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Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Responses of soils to climate warming during winter can be studied by monitoring soil temperature variations in the vadose zone. Freeze–thaw cycles during winter can have a significant impact on soil biogeochemical and physical processes. Observing soil temperature at different depths offers important insights into heat availability, which influences biogeochemical activity and solute movement driven by temperature gradients. However, it is difficult to replicate the relevant processes in soil columns without maintaining freezing temperatures with an unfrozen soil layer below the freezing interface. This paper describes the development and experimental verification of a laboratory-scale physical model to assess the effect of freeze–thaw cycles on biogeochemical processes in unsaturated soil. The results show that the experimental design can (i) induce cyclical freezing of soil down to desirable depths, (ii) maintain vertical temperature gradients and (iii) ensure the rest of the column remains unfrozen below the freezing interface for pore water sampling. The rate of freezing is suitable for quick freeze–thaw cycles (0.19 °C/min). This setup can be further developed to observe solute transport and attenuation in variably-saturated soil and soil moisture status for different freeze–thaw regimes under simulated climate change scenarios. [ABSTRACT FROM AUTHOR]

Suction stress, the part of effective stress induced by soil–water interaction, is the source for the intrinsic cohesion of fine-grained soil slurries. Here, the previous unified effective stress equation is generalized to extend the suction stress variation from the liquid state to the oven-dry state, yielding an augmented closed-form equation. This equation includes a new term, named slurry adsorptive suction stress, to incorporate the adsorptive mechanism of soil slurries at the liquid state. This adsorption mechanism involves the interparticle van der Waals attraction, face-to-edge attraction, and electrical double-layer repulsion when soils are in the liquid state. The proposed equation is validated with a wide array of 12 fine-grained soils' shrinkage curves, modulus, and suction stress data measured by the drying cake test. It is demonstrated that the proposed equation can excellently capture the experimental data across all saturations. Furthermore, the practical implications of the proposed model are illustrated via its relevance to rheological properties of soil slurries and correlations with both liquid limit and plastic limit. [ABSTRACT FROM AUTHOR]

Rainfall infiltration is a primary cause of slope failure. Analyzing the entire process of a landslide triggered by rainfall is crucial for the design of infrastructure. However, the complexity associated with simulating large deformations has often hindered previous studies from modeling the entire landslide process subsequent to rainfall infiltration. This study aims to provide a method to simulate the entire process of landslides considering rainfall and more insight into the mechanism of landslides. The discrete element method (DEM) is first applied to model the entire process of shallow landslides triggered by rainfall. The numerical results indicate that the intensity and duration of rainfall infiltration have significant impacts on the slope stability. The particle displacement field, resulting from landslides due to rainfall, corresponds with three distinct stages within the landslide process. The increased rainfall intensity causes the area of the particles within failure mass grows rapidly during the initial stage of the landslide. The closer to the slope surface the faster the particle velocity. The simulations demonstrate that the slope surface transitions from a linear to a concave downward geometry during the landslides. Larger particles display greater displacement and velocity compared to smaller particles. [ABSTRACT FROM AUTHOR]

Most previous experimental studies on the behavior of piles subjected to lateral loading have focused on testing model piles embedded in dry or fully saturated soils, and little attention has been paid to the impact of the soil partial saturation on the results. This paper presents results of 1g model tests on a single pile embedded in dry and unsaturated sand subjected to two-way constant displacement amplitude loading. The tests were aimed at examination of the effects of degree of soil saturation and density on the pile internal forces and lateral capacity and the deformation patterns of the adjacent soils. Five degrees of saturation (Sr = 0, 10, 20, 35 and 50%) for loose and medium-dense sand (Dr = 20% and 50%) were chosen and a 65-mm-diameter and 900-mm-long polyethylene model pile was used. Test results indicated that at each soil relative density, the pile head horizontal load, and the maximum bending moment, shear force, and soil reaction in the pile increase with increase in the degree of saturation up to about Sr = 35%. However, further increase in Sr led to decrease in these values. Moreover, the cyclic loading led to depressions in the surface of the dry sand and bulging associated with soil–pile separation in the unsaturated sand. For the model testing conditions used, results indicated that the sand degree of saturation can have a greater impact on the pile behavior than its density. [ABSTRACT FROM AUTHOR]

