Acta Geotechnica最新文献

This study utilized advanced deep learning algorithms to predict consolidation settlement in deep soft clay deposits, with a specific focus on the construction design phase of port facilities. Two innovative hybrid models, namely, the sequence long short-term memory (LSTM)-transformer (SLT) and the parallel LSTM-transformer (PLT) models, were introduced to generate accurate time-settlement predictions by incorporating geotechnical and construction information from sites where preloading was applied. The models were developed and tested using a dataset from study sites in Busan Newport, South Korea. This dataset was constructed through 3D interpolation, which provided a detailed and accurate representation of subsurface conditions. A case study was conducted to evaluate the performance of the model in real-world scenarios. The accuracy of the proposed models was compared with that of traditional methods, including the Hansbo method and a basic transformer model. Results indicated that the proposed models outperformed these traditional methods by producing more accurate predictions. In addition, a parametric study highlighted the effectiveness of the model in capturing the effects of critical factors, such as step loading period, maximum fill height, and clay layer thickness. The SLT and PLT models demonstrated significant potential for enhancing settlement prediction accuracy during the design phase. This improvement in accuracy aids in planning and increases cost effectiveness in projects involving soft deposits.

Alkali-activated ground-granulated blast-furnace slag (GGBS) has emerged as a promising sustainable alternative to traditional high-carbon binders for stabilizing high-water-content dredged slurry. Phosphogypsum (PG), a byproduct of phosphate fertilizer production, has been identified as an effective activator that enhances the strength of GGBS-stabilized soil. This study investigates the use of PG, MgO, and GGBS as composite binders for bidirectional activation to stabilize soil. Through physical experiments, unconfined compressive strength (UCS) tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM), the physical and mechanical properties of bidirectionally activated slag-stabilized soil and the micro-mechanisms of strength formation were studied. Results demonstrate that PG significantly enhances the UCS of GGBS-stabilized soil, achieving a 40% improvement at the optimal PG content compared to systems without PG. The optimal PG content in this study, determined to be 2.5% of dry soil weight, is strongly correlated with pH and the E₅₀ modulus. Strength improvements are attributed to the increased formation of cementitious phases, including C-S-H, C-A-H, hydrotalcite, and ettringite (Aft/AFm). PG regulates the system's pH, promoting ettringite formation, which reinforces the stabilized soil structure. However, excessive PG negatively impacts strength by hindering the formation of C-S-H and hydrotalcite while promoting excessive Aft/AFm. From an economic and environmental perspective, the bidirectional activation system reduces costs by 43% and carbon emissions by 37% compared to ordinary Portland cement. Additionally, the proposed method achieves a maximum reduction of 70% in carbon emissions per unit compressive strength (C_f) compared to common alkali activation GGBS methods. These findings highlight the role of PG in enhancing soil stabilization strength and environmental performance, contributing to sustainable engineering practices.

The long-term depressurization-induced gas production in hydrate reservoirs requires an in-depth geomechanical understanding of hydrate-bearing sediments during hydrate dissociation. In this study, a customized triaxial apparatus was employed to investigate the stress and volumetric behaviors of hydrate-bearing sediments with sandy and clayey–silty skeletons subjected to various hydrate dissociation ratios and effective confining pressures. The results show that the peak strength, secant modulus and dilation angle of hydrate-bearing sediments generally decrease with increasing hydrate dissociation ratio and decreasing effective confining pressure, but the variations in Poisson’s ratio slightly decrease with hydrate dissociation. Hydrate dissociation decreases the peak strength of sandy hydrate-bearing sediments by decreasing the cohesion and friction angle, while that of clayey–silty hydrate-bearing sediments is mainly related to decreasing hydrate dissociation-induced cohesion. A slight hydrate dissociation can lead to a significant strength reduction, and even under final identical hydrate saturations, the strength parameters of hydrate-bearing sediments that experienced hydrate dissociation are lower than those without hydrate dissociation. Thus, a semiempirical peak strength prediction model for hydrate-bearing sediments during hydrate dissociation is proposed and validated in this work, which allows for the estimation of the peak strength of hydrate-bearing sediments through hydrate saturation, skeleton type and stress state.

The extent of passive soil arching effect in the loading zone above underground structures is significantly influenced by the uplift displacement, a phenomenon that remains theoretically unresolved. In this study, a deformation-dependent model is developed for the passive soil arching by correlating the stress redistribution, with the normalized loading displacement and the shear strain. The relationships among the internal friction angle, dilatancy angle and shear strain of the soil in the shear band were established. Compared with previous models, the proposed model shows a higher performance in calculating the maximum/ultimate stress ratios. Moreover, the applicability of the proposed model is greatly supported by the experimental data from literatures. In addition, the model succeeds in appropriately evaluating the evolution of the soil stress above the loading zone with the normalized loading displacement. A parametric study was undertaken, indicating that a higher fill height, a narrower trapdoor width or a greater relative density of soil induces more significant passive soil arching effect.

