Search Results (252)

Loess slopes are prone to rapid infiltration, surface erosion, and shallow instability under intense rainfall, highlighting the need for eco-friendly shallow protection methods with enhanced anti-seepage and erosion resistance. To improve the applicability of microbially induced calcite precipitation (MICP) in loess slope protection, this study proposes a combined MICP–sesbania gum (SG) modification method. Permeability tests, surface hardness tests, and indoor artificial rainfall model tests were conducted to systematically evaluate its effects on seepage control and the erosion resistance of loess slopes. The results show that calcium chloride provides a stronger permeability-reducing effect than calcium acetate. Compared with the MICP-only treatment, the combined MICP-SG treatment significantly reduces the permeability coefficient and increases surface hardness. Based on the overall modification performance, a cementation solution concentration of 1.0 mol/L and a curing time of 7 d were selected as suitable treatment parameters. Rainfall model tests further demonstrate that the combined treatment delays erosion failure, reduces infiltration rate and soil loss, and suppresses wetting front migration and internal water content response. These findings indicate that MICP combined with SG can effectively improve the anti-seepage, erosion resistance and surface stability of shallow loess slopes, providing experimental support for eco-friendly shallow slope protection in loess regions. Full article

Red clay in humid-hot environments suffers from severe water sensitivity and rainfall-induced slope instability, while traditional cement/lime stabilization faces high carbon emission challenges. Existing studies on plant ash-modified red clay mainly focus on basic mechanical properties, while systematic research on water retention characteristics and slope stability under extreme rainfall in humid-hot climates remains insufficient. To address this gap, this study proposes a sustainable stabilization method using agricultural waste-derived plant ash for red clay modification in humid-hot regions. Red clay exhibits distinct engineering behaviors owing to its unique physicochemical properties, leading to compromised slope stability and reduced resistance to rainwater infiltration. In this study, red clay was stabilized with 5%, 10%, 15%, and 20% plant ash. Laboratory tests evaluated compaction characteristics, shear strength, and water retention, supported by microstructural analysis via scanning electron microscopy (SEM). Slope stability under rainfall conditions was further simulated using ABAQUS 2022 software. Key findings include: (1) The addition of plant ash significantly altered the compaction properties. As the plant ash content increased from 0% to 20%, the maximum dry density of the modified red clay decreased linearly from 1.68 g/cm³ (unmodified soil) to 1.53 g/cm³, while the optimum moisture content rose from 21.86% to 23.85%. (2) The mechanical properties exhibited a non-linear response, peaking at 10% ash content. At this optimum dosage, the unconfined compressive strength, cohesion, and internal friction angle increased by 70.4%, 83.0%, and 37.1%, respectively, compared to untreated soil. (3) Plant ash enhanced water retention capacity, shifting the soil-water characteristic curve (SWCC). The modified soil demonstrated faster dehydration at low suction but improved water retention at high suction. The permeability coefficient decreased by an order of magnitude. Microstructural analysis revealed reduced porosity and fracture infilling by cementitious gels. (4) Numerical simulations confirmed that 10% plant ash reduced maximum slope displacement from 0.96 m to 0.61 m under heavy rainfall (90 mm total precipitation over 36 h, peak intensity 90 mm/day), elevating the safety factor from 0.85 to 1.45. Failure modes transitioned from deep-seated slip to localized shallow erosion. These results demonstrate that plant ash is a sustainable and effective additive for red clay slope stabilization in tropical climates. Full article

In the face of the raw materials crisis and environmental concerns, sustainable waste management has become a priority for current and future generations. Recycling waste from wastewater treatment plants in a closed loop protects natural resources, reduces landfill volumes, and lowers disposal costs. This paper presents the results of tests on the physical, filtration, and mechanical properties of mixtures of washed mineral waste (WMW) from grit chambers with fly ash from the thermal treatment of municipal sewage sludge (SSA) in a fluidized bed furnace. Additionally, radiological tests of the mixture components were conducted. Based on the conducted tests, the possibility of sustainable use in civil engineering, such as soil backfills and embankment construction materials, was assessed. The possibility of safely using waste materials in the indicated construction solutions was demonstrated for mixtures with dominant WMW content (90% and 70% by total weight). The waste mixtures correspond to poorly or medium-grade sands with a small amount of silt (uniformity coefficients of 3.33, 3.50, and 8.00). They are characterized by maximum dry densities of 1.542, 1.770, and 1.780 g/cm³; optimal moisture contents of 12.54, 12.86, and 20.25%; permeability coefficients of 0.08, 0.22, and 0.39 m/d; and internal friction angles of 38.4, 39.5, and 40.1°. The values of the determined parameters of some mixtures are similar to those of natural sands used as construction aggregates. All mixtures meet the geotechnical criteria for use in road embankments, below frost depth, and in flood embankment bodies. Mixtures with a 90% mass fraction of WMW were also approved for application as backfill for installation trenches. However, none of the mixtures met the hydraulic conductivity threshold required for the upper layers of embankments nor for backfill of abutments and retaining structures without the use of an additional binder (cement or lime), which is considered a prerequisite for these applications. Full article

