Search Results (202)

Argillaceous siltstone is widely distributed along expressways in southern China; however, its strong water sensitivity and slaking properties severely restrict its utilization as subgrade fill, particularly under wet–dry cyclic conditions where bearing capacity deteriorates sharply. Existing studies have predominantly focused on mechanical performance evaluation of stabilizers, while systematic comparisons of lime and cement improvement effects and durability evolution under wet–dry cycles remain insufficiently understood. Drawing on the Yongjin Expressway reconstruction and expansion project, this study systematically investigates the durability of lime- and cement-improved argillaceous siltstone fill. Through unconfined compressive strength (UCS) tests, California bearing ratio (CBR) tests, and five wetting–drying cycles, the evolution differences in strength development, water stability, and durability between the two improvement schemes are revealed. Results indicate that, under identical stabilizer contents (3–7%) and curing conditions, the UCS and CBR of cement-improved soil are significantly higher than those of lime-improved soil. At the same dosage, the strength of cement-improved soil is approximately 1.5–1.7 times that of lime-improved soil, and the absolute strength gap further widens with increasing dosage. Both stabilizers effectively inhibit water immersion swelling, but the swelling rate of lime-improved soil is about 1.3–1.5 times that of cement-improved soil at the same dosage. At 7% dosage, the swelling rates of cement- and lime-improved soils decrease to 0.40% and 0.60%, respectively, both meeting subgrade fill swelling control requirements. After five wet–dry cycles, the UCS retention rate of 7% cement-improved soil is 78.3%, while that of lime-improved soil is 69.0%; the residual strengths are 507.0 kPa and 303.6 kPa, respectively, both satisfying general subgrade engineering strength requirements. However, the 3% lime-improved soil declines to 47.5 kPa after cycling, falling below the engineering threshold. Integrating strength, deformation, and durability indices, high-grade highway roadbeds and other high-load-bearing sections should prioritize 7% cement improvement, whereas general subgrade sections and locations emphasizing crack resistance may adopt 7% lime improvement as an alternative. Low-dosage (<5%) lime improvement is not recommended for argillaceous siltstone subgrade engineering. The findings provide a scientific basis for the engineering application of argillaceous siltstone as subgrade fill and for optimization of improvement schemes. Full article

Airports, as Critical National Infrastructure (CNI), operate as tightly coupled socio-technical systems exposed to multifaceted threats, including cyber, physical, social, environmental, and Chemical, Biological and Radiological (CBR) threats. This study presents a structured review of the synthesis of conceptual frameworks, airport structural configurations, sensor networks, and multi-domain threat landscapes, as well as airport security and resilience analysis, while comparatively examining risk assessment approaches. The review shows that existing approaches are effective for threat identification and prioritisation but remain predominantly static, with limitations in scalability, data dependency, and real-time applicability. To address these limitations, Threat-Vulnerability-Risk Assessment (TVRA) is adopted as a structured, reusable approach to support metric allocation, redundancy design, and emergency capability development. It further serves as a bridge between traditional risk assessment and resilience-oriented system design by enabling the transformation of static risk scores into scenario-based inputs, thereby supporting stress-testing and lifecycle-based resilience planning across the prepare, act, and recover phases. However, its inherently static structure limits its ability to capture temporal dynamics and cascading interdependencies, highlighting the need to integrate it with dynamic modelling approaches. Full article

