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Aeolian sand and loess are both natural materials with poor engineering-related properties, and no research has been devoted to exploring aeolian sand–loess composite materials. In this study, we used aeolian sand and loess as the main raw materials to prepare unfired bricks by using the pressing method, along with cement, fly ash, and polypropylene fiber. The effects of different preparation conditions on the physical properties of the unfired bricks were investigated based on compressive strength, water absorption, and softening tests and a freeze–thaw cycle test combined with X-ray diffraction and scanning electron microscope analysis to determine the optimal mixing ratio for unfired bricks, and finally, the effects of fibers on the durability of the unfired bricks were investigated. The results reveal that the optimal mixing ratio of the masses of aeolian sand–loess –cement –fly ash–polypropylene fiber–alkali activator–water was 56.10:28.05:9.17:2.40:0.4:0.003:4.24 under a forming pressure of 20 MPa. The composite unfired bricks prepared had a compressive strength of 14.5 MPa at 14 d, with a rate of water absorption of 8.8%, coefficient of softening of 0.92, and rates of the losses of frozen strength and mass of 15.93% and 1.06%, respectively, where these satisfied the requirements of environmentally protective bricks with strength grades of MU10–MU15. During the curing process, silicate and sodium silicate gels tightly connected the particles of aeolian sand and the loess skeleton, and the spatial network formed by the addition of the fibers inhibited the deformation of soil and improved the strength of the unfired bricks. [ABSTRACT FROM AUTHOR]

High-resolution air temperature distribution data are of crucial significance for studying climate change and agriculture in the Yellow River Basin. Obtaining accurate and high-resolution air temperature data has been a persistent challenge in research. This study selected the Yellow River Basin as its research area and assessed multiple variables, including the land surface temperature (LST), Normalized Difference Vegetation Index (NDVI), Digital Elevation Model (DEM), slope, aspect, longitude, and latitude. We constructed three downscaling models, namely, ET, XGBoost, and LightGBM, and applied a stacking ensemble learning algorithm to integrate these three models. Through this approach, ERA5-Land reanalysis air temperature data were successfully downscaled from a spatial resolution of 0.1° to 1 km, and the downscaled results were validated using observed data from meteorological stations. The results indicate that the stacking ensemble model significantly outperforms the three independent machine learning models. The integrated model, combined with the selected set of multiple variables, provides a feasible approach for downsizing ERA5 air temperature data. The stacking ensemble model not only effectively enhances the spatial resolution of ERA5 reanalysis air temperature data but also improves downscaled results to a certain extent. The downscaled air temperature data exhibit richer spatial texture information, better revealing spatial variations in air temperature within the same land class. This research outcome provides robust technical support for obtaining high-resolution air temperature data in meteorologically sparse or topographically complex regions, contributing significantly to climate, ecosystem, and sustainable development research. [ABSTRACT FROM AUTHOR]

Bored piles comprise an advanced pile foundation technology that has the advantages of high bearing capacity, fast construction speed, stable construction technology, and no noise or mud pollution. To study the applicability of bored piles to collapsible loess sites, the compaction effect and load-bearing characteristics of bored piles before and after immersion were studied via a full-scale field test combined with the theory of hole expansion. The results indicate that when the pile spacing is 1.0, 1.25, and 1.5 m, the average dry density of the soil between piles increases by 23.8%, 18.5%, and 3.1%, respectively, compared with that of untreated foundation soil. When bored piles are used to treat deep collapsible loess foundations, the reasonable pile spacing to eliminate the collapsibility of the loess foundation is 2.5 times the pile diameter. It is feasible to estimate the effective compaction range using the pore expansion theory, and the effective compaction coefficients of similar sites are given. The positive friction of bored piles in the collapsible loess area is more than 95.5 kPa, which increases by more than 48.5% compared with that of non-extruded piles. Therefore, the bearing capacity of a single pile is significantly improved, and it is an effective treatment method for collapsible loess areas. Under immersion, the pile side negative friction did not change significantly with a pile diameter of approximately 27 kPa, and the increase was approximately 14% compared with that of non-extruded piles. Consequently, to avoid the adverse effects of negative friction resistance on the bearing capacity of pile foundations and to fully utilize the technical advantages of bored piles, it is necessary to eliminate or partially eliminate site collapsibility before applying bored piles. The results can provide experimental support and theoretical guidance for the popularization and application of screw–squeeze piles in deep, collapsible loess areas. [ABSTRACT FROM AUTHOR]