The localized high hydraulic gradient at the bottom of concrete cutoff walls in deep overburden foundations poses a significant seepage failure risk. This stability is heavily influenced by the high-stress state, a critical factor often overlooked in conventional evaluations. Taking a specific engineering project as the research background, this study investigates the seepage stability of gravelly medium-coarse sand by simulating the coefficient of earth pressure at rest (K₀) condition. A comprehensive series of triaxial seepage tests was conducted across burial depths from 120 m to 260 m, supplemented by conventional zero-stress permeability tests as a baseline. The results indicate that the seepage failure mode is characterized by overall soil flow. For soil deeply buried at the wall bottom, the risk of seepage failure is relatively low, provided there are no significant geological defects or internal seepage outlets nearby. Compared to conventional tests, the K₀ stress condition significantly increases the failure gradient and reduces the permeability coefficient. Under the same gradation, variations in burial depth have a negligible influence on these parameters. However, at the same burial depth, particle gradation has a major effect; the mean envelope line is the most sensitive to stress, followed by the upper and lower envelope lines. Based on these findings, an allowable hydraulic gradient of 3.0 is proposed—approximately five times the traditional design value (0.6–0.65). This study provides a critical scientific basis for the seepage-control design and stability assessment of high dams on deep overburden foundations. Full article

To accurately assess foundation behaviour under urban conditions, it is essential to integrate geotechnical analysis with continuously evolving hydrogeological parameters. In rapidly developing cities such as Astana, long-term fluctuations in seasonal groundwater levels, salinity dynamics, and changes in soil permeability significantly influence stress–strain behaviour and structural settlement. This study employs multiple software tools, supported by detailed hydrogeological monitoring, laboratory testing, and integrated numerical simulations, to analyse the development of settlement and stress–strain characteristics for both the synagogue and the Independence Palace. The results show that between 2002 and 2020, groundwater salinity at the synagogue site increased from 1.10 g/L to 3.39 g/L, accompanied by a 23% rise in soil permeability. At the Independence Palace site, salinity reached 2.01 g/L, with an 18% increase in permeability. Numerical simulations conducted using GEO5, PLAXIS 2D, and LIRA SAPR revealed consistent trends but varying magnitudes of subsidence. PLAXIS 2D predicted settlement values approximately 15–25% higher than GEO5, while LIRA SAPR produced estimates 10–20% lower. Among the models, GEO5 demonstrated the closest agreement with field observations. The Independence Palace underwent relatively rapid stabilisation due to an effective drainage system, with consolidation occurring over approximately 100–150 days. In contrast, the synagogue experienced prolonged settlement over a period of 10–15 years, driven by high groundwater saturation and river recharge. These findings confirm that hydrochemical evolution plays a critical role in governing soil permeability. Consequently, cross-validation using multiple modelling platforms is essential, and long-term settlement assessments in complex hydrogeological environments must account for time-dependent changes in permeability. Full article

Aiming to address the problems of shield chamber blockage and poor muck discharge faced by earth pressure balance shields during tunneling in sandy strata, bentonite slurry is used for muck improvement. Using a multi-scale approach combining macro-scale experiments, micro-scale analysis, and molecular dynamics simulations, this study systematically investigates the interface interactions between particles of sandy soil in shield tunneling and the improvement mechanism of sodium-based bentonite slurry additives. Through the macroscopic experiment, the sodium bentonite slurry soil–water ratio of 1:7 and injection ratio of 25% showed the best improvement effect. After improvement, the permeability coefficient decreased by 99.72%; the cohesion of the excavated soil increased from 3.055 kPa to 11.458 kPa, representing a 275.06% increase; and the angle of internal friction decreased from 42.318° to 36.985°, a decrease of 12.60%. The improvement was significant. Through SEM, XRD, and FTIR microanalysis, it is found that bentonite slurry forms a flexible film on the surface of sandy soil. By coating sand particles, filling voids in the soil, and enhancing interparticle cohesion, it improves the properties of the soil. On the nanoscale, a Na-MMT/SiO₂ system model is established based on molecular dynamics simulations to elucidate the interactions between bentonite slurry and sand particle interfaces. The results indicate the presence of van der Waals forces and hydrogen bonds between Na-MMT and SiO₂. Interlayer water molecules form a hydrogen bond network that strengthens interfacial bonding, enabling bentonite slurry to tightly adhere to soil particle surfaces. This improves the microstructure of the soil, thereby enhancing its macroscopic properties. Full article

