Environmental Earth Sciences最新文献

Soil erosion is a major issue in the Indian Himalayan region, affecting both mountainous areas and the Terai. In the Terai, significant surface soil loss is driven by factors such as sandy soils, shallow soil depth, high rainfall, and the erosive force of young rivers. Human activities, including the conversion of forests and grasslands to croplands and settlements, along with poor agricultural practices, exacerbate the problem. This pilot-scale study aimed to quantify surface soil erosion and the loss of soil organic matter and nutrients in a watershed of the eastern Himalayan Terai region of India, utilizing the Revised Universal Soil Loss Equation (RUSLE) model on a Geographic Information System (GIS) platform. The results revealed substantial soil loss ((overline{x }) = 32.0 Mg ha⁻¹ yr⁻¹), along with the removal of organic matter ((overline{x }) = 0.95 Mg ha⁻¹ yr⁻¹), available nitrogen ((overline{x }) = 1.49 kg ha⁻¹ yr⁻¹), available phosphorus (P₂O₅) ((overline{x }) = 0.50 kg ha⁻¹ yr⁻¹), and available potassium (K₂O) ((overline{x }) = 5.02 kg ha⁻¹ yr⁻¹). Ground surveys indicated that a significant portion of the local population was directly or indirectly affected by the annual loss of fertile topsoil, with farmers, agricultural workers, and tea garden owners being the most impacted. The erosion problem of Terai region remains unheard of as it does not cause direct damage like landslides. However, loss of topsoil every year declines the land productivity and curbs the agricultural financial benefit margin. The study recommends expanding soil erosion monitoring and modelling across the entire eastern Himalayan Terai region. Being a cost and time friendly reliable method, use of RUSLE on the GIS platform can be the best option for that. With updated erosion data, comprehensive management measures can be developed involving policymakers, administrators, researchers, and local communities.

High and Steep Dangerous Rocks (HSDRs) are widespread worldwide, and have always been one of the hot research topics in the field of engineering geology. To enable researchers in this field to better clarify the research object, content, and key scientific issues throughout their research process. This paper summarizes from previous studies: the classification system, triggering factors, and global distribution of HSDRs. This paper has garnered the following new insights and findings: (1) A new classification system for HSDRs has been modified and improved, named Shape Features-Stress State (SFSS). SFSS classification system has three basic categories, five general categories and ten subcategories; (2) The main triggering factors for the instability of HSDRs include seismic effect, glacial effect, natural rainfall effect and river effect. The theoretical study of mechanical models under each type of triggering factors has specificity under SFSS classification system; (3) A global distribution map of HSDRs is drawn based on the triggering factors, covering North America, South America, Europe, Asia, Africa, Oceania and Antarctica. Researchers in this field can refer to the classification system, triggering factors, and global distribution of HSDRs presented in this paper to conduct targeted studies, thereby facilitating the efficient advancement of research outcomes related to HSDRs.

Brazil is the ninth largest user of groundwater worldwide. More than 70% of the cities in São Paulo state are partially or entirely supplied by groundwater, making it the largest user in the country, but generating problems associated with intense exploitation in some regions. Managed aquifer recharge (MAR) can improve water security by purposeful water recharge to aquifers for subsequent recovery of stored water or environmental benefit; however, the extent of MAR practice is relatively limited in the region. There is a gap in the scientific, technical, and governance dimensions, with lost opportunities in the quest for greater societal resilience. The resistance to MAR practice derives from sources beyond technical or legal issues, including socio-cultural acceptance and technician uncertainty due to a lack of knowledge. The present paper evaluates the opportunities for MAR implementation in São Paulo and discusses how to increase its uptake in water resource management Therefore, it is necessary to create risk-based MAR guidelines for policymakers, water resource managers, and technicians. Furthermore, it is essential to identify the locations in São Paulo where MAR could replenish depleted aquifers by evaluating the technical, social, and institutional aspects. The result of this study shows that in critical regions such as Ribeirão Preto and Bauru, where the Guarani Aquifer System has experienced potentiometric water level drops of more than 50 m, or even in São José do Rio Preto, where thousands of private wells compete for the groundwater of the Bauru aquifer, MAR could prolong and sustain groundwater exploitation.

