Chloride-bearing high water content soils generated from reclamation, dredging, and site formation commonly exhibit poor mechanical stability and high seepage susceptibility, posing challenges for saline ground improvement. This study investigates the hydro-mechanical behavior of chloride-bearing soils stabilized with ground granulated blast-furnace slag (GGBS) activated by MgO and desulfurized gypsum (DG). Unconfined compression, permeability, X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry, and ion chromatography testing were employed to link mechanical behavior with mineralogical and pore-structure evolution. Results indicate that chloride alters hydration pathways and produces DG dependent responses. At low DG contents, chloride promotes weakly cementitious Friedel's salt and sodium-bearing products while suppressing ettringite formation, resulting in reduced strength. With sufficient DG, concurrent ettringite and Friedel's salt formation refined the pore structure and improved strength retention. Synthetic saline-water permeation increased hydraulic conductivity by 1.8–29.4% compared with freshwater permeation, indicating that saline infiltration may increase seepage risk even when compressive strength remained acceptable. Permeability correlated strongly with the fraction of effective pore throats larger than 0.12 μm, demonstrating that connected transport-governing pores controlled seepage. These findings clarify the hydrochemical boundary conditions regulate hydro-mechanical performance and provide guidance for low-carbon stabilization of saline fine-grained ground where both strength retention and seepage control are critical.

Ecological slope protection offers a sustainable strategy for mitigating rainfall-induced geological hazards triggered by engineering slope instability. This study explores the reutilization of high-water-content dredged soil as a functional ecological substrate to enhance slope revegetation and erosion control. A novel dual-layer eco-slope system was developed: a base layer comprised dredged soil amended with superabsorbent polymer (SAP) and rice husk to improve water retention, soil structure, and plant establishment; the cover layer consisted of the same substrate stabilized with a magnesium oxide-slag (MgO-slag) binder to enhanve mechanical strength and erosion resistance. A series of laboratory experiments were conducted to evaluate vegetation performance and erosion resistance. Results revealed an inverse relationship between plant height and the unconfined compressive strength (qu) of the stabilized cover layer, indicating that excessive rigidity suppressed plant growth. Vegetation coverage exhibited a unimodal trend with increasing qu, peaking before declining sharply beyond a critical threshold (qu_cr = 158.7 kPa), highlighting a trade-off between structural reinforcement and ecological viability. Under simulated extreme rainfall (200 mm/h), the MgO-slag-stabilized cover layer delayed erosion onset and reduced cumulative soil loss by up to 34.1 %, verifying its engineering effectiveness. Erosion resistance further improved with vegetation maturity due to root reinforcement. A parabolic correlation between cumulative erosion mass and quunderscored the coupled influence of mechanical strength on erosion control and substrate behavior. By balancing the competing demands of vegetation growth and erosion control, the optimal qu range for the stabilized cover layer was determined as 121.4-158.7 kPa. These findings provide a practical framework for the sustainable reuse of dredged soil in eco-slope engineering, contributing to both geohazard mitigation and solid waste valorization.