In oil-rich countries, petroleum contamination of soils frequently occurs during refining, transportation, and exploitation. Such contamination significantly alters soil behavior and properties from a geotechnical perspective. Given that some fine-grained soils exhibit insufficient bearing capacity or excessive settlement, soil improvement is often necessary. The selective use of nanoparticles offers a promising novel approach in this regard. This study investigates the effects of diesel contamination and nanosilica modification on the physical and mechanical properties of clayey sand and aims to interpret the variations in the mechanical properties and the permeability of the treated soil based on microstructural observations. Diesel (0–10% in 2% increments) and nanosilica (0%, 1%, 2%) were added to the soil, preparing a total of 18 mixtures for testing. The microstructural changes directly alter the physical parameters such as specific gravity, optimum moisture content (OMC), and maximum dry unit weight, consequently affecting the permeability and the mechanical behavior. The microstructural analysis via scanning electron microscopy revealed diesel-induced clay flocculation and increasing macroporosity, while the nanosilica at 1% improved the soil fabric through pore filling and interparticle bonding, whereas 2% nanosilica led to partial dispersion and agglomeration. The findings demonstrate that soil behavior is controlled by the interplay between diesel (lubrication, pore blocking, hydrophobicity) and nanosilica (surface activation, micro-bonding, agglomeration). Increasing the diesel content consistently reduces the specific gravity across all the mixtures, due to the replacement of heavier mineral particles by lighter hydrocarbon, diesel adsorption onto the soil grains, the formation of low-density organic films, and increased micro-voids. Diesel addition reduces the OMC but increases the maximum dry unit weight due to its lubrication effect. Mechanically, the unconfined compressive strength (UCS) peaked at approximately 4% diesel contamination, with the addition of 1% nanosilica yielding the highest strength overall. Conversely, the California Bearing Ratio (CBR) increased continuously with diesel due to improved packing and frictional resistance and was further improved by nanosilica. The results show that permeability decreases with increasing diesel content due to hydrophobic diesel molecules coating soil particles, filling micro-voids, and blocking pore channels, while the consolidation parameters exhibit non-monotonic trends, peaking at moderate contamination levels. An optimal nanosilica content effectively mitigated some of the adverse effects of diesel and enhanced the mechanical performance, providing valuable insights for managing hydrocarbon-contaminated soils. Full article

Stabilizing weak soils is a well-known pavement and geotechnical engineering technique. This technique involves introducing minimal cementitious materials to improve the soil’s geotechnical characteristics. This paper investigates the use of recycled industrial polymer waste (IPW) as a reinforcement material in the presence of cementitious binders to stabilize weak silty sand soil (SM), supporting sustainable engineering practices. The randomly distributed IPW were added as percentages of 0%, 5%, and 10% to a mixture of lime soil and cement soil, with varying amounts of 0% to 6% of lime (L) and 0% to 6% of ordinary Portland cement (OPC), respectively. The laboratory experiments were conducted on natural and stabilized samples in wet (unsoaked) and submerged (soaked) conditions. The experimental program included Proctor compaction, California bearing ratio (CBR), unconfined compressive strength (UCS), durability tests, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction analyses. The resilient modulus (Mr) was estimated using an empirical equation. The outcomes of this experimental study show that adding a combination of IPW shreds with a small amount of L and/or OPC to the SM soil provides a significant increase in the UCS, CBR, durability and Mr values compared with case of SM with only L, which allows for superior characteristics and increases strength and stiffness parameters throughout any phase of earthwork construction design, resulting in stronger and stiffer subgrades. These results were reinforced by microstructural observations from SEM, EDS, and DRX, confirming the formation of cementitious gels and chemical compounds, consistent with the macro-scale mechanical improvements. The expected practical outcomes include potential reductions in pavement thickness, which can help lower pavement stabilization costs and extend its service life. Additionally, the use of waste materials to replace raw materials contributes to decreased energy consumption and emissions, although detailed assessments are needed to quantify these effects. Full article