This study focused on the coupling heat transfer mechanism and the cooling efficiency of L-shaped two-phase closed thermosyphons (L-shaped TPCTs) in the wide subgrade of permafrost regions. Considering the fact that time–space dynamics change the effects of the air temperature, wind speed, and geotemperature, a coupled air temperature–L-shaped TPCT–subgrade soil heat transfer model was established using the ANSYS 15.0 software platform, and the rationality of the model was verified through measured data. The heat-transfer characteristics of the L-shaped TPCTs and the long-term thermal stability of the subgrade were studied under different inclination angles of the evaporator (α = 15°, 30°, 50°, 70°, and 90°). Then, the cooling effectiveness of a composite subgrade with TPCTs and an XPS insulation board was numerically calculated. The results show that the heat flux of the L-shaped TPCT was the greatest when α = 50°, and the heat flux reached the maximum value of 165.7 W·m−2 in January. The L-shaped TPCT had a relatively good cooling effect on the subgrade as a whole when α = 50° and 70°, but the thawing depth at the center of the subgrade with L-shaped TPCTs reached 9.0 m below the ground surface in the 30th year. The composite subgrade with L-shaped TPCTs/vertical TPCT/XPS insulation board is an effective method to protect the permafrost foundation and improve the long-term thermal stability of the wide subgrade. The maximum heat flux of evaporation section of the L-shaped TPCT is 18.8% higher than that of the vertical TPCT during the working period of the TPCTs of the composite subgrade. [ABSTRACT FROM AUTHOR]

In permafrost regions, long distance buried pipelines are widely used to transport oil and natural gas resources. However, pipeline problems occur frequently due to the complicated surrounding environment and transportation requirement of positive temperature. In this study, a thermal insulation layer was applied to mitigate permafrost degeneration around the buried oil-gas pipelines. Based on engineering background of the Sebei-Xining-Lanzhou natural gas pipeline in China, an indoor model test was designed and carried out in which many key indices, such as the temperature regime, vertical displacement, pipeline wall stress, and water content, were closely monitored. The test results indicate that the large heat loss of the buried pipeline produces a rapid increase in ground temperatures which seriously reduces the bearing capacity of the permafrost foundation. The buried oil-gas pipelines with a thermal insulation layer can effectively reduce the thawing range and vertical displacement of the permafrost foundation around the buried pipelines, so as to control the stress of the pipeline wall in the normal range and protect the safe and stable operation of the buried oil-gas pipelines. The experimental results can serve as a reference for the construction, operation, and maintenance of buried oil-gas pipelines in permafrost regions. [ABSTRACT FROM AUTHOR]

In order to study the physical and mechanical properties of loess reinforced with F1 ion curing agent, California bearing ratio (CBR) test, unconfined compressive strength test and triaxial unconsolidated undrained test were carried out. Based on the results of scanning electron microscope (SEM), nuclear magnetic resonance (NMR) and X-ray diffraction (XRD), the mechanical properties and micro-pore structure of loess reinforced by F1 ion curing agent were studied. The test results show that the F1 curing agent can reduce the plastic limit, increase the liquid limit, plastic index and maximum dry density of soil by cation exchange, destroy the double layer structure and the hydrophobic effect of sulfonated oil, and improve the water sensitivity and compaction characteristics of soil; F1 can significantly increase the CBR value, unconfined compressive strength and shear strength parameters, and 0.3 L/m³ is the best dosage of loess reinforcement; F1 changes the pore structure and contact form between particles, promotes the aggregation and condensation between particles, reduces the fractal dimension of the pore distribution of microstructures from 1.244 to 1.076, and greatly reduces the total pore area and total pore number of soil. Under the action of rolling, a laminated stack structure with tighter arrangements, larger agglomerates and surface-to-face contact is formed as main contact style, which enhances the compactness and bearing capacity of the soil. [ABSTRACT FROM AUTHOR]