As one of the significant objects of remote sensing monitoring, landslides not only lead to huge economic losses, but also result in catastrophic environmental damage and human casualties. In the past few decades, piles are widely accepted and successfully applied in slope stabilization. Through numerical calculation based on limit equilibrium method, pile reinforcement effects on cohesive and cohesionless soil slopes are studied in this paper. The potential influencing factors are systematically analyzed, including cohesion, friction angle, pile truncation length, slope gradient, and soft band. A correlation was developed to predict the safety factor as a quadratic function of pile truncation length. The results show that pile reinforcement effect was related to the slope gradient and not to cohesion or friction angle. As the slope gradient increases, the pile reinforcement effect on the cohesive soil decreases, while that of the cohesionless soil increases. On the whole, the pile reinforcement effect of cohesive soil slope is better than that of cohesionless soil slope. For the slope with a soft band, the pile reinforcement effect gradually increases as the strength of soft band decreases. During the pile truncation process, the change in safety factor for slopes with a soft band can be divided into three phases: pile control phase, pile-soft band control phase, and soft band control phase. Piles are more suitable for reinforcing cohesive soil slopes containing soft bands, which can effectively improve the slope stability. The research results can provide reference for the rational use of piles and the reduction of geotechnical engineering hazards related to landslides.

In a fluviokarst region, three rarely used natural tracers, SiO₂, Na and Ba, were considered for tracking the allogenic, silicate-derived water contribution to cave streams and to final karst outflows. The concerned allogenic recharge originates in watersheds that consist of metamorphic formations intruded by magmatic rocks, for which available whole rock chemistry data indicate rather uniform contents of SiO₂ and Na but contrasting (up to one order of magnitude) contents of Ba. All three considered natural tracers proved to behave conservatively along karst flow-paths and indicated binary mixing between allogenic and autogenic inputs. However, only the dissolved Ba concentrations enabled chemical distinction between two adjacent karst catchments: one with allogenic inputs presumably derived mainly from the weathering of Ba-rich rocks (essentially granites), and the other with allogenic recharge originating mostly from the weathering of Ba-poor formations. In contrast, if only the SiO₂ and Na concentrations of the sampled waters had been considered, it would have been virtually impossible to establish whether the two adjacent karst catchments were distinct - or not - from each other. When considering each of the two karst catchments separately, the concentrations distribution of each of the three natural tracers, SiO₂, Na and Ba, consistently indicated that between a swallet and a connected cave stream, then further between cave streams and final karst outflows, the allogenic water relative contribution gradually diminished to the benefit of autogenic water.

Rock bridges play a critical role in controlling the overall stability of locked rock slopes. In order to explore the influence of freeze–thaw cycles on the shear characteristics of locked rock masses, an experimental study was conducted to analyze the deformation, crack initiation, and propagation patterns of freeze–thaw granite containing rock bridges under compressive-shear conditions. Utilizing digital image correlation (DIC) technology, direct shear tests of specimens that contained rock bridges were conducted on the DTW_1000 variable-frequency and variable-amplitude rock dynamic shear testing system. The results indicate that an increase in the number of freeze–thaw cycles (FT = 0 ~ 60) has a significant impact on the shear strength of rocks. Under constant normal stress, after 60 freeze–thaw cycles, the shear stress decreases by 22.37%, the macroscopic failure of the rock transitions from brittle to ductile, and the plastic deformation zone at the end face gradually increases, making shear failure more prone to occur. The DIC two-dimensional shear strain E_xy evolution contour map showed that under the action of horizontal stress, an uneven tensile stress field is formed at the upper and lower ends, causing tensile cracking at the tip of the rock bridge, ultimately leading to the failure of the specimen. With an increase in the number of freeze–thaw cycles, the damage parameters for θ, K_IIc, σ_r, and σ_θ decrease, and the crack propagation angle reduces from 41.3° to 24.5°. The image of crack propagation angle obtained by DIC visually shows the degree of freeze–thaw damage to the rock, and the fundamental reason is the reduction of internal friction angle and cohesion in the rock. Freeze–thaw aggravates the damage of rock bridge, which is the main reason why the shear stress deteriorates with the increase of freeze–thaw cycles. The damage to rock bridges caused by freeze–thaw cycles can lead to geological hazards such as collapses and landslides. In-depth research under freeze–thaw conditions on the crack initiation, propagation, and shear-through behavior of rock masses that contain rock bridges is crucial for understanding the deformation and fracturing mechanisms of such masses.

