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Metro transit construction has begun to develop rapidly in northwest China because of the acceleration of urbanization. Accordingly, metro depots are also regarded as an essential auxiliary facility for stopping, operation, and maintenance of trains. Meanwhile, many commercial buildings are constructed over metro depots to improve the utilization rate of land due to the increasingly scarce urban land resources, known as transit-oriented development (TOD). These buildings have a large covered area and transfer concentrated loads to the bases. Therefore, pile bases under metro depots have the bearing characteristics of undertaking large concentrated loads, while lesser loads are placed on the soil between the adjacent pile bases. Additionally, the main ground in northwest China is collapsible loess, so the collapsibility should also be considered. Based on the above background, this research performed static loading tests with and without immersion in a reduced scale of adjacent pile bases under a metro depot in Xi'an. The remolding process of natural loess could destroy its structure and the anisotropy of natural loess could also affect the test results. Therefore, four kinds of artificial collapsible loess with different mass ratios of barite powder, kaolin, river sand, cement, industrial salt, and calcium oxide were made by the free-drop method. This method could make the artificial loess simulate the structure of natural loess reasonably. Then, the artificial loess with the most similar properties to intact loess was selected by comparison. Finally, static loading tests with this artificial loess were implemented. The results showed that the ultimate bearing capacity was 4.5 kN. At the same time, the axial force decreased along depth, since the pile shaft friction was positive, and the load sharing ratio of pile tip force increased to 0.58 when the load exceeded 4.5 kN in the situation without immersion; the settlement of pile bases increased significantly after immersion, while the negative shaft friction occurred at the depth of −8 cm~−35 cm, and the load sharing ratio of pile tip force reached 0.92. [ABSTRACT FROM AUTHOR]

The present study aims to establish how the agricultural lands in Sălcuța Plain, a piedmont subunit of the Romanian Plain, are affected by the presence of micro-depressions on loess deposits. The formation of these microdepressions is closely related to the chemical and mechanical compaction process, which is conditioned by several factors, including the thickness of the loess deposit, the quantity of carbonates in the deposit, local morphometry, paleogeographic evolution, and climatic conditions. Based on satellite imagery from the 2010-2019 period, 303 microdepressions were identified. Out of the total number of depressions, 293 are located on agricultural lands, covering approximately 9.31 km2. On the surface of some of these depressions, soils with stagnant horizons (0.7 km2) have formed due to prolonged excess moisture. These types of soils gradually lead to the long-term degradation of agricultural lands. It is recommended to constantly monitor the evolution of soils with stagnant horizons and implement ameliorative agricultural measures in case an expansion of their area is observed in the long term. [ABSTRACT FROM AUTHOR]

Deformation Prediction of compacted loess is important for the constructions on the land created with such soil. In this study, in-situ fiber-optic monitoring was employed through a 77 m-deep borehole to obtain the variations of deformation and water content in both compacted and natural loess. The monitoring results were analysed together with the sampled soil properties. Initial field studies indicated that natural loess experienced much smaller deformation than compacted loess because of its cementation and different structure. Further analysis showed that the variations of stress and water content increment are the most significant factors in compacted loess, exhibiting a logarithmic relationship with loess deformation. Dry density is also important but needs to be considered in conjunction with stress in the vertical direction, while initial volumetric water content and clay-size fraction exhibit insignificant effects on the time-dependent deformation of compacted loess. Based on the analysis of these factors, a time-dependent model was developed, allowing the compacted loess deformation to be estimated. The proposed model was further verified by a numerical analysis using the artificial neural network (ANN) method, showing the relevance of the factors identified from the field data analysis and adopted in the proposed model. • Field investigations were conducted through a 77 m-deep fiber-optic borehole. • Coupled influences of various factors on compacted loess deformation were investigated. • A time-dependent deformation prediction model for compacted loess was developed. [ABSTRACT FROM AUTHOR]