Soil erosion is a significant geo-environmental challenge, causing destabilization of riverbanks and compromising infrastructure. Effective mitigation requires advanced soil stabilization techniques to prevent land loss, protect ecosystems, and reduce fugitive dust emissions contributing to air pollution. In this study, biochar-assisted biocementation enhances sand stability against erosion by applying urease-producing bacterial cell solutions to the soil surface layer. To achieve this goal, the erosion resistance of biocemented soil samples was examined through experimental testing in a wind tunnel under high-speed wind conditions, while subjecting the similarly treated specimens to flowing water velocity surpassing the critical threshold in a flume setup. Compared to biocemented sand samples (S₀BCS) with an 85.5% reduction in rate of erosion, sand–biochar composite specimens (S₂BCS) demonstrate a superior erosion rate reduction of 98.5%. Similarly, the incorporation of biochar into the biocementation method significantly enhances resistance to hydraulic shear due to running water, as evidenced by approximately 25% greater soil retention in biochar-amended specimens. The study also highlights biochar’s effectiveness in reducing NH₄⁺–N concentrations through adsorption mechanisms to mitigate groundwater contamination and eutrophication. The experimental investigation concluded that biochar, as a nutrient, showed minimal impact on ureolytic bacteria’s growth and metabolic activity. This strategy, as a sustainable and environmentally friendly approach, has the potential to reform soil preservation practices and contribute to protection against soil erosion by binding soil particles with the help of enhanced calcium carbonate precipitation facilitated by the presence of biochar. Overall, this phenomenon promotes soil conservation and contributes toward the maintenance of ecological sustainability.

Phosphoric acid-based geopolymer owns a great solidification/stabilization (S/S) effect on acidic Pb²⁺ contaminated soil, especially the modified phosphoric-based geopolymer (named MAPG) synthesized from fly ash, metakaolin and aluminum dihydrogen phosphate. Nevertheless, the long-term S/S performance of MAPG on the acidic Pb²⁺ contaminated soil subjected to freeze–thaw (F–T) cycles is not yet investigated. In this article, the long-term S/S performance of MAPG stabilized acidic lead contaminated soil subjected to F–T cycles through many test methods was studied, and a long-term stability evaluation model based on the resistivity index ρ was proposed to reflect the degradation performance of MAPG stabilized acidic Pb²⁺ contaminated soil subjected to F–T cycles. The results show that the F–T cycles could destroy the stabilized soil structure, causing a mechanical diminution of the stabilized contaminated soil, but the compressive strength still met the strength standard (> 0.35 MPa) after 8 F–T cycles. The stabilized contaminated soil resistivity firstly declined rapidly under 0–4 F–T cycles and then stabilized after 4 F–T cycles. In deionized water, acetic acid and sulfuric acid-nitric acid environments, the MAPG binder had good S/S impact on acidic Pb²⁺ contaminated soil subjected to F–T cycles, but when the binder dosage was 6%, the Pb²⁺ leaching after F–T cycle exceeded 5 mg/L (hazardous waste leaching toxicity limit) for the stabilized soil under acetic acid environment. According to the established evaluation model, the service time of MAPG binder stabilized acidic Pb²⁺ contaminated soil in typical F–T region could reach 100 years. The stabilized contaminated soil pH decreased with a rising F–T cycles times, while electrical conductivity rowed with the raising F–T cycles times with a good relevance. Lead phosphate compounds and berlinite were found in the MAPG stabilized contaminated soil, and F–T cycles could induce the microstructure damage of stabilized contaminated soil.

The emergency repair of base and subbase structures in large-volume engineering projects presents significant challenges in terms of materials and construction techniques. To address these challenges, this study introduces a novel ultra-early-strength geopolymer (UESG) grouting material and a layer-by-layer gravel filling and infiltration grouting (LLGF-IG) construction technique. Unlike conventional materials, the UESG grouting material offers superior flowability, rapid setting, and high early strength, making it particularly suitable for emergency repair scenarios. This study successfully resolves the contradiction between construction performance (flowability) and functional indicator (early strength) through formulation optimization and performance regulation. While maintaining high strength of the material, excellent flowability is ensured. Laboratory tests were conducted to optimize the UESG mixture proportions, focusing on pH value, setting time, flowability, and mechanical properties. The grouting quality was evaluated through on-site LLGF-IG construction, employing visual examination, strength test of core-drilling specimens, and X-ray computed tomography (XCT) to analyze the distribution of gravels, UESG skeletons, and pores/defects. The results demonstrated that the optimal UESG achieved a flowability of 200 mm, an initial setting time of 30 min, a final setting time of 37 min, and a 1-h compressive strength of 2.2 MPa. Core-drilling specimens exhibited tight aggregate-matrix bonding and a high compressive strength of 36.5 MPa. XCT analysis revealed no significant interlayer spaces and a relatively homogeneous spatial distribution of pores across five segments. The study also identified the formation of interfacial transition zones (ITZs) and weak phases, primarily attributed to the natural flow behavior of slurries and air retention in inter-particle spaces. These findings highlight the practical advantages of the UESG material and LLGF-IG technique for rapid road repairs, offering a significant improvement over traditional methods in terms of efficiency, strength, and reliability. This research provides a robust foundation for the application of UESG-based solutions in emergency repair engineering.

