Search Results (398)

The formation of geotechnical structures on foundations composed of low-strength soils is associated with a number of risks and difficulties. Soils such as clay-salt slurries are characterized by low bearing capacity and a tendency to deform under load. In this study, a numerical simulation of the stability analysis of an embankment constructed on low-strength soils consisting of clay-salt slurries is carried out, and the study of the dependence of the stability and behavior of the embankment on the configuration of this foundation, without taking into account the embedment of rocks and with introduction of rocks into the geotechnical system, is considered. The results prove that the sloping configuration of low-strength soils greatly complicates the stability of the embankment. It is noted that the stability factor is significantly reduced under the influence of loads on low-strength soil, particularly when the geotechnical system has a configuration with slope angles of 5° and 10°, and, in addition, when rocks are embedded in low-strength soil if the underlying soil layer is a weak foundation. In view of this, the assessment of embankment stability on clay-salt slurries requires careful analysis due to a number of specific characteristics of these soils that create complex geotechnical conditions. Full article

Cemented paste backfill (CPB) is a cemented void filling method gaining popularity over traditional hydraulic or rockfill methods. As mining depth increases, CPB-filled stopes are subjected to higher confining pressures. Due to the soil triaxial apparatus limitations, as the conventional method of triaxial testing on CPB, no confining pressures higher than 5 MPa can be applied to CPB over a range of curing time. This lack of data introduces uncertainty in predicting CPB behavior, potentially leading to an overestimation of the required strength. To address this, this study introduces a new testing method that allows for higher confinement beyond traditional limitations by modifying the Hoek triaxial cell to accommodate low-strength materials. This study then investigates the coupled influence of confining pressure and curing time (hydration) on CPB characteristics, specifically examining the impacts of different curing times and confining pressures on the mechanical and rheological properties of CPB. A total of 75 triaxial tests were conducted using 42 mm cylinder shape samples at five various curing times from 7 to 96 days, and applied at low and high confinement condition levels (0.5 to 30 MPa). The results reveal that hydration and confinement positively impact the CPB strength. The modified structured Cam-Clay model was selected to predict the behavior, and its yield surface was updated using the experimental results. The proposed yield model can be utilized to describe CPB material subjected to various curing and pressure conditions underground. Full article

Energy piles are highly favored for their excellent, low energy consumption in providing heating for public residences. The temperature field changes the activity of the diffuse double electric layer (DEL) on the particle surface, thereby altering the distribution of the stress field in the soil and ultimately affecting the mechanical properties of the interface between the energy pile and the soil. Therefore, studying the influence of water content on the mechanical behavior of the soil–structure interface in the temperature field is crucial for energy pile safety. This study used a modified temperature-controlled direct shear apparatus to obtain the influence of water content and temperature on the shear behavior of the soil–structure interface. Then, the test results were analyzed and discussed. Finally, three results were obtained: (1) The water content of bentonite (w_bent) had a significant impact on the shear stress–shear displacement curve of the soil–structure interface; when the w_bent was less than the w_p of the bentonite, the τ-l curve exhibited a softening response, then displayed a hardening response. (2) The shear strength of the soil–structure interface gradually decreased with the increase of w_bent. (3) The shear strength of the soil–structure interface increased with increasing temperature under various w_bent and vertical loads. Full article

From both economic and environmental points of view, the reuse of dredged sediments in the direct onsite casting of concrete represents a promising method for replacing sand. The aim of this study was to develop a cementitious material that (i) reuses the thin particles of sediments; (ii) has a low density due to the incorporation of air foam in the material; and (iii) achieves a minimum mechanical strength of 0.5 MPa for embankment applications. This study focused on the characterization of a non-standard “concrete”, which is a mixture of a synthetic soil (80% montmorillonite and 20% calibrated sand) and cement. To reduce its density, air foam was incorporated into the material during the manufacturing process (air-foamed lightweight clay concrete—AFLCC). The study results highlight that a density around 1.2 (unit: g/cm³/1 g/cm³) can be obtained. This density reduction can be obtained with a certain degree of workability when the material is in a fresh state. To obtain this workability, a certain amount of water must be added; however, the addition of water has a significant impact on the compressive strength of the AFLCC. As such, a mathematical equation correlating the compressive strength, the density, and the percentage of cement is proposed in this study. The mechanical strength results of the AFLCC at different times, in conjunction with the Vicat results, show that the porosity created by the air foam has the effect of slowing down the hydration mechanism of the cement. The porosities obtained are consistent with the density results. The characteristic radii indicate large pore sizes for formulations with low fluidity in the fresh state when air bubbles are incorporated. Full article

