Soil Behavior Research Articles

A General Framework to Simulate Soil–Structure Interface Behaviour Using Advanced Constitutive Models

The importance of using sophisticated interface models to obtain realistic numerical solutions of soil–structure interaction (SSI) problems has been recognised in recent decades. With this aim, various advanced interface models have been developed, which assume that the same advanced constitutive model can describe the soil behaviour inside and outside the shear zone. These models fail to adequately address the experimentally observed stick–slip transition, assuming permanent sticking between the soil and structure. Furthermore, the influence of interface roughness requires model parameter adjustments, e.g., in the critical state of the soil, which are questionable from a physical point of view. To overcome these shortcomings, we propose a general relationship to describe the evolution of the shear strain in the shear zone as a function of the surface roughness, the density, and the normal stress. This relationship, which assumes a stick–slip transition at the interface, can be combined with an advanced constitutive model to describe soil–structure interface behaviour using the same set of model parameters as for the surrounding soil. Depending on the surface roughness of the interface, this transition leads to a localisation within the soil in the shear zone (for rough surfaces) or at the contact surface (for smooth surfaces). The proposed model was validated using interface shear tests from the literature on dry granular soils. A hypoplastic constitutive model was used in the simulations. The comparison of experimental and calculated results demonstrates the ability of the proposed model to realistically reproduce shear stress and relative displacements, including the stick–slip transition observed in the experiments. This instils confidence in the model’s reliability and accuracy, thus providing a reliable numerical tool for SSI analyses.

Experimental Study on the Flexural Performance of Geogrid-Reinforced Foamed Lightweight Soil

The flexural behavior of geogrid-reinforced foamed lightweight soil (GRFL soil) is investigated in this study using unconfined compressive and four-point bending tests. The effects of wet density and reinforcement layers on flexural performance are analyzed using load–displacement curves, damage patterns, load characteristics, unconfined compressive strength, and flexural strength. A variance study demonstrates that increasing the wet density significantly increases unconfined compressive strength. Bond stress mechanisms enable geogrid integration, efficiently reroute stresses internally, and greatly increase flexural strength. With a maximum unconfined compressive strength of 3.16 MPa and a peak flexural strength increase of 166%, this reinforcement increases both strength and ductility by changing the damage pattern from brittle to ductile. The principal load is initially supported by the foamed lightweight soil, and in later phases, geogrids take over load-bearing responsibilities. Additionally, the work correlates the ratio of unconfined compressive to flexural strength with wet density and informs the development of predictive models for unconfined compressive strength as a function of reinforcing layers and wet density.

A coupled and parallel peridynamics–SPH modeling and simulation of buried explosion induced soil fragmentation and cratering

In this work, we develop a coupled peridynamics (PD) and smoothed particle hydrodynamics (SPH) model for simulating soil fragmentation, ejection, and cratering under buried explosions. Specifically, the non-ordinary state-based PD theory describes the dynamic response of soil, while the SPH method governs the motion of the explosive gas products. A stable and efficient coupling algorithm for data transfer between PD and SPH is adopted. To accurately capture soil behaviors under blast loading, we propose a modified Drucker–Prager plasticity model incorporating an additional high-pressure compaction equation of state (EoS). Additionally, a parallel code using the OpenMP algorithm is developed for the coupled PD–SPH model to handle large-scale, long-duration soil explosions. PD–SPH predictions are compared with two sets of well-designed centrifugal model tests. The gravitational effect is considered in the simulation to replicate the true physical process of buried explosions in soil. It is found that the coupled PD–SPH model successfully captures the entire physical process of soil fragmentation, ejection, and cratering induced by buried explosions. The predicted soil ejection and cratering morphologies, as well as quantitative results such as ejection speed, ejection height, and crater diameter, align well with the test results. Furthermore, the results indicate that the gravitational effect significantly influences the soil ejection and cratering processes. With increased gravitational acceleration, the soil ejection height and crater size decrease markedly.