High-water-content dredged sludge and shield tunneling residues remain largely underutilized despite their potential for ecological reuse. This study proposes a direct modification method that transforms such waste slurries into functional eco-soils through the incorporation of superabsorbent polymer (SAP), biochar, and rice husk, thereby eliminating the need for energy-intensive dewatering. The effects of SAP and biochar contents on the physical properties and vegetation performance of the modified eco-soils were systematically investigated, with particular emphasis on the coupling between soil parameters and plant growth responses. Results showed that increasing SAP and biochar contents reduced specific gravity, void ratio, and total porosity, while increasing bulk density and pH. Within the investigated ranges, the modified soils satisfied regulatory requirements for green planting substrates in terms of bulk density, pH, and non-capillary porosity (at SAP contents of 1.5% and 1.7%), demonstrating their applicability for ecological restoration. Vegetation tests indicated that 1.7% SAP yielded the highest germination rate, vegetation cover, plant height, and biomass. Vegetation cover exhibited a non-linear dependence on void ratio and bulk density. At 1.5% SAP, vegetation cover increased with both parameters, whereas at 1.7-2.0% SAP, it increased with void ratio but decreased with bulk density. Plant height showed a comparable trend at higher SAP contents. To characterize the combined structural effects, a Synergistic Loosening Index (SLI) was introduced, integrating void ratio and bulk density. The SLI showed a clear linear correlation with vegetation cover and plant height. These findings establish a quantitative basis for converting high-water-content waste into engineered eco-soils and contribute to sustainable reutilization of waste slurry in geotechnical and ecological engineering practice. (c) 2026 Japanese Geotechnical Society. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Granular soils are usually unsaturated consisting of solid particles, pore water, and air, and the thermal conductivity of unsaturated granular soils is a basic parameter for evaluating the deformation properties of geothermal structures. However, the natural physical properties, structure evolution, and heat transfer mechanism were not fully considered in previous work. To this end, the unsaturated soil is considered a mixture of matrix (consisting of solid particles and pore water) and air inclusion. In this study, an effective model is developed based on the homogenization method to estimate the thermal conductivity of three-phase granular materials. It is done by introducing a structure variable related to the evolving soil structure, and a structure parameter is adopted to evaluate the sensitivity of the structure variable to the fraction of inclusion, which is affected by the shape, dimension, and size-polydispersity of the matrix. The structure parameter decreases significantly with the rising degree of saturation at first (Sr = 0%-25%) but varies slightly with a degree of saturation beyond 25%. Considering the similarity between the structure parameter-saturation curve and soil-water characteristic curve, the structure parameter is defined in relation to the degree of saturation that is analogous to the classical soil-water characteristic curve. A thermal conductivity model is proposed by integrating the structure parameter into the homogenization equation. It is verified based on the test data extracted from literature studies, demonstrating strong predictive capability for the thermal conductivity of granular soils across a broad range of saturation.

Phosphogypsum, an industrial solid waste, is an effective binder for partially replacing cement in stabilizing dredged sediments. Acid rain, as a worldwide ecological problem, also affects the long-term stability and sustainability of geotechnical materials and structures. However, the research on leaching effects and long-term durability of phosphogypsum-stabilized soils under acid rain conditions is limited and remains a significant challenge for practical applications. This study investigates the leaching effects and long-term durability of phosphogypsum-stabilized soils by simulating acid rain erosion through semi-dynamic leaching tests. Key parameters, including leached Ca2+ concentration, leachate pH, and unconfined compressive strength after leaching, were evaluated. Microscopic analyses with X-ray diffraction (XRD) and scanning electron microscopy (SEM) were also conducted to explore the underlying mechanisms. The results indicate that the presence of phosphogypsum in stabilized soil with high water content shows a significant improvement in leaching resistance subjected to acid ions, evidencing a lower Ca2+ concentration and pH value in the leachate, and a higher strength after leaching compared to those samples without phosphogypsum. SEM images and XRD analysis revealed that samples with higher phosphogypsum content possess denser structures due to more needle-shaped ettringite and other minerals in the soil matrix, contributing to improved strength and leaching resistance. The enhanced strength and leaching resistance of phosphogypsum-stabilized soil can be attributed to additional gel formation, a rise in swelling potential, ettringite bridging, and a denser microstructure, which reduces Ca2+ availability for leaching in acidic environments.

Clay particles typically bond together to form aggregates, resulting in a double-porosity structure. As water content increases, coarse aggregates may disintegrate into finer clay particles. However, both the disintegration process and the double-porosity structure are rarely considered in existing thermal conductivity models. In this study, the thermal conductivity of aggregated clays is analyzed using homogenization theory and the disturbed state concept (DSC). A reference model is first developed to describe the thermal conductivity of dry aggregated soils, incorporating a structural parameter to account for the effect of inter-aggregate pores. This model is expressed as a function of the thermal conductivities of air and clay particles within a homogenization framework. To capture the effects of saturation and aggregate disintegration, a disturbance factor is introduced. Based on the DSC, a new model is proposed that integrates the combined effects of inter-aggregate porosity and aggregate disintegration. A simplified version of this model is derived by assuming complete aggregate disintegration at full saturation, requiring only three parameters for practical application. The disintegration process is validated through mercury intrusion porosimetry (MIP) tests, which reveal that the disturbance factor follows an inverse S-shaped trend with respect to the inter-aggregate pore ratio. Validation of the proposed model using both experimental results and data from the literature demonstrates its effectiveness in predicting the thermal conductivity of various types of aggregated clays across a wide range of saturation levels.

Carbon sequestration lightweight soil (CLS) represents a novel sustainable construction material developed by incorporating CO2 foam into stabilized soils composed of industrial byproducts and high-water-content waste slurry. This strategy offers a dual-benefit solution, achieving material lightweighting alongside permanent carbon dioxide storage. This study evaluates the properties of CLS through a series of physicomechanical tests, as well as microstructural analyses. Results demonstrate that the integration of CO2 foam enables a simultaneous enhancement of mechanical strength and reduction in bulk density. The UCS initially increases and then decreases with rising foam content, with an optimal dosage identified at 800 mL/kg. At this optimal content, CLS achieves high-performance metrics, including a 28-d UCS (uniaxial compressive strength) exceeding 2200 kPa, a substantial carbon sequestration capacity and higher durability. Microstructural analysis confirms that the enhanced strength originates from extensive carbonate mineralization, which fills pores and densifies the matrix. Scaling analysis underscores its substantial environmental potential: using CLS as a subgrade fill could sequester over 200 tons of CO2 per kilometer of highway construction. Hence, CLS emerges as a high-performance, sustainable material that effectively integrates essential structural functionality with carbon sequestration, advancing the frontier of low-carbon infrastructure technology.

The sustainable management of high-water-content slurry is hindered by the high cost and limited feasibility of conventional dewatering pretreatments. This study proposes a dewatering-free methodology for fabricating unfired bricks by directly incorporating slurry into a synergistic binder system comprising desulfurized gypsum (DG), magnesium oxide (MgO), and ground granulated blast-furnace slag (GGBS). A comprehensive test program was undertaken to optimize mixture proportions and evaluate mechanical behavior, durability against wetting-drying cycles, and environmental performance. The unconfined compressive strength (UCS) exhibited a rise-fall trend with increasing DG content, whereas the softening coefficient declined consistently. An optimal composition of 10 % DG, 10 % MgO, and 15 % GGBS achieved a 28-day UCS of 16.2 MPa and a water stability coefficient of 0.86, and preserved 10.7 MPa after ten wetting-drying cycles. DG incorporation also mitigated drying shrinkage by 57 %. Life-cycle assessment confirmed that eliminating dewatering and sintering enables 95 % solid-waste utilization and significantly reduces embodied energy (about 62 %) and CO2 emissions (about 96 %) compared with conventional clay-fired bricks. These results verify the technical feasibility and environmental superiority of the proposed slurry-based unfired brick technology.

Emergency geotechnical engineering and post-disaster reconstruction require soil stabilization technologies capable of achieving rapid strength gain with low environmental impact. However, conventional cement-based stabilization of excavated soils and construction and demolition waste (CDW) is constrained by high-carbon emissions, long curing durations, and insufficient early strength. The development of low-carbon binders capable of rapid strength gain therefore remains a critical challenge. In this study, a CDW-based geopolymer composed of ground granulated blast-furnace slag (GGBS), waste glass, and clay red brick powder is proposed for the stabilization of excavated soils. To further accelerate strength development, microwave curing is introduced as a rapid and energy-efficient activation technique. A series of mechanical properties tests and microstructural characterization techniques, including unconfined compressive strength (UCS) testing, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR), were employed to investigate the effects of alkali activation parameters (NaOH concentration, Na2SiO3 modulus, and alkali-to-solid ratio), precursor composition, and microwave curing conditions on the mechanical performance and strength improvement mechanisms of stabilized soils. The results demonstrate that the UCS of the geopolymer-stabilized soil exhibits a nonlinear relationship with the alkali activation parameters: Strength initially increases and subsequently decreases beyond an optimal threshold for NaOH concentration, Na2SiO3 modulus, and alkali-to-solid ratio. Microwave curing significantly enhances early strength development, achieving more than 50

The simplified physically-based dam breach models are effective tools for predicting outburst flood hydrographs of landslide dams. However, their predictive reliability is severely constrained by parameter uncertainties, particularly regarding in soil erosion. To address this, this study applies an established Bayesian multilevel framework to develop a probabilistic modeling approach for landslide dam breaches. A highly computationally efficient simplified model is developed and subsequently embedded into a Bayesian multilevel framework to systematically quantify the uncertainties in the erosion parameters. Using observational data from ten documented landslide dam failure cases, model inversion is executed via a Markov chain Monte Carlo simulation combining Gibbs and Metropolis-Hastings sampling. As a primary contribution, this study quantifies the uncertainty of the erosion parameter specifically for landslide dams for the first time. Following inversion, parameters with non-informative priors are updated to well-defined posterior distributions with distinct peaks. Furthermore, the results reveal that approximately two-thirds of the uncertainty in the predicted peak discharge stems from the epistemic uncertainty of key parameters, with the remainder attributed to residual error. This framework significantly improves the reliability of outburst flood predictions and substitutes subjective empirical assumptions with data-driven probabilistic inference, providing highly valuable insights for downstream hazard mitigation.

Compressibility of reconstituted clay generally plays a critical role in evaluating the workability of geo-structures. Previous empirical models may show limited accuracy beyond the range of database. Meanwhile, pure data-driven models may not well reproduce mechanical behavior of soils even with sufficient data. Therefore, a multi-fidelity neural network (MFNN) is proposed to capture the compression behavior of reconstituted clay. The synthetic data generated by empirical equations are utilized for training the low-fidelity model (LFM), while the high-fidelity model (HFM) is trained by tests results. This training strategy enables the MFNN to combine the easy accessibility of synthetic data and high accuracy of the test results. Initial water content, liquid limit, and effective vertical stress are adopted as input variables for predicting the void ratio. The LFM provides a baseline for the whole model and the HFM is decomposed into linear and nonlinear parts for a more precise prediction. The parameters (i.e., weights and biases) of sub-networks of the MFNN are updated independently to obtain optimal outputs of each network. The final predictions are further obtained by a weighted optimization of linear and nonlinear networks outputs. Results indicate that the distinctive structure of MFNN can reduce the requirement of the data for model training and maintain the generalization ability of the model simultaneously. Only two sets of experimental data are required for satisfied predictions within a wide range of initial water content.

Traditional cement-solidified sludge often exhibits low strength and brittle failure. This study systematically investigates the effects of straw fiber length (0.3-9 mm) and content (0-1.0 %) on the early (7-day) mechanical behavior of cement-stabilized sludge. Unconfined compressive strength (UCS), stress-strain behavior, brittleness index, and microstructure were evaluated. Results show that UCS of solidified sludge rises then falls with increasing straw length, peaking at 0.5 mm. UCS also increases then decreases as straw content grows and the optimal content is 0.1 % within 0.3-9 mm lengths. In terms of failure patterns, the straw-free sample exhibits splitting failure, while those with straw show increased cracks, manifesting as varying degrees of shear failure. Additionally, the brittleness index demonstrates non-linear behavior with changes in straw content. Below 0.1 % content, the brittleness index increases for most straw lengths (except 0.5 mm). Beyond 0.1 % content, the brittleness index exceeds 0.62 for most straw lengths, indicating a significant increase in material brittleness. Microstructural and compositional analyses using XRD, SEM, and EDS reveal that the addition of wheat straw enhances the density and uniformity of the cement-stabilized sludge matrix by improving particle bonding and hydration product distribution. XRD confirms consistent mineral phases with modified peak intensities. SEM shows reduced porosity and improved structural compactness at optimal fiber lengths, and EDS highlights increased carbon and oxygen content due to chemical interactions between straw fibers and hydration products, optimizing mechanical properties. Based on these findings, this study recommends the use of 0.1 % straw content with a straw length of 0.5 mm for solidifying highwater-content sludge, providing an effective approach for sludge resource utilization.

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

Bimsoils, consist of fine soil matrix and coarse rock aggregates, and are widespread as sedimentary soils. The bearing behavior of bimsoils are significantly affected by rock fraction. However, the mechanism governing the coarse fraction effect remains unclear. The traditional analysis methods are not effective in describing the rock fraction effect due to heterogeneous structure. To this end, 91 simulations have been performed to investigate the bearing capacity of bimsoils (mainly of two-dimensional, 2D) under shallow foundations using finite element method (FEM). It is found that the densified matrix bridge as well as the coarse aggregates forms a strong contact network which is responsible for the coarse fraction effect. A structure variable is introduced to quantify the reinforcing effect of rock aggregates. Then, a model incorporating the structural variable is proposed to evaluate the coarse fraction effect on the bearing capacity of bimsoils. Compared with the conventional method for pure soil matrix, only two additional parameters are required, and they can be readily calibrated by laboratory tests. The model is further validated by data available in literature, which can effectively estimate the bearing capacity of bimsoils under shallow foundations with a various of rock contents and rock characteristics.

This study evaluates biochar's impact on MgO-slag stabilized slurry soil using physical, mechanical, and microstructural analyses (unconfined compressive strength tests, one-dimensional compression tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results show biochar significantly reduces stabilized soil density and post-curing water content. Soil pH decreased initially (0-10 % biochar), then increased (10-20 %), stabilizing beyond 20 %. Unconfined compressive strength (UCS) follows pH trends, indicating strength gains arise from supplementary reactions. Hence, an optimal biochar content of 20 % is identified with 48.1 % increase of 28-day UCS compared to biochar-free samples. Compression index (Cc) also shows a significantly improvement, decreased by 24.1 % (14-day) and 23.4 % (28-day) with 20 % biochar. Microstructural analysis revealed optimal biochar content enhances cementitious phase organization (e.g., C-S-H, hydrotalcite) and refines pores by absorbing free water and acting as nucleation sites. Optimized biochar integration thus improves mechanical performance, offering a low-carbon strategy for sustainable reuse of underground excavation slurries.

Rockfill materials produced from weathering and blasting usually possess a spatial variability of particle size distribution (PSD). Thus, a large number of laboratory tests are required to determine the engineering properties of rockfill materials with various PSDs. To reduce the number of redundant tests, a novel approach based on the mixture concept is proposed to describe the grading curves within the PSD envelopes of rockfill materials. The constituents of rockfills with varying PSDs are divided into two parts, termed as the fine matrix and coarse aggregates according to a threshold distinguishing fine and coarse particles. Then, the original PSDs of rockfill materials are reproduced by assigning different coarse fractions. The applicability of the proposed method is evaluated based on Discrete Element Method (DEM). The mechanical behavior of the sample with fitted PSDs are found to be approximately consistent with the corresponding values of the original PSDs at the same relative density. This method can be adopted into classical elastoplastic models to predict the mechanical behavior of rockfill materials through only a few laboratory tests. The findings in this study provide an approach for evaluating the mechanical behavior of rockfill materials with numerous PSDs based on the mixture concept.

The consolidation behavior of a foundation with vertical drains under vacuum preloading is affected by the lateral deformation and well resistance. In this study, a nonlinear consolidation model is developed based on the assumptions of equal volumetric strain and time-dependent well resistance. The model considers the relationships between various factors, such as well resistance, linear attenuation of vacuum pressure, lateral deformation, and simultaneous vertical-radial seepage. An analytical solution of the model is provided, and its universality is verified. Additionally, the effects of different consolidation factors on the average consolidation degree (U over bar ) are analyzed, and the error in calculating U over bar without considering a single factor is evaluated. The results indicate that well resistance significantly affects the consolidation rate of soil without vertical seepage, particularly at the later stage of consolidation when the constant parameter A, which represents time-dependent well resistance, exceeds 1.0 x 10(-7) (s(-1)). Not considering the lateral deformation can result in an overestimated soil consolidation rate. For thin layer soils with low liquid limits, the effects of the consolidation factors on U over bar are ranked as follows: c(c)/c(k) (ratio of compression index to permeation index) > k(v) (vertical permeability coefficient) > v (Poisson's ratio) > k(1) (attenuation residual coefficient of vacuum pressure) > qw (discharge capacity of prefabricated vertical drains).

The expansion of megacities and the need to reduce carbon emissions have prompted the exploration of urban underground space as an important option. However, the lack of quantitative analysis on the low carbon effect of underground space hinders its further development. This study aims to address this gap by proposing a method to quantify the low carbon capacity and carbon emissions of urban underground space. The dynamic relationship between these factors under different development intensities is also investigated. A case study was conducted in the Nanjing Xinjiekou area, using data on underground space development since 2006. The results indicate that the low carbon capacity of underground space is lower than the carbon emission in the initial stage. However, over time, the net CO2 emission gradually decreases and eventually reaches zero carbon emission. The time to achieve zero carbon emission depends on the intensity of underground development and socioeconomic factors. When ignoring socioeconomic impact, a higher intensity of underground space corresponds to a faster time to reach zero carbon emissions. However, excessively high levels of development can result in a high vacancy rate, which negatively affects the low carbon capacity and delays the achievement of zero carbon emissions. Therefore, an optimal development intensity of underground space can be determined to minimize the time required to achieve zero carbon emission. Furthermore, a quantitative relationship between the optimal development intensity and urban economic indicator (i.e. civilian motor vehicles in this study) was established in this study based on zero carbon emission analysis. These findings provide valuable insights for achieving faster carbon neutrality in underground space development and inform future city planning strategies.

In this paper, a finite element numerical model of thermal-hydro-mechanical of energy piles under multi-layer geological conditions was established, and field tests of ultra-long energy pile (1000-mm-diameter, 44-m-long) were carried out to reveal the temperature distribution and mechanical properties of energy pile under typical working conditions. Based on the analytical results, a softening shear model of the energy–soil interface under the condition of large shear displacement was proposed with the load transfer method, and the reliability of the model was verified. The model can simulate the shear–displacement relationship of the pile–soil interface under different geological conditions.

The treatment and resource utilization of municipal sludge and dredged silt have been rendered urgent by the acceleration of urbanization and stricter environmental protection demands. An effective solution was developed to address the challenges of poor mechanical properties and the difficulty in directly using cement-based materials for municipal sludge treatment. The utilization of dredged silt with high water content served as the foundational skeleton material. Appropriate proportion (0.5:1.0) of sodium silicate, which accelerates cement hardening, and polyurethane, which facilitates chemical bond cooperation, was combined to form SP material, partially replacing cement. Unconfined compressive strength (UCS) tests were subsequently conducted on the solidified municipal sludge. These tests aimed to investigate the influence of the dredged silt mixing ratio, initial water content of dredged silt, and the SP mixing ratio on the strength of the solidified municipal sludge. Furthermore, a strength prediction model was established for solidified municipal sludge, taking into consideration the mixing ratios of dredged silt and SP. The research findings indicate that dredged silt can serve as a skeleton structure for solidified municipal sludge. The UCS of the solidified municipal sludge increases with the increase in the dredged silt mixing ratio, and reaches a maximum value at mixing ratio of 1.0. SP materials can partially replace cement, the appropriate proportion of SP and cement can synergistically improve the strength of solidified municipal sludge, and the optimal SP mixing ratio is 50%. Furthermore, the strength prediction model constructed with independent variables such as dredged silt mixing ratio, curing age, water-to-cement ratio, and SP mixing ratio demonstrates better predictability for the strength development of solidified municipal sludge.