Grassland degradation and reduced yields are often linked to the root soil composite of perennial alfalfa roots. This study introduces a novel modeling approach to accurately characterize root biomechanical properties, assist in the design of soil-loosening and root-cutting tools. Our model conceptualizes the root as a composite structure of cortex and stele, applying transversely isotropic properties to the stele and isotropic properties to the cortex. Material parameters were derived from longitudinal tension, longitudinal compression, transverse compression, and shear tests. The constitutive model of stele was Hashin failure criteria, accounting for differences in tensile and compressive strengths. Results reveal that root tensile strength mainly depends on the stele, with its tensile properties exceeding compressive and transverse strengths by 4–10 times. In non-longitudinal tensile stress scenarios, like shear and transverse compression tests, the new model demonstrated superior accuracy over conventional models. Results of shear tests were further validated using non-parametric statistical analysis. This study provides a finite element method (FEM) modeling approach that, by integrating root anatomical features and biomechanical properties, significantly enhances simulation accuracy. This provides a tool for designing low-energy consumption components in grassland degradation restoration and conservation tillage. Full article

Expanded polystyrene (EPS) bead–lightweight soil composites are a new type of artificial geotechnical material with low density and high strength. We applied EPS bead–lightweight soil in this project, replacing partial cement with fly ash to reduce construction costs. EPS beads were used as a lightweight material and cement and fly ash as curing agents in the raw soil were used to make EPS lightweight soil mixed with fly ash. The EPS bead proportions were 0.5%, 1%, 1.5%, and 2%; the total curing agent contents were 10%, 15%, 20%, and 25%; and the proportions of fly ash replacing cement were 0%, 15%, 30%, 45%, and 60%, respectively. Unconfined compressive strength (UCS) and scanning electron microscopy (SEM) tests were conducted. The results showed that the EPS content, total curing agent content, and proportion of fly ash replacing cement had a significant impact on the UCS of the lightweight soil. This decreased with an increase in EPS content and decrease in total curing agent content and decreased with increased proportions of fly ash replacing cement. When the proportion of fly ash replacing cement was not too high, the strength of the lightweight soil decreased less, and its performance still met engineering needs. At the same time, the soil can also consume fly ash and reduce environmental pollution. EPS lightweight soil mixed with fly ash still has advantages, and it is recommended to keep the proportion of fly ash replacing cement less than 30%. The failure patterns for lightweight soil mainly include splitting failure, oblique shear failure, and bulging failure, which are related to the material mix ratio. Full article

The study of dredged fill in Guangdong (GD), China, is of great significance for reclamation projects. Currently, there are relatively few studies on dredged fill in Guangdong, and there are many differences in the engineering characteristics of dredged fill foundations formed through land reclamation and natural foundations. In order to have a more comprehensive understanding of the physico-mechanical properties of blowing fill in the coastal area of GD and to understand the effect of its long-term creep row on the long-term settlement and deformation of buildings, the material properties, microstructure, elemental composition, triaxial shear properties, and triaxial creep properties of dredged fill in Guangdong were studied and analyzed through indoor geotechnical tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), and conventional triaxial shear tests and triaxial creep tests. The test results showed that the Guangdong dredged fill is characterized by a high water content, high pore ratio, and high-liquid-limit clayey sand, and the mineral composition is dominated by quartz and whitmoreite. The scanning electron microscopy results showed that the particles of the dredged fill showed an agglomerated morphology, and the surface of the test soil samples had scaly fine flakes and a fragmented structure. In the triaxial shear test, the GD dredged fill showed strain hardening characteristics, and the effective stress path showed continuous loading characteristics; the consolidated undrained shear test showed that the GD dredged fill had shear expansion characteristics under low-perimeter-pressure conditions. It was found that, with an increase in bias stress, the axial strain in the consolidated undrained triaxial creep test under the same perimeter pressure conditions gradually exceeded the axial strain in the consolidated drained triaxial creep test. The results of this study are of theoretical and practical significance for further understanding the mechanical properties of silty soils in the region and for the rational selection of soil strength parameters in practical engineering design. Full article

