Soil Behavior Research Articles

Hydro-mechanical response of volcanic ash on removal of fines: Shear stiffness to critical state mechanics

Natural volcanic soils containing pumice particles are commonly found in Hokkaido, Japan, and this type of soil is prone to landslides, internal erosion, and liquefaction. Therefore, the purpose of this paper is to summarise the hydro-mechanical response of volcanic ash soil subjected to internal erosion using the modified erosion triaxial apparatus, based on the literature and additional investigations. The results of the study show that the rate of erosion and shear strain during the erosion process are influenced by initial density, stress state, and hydraulic gradient. Notably, anisotropic consolidation is experienced by specimens under seepage flow. Additionally, the removal of fines leads to a slight decrease in the grading state index. Moreover, suffosion increases the maximum shear modulus and Poisson’s ratio of the soil, while increasing seepage time stabilises the peak shear strength of eroded specimens. Furthermore, the critical state line does not change much with internal erosion. To sum up, this study offers valuable insights into the behaviour of volcanic ash soil subjected to internal erosion and provides an integrated interpretation of hydro-mechanical response of volcanic ash on removal of fines.

Prediction of Liquefaction Behaviour of Fine-Grained Soil Using Nature-Inspired Optimized Algorithms Coupled with Neural Network

Prediction of Liquefaction Behaviour of Fine-Grained Soil Using Nature-Inspired Optimized Algorithms Coupled with Neural Network

Freezing‐Thawing Hysteretic Behavior of Soils

AbstractThe soil freezing characteristic curve (SFCC) plays a crucial role in investigating the soil freezing‐thawing process. Due to the challenges associated with measuring the SFCC, there is a shortage of high‐quality or rigorous test results with sufficient metadata to be effectively used for applications. Current researchers typically conduct freezing tests to measure the SFCC and assume a singular SFCC when studying the freezing‐thawing process of soils, although limited studies indicated that there is a hysteresis during the freezing and thawing process. In this paper, a series of freezing‐thawing tests were performed to assess the SFCC, utilizing a precise nuclear magnetic resonance apparatus. The test results reveal a hysteresis between the SFCC obtained from the freezing process and that from the thawing process. Through analyzing the test results, the hysteresis mechanism of the SFCC is attributed to supercooling. Supercooling inhibits initial pore ice formation during freezing, causing a drastic liquid water‐ice phase change once supercooling ends. Despite being considered closely related, the hysteresis of the SFCC differs from the soil water characteristic curve (SWCC), and the models used to simulate the hysteresis of SWCC cannot directly be used. To address the impact of supercooling on soil freezing‐thawing hysteresis, a novel theoretical model is proposed. Comparisons between the measured and predicted results affirm the validity of the proposed model.

Preliminary Experiences in Determining the Soil–Water Characteristic Curve of a Sandy Soil Using Physical Slope Modeling

Relating soil moisture content to soil suction, the soil–water characteristic curve (SWCC) represents an essential feature in unsaturated soil mechanics that enables estimation of different unsaturated soil property functions and modeling of the macro-scale soil behavior. However, depending on the soil and processes under consideration, proper hydraulic characterization of a soil through direct laboratory measurements can be difficult, time-consuming, and involve many uncertainties. In the case of uniformly graded sands, there is a highly nonlinear and steep shape of the SWCC, with only a few kPa of soil suction separating saturated and residual soil moisture conditions, which makes measurements for determinations of SWCC especially challenging. This study encompasses an investigation of the sandy type of soil’s behavior and presents some preliminary results and experiences on the determination of SWCC through the use of physical slope model tests. The 30 cm deep slope, inclined at 35 degrees and instrumented with soil moisture and pore water pressure sensors, was exposed to series of rainfall intensities, ranging from 37 up to 300 mm/h. The results indicated that the data on hydraulic response in monitored points are not only useful for the determination of SWCC, but that the approach is useful for investigation of hydraulic hysteresis phenomena, as well as its effects on soil moisture and pore water pressure conditions, which also affects the stability conditions of a slope. In particular, the best-fit parameters of the van Genuchten model suggested air entry values of 1.6 and 1.1 kPa for the drying and the wetting curves of the SWCC, respectively, with the two branches shifted by about 1 kPa of soil suction.