The growing population and rapid urbanization have led to an increase in generation of solid wastes. Utilization of these wastes as backfilling materials promotes sustainability because it mitigates landfilling of solid wastes, produces valuable backfilling materials, and conserves natural resources. Hence, this study proposes a solution to use two solid wastes, fine incineration bottom ash (FIBA) and marine clay, to produce liquefied stabilized soil (LSS) for backfilling. The influential factors including initial water content of marine clay slurry, cement content, and FIBA content in the production of LSS were investigated and discussed. The flowability, water content, void ratio, elastic modulus, unconfined compressive strength (UCS), leaching concentrations of heavy metals, mineralogy, and microstructure of the LSS were evaluated. The costs and benefits of the proposed LSS were also analyzed. The results showed that FIBA affected the flow value of LSS through decreasing water content and cation exchange. The addition of FIBA not only reduced water content and void ratio of LSS, but also promoted formation of hydration products such as calcium silicate hydrate and ettringite, thereby increasing the strength of LSS. LSS with a cement content of 60 kg/m³ and a FIBA content of over 200 kg/m³ achieved a similar or even higher UCS than LSS with 80 kg/m³ of cement but without FIBA, demonstrating its potential for cement reduction. The leaching concentrations of heavy metals from LSS were considerably reduced compared with raw FIBA due to the sorption by clay minerals and the stabilization/solidification by hydration products. The cost–benefit analysis indicated that compared to commercial LSS, producing LSS using only marine clay reduced material costs by 91%, while incorporating FIBA can further generated revenue through waste recycling fees. In summary, the proposed eco-friendly waste-based LSS possesses good engineering properties and improves cost-effectiveness for backfilling applications.

Termite nests exist widely in earth levees and pose a significant yet often underestimated threat to their structural integrity. However, the mechanistic pathway by which termite nests trigger levee failure has remained poorly understood. This study, for the first time, systematically elucidated the complete chain reaction process of termite nest-induced levee breach through a series of well-designed physical model tests. Experimental observations indicated that the breach evolution could be broadly divided into five sequential stages: the presence of termite nests, concentrated leak erosion, levee crest collapse, overtopping, and final breach. As well as quantitatively characterizing the triggering mechanism of each stage, four critical factors driving the transition from one stage to the next were identified. Specifically: (1) concentrated leak erosion was initiated when the seepage velocity exceeded a threshold, primarily controlled by the riverine water level; (2) the seepage channel diameter expanded up to 3.8 times the original termite tunnel, leading to crest collapse; (3) overtopping occurred when the difference between the effective water-retaining height following collapse and the riverine water level reached zero; and (4) breach onset was marked by a novel dimensionless index, η, defined as the ratio of levee volume loss to breach-zone volume, with a critical value of 0.51. These threshold-based findings constitute the first quantitative criteria for predicting termite-induced levee breach progression and provide a scientific foundation for early warning and long-term strategies to mitigate biologically induced levee risks.

This paper presents a novel method for estimating shear strength of sands by using shear wave velocity V_s. The key of the method is a correlation between V_s and the peak stress ratio (q/p’)_p, established through a comprehensive experimental program comprising small-strain shear wave measurements and large-strain drained triaxial compression tests conducted over a wide range of states of sands. By analyzing the data within the framework of critical state soil mechanics, the stress ratio factor K, defined as the ratio of peak stress ratio (q/p’)_p and critical state stress ratio (q/p’)_cs, is uniquely linked to the initial state parameter ψ₀. Furthermore, using the relation between stress-corrected shear wave velocity V_s1 and ψ₀, the stress ratio factor K is related to V_s1. The salient feature of the relationship lies in its sound theoretical framework, offering a lucid illustration of the interplay between small-strain and large-strain behavior, encompassing the combined influence of void ratio, confining pressure, and soil characteristics concurrently. The new relationship is substantiated using extant literature data, and the parameters involved can be readily fine-tuned, thereby showing a great potential in geotechnical engineering applications.