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Red clay is widely distributed globally and is closely related to human production and life. The middle reaches of the Yellow River basin in China are characterized by complex geological structures, concentrated rainfall periods. The soluble salts such as sodium sulfate enter the red clay particles along with the infiltrating water, forming a red clay-like saline soil. In order to study the effects of water and salt on red clay soils, this paper uses red clay in the Heyang of Weinan with different ratios of distilled water (10–20%) and Na2SO4 (0–4%), and obtains the resistivity of red clay soils at different frequencies (100 Hz–100 kHz) using an inductance, capacitance and resistance digital bridge tester. The results show that the resistivity of red clay is negatively correlated with water and salt content. With the increase of water content, the increase of conductive paths in the pore water improved the electrical conductivity of the red clay; while when the concentration of Na2SO4 increased, the free moving anions and cations in the pore water increased, the electrical conduction efficiency increased and the resistivity decreased. The high frequency increased the conductivity of red clay by contributing to electrical double layer deformation, whereas the electrode polarization led to inhibition of conductivity under low frequency. A negative power exponential relationship exists between the resistivity of red clay and the test frequency. This study may provide a valuable reference for the rapid identification of the physical properties of red clay and its internal structure. [ABSTRACT FROM AUTHOR]

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In previous research concerned on mercury intrusion porosimetry (MIP), the fractal curves of six fractal models tended to have segmentation characteristics. However, most of these models are rarely applied to loess pores and often have inconsistent results. Therefore, this paper used a combination of techniques to study the loess pore structure and permeability properties, including routine tests, MIP analysis, and scanning electron microscope (SEM) image analysis. The results indicate that different models have various goodness of fit and fractal dimensions. Among them, the Zhang-Li model had the best fractal features. However, there are certain similar segmentation diameters between different fractal curves, suggesting that the segmentation diameters are determined by the pore structure, rather than by the fractal models. By using a new modeling detection method, the paper determined that the segmentation diameters are centrally distributed around two diameters: d1 (7.08 μm) and d2 (0.035 μm). The pore structure is divided into three regions based on these two diameters. Furthermore, the paper proposes a new parameter λ, the relative content for pores with diameters larger than d2 (0.035 μm), which is used to correct effective porosity and permeability prediction. The traditional K-C equation is only 68.41% of the goodness of fit in predicted and measured values. After correcting the porosity, it rises to 77.99%, while the correcting prediction equation based on the pore-size distribution function is 80.46%. These results prove that our new segmentation method for loess pore structure and effective porosity correction is reasonable for permeability estimation. [ABSTRACT FROM AUTHOR]

Loess has a loose metastable structure, which is not difficult to destroy under loading. As the core of loess structures, the current main research directions of loess engineering properties are studying their microscopic behaviours and then interpreting and predicting macroscopic mechanical properties. In this study, based on the analysis of the basic physical properties of loess samples from seven different places, each sample is scanned using X-ray with continuous slice computed tomography (CT), and the three-dimensional microstructure of loess samples is established. According to the computer graphics method, each particle is equivalent to an ellipsoid, and the flattening rate and elongation rate of particles in each sample are quantitatively counted. Taking the particle size distribution (PSD) and shape parameters (flatness and elongation) of each sample as the control factors for generating discrete element method (DEM) samples, a series of triaxial compression simulation tests are conducted, and the microscopic behaviours of each sample are studied within the entire test framework. Comparing the results of seven different samples, it is shown that both PSD and particle shape have effects on the stress–strain relationship, dry density and normal contact force of loess samples. Most of the sand particles (> 0.075 mm) are flat particles, while the clay particles (< 0.005 mm) are mainly near spheres. When the volume fraction of sand particles is large, the dry density of the sample is the lowest. However, when the content of near-spherical clay particles is large and the PSD is good, the average coordination value is large, which shows that it has a strong normal contact force and thus a higher shear strength. [ABSTRACT FROM AUTHOR]

Geophysical exploration can be effective in detecting and monitoring potential sources of coal mine water in-rushes and underground watercourses. Generally, in-mine seismic, DC resistivity, and transient electromagnetic methods are used for such purposes in China. However, such technologies can be influenced by many factors, such as roadways, fissures in the surrounding rocks, and various secondary conditions. Our review of current geophysical methods and tools concludes that further basic research should be carried out on geophysical field propagation in the whole space, data collection methods, and inversion methods appropriate for the special environment of coal mines. Moreover, borehole and roadway space should be designed to incorporate effective geophysical drilling, cross-hole exploration, drilling-roadway exploration, and roadway-roadway exploration. Future hydrogeophysical exploration research should focus on comprehensive geophysical methods combining multi-field synergistic observations with multi-field data integration and automatic monitoring as well as early warning systems for mine water disasters combining real-time processing and analysis of exploration equipment with Internet of Things technology. [ABSTRACT FROM AUTHOR]

The original article can be found online at https://doi.org/10.1007/s10064-022-03016-z. B Correction to: Bulletin of Engineering Geology and the Environment (2022) b https://doi.org/10.1007/s10064-022-03016-z The above article was published with error. [Extracted from the article]