Degradation of Oxolinic Acid in Soil Under Simulated Natural Degradation Processes

Oxolinic acid (OA), a quinolone-class antibiotic commonly used in domestic agriculture, exhibits low bioavailability, raising concerns about its potential environmental persistence. Residual OA in the environment can undergo partial degradation through natural processes, which are influenced by various factors. This study aimed to investigate the photodegradation and biodegradation patterns of OA under various environmental factors, including temperature, light intensity, soil usage, soil organic matter content (OM). Additionally, adsorption and desorption experiments were conducted to elucidate the relationship between OA degradation and its adsorption-desorption behavior in soil. In this study, two UV-A intensities (2.3 and 1.5 mW cm<sup>-2</sup>) and two temperatures (21.8 and 35.0<sup>o</sup>C) were applied to examine the OA degradation behavior. Biodegradation tests were conducted using soil samples with varying land uses (rice paddy, field) and OM (6.4% and 2.3%). Additionally, sorption tests were performed using the soil samples and OA solutions, followed by desorption tests on the OA-sorbed soil samples. In the photodegradation experiment, the OA degradation rate ranged from 16.6% to 51% across all conditions after 20 d. Compared to other antibiotics reported in previous studies, OA exhibited relatively slow photodegradation, and the variations in degradation rates under the tested experimental conditions were not statistically significant. In the case of biodegradation, similar degradation rates were observed in the field and rice paddy soils, with faster degradation occurring in soils with lower OM. The differing biodegradation patterns observed across soil samples could be partially explained by the adsorption-desorption characteristics of OA in soils. The degradation of antibiotics through simulated natural processes such as photodegradation and biodegradation did not exhibit consistent trends depending on the environmental factors or soil properties. This suggests that the degradation of antibiotics is a complex process influenced by various factors, including, but not limited to, environmental factors and soil properties. This study highlights the need for further research to better understand the behavior of residual antibiotics in soil environments.

A comparative study of ionic pesticide sorption and degradation in contrasting Brazilian soils and the development of a novel 3-Phase Assay to assess sorption reversibility.

Brazilian soils have distinctive characteristics to European and North American soils which are typically used to investigate pesticide fate. This study aimed to compare soil-water partition coefficient (Kd), reversibility of adsorption and degradation half-life (DT50) of 5 pesticides covering a wide range of physico-chemical properties in contrasting Brazilian soils (Argissolo, Gleissolo, Latossolo and Neossolo) and a temperate (UK) alfisol soil, and to study their relationship with soil OM, clay and expandable clay content, CEC and pH. In addition, we used a novel laboratory test to evaluate sorption reversibility, the 3-Phase Assay (3PA). This stationary extraction system uses an organic solvent that sequesters compounds present in the soil aqueous solution and forces the diffusion of reversibly sorbed compounds. Kd (mL/g) values ranged from 4.85 to 79.26 for ametryn, 0.80 to 37.58 for clodinafop, 1.49 to 6.57 for fomesafen, 9.93 to 488.90 for thiabendazole and 2.52 to 6.77 for trifloxysulfuron. Desorption of the test compound (% applied radioactivity) ranged from 37.29 to 101.91 for ametryn, 32.05 to 100.67 for clodinafop, 34.73 to 73.33 for fomesafen and 4.15 to 66.87 for thiabendazole. Sorption reversibility was not assessed for trifloxysulfuron due to hydrolytic instability. DT50 (days) ranged from 29 to 90 for ametryn, 1 to 466 for clodinafop, 49 to 601 for fomesafen, 4 to 342 for thiabendazole and 22 to 38 for trifloxysulfuron. The data generated gives an overview of pesticide fate in Brazilian soils used for regulatory testing and is helpful for exposure risk assessment. The results showed that pesticide behaviour in Brazilian soils was not systematically different from those in European and North American soils. The 3PA was shown to be a reliable and simple method for assessing pesticide desorption in soil and could be adapted to assess pesticide bioavailability. The use of the 3PA allowed a more thorough explanation of the observed differences in degradation behaviour between the compounds.