Influence of soil base deformation methods on the formation of the stress-strain state of retaining walls

The results of numerical modeling of the interaction between a pile retaining wall and the soil base using the software complexes "Plaxis" and "LIRA-SAPR" are presented. A comparison of the stress-strain state of retaining walls using different calculation methods, taking into account the presence of rock soil, has been performed. In the first variant, the active pressure on the wall was determined manually in accordance with the current standards [3], and the subsequent calculation was carried out in the "LIRA-SAPR" software complex. The "pile-soil" system was modeled using FE 57, which are interconnected by FE 10 (rod), and the values of horizontal stiffness (Rx,y) were determined according to the requirements of [3]. In the second variant, the retaining wall calculation was performed in "Plaxis 2D". The soil behavior model is "Mohr-Coulomb", and for rock - "Hoek-Brown". It was considered that rock soils lie at the base of the retaining wall, which revealed significant differences in the distribution of bending moments along the length of the retaining wall. It was established that the stress-strain state in the first variant significantly differs from the second. The difference in maximum horizontal displacements after the calculation by the first and second methods was shown. Differences and variations in the values of bending moments occurring in the retaining wall were investigated. The importance of using modern geotechnical calculation software complexes for a more detailed and accurate analysis of structures and foundations was demonstrated. Additionally, an assessment of the impact of variations in the parameters of the soil and retaining wall models on the calculation results was conducted. The research results allow recommending the use of a comprehensive modeling approach to enhance the reliability and efficiency of retaining wall design. The analysis also shows that the application of different soil behavior models can significantly affect the final calculation results, highlighting the need for careful selection of modeling parameters. The obtained results have significant practical value for engineers and designers, as they allow for more accurate prediction of the behavior of retaining walls under various operating conditions. This contributes to improving the safety and cost-effectiveness of construction projects.

Cantilever piled-wall design criteria in cohesionless soil: a review

Purpose The design of cantilever pile walls (CPWs) presents several common challenges. These challenges include soil variability, groundwater conditions, complex loading conditions, construction considerations, structural integrity, uncertainties in design parameters and construction and monitoring costs. Accordingly, this paper is to provide a detailed literature review on the design criteria of CPWs, specifically in cohesionless soil. This study aims to present a comprehensive overview of the current state of knowledge in this area. Design/methodology/approach The paper uses a literature review approach to gather information on the design criteria of CPWs in cohesionless soil. It covers various aspects such as excavation support systems (ESSs), deformation behavior, design criteria, lateral earth pressure calculation theories, load distribution methods and conventional design approaches. Findings The review identifies and discusses common challenges associated with the design of CPWs in cohesionless soil. It highlights the uncertainties in determining load distribution and the potential for excessive wall deformations. The paper presents various approaches and methodologies proposed by researchers to address these challenges. Originality/value The paper contributes to the field of geotechnical engineering by providing a valuable resource for geotechnical engineers and researchers involved in the design and analysis of CPWs in cohesionless soil. It offers insights into the design criteria, challenges and potential solutions specific to CPWs in cohesionless soil, filling a gap in the existing knowledge base. The paper draws attention to the limitations of existing analytical methods that neglect the serviceability limit state and assume rigid plastic soil behavior, highlighting the need for improved design approaches in this context.

Arsenic accumulation in spolic technosols in the area of a large copper smelting plant in the Middle Urals

Relevance. The necessity to study arsenic behaviour in soils as one of the main pollutants of depositing environments in areas of mining and metallurgical industry. In recent decades, arsenic emissions into the environment have reached a huge scale, so this element attracts the attention of researchers around the world. But in spite of all the studies of this problem, there are still some aspects that need to be clarified to understand the geochemistry of arsenic. This paper deals with spolic technosols with critically high arsenic content in the soil profile with alternating water-logged and dry conditions. As one of the main soil-forming elements, orthosteins contain significant amounts of iron and manganese compounds and are capable of adsorption and involvement of the elements in nodule formation. Aim. To determine the influence of orthosteins on arsenic accumulation in soil subjected to intensive anthropogenic load. Object. Ortsteins spolic technosols in the zone of operation of copper smelting plant and background soils not exposed to pollution. Methods. Arsenic was determined by inversion voltammetry method. Morphological characterisation and patterning of the orthosteins were performed by scanning electron microscopy using a Thermo Fisher Phenom XL G2 Desktop SEM unit. Results. The study of morphological features of orthosteins revealed differences in soils subjected to greater anthropogenic load. Arsenic was not detected inside the orthosteins in all studied soils. Also arsenic concentrations in the total mass of ortstein is up to 40–50% of the soil mass. This fact indicates the accumulation of arsenic by surface adsorption and the appearance of orthosteins as a geochemical barrier. The data obtained in the course of this work can contribute to the search for ways to clean up soils contaminated with arsenic, as well as provide an understanding of the basic processes of the behaviour of this element in soil formation.

Simulating Two-Phase Seepage in Undisturbed Soil Based on Lattice Boltzmann Method and X-ray Computed Tomography Images.