The widespread use of nanoplastics inevitably contributes to pollution in aquatic environments and soils. Therefore, it is crucial to understand how these particles migrate in soils with diverse organic matter. This study investigated the effects of low-molecular-weight organic acids (LMWOAs) on the migration of polystyrene nanoplastics (PS-NPs) in goethite-coated quartz sand. The experiments utilized two organic acids, propanoic acid (PA) and tartaric acid (TA), under varying aqueous conditions, including pH levels (4.0, 7.0), ionic strengths (1 mM, 10 mM), and cations (Na⁺, Ca²⁺, Ba²⁺). The experimental results indicated that with the presence of Na⁺, organic acids promoted the migration of PS-NPs through electrostatic forces and steric hindrance, with TA having a greater effect than PA. When pH < pH_pzc, increased concentrations of positively charged goethite coating provided favorable deposition sites for the negatively charged PS-NPs, thereby increasing their deposition. Using the DLVO theory, low pH and high ionic strength (IS) decreased the energy barriers between PS-NPs and porous media, whereas high pH and low IS increased these barriers, thus enhancing PS-NPs transport. Divalent cations Ca²⁺ and Ba²⁺ enhanced the migration of PS-NPs through complex-forming and -bridging agents. These findings offered significant insights for predicting and analyzing the migration behavior of plastic nanoparticles. Full article

The Ethylene Diamine Tetra-acetic Acid (EDTA) titration test is widely used for determining cement content, but its reliability is influenced by the hydration process of cement, which is affected by factors such as water content and hydration time. Despite their importance, these factors have received limited attention in existing research. This study explores the relationships between the volume of titrant required for stabilization, cement content, water content, and hydration time. Using a regression orthogonal test, the primary and secondary relationships, as well as the interdependencies among these factors, are analyzed. Results reveal a negative linear relationship between the titrant volume and both water content and hydration time. Cement content, water content, and hydration time are identified as the most significant factors, with minimal interdependencies observed. Within the test parameters, calculated values exhibit an error margin below 2.4%. Deviations of 2.9% in water content and 86 min in hydration time correspond to an approximate 0.5% change in cement content. These findings offer valuable insights for optimizing cement content detection in Controlled Low-Strength Material (CLSM) mixes, promoting more sustainable construction practices. Full article

Unsupported excavations are frequently performed in several geological and geotechnical projects, particularly for constructing roads and railways, and they are often carried out in different materials. The design of such cuts in soils needs the determination of representative values of its mechanical properties, particularly of the strength parameters, and the application of adequate safety factors. The procedure should ensure a sustainable design of those cuts, allowing for economical solutions that guarantee a low probability of geological–geotechnical failure. This paper assesses the reliability of unsupported cuts in soils, under drained conditions, assuming a Mohr–Coulomb strength criterion. Statistical meshes are generated considering the spatial variability of the friction angle and of the true effective cohesion, which are assumed to be uncorrelated. In this process, typical values of the coefficients of variation and of the horizontal and vertical scales of fluctuation are applied. Soil characterisation is simulated in each statistical mesh, and the characteristic values of the strength parameters are determined using statistical methods. Unsupported cuts of different heights and inclinations are designed using typical safety factors. Slope stability analyses are carried out using Random Finite Element Limit Analysis. The uncertainty in the actions is considered, and the probability of failure is determined by direct reliability analysis. The results show the relevance of the ratio between the scale of fluctuation and the excavation depth, the slope inclination, and the characteristic value of the soil strength parameters on the probability of failure. Values of adequate safety factors are proposed towards obtaining an appropriate probability of failure, compatible with the sustainable design of the cuts. Full article

