Bulletin of Engineering Geology and the Environment最新文献

Rainfall-induced erosion on slopes is a prevalent natural process leading to soil loss. One promising application of microbially induced carbonate precipitation (MICP) is to mitigate rainfall-induced erosion. Conducting field tests is an essential step to verify and improve its performance. In the current work, field tests were conducted to assess the feasibility of using MICP to mitigate rainfall-induced erosion on a gravelly clay slope in Longyan, Fujian, China. A temporary laboratory was set up to cultivate bacteria, and a non-sterilizing method was employed to prepare large volumes of bacterial suspensions in a single batch. Slopes were treated by spraying solutions onto their surfaces. The amount of discharged soils and 3D surface scanning results were used for evaluating the erosion intensity of the slopes. The results demonstrated that the method could effectively mitigate the surface erosion caused by natural rainfall and prevent erosion-induced collapse. Notably, approximately one year after the treatment, the grass had started to grow on the heavily cemented slope, indicating that the MICP method is both effective and eco-friendly for soil stabilization method. However, further improvements are needed to enhance the uniformity and long-term durability of the MICP treatment.

Compressed air energy storage (CAES) technology is a vital solution for managing fluctuations in renewable energy, but conventional systems face challenges like low energy density and geographical constraints. This study explores an innovative approach utilizing deep aquifer compressed carbon dioxide (CO₂) energy storage to overcome these limitations. To identify the factors affecting compressed CO₂ energy storage system in deep aquifers, numerical simulations using T2well/ECO2N investigate hydrodynamic and thermodynamic behaviors, focusing on the impact of aquifer properties (depth, thickness, porosity, and permeability) and operational parameters (wellbore penetration depth through the aquifer and energy storage scale) on system performance. The findings reveal notable pressure variations in both the wellbore and aquifer during system operation and the injected supercritical CO₂, input by geothermal energy from the surrounding formations, contributes to high energy storage efficiency across the entire system. The impact factor analysis suggests medium aquifer depth and permeability, a storage space with high porosity, increased aquifer thickness, greater wellbore penetration depth, and larger energy storage scales contribute to the safe and efficient operation of the system.

The complex interaction between the cutters and rocks in the tunnel face makes it difficult to predict the cutter wear, exactly. Therefore, many researchers have tried to study this process and introduce different ways to predict the wear extent of cutters and the number of cutters required to complete a mechanized tunneling project. In this study, in addition to investigating the effect of geological parameters on cutters wear/life, new empirical equations were proposed for predicting cutter wear/life, based on data collected from a long tunnel constructed in central parts of Iran, namely Kerman Water Conveyance Tunnel (KrWCT). The data collected from this project, including information related to cutter change stations, variations of geological parameters along the bored section of the tunnel, and actual machine’s operational and performance parameters, were compiled in a database and analyzed statistically. The results of statistical analyses revealed a significant relationship between the cutter wear/life and intact rock properties. Consequently, the proposed empirical prediction equations just employ two important intact rock properties, including rock strength (UCS) and Cerchar abrasivity index (CAI), as inputs. The results showed that the presence of discontinuities with moderate-wide spacing has a negligible effect on cutter consumption. These results also proved that models focusing only on rock abrasivity without considering the rock strength as an input will not provide an accurate assessment of the cutting tool wear. The new models are based on information from a wide range of igneous, pyroclastic, and sedimentary rocks with the UCS and CAI ranges of 50–250 MPa and 0.5-5.0, respectively.

Hydraulic fracture dynamics are complex due to interactions with geological features such as bedding, joints, and microcracks, which complicate multi-cluster fracking processes. This study employs a discrete element method-based numerical simulation to investigate competitive fracture propagation in multi-cluster fracking of laminated shale, focusing on how perforation cluster settings influence fracture geometry in layered formations. Additionally, considering the prevalent high-angle natural fractures (NFs) in continental shales, the research examines the competitive propagation of multiple hydraulic fractures within these NF zones. Fracture propagation near certain perforation clusters exhibits unevenness, resulting in diverse final fracture geometries due to competitive propagation effects. A greater number of clusters lead to more diverse fracture patterns, while larger cluster spacing reduces stress interference during multi-fracture propagation. Varied fracture shapes may result from stress disruptions that unevenly affect adjacent fractures, causing early termination in some and reducing cluster efficiency. For more than five clustered stages, refracturing with temporary diversion is recommended to enhance cluster efficiency. Furthermore, the reservoir zone after multi-cluster fracturing features complex fractures near the well (Area I) and simpler ones farther out (Area II). Proximity to NFs enhances complexity near the well but inhibits hydraulic fracture propagation farther from the wellbore. Therefore, designing reasonable cluster spacing based on the reservoir’s permeability and drainage radius is essential for maximizing the pay zone of Areas I and II. This research elucidates competitive fracturing dynamics in multi-clustered laminated shale reservoirs, informing the theoretical basis for reservoir unit division and providing foundation for further optimized development strategies.

Fabric anisotropy significantly influences the mechanical behavior of sandy soils, potentially resulting in diverse failure patterns during shield tunneling owing to insufficient support pressure. In this paper, a set of specimens with bedding angles ((alpha)) and an isotropic specimen are well generated to simulate active failure at the tunnel face using DEM. The evolving failure of the soil in distinct (alpha) are scrutinized, and ground settlement is further explored. Furthermore, microscopic information is juxtaposed to systematically elucidate the influence of (alpha) on failure patterns at a microscopic level. Macroscopic findings reveal that, aside from specimens with (alpha) = 0° and 90°, particle displacement experiences deflection as it extends toward the ground surface in other specimens. However, this deflection behavior is only noticeable under conditions of large deformation. Additionally, across all specimens, the maximum displacement of the ground surface is observed in those with (alpha) = 90°, while the minimum value is noted in specimens with (alpha) = 45°. Notably, considerable particle rotation occurs within the shear face. However, the deflection behavior has not been found in specimens with (alpha) = 0° and 90°. Similarly, in specimens with these two specimens, there is no noteworthy deflection observed in the principal direction of contact normal.

Rock masses are inherently complex media, composed of intact rocks and fractures, and their mechanical behavior and deformation characteristics are significantly influenced by the characteristics and development of fractures. In this study, a discrete fracture network (DFN) model was constructed based on comprehensive field surveys and meticulous laboratory tests. By utilizing the finite-discrete element method (FDEM), we conducted simulated compression tests on the rock mass in the cavern area of the GS hydropower station. The expansion patterns and stress–strain characteristics of fractures during compression were meticulously analyzed, allowing the rock mass failure process to be categorized into four distinct stages. Furthermore, the properties of the rock mass were calculated and validated against empirical formulas derived from established engineering rock mass classification systems. The findings revealed that the DFN model accurately captures the impact of fracture development on the deformation modulus of rock masses. The orientation of fractures was found to significantly influence the mechanical properties of the rock mass, and the patterns of fracture expansion and connectivity emerged as crucial factors affecting rock properties. This methodology allows for a more accurate calculation of the mechanical characteristics of the rock mass, providing reliable parameters for engineering design.

Rock pores crack and expand subjected to freeze-thaw cycles, resulting in the reduction of their physical and mechanical properties, it is necessary to study its evolution and deterioration mechanism. However, the majority of existing studies employ a singular pore testing methodology, and neglecting the impact of the thawing process on frost heave damage in rocks. To address this, this study employs a combination of non-destructive testing techniques, including nuclear magnetic resonance (NMR) and computed tomography (CT) scanning, to comprehensively analyze the evolution of pores during freeze-thaw cycles. Investigating the migration and redistribution of pore water and its effect on frost heave damage in sandstone during the freeze-thaw process. Finally, the study examines the mechanisms of pores frost heave initiation and propagation in sandstone during freeze-thaw cycles. The results demonstrate that freeze-thaw cycles result in an expansion of pore volume at all scales within the samples. However, the degree of expansion varies, with macropores, mesopores, and micropores exhibiting a less pronounced increase in sequence. During the freeze-thaw process, water in sandstone pores redistributes, moving from larger to smaller pores. The saturation of water increases in micropores, but decreases in mesopores and macropores, thereby rendering micropores more susceptible to frost heave initiation in subsequent freeze-thaw cycles. With repeated freeze-thaw, the expansion of rock pores will continue in the direction of the lowest tensile strength, eventually forming macroscopic cracks. This study provides valuable insights into the mechanisms of freeze-thaw disaster genesis in rock masses.

This paper aims to comprehensively update seismic hazard assessments for Sudan and South Sudan using the Probabilistic Seismic Hazard Analysis (PSHA) method. To achieve this goal, a new and up-to-date earthquake database was developed, which includes a newly unified and updated declustered catalog, earthquake sources, and focal mechanism database. Different magnitudes were homogenized to the moment magnitude (Mw) using region-specific conversion relationships based on orthogonal regression. In addition, two types of seismotectonic idealization were considered in the seismicity assessment: the area source model and the linear (fault) source model. Focal mechanisms were used to refine the stress regime for seismicity sources derived from formal inversion analysis. To handle uncertainty, the logic-tree framework is employed, with three different Ground Motion Prediction Equations (GMPEs). The results are obtained in terms of the PGA and for the first time the spectral accelerations at two vibration periods of 0.1 s and 1 s for 475 and 975 years return periods, respectively. Hazard curves and Uniform Hazard Spectra were obtained for three considerably vulnerable cities, and PSHA disaggregation was performed in the highest risk regions with nearby seismic sources. The highest PGA values were 0.195 g and 0.285 g, with a 10% and 2% chance of exceeding these values in 50 years, respectively, in South Sudan along the western branch of the East African Rift System (EARS). In view of the increase in population and infrastructure development in the region, these results will be invaluable for seismic safety and design.

Anti-dip rock slopes are common in nature, and it is necessary to investigate their failure mechanism. In this study, a numerical calculation model of anti-dip rock slopes was established using the discrete element method. The failure mechanism of the anti-dip slopes was analyzed from macro- and meso-views, and the flexural toppling failure characteristics and development of the anti-dip slopes failure zone were investigated. The accuracy of the numerical simulation was verified using the model test. Furthermore, the influence of the height-width ratio and the bedding surface bonding strength of the anti-dip rock slope was analyzed by numerical simulation. The results showed that the slope angle and rock bed inclination affect the dip angle of flexural toppling failure and the shape of the failure zone, thereby affecting the slope stability. As the slope angle and rock bed inclination increase, the tendency of flexural toppling becomes more pronounced and the shape of the failure zone becomes steeper. Excessive height-width ratio led to incomplete development, steeper shape, and poorer stability of the failure zone. The slope stability increased when the bonding strength of the joints increased but decreased vice versa. The DEM simulation and model test of the anti-dip rock slope can achieve the expected effect when the height-width ratio is no greater than 3:2. The friction coefficient µ of the joints had the greatest influence on θ₂ and ϕ₁, and the normal-to-shear stiffness ratio k_ns/k_ss had the greatest influence on the slope displacement. These results provide a reference for analyzing the failure mechanism and stability evaluation of anti-dip rock slopes.

The saturation line serves as the foundation for the safety analysis and seepage control design of tailings dams. The primary cause of the saturation line formation in dry-stack tailings dams is the cumulative infiltration of years of rainfall. Previous studies have indicated that, under the cumulative infiltration of years of rainfall, a relatively stable seepage field eventually forms within dry-stack tailings dams, but there is a lack of theoretical research on this seepage field. This paper aims to establish a theoretical solution for the saturation line of dry-stack tailings dams under the accumulation of rainfall over many years. Based on this, the gradual seepage differential equations of the saturation line in dry-stack tailings dams were derived using Darcy's law and the energy equation. By incorporating downstream boundary conditions and rainfall boundary conditions, an analytical solution for the saturation line of dry-stack tailings dams under multi-years rainfall conditions was derived. A comparison between the analytical solution and numerical simulation results was conducted, indicating that the analytical solution closely matches the numerical solution, with a maximum difference of 5.17%. The findings of study can fill the gap in the theoretical study of seepage fields in dry-stack tailings dams under the accumulation of rainfall over many years, which is of significant importance in enriching the theoretical framework of seepage in dry tailings dams. It can serve as the basis for drainage design and slope stability analysis of dry-stack tailings dams, and is crucial for designing safer and more efficient waste management practices in mining and construction.