The soil organic carbon isotope indicator (δ13C org) is widely used in paleoecology and paleoclimate reconstruction due to its ability to record the history of paleovegetation change. Although it has been used as a proxy for precipitation reconstruction, increasing evidence suggests that temperature has played a crucial role in influencing the relative abundance of C 3 /C 4 plants in the mid-latitudes during the interglacial period. This opens up the possibility of reconstructing Holocene temperature using δ13C org. In this study, the variation of δ13C org values in a Holocene loess profile (GLH profile), located in the eastern Hunshandake Sandy Land, China, was investigated. And we analyzed the correlation between δ13C org values and modern temperatures for a total of 792 surface soil samples from mid-latitudes of the Northern Hemisphere, which had thermal conditions comparable to the GLH profile. Strong positive correlations were found between δ13C org values of surface soil samples and both summer temperatures (r = 0.672, p < 0.001) and growing season temperatures (r = 0.669, p < 0.001). Additionally, δ13C org values showed significant positive correlations with accumulated temperatures above 10 °C (r = 0.641, p < 0.001) and above 0 °C (r = 0.527, p < 0.001). However, the correlation with mean annual temperature was weak (r = 0.280, p < 0.001). The δ13C org variation in the GLH profile recorded a mixed C 3 /C 4 vegetation composition, with C 4 plants comprising between 23.40% and 1.70% of the total abundance during the Holocene. The combined evidence from modern processes and profile variations confirms that warm-season temperature was the main factor driving variations in the δ13C org values in the GLH profile. Therefore, we used δ13C org –temperature conversion equations to quantify Holocene seasonal and accumulated temperatures based on the GLH profile. The reconstructed summer temperatures peaked at 9.3 ka, followed by a fluctuating downward trend during the mid- and late-Holocene, which is consistent with variations in summer solar insolation. Mean summer temperatures were relatively high at 23.3 °C and 22.5 °C in the early and mid-Holocene, respectively, while the lowest mean summer temperature of 20.5 °C occurred in the late Holocene. Accumulated temperatures above 10 °C and above 0 °C in the early Holocene were 3722 °C·d and 4641 °C·d, respectively, similar to modern observations in the Beijing area, indicating a southward shift of the temperature zone by nearly three degrees of latitude since the early Holocene. These reconstruction results are supported by modern observations, TraCE21 simulations, and other studies. This study is significant for extending the application of the δ13C org indicator for quantitative paleoclimate reconstructions. It verifies its effectiveness in quantifying Holocene temperatures in the marginal zone of the East Asian summer monsoon. • Attempt to reconstruct paleotemperatures quantitatively using the δ13C org indicator. • Conversion equations established between δ13C org - temperature in mid-latitude regions. • Holocene summer temperature and accumulated temperature (T ≥ 0 °C, T ≥ 10 °C) obtained. • Holocene summer temperature peaked at 9.3 ka and was controlled by solar insolation forcing. • Temperature zone shifted nearly three latitudes southward since early Holocene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple isotopes revealed nitrate transport and transformation processes. • Old apple orchards had large water deficit and nitrate accumulation. • High transpiration effects resulted in no water and nitrate fluxes in deep layers. • The fertilizer-based nitrate bombs would reach the aquifers after hundreds of years. The deep-rooted economic trees decrease water storage but increase nitrate-nitrogen (NO 3 –N) accumulation in the soil due to the root water uptake and excessive use of fertilizers. Knowing how the NO 3 accumulates in the soil and to what extent it can be flushed out or transformed can provide insights on the processes controlling N flux to waterways. We sampled cultivated farmland and orchards with varying ages of apple and peach trees in the loess deposits to > 15 m depth to measure the contents and isotopes of water and NO 3 in soils. The novelty of this study is that the water isotopes are used to analyze water and NO 3 transport, while the NO 3 isotopes are further employed for NO 3 source and transformation analysis. The parabolic NO 3 –N profiles (258–3579 kg N ha−1) were mainly observed within 0–5 m under different land use types. The surface-aggregated NO 3 reservoirs under old apple orchard were about six times of farmland due to the overuse of chemical fertilizers, while those of peach orchard were only half of farmland because of less fertilizer inputs and possible root absorption effects. Piston flow resulted in the overall slow water movement and low NO 3 flux under different land use types in deep loess deposits. Despite the soil water recharge by precipitation and low surface evaporation, the strong transpiration effects further resulted in no water and NO 3 fluxes in the deep layers under old apple orchard. Nitrate reservoirs were mainly contributed by soil organic N (44 % ± 26 %) and ammonium N fertilizer (36 % ± 20 %), but their transformation was dominated by nitrification under old apple orchard and by mineralization in deep layers. The risks of NO 3 bombs are temporarily weakened by lower dried soil layers under deep rooted plants; however, with lower water movement rates and limited denitrification potential, NO 3 would eventually reach the aquifers in a few hundred years or more. This study provides new insights for clarifying NO 3 transport and transformation processes by combing multiple isotopes, and the NO 3 bombs would chronically endanger the sustainable development of terrestrial ecosystems and the environment in arid regions. [ABSTRACT FROM AUTHOR]