Through extensive laboratory experiments on unsaturated soils, it has been discovered that particle shape and matric suction significantly influence their mechanical properties. Prior studies have typically examined these factors individually and from a macroscopic perspective. In this study, the aspect ratio is utilized as a representative parameter for particle shape. Employing the Hill constitutive model, a series of triaxial shear numerical experiments of simulations on unsaturated soil were conducted. The results indicate a non-linear relationship between peak deviator stress and aspect ratio, with peak deviator stress initially increasing, then decreasing, and reaching its maximum at an aspect ratio of 1.2. The patterns observed in friction angle, cohesion, and critical stress ratio in relation to aspect ratio mirror those seen in peak deviator stress, with the friction angle exhibiting fluctuations as the particle aspect ratio increases. At a matric suction of 0 kPa, changes in particle shape have a negligible impact on mechanical properties. However, as matric suction increases, the volumetric strain’s dilatancy turning point is advanced, and the effect of particle shape becomes progressively more pronounced. Under varying conditions of particle shape and matric suction, the alteration in bedding angle affects the peak deviator stress and stress ratio, albeit the extent of this influence is limited. [ABSTRACT FROM AUTHOR]

Slope stability is crucial in civil engineering, especially in urban areas like Singapore, where heavy rainfall may result in catastrophic slope failures. This study aims to evaluate the effectiveness of three rectification methods, i.e., vegetation covers, GeoBarrier Systems (GBS), and Capillary Barrier Systems (CBS), in reducing rainwater infiltration for maintaining slope stability. Numerical analyses were conducted using finite element seepage and limit equilibrium slope stability software incorporating various rainfall and soil conditions to simulate real-world scenarios, focusing on the Factor of Safety (FOS) and Overdesign Factor (ODF) variations during and after rainfall events. The results from numerical analyses indicate that all three rectification methods significantly reduced negative pore pressure across slope layers under different rainfall scenarios, with CBS being slightly less efficient compared to other methods. Compared to simulations of slopes without rectification methods, the negative pore pressures of the rectified slope are improved by 50 kPa, demonstrating the effectiveness of the rectification methods in mitigating rainwater infiltration. The rectification methods showed similar trends in FOS values, with significant improvements over bare slope simulations. The FOS of the bare slope dropped by 0.7, reaching 1.0 under short, intense rainfall and 0.94 under prolonged heavy rainfall. The FOS of the slope with rectification methods remained stable, with only a 0.05 drop under different rainfall scenarios. The ODF showed similar results. Simulations with high-permeability soils revealed the same trends, confirming the rectification methods' reliability in representing negative pore pressure and FOS accurately. These findings suggest that all three rectification methods are highly effective in maintaining slope stability under heavy rainfall, making them viable options for slope stabilization in Singapore. [ABSTRACT FROM AUTHOR]