Effect of moisture change on water retention behavior of unsaturated silty soil under loading–unloading conditions

Earthen embankments either natural or constructed artificially often comprise of unsaturated soils being considered stronger in terms of compressibility and permeability. However, the internal nomenclature of unsaturated soils due to the presence of air, water, and soil particles makes it more complex while such soils interact with moisture under the circumstances of applied stress history during the earthen structure’s life span. To investigate this behavior, this study is designed to understand the soil–water interaction and quantify the retention behavior during loading and unloading conditions. To serve this idea, custom-designed static compaction tests were carried out under un-drained water and drained air conditions at the applied stress history. The results show application of loading and unloading cycles impact water retention behavior of soil with varying soil water contents. During the initial stages of the loading process, suction increases with decreasing void ratio due to the heterogeneous distribution of water in the soil. However, there is a unique increasing trend in suction at the reloading or wetting phases of the water retention curve for all moisture contents. To examine the impact on the void ratio, the experimental data have been compared with the selected model incorporating suction, void ratio, and degree of saturation for prediction of soil water retention behaviors. The model prediction deviates from the experimental data and shifts away from the model prediction indicating that the loading–unloading sequence coupled with the variation in moisture does affect the soil behavior.

The geotechnical behavior and microstructural characteristics of the alkaline residue/cement stabilized expansive soil under wetting-drying cycles

In order to explore the geotechnical behavior of expansive soil stabilized by alkaline residue/cement (ARC) under wetting-drying (W-D) cycles, the shrink-swell characteristics, unconfined compressive strength (UCS), compressibility and microstructural characteristics are experimentally investigated in this study. The findings indicate that the incorporation of ARC, particularly with an alkaline residue (AR) content of less than 5%, significantly mitigates the shrink-swell behavior, reduces soil compressibility, and enhances the UCS of the soil. Beyond this threshold, the soil's strength decreases and compressibility increases with increasing W-D cycles. Microstructural analysis reveals the formation of beneficial cementitious products such as C-A-H, C-S-H, and AFt, which contribute to improve engineering performance in the early stages of W-D cycles. Nevertheless, as the W-D cycles continue, these beneficial products diminish, leading to an increase in soil cracks and pores, which indicates a degradation in soil performance. The research posits that ARC can effectively serve as a partial substitute for cement in the stabilization of expansive soils, with the amount of AR within 5%. Despite ARC's environmental advantages as an alternative binder, it may encompass harmful elements. Therefore, a comprehensive environmental risk assessment is essential. Further studies are needed to discern the enduring effects of environmental variables on soils stabilized with ARC.

Triaxial behavior and microstructural insights of loose sandy soil stabilized with alkali activated slag

This study investigates the mechanical and microstructural properties of loose sandy soil stabilized with alkali-activated Ground Granulated Blast Furnace Slag (GGBFS). To examine the effects of varying GGBFS contents, curing times, and confining pressures on mechanical behavior, undrained triaxial and unconfined compressive strength (UCS) tests were conducted. Microstructural analyses using FE-SEM, EDX, and FTIR were performed to elucidate the nature and development of cementation. The results of mechanical behavior demonstrate that even with limited GGBFS content (1–6%), the treated samples exhibited significant improvements in strength, stiffness, and energy absorption, underscoring the efficiency of alkali-activated GGBFS as a soil stabilizer. Moreover, mechanical parameters from triaxial tests revealed a nearly constant internal friction angle with increasing GGBFS content and curing duration, while cohesion showed remarkable enhancement. A strong linear correlation between UCS and cohesion was also identified, enabling cost-effective estimation of shear strength parameters. These findings highlight the potential of alkali-activated GGBFS for improving granular soils, offering practical implications for sustainable geotechnical applications, particularly in road construction.