Given the severe threats posed by heavy metal pollution to ecological environments and human health, developing effective remediation technologies is of paramount importance. This review delves into the mechanisms, recent advancements, and future prospects of clay mineral-based materials in the adsorption of heavy metals. Clay minerals such as kaolinite, montmorillonite, and bentonite have demonstrated immense potential for the removal of heavy metals from water and soil due to their natural abundance, low cost, and high efficiency. This article summarizes the latest advancements in the adsorption of heavy metals like chromium, copper, lead, cadmium, arsenic and hydrargyrum by clay minerals, while examining how chemical and physical modifications can enhance the adsorption capacity, selectivity, and stability of these minerals. Furthermore, this review discusses how factors such as pH, temperature, and ionic strength affect adsorption efficiency and outlines challenges and future research directions for optimizing clay-based adsorbents in environmental applications. Full article

Weak clayey soils in construction are considered problematic due to their high compressibility and low bearing capacity. This study proposes an environmentally friendly replacement for conventional soil stabilizers through the use of geopolymer (GP) containing Cashew Nut Shell Ash (CNSA) to improve soil characteristics. In this study, the CNSAGP was compared with lime-stabilized soil for unconfined compressive strength (UCS), durability, and improved microstructure. The experimental outcomes showed that 9 M + CNSAGP with 4% CNSA provided a UCS of 1900 kPa, which was higher than the lime-stabilized soil (6% lime with 4% CNSA) at 1400 kPa. Durability test results revealed that the CNSAGP-treated sample had better protection against water damage with a strength loss of about 18%, while the lime-treated sample had a strength loss of about 25%. Thermal stability analysis showed that CNSAGP had lower LOI values compared to lime-stabilized samples (0.17% at 900 °C), which indicates CNSAGP’s heat resistance. Microstructure analysis revealed that CNSAGP-stabilized soil was less porous, the microstructure being denser because of reactions of aluminosilicate and pozzolanic activity. Moreover, it affected the soil’s alkalinity, making it better, and improved Atterberg limits, which affected the plasticity and workability. These findings show that CNSAGP is a long-lasting and eco-friendly means of soil stabilization with higher strength, thermal stability, and durability than traditional methods and can be used in engineering. Full article

Improving saline soils’ properties by incorporating limes is a practical technique, generally due to cation exchange, pozzolanic reaction, and carbonation. This study explores how soil salinity, measured by electrical conductivity, affects untreated and lime-treated saline soils. An Algerian sebkha soil (from Ain M’lila) with an original high salinity (ECe3 = 23.2 dS.m⁻¹) was used. The same soil was washed to create medium (ECe2 = 8.3 dS.m⁻¹) and low (ECe1 = 2.32 dS.m⁻¹) salinity soil samples. The results of this study indicate that salinity influenced the shape of the particle size distribution curve, particularly in the silt range. Salinity also had a significant effect on carbonate content (CaCO₃) and unconfined compressive strength (UCS). For the untreated soil, when salinity decreased, the UCS and CaCO₃ content increased. However, when salinity decreased for the treated soil, the UCS increased, while the CaCO₃ content decreased. X-ray diffraction (XRD) analysis of untreated soils showed halite (NaCl) disappearance and gypsum (CaSO₄ 2H₂O) reduction with decreasing salinity in ECe1. In treated soil at ECe3, these mineral phases remained constant. While XRD detected no new cementitious phases in treated ECe3 or ECe1 samples, thermogravimetric analysis confirmed the presence of portlandite in both. As Ain M’lila sebkha is a chloride–sulfate soil, the dissolution of the halite and gypsum phases released more Cl⁻ and SO₄²⁻ ions into the interstitial solution. In a low fraction of clay, these ions obstructed and slowed the pozzolanic reaction in the ECe3 soil. Identifying the season when this type of soil has lower salinity can be beneficial for treatment from a technical, economic, and environmental point of view. Full article