This paper presents a reliability analysis of circular footings on unsaturated soils. Two methods were used to capture the unsaturated soil behavior: implementing two elastoplastic constitutive models, including the Barcelona Basic Model (BBM) and the Sun Model (SM), which are explicitly proposed for unsaturated soils, and incorporating the apparent cohesion in the Mohr–Coulomb Model (MCM). The effect of soil suction on the bearing capacity of circular footings was investigated. It was shown that for low values of suction, the bearing capacities obtained from MCM were higher than those obtained from BBM and SM. However, as suction increased, MCM tended to predict lower bearing capacities. In practice, geotechnical engineers are still concerned with the measurement and determination of suction as a key stress state variable of unsaturated soils. In this context, the Monte Carlo simulation technique has been incorporated into numerical modeling for the investigation of the effect of suction uncertainties on the bearing capacity. Uncertainties associated with the suction value were modeled as normally and log-normally distributed random variables. It was shown that assuming a normal distribution for suction resulted in slightly lower probabilistic bearing capacity values (i.e., more conservative design) compared to the log-normal distributions. The results emphasized the important role of the coefficient of variation (COV) of suction in determining the probabilistic bearing capacity. A negative linear correlation was observed between the COV of suction and the probabilistic bearing capacity. Finally, a simple relationship was proposed to estimate the probabilistic bearing capacity of the circular footing in an unsaturated soil when its deterministic value and the COV of suction are known. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is crucial to accurately measure the volume change of specimens in triaxial tests on unsaturated soils. A new type of inner chamber structure has been designed for measuring volume changes, which can accurately measure the volume change of unsaturated soils during monotonic loading tests. Compared to conventional double chamber triaxial systems, the new inner chamber structure has higher precision and compatibility, and the inner chamber can be assembled under air-free water. The inner chamber assembled underwater avoids the problem that the air bubbles being trapped in the inner chamber, significantly reducing the impact of residual air in the system. A solid specimen made of stainless steel was used to calibrate the newly designed inner chamber. Under the net confining pressure (the difference between cell pressure and the initial cell pressure) of 400 kPa, the volume change error of system is only 0.037% of specimen volume, the measurement error is very small. The contact surface between the loading ram and the top cover is coated with Teflon material and smeared with Vaseline to reduce friction, and the friction force measured by high-precision force gauge is 4.14 N. Drained shear test was conducted on an undisturbed saturated soft clay specimen, where the volume change in the saturated soil specimen during drainage was used to verify the accuracy and precision of the inner chamber volume measurement method. The volume change error measured by the system during consolidation and shearing are 0.102% and 0.067% of specimen volume, respectively. The results indicate that the newly designed inner chamber structure is feasible for volume change measurement and has high precision. [ABSTRACT FROM AUTHOR]

Unsaturated shear strength (τus) is a critical parameter in many geotechnical engineering designs, including embankment stability assessments and slope antiskid design. This paper investigates the hydromechanical behavior of unsaturated reconstituted clay by conducting suction-controlled triaxial shear tests. The results show a nonlinear increase in τus over a wide range of suction, as well as a nonzero τus value at high suctions. However, using existing strength equations to predict τus may result in an overestimation or underestimation in the residual zone. To address this limitation, a fitting-type strength model of unsaturated soils that takes the impact of void ratio into account is proposed based on the unified effective stress equation that separates capillary stress from adsorbed stress. The proposed model accurately describes various types of strength behaviors over a wide range of suction, such as nonlinear increasing strength type and peak strength type. Finally, the proposed model is evaluated against experimental results of the test soil in this study and different soils reported in other resources, showing that it can reasonably capture important features of the strength behavior of unsaturated soils over a wide range of suction. [ABSTRACT FROM AUTHOR]

In order to explore the deformation and failure characteristics of reinforced unsaturated soil structure, soil-water characteristic curves of unsaturated soil were tested; stress-strain curves of unsaturated soil and reinforced soil with matrix suctions of 30 kPa, 80 kPa and 130 kPa, respectively under different confining pressures were measured based on the consolidated drainage triaxial test; deformation modulus and shear strength indexes of soil and reinforced soil under different matrix suctions were compared and analyzed; based on the triaxial test results, the confining pressure of geocell on unsaturated soil was analyzed. The results show that with the increase of axial strain and the decrease of confining pressure, the increase of deformation modulus of reinforced soil in geocell gradually increases; the effective internal friction angle of unsaturated soil is less affected by the reinforcement effect of the geocell; due to the restraint effect of the geocell, the cohesion of the reinforced soil and the internal friction angle reflecting the contribution of matrix suction to the strength increase; with the increase of matric suction and the decrease of confining pressure of unsaturated soil, the deformation modulus and apparent cohesion of reinforced soil in geocell increase gradually due to the enhancement of dilatancy trend. [ABSTRACT FROM AUTHOR]

This paper proposes a coupled hydro-mechanical constitutive model for unsaturated clay and sand (CASM-U) in a critical state framework. The mechanical behaviour of unsaturated soils is modelled by modifying the unified clay and sand model (CASM) with Bishop's effective stress, bounding surface concept and loading collapse (LC) yield surface. The hydraulic behaviour is described by a soil–water characteristic curve (SWCC) with nonlinear scanning law, considering the coupled effects of soil deformation and hysteresis. CASM-U is implemented into a commercial finite element software through the user-defined material subroutine (UMAT), and the implementation is benchmarked by a new semi-analytical cavity expansion solution adopting CASM-U. Finally, the performance of CASM-U in predicting hydro-mechanical behaviour of unsaturated clays and sands is examined by comparing with experimental data from tests along various loading paths, including isotropic compression, cyclic drying–wetting, triaxial shearing, and their combinations. It is shown that CASM-U can provide reasonable predictions for hydro-mechanical behaviour of unsaturated soils with a total of 15 material parameters. [ABSTRACT FROM AUTHOR]

