Crack is one of the dominant factors affecting the stability of expansive soil slopes, which tend to act unfavorably upon slope stability. A series of centrifuge model tests were carried out investigate the performance of expansive soil slopes with different crack connectivity rates and crack inclination before and after humidification. The slope cracks were filled with strong expansive and glass drops, which yields high permeability and low strength of the cracked mass, and addresses the drawbacks of conventional crack simulation methods. Expansive soil slopes with diverse crack distribution patterns were generally stable under natural conditions. After humidification, however, slopes with higher crack connectivity rates show poorer stability. Specifically, the relative stability index of T1, T2, and T3 slopes were 0.9, 0.5, and 0.6, respectively. Sliding deformation occurred along the steeply inclined cracks at the slope crest. Increased crack connectivity intensifies the chain reaction of “shear stress concentration-directional accumulation of deformation-coordinated sliding”, speeding up the transition from local deformation to global slope failure. These results provide theoretical references for revealing the failure mechanism of cracked expansive soil slopes and mitigating relevant slope hazards. Failure characteristics of cracked expansive soil slopes under humidification. Increasing crack connectivity significantly reduces slope stability. This study reveals the deformation and instability mechanism of cracked expansive soil slopes, and elucidates the influence mechanism of crack connectivity on the stability of such slopes.

In geotechnical engineering, soil deposits are frequently subjected to complex three-dimensional cyclic loading conditions, such as those induced by traffic, which significantly influence the long-term deformation and stability of infrastructure, particularly in rapidly developing regions like the Greater Bay Area (GBA). This study presents an experimental investigation on the deformation behavior of undisturbed granite residual soil (GRS) under such three-dimensional cyclic stresses. A series of cyclic true triaxial tests were conducted to systematically examine the effects of cyclic deviatoric stress, cyclic intermediate principal stress, and cyclic mean stress. The results show that the cyclic deviatoric stress is the primary driver of permanent major principal strain. The cyclic mean stress consistently restrains permanent strains in both principal directions. Most notably, the cyclic intermediate principal stress plays a dual role: it suppresses the accumulation of permanent major principal strain but concurrently promotes permanent intermediate principal strain. In addition, the accumulation rate of the permanent major principal strain exhibits a nonlinear decay trend, which shows significant correlation with the rearrangement of microstructure. Based on an exponential-hyperbolic model, an empirical formula is proposed to estimate the ultimate permanent strain of GRS under three-dimensional cyclic stress states, which comprehensively incorporates the influences of cyclic deviatoric stress, cyclic intermediate principal stress, and cyclic mean stress.

The novel modular moving bed constructed wetland (MMB-CW), which integrates constructed wetlands (CWs) with moving bed biofilm reactor (MBBR) technology, has demonstrated significant potential for treating various low carbon-to-nitrogen (C/N) ratio wastewater and mitigating clogging. However, further investigation is needed to optimize the suspended substrate in MMB-CWs and clarify how substrate type affects system performance. This study applied the innovative MMB-CW technology to treat low C/N ratio wastewater under high-nitrogen and high-phosphorus conditions. Meanwhile, the practical performance of two engineering materials, ceramsite and high-density polyethylene (HDPE) filler, was compared under these identical conditions. Results indicated that under extremely low C/N ratio (0.5) conditions, MMB-CW filled with ceramsite demonstrated relatively better pollutant removal performance compared to those filled with HDPE filler during the system stabilization period. Within the MMB-CW, in situ self-enrichment facilitated the accumulation of nutrients-removing bacteria, including Candidatus_Competibacter (0.9-5.2%), Ferruginibacter (1.7-9.0%), and Nitrospira (0.3-1.5%). Nutrient metabolism-related gene analysis revealed higher abundances of nitrification-associated genes and a higher nosZ/(nirS + nirK) ratio in the ceramsite-filled MMB-CW than in the HDPE filler-filled MMB-CW. Therefore, ceramsite may be more suitable than HDPE filler as a suspended substrate for MMB-CWs. Notably, within the MMB-CW, the spatial assembly of bacterial communities was jointly governed by stochastic and deterministic processes, with a greater contribution from stochastic processes in the ceramsite-filled system (87.1%) than in the HDPE filler-filled system (76.2%). This study optimized suspended substrates for MMB-CWs, offering a promising approach to overcome conventional CW limitations and mitigate environmental risks from low-C/N wastewater discharge.

The penetration of sampling tubes is a primary source of sampling disturbance, affecting the quality of undisturbed soil samples and the reliability of subsequent laboratory test results. To investigate the patterns of soil disturbance and deformation during sampling tube penetration and their influencing factors, a visualization test apparatus for sampling tube penetration was developed using Particle Image Velocimetry (PIV) technology. Penetration tests were conducted in sands with different sampling tube diameters and wall thicknesses, revealing the distribution characteristics of soil disturbance deformation during penetration. The results indicate that the soil inside the tube consistently exhibits a three-stage deformation sequence—compression, heave, and re-compression—throughout penetration, independent of sampler geometry. In the heaving zone, disturbance deformation reaches its maximum at the tube axis and decreases toward the tube wall, while in the compressive zone, disturbance deformation is minimal at the tube axis and gradually increases toward the tube wall. The tube diameter exerts a dominant control on the spatial pattern of disturbance, while wall thickness mainly affects its magnitude.

Weathered granite masses, due to the heterogeneity of weathering, always exhibit significant variability, which induces a great challenge for the evaluation of their engineering properties. To investigate the in-situ strength and stiffness behaviors of weathered granite, this study conducted a series of self-boring pressuremeter (SBPM) tests, pre-bored pressuremeter tests (PMT) and standard penetration tests (SPT) on weathered granite at a highway overpass site in Lincang, Yunnan Province, China. The test results show that the strength and stiffness of weathered granite increase with depth, corresponding to the decreasing degree of weathering. Good linear correlations are established between the pressuremeter-derived strength and stiffness parameters and the SPT-N’ values. In addition, the effect of loading rate on the mechanical properties is investigated, revealing that higher loading rates yield higher strength and stiffness of weathered granite. A comparison between in-situ SBPM and laboratory resonant column tests demonstrates that the shear modulus from laboratory tests is generally lower, which is attributed to the loss of structure and cementation caused by sampling disturbance. These insights enhance the understanding of the in-situ mechanical properties of weathered granite and provide guidance for design and construction in such materials.

In recent years, the impact of alkali contamination on lateritic clay has gained increasing attention, but studies on small-strain stiffness remain limited. This study investigates how different concentrations of alkali contamination affect the small-strain stiffness of undisturbed lateritic soil using resonant column tests (RCTs). Thermal analysis, scanning electron microscopy (SEM), nitrogen adsorption, and mercury intrusion porosimetry (MIP) were employed to analyze the chemical reactions and structural evolution at the microscopic level, providing a rational basis for explaining stiffness evolution. Results indicate that alkali contamination dissolves kaolinite, forming aluminosilicate gel. Dissolution increases with concentration, and gel yield peaks at pH value of 11.4 while inhibited at pH value of 12.4. The structural reorganization caused by dissolution and gel filling significantly reduces the macropore volume (>100 nm), leading to an overall densification of the structure, with the sample with pH value of 11.4 being the most compact. Alkali contamination enhances the stiffness, with maximum dynamic shear modulus (G(0)) increasing and then decreasing as pH rises, while its attenuation rate first slows down and then accelerates. Both trends exhibit turning points at pH value of 11.4, where the enhancement effect is optimal. This is mainly attributed to the peak gel production at this pH, which compensates for the loss of aggregate stiffness and, together with structural reorganization, enhances inter-aggregate contact stiffness, resulting in the highest G(0 )and the lowest attenuation rate. This study identifies a critical pH threshold for enhancing the self-cementation and structural densification of lateritic soil, thereby providing new insights into underground contamination monitoring and sustainable foundation reinforcement. (c) 2026 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. 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/).

There is a strong correlation between the desiccation environment and the cracking evolution of expansive clay, which thereby exerts a notable impact on the small-strain stiffness properties of subsoils subjected to dynamic loadings in service. To investigate how desiccation environment affects the shrinkage cracking and small-strain stiffness (G) of intact expansive clays, desiccation test, resonant-column test, and microstructural analyses including computerized tomography (CT) and scanning electron microscopy (SEM) were carried out in series. The results indicate that low humidity environments raise the desiccation rate of expansive clay, arrest the shrinkage deformation, and speed up the development of shrinkage cracks. Besides, the degradation of G is hence enhanced and maximum dynamic shear modulus (Gmax) is lowered down. Incremental confining pressure hinders the degradation of G, which is significantly manifested in the cases of low desiccation rates. During desiccation, expansive clay at a lower moisture content or a higher confining pressure records a greater Gmax, and at each confining pressure, Gmax increases at a low rate initially but shoots up thereafter with the decrease in moisture content, which can be formulated in terms of moisture content and confining pressure. In addition, at each confining pressure, the degradation rate of G decreases initially, followed by a dramatic rise with the progressive drop in moisture content, i.e. there exists an optimum moisture content, at which the degradation of G can be suppressed to the uttermost. This work provides a valuable reference for evaluating the small-strain stiffness degeneration of expansive clay exposed to different desiccation environments.

Expansive soil commonly exhibits over-consolidation, yet its influence on damage-induced softening remains insufficiently understood. In this study, ring shear tests were conducted on expansive soils with varying over-consolidation ratios to quantify the damage softening behavior under large deformation. Three representative damage evolution equations were introduced to model the observed softening responses. The results show that the peak-to-residual strength reduction ratio ranges from 17.1

In some marine and offshore geotechnical engineerings, the stress state of marine clay is plane strain state. In this study, comparisons between static and dynamic responses under the axisymmetric condition and those under the plane strain condition were studied. The static test results show that the stress–strain and pore pressure characteristics under axisymmetric and plane strain conditions are similar. However, the strength for the triaxial test is smaller than that for the plane strain test, which can be attributed to the fact that the coefficient of the intermediate principal stress under the plane strain condition is larger than 0. The dynamic test results show that the plastic vertical strain ( ε_1p ), hysteresis characteristics, and resilient modulus ( M_r ) are significantly different. Under same conditions, _1p under the axisymmetric condition is greater than that under the plane strain condition, but inclinations of hysteresis loop and M_r under the axisymmetric condition are smaller than those under the plane strain condition. This is because that the compression in horizontal direction of samples by the cyclic horizontal stress under the plane strain condition. Besides, ε_1p under axisymmetric and plane strain conditions is described by a unified model considering the effects of strengths in different stress states.

The accumulation of biodegradable plastics (BPs) in wastewater treatment plants (WWTPs) presents a novel environmental concern, while carbon deficiency concurrently limits advanced biological denitrification. Herein, this research explored the fate of BPs and their viability as solid-phase carbon donors for denitrification. Six prevalent BPs were selected, results showed that dissolved organic carbon (DOC) release from BPs varies considerably with the synthesis type, microbially synthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as the optimal solid-phase carbon source with superior DOC bioavailability, achieving the denitrification rate of 0.72 mg/(g·h). Light irradiation and pH variations accelerated DOC release via surface micro-cleavage, predominantly yielding highly active aliphatic oligomers without disrupting the primary polymeric backbone. Furthermore, macromolecular depolymerization genes (acsABCDE, cdhCDE) and nitrous oxide reductase genes (nosZ, nosD) were strongly temperature-dependent, which induced the directional enrichment of the core denitrifying genus Thauera, and upregulated expression at 25 °C that promoted NO₃⁻ reduction. This research provided the theoretical basis for the in-situ resource utilization of BPs for advanced wastewater denitrification.

Biochar-modified clay has garnered growing interest in geotechnical engineering, yet existing research has predominantly focused on swelling–shrinkage behavior, strength, and hydraulic conductivity, with comparatively little attention given to stiffness evolution. This study systematically investigates the effects of biochar particle size (< 0.075 mm, 0.075–0.425 mm, and 0.425–2 mm) and mass content (0

Constructed wetlands (CWs) are widely used for advanced treatment of wastewater treatment plant effluents and their nitrogen (N) removal performance is often inhibited by antibiotics. Biofilms on CW substrates play a fundamental role in pollutant biodegradation, microbial community stability and antibiotic resistance gene (ARG) dissemination. This study investigated the effects of substrate filling ratios (90% and 60%) in modular moving bed constructed wetlands (MMB-CWs) on operational performance, biofilm properties and antibiotic resistance risks. The MMB-CW with higher substrate filling ratio exhibited a better N removal efficiency of 83.7% and a significant reduction of nitrous oxide emission by 72.6%. The higher substrate filling ratio increased the protein/polysaccharide ratio of extracellular polymeric substances (EPS), potentially forming a hydrophobic barrier and structured a highly modular microbial network with pronounced niche differentiation. Genome-centric analysis revealed that core taxa carrying denitrification and anammox genes (narG, narH, nirS, nosZ, hzs, hdh) enriched by 1.5- to 12.6-fold in abundance in the MMB-CW with 90% substrate filling ratio. Notably, Desulfobacillus increased by 1.7-fold in abundance, which served as a keystone species driving denitrification, EPS construction, oxidative stress adaptation and energy production. The elevated abundances of enzymes catalyzing key electron- and energy-generating steps in the tricarboxylic acid cycle and denitrification enzymes drove a more complete denitrification process. The highly modular network restricted horizontal gene transfer of ARGs, mitigated the enrichment of pathogenic antibiotic-resistant bacteria (PARBs) and occurrence of high-risk ARGs in MMB-CW. The findings provide an optimization strategy for MMB-CW in view of treatment performance and ecological risk.

Disposal of harvested wetland biomass is a crucial challenge for the efficient and sustainable application of constructed wetlands. Hydrothermal carbonization (HTC) is an emerging low-energy technology for processing wetland biomass, which is a renewable resource, producing hydrochar with potential for long-term carbon sequestration and ammonia nitrogen (NH4+-N) adsorption capacity. However, the carbon sequestration ability and adsorption capacity of hydrochar require enhancements to improve the feasibility of HTC. Here, we developed a natural zeolite-enhanced HTC to convert wetland biomass to hydrochar-zeolite composites (HZCs). Results showed that the carbon sequestration potential of hydrochar significantly increased by 49.7% due to the enhancement of yield, aromaticity, and stability under optimal conditions (180 °C, an NZ-to-biomass ratio of 2, 150 rpm, and 1 h). The resulting HZCs exhibited the most excellent adsorption capacity of 1.46 mg/g and the highest microbial loading of 1309.91 nmol P/g, achieving a 96.94% NH4+-N removal efficiency after 24 h (a 57.50% enhancement through co-culture with Pseudomonas stutzeri). This study demonstrated that integrating natural zeolite into low-temperature HTC of wetland biomass is a promising approach that not only solves the biomass disposal problem but also enhances carbon sequestration and wetland wastewater remediation performance.

Expansive soils are prone to strength degradation after rainfall, yet conventional slope stability analyses often rely on laboratory-derived shear strength parameters that may overestimate in-situ conditions. This study evaluates and compares the shear strength of expansive soils using the borehole shear test (BST), laboratory direct shear test (DST), and consolidated undrained test (CUT) under natural and flooding conditions. Results show that shear stress- shear displacement (or axial strain) curves generally exhibit weak hardening characteristics. Significant reductions in cohesive strength occur after flooding. The cohesive force obtained by DST and BST decreases by 18.2 kPa and 13.1 kPa after flooding respectively, while the internal friction angle decreases slightly within 3°. Laboratory tests consistently yield higher strength parameters than BST, while flooding BST values closely align with those measured on actual slip surfaces. Numerical modeling of an unstable cut slope confirms that using flooding BST parameters produces more realistic safety factors. The findings highlight the importance of incorporating in-situ testing under representative moisture conditions for reliable slope stability design in expansive soils.

Natural granite residual soil (GRS) usually exhibits a metastable structure characterized by an inherited relict structure from the parent rock, cemented by free iron oxides and clay, which confers a complex mechanical behavior. However, existing research has rarely established constitutive models that account for the unique structured characteristics of GRS. Accordingly, this study introduces a constitutive model for GRS, referred to as the Modified Cam Clay (MCC) model, to simulate the mechanical behavior considering the degradation of inherited structure and cementation. In this model, a non-linear failure envelope is formulated to merge with the Critical State Line of the remolded soil at high stress levels in order to capture the degradation of inherited structure. And a damage function is introduced to capture the cementation degradation during shearing. Finally, four structured GRS and three tuff residual soils are employed to validate the model’s accuracy through triaxial experiments and true triaxial experiments. Simulation results show the effect of stress level, and the deformation change from dilation to compression can be successfully reproduced. The introduced model can accurately capture the mechanical behavior of not only structured GRS but also other structured residual soils, proving its extended suitability, which could provide more guidance for engineering design and construction in weathered strata.

Global climate change increases extreme rainfall events, significantly elevating the frequency of geological hazards in granite residual soil (GRS) regions. The stress path of slope soils under extreme rainfall conditions differs from conventional triaxial scenarios, characterized by nearly constant deviatoric stress (CQ) and continuously varying mean effective stress ( p^' ). To investigate the instability and deformation behaviors of GRS under cyclic variations in p^' along the CQ path, consolidated drained (CD) tests, constant shear drained (CSD) tests, p^' cyclic tests along the CQ path and stepped stress level tests along the CQ path were conducted. The test results demonstrate that GRS under the CSD path exhibits instability characterized by dilative volumetric behavior and a rapid increase in axial strain. p^' cyclic tests along the CQ path reveal the existence of a potential instability stress ratio ( η_I_p ) less than instability stress ratio ( η_IS ), at which specimens undergo instability under multiple p^' cycles. Instability-type specimens demonstrate progressive accumulation of both deviatoric strain and volumetric strain with increasing cycle numbers, while exhibiting delayed deformation. Specifically, dilation occurs when p^' increases. In contrast, stability-type specimens primarily undergo elastic deformation. Stepped stress level test results indicate that abrupt changes in strain rate drive this delayed deformation pattern, leading to a corresponding delay in the η_IS values determined by current instability criteria. Deformation behaviors under cyclic loading show that the stability of GRS is critically dependent on the evolution of plastic volumetric strain increment ( Δε_v^p ). Consequently, a methodology utilizing the strain increment ratio ( Δε_v /Δε_q )—stress ratio ( η ) curve from CSD tests is proposed to determine η_I_p . The results demonstrate that this method provides accurate predictions of instability under cyclic loading. The research findings provide critical references for geological hazard prevention and mitigation in GRS regions under extreme rainfall conditions.

The presence of confined gas bubbles in gas-bearing strata alters soil properties, which poses safety hazards to ocean engineering. This study investigates the quantitative relationship between gas content and electrical conductivity and aims to identify shallow gas strata and mitigate associated risks accurately. Despite the recognized sensitivity of electrical parameters to gas-bearing characteristics, the absence of robust quantitative models correlating volumetric gas content (theta g) with bulk conductivity (sigma) remains a fundamental limitation in geophysical prospecting. A novel test vessel integrating consolidation and electrical testing is developed to address this critical gap. Using indoor remodeled gas-bearing fine-grained soil as the research object, the electrical conductivity of soil samples with varying initial gas contents is measured using the quadrupole electrode method. The effect of gas content on microstructure was analyzed in conjunction with scanning electron microscopy (SEM). This study showed that conductivity nonlinearly decays with increasing gas content, showing a sharp decline of 12.3 mS/m from the initial 5.04 % gas increment (53 % water content), with attenuation rate progressively decreasing. SEM showed that the particle contact shifted from face-to-face contact to edge-to-side contact with increasing gas content, and the number of pores, volume, and nonhomogeneity increased significantly, which led to changes in the conductive network. A model for calculating the electrical conductivity of gas-bearing fine-grained soil considering the volumetric gas content was developed by introducing the volumetric gas content index and optimizing the development of shallow gas resources.

Constructed wetlands (CWs) are a sustainable, low-cost solution for tail water treatment. Lab-scale studies provide detailed insights into pollutant removal mechanisms, but their results cannot be directly applied to field scale systems due to differences in hydrodynamics, influent load, and environmental heterogeneity. In this study, we systematically quantify scale-dependent effects using machine learning (ML). A dataset of 1198 observations from 141 peer-reviewed studies was compiled to benchmark six ML algorithms, with random forest models selected under both global and scale-specific strategies. Scale-specific models outperformed the global model, compared to the global model, the scale-specific models achieved R2 improvements of 0.215 (lab-scale) and 0.149 (field-scale), highlighting the benefit of scale-aware modeling. Feature importance analysis revealed that treatment capacity dominates lab-scale systems (69.6%), whereas influent concentration and wetland area govern field-scale performance (41.8%). Partial dependence and two-way interaction analyses, based on field-scale models, identified optimal parameter ranges for full-scale CW operation, including total inflow of 30,000-240,000 m3/day and hydraulic loading rates of 0.45-0.65 m/day. While optimal parameters from the lab-scale cannot be directly transferred to the field-scale, they are still of great value in interpreting mechanisms such as fluid dynamic interactions and microbe-substrate processes during scale-up, and can provide qualitative guidance to supplement quantitative field-scale analysis. This study establishes a data-driven framework that links mechanistic understanding from laboratory experiments with predictive field-scale modeling, enabling more reliable, efficient, and scalable CW design while systematically addressing differences between controlled experiments and real-world systems.