The purpose of this study was to evaluate how an alkali activator, specifically soluble glass, influences the geotechnical performance of sandy-pebble soil when combined with biomass bottom ash (BMA) as a sustainable stabilizing material. This work focused on understanding whether alkali activation could increase the strength, compactness, and overall engineering suitability of these mixtures while also examining how the activator affects permeability. To accomplish this, mixtures containing different proportions of BMA were prepared and treated with soluble glass at controlled water-to-activator ratios, followed by standard geotechnical procedures including Proctor compaction and California Bearing Ratio testing to assess density and load-bearing capacity. The results showed that soluble glass substantially improved the mechanical behavior of the mixtures, with both Proctor density values varying from 1.48 to 2.04 Mg/m³, depending on BMA content and activator dosage, while CBR values more than doubled for mixtures containing 20% BMA at a water-to-soluble-glass ratio of 1:3. Water permeability decreased with increasing BMA and activator content, from 8.11 × 10⁻⁵ to 5.91 × 10⁻⁵ m/s, although the permeability threshold of ≤2 × 10⁻⁵ m/s was not reached. These enhancements were linked to better packing of soil particles due to the void-filling effect of BMA and the formation of new binding compounds produced through alkali-activation reactions, including N-A-S-H and C-S-H gels. However, this study also found that higher amounts of soluble glass reduced water permeability, an effect associated with the denser microstructure created during geopolymerization. Overall, the findings demonstrate that stabilizing sandy-pebble soil with alkali-activated BMA is an effective approach to improving essential geotechnical properties while simultaneously offering environmental benefits by repurposing biomass waste in ground-improvement applications. Full article

Background/Objectives: This study evaluated carotid baroreflex sensitivity (cBRS) during graded exercise tests to exhaustion in healthy individuals. It aimed to elucidate whether the augmented blood pressure response during heavy- and maximal-intensity dynamic exercise alters carotid baroreflex control of heart rate and contributes to exercise intolerance. Methods: Thirteen healthy males (age 33 ± 2 yrs, body mass 74.6 ± 2.4 kg, and $\dot{V}$O_2max 54.12 ± 1.88 mL·kg⁻¹·min⁻¹) performed a 4 min constant-load cycling exercise at low—(30% PPO), moderate—(60% PPO), high—(80% PPO), and maximal—(100% PPO) intensity, in two experimental conditions: (a) with unrestricted muscle blood flow (no-BFR) and (b) with partial muscle blood flow restriction (BFR). Results: A significant decline in cBRS was observed during the graded maximal exercise test compared to baseline (p < 0.001), accompanied by an upward and rightward relocation of the linear relationship between systolic blood pressure (SBP) and heart rate (HR). However, the magnitude of cBRS reduction was attenuated towards maximum exercise. Application of BFR during exercise exaggerated the blood pressure rise (p < 0.01), the perceptual response (p < 0.001), the exercise-induced cBRS reduction (p < 0.001), and induced a further relocation of the SBP-HR relationship. Additionally, BFR limited the HR increase and resulted in reduced exercise performance compared to the no-BFR condition. Conclusions: These findings suggest that the pronounced increase in blood pressure during heavy- and maximal-intensity exercise may limit further increases in heart rate through arterial baroreflex activation. This may contribute to reduced exercise tolerance, as evidenced by the lower peak power output and attenuated maximal heart rate observed in muscle BFR condition. Full article

Published laboratory data on soil stabilisation are abundant, yet they remain fragmented across studies and are often difficult to reuse because of inconsistent reporting formats, heterogeneous testing conditions, and incomplete metadata. This article presents a curated experimental dataset compiled from 20 published studies on fine-grained soils, comprising 560 records, including 397 unconfined compressive strength (UCS) results and 163 California Bearing Ratio (CBR) results. The dataset is defined by the inclusion of laboratory studies designed around biopolymer-based two-additive stabilisation frameworks, while intentionally retaining untreated and single-additive comparator records reported within the same experimental programmes. This design is a key distinguishing feature of the dataset because it enables analysis of baseline soil behaviour, isolated additive effects, and combined-additive responses within a traceable study context. Across the included studies, the treatment systems cover a wide range of biopolymer- and lignin-related materials, including xanthan gum, guar gum, chitosan, sodium lignosulfonate, and electrolyte lignin stabiliser, together with complementary additives such as cement, lime, fly ash, ground granulated blast-furnace slag, rice husk ash, glass powder, concrete waste, nano-additives, and natural or synthetic fibres. In addition to UCS and CBR outcomes, the dataset preserves key contextual variables required for meaningful secondary reuse, including soil classification, grain-size fractions, Atterberg limits, compaction properties, curing duration, additive identities and dosages, and source-level traceability. The data are distributed as a structured Excel workbook comprising two cleaned outcome-specific sheets (CBR_clean and UCS_clean) and four supporting documentation sheets (StudyInventory, DataDictionary, VocabularyMap, and QC_Log). Record-level identifiers, DOI-linked source fields, inferred-curing flags, and qualified outcome descriptors are retained to support auditability, selective filtering, and reproducible reuse. The resulting dataset provides a practical foundation for comparative assessment of stabilisation strategies, pavement and subgrade engineering studies, meta-analysis, and machine learning applications in geotechnical engineering. Full article

