Bulletin of Engineering Geology and the Environment最新文献

With the continuous increase in mining depth, the effects of groundwater and in-situ stress on rock mass strength have become key controlling factors in mining engineering. Through blasting experiments integrating CT (Computed Tomography), SEM (Scanning Electron Microscroscope), 3D reconstruction and fractal analysis, this study investigates water content effects and in-situ stress impacts on sandstone damage mechanisms. Comparative analysis of oven-dried (0%), natural (3.89%) and saturated (7.81%) specimens reveals non-monotonic damage evolution: decreasing from dry to natural states then increasing to saturation. The blasting damage in natural sandstone is significantly reduced under in-situ stress compared to the unstressed condition. Fracture morphology analysis demonstrates two competing water effects: weakening mechanisms (lubrication and cementation hydrolysis) dominate at high water content, while strengthening effects (Stefan adhesion and meniscus forces) peak then decline during intermediate water.

Evaluating rock properties under different thermal treatments has gained substantial attention in the last few decades concerning its implication in various sub-surface rock engineering applications. Although basaltic rock masses are frequently subjected to high temperatures, the impact of thermal damage, especially under rapid cooling with liquid nitrogen, has received relatively little attention over the years. This study investigates these effects by analyzing changes in effective porosity, ultrasonic wave velocities, Brazilian tensile strength index (BTS), and microstructure following thermal treatment, where specimens were heated at 100–800 °C, followed by immediate cooling with atmospheric air for one cycle (AC-1), liquid nitrogen (LN₂) for one cycle (LN₂C-1) and five cycles (LN₂C-5). Broadly, AC-1 and LN₂C-1 show decreased porosity, minimal change in ultrasonic velocities, and higher BTS values at ≤ 200 °C, while LN₂C-5 shows similar behavior at ≤ 100 °C. This could be attributed to dehydration and thermal expansion, which lead to pore closure and the formation of a more compact structure. Between 200 and 600 °C in AC-1 and LN₂C-1 and 100 °C–600 °C in LN₂C-5, effective porosity and damage coefficients gradually increase, while BTS decreases. From 600 to 800 °C, rock properties change more rapidly, primarily due to the formation and propagation of thermal microcracks that weaken the grain bonding. These trends were supported by microstructural analysis. Given the frequent exploration of basaltic terrains for geothermal energy, thermal energy storage, and other underground rock engineering projects, the findings of this study will help optimize drilling parameters and build the sustainable design of rock structures.

Salt crystallization, one of the key deterioration mechanisms, can cause significant damage to heritage structures over time. This study investigates the effects of salt crystallization on the physical, mechanical, and microstructural properties of two granite types with distinct pore characteristics. A comprehensive experimental campaign, including mercury intrusion porosimetry, capillary absorption, ultrasonic pulse velocity, uniaxial compressive tests, and digital image correlation, was conducted to evaluate the progression of salt-induced damage. Results from MIP, capillary absorption, and UPV primarily reflected the initial formation and growth of sodium chloride crystals within the pore network, highlighting their utility in capturing early-stage processes. Uniaxial compressive tests provided clear evidence of damage, revealing significant reductions in compressive strength and elastic modulus. The interplay between pore characteristics, crystallization pressures, and mechanical degradation revealed distinct damage behaviors in the two granite types. Granite with a capillary-active pore network showed greater susceptibility to salt crystallization, with a 55% reduction in compressive strength and a 14% increase in open porosity. DIC analysis complemented these findings, capturing early strain concentration and crack propagation patterns in salt-contaminated samples. The findings provide valuable insights into the salt-induced deterioration mechanisms of granite, emphasizing the importance of integrating multiple assessment methods for reliable damage evaluation strategies.