The tensile strength and soil water characteristics of unsaturated soils plays a critical role as a fundamental property in various road engineering projects. The purpose of this study is mainly to investigate the tensile strength and soil water characteristics of compacted and desiccated specimens with varying water contents with under the dry density of 1.5, 1.6, and 1.7 g/cm3 using the filter paper method and Brazilian splitting test. The research findings reveal that during the drying process, as the water content decreases, the overall morphology of the pore size distributions remains largely consistent with a tri-modal distribution, in contrast to the bimodal distribution observed in compacted specimens. Furthermore, desiccated specimens exhibit better water retention behavior compared to compacted specimens. Additionally, compacted specimens reach their peak tensile strength at a critical water content, whereas desiccated specimens progressively increase their tensile strength until stabilizing. In the desiccated specimens, a significant amount of bonding material fills the soil pores, resulting in the formation of a stable bonding force between particles and aggregates. This phenomenon leads to a continuous increase in the tensile strength of the desiccated specimens. The study further establishes a tensile strength model that incorporates the influence of physicochemical forces. The accuracy and reliability of this model were confirmed by comparing its results with experimental data from the test soil in this study, as well as other available resources. [ABSTRACT FROM AUTHOR]

This paper aims to determine a non-liquefiable domain corresponding to the threshold of saturation degree where liquefaction does not occur under cyclic loading. To determine this threshold, sample volumetric strain at liquefaction state of unsaturated soil was modeled considering the suction. In low saturation degree zones, capillary suction is taken into account. In a high saturation degree zone, spherical suction caused by surface tension of air bubbles is considered by using its microscopic analysis and its equivalent size. Finally, three series of experimental tests have been made to give the data and verify the presented model. [ABSTRACT FROM AUTHOR]

Though nuclear magnetic resonance (NMR) has been applied in soil science over several decades, the quantitative relation between NMR signals and soil pore-water distribution is complex and still covered by some cloud. The major debates include: 1) the quantitative relation between transverse relaxation time (T2) and pore radius varies in different studies; 2) Is the relation between NMR signals and soil-water contents unique? To clarify the aforementioned issues over the application of NMR in soil science, a comprehensive study was carried out. The results demonstrate that: 1) a unique linear relationship between peak area of NMR signals and soil volumetric water content (θ) exists, independent of the soil's initial molding conditions, such as molding dry density (ρd) and molding water content (wini); 2) the ratio between T2 and pore radius, defined as the pore structure coefficient (Cr) of NMR, varies with pore water morphologies and soil types; 3) three methods were proposed to determine the value of Cr and can help to provide insights for better understanding of the NMR results in soil science. [ABSTRACT FROM AUTHOR]

Cut-fill slopes, as an economical solution in mountainous road construction, are typically jeopardized by cracks and rainfall. Deep patch repair with geosynthetics is an effective technique to mitigate these issues. This paper proposes an upper-bound analytical framework for evaluating the stability of cracked cut-fill slopes and deep patch slopes under one-dimensional steady infiltration. The proposed framework is employed to investigate suction-induced effects on slope stability and critical failure surface through a series of parametric analyses. The findings indicate that the suction-induced effect generally increases with air-entry pressure and approaches a constant value. The stability of a cracked cut-fill slope can be enhanced by deep patch repair with geosynthetics. Increasing the deep patch depth enhances local stability and reduces the required reinforcement strength. Generally, the depth of the deep patch should be greater than the crack depth to avoid local failures. Furthermore, a design method involving both local and global stability for deep patch slopes is presented, along with a design example for illustration. [ABSTRACT FROM AUTHOR]

