Bulletin of Engineering Geology and the Environment最新文献

The study of the changes in heat transfer properties of oil-rich bedded rock layer at high temperatures is important for the development of projects such as underground coal gasification, geothermal mining and nuclear plant construction. In this paper, the change characteristics of heat transfer performance of oil-rich bedded rock layer after high-temperature treatment were studied from macro-meso-microscopic perspective by systematic testing means such as thermal parameter test, NMR, XRD and SEM, and the influence law of temperature and heating time on heat transfer performance was grasped, and the deterioration mechanism of heat transfer performance was revealed. The results show that the heat transfer performance of baseboard rock layer undergoes significant deterioration after high-temperature treatment, with the greatest deterioration rate in the temperature interval of 400 ℃-600 ℃ and 500 ℃ as the temperature threshold for rapid deterioration. The content of the main mineral components such as quartz and kaolinite, which affect the density of the geotechnical structure within the specimens, changed significantly, with the percentage of quartz in the mudstone specimens decreasing from 93 to 83% and kaolinite from 5 to 2%. The percentage of quartz in the siltstone decreased from 91 to 82%, and kaolinite decreased from 6 to 1%. This led to a rapid deterioration of the heat transfer properties of baseboard rock layer, with a reduction in thermal conductivity of 47.2% for mudstone and 58.9% for siltstone.

To accurately predict tunnel water inflow under complex geological conditions, this study established a unified geomechanical calculation model for such environments. Using groundwater dynamics and Bernoulli's energy equation, a theoretical approach to calculate the tunnel face water inrush under non-Darcy flow conditions was proposed, which comprised a confined water formula and a phreatic water formula. This methodology considers temporal and geological variations to enable short-, medium-, and long-term dynamic predictions of water inflow. The research findings indicate that: for short-term predictions, the theoretical water inflow derived from both formulas exhibited at most 5% deviations from the actual measurements. When a 90% confidence interval was adopted for the medium-to-long-term predictions, the relative errors for both maximum and normal water inflow remained below 5%. Notably, during the decaying water inrush phase, the phreatic water formula predicted a 2–3 times slower decay rate than the confined water formula. The maximum water inflow positively correlates with the permeability coefficient (K), water head height (H), and diameter of the water inrush channel (d), whereas it negatively correlates with the length of the water inrush channel (L). Conversely, the normal water inflow negatively correlates with K and d but positively correlates with H and L. After the feasibility of this method had been validated in the Yongshun Tunnel and Zhongliangshan Tunnel, it was successfully applied to a mountainous tunnel project in southwestern China.

Loess in Northwest China is widely deposited atop the Hipparion Red Clay. Unlike red clay stratigraphy, loess is mostly seasonally frozen, with physical properties that change easily at low temperatures, increasing the risk of natural disasters like slope instability and landslides. To study the low-temperature properties of loess and red clay strata, loess-red clay composite samples with varying water contents were subjected to freezing at different low temperatures. Their resistivity and P-wave velocity were measured postfreezing. The results indicate that as water content increases, soil resistivity decreases due to enhanced electrical conduction, with a slower rate of decline. When the temperature decreases, resistivity rises gradually in the unfrozen stage (25 °C to − 5 °C) and increases rapidly in the frozen stage (–10 °C to − 20 °C) as water transitions to solid ice. At low water contents, soil resistivity is more sensitive to temperature changes due to reduced liquid conductive pathways. P-wave velocity decreases almost linearly with increasing water content in unfrozen soils, but this trend reverses in frozen soils. With decreasing temperature, P-wave velocity shows minimal change in unfrozen soils but increases significantly after freezing, with greater sensitivity to temperature changes at higher water contents. This experiment provides valuable data support for engineering construction, soil frost heave risk assessment, and geophysical investigations in permafrost regions. 

This study aims to assess several factors affecting Leeb hardness (LH) test results for rock materials. Regression models for predicting some strength and deformability properties from L_D values were proposed and compared based on a larger database from a comprehensive experimental program conducted and those compiled from the literature. The results indicate that Single Impact Method (SIM) is the most suitable method to obtain more reliable L_D values when compared to Repeated Impact Method (RIM). In addition, RIM causes the formation of pits and bulges on the sample surface. 15 single impacts are sufficient to determine L_D value that statistically represents optimal number of impacts to be applied. The test should be performed on samples with a length of (L) ≥ 50 mm (L/D ≥ 1) and the impacts should be applied by leaving a minimum distance at least equal to the diameter of the tester supporting ring from sample edge.