The state of water and its transformation exert strong controls on the properties of soils, which has long been concerned in soil science and engineering practice. Under various environmental conditions, the water in soils may undergo dynamic migration and phase changes, for which conventional methods usually lack sufficient resolution or provide inaccurate results. To resolve these issues, the low-field nuclear magnetic resonance (NMR) technology capable of directly detecting hydrogen nuclei in water, has been introduced in the field of petroleum and geotechnical engineering with successes. Even though low-field NMR has shown its great potentials in identifying and quantifying fluids of different constituents in geotechnical porous media, this technique has not been fully explored in investigating the state of water in clayey soils, and very limited works have been made to summarize the existing progresses. In this work, we conduct a systematical review on the application of low-field NMR in investigating the state of water in clayey soils. We first summarize practical strategies for optimizing acquisition parameters and measurement sequences. Next, we review the application of low-field NMR techniques in quantifying the content, detecting the migration, and tracking phase transition processes of water in clayey soils, with particular emphasis on how T₁ and T₂ relaxation times enable differentiation of adsorbed, capillary, and bulk water. We then discuss the advantages and limitations of current experimental methods. This paper finally provides recommendations for advancing the use of low-field NMR technology in clayey soils.

Characterizing rock hardness and abrasivity is essential for drill-bit design. However, intact cores are often unobtainable in complex formations and in extraterrestrial settings, precluding conventional laboratory determination of these indices. In this context, we develop models that relate hardness and abrasivity to mineral composition and microstructural parameters, and examine how these factors connect to mechanical behavior. The dataset comprises 64 rock samples with quartz and feldspar contents and grain sizes, together with hardness and abrasivity. The key advance is a fully automated workflow for microstructural quantification. Gray-level co-occurrence matrix (GLCM) texture features are extracted from thin-section images and then interpreted qualitatively to tie these statistics to grain size, surface condition, cleavage development, and fabric, thereby improving interpretability. Before feature extraction, histogram equalization enhances image texture. Correlation analysis reveals strong cross-orientation redundancy among texture metrics and significant correlations among quartz and feldspar contents and grain sizes, which supports feature reduction. For hardness prediction, support vector regression with a Gaussian kernel performs best. Quartz content is the dominant control, and adding physically meaningful texture measures such as contrast and energy significantly improves accuracy, and highlights the nonlinear microstructural effects. For abrasivity, a linear kernel is more suitable, reflecting a stronger linear dependence on mineral composition; quartz grain size is the primary control, followed by quartz and feldspar contents. Texture features add little to abrasivity prediction. Together, these results unite interpretable automated texture metrics with mineralogical information, clarify the differing controls on hardness and abrasivity, and offer guidance for bit design and engineering applications.

Rigid and flexible boundary limits are two main types of boundary conditions used in subgrade construction, and they have significant effects on the deformation and settlement of foundation soil. In this paper, cube-triaxial compression tests were conducted on compacted loess under different compaction degrees using both rigid and flexible boundary conditions, and the resulting deformation differences of the compacted loess were studied. Additionally, the effects of lateral deformation of compacted loess under triaxial compression using these two boundary conditions on compaction degree, void ratio, and vertical strain and volume strain were analyzed. The relationship between vertical strain and volume strain was proposed, and the relationship between vertical strain and lateral strain was derived. The research results indicate that the deformation coordination ability of flexible constraints is greater than that of rigid constraints. These findings provide important theoretical reference and engineering application value for settlement calculation and maintenance of subgrade filling in loess areas.

Coal mining leads to the formation of caving zones, fracture zones and bending zones from bottom to top of the overburden. The mechanical compaction properties of the broken rock mass in the caving zone are completely different from those of the original rock and have a significant impact on the movement mechanism of the overlying strata. To study the influence of particle size and gradation on the mechanical compaction properties of broken rock in the caving zone, broken blocks with different particle sizes are made by physical modeling, and broken rock specimens with different characteristics are prepared for compaction testing according to uniform mixing and graded mixing. The results show that a small particle size is the main size controlling the mechanical compaction properties of broken rock masses. At the initial stage of compaction, the rotation, translation and sliding of broken rock blocks lead to the reduction of voids and specimen volume. The contact between them is mainly “point-to-point” and “point-to-face”; with the increase of axial stress, the contact gradually changes to “face-to-face”, and the small particles produced by grinding will fill the gap between blocks and strengthen the bearing capacity of the “face-to-face” contact of the broken rock mass. After compaction, the crushed rock mass with uniform particle size is mainly composed of rounded blocks and small particles generated by grinding, whereas the crushed rock mass with graded particle size is mainly composed of complete rounded blocks. The stress-strain curves of broken rock masses with uniform particle sizes and graded particle sizes can be well fitted by the Salamon hyperbolic model.