Soils in cold seasonally frozen regions undergo repeated freeze–thaw (F–T) cycles, during which soil moisture content, pore structure, and permeability can change substantially. Previous studies have mainly focused on the mechanical behavior of such soils, whereas few have clarified how moisture content fluctuation regulates pore-structure evolution and permeability response during F–T cycling. In this study, black soil specimens were prepared with initial moisture contents of 15%, 20%, 25%, and 30% on a dry-weight basis and were denoted as 15%-MC, 20%-MC, 25%-MC, and 30%-MC, respectively. The specimens were subjected to 0, 1, 3, 6, 9, and 12 F–T cycles. Mercury intrusion porosimetry, scanning electron microscopy image analysis, and variable-head permeability tests were used to characterize pore-structure parameters and hydraulic responses. The results showed that porosity and mean pore diameter generally increased with increasing F–T cycle number, and the magnitude of these increases depended on the initial moisture content. The 15%-MC group exhibited limited pore expansion, mainly characterized by a transition from micropores to small pores, whereas the 25%-MC and 30%-MC groups developed more mesopores and macropores. In the 30%-MC group, porosity reached its maximum after 9 F–T cycles and then decreased slightly after 12 cycles, indicating particle rearrangement or partial filling of larger pores. The permeability coefficient and cumulative infiltration also increased with increasing F–T cycle number, with more pronounced increases observed in the high-moisture groups. Tukey’s post hoc test showed that the permeability coefficients in the later F–T stages were higher than those in the early stages, particularly in the 25%-MC and 30%-MC groups. Correlation analysis and principal component regression indicated that the permeability coefficient and cumulative infiltration were positively correlated with porosity, mean pore diameter, mesopores, and macropores, but negatively correlated with micropores. Overall, the initial moisture content regulated pore-size redistribution and seepage-channel development, thereby shaping the hydraulic response of black soil under repeated F–T cycling. Full article

Given the challenges posed by high groundwater levels, thick sand layers, and strong permeability in water-rich sandy strata, cut-off walls often fail to fully isolate the hydraulic connection between the inside and outside of a foundation pit. As a result, dewatering inside the pit—especially from confined aquifers—can cause significant external groundwater drawdown and subsequent ground settlement. Using a deep excavation conducted in Xiamen as a case study, this study developed a two-dimensional hydro-mechanical coupled finite element model to systematically investigate the effects of various dewatering scenarios and soil permeability coefficients on surface settlement around the pit, and to reveal settlement patterns induced by dewatering and excavation in such strata. Field monitoring data were incorporated to validate the numerical model, ensuring accuracy and reliability. Key findings include the following: (1) Dewatering contributes to over 76% of the total settlement at each stage, with confined drawdown being the dominant factor, implying that dewatering optimization should take priority over controlling excavation rate. (2) Under confined dewatering, the settlement influence zone extends beyond 80 m, far exceeding the extension caused by excavation alone; thus, monitoring and protection ranges must be adjusted dynamically. (3) The horizontal permeability of sand shows a nonlinear positive correlation with settlement, and this sensitivity grows with depth, highlighting the need for accurate permeability determination and stricter controls in deep excavations within water-rich sand layers. From an engineering perspective, these findings underscore the importance of prioritizing confined aquifer dewatering management, dynamically expanding settlement monitoring zones, and rigorously characterizing permeability profiles to mitigate excessive ground settlement and protect adjacent infrastructure. Full article