Freeze–thaw cycles are the main cause of subgrade damage in cold regions. To investigate how straw fibers affect the road performance of reinforced black soil in these areas, this study conducted unconfined compressive strength (UCS), California bearing ratio (CBR), and resilient modulus (RM) tests, supplemented by CT scanning. The novelty lies in comparing coarse and fine straw fibers and establishing a freeze–thaw damage prediction model. It analyzed the effects of straw fiber types (coarse and fine) and contents (0, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%) on the soil’s mechanical properties and reinforcement mechanisms. Results showed that straw fibers enhance soil mechanics by distributing stress, limiting soil particle movement, inhibiting crack growth, and reducing porosity. Fiber content impacts the mechanical properties of reinforced soil more significantly than fiber type. The optimal fiber content for both coarse and fine straw fibers is 1%. At this content, the UCS of coarse fiber-reinforced soil (CFS) reached 1.11 MPa, a 32.14% increase compared to the reference group (B-0), and the RM reached 207.39 MPa, a 63.70% increase compared to B-0. Meanwhile, the UCS of fine fiber-reinforced soil (FFS) reached 1.01 MPa, a 20.24% increase, and the RM reached 150.33 MPa, an 18.66% increase. Freeze–thaw cycles degrade mechanical properties by weakening the bond between soil and straw fibers. As the number of freeze–thaw cycles increases, both the UCS loss rate and RM loss rate rise. FFS exhibits superior freeze–thaw resistance compared to CFS, due to its lower porosity and fewer cracks. The developed freeze–thaw damage evolution equation shows a strong fit (R² > 0.85) and applies to straw fiber-reinforced black soil under the conditions of this study. This research provides a theoretical basis for designing eco-friendly straw fiber-reinforced subgrades in cold regions. Full article

The California Bearing Ratio (CBR) is a critical parameter in pavement design and building foundation assessment; however, it requires labor intensive laboratory testing, including a 96 h soaking period. This study evaluated nine machine learning algorithms for predicting CBR from soil index properties: Extra Trees, Support Vector Regression (SVR), Random Forest, Gaussian Process Regression (GPR), CatBoost, LightGBM, XGBoost, Artificial Neural Network (ANN), and ElasticNet. Using 236 soil samples characterized by eight features, we conducted repeated stratified 10-fold cross validation (100 iterations). Extra Trees achieved the highest cross validation R² of 0.789 ± 0.095 (RMSE = 2.064 ± 0.481, MAE = 1.482 ± 0.294), followed by SVR (R² = 0.783 ± 0.102, RMSE = 2.090 ± 0.511, MAE = 1.446 ± 0.300) and Random Forest (R² = 0.777 ± 0.104, RMSE = 2.117 ± 0.460, MAE = 1.518 ± 0.299). The Friedman statistical test confirmed significant performance differences (χ² = 191.97, p < 10⁻³⁷), and Nemenyi post hoc analysis identified Extra Trees, SVR, Random Forest, and GPR as statistically equivalent superior groups. SHAP analysis highlighted gravel content (29.0%), maximum dry density (23.8%), and fines content (14.8%), which is consistent with geotechnical principles. Systematic noise injection (20% perturbation) demonstrated model stability, with less than 7% performance degradation at 15% noise. On this heterogeneous compiled dataset, which extends beyond the calibration domain of the empirical equations, all six empirical methods yielded negative R² (range: −0.803 to −22.639), while all ML models achieved positive R² (≥0.655 to 0.789). Extra Trees achieved a 3.1× lower RMSE than the best empirical equation, confirming substantially better predictive performance in this out-of-calibration setting. The framework provides a practical five step implementation workflow that may reduce the need for preliminary CBR tests under project specific accuracy thresholds. Full article