The rock mass rating (RMR) system is a widely used tool for assessing rock quality and recommending support, relying on six parameters: rock quality designation, uniaxial compressive strength, groundwater conditions, discontinuity spacing, condition, and orientation. The conventional RMR classification system necessitates the presence of all parameters. This study introduces a machine learning (ML) approach utilizing the random forest (RF) algorithm to predict rock mass classification with a reduced set of easily accessible parameters. A synthetic database of RMR parameters was generated to train the RF model, with Bayesian optimization applied to refine key settings such as learning rate, ensemble cycles, and maximum splits. The ML model was validated for accuracy and reliability through several performance metrics. Predictions of the proposed ML model using data from 41 real-world field cases demonstrate a high accuracy of 100%. With the advantages of the artificial intelligence (AI), the proposed ML model maintained over 90% accuracy even when key parameters such as discontinuity length, separation, or infilling were unavailable. This AI-powered approach offers a significant improvement over traditional methods, providing superior accuracy, adaptability, and reliability for rock quality assessment and support recommendations.

Understanding the effects of weathering on the porous structure of ballast materials is crucial for optimizing their selection and application in various environmental conditions. However, limited research exists on the porosimetric behavior of ballast materials under accelerated weathering conditions. This study investigates the porosimetric behavior of LD steel slag, basalt, and gneiss under accelerated weathering conditions, simulating 75 freeze-thaw and 40 sulfate soundness cycles. The research employed X-ray microtomography (Micro-CT) to analyze the three-dimensional pore structure of the materials before and after weathering. Additionally, standard laboratory tests were conducted to determine specific gravity, water absorption, and apparent porosity. Results indicate that weathering significantly impacts the porous structure of all materials. Basalt exhibited increased susceptibility to chemical weathering, leading to a notable rise in open porosity. Gneiss demonstrated superior resistance to both weathering cycles, maintaining a stable pore structure. LD steel slag, however, proved highly vulnerable to physical weathering, experiencing significant increases in both open and closed porosity. These findings provide valuable insights into the long-term durability and performance of these materials as railway ballast.

The anisotropic characteristics of rocks elastic deformation is determined through digital borehole testing, which is crucial to evaluate the engineering performance of rocks. This paper presents a new approach for assessing the elastic deformation characteristics and its directional changes. A segmented function correlating drilling strength and the specific energy is attributed to crushing failure. An equivalent parameter is offered to calculate the elastic modulus of rocks. Furthermore, an anisotropy index is introduced based on the variation in the equivalent elastic modulus across various drilling directions. Digital borehole tests were used to demonstrate the anisotropic characteristics of three types of rocks at drilling directions of 0°, 60° and 120°. The rock’s elastic modulus and anisotropy index are verified through compression experiments. The results show that the cutting and friction states are distinguished by a critical point in the drilling response and exhibit anisotropy along the borehole direction. The anisotropy along the drilling directions is quantified by the coefficient of variation (CoV). The order of anisotropy for rocks is ranked as Granite (0.94) < Shale (0.81) < Sandstone (0.70). In addition, the equivalent elastic modulus derived from drilling data can accurately calculate the rock’s modulus with a linear function correlation coefficient reaching 0.94. This study provides an effective approach to assess the elastic modulus and anisotropy of rocks using digital drilling.