In recent years, with the development of geothermal resources, the thermal conductivity of soil has become a research hotspot. In this study, the thermal conductivity measured by the transient plane ...heat source method was used to evaluate five common thermal conductivity models from the previous literature. The influences of water content and salt content on the internal heat transfer mode of this soil are explored. It was found that the presence of water in soil changes the conventional mode of point-to-point heat transfer between solid soil particles. With increases in water content, “liquid bridges” are formed between particles. During their formation, NaCl brine can transfer heat in a similar way to water. In this experiment, the model of Usowicz et al. (Intern J Heat Mass Transfer 57:536–571, 2006) was found to best describe the thermal conductivity of soil with salt contents of 0%, 2%, 4% and 6%. This study provides a valuable reference for the development of geothermal resources in the Guanzhong area and for engineering projects in loess areas.
Saline loess is an important cause of environmental geo-issues in northwest China. In this research, electrical resistivity of loess with different moisture contents and NaCl concentrations was ...measured at three test frequencies. Results indicates the plastic limit (16%) and around 2% NaCl concentration are the critical content affecting the variation of loess electrical resistivity. The variation and conductivity for conductive paths are affected by moisture content and NaCl concentration respectively. Combined with three-phase composition and diffuse double-layer structure, new models that consider the effect of moisture content and NaCl concentration indicate good applicability in the validation datasets from different types of soil. A new model was verified by comparison between previous studies and experimental results. This research provides (i) theoretical support for the calibration of large-scale electrical field surveys and the observation of saline loess and (ii) a valuable reference for the prevention of environmental geo-crisis and the utilization of soil resources in northwestern China.
As a special soil widely existing in world, loess engineering properties are often disturbed by water and salt. Hence, the influence of water content and salt content on the conductivity properties ...of loess was analyzed using the electrical resistivity of loess obtained by LCR digital bridge tester in this study. Loess electrical resistivity with different water content (8–20%) and NaCl content (0–6%) was obtained at test frequencies of 100 Hz, 1 kHz, and 10 kHz. Results show that loess electrical resistivity exhibited an exponential function with a change in water content. As water content increased, loess electrical resistivity decreased significantly. When water content exceeded the plastic limit, loess electrical resistivity decreased slowly. When NaCl content around 2%, the increase of ion content in conductive path of loess enhanced loess conductivity. When NaCl content reached 6%, the conductive capacity of the loess tended to reach its maximum, and the resistivity slowly decreased and stabilized. There was a nonlinear functional relation between loess electrical resistivity and test frequency. As the test frequency increased, the number of ions that could be used to form a conductive path increased, and loess electrical resistivity decreased. In addition, three paths model of loess electrical resistivity and double-layer structure can well explain above phenomena. This research can provide theoretical basis for electrical resistivity technology to predict water content and salt content, and valuable reference for large-scale field application of electrical resistivity observation technology.
Self-sealing performance of compacted bentonite is the key to reduce the threat posed by high-level radioactive waste in deep geological repositories to the geological environment and human habitat. ...However, it will be inevitably affected by the field groundwater chemistry, thus influencing the water retard capacity of the engineering barrier. For this reason, a series of hydration tests with simulated radial technological voids were conducted on compacted bentonite, and the evolutionary process was visualized using a custom-designed device. Effect of groundwater concentration was considered using synthetic water with different total dissolved solids. Results show that the filling of the technological void is actually a free swell process, and the fast increase of crack area coincided with the rapid expansion of the primary swelling. As the salinity increased, the crack development extent decreased in terms of both propagation rate and the maximum crack area and so was the time duration to reach the peak of cracking. However, in the cases of higher salinity, a slower sealing rate and longer sealing period were observed. At the end of the hydration test, the water content decreased as the water salinity increased at all sample locations; the dry densities of the inner and middle sections were larger than that in the outer section. Those observations are of great importance in the evaluation of the self-sealing capacity in the field of water chemistry conditions and thus guide the design of the engineering barrier.
Radon gas is a cancer risk and exists naturally in certain soils, such as loess, which is an important raw earth construction material in arid regions such as northwestern China and southern USA. ...Accordingly, the radon exhalationed from building materials is of increasing concern; however, there is little research on radon exhalation from loess. In this study, the pore structure and radon exhalation characteristics of heat-treated loess were investigated by nitrogen adsorption tests, swept surface electron microscopy, and radon measurements. The rate of radon exhalation increases linearly with temperature until 400 °C and then decreases exponentially. Changes in the internal pore structure (pore type, surface morphology, and specific surface area) of loess are strongly correlated with the radon exhalation rate. The volume of micropores (<2 nm diameter) is an important influence on radon exhalation ability, which is closely related to the fractal dimension of the micropore structure after heating. The results provide guidance for predicting the radiation risk posed by radon diffusing from loess.
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•The radon diffusion rate of high temperature loess was studied in detail.•High temperature seriously affects the diffusion rate of radon in loess.•Micro-pore volume is positively correlated with the radon diffusion rate.•The diffusion rate of radon in loess is the fastest at 400 °C.
During anaerobic fermentation of food waste (FW), acidification destabilizes the fermentation, and affects methane production. This study analyzed the anaerobic fermentation of FW to produce acid and ...gas under different food-to-microorganism (F/M) ratios after adding zero-valent iron (ZVI) to improve the performance of anaerobic fermentation. Results showed that when the F/M was 2, ZVI had a significant promoting effect on acetic acid, ethanol, and butyric acid production but significantly reduced propionic acid production. Moreover, optimal acid production was observed when 6 g L−1 ZVI powder was added. Furthermore, at ≥6 g L−1 ZVI, the biodegradation rate increased to >70%, and the cumulative methane production of the load increased to >440 mg L−1. Therefore, these results indicate that adding ZVI to FW digestion under different F/M ratios can increase methane production in an anaerobic fermentation system by promoting acetic acid production and reducing propionic acid production.