A Pilot Study on Influence of Natural Rubber Latex Stabilization on Swelling-Consolidation Behaviour of Soil

A Pilot Study on Influence of Natural Rubber Latex Stabilization on Swelling-Consolidation Behaviour of Soil

Parameter Study and Engineering Verification of the Hardening Soil Model with Small-Strain Stiffness for Loess in the Xi’an Area

With the advancement of the construction of urban underground spaces, it is inevitable that new tunnels will pass through existing pipelines. To ensure the safety and stability of these pipelines, it is essential to strictly control the impact of shield tunneling. The hardening soil model with small-strain stiffness (HSS) comprehensively accounts for the small-strain behavior of soil, and the calculated results are closer to the values measured in engineering compared to those of other models. Consequently, it has been widely adopted in the development and utilization of underground spaces. The selection of parameters for the HSS model is particularly critical when performing numerical simulations. This article establishes the proportional relationships between the small-strain moduli of the HSS model in the loess region of Xi’an through standard consolidation tests, triaxial consolidation drained shear tests, and triaxial consolidation drained loading−unloading shear tests. Additionally, an empirical formula for the static lateral pressure coefficient applicable to loess was derived and validated through engineering examples.

Investigation into the PSD characteristics of internally unstable soils susceptible to suffosion

Internal instability of embankment soils under seepage can occur in two distinct ways: suffusion and suffosion. Suffusion involves the removal of fine particles from the matrix without causing significant disturbance to the soil skeleton, while suffosion is characterized by the movement of fine particles accompanied by skeleton collapse or deformation. In terms of dam safety, suffosion poses a greater threat than suffusion. While extensive research has focused on establishing geometric criteria to assess the internal instability of soils prone to suffusion, current criteria fail to predict the occurrence of suffosion. To address this gap, this paper presents a comprehensive analysis by collecting a large amount of experimental data from existing literature, as well as conducting a series of suffusion/suffosion tests. Through this analysis, two characteristic parameters have been identified: fines content (Ff) and the retention ratio (D’15/d’85) which represents the relationship between coarse and fine particles. Soils including fines content greater than 35% are susceptible to suffosion, while soils with fines content lower than 20% are prone to suffusion. For soils with fines content ranging between 20 and 35%, suffosion occurs when Ff > 2.73 D’15/d’85 + 0.89. These findings provide valuable insights for future analyses of soil internal stability and contribute to enhancing dam safety. The combination of literature data and suffusion tests offers a robust base for assessing the risk of suffosion and suffusion in soils, allowing more accurate evaluation of soil behavior and effective mitigation strategies in dam engineering.

Studying the Behavior of Collapsible Soil Treated with Biopolymer—Numerical Study

Studying the Behavior of Collapsible Soil Treated with Biopolymer—Numerical Study

Coupling effect of cyclic wet-dry environment and compaction state on desiccation cracking and mechanical behavior of low and high plastic clays

This study investigates the complex interplay between wetting–drying (W-D) cycles and initial compaction states on desiccation cracking and the mechanical behavior of different clayey soils. Natural CH, CL, and ML soils, distinguished by their chemical composition and plasticity, are subjected to a meticulously designed experimental program. The specimens are remolded at various initial compaction states, including the optimum moisture content (wopt) having maximum dry density (γdmax), and wet and dry sides of the compaction curve having identical initial dry density (γd0). Subsequently, they undergo multiple W-D cycles, systematically documented through cinematography. Mechanical response is assessed after different W-D cycles. It is observed that desiccation cracking within both CL and CH initiates after the first W-D cycle, intensifying rapidly after the second cycle and reaching an optimal cracking state after the third cycle. The crack analyses indicate a transition from surface cracking to deeper-seated cracks with an increase in W-D cycles. CH soil, characterized by a 2:1-layered clay mineral with a high propensity for swelling and shrinkage, exhibits elevated desiccation cracking at high w0 for identical γd0. Notably, CH soil exhibits maximum cracking at the wopt and γdmax. In contrast, CL soil, characterized by a 1:1-layered clay mineral, displays an inverse response across all compaction states, and ML soil, characterized by a scarcity of clay mineral, shows insignificant cracks. This disparity in behavior is closely attributed to clay mineralogy and microstructure, which define the underlying mechanism responsible for the generation of internal stresses in the soil structure induced by moisture fluctuations causing desiccation cracking. Stiffness and unconfined compressive strength (qu) of CH and CL increase and compressibility decreases as w0 increases after undergoing W-D cycles due to the volume shrinkage response of specimens. Meanwhile, for a particular compaction state, strength decreases while compressibility increases with increasing W-D cycles.

Effects of interface roughness and layer thickness on the cracking characteristics of fine-grained coral soil

Fine-grained coral soil, prevalent in tropical shallow marine environments, demonstrates significant potential as a natural engineering material. This study presents laboratory experiments employing digital image technology to investigate the effects of soil layer thickness and interface roughness on its cracking characteristics. By analyzing soil particle displacement during the cracking process, we examined the relationship between particle movement and the observed macroscopic crack patterns. The results indicate that both interface roughness and soil thickness substantially influence crack development and morphology. Increased interface roughness accelerates the cracking rate and transforms the pattern from overall contraction to multi-directional expansion, resulting in dense crack networks. Thinner soil layers facilitate more intricate crack formations, whereas thicker layers lead to more pronounced settling, longer and wider cracks, reduced horizontal cracking, and a simplified overall cracking pattern. This study elucidates the impact of interface roughness and soil layer thickness on the cracking behavior of fine-grained coral soil, providing valuable insights for its potential engineering applications.

A study of the undrained monotonic behavior of geotextile reinforced sand-silt mixtures using triaxial tests

“Investigating the behavior of silty soils reinforced with geotextile layers in terms of shear strength and deformation in a laboratory setting is the study’s objective described in this paper. This work includes an experimental study based on a series of undrained monotonic triaxial tests, which were carried out on clean sand from Chlef, medium dense (Dr = 50%), mixed with silt content fluctuating between 0 and 30%. The mechanical behavior was examined and discussed in this paper by varying the number of geotextile layers (Ng = 1, 2, 3) and the fines content where the samples were consolidated under 100 kPa confining pressure. Experimental results on unreinforced and reinforced silt/sand soils by geotextile layers show that the quantity of geotextile layers is growing in the studied samples improves the shear strength characteristics of the soil, nevertheless, lessen the radial deformations cause the pore water pressure to rise instead. However, the pore water pressure increases while the deviatoric stress decreases as the percentage of fines increases.”

Modeling Soil Behavior with Machine Learning: Static and Cyclic Properties of High Plasticity Clays Treated with Lime and Fly Ash

Modeling Soil Behavior with Machine Learning: Static and Cyclic Properties of High Plasticity Clays Treated with Lime and Fly Ash

Macro-Micro Mechanics of Granular Soils Under Shear Considering Coupled Effects of Particle Size Distribution and Particle Morphology.

This paper investigates the effects of particle morphology (PM) and particle size distribution (PSD) on the micro-macro mechanical behaviours of granular soils through a novel X-ray micro-computed tomography (μCT)-based discrete element method (DEM) technique. This technique contains the grain-scale property extraction by the X-ray μCT, DEM parameter calibration by the one-to-one mapping technique, and the massive derivative DEM simulations. In total, 25 DEM samples were generated with a consideration of six PSDs and four PMs. The effects of PSD and PM on the micro-macro mechanical behaviours were carefully investigated, and the coupled effects were highlighted. It is found that (a) PM plays a significant role in the micro-macro mechanical responses of granular soils under triaxial shear; (b) the PSD uniformity can enhance the particle morphology effect in dictating the peak deviatoric stress, maximum volumetric strain, contact-based coordination number, fabric evolution, and shear band formation, while showing limited influences in the maximum dilation angle and particle-based coordination number; (c) with the same PSD uniformity and PM degree, the mean particle volume shows minimal effects on the macro-micro mechanical behaviours of granular soils as well as the particle morphology effects.