The two-phase seepage fluid (i.e., air and water) behaviors in undisturbed granite residual soil (U-GRS) have not been comprehensively studied due to a lack of accurate and representative models of its internal pore structure. By leveraging X-ray computed tomography (CT) along with the lattice Boltzmann method (LBM) enhanced by the Shan-Chen model, this study simulates the impact of internal pore characteristics of U-GRS on the water-gas two-phase seepage flow behaviors. Our findings reveal that the fluid demonstrates a preference for larger and straighter channels for seepage, and as seepage progresses, the volume fraction of the water/gas phases exhibits an initial increase/decrease trend, eventually stabilizing. The results show the dependence of two-phase seepage velocity on porosity, while the local seepage velocity is influenced by the distribution and complexity of the pore structure. This emphasizes the need to consider pore distribution and connectivity when studying two-phase flow in undisturbed soil. It is observed that the residual gas phase persists within the pore space, primarily localized at the pore margins and dead spaces. Furthermore, the study identifies that hydrophobic walls repel adjacent fluids, thereby accelerating fluid movement, whereas hydrophilic walls attract fluids, inducing a viscous effect that decelerates fluid flow. Consequently, the two-phase flow rate is found to increase with then-enhanced hydrophobicity. The apex of the water-phase volume fraction is observed under hydrophobic wall conditions, reaching up to 96.40%, with the residual gas-phase constituting 3.60%. The hydrophilic wall retains more residual gas-phase volume fraction than the neutral wall, followed by the hydrophobic wall. Conclusively, the investigations using X-ray CT and LBM demonstrate that the pore structure characteristics and the wettability of the pore walls significantly influence the two-phase seepage process.

Profiles of suction stress of layered soils under infiltration conditions and its applications

Suction stress is critical for understanding the hydrological and mechanical behavior of unsaturated soils in construction and engineering. Many soils encountered in these fields exhibit layering due to geological sedimentation or artificial reinforcement. This study establishes the vertical distributions of matric suction and degree of saturation for layered soils under one-dimensional (1D) steady-state seepage, using the Darcy law and constitutive relationships of unsaturated soils. A closed-form suction stress is derived for an arbitrary number of layers and soil types. Hypothetical layered soils with varying hydraulic properties at four infiltration rates are assessed. Results show that soil stratification affects the suction stress profiles, with the impact depending on infiltration rates, soil configuration, and layer thickness. Abrupt variations in suction stress occur at most layered interfaces due to differences in permeability between adjacent layers. The suction stress profiles can be used to evaluate the earth pressure and stability of layered slopes under seepage conditions. Several case studies of multi-layered slope failures in Southern Italy are presented to demonstrate the suitability of the proposed framework for evaluating the stability of layered slopes under rainfall conditions.

Biopolymers in geotechnical engineering for soil improvement

AbstractSeveral biopolymer applications in geotechnical engineering have been adopted in recent years, notably dust control, soil strengthening, and erosion control. Although biopolymer soil treatment approaches can assure engineering efficiency while satisfying environmental protection standards, this technology requires more validation regarding site adaptability, durability, and economic feasibility. The influence of biopolymers on soil behavior is discussed within geotechnical engineering applications and practices, including soil consistency limits, strength and deformation parameters, hydraulic conductivity, soil-water properties, and erosion prevention.Laboratory studies were performed to confirm the behavior of the treated soil, including Atterberg limits, proctor, and direct shear tests utilizing two types of biopolymers: guar gum and xanthan gum.

The Effect of Thermal Regimes on the Dispersive Behavior of Natural Soils from the Perspective of Microstructure and Morphology

The Effect of Thermal Regimes on the Dispersive Behavior of Natural Soils from the Perspective of Microstructure and Morphology

Modelling internal erosion using 2D smoothed particle hydrodynamics (SPH)

This paper presents a stabilised multi-phase smoothed particle hydrodynamics (SPH) model applicable to seepage-induced internal erosion and the resulting deformation in soils. Based on the continuum mixture theory, a new single-layer SPH model in the u-w-p formulation is derived for the mathematical description of the erodible porous material. A new modified constitutive model is formulated to account for the influence of erosion on the mechanical behaviour of soils. Extensions of a first-order consistent boundary condition as well as the diffusion algorithm for hydro-mechanical coupling in SPH are also proposed to accommodate the analysis of erosion-transport process. A novel viscous dissipation term is designed to mitigate the numerical instability commonly encountered in coupled problems. In contrast to existing stabilisation terms in the SPH literature, which operate on both the bulk component and shear component, this new stabilisation term offers the possibility to increase the dissipation of unphysical oscillation due to the shear deformation. The proposed method is validated through a series of benchmark tests. The results demonstrate the effectiveness of the proposed approach in addressing the coupled problem in porous materials involving multi-phase flow, phase interaction/transfer, and large deformation with enhanced accuracy, stability, and robustness.

