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Collapse of soil skeleton due to variation in its loading and boundary conditions impacts the strength and stability of soil in its unsaturated state. The present study is focused on the influence of matric suction on collapsible behaviour and stiffness degradation of compacted unsaturated cohesive soil. Collapse characteristic of unsaturated soil is assessed under sudden inundation and varying vertical stress application. A series of dynamic triaxial, double oedometer and filter paper tests were conducted on unsaturated Ahmedabad cohesive soil under as-compacted conditions at varying dry density and water content to determine cyclic degradation index (δ), collapse potential and matric suction (ua – uw), respectively. Significant influence of matric suction was observed on collapse potential and stiffness degradation of unsaturated cohesive soil. Larger collapse potential at higher matric suction clarified the meta-stable state of compacted unsaturated cohesive soil under dry conditions. Cyclic degradation index (δ) with number of loading cycles was found to be decreasing with increase in matric suction representing brittle nature of soil possessing higher matric suction signifying soil skeleton to be highly volatile and unsafe under dynamic loading conditions. [ABSTRACT FROM AUTHOR]

In recent years, many examples of soil structure collapse due to heavy rainfall have occurred. Because of this, it is urgent to establish a method to evaluate and examine long-term embankment structure quality. Japan's conventional design method insufficiently evaluates embankments. Although this method is shifting to a performance-based design to cope with recent abnormal weather, an effective design method has not yet been established. Therefore, this research performs an initial stress analysis of embankment, accounting for differences in construction conditions. Notable in this study, is the comparative analysis of results, considering the initial water content ratio, one layer of discharge thickness, rolling compaction, and other given structural conditions that differed from conventional design standards. To do this, first the initial moisture content ratio was determined by reproducing the compaction by analysis. Second, based on the dynamics of unsaturated soil, the rainfall intensity was analyzed in order to confirm the variation of the initial stress due to rainfall. Lastly, and most critically, the dynamic change in embankment performance was analytically expressed, and the optimal structural conditions of embankment, grouped by rainfall history, was examined. [ABSTRACT FROM AUTHOR]

The present study focuses on some tentative laboratory tests using a newly-constructed modified direct shear test apparatus. The single-stage and multistage direct shear tests were performed to determine the shear rate and test scheme of unsaturated shear test. Shear strength parameters of unsaturated soil in different conditions are obtained and the tests indicate good agreement with typical theories of unsaturated soil, the nonlinear matric suction failure envelope is determined. Some shear strength equations are also fitted through the experimental results.

Summary: The study presents semi‐analytical solutions of two‐dimensional plane strain consolidation problem in unsaturated soils incorporating the lateral semipermeable drainage boundary by adopting Fourier sine series and Laplace transform. The two‐dimensional plane strain consolidation equations in the form of two‐order partial differential equations with three variables are firstly converted to two‐order partial differential equations with two variables, which are similar to those of one‐dimensional consolidation problem. The four‐order ordinary differential equations about excess pore‐air and excess pore‐water pressures are got by applying Laplace transform and the substitution method. Then, the solutions of excess pore pressures and settlement are achieved in the Laplace transform domain. Afterwards, on the basis of Crump's method, the inverse Laplace transform is conducted to obtain the analytical solutions in time domain. The comparison is conducted to verify the exactness of the obtained solutions, and the two‐dimensional plane strain consolidation property with the lateral semipermeable drainage boundary is illustrated and discussed. Parametric studies are demonstrated for the excess pore pressures and normalized settlement with the change of the boundary parameters, air‐water and lateral‐vertical permeability coefficients, and the distance and depth. It can be found that the lateral semipermeable drainage boundary impedes the consolidation rate obviously, and when different investigated parameters are adopted, the consolidation property is similar to each other under the later permeable and semipermeable drainage boundary conditions. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology 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.)

To study the influence of matric suction on the strength characteristics of soil, consolidated and drained triaxial shear tests on undisturbed silty clay were conducted using GDS unsaturated soil triaxial apparatus under different matric suction conditions. The results show that the peak strength of soil increases with the increase of matric suction, and the rate of increase increases first and then decreases. With increased matric suction, the total cohesion increases and the extent of this increase gradually decreases, while the effective internal friction angle decreases slightly and then tends to be stable. The effect of matric suction on shear strength is mainly reflected in the total cohesion. Matric suction has the most significant influence on soil strength at 50 kPa to 100 kPa. In the presence of matric suction, the area of action of water film on soil particles determines the change of total cohesion, and the pore air pressure and pore water determine the change in effective internal friction angle. The angle used to describe the increase in the shear strength of soil with an increase in matric suction is φb=28.2°. According to Fredlund's strength theory, the formula of shear strength parameters of unsaturated silty clay in the study area under consolidation and drainage conditions was given, and the relationship between strength parameters and matric suction was fitted. [ABSTRACT FROM AUTHOR]