This study considers the potential of utilizing waste glass powder as a sustainable additive to improve the characteristics of clay subgrade soils. A comprehensive experimental program was designed, wherein a selected clay soil was amended with four distinct contents of glass powder that were finely ground: 0%, 3%, 6%, and 9% by weight. The primary objective was to evaluate the resultant improvements in soil strength and the enhanced interfacial bond between the treated subgrade and an overlying Type B granular subbase layer, which was further reinforced with an SS2 Geogrid. To characterize these effects, a suite of laboratory tests was performed, including the Modified Proctor Test, Atterberg Limits Test, California Bearing Ratio (CBR) test, and a large-scale direct shear test. A specially made large-scale instrument for direct shear was employed for the interface testing. The results demonstrate a clear positive correlation between the proportion of glass powder and the improvement in geotechnical properties. The most significant enhancement was observed at the 9% inclusion rate, which yielded a 6.6% increase in the maximum dry density and a substantial 49% improvement in the CBR value. Concurrently, this optimal mix design resulted in a 14% reduction in optimum moisture content, alongside notable decreases in the swelling and plasticity indices by 33% and 39%, respectively, confirming the efficacy of glass powder in stabilizing the clay subgrade. Full article

Enzyme-based stabilizers have been used in soil stabilization in the construction industry for many years as alternatives to traditional stabilizers and have produced successful results. These novel stabilizers gained popularity over standard stabilizers such as cement and lime due to their non-toxic and non-hazardous properties. Although enzymatic stabilizers perform very well for a variety of soil types under different environmental conditions, their effectiveness under varying temperatures has not been sufficiently investigated. This is more important in countries where there are significant fluctuations in temperature that are further exacerbated by the impact of climate change. As enzymatic products are organic and biodegradable, their susceptibility to temperature variations must be well understood. In this study, the efficiency of a commercially available enzymatic stabilizer was investigated. Tests were carried out to assess the influence of temperatures ranging from 4 °C to 80 °C on the geotechnical properties of enzymatically stabilized soil. The investigation was conducted into the compaction characteristics, index properties, compressive strength, and CBR of the stabilized soil. The results indicate that the stabilizing effect of the enzyme remains largely unchanged up to approximately 40 °C. The outcome of the study enables practitioners to use more sustainable stabilizers to treat problematic soils in regions where temperature fluctuations are within the tested range. Full article

This study investigates the mechanical properties, moisture stability, and environmental safety of microbial-induced carbonate precipitation (MICP)-treated phosphogypsum (PG)-based mixtures (MPGT) for road base utilization. Optimal cementation solution concentrations and bacterial-to-cementation solution ratios were determined via unconfined compressive strength (UCS), California bearing ratio (CBR), and splitting tensile strength tests. Durability was compared with untreated mixtures, and enhancement mechanisms were analyzed using XRD, SEM, and FTIR. Additionally, toxicity leaching tests evaluated environmental safety. Results indicated optimal parameters of 2.0 mol/L cementation solution and a 2:1 bacterial/cementation solution ratio for maximum mechanical strength. Under these conditions, MPGT durability significantly improved compared to untreated mixtures. Mechanism analysis revealed that MICP-generated calcium carbonate coats PG particles and fills voids, enhancing strength and durability. Furthermore, F⁻ and PO₄³⁻ leaching concentrations were significantly reduced. In summary, MICP improves the mechanical performance, durability, and environmental safety of PG-based mixtures, promoting PG recycling in road engineering. Full article

