Search Results (332)

The durability of concrete in immersed tunnels is critically influenced by the coupled effects of stress, seepage, and chemical erosion, particularly in inland water environments. However, the spatio-temporal evolution of mechanical property degradation under such multi-field coupling remains insufficiently quantified. Unlike previous studies focused on “load-ion” or “hydraulic pressure-ion” dual coupling, this work introduces a complete stress–seepage–chemical tri-coupling that incorporates the critical seepage effect, representing a fundamental expansion of the experimental scope to better simulate real-world conditions. This study investigates the degradation mechanisms of concrete in the Shunde Lungui Road inland immersed tunnel subjected to such coupled erosion. A novel aspect of our approach is the application of the micro-indentation technique to quantitatively characterize the spatio-temporal evolution of the local elastic modulus at an unprecedented spatial resolution (0.5 mm intervals), a dimension of analysis not achievable by conventional macro-scale testing. Key findings reveal that the mechanical properties of concrete exhibit an initial enhancement followed by deterioration. This behavior is attributed to the filling of pores by reaction products (gypsum, ettringite, and Friedel’s salt) in the short term, which subsequently induces microcracking as the volume of products exceeds the pore capacity. Furthermore, increasing hydro-mechanical loading significantly accelerates the erosion process. When the load increases from 1.596 kN to 3.718 kN, the influence range of elastic modulus variation expands by 9.2% (from 5.186 mm to 5.661 mm). To quantitatively describe this acceleration effect, a novel load-acceleration erosion coefficient is proposed. The erosion rate increases from 0.0688 mm/d to 0.0778 mm/d, yielding acceleration coefficients between 1.100 and 1.165, quantifying a 10–16.5% acceleration effect beyond what is typically captured in dual-coupling models. These quantitative results provide critical parameters for employing laboratory accelerated tests to evaluate the ionic erosion durability of concrete structures under various loading conditions, thereby contributing to more accurate service life predictions for engineering structures. Full article

Utilization of ozone micro-nano bubbles during uranium leaching process has attracted attention in recent years because of ozone’s potent oxidizing capacity, high efficiency in mass transfer, and environmental compatibility. This review systematically presents the properties, generation methods and characterization approaches pertaining to ozone micro-nano bubbles (OMNBs) for the application of uranium leaching. In addition, the potentials and challenges of using ozone micro-nano bubbles to enhance uranium resources recovery are summarized. A lack of comprehensive understanding regarding uranium oxidation mechanism by ozone micro-nano bubbles under different pH conditions, along with the gaps in field experiments, has hindered the exploration and development of uranium leaching by OMNBs. In summary, further research endeavors on uranium oxidation mechanism by OMNBs and field trials are needed to facilitate the implementation of uranium leaching by OMNBs. Full article

This paper presents results of numerical modeling of tunneling using mechanized tunnel boring machines (TBMs) based on a methodology for determining the volume loss cohesionless (loose) soils, denoted as V_L,LSR, for shallow tunnels in dispersive soils to estimate surface and foundation on settlement natural ground. Existing methods for estimating ground surface and structural settlements have significant drawbacks, caused by several factors, including the complexity of determining volume loss using the proposed methodologies, a limited number of empirical parameters describing the technological features of TBM operations, the absence of methods in Russian regulatory documentation for determining volume loss in tunnels with diameters of 6 m or more, among other issues. The study aims to validate a previously developed method for estimating V_L,LSR and an empirical equation for predicting surface settlements, S_max, to assess additional settlements induced by tunneling. The proposed volume loss methodology and the modified S_max expression from Peck R.B. (1969), derived from monitoring data, are used in empirical calculations and numerical modeling of surface and building settlements during TBM tunneling. Validation results include back-analysis of geotechnical “tunnel–ground–structure” interaction models, comparisons of additional settlements from design calculations and field monitoring data, as well as comparisons with existing empirical relationships and relevant regulatory documents, followed by recommendations for their integrated application. The validated methods demonstrate good agreement with observed monitoring data, while providing sufficient engineering safety margins, confirming the applicability of the V_L,LSR and the modified S_max expression by Peck R.B. (1969) for predicting settlements of tunneling and identifying directions for further research. Full article

Soil permeability is an important factor in the mining and geotechnical industry, impacting slope stability and tailings management. It directly influences the stability of structures, the control of water in tailings ponds, and the safety of workers. Various additives, such as cement kiln dust (CKD), bentonite, fly ash, polymers, lime, and asphalt, are incorporated into soil structures to improve permeability and stability. Any significant changes in soil permeability will alter the soil’s behavior. However, the long-term effect of most additives on structures remains unexplored. This study investigates the long-term impact of CKD on the permeability of a CKD-treated slope. The slope surface was treated with 0%, 5%, 10%, and 15% of CKD by the dry weight of the soil in 2008 and was evaluated in 2024. The permeability test results of the collected soil sample from the slope (2024) showed that the permeability of the soil decreases with an increase in the soil CKD content. The coefficient of permeability, k, is more than 100 times less for a CKD content of 15% by the dry weight of the soil compared to the permeability of the untreated native soil. The treated soil becomes almost impermeable when the CKD content increases to 20% (by the dry weight of the soil). However, the treated slope’s permeability increased over time, possibly due to erosion, resulting in a reduction in CKD content. The surface permeability of the slope exhibits an irregular distribution, resulting from the evolving spatial distribution of Cement Kiln Dust over time. Full article

On 23 April 2023, a rotational landslide occurred at El Florón III (Portoviejo, Ecuador), triggered by intense rainfall that increased saturation and water pressure in the pores of the colluvial materials. Therefore, the current research predominantly aimed to (i) characterize the geological, geophysical, and geotechnical conditions that controlled the instability, (ii) identify and validate the fault surface, and (iii) evaluate a stabilization alternative in accordance with the Ecuadorian Construction Standard (NEC-15). Additionally, a probabilistic analysis was conducted based on the post-landslide geotechnical characteristics of the material, obtained from direct shear tests, which served as the basis for the back-analysis that determined the parameters governing the soil’s behavior during the event. Based on the parameters obtained for the landslide analysis and the determination of safety factors in accordance with the guidelines of the Ecuadorian Construction Standard, a ground reinforcement configuration was proposed through the implementation of micropiles combined with terracing. This approach allowed for establishing a methodology applicable to landslide scenarios in equivalent environments, considering the specific geotechnical and climatic conditions of the area. Full article

The bell tower of Murcia Cathedral (1521–1793) exhibits a documented inclination whose origin and structural significance have never been examined through an integrated geotechnical–structural approach. This study aims to identify the causes, quantify the magnitude, and assess the safety implications of the tower’s long-term differential settlement. A multidisciplinary methodology is adopted, combining historical construction records, geological and geotechnical data from the Segura alluvial plain, non-destructive testing of masonry, and classical analytical modelling based on Heyman’s masonry theory, consolidation mechanics, and elastic column behaviour. This approach is selected in place of finite element modelling because the tower’s geometry, construction sequence, and material parameters are sufficiently constrained to allow a non-invasive and verifiable assessment suited to heritage structures. Results indicate a total horizontal displacement of approximately 0.56 m toward the northwest, produced by the slow consolidation of compressible silty–clayey deposits influenced by groundwater fluctuations and by historical eccentric load redistributions during the eighteenth-century construction phase. The calculated working compressive stresses (0.83–1.02 N/mm²) remain far below the estimated strength of the limestone masonry, and the bearing capacity analysis suggests a safety factor of about 1.5 against foundation failure. These findings confirm that the tower’s deformation reflects the long-term geotechnical response of the subsoil rather than structural instability. The study provides a non-destructive analytical framework for interpreting settlement mechanisms in historic masonry towers and contributes a quantitatively grounded explanation of the Murcia Cathedral tower’s inclination, offering guidance for future assessment of similar heritage structures. Full article

Three-dimensionally printed (3DP) samples with quartz sand effectively avoid the heterogeneity of reservoir rocks in underground gas storage (UGS), providing reliable supports for rock mechanics research under cyclic injection–production pressures. A study on the mechanical properties of 3DP rock samples was conducted by coupling triaxial tests with discrete element method (DEM) simulation. Key results are as follows: (1) The graded particle model (GPM) based on actual particle size distribution (PSD) closely matched experimental data, with an average peak strength error of 1.13%. (2) Cyclic saturation post-processing with silica sol significantly enhanced mechanical properties, increasing peak strength from 5.70 to 52.84 MPa and inducing a plastic-to-brittle failure transition. A power-law relationship was identified between saturation cycles and macroscopic strength. (3) DEM simulations revealed that bond effective modulus linearly controls Young’s modulus. The influence of cohesion on peak strength is greater than that of the friction angle, and the bond stiffness ratio regulates shear failure threshold. The cohesion force is 50 MPa, and the peak strength has been increased to 107.89 MPa. (4) Enhancing particle cohesive strength was key to improving the mechanical properties of 3DP rock samples. This study provides a reliable framework for customized 3DP rock preparation and UGS-related mechanical simulations. Full article

This study systematically investigates the evolution of mechanical damage and the permeability response of tight sandstone under triaxial compression and alternating load conditions, with a focus on the safety and stability of deep underground tight sandstone gas storage reservoirs in China subjected to complex geological environments and alternating stress conditions. By integrating conventional triaxial testing, cyclic loading experiments, CT scanning, and fractal dimension analysis, this study elucidates the enhancement effects and transformation mechanisms of confining pressure on the strength behavior and failure patterns of sandstone. It identifies the influence mechanisms of fault roughness on permeability and its convergence behavior under high-stress conditions and comprehensively characterizes the three-stage evolution of sandstone damage at the microscale under cyclic loading. Experimental results showed that with increasing confining pressure, both the peak strength and elastic modulus of sandstone displayed an increasing trend. With confining pressure increasing from 10 MPa to 40 MPa, the peak deviatoric stress increased from 98.42 MPa to 171.00 MPa and the elastic modulus rose from 8.70 GPa to 12.65 GPa. The failure mode transitioned from brittle shear failure under low confining pressure to a ductile-plastic failure pattern under high confining pressure. Alternating loading resulted in a 17.23% reduction in sandstone strength (from 98.42 MPa to 81.46 MPa at 10 MPa confining pressure). At confining pressures > 25 MPa, the permeability differences among faults with different roughness converged to within 10%. These research findings offer a robust experimental foundation and theoretical framework for evaluating the long-term stability and predicting the sealing performance of deep underground gas storage reservoirs. Full article

This study proposes a predictive framework for the compressive strength (CS) of manufactured-sand concrete (MSC), integrating six machine learning (ML) models—artificial neural network (ANN), random forest (RF), extreme learning machine (ELM), kernel-ELM (KELM), support vector regression (SVR), and extreme gradient boosting (XGBoost) with the newly developed Dream optimization algorithm (DOA) for hyperparameter tuning. A database of 306 samples with eight features is used to train and test models. Results demonstrate that all models achieved satisfactory predictive accuracy, with the DOA-RF model exhibiting the best performance on the testing dataset (R² = 0.9755, RMSE = 2.7836, MAE = 2.1716, WI = 0.9933). The DOA-XGBoost model also yielded competitive results, whereas DOA-ELM showed relatively weaker performance. Compared with existing optimization-based approaches, the proposed DOA-RF model significantly reduced RMSE and MAE, validating the effectiveness of the DOA. SHAP analysis further revealed that the water-to-binder ratio (W/B) and curing age (CA) are the most influential factors in predicting MSC strength. Overall, this work not only establishes an accurate and interpretable predictive tool but also underscores the potential of novel optimization algorithms to advance data-driven concrete design and sustainable construction practices. Full article

Gas storage in depleted gas reservoirs has become a core facility for ensuring energy security and a key means of guaranteeing a safe and stable supply of energy. Steep pressure rise and fall cyclic fluctuations caused by strong injection and production are likely to lead to the destabilization of the geological structure of the gas storage reservoir. Among the geological formations, fault activation is a serious threat to the safety of gas storage reservoirs. In this study, faults with different filling types were depicted by real downhole cores. Through a series of shear tests, the effects of normal stress, filling thickness and fault angles on the lithology of rocks on both sides were investigated. (1) A novel testing method was developed for finely engraving faults on downhole cores, allowing for the simulation of real reservoir conditions. (2) An increase in normal stress results in enhanced shear strength, which in turn elevates the critical initiation stress of the fault. (3) Shear strength decreases with an increasing amount of fault mud, indicating that the critical initiation stress in faults filled with minor amounts of fault mud is higher than that in faults filled with significant amounts of fault mud. (4) For equal amounts of fault mud, the shear strength of fault specimens at a 40° angle exceeds that of specimens at a 10° angle. This implies that a greater degree of fault undulation corresponds to a higher critical slip initiation stress, reducing the likelihood of fault slip and enhancing stability. (5) The shear strength of fault specimens composed of sandstone-mudstone combinations is lower than that of specimens containing sandstone-sandstone combinations, suggesting that the critical slip initiation stress for sandstone-mudstone combination faults is comparatively lower. Full article

Despite technological advancements in mining, Chile lacks comprehensive risk management models for tailings storage facilities (TSFs), which hinders the prevention and mitigation of structural and environmental risks. This study aims to develop an integrated risk management model for TSFs in Chile, combining geological and mining engineering with an updated regulatory framework to enhance safety and reduce environmental impacts. The research adopts a mixed-methods approach. Qualitatively, it draws on 10 semi-structured interviews with engineers, geologists, academics, and professionals from the Chilean mining industry, selected through purposive sampling, to explore how and why the current risk management model should be improved. Quantitatively, it analyzes data from 303 surveys assessing the existing regulatory framework, a proposed new regulatory decree for Chile, and key variables to be considered in TSF risk management. The results present a new model that integrates geochemical and geotechnical characterization, process variables, in situ sensors, remote sensing, and artificial intelligence to generate dynamic risk indicators and early warning systems throughout the life cycle of the facility, including closure and liability valuation. Its multiscale design, adaptable to seismic and hydrogeological conditions and suitable for small- and medium-scale mining, overcomes existing static and fragmented approaches, enabling more effective decision-making with a focus on environmental and community safety. The study concludes that the model provides a robust and coherent tool for TSF risk management by integrating technical expertise, the current regulatory framework, and the management of key variables that enhance the ability to anticipate and mitigate structural and environmental risks. Full article

Sinkholes caused by historical underground mining operations are significant geotechnical and safety hazards for new residential developments. This paper presents a case study concerning the assessment of the condition of the foundations of a planned multi-family residential building located within a former mining operations area in southern Poland, which is exposed to the risk of discontinuous ground deformation. This study aimed to identify potential voids within the rock mass and develop safe structural solutions for building foundations. To this end, a comprehensive site investigation was conducted, including two-dimensional electrical resistivity profiling to detect zones of high-resistivity anomalies. High-resistivity anomalies were identified beneath several building segments, suggesting the presence of voids or loose soil resulting from shallow coalmining operations. Based on these findings, a finite element analysis (FEA) of the reinforced concrete foundation slab was performed to simulate the presence of subsurface cavities. The results indicated local tensile stress in the slab of up to 0.34 MPa, which necessitated subsequent design adjustments. Consequently, the use of additional bottom reinforcement and continuous reinforced concrete ribs was proposed to enhance structural safety. This study highlights the necessity of detailed geotechnical and geophysical analyses of planned development zones located in former mining operation areas to address the risks related to sinkholes and ensure the long-term safety of new buildings. Full article

The development of underground space in the South China Sea islands is an important way to enhance their protection capabilities. This study focuses on the stress loading and unloading conditions of surrounding rock during the excavation of underground caverns in island reefs. Laboratory variable confining pressure permeability tests were conducted to quantify the stress sensitivity of permeability in coral reef limestone based on Darcy’s law and the stress sensitivity index model equation for permeability. In addition, the use of nuclear magnetic resonance technology reveals the microscopic mechanism of coral reef limestone permeability evolution. The results of the experiments show that the permeability of coral reef limestone sample is mainly controlled by the advantaged permeable channels formed by large pores. During the stress loading stage, the pore structure inside the sample changes, with compression of large pores and generation of smaller pores, resulting in a decrease in effective permeable pathways and a decrease in permeability. When the stress loading reaches 4 MPa, the damage rate of the sample’s permeability is 19.6%. During the stress unloading stage, the recovery of the sample’s permeability shows a significant hysteresis effect. Due to the irreversible damage caused by the compression and collapse of the pore structure during the loading stage, the permeability of the sample cannot fully recover when unloaded to the initial stress state. Based on the experimental results, calculations show that the stress sensitivity coefficient of coral reef limestone permeability is 1.1 × 10⁻¹ MPa⁻¹, which is higher than that of conventional land-based rocks. The conclusions of this study can provide important design references for the stability control of surrounding rocks and geological hazard prevention during the excavation of underground chambers on the islands. Full article

In recent years, the correlation mechanisms between geopolitical risks and financial markets have drawn considerable attention from both academic circles and investment communities. However, their multiscale, nonlinear interactive characteristics still require further investigation. To address this, this paper proposes a dynamic nonlinear causal information network combined with a wavelet transform model and the transfer entropy method. We select the geopolitical risk index, the US dollar index, Brent and WTI crude oil prices, COMEX gold futures, and London gold prices time series as the research objects. The results suggest that the network’s structure changes with time at different time scales. On the one hand, COMEX gold (London gold) acts as the major causal information transmitter (receiver) at all scales; both of their highest values appear at the mid-scale. The US dollar index plays a bridging role in information transmission, and this mediating ability decreases with increasing time scales. On the other hand, the fastest speed of causal information transmission is at the short scale, and the slowest speed is at the mid-scale. The complexity and systematic risk of causal network decrease with increasing time scales. Importantly, at the short-scale (D1), the information transmission speed slowed during the Russian–Ukrainian conflict and further decreased after the start of the Israel–Hamas conflict. Systematic risk has increased annually since 2018. This study provides a multiscale perspective to study the nonlinear causal relationship between geopolitical risk and financial markets and serves as a reference for policy-makers and investors. Full article

With the comprehensive implementation of the “Belt and Road” initiative and the Western Development Strategy, the scale of tunnel construction has been continuously expanding, with many tunnels being built in high ground stress and fractured soft rock strata. The design, construction, and operation of tunnels all rely on the surrounding rock pressure as a fundamental basis. Therefore, determining the surrounding rock pressure is essential for ensuring the safe construction of tunnels. However, due to the complexity of geological conditions, differences in construction methods, variations in support parameters, and time–space effects, it is challenging to accurately determine the surrounding rock pressure. This paper proposes a design approach using the surrounding rock pressure design value as the “support force” for the tunnel, starting with the reserved deformation of soft rock tunnels. Based on the calculation principle of the surrounding rock pressure design value, a relationship curve between the support force and the maximum deformation of surrounding rock in high ground stress soft rock tunnels is developed. By combining the surrounding rock deformation grade with the tunnel’s reserved deformation index, a calculation method for the surrounding rock pressure design value for high ground stress soft rock tunnels is proposed. The method is verified by the measured surrounding rock pressure data from the Mao County Tunnel of the Chengdu–Lanzhou Railway. Furthermore, the study integrates the creep characteristics and strain softening properties of soft rock to implement a secondary development of the viscoelastic–plastic strain softening mechanical model. Based on a custom-developed creep model and the calculation method for the surrounding rock pressure design value, the relationship among time, support force, and surrounding rock deformation is comprehensively considered. A calculation method for the surrounding rock pressure design value, accounting for time effects, is proposed. Based on this method, a time-history curve of the surrounding rock pressure design value is obtained and used as the input load. The safety factor time evolution of the rock-anchor bearing arch, spray layer, and secondary lining is derived using the load-structure method, and the overall safety factor time evolution of the tunnel support structure is evaluated. The overall stability of the support structure is assessed, and numerical simulations are compared with field measurements based on the mechanical behavior evolution law of the secondary lining of the Chengdu–Lanzhou Railway Mao County Tunnel. The results indicate that the monitoring data of the internal forces of the field support structure is in good agreement with the numerical calculation results, validating the rationality of the proposed calculation method. Full article