Against the backdrop of growing demand for environmentally friendly reinforcement in geotechnical engineering, natural fiber reinforcement combined with microbial-induced calcium carbonate (MICP) and enzyme-induced calcium carbonate (EICP) technologies has garnered significant attention due to their eco-friendly and efficient advantages. However, few studies have reported the combined application of these three techniques for sand consolidation. This study employs a combined MICP-EICP approach with natural fiber reinforcement to enhance the overall strength of sandy soils and investigate related rock fracture permeability phenomena. Tests conducted include calcium carbonate content, unconfined compressive strength, permeability coefficient, and permeability flow rate. Results indicate that when brown fiber length is 6 mm and dosage is 0.8%, the unconfined compressive strength of MICP-EICP composite specimens reaches a maximum of 0.61 MPa, calcium carbonate content peaks at 7.07%, and permeability coefficient drops to a minimum of 0.0044 cm/s. This composite method offers a highly promising and sustainable improvement solution for geotechnical engineering applications such as sand consolidation, crack sealing, and cultural relic restoration. It not only optimizes mechanical properties but also enhances the utilization rate of waste materials. Full article

In the cement-based stabilization of organic soil, the alkaline environment produced by cement hydration dissolves organic matter from the soil skeleton while simultaneously promoting the precipitation of neophases. This study investigates the coupled effects of structural deterioration and neophase compensation on the microstructural and mechanical properties of organic soil. Organic soil was treated with an alkaline Ca(OH)₂ solution (pH = 12.0) utilizing a model testing apparatus over an 80-day duration. Consolidation and permeability tests were combined with microstructural analyses (FTIR, XRD, and SEM-EDS) to elucidate the fundamental mechanisms. The results show that humus acid in organic soil was dissolved in an alkaline environment, significantly enlarging soil pores and forming interconnected dissolution channels. Consequently, the permeability coefficient and additional settlement increased by 49.21% and 18.07%, respectively, compared to the pristine soil samples. Concurrently, within the OH⁻-and Ca²⁺-rich environment, clay minerals underwent a pozzolanic reaction, generating C-(A)S-H gels. Dissolved humus acid formed complexes with Ca²⁺ ions. While these formed neophases provide microstructural compensation for the organic soil, their compensatory effect is limited. These findings provide a critical theoretical framework for understanding the coupled deterioration–compensation mechanisms, which is essential for optimizing engineering design and promoting the long-term durability of alkaline-reinforced organic geotechnical environments. Full article

Stabilization/solidification (S/S) is a crucial technology for the engineering reuse of oil-contaminated soil. A key challenge, however, is preventing the migration of residual oil under varying hydraulic conditions. This study investigates the efficacy of a lime and fly ash binder in treating oil-contaminated soil. We systematically compared the performance of untreated (UOCS) and treated (TOCS) soils under different aqueous environments (humidity injection, water injection, and permeation). We evaluated oil migration, water-holding capacity, and permeability characteristics. The results demonstrate that the lime–fly ash treatment effectively adsorbed and immobilized oil contaminants, restricting their mobility to a remarkably low range of 0.54% to 4.90%. Furthermore, the S/S treatment significantly improved the soil’s hydraulic properties: it enhanced the water-holding capacity, reduced the soil-water characteristic curve hysteresis, and counteracted the oil-induced hydrophobicity. Consequently, the effective permeation channels were restored, leading to a higher permeability coefficient in TOCS compared to UOCS. Crucially, the hydro-mechanical performance of the treated soil met the criteria of the Solidification/Stabilization Resource Guide, confirming its suitability for engineering applications. Full article

The coupling between the key parameters of rock and soil particle composition and slurry diffusion paths exerts a significant influence on actual grouting effectiveness. Based on the spherical penetration grouting model for Bingham cement grout, this study optimizes the fractal permeability model by coupling the characteristic particle size, porosity, and tortuosity, overcoming the deficiency of single-factor porosity consideration in existing permeability models. Unlike existing studies that only use experimentally measured permeability coefficients, this study employs a physically meaningful permeability model that realizes the synergistic coupling of soil particle composition, pore microstructure, and macroscopic permeability, and further establishes a penetration grouting mechanism that integrates the actual slurry diffusion path tortuosity into the classical spherical diffusion framework. A novel high-precision volume measurement method for grouting stone bodies based on point cloud 3D reconstruction is proposed, and a COMSOL-based visual numerical simulation program is developed by embedding the above coupling permeability model. The accuracy of the optimized mechanism is verified by a combination of model tests, numerical simulations, and theoretical analysis, which makes up for the existing grouting mechanism for loose gravelly soil failing to consider the synergistic influence of rock–soil particle composition parameters and the actual diffusion path. The research results indicate the following: (1) Adopting loose gravelly soil—which is more consistent with actual field conditions—as the grouted medium can effectively predict the reinforcement effect of heterogeneous media in grouting engineering. (2) Compared with theoretical values calculated by mechanisms that ignore the effect of the diffusion paths, those derived from the grouting mechanism that couples the rock and soil characteristic particle size with the Bingham cement grout diffusion path are closer to the experimental values. (3) The visual simulation results exhibit high morphological consistency with the actual grouting stone bodies, and the vast majority of the grout diffusion range falls within the numerical simulation domain. The findings of this study provide targeted theoretical and technical guidance for grouting design under complex geological conditions of loose gravelly soil layers. Full article

This research investigates the relationships between the parameters of the GR4J hydrological model and a set of morphometric descriptors, climatic indices, land-cover characteristics, and soil properties across the Caquetá River Basin (Colombia). Twelve limnimetric–limnographic gauges with consistent records for the period 2001–2022 were selected for model calibration and validation. The corresponding sub-watersheds were delineated and characterized in terms of geomorphometry, vegetation cover, and soil permeability. According to that, the morphometric assessment focused on estimating key geomorphometric parameters, while land-cover descriptions utilized NDVI data. Soil type identification was based on the average approximate permeability across each analyzed sub-watershed. Model calibration was performed using the Differential Evolution Markov Chain (DE-MC) algorithm with 8000 simulations, forced by CHIRPS satellite precipitation and ERA5 potential evaporation data. Relationships between GR4J parameters and watershed attributes were assessed using Spearman’s rank correlation and curve-fitting analyses. The results reveal strong and consistent relationships between GR4J parameters (X1–X4) and key morphometric variables, including basin perimeter, circularity ratio, main channel length, and channel slope. Coefficients of determination ranged from 0.80 to 0.98, highlighting the potential for parameter regionalization based on physiographic and environmental descriptors. Full article

Circular pipe-jacking construction in gravel strata faces significant technical challenges, including high frictional resistance, elevated permeability, and susceptibility to collapse. Optimizing the formulation of thixotropic slurry is crucial for improving the construction quality and efficiency of such projects. This study, based on the Ruyang Water Supply Project of the North Main Canal in the Qianping Irrigation Area, Henan Province, China, systematically investigated slurry formulation using bentonite, soda ash, sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and shell powder as raw materials. An orthogonal experimental design was employed to optimize the mix proportions, and the friction-reduction performance was validated through drag-friction model tests. The results indicate that the optimal slurry formulation is: bentonite 8%, soda ash 0.3%, CMC 0.2%, PAM 0.15%, shell powder 4%, and water 87.35%. This formulation exhibits excellent fluidity and thixotropy, facilitating the formation of a stable slurry film. Consequently, the friction coefficient between concrete specimens and gravel soil was reduced by 35.6%. The inclusion of shell powder significantly enhanced the slurry’s cohesiveness and improved the anti-seepage capacity of the surrounding stratum due to its filling effect. The optimized thixotropic slurry effectively mitigates frictional resistance during pipe jacking in gravel strata and enhances the formation’s resistance to collapse. The findings of this study provide a viable technical reference for pipe-jacking projects under similar geological conditions. Full article

While early ideal consolidation theories for vertical drains focused primarily on radial flow, numerous coupled radial–vertical seepage models have since been developed to better capture complex flow behavior in practice. To overcome this limitation, a nonlinear large-strain consolidation model for vertical drains with coupled radial-vertical flow is proposed, explicitly incorporating Hansbo’s non-Darcy flow, smear effects, and soil nonlinearity. The finite difference method is then employed to obtain numerical solutions, and the reliability of the proposed numerical scheme is verified by degenerating the model to the radial consolidation case and comparing the results with the corresponding analytical solution. The results indicate that consolidation develops fastest when the permeability coefficient within the smear zone follows a parabolic distribution. Increasing the Hansbo’s flow parameter m and threshold hydraulic gradient parameter I₁ markedly slows down the consolidation process, while the contribution of vertical flow is primarily confined to the early stage. In addition, larger soil nonlinearity parameters I_c and α amplify the influence of radial–vertical coupled flow. Parametric analysis further shows that when the ratio of soil layer thickness to the radius of the influence zone (H/r_e) exceeds 10, the effect of vertical flow becomes negligible, and the consolidation behavior can be reasonably approximated using a radial-flow-only model. Full article