focused on compression and collapse behaviour of the intact loess under isotropic stress condition. To this purpose, an improved technique was introduced for the unsaturated triaxial apparatus that was capable of precise injecting know the amounts of water into the specimen, while continuously monitoring the suction. Tests were performed under two separate hydro-mechanical paths: isotropic compression at various suctions and wetting in steps at various net isotropic stresses. Experimental measurements indicated that the compression behaviour of the intact loess was highly affected by the extent of the level of the suction. The wetting-induced collapse behaviour depended on both the extent of applied net isotropic stress and the hydro-mechanical path. The collapse potential reached a maximum when the specimen was wetted at the initial yield stress. No unique of yield curve was identified from loading and wetting paths in a suction–net mean stress plane. For the same plastic volumetric strain, the suction decrease yield curve identified from wetting path appeared under the loading–collapse yield curve identified from loading path. Interestingly, the uniqueness of the yield curve was identified from loading and wetting paths in a suction–mean effective stress plane. An elastoplastic model of the intact loess under isotropic stress condition incorporating soil water retention behaviour was proposed, using the mean effective stress as constitutive stress. This model is able to reproduce the volumetric behaviour of the intact loess along constant suction paths and wetting paths quite well, using a single-valued compressibility index.

PurposeDifferent compaction conditions (i.e., molding water content or compaction degree is varied) can lead to great differences in the microstructure, which has a control on the mechanical and hydraulic properties of compacted loess. The effect of molding water content on both the microstructure and properties of compacted loess has been rarely reported. This study aims to gain a deep insight into the microstructure and water retention capacity of compacted loess under different compaction conditions.Materials and methodCompacted loess specimens with different molding water contents or compaction degrees were prepared, and their pore-size distribution curves (PSDs) and soil–water characteristic curves (SWCCs) were measured by various methods.Results and discussionThe pore-size distributions of small pores and mesopores are mainly affected by molding water content, while compaction degree only changes the density of mesopores in compacted loess. The influence of molding water content on the SWCC is mainly on the air-entry value (AEV) and slope of the curve in the transition zone, while compaction degree mainly influences the AEV.ConclusionsMolding water content has a control on the size of aggregates; with the increase of molding water content, the size of aggregates decreases, and the shape of PSD changes from bimodal to trimodal and then back to bimodal. The AEV corresponds to a diameter at which there is a sharp increase in the pore-size density. The slope of SWCC in the transition zone is related to the range of dominant diameter of inter-aggregate pores.

Abstract Rock avalanches are a significant threat to infrastructure as they can cause catastrophic damage far away from their source. To ensure the safe construction and operation of the Sichuan–Tibet railway in China, there is an urgent need for a comprehensive understanding of the initiation and movement of rock avalanches in the Sichuan–Tibet traffic corrido. The ancient Luanshibao (LSB) rock avalanche that occurred in the SE Tibetan Plateau, had a total volume of more than 64 million m3, a run-out distance of about 4 km, and a low Fahrböschung angle, making it an ideal case for understanding the underlying physical mechanisms of rock avalanches in the region. In this study, the geomorphological features of the initiation and movement of the LSB avalanche were revealed in details, through field investigations, satellite image interpretation, and UAV surveying, thereby obtaining a fault-controlled geomechanical model. The results of laboratory tests confirmed that freeze–thaw weathering created and extended microfractures that exponentially reduced the strength parameters of the rock, resulting in considerable deterioration of the rock mass. The numerical simulations indicated that although strong ground vibrations due to earthquakes were the primary trigger of the avalanche, freeze–thaw weathering and oblique-thrusting of active faulting played important roles, as reflected in the quasi-rotational sliding feature observed on-site and in the simulation. The deposition features observed in the field corresponded to three kinematic regime of rock avalanche experienced. These analyses allowed the proposal of a destabilization model that clarified the different phases leading to the initiation and development of the avalanche.

Space division multiplexing elastic optical networks (SDM-EONs) are one of the most promising network architectures that satisfy the rapidly growing traffic of the internet. However, different from traditional wavelength division multiplexing (WDM)-based networks, the problems of resource allocation become more complicated because SDM-EONs have smaller spectrum granularity and have to consider several novel network resources, such as modulation formats and spatial dimensions. In this work, we propose an integer linear programming (ILP) model without space lane change (SLC) that provides theoretically exact solutions for the problem of routing, modulation format, space, and spectrum assignment (RMSSA). Moreover, to more efficiently solve our model which is difficult to solve directly, we propose three exact algorithms based on model decomposition and evaluate their performance via simulation experiments, and we find that two of our exact algorithms can solve the model effectively in small-scale instances.