Accurate prediction of the shear strength (({tau }_{p})) of rock joints is essential for ensuring the stability and safety of geotechnical structures. This study introduces a novel framework for integrating the CatBoost gradient boosting decision tree algorithm with six cutting-edge metaheuristic optimization techniques, offering enhanced accuracy and reliability in shear strength prediction. The research employs advanced evaluation tools, including error metrics, Taylor diagrams, relative deviation distribution diagram, relative absolute error-cumulative frequency, and uncertainty analyses, to validate model robustness under diverse geological conditions. Among the optimized models, the CatBoost-Grey Wolf Optimizer (CatB-GWO) emerged as the most accurate, while the CatBoost-Whale Optimization Algorithm (CatB-WOA) demonstrated superior consistency and minimal bias. Sensitivity analysis identified normal stress (({sigma }_{n})) as the most influential parameter affecting shear strength. Unlike traditional approaches, this study combines computational intelligence and geomechanical insights to advance predictive modeling in rock mechanics, establishing a novel methodology for handling complex geotechnical challenges. These findings highlight the transformative potential of hybrid machine learning models in enhancing shear strength prediction for rock joints.

This experimental and numerical study examines the propagation of dynamic compressive stress waves within geological lithological layers. In contrast to conventional split Hopkinson pressure bar (SHPB) systems, this research employed a custom-designed electromagnetic pendulum impact testing (EPIT) system. The electromagnetically controlled EPIT system was developed to allow precise and consistent repetition of impact tests at varied speeds. The EPIT system was integrated into a modified SHPB apparatus, featuring an extended length of up to 3 m and using rock bars exclusively, rather than conventional steel bars. Three types of modified SHPB configurations-single-rock-bar, double-rock-bar, and triple-rock-bar systems-were analyzed. Testing was conducted on limestone, marble, and sandstone specimens, each measuring 1 m in length and 0.05 m in diameter. Results indicate that sandstone exhibits the highest peak compressive strain and attenuation rate along the propagation path, distinguishing it from the behaviors observed in limestone and marble. The dynamic response characteristics of each rock layer are affected by the source of dynamic load, the inherent properties of the rock layer, and the properties of subsequent layers. A significant negative correlation was found between the average compressive strain amplification ratio and density ((rho )) ratio (( R = -0.92 )). Ratios of elastic modulus (( E )), P-wave velocity ((v_p)), and wave impedance ((Z_w)) also notably influence compressive strain amplification (( R = -0.85, -0.86, ) and ( -0.85 ), respectively). The UCS ratio has the least impact on strain amplification (( R = -0.7 )). Additionally, the pattern of stress attenuation was effectively described using a combination of power and Gaussian functions.

Desiccation crack patterns are commonly observed in natural and engineered soils and provides preferential pathways for moisture infiltrating into the soil. Cracks occur easily in soil when moisture is lost due to desiccation. Crack formation and development are closely related to moisture content and have a marked impact on the soil deformation characteristics and hydraulic properties. However, the critical moisture content below which desiccation cracks appear in the soil is usually determined by experiment because there is a lack of research on theoretical calculation models. Therefore, a theoretical calculation model is proposed to calculate the critical moisture content, and a parameter, (lambda), based on the following relationships: between soil grain size and suction, between suction and tensile strength, and between soil cracking and tensile strength. The critical moisture content values of different grain compositions were calculated and compared with laboratory experiments of desiccation crack. The critical moisture content of the granite residual soil is between 20% (50% liquid limit) and 30% (75% liquid limit). The presented model provides a means to estimate the critical moisture content of crack formation from soil desiccation using basic soil properties. This method can estimate the characteristics of soil desiccation cracks under extreme weather condition.

Oil storage in abandoned coal mines can effectively alleviate the shortage of space for oil reserves, however, the mechanical effects of oil storage on the mining envelope (sandstone) need to be further explored. To clarify the weakening effect of crude oil saturation on sandstone at different reservoir depths, triaxial mechanical tests of oil-saturated sandstone under different confining pressures were carried out on the GCTS rock mechanics testing machine. The mechanical properties, energy dissipation characteristics, and crack extension evolution process of oil-saturated sandstone were obtained. The results show that the softening coefficient of oil-saturated sandstone has a change rule of increasing and then decreasing with the increase of confining pressure. The oil-saturated treatment does not change the energy evolution process of the sandstone, but it has a greater influence on the energy parameters. The number of AE events and the released energy of oil-saturated sandstone is lower than that of natural sandstone at different confining pressures. However, due to the influence of the Kaiser Effect, the difference gradually decreases with the increase of the confining pressure, which macroscopically shows that the increase of the confining pressure moderates the effect of oil saturation on the energy parameters and crack extension of sandstone. In engineering applications, this research provides a theoretical basis for understanding the mechanical changes in surrounding rock at different oil storage depths in abandoned mine rock channels. Additionally, it offers scientific recommendations for selecting optimal depths for oil storage in rock tunnels.