Concrete waste generated from the demolition of structures constitutes a significant source of waste worldwide. Recycled concrete aggregates (RCA) obtained from this waste exhibit disadvantages such as high porosity and low mechanical strength; therefore, they are not used in pavement structures without improvement. This study investigates the feasibility of using RCA improved with waste-based stabilizers as highway subbase material. RCA was used as fine aggregate and blended with basalt aggregate (BA) at different replacement ratios. The mixtures were subjected to California Bearing Ratio (CBR) tests to determine the optimum RCA content. Subsequently, unconfined compressive strength (UCS) tests were conducted using calcium carbide slag (CCS) as an activator and sewage sludge ash (SSA) as pozzolanic material at various proportions. The experimental results indicated that the mixture containing 35% RCA exhibited the most favorable performance, while higher RCA contents resulted in significant reduction in CBR values. The highest UCS value was obtained in the mixture containing 30% waste additive by weight of RCA with a CCS:SSA ratio of 3:7. For this mixture, CBR reached 315%, and displacement measured in the cyclic plate loading test under a load of 35 kN was 2.5 mm. This mixture provides sustainable and mechanically suitable alternatives for highway subbase applications. Full article

The disposal of tunnel waste slag has emerged as a major ecological challenge. Highway pavement bases require large quantities of graded crushed stone as fill material, but large-scale quarrying of such stone also poses significant environmental problems. An innovative approach involves crushing tunnel waste slag into graded crushed stone for use as fill material, offering an economical and environmentally friendly solution to both issues. However, the performance of this recycled graded crushed stone needs to be carefully evaluated. This study employed particle flow analysis software to simulate the California Bearing Ratio (CBR) test process, followed by analysis and verification to assess its performance. A CBR model was developed and validated, the meso-mechanical parameters of the penetration process were analyzed, and the results were examined in terms of both CBR values and particle contact force fields. The findings indicated that different particle stiffness ratios $k_n/k_s$ had no significant effect on the CBR test, while the friction coefficient $\mu$ showed a linear positive correlation with the CBR value. It was also concluded that the slenderness ratio of the contact force field first increased and then decreased with an increase in the stiffness ratio $k_n/k_s$. As the friction coefficient $\mu$ increased, the slenderness ratio of the contact force field decreased accordingly. This study provides valuable insights into the influence of meso-mechanical parameters on the performance indicators of graded crushed stone pavement and offers a promising approach for the processing and reuse of tunnel waste slag to alleviate ecological pressures. Full article

Land degradation in drylands increasingly threatens infrastructure and the performance of renewable energy (RE) systems through coupled hydro-chemo-mechanical changes in soil fabric, density, matric suction, and pore–water chemistry. A key gap is the limited integration of unsaturated soil mechanics with practical indicator sets used in engineering screening and operations. This narrative review synthesizes evidence from targeted searches of Scopus, Web of Science, and Google Scholar. Searches are complemented by key organizational reports and standards, as well as citation tracking. Priority is given to sources that report mechanisms linked to measurable indicators, thresholds, tests, or models relevant to dryland infrastructure. The synthesis uses the soil-water characteristic curve (SWCC) and hydraulic conductivity k(θ) to connect hydraulic state to strength and deformation and couples these with chemical indices, including electrical conductivity (EC), exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR). Practical diagnostics include the dynamic cone penetrometer (DCP) and California Bearing Ratio (CBR) tests, infiltration and crust-strength tests, monitoring with unmanned aerial vehicles (UAVs), geophysics, and in situ moisture and suction sensing. The contribution is an indicator-driven, practice-oriented framework linking mechanisms, monitoring, and mitigation for photovoltaic (PV), concentrating solar power (CSP), wind, transmission, and well-pad corridors. This framework is implemented by consistently linking unsaturated soil state (SWCC, k(θ), and matric suction) to degradation processes, measurable indicator/test sets, and trigger-based interventions across the review. Full article