Copyright of Kufa Journal of Engineering is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this investigation, the soil-water-retention is described in the soil-water-characteristics-curve (SWCC). SWCC contains the data required to explain the unsaturated soils' mechanical behavior. The reliable findings of unsaturated sand soil tests and the impact of initial density on the hydraulic properties under various matric suction and net normal stresses are examined. The tests are carried out on a sample of soil from the northern region of Al-Najaf city, Iraq. The sample of soil has been disturbed and remolded in the cell of Oedometer device. A modified high-air-entry-disc-based Oedometer is used with accessories to control the air and water pressures to achieve the specific matric suction in the unsaturated test. Two sets of tested specimens are prepared, first, at 90% and second at 95% of the maximum dry unit weight from the standard Proctor experiment. Each set is performed for different matric suction under 200 and 400 kPa net normal stress. (SWCC) The soil water retention curve is affected by the application of net normal stress and initial density. There is a decrease in water volume change with wetting progress in unsaturated soil tests due to an increase in soil density.

Abstract The effectiveness of using vegetation to reinforce slopes is influenced by the soil and vegetation characteristics. Hence, this study pioneers the construction of an extensive soil database using random forest machine learning and ordinary kriging methods, focusing on the influence of plant roots on the saturated and unsaturated properties of residual soils. Soil organic content, which includes contributions from both soil organisms and roots, functions as a key factor in estimating soil hydraulic and mechanical properties influenced by vegetation roots. This innovative approach of using organic content to estimate soil properties performs well when applied to machine learning models for soil database development. The results reveal that organic content markedly affects the hydraulic properties of soils, more than their mechanical properties. The finding illustrates the importance of exploring the hydraulic effects of vegetation on slope stability in addition to the traditional emphasis on mechanical reinforcement. This rooted soil database has practical applications in GIS-based analyses for mapping regional slope stability, incorporating the role of plant roots. A case study demonstrated the database’s utility, showcasing that vegetation effectively limited rainwater infiltration and improved slope stability. Therefore, this research offers a valuable approach to improving slope stability through informed vegetation strategies.

The bearing capacity of a foundation is crucial for ensuring the stability and safety of structures. However, shallow foundations on unsaturated soils pose challenges due to the complicated behavior of such soils. To address this issue, engineers have developed analytical and numerical methods of analysis, which can be used to determine the bearing capacity of these foundations. This study explored the advantages and disadvantages of these methods, offering a thorough understanding of their role in ensuring the safety and longevity of structures built on unsaturated soil. The analysis in this study was conducted using finite element method simulations on soil sections with varying groundwater levels and degrees of saturation. The results obtained from PLAXIS 2D simulations revealed the effects of fluctuations in groundwater levels and changes in saturation degree on foundation displacements, emphasizing aspects often overlooked in empirical approaches. Under unsaturated conditions, as the degree of saturation decreased, the soil was better able to maintain its structural integrity, resulting in reduced foundation displacements. However, at near-complete saturation (%99), displacements increased significantly, highlighting the risks to foundation stability in soils with high saturation levels, particularly in flood-prone areas. Variability in excess pore water pressure in sections with high saturation indicated potential soil instability under high stresses, impacting structural integrity. Furthermore, finite element analyses showed that classifying soil as drained or undrained impacted foundation displacements. In conclusion, the comprehensive analysis provided by numerical methods emphasized the limitations of empirical approaches and underscored the importance of advanced simulation tools in modern geotechnical practices.

Existing solutions for electro‐osmotic consolidation assume a linear voltage distribution, which is inconsistent with the experimental findings. The present study introduces a novel two‐dimensional electro‐osmotic consolidation model for unsaturated soils, which considers the influence of non‐linear voltage distribution. The closed‐form solution is derived by employing the eigenfunction expansion method and the Laplace transform technique. The accuracy of the analytical solutions is validated through the implementation of finite element simulations. The findings from the parametric studies indicate that the excess pore water pressure (EPWP) observed in electro‐osmotic consolidation is influenced by the distribution of voltage. The dissipation rate of EPWP is observed to be higher when subjected to non‐linear voltage conditions compared to linear voltage conditions. Moreover, the impact of non‐linear voltage distribution becomes more pronounced in unsaturated soil characterised by higher electro‐osmosis conductivity and a lower ratio of kx/ky. In contrast, the excess pore air pressure (EPAP) remains unaffected by the voltage distribution. [ABSTRACT FROM AUTHOR]