Revealing Topsoil Behavior to Compaction from Mining Field Observations

Soils are a finite resource that is under threat, mainly due to human pressure. Therefore, there is an urgent need to produce maps of soil properties, functions and behaviors that can support land management and various stakeholders’ decisions. Compaction is a major threat to soil functions, such as water infiltration and storage, and crops’ root growth. However, there is no general agreement on a universal and easy-to-implement indicator of soil susceptibility to compaction. The proposed indicators of soil compaction require numerous analytical determinations (mainly bulk density measurements) that are cost prohibitive to implement. In this study, we used data collected in numerous in situ topsoil observations during conventional soil survey and compared field observations to usual indicators of soil compactness. We unraveled the relationships between field estimates of soil compactness and measured soil properties. Most of the quantitative indicators proposed by the literature were rather consistent with the ordering of soil compactness classes observed in the field. The best relationship was obtained with an indicator using bulk density and clay (BDr2) to define three classes of rooting limitation. We distinguished six clusters of topsoil behaviors using hierarchical clustering. These clusters exhibited different soil behaviors to compaction that were related to soil properties, such as particle-size fractions, pH, CaCO3 and organic carbon content, cation exchange capacity, and some BDr2 threshold values. We demonstrate and discuss the usefulness of field observations to assess topsoil behavior to compaction. The main novelty of this study is the use of large numbers of qualitative field observations of soil profiles and clustering to identify contrasting behavior. To our knowledge, this approach has almost never been implemented. Overall, analysis of qualitative and quantitative information collected in numerous profiles offers a new way to discriminate some broad categories of soil behavior that could be used to support land management and stakeholders’ decisions.

DEM analysis of constrained modulus nonlinearity and damping factor of dry granular soils

The seismic site response analysis requires the dynamic soil properties (i.e., the modulus and damping). While it is well understood that the shear modulus and damping ratio are nonlinearly shear-strain dependent, the knowledge on the constrained modulus and damping ratio of compressional waves is still very limited due to lack of laboratory testing equipment. This study aims to simulate cyclic tests of constrained compression for granular specimens by discrete element method (DEM) to understand the dynamic soil properties of compressional waves, i.e., the nonlinearity in constrained modulus and damping ratio with the compression strain. The evolution in microstructure of granular specimens is revealed to provide micromechanical interpretations for the compressional soil nonlinearity. The results show that the dependency of constrained modulus on compression strain is different in compression and extension stages, and the modulus reduction is only observed in the extension path. The damping ratio of samples under cyclic constrained compression is smaller than that of cyclic shear. The nonlinear soil behavior is more obvious at lower confining pressure and for dense sample. The nonlinearity of constrained modulus depends on the coordination number, contact normal force and fabric anisotropy, while the associated damping ratio is only related to fabric anisotropy.

Gamma-rays and X-rays spectrometries applied to evaluate soil redistribution

This work responds to the growing global demand for food, which requires improvements in agricultural production and sustainable management of natural resources. The focus is on soil erosion as a critical element in preserving agricultural productivity. From this perspective, the levels of radionuclides and chemical elements present in the soil, quantified through Gamma-Rays Spectrometry (GRS) and Energy Dispersive X-ray Fluorescence (EDXRF), were used to investigate soil redistribution over time. 27 soil samples ranging from 0 to 30 cm in depth were collected in an agricultural plot located in southern Brazil. Quantitative analysis indicated high mean concentrations of Fe (161 ± 7 gkg−1), Al (110 ± 17 gkg−1), Ca (2.6 ± 0.5 gkg−1), Mn (2.4 ± 0.3 gkg−1) and K (543 ± 165 mgkg−1) in comparison with the other detected elements. The quantification of 137Cs provided a mean inventory of 27 ± 17 Bqm−2. Using the proportional model, an estimated gross erosion rate of 28.2 tonha−1year−1 and a net soil deposition of 6.6 tonha−1year−1 were calculated. Therefore, a net soil loss of 21.6 tonha−1year−1 was experienced within the agricultural plot studied. The data set combination of both techniques with Principal Component Analysis (PCA) revealed correlations between the variables studied and the soil erosion dynamics. The PCA showed a tendency to separate the samples according to their sampling depth. Moreover, 137Cs behavior in soil proved to be similar to the behavior of elements found in fertilizers, like K. On the other hand, the individual influence of 137Cs was not enough to cause significant changes in the samples distribution in the scores plot, highlighting EDXRF as a promising technique to complement soil erosion studies.