This research explores the relationship between aquifer vulnerability, water quality and agricultural and mining activities carried out in a southern portion of the Central Valleys of Oaxaca. This site is located on a shallow aquifer with an average thickness of 30 – 40 m, composed mainly of gravel, sand, clay and silt. These materials constitute the alluvial fill that is considered the main hydrogeological unit, which overlies the metamorphic basement of the Oaxacan complex, which acts as a lower limit restricting the flow of water towards deep infiltration. The study applies a comprehensive methodology, which combines several approaches: the thematic weighting of layers through the DRASTIC method, the analysis of physical–chemical parameters of 145 water samples to determine quality and contamination indices, the interpretation of geological-geophysical data obtained from 11 Transient Electromagnetic Surveys (TEM) that allowed the identification of isoresistive units associated with the geology of the area, these data were complemented with geological field work. The results show that the area dedicated to agriculture has a medium to high vulnerability, with water quality varying from slightly contaminated to highly contaminated, which translates into a moderate to high level of contamination. According to the geological-geophysical interpretation, this area is located in U2b, which presents resistivities that range between 200 and 300 Ohm.m related to alluvial deposits and conglomerates. In the mining activity area, a medium vulnerability was identified, with water quality indices varying from very contaminated to contaminated and contamination levels from moderate to high. The isoresistive unit at this site corresponds to U3, with values greater than 350 Ohm.m, associated with andesitic rocks. At the recharge sites, a low vulnerability was determined, with acceptable water quality indices and low levels of contamination.

Based on a series of cyclic impact and uniaxial compression tests, this study investigates the effects of prior dynamic damage on the mechanical behavior of granite specimens and their damage precursor characteristics. The results indicate that the primary wave (P-wave) velocity of granite specimens decreases as the number of cyclic impacts increases, while their internal damage variable gradually increases. Additionally, as the number of cyclic impacts rises, the ratio of crack closure stress to strength increases, while the ratio of crack initiation stress to strength and the ratio of damage stress to strength decrease for granite specimens. In order to investigate the evolution process of microcracks in different stress stages of granite specimens under different damage conditions, the acoustic emission (AE) event rate of granite specimens during deformation and failure under different dynamic damage states was statistically analyzed. Moreover, the main-frequency of AE signals from granite specimens during deformation and damage exhibits clear fractal characteristics over time. When the main-frequency fractal dimension of the AE signal before peak damage decreases to a minimum value, it is considered to be a precursor feature of critical damage of granite specimens in different damage states. These research findings offer a theoretical foundation for evaluating stability and designing support systems for tunnel surrounding rock under the influence of multiple blasting events.

Singular rock columns or blocks resting on tilted irregular rough joints can be found in rock masses in various geological environments. Their stability can be estimated based on traditional limit equilibrium approaches. However, the geometry of these rock blocks may not be regular, which makes uneasy stability computation tasks. Previous studies have addressed toppling mechanisms of rock blocks having various geometries and accounting for eroded or non-sharp-edged corners. Moreover, an analytical approach to consider the influence of regular roughness on the base of the block on its toppling response has been recently proposed. In this study, the authors advance towards a better understanding on how irregular roughness may affect the stability against toppling of cylindrical physical models with an irregular rough base in the lab, which are analyzed based on proposed analytical expressions. The study shows consistent empirical and analytical results regarding the toppling response of the samples tested, which indicates that toppling of blocks with irregular rough bases can be studied based on analytical formulations. Moreover, this roughness can slightly influence the instability mechanism of toppling, as shown in an illustrative example.

Determining the effect of loading rates on rock mechanical properties and deformation behavior is of vital importance for underground engineering with high-intensity excavation. In this study, uniaxial compression experiments with the digital image correlation technique were conducted to investigate the mechanical properties, failure modes, and apparent strain fields of the sandstone samples under different quasi-static loading rates. The loading rate effect on the characteristics of strain localization and energy was subsequently analyzed. Results show that with increasing loading rates, both the elastic modulus and uniaxial compressive strength increase logarithmically, and the failure mode changes from shear failure to tensile failure. Meanwhile, there are relationships between the initiation and development of strain localization and the loading rates. As the loading rate increases, the stress and stress level of strain localization initiation and the expansion rate of strain localization at most time increase gradually, while the duration from strain localization initiation to macro-failure decreases. The expansion area of strain localization has no obvious change pattern. In addition, the increase of loading rates enhances the energy absorption, storage, and dissipation properties of the samples, resulting in a higher energy state. It is the essential reason for the differences in mechanical behavior and strain localization of sandstone under different loading rates.