Modeling suction of unsaturated granular soil treated with biochar in plant microbial fuel cell bioelectricity system

There is an initiative driven by the carbon-neutrality nature of biochar in recent times, where various countries across Europe and North America have introduced perks to encourage the production of biochar for construction purposes. This objective aligns with the zero greenhouse emission targets set by COP27 for 2050. This research work seeks to assess the effectiveness of biochar in soils with varying grain size distributions in enhancing the soil–water characteristic curve (SWCC). This work further explores the effect of different combinations of biochar content (0 to 15 mass %) on the bioelectricity generation from biochar-improved plant microbial fuel cells (BPMFC). Additionally, different machine learning models such as the “Gradient Boosting (GB)”, “CN2 Rule Induction (CN2)”, “Naive Bayes (NB)”, “Support vector machine (SVM), “Stochastic Gradient Descent (SGD)”, “K-Nearest Neighbors (KNN)”, “Tree Decision (Tree)”, “Random Forest (RF)”, and “Response Surface Methodology” (RSM), have been developed to predict SWCC based on soil suction, electric current, electrical potential, volumetric water content, temperature, and bulk density. The newly established model demonstrates a reasonable ability to predict SWCC and a cheaper technology in predicting the suction of unsaturated soils in relation to the studied bioelectric factors of the BPMFC. Overall, in this research paper, the GB, SVM and CN2 outclassed the other regression techniques in this order thereby proposing the cheapest technology with the highest performance index to predict the SWCC behavior of unsaturated soils in a BPMFC system.

Effect of Changing Sand Content on Liquid Limit and Plasticity Index of Clay

Middle–Late Miocene clay layers, which occur in several places in Budapest (Hungary), contain varying amounts of sand, with predominance of sand in some cases. In this paper, the impact of this variability on the engineering properties of these clays is investigated, and comprehensive analysis is conducted on clay samples. The results of measurements are presented; in addition to the analysis of plastic soil (i.e., liquid limit, plasticity index), the grain size distribution was also investigated by performing standard geotechnical laboratory tests, including Atterberg limit tests and grain size analyses. Statistical analysis of the results was employed to define correlations between sand contents and both the liquid limit and the plasticity index. It was shown that both the plasticity index and the liquid limit decrease linearly with increasing sand content. This finding aligns with observations reported in the international literature. A general equation was derived to quantify this relationship, setting up a method for better estimation of the plastic properties of similar clay soils based on their sand content and a better understanding of the engineering geological behaviors of clay soils with varying sand content, which as a result have a practical implication for geotechnical engineers.

Integration and Application of a Fabric-Based Modified Cam-Clay Model in FLAC3D

In order to consider the effect of fabric anisotropy in the analysis of geotechnical boundary value problems, this study proposes a modified model based on a fabric-based modified Cam-clay model, which can account for the anisotropic response of soil. The major modification of the original model aims to simplify the equations for numerical implementation by replacing the SMP strength criterion with the Lade’s strength criterion. This model comprehensively considers the inherent anisotropy, induced anisotropy, and three-dimensional strength characteristics of soil. The model is first numerically implemented using the elastic trial–plastic correction method, and then it is encapsulated into the FLAC3D 6.0 software, and tested through conventional triaxial, embankment loading, and tunnel excavation experiments. Numerical simulation results indicate that considering anisotropy and three-dimensional strength in geotechnical engineering analysis is necessary. By accounting for the interaction between microstructure and macroscopic anisotropy, the model can more accurately represent soil behavior, providing significant advantages for geotechnical analysis.