Collapsible loess is characterized by its unique soil-forming environment, mineral composition, and microstructure, resulting in poor engineering properties such as high water sensitivity, high collapsibility, high compressibility, and low strength. To improve the poor engineering properties of collapsible loess, we selected a suitable eco-friendly material—guar gum (GG)—for its improvement and reinforcement, and investigated the improvement effect of different GG dosages (0.5~1.5%) and curing ages (0~28 days) on collapsible loess. The mechanical properties of soil samples were determined by direct shear tests, unconfined compressive strength tests, and splitting tests. The water stability of soil samples was evaluated by both cube and sphere crumb tests. SEM and EDS analyses were also conducted to determine the microstructural and mineral changes in soil. The results indicate that the incorporation of GG is beneficial to inhibit the collapsibility of the soil and improves the water stability and strength of the soil. The collapsibility coefficient of loess is reduced to below 0.015 when 0.75% and above of GG is admixed, which is considered a complete loss of its collapsibility. When the GG dosage increases from 0% to 1.25%, the compressive strength and tensile strength of the soil samples increase by 43.5% and 34.9%, respectively. However, by further increasing the GG dosage to 1.5%, the compressive strength and tensile strength decrease by 3.8% and 6% compared to those with 1.25% GG. This indicates that the strength of the specimens shows an increasing trend and then a decreasing trend with the increase in GG dosage, and 1.25% GG was found to be the best modified dosage. Microstructural and mineral analyses indicate that the addition of GG does not change the mineral composition of loess, but, rather, it significantly promotes the agglomeration and bonding of soil particles through cross-linking with Ca²⁺ ions in the soil to form a biopolymer network, thus achieving a reliable reinforcement effect. Compared with the existing traditional stabilizers, GG is a sustainable and eco-friendly modified material with a higher low-carbon value. Therefore, it is very necessary to mix GG into collapsible loess to eliminate some of the poor engineering properties of loess to meet engineering needs. This study can provide test support for the application and promotion of GG-modified loess in water agriculture and road engineering. Full article

In greenhouses, high humidity, low light, and inadequate ventilation conditions, along with continuous and high-density planting, promote the proliferation of soilborne pathogens. Among these pathogens, Fusarium oxysporum Schltdl (F. oxysporum) is a notably challenging one, causing root rot of tomato plants in greenhouse cultivation. To address this issue, this study applied a pulsed electric field (PEF) to target the elimination of F. oxysporum in suspension and soil media. Initially, PEF parameters were systematically explored in suspensions to determine the effective ranges for the elimination of F. oxysporum. The results revealed that the effective ranges for achieving the desired microbial reduction were an electric field strength (EFS) between 5–15 kV·cm⁻¹, a pulse number within the range of 100–500, and a pulse width of 10–20 µs. Subsequently, the impact of soil moisture content, soil bulk density, and soil type on soil dielectric breakdown field strength was analyzed within the range from previous results. Based on these findings, the soil experiments were conducted with parameters designed to prevent dielectric breakdown. Specifically, for sampling soil with a moisture content of 16.2% and a bulk density of 1.31 g·cm⁻³, the maximum effective application of electric field strength was 9.5 kV·cm⁻¹, accompanied by 1000 pulses and a pulse width of 20 µs. Finally, building on these results, soil samples were sterilized within a parameter range that spanned an electric field strength of 5–9.5 kV·cm⁻¹, a pulse number between 100–500, and a pulse width of 10–20 µs. Response surface methodology (RSM) analysis further identified the optimal parameter combination: an electric field strength of 8.2 kV·cm⁻¹, 306 pulses, and a pulse width of 15 µs, resulting in an average lethal rate of 76.16% for F. oxysporum sterilization in soil. These findings suggest the potential use of PEF against F. oxysporum and other pathogens in greenhouse soils, and provide theoretical foundations for further experiments, thereby contributing to the sustainable advancement of greenhouse agriculture. Full article