A Novel Method for Estimating the Undrained Shear Strength of Marine Soil Based on CPTU Tests

The undrained shear strength is an essential parameter in the foundation design of marine structures. Due to the complex marine environment and technical limitations, it is difficult and costly to obtain offshore samples. Piezocone penetration tests (CPTU) are relatively low-cost compared to drilling and sampling methods. Therefore, based on the soil behavior type index (Ic) derived from CPTU results, a model for estimating cone factors (Nkt, Nke) is proposed to improve the accuracy of estimation of undrained shear strength. The result shows that the soil behavior type index (Ic) and cone factors take on a negatively correlated exponential relation. Incorporating a cone factor that varies with the soil behavior type index (Ic) significantly enhances the accuracy of undrained shear strength predictions compared to the conventional method of using a constant cone factor. This approach reduces the root mean square error (RMSE) for Nkt (Nke) from 0.124 (0.126) MPa to 0.056 (0.06) MPa, and the mean absolute error (MAE) from 0.0154 (0.016) MPa to 0.0032 (0.0036) MPa. The method was validated at an additional location and the predictions were in high agreement with the results of the consolidated quick direct shear test. The developed method can serve as an effective tool used in the design of foundations of marine structures.

Assessing the effect of layered spatial variability on soil behavior via DEM simulation

Assessing the effect of layered spatial variability on soil behavior via DEM simulation

Combined Effect of the Microstructure and Mechanical Behavior of Lateritic Soils in the Instability of a Road Cut Slope in Rwanda

A very common hazard in Rwanda is represented by the instability of steep road cut slopes in lateritic soil. In its natural state, this material appears as a fine-grained weak and altered rock, generally in unsaturated conditions. Steep cut slopes made by this material could remain stable for a long time unless weathering weakens its mechanical behavior and heavy rainfall provokes a rapid landslide. This paper presents the results of an experimental investigation on the microstructural, petrophysical, and geotechnical properties of lateritic soil from a road cut slope located in Kabaya (Ngororero District—Rwanda), which was recently subjected to a landslide. The mechanical properties of the material are strictly related to the geological origin and history of the deposits, their formation environment, and weathering processes. These characteristics were revealed by peculiar microstructural features (micro-texture, porosity, and degree of alteration of original mineral paragenesis). The experimental investigations included identification and classification tests, direct shear tests on saturated samples, and swelling tests. This multidisciplinary approach provided insights into the relationship between geotechnical properties and the microstructural, petrophysical, and chemical characteristics of the altered rocks. This study showed how different levels of chemical alteration operated by weathering processes, in conjunction with brittle deformation related to the tectonic history, formed in the same site two shallow rock layers with similar macro-scale features and mechanical behaviors but markedly different microstructural and chemical properties. The innovative aspect of this research suggests an integrated multidisciplinary approach to considering microstructural aspects in addition to mechanical behavior in the slope stability analyses in lateritic soil. In particular, this study demonstrates the importance of such an approach since the failure mechanism is better explained if it is based on microstructural observations instead of considering the soil shear strength parameters only. This research helped to explain the formation of the landslide failure mechanism in a specific road cut slope, which could be assumed as representative of many other similar slopes subjected to landslides in Rwanda.

Experimental and Numerical Study of the Mechanical Behavior of Cemented Soil Stiffened with Large-Size Prestressed High-Strength Concrete Pile Under Compression

Experimental and Numerical Study of the Mechanical Behavior of Cemented Soil Stiffened with Large-Size Prestressed High-Strength Concrete Pile Under Compression

Static liquefaction as a form of material instability in element test simulations of granular soil

Static liquefaction is a form of unstable behaviour of granular soil. It is most common in saturated loose sands under monotonically loaded undrained conditions. Predicting static liquefaction using an elastic-plastic model that incorporates the non-associated plastic flow rule and strain hardening is possible. The article briefly describes the unstable behaviour of saturated sand in undrained conditions under a monotonic load. A simple elastic-plastic model with deviatoric hardening and a Drucker–Prager load surface is presented. The constitutive relationships were programmed in a Python script. Simulations of triaxial tests under mixed stress-strain control demonstrated the model’s ability to predict various undrained sand responses, including fully stable responses (no liquefaction) and partial and complete liquefaction under triaxial compression and tension. Predicting static liquefaction is possible by properly selecting the proportions of the parameters involved in plastic potential and loading functions and the parameter A used in the deviatoric hardening rule of hyperbolic type.