Traditionally, the analysis of the rainfall-induced slope failure was assumed to be under saturated condition. Nevertheless, lots of colluvium slopes are unsaturated in the normal condition in Taiwan. Unsaturated slopes have matric suction, contributing to their high slope stabilities in the dry season. With the rainfall infiltration, the decrease of matric suction may lead to the failure of the slope. This paper presents the numerical analysis of a case located in Wenshan Dist., Taipei City, Taiwan. The slope collapsed during Typhoon Jangmi in September 2008. Since the remediation program was urgent then, there was not enough time to comprehensively figure out the failure mechanism of the case. Consequently, this study conducts the site investigation and performs the numerical analysis to better understand the real failure mechanism of this slope. Results reveal that the failure is shallow and progressive. Additionally, the toe of colluvium was the most susceptible part of the whole slope during infiltration. Furthermore, the critical volumetric water content existed, when the slope collapsed. Accordingly, the monitoring system ought to be set in the toe of the colluvium and the volumetric water content may be considered as an index parameter for the early warning system of landslide disasters in the future. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shanghai University / Shanghai Daxue Xuebao is the property of Journal of Shanghai University (Natural Sciences) Editorial Office 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.)

Microbial aerobic methane oxidation (MAMO) has been considered as an environmental-friendly method for mitigating methane emission from municipal landfill sites. Soil column has in a landfill cover under one-dimensional (1-D) condition. However, most of the published soil column tests failed to simulate 1-D heat transfer due to the use of thermal conductive boundary at the sidewall. In the present study, a heavily instrumented soil column was developed to quantify the effects of thermal boundary condition on the methane oxidation efficiency under different ambient temperatures in landfill cover soil. The sidewall of the soil column was thermally insulated to ensure 1-D heat transport as would have been typically expected in the field condition. Two soil column tests with and without thermal insulation were conducted at a range of controlled ambient temperatures from 15 to 30 °C, for studying how soil moisture, matric suction, gas pressure, soil temperature and gas concentration evolve with MAMO. The test results reveal that ignoring thermal insulation in a soil column test would result in a greater loss of soil heat generation by MAMO and hence oxidation efficiency by up to 100% for the range of temperature considered. When the ambient temperature increased to 30 °C (but less than the optimum temperature for MAMO), the MAMO efficiency increased abruptly at first but then decreased substantially with time, and this is likely due to the accumulation of biomass generated by MAMO. Unlabelled Image • Thermal-insulated soil column is developed to better present field condition. • Thermal boundary affects soil temperature and CH 4 mitigation a lot. • CH 4 oxidation decreased as temperature increased to 30 °C (

The unsaturated zone in the soil generally plays an important role in the transfer of water and pollutants in the underground environment. To simulate the water flow in this area, the relationships that express the variations of the water content and the hydraulic conductivity of the soil as a function of the pressure must be defined. In this context, determination of the hydrodynamic parameters constitutes an essential step for any study of the water and solutes transfers in the unsaturated zone. The purpose of this article is to identify the soil hydrodynamic parameters by direct method and inverse method, from the infiltration data by using the disc infiltrometer. These two methods of the characterization were applied on two plots: a plot of R'mel, sandy soil, and a M'risa plot, clay-loamy soil in northern Morocco. The results of the analytical and numerical modeling reproduced correctly the experimental measurements. A performance analysis of the models used was implemented to study the reliability of the estimated parameters. The values of RMSE ≈ 0.20 and R2 ≈ 0.90 show that the inverse method remains a robust and accurate method for determining the soil hydrodynamic parameters compared to other conventional methods. [ABSTRACT FROM AUTHOR]

In the Tianjin Port 8·12 explosion, the leakage of enormous amounts of nitrate into the coastal soil-water system threatened the environment and human health. This work aimed to assess the nitrate transport process in unsaturated dredger fills and to conduct an environmental risk assessment to establish guidelines that safeguard groundwater against contamination. The impacts of the bulk density, initial water content, recharge rate, and initial concentration of the nitrate transport process were investigated through an L9 (34) matrix. A field simulation was conducted with Hydrus-1D to explore nitrate transport at the accident site. The results showed the recharge rate and initial water content were the dominant factors affecting the nitrate transport rate and concentration distribution, followed by the initial concentration and bulk density. The contaminant reached the water table in approximately 1.2 years and that approximately 9% of the leaked nitrate entered the aquifer after two years, while the rest of the nitrate remained in the unsaturated zone. The nitrate concentration at a depth of 5.0 m was nearly 1000 mg L–1, which was much higher than the groundwater concentration standard of 30 mg L–1. The soil and groundwater quality warrant special attention due to the excessive nitrate contaminants. [ABSTRACT FROM AUTHOR]

In soil physics, accurate estimation of hydrodynamic properties is essential for effective groundwater management. Experimentally, determination of these properties in the laboratory or in-situ conditions is difficult step, long and may involve uncertainties significant for the vast majority practice use. Frequently, inverse methods were established to determine accurate parameters in the field scale based on measured soil moisture and hydraulic conductivity over time and depth. These inversions methods involve hydraulic soil-models using adapted optimization algorithms that ensure a best combination of parameters minimizing a cost function. In this work, direct and inverse optimization approaches has been proposed to estimate the effective hydraulic parameters, based on the temporal description of the soil physical and hydraulic parameters using field water content measurements from located in Mnasra area (northwest of Morocco). The Levenberg Marquardt optimization algorithm coupling with the vadose zone model (VZM), numerical code in Fortran, has been used to inverse estimation of hydraulic parameters based on transients soil water content measurements. These uses have been conducted using temporal measurements of soil moisture in depths: 20, 40, 60 and 80 cm. The estimated properties are in good agreement with those measured in-situ. Overall, it was concluded that this technique can greatly widen the range of hydrological problems admissible for inversion and can be used for many applications in hydrologic engineering, either alone or in conjunction with traditional techniques. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office 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.)

A mathematical formulation is presented to investigate the dynamic response of a single pile embedded in a semi-infinite partially saturated soil subjected to lateral dynamic excitations. An approximate scheme is implemented to decompose the pile–soil system into an extended water–air-filled poroelastic half-space and a fictitious pile. The extended porous medium is governed by the three-phase elastodynamic theory, whilst the fictitious pile is treated as a beam and described by the conventional one-dimensional beam vibration theory. By virtue of the Green's function for a set of interior horizontal patch loads in unsaturated soil and the combination with the compatibility condition, the formulation of the interaction problem is reduced to a Fredholm integral equation of the second kind governing the unknown bending moments and displacements along the fictitious pile. The pile head impedance function in the frequency domain is derived and resolved numerically by a discretised method. Its accuracy was validated through a comparison with the existing solutions corresponding to single-phase and fully saturated soils. The numerical results show that the effects of saturation and permeability on the dynamic behaviour of pile are insignificant for the partially saturated cases, whilst remarkable for the nearly saturated case. When the soil approaches the full saturation, the impedance increases rapidly as the degree of saturation increases, but diminishes gradually with increasing permeability. [ABSTRACT FROM AUTHOR]

The long-lived debate on the principle of effective stress is rooted in the obscure physical significance of stresses. For the sakes of clarifying stress concepts and establishing a reasonable principle of effective stress, unsaturated soil is divided into six phases and the bearing structure of it, named generalized soil structure, is defined based on considering soil as a special structure. Then the essence of effective stress equation, named stress relation equation, is derived according to analysis of interphase interactions and independent-phase equilibrium. The stress relation equation indicates the corresponding relation between two series of stress variables used in mixed and multiphase continuum models, respectively. Furthermore, a reasonable concept of suction stress is redefined to describe interparticle connection properties. Then, a generalized stress framework is constructed by associating stress relation equation with suction stress. After demonstrating the concept of neutral stress, a generalized principle of effective stress is established and the total soil skeleton stress is searched out, which is the predominant stress controlling the strength and deformation of soil. Finally, the collapse phenomenon is analyzed and the time- and spatial-dependent stress frameworks are developed. [ABSTRACT FROM AUTHOR]

Rainfall-induced diffuse shallow landslides are one of the most critical natural hazards as they often evolve into highly destructive flow slides and debris flows. Vegetation is recognised to play a key role in landslide occurrence and is frequently invoked as a potential remedial measure for slope stabilisation at the catchment scale. The beneficial action of vegetation is generally associated with mechanical (root anchoring) and hydrological (suction generated by root water uptake) effects. There is indeed a third effect that has thus far been little explored. The rhizosphere, the portion of soil directly affected by plant roots, is characterised by hydraulic conductