Bulletin of Engineering Geology and the Environment最新文献

This study investigates the influence of age on the mechanical properties of lime-modified dispersed soils through consolidation undrained triaxial tests conducted at various age (t) and lime content (a). Empirical equations for Duncan-Chang model parameters K, n, c, and φ incorporating the age factor were established based on experimental results, focusing on lime modification at 2% content. The stress-strain curves of dispersed soils exhibit strain-hardening characteristics, with stress levels increasing notably with age, displaying significant variation between short and long durations. Conversely, the stress-strain curve for lime-modified dispersed soil at 2% content shows strain-softening behavior. Age exerts a substantial influence on model parameters K, n, c, and φ of the Duncan-Chang model, with a minor impact on Rf. The modified model demonstrates a strong fit to stress-strain curves of lime-modified dispersed soil before reaching failure, validated against experimental data at age of 14 days and 90 days. Importantly, the modified model accurately predicts stress-strain relationships for modified soils over extended age beyond 28 days, providing meaningful insights for the long-term stability assessment of soil-modified structures.

Compacted bentonite has been commonly recognized as an effective buffer/backfill material in deep geological repositories for high-level nuclear waste disposal. Anisotropic microstructure can be inevitably generated during the bentonite block compaction. More importantly, this anisotropy can be intensified by the stress-induced anisotropy produced during the subsequent engineering service while the bentonite block is being submitted to external stresses. In this work, using a modified suction-controlled high-pressure consolidation setup, one-dimensional compression tests were conducted on the compacted GMZ bentonite specimens along the directions both parallel (V-type specimen) and perpendicular (H-type specimen) to the compaction surface (bedding) formed during the specimen preparation processes. Quantitative analyses on the anisotropic compression characteristic, as well as insights into the formation and evolution mechanisms of anisotropic degree, were performed. The vertical (bedding) type (V-type) specimens exhibited more significant compression deformation, lower yield stress, and higher swelling index when compared to the horizontal type (H-type) specimens. The compaction-induced anisotropy could be intensified with increasing dry density and could be either strengthened or weakened during the subsequent compression processes, in which, the anisotropy of the horizontal type specimen kept continuously increasing, while that of the vertical type specimen decreased first and then gradually turned to increase. Development and evolution of stress-induced anisotropy closely depended on the stress level applied and the stress path followed. Relationships among the pre-consolidation pressures (major/minor principal stresses) during the specimen compaction and the subsequent one-dimensional compression played a vital role in the generation and evolution of the stress-induced anisotropy of the specimen.

Saline soils are always treated as waste materials due to the salt in the soil deteriorating the soil structure, decreasing the strength, and causing salt expansion. Especially for large-scale urbanization in developing countries, how to use the waste saline soils to realize resource utilization, decrease construction costs, and further reduce carbon emissions are the biggest problems for the researchers. Hence, in this research context, a novel solid waste additive composed of slag, fly ash, and polyacrylamide, referred to as SFP, was adopted to investigate its impact on saline soil’s improvement and reinforced mechanisms based on a highway project in Urumqi, Xinjiang, China. The investigation involved laboratory experiments and Scanning Electron Microscope (SEM) analysis, specific indicators presenting the Atterberg limits, salt expansion, Unconfined Compressive Strength (UCS), resistance to freeze-thaw (FT) cycles, and water stability. The results demonstrate that the SFP additive can increase the plasticity index of the stabilized soil. From the perspective of salt expansion and UCS, the optimal SFP content is determined to be 15%, resulting in a salt expansion rate of less than 1% and approximately a threefold increase in strength compared to unstabilized saline soil. Also, the SFP additive improved the soil’s resistance to freeze-thaw cycles and enhanced water stability. SEM analysis revealed that inorganic compounds underwent chemical reactions with ions in the soil, generating a substantial amount of hydration products. When combined with the polyacrylamide, a synergistic effect substantially improved the geotechnical properties of saline soil.

Compared with large-scale geological disasters such as landslides and earthquakes, small-scale urban geological disasters such as collapses and ground fissures are often overlooked. However, the socioeconomic impacts of these small-scale events can often exceed those of larger disasters in major cities. Although the use of machine learning for susceptibility assessment is a well-established aspect of large-scale geological disaster prevention, insufficient disaster samples and resultant dataset imbalances have hindered its application to small-scale urban geological disasters. To address this issue, we propose a comprehensive process that involves defining disaster risk areas to expand disaster sample points, optimizing the extraction method for training and test sets to balance the dataset, and selecting models with high generalization capabilities to enhance prediction accuracy. By focusing on all urban road collapse incidents from 2015 to 2023 in Binjiang District, Hangzhou’s most economically developed areas, we demonstrated the reliability of this process. Furthermore, to support urban policymakers, we employed the SHAP model to demystify the predictive process and assess the impact of factors, providing reliable analytical results. Our approach provides a replicable and comprehensive solution for susceptibility assessments of cities impacted by small-scale geological disasters using machine learning and subsequent analyses.

Red sandstone is selected for freeze–thaw cycles, nuclear magnetic resonance, and triaxial compression tests to study the changes in macro-meso physical and mechanical properties under freeze–thaw cycles. Based on the expansion characteristics of meso structure, the porosity and fractal dimension are introduced to determine initial and freeze–thaw damage variables. During loading process, considering the dynamic evolution process from non-damage to damage, the load damage variable is determined. Based on the impact of reducing the effective bearing area on each damage, the total damage variable and constitutive prediction model of rock under freeze–thaw cycles are established. The results show that with the increase of freeze–thaw cycles, the meso structure undergoes penetration and expansion, and the porosity increases by nearly 30% when freeze–thaw cycles reaches 60 times. From a macro perspective, it shows that the decreases of compressive strength and deformation resistance. With the increase of confining pressures, the pores are compacted, and the lateral deformation is limited. At the same time, the bonding force between particles is strengthened, so the damage is suppressed. Macroscopically, it shows that the resistance to failure is enhanced. Under freeze–thaw cycles and confining pressure, the predicted mechanical parameters have a small deviation from test obtained mechanical parameters, generally not exceeding 5%. So the prediction model can describe the entire process of deformation and failure of rock under freeze–thaw and load, and can effectively reduce mechanical parameters data required to determine model parameters, making model more adaptable, so as to provide a new idea for the theoretical research of rock mechanics in cold regions.

The right bank plant of Baihetan Hydropower Station has exposed C₄, C₅, and other fault fracture zones (FFZs), thereby increasing rock mass instability. In this paper, the effects of the number and location of FFZ on rock mass deformation were analyzed using field monitoring data. In addition, a validated numerical simulation method was employed to discuss the influence of excavation methods and FFZ properties on rock mass deformation. Results show that as the width of the middle pilot tunnel increases, the top arch deformation initially rises and then falls. Excavating the sidewalls first will significantly aggravate the deformation. As the width or dip-angle of FFZ increases or its height from the top arch decreases, the top arch deformation becomes more significant. The first layer excavation of the plant significantly influences the rock mass deformation. The rock mass located more than twice the width of the tunnel is almost unaffected by FFZ. This study is significant for the stability analysis of deep-buried caverns across FFZ.

This study investigates the potential and limitations of using partial image orientation in Structure from Motion (SfM) photogrammetry to assess geometric properties of rock mass discontinuities investigated under various conditions. The photogrammetric point clouds were produced from images taken with a low-cost camera. An arbitrary (local) coordinate system was established by aligning a leveled 3D box with all axes oriented to the geographical North. Consequently, the need for terrestrial surveys to obtain ground control points was eliminated as the translation parameters required for photogrammetric image orientation could be disregarded in the proposed method. The investigations were conducted at various experimental sites to measure discontinuities in rock masses with diverse structural properties. The discontinuity properties such as orientation, persistence, weathering, aperture, filling, roughness, and waviness were measured by applying traditional scan-line surveys. Traditional orientation measurements and photogrammetric point cloud values were compared across different rock masses and discontinuity conditions. The results indicated that using a smartphone for image capture and a prismatic scale box for partial absolute orientation produced highly accurate point cloud data for characterizing rock mass discontinuities. Additionally, a new method, LCP + LSPF (Least Cost Path + Least Square Plane Fitting), was introduced for measuring partially closed-trace discontinuities. This method was found to be essential for sedimentary formations, primarily characterized by bedding planes. Moreover, it became evident that as the level of structural blocking increased and the interlocking of rock fragments decreased, the LCP + LSPF method was crucial for accurately representing rock masses, especially when considering Geological Strength Index (GSI) values.

Using recycled waste for soil improvement is a sustainable strategy that can reduce resource consumption. In this paper, recycled polyester fiber (RPF) is proposed to improve the engineering performance of red mud- improved volcanic ash (RV). A series of mechanical test were performed for RVs with five different content of RPF. And the microstructure was also investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and mercury intrusion porosimetry (MIP) tests. Results show that RPF significantly reinforces the mechanical strength and toughness of RV and the optimum content of RPF is 0.9%. The Unconfined compressive strength (UCS), cohesion (c) and internal friction angle (φ) of reinforced soil enhanced by up to 122%, 40% and 8% compared to untreated soil at the optimum incorporation and optimum water content, respectively. The failure model of RPF-reinforced RV is converted from brittle to ductile, and the toughness parameters are significantly improved. Microscopic investigations reveal that RPF forms a complex three-dimensional structure within the reinforced soil. Adhesion and friction interactions at the fiber-matrix interface are the main reasons for the enhancement of strength and toughness. However, the performance of composites does not continue increasing with RPF content. Excessive fibers gather and twist to form weak zones, reducing the strength and stiffness of material. In practice, the optimal fiber content needs to be controlled to ensure the best mechanical properties. This eco-friendly soil improvement can promote the harmless utilization of red mud and waste polyester materials contributing to ground improvement techniques in volcanic areas.

Desiccation cracks in soil cause undesirable impacts on soil properties. Increasing extreme heat and drought events may lead to more severe soil salinization and desiccation cracking. However, the discrepancies and intrinsic mechanisms of the cracking behaviors of different fine-grained soils affected by pore-fluid salinity are unclear. This study investigates the pore-fluid salinity effect on cracking characteristics of different fine-grained soils. Desiccation crack tests with a wide range of salt concentrations are conducted for three fine-grained soils with different sensitivity to pore-fluid chemistry. Liquid limit tests and scanning electron microscopy analyses are carried out to investigate the effect of particle-fluid interactions and microstructure changes on cracking. The degree of cracking is the largest in bentonite and varies greatly with the change of pore-fluid salinity. Cracking in kaolin is less affected by pore fluids, showing a slight decrease at large NaCl concentrations. The degree of cracking is the lowest in silt and shows no clear trend with the change of pore-fluid salinity. Detailed quantitative characteristics of crack patterns are compared. Liquid limit tests and scanning electron microscopy analyses reveal different electrical sensitivity of the three soils to pore fluid influenced by particle-fluid interactions and changes in microstructure. Crack parameters exhibit a larger variation for bentonite with high electrical sensitivity and are relatively stable for soils with low electrical sensitivity. The correlation between the electrical sensitivity and the crack parameters is relevant to the evaluation and control of desiccation crack in fine-grained soils with various pore-fluid salinities.

To address the issue of debris flow high-tide often lagging behind earthquakes by 1–2 years in a region, this study uses the case of the Xifan Gully debris flow, which occurred on June 25, 2018, in the Jiuzhaigou area. The research was conducted as follows: First, the amount of new material sources in Xifan Gully was determined by comparing drone images taken before and after the earthquake. Second, regional daily rainfall data from meteorological stations were used to calculate the runoff and infiltration in the gully. Third, indoor shear tests were conducted on soil samples collected on-site to determine the relationship between cohesion (C) and internal friction angle (φ) with changes in moisture content. Finally, numerical simulations were used to calculate how the factor of safety (FS) of the soil in Xifan Gully changes with rainfall. Results show that the peak acceleration brought by the Jiuzhaigou County earthquake to Xifan gully was 164.3 Gal. The materials of Xifan gully and newly added landslide and channel materials occupied 78.81 × 10⁴ and 16.07 × 10⁴ m³, respectively. Although the rainfall in September 2017 was the highest in the last decade, the loose material did not reach saturation. The peak rainfall before debris flow eruption in the Xifan Gully (June 21, 2018) was 21.8 mm, and the effective rainfall reached 68.5 mm until the occurrence of debris flow (June 21–25). At this time, the loose source reached saturation and debris flow started. The results demonstrated that High-tide hysteresis of post-earthquake debris flows is due toe the earthquake not only amplifying the amount of loose material but also increasing the amount of rainfall required to saturate the soil, thereby extending the time needed for the soil to reach saturation. Overall, our results are beneficial for monitoring and early warning of debris flow disasters in mountainous areas.