The Huainan-Huaibei mining area is widely covered with calcareous clay layers, characterized by low freezing points, high frost heave, easy disintegration upon water exposure, and low strength. Its mechanical properties are complex and variable, posing significant challenges for the construction of frozen walls. To optimize the design of frozen walls in calcareous clay, this study examined remolded calcareous clay from deep layers in the Huainan-Huaibei area, utilizing equal-stress ratio true triaxial loading tests to systematically analyze the stress-strain behavior of frozen calcareous clay under varying confining pressures and temperatures. The results indicate that variations in confining pressure and the intermediate principal stress ratio significantly affect the mechanical properties of frozen calcareous clay. The stress-strain curves of frozen calcareous clay reveal typical nonlinear characteristics: the material exhibits an elastic response in the small-strain stage and gradually transitions into plastic deformation with increasing strain, showing significant strain hardening during the plastic deformation phase. Based on a hyperbolic model and fractional calculus, a fractional hyperbolic model was developed to suit complex stress conditions, with relevant model parameters derived. The study's findings provide a theoretical basis for rational shaft frozen wall thickness design and serve as valuable references for improving artificial ground freezing construction techniques.
Characterizing complex water-conducting channels in high plateau karst regions is critical for mitigating engineering risks associated with fragile geological structures. Conventional geophysical surveys are hindered by this challenging environment: ground-based methods are limited by steep terrain, while airborne electromagnetics (AEM) often lack the required investigation depth and can be cost-prohibitive. Here, we demonstrate the efficacy of the ground-airborne transient electromagnetic (GATEM) method for mapping water-conducting channels within a geologically complex karst zone on the eastern margin of the Qinghai-Xizang Plateau. GATEM synergizes a high-power, ground-based electric dipole source for deep penetration with a drone-borne magnetic field receiver for rapid, terrain-independent data acquisition. A comprehensive processing workflow—including noise attenuation, full-field apparent resistivity imaging, terrain correction, and time-to-depth conversion—was implemented to generate robust subsurface models. The resulting models reveal coherent, low-resistivity anomalies that spatially correlate with known fault zones and stratigraphic boundaries. These features are interpreted as likely preferential groundwater pathways, offering critical insights for infrastructure planning and geological hazard mitigation. Our findings establish GATEM as a cost-effective, high-resolution geophysical tool for hydrogeological characterization in challenging plateau environments.
In the field of frequency-domain electromagnetic (EM) exploration with artificial sources, various signals have been employed. However, these signals often fail to encompass all relevant frequencies of interest (or effective frequencies), necessitating signal replacements during operations, which significantly affects fieldwork efficiency. To address this issue, a novel method for generating pseudo-random binary signals has been proposed, which can include a wide range of frequency components. With this method, the frequency requirements for most frequency-domain EM exploration projects can be met using only one waveform which is specially designed for the project. Therefore, the need for signal replacement during operations can be eliminated, leading to a great improvement in the efficiency of field work. The generation method is based on waveform superposition and hard clipping, combined with unit integration. To improve the efficiency of signal generation, a targeted improved multi-objective particle swarm optimization algorithm is used. In order to ensure the practicality of the generated signal, optimization targets the energy concentration and uniformity of effective frequencies, allowing for rapid generation of signals that satisfy engineering application requirements in just a few minutes. This type of signal has been successfully applied in numerous practical exploration projects, yielding excellent results and confirming its effectiveness in enhancing work efficiency and resistance to interference.
Per- and polyfluoroalkyl substances (PFAS) are characterized by their ability to repel both grease and water, properties that led to their initial development as surfactants and surface protectors. As novel PFAS alternatives emerge and are detected in the environment, these substances present significant challenges related to environmental media, human exposure, and health risk assessments. This article reviews current knowledge on the origins of PFAS and their pathways from production facilities and PFAS-containing products to environmental organisms and humans and summarizes existing data on toxicity and toxicological mechanisms in laboratory animals and examines associated adverse health outcomes in humans through various epidemiological studies. Although risk assessments of PFAS alternatives are complicated by unclear chemical structures and complex effects, quantitative structure–activity relationship (QSAR) models and prioritization approaches offer potential strategies for PFAS management. A comprehensive understanding of the environmental behavior and toxicology of novel PFAS will enhance their management and improve human health risk assessments.