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•New fracture developed in open mode at 0°-40°, and in closed mode at 60°.•New cracks emerged from the tip of pre-cracks and developed to the upper point.•Shear damage mode dominates the nascent ...crack development process.•Tension damage mode plays a facilitating role in crack expansion.•Misalignment caused by local stress concentrations develops into nascent cracks.
Fracture damage in loess poses a significant threat to the safety of loess-based infrastructure in the China Loess Region. To investigate the fracture damage behavior of loess, three-point bending tests were performed on semi-circular loess specimens containing cracks prefabricated at four angles relative to the loading direction. High-speed photography and acoustic emission monitoring were used to record the fracture damage process. Mechanical strength, crack evolution and acoustics emission signals were investigated in relation to prefabricated crack angles. Based on the results, a fracture damage mechanism for loess was obtained. This paper provides an in-depth understanding of the fracture damage behavior of loess, and a meaningful reference for the prevention and control of geo-crises caused by cracking.
The main goal of this study is to assess and compare three advanced machine learning techniques, namely, kernel logistic regression (KLR), naïve Bayes (NB), and radial basis function network ...(RBFNetwork) models for landslide susceptibility modeling in Long County, China. First, a total of 171 landslide locations were identified within the study area using historical reports, aerial photographs, and extensive field surveys. All the landslides were randomly separated into two parts with a ratio of 70/30 for training and validation purposes. Second, 12 landslide conditioning factors were prepared for landslide susceptibility modeling, including slope aspect, slope angle, plan curvature, profile curvature, elevation, distance to faults, distance to rivers, distance to roads, lithology, NDVI (normalized difference vegetation index), land use, and rainfall. Third, the correlations between the conditioning factors and the occurrence of landslides were analyzed using normalized frequency ratios. A multicollinearity analysis of the landslide conditioning factors was carried out using tolerances and variance inflation factor (VIF) methods. Feature selection was performed using the chi-squared statistic with a 10-fold cross-validation technique to assess the predictive capabilities of the landslide conditioning factors. Then, the landslide conditioning factors with null predictive ability were excluded in order to optimize the landslide models. Finally, the trained KLR, NB, and RBFNetwork models were used to construct landslide susceptibility maps. The receiver operating characteristics (ROC) curve, the area under the curve (AUC), and several statistical measures, such as accuracy (ACC), F-measure, mean absolute error (MAE), and root mean squared error (RMSE), were used for the assessment, validation, and comparison of the resulting models in order to choose the best model in this study. The validation results show that all three models exhibit reasonably good performance, and the KLR model exhibits the most stable and best performance. The KLR model, which has a success rate of 0.847 and a prediction rate of 0.749, is a promising technique for landslide susceptibility mapping. Given the outcomes of the study, all three models could be used efficiently for landslide susceptibility analysis.
Saline loess is widely distributed in Africa, Latin America and Asia and is characterized by wet expansion and dry shrinkage, which has a large impact on the environment. In this study, the ...electrical resistivity of sodium sulfate loess and sodium chloride loess with moisture content (8–24%) and salt content (0.3–2.7%) was measured by an LCR digital bridge instrument. The experimental results demonstrated a decrease in the resistivity with the increase in moisture and salt content. When the salt content was greater than 0.9%, the rate of reduction in resistivity decreased and showed a tendency to be stable. With the increase in moisture content, the water conductive path changes from water in diffusion double layer (DDL) to capillary water and finally to gravity water, which in turn leads to a gradual decrease in the rate of reduction in resistivity. At the same salt content, the resistivity of sulfate loess is higher than that of chloride loess. This study analyses the resistivity changes of two kinds of salt-bearing loess under different water and salinity conditions, which has certain guiding significance for environmental monitoring and pollutant assessment based on resistivity data.
As the first hyperspectral infrared sounder onboard a geostationary satellite, FengYun 4A (FY-4A) Geostationary Interferometric Infrared Sounder (GIIRS) plays an important role in high-impact weather ...forecasting with a high spatial and temporal resolution. Because hyperspectral infrared data are highly sensitive to clouds and these cloud-affected data are currently challenging to assimilate, cloud detection is a necessary step to assimilate hyperspectral infrared data better. FY-4A GIIRS has been operationally assimilated in the Chinese operational numerical weather prediction (NWP) system China Meteorological Administration Global Forecast System (CMA-GFS), which uses an imager-assisted cloud detection method to detect the clear-sky field of view. This article develops a new cloud detection method to detect clear channels for FY-4A GIIRS in CMA-GFS, extending the original method from two-dimensional (2-D) to three-dimensional (3-D) space. Compared to the original method, the 3-D cloud detection (3DCD) method increases the number of observations to two to three times for the middle- and lower-tropospheric channels and three to four times for the upper-tropospheric channels. The additional observations are of the same quality as those retained by the original cloud detection method, and the averaged observation minus background (OMB) biases after bias correction for upper-tropospheric channels decreased 54% compared to the original. Experiments results indicate that this method successfully achieves the cloud detection in 3-D for GIIRS data and shows the potential in improving data utilization. Also, the results show that 3DCD has a slightly positive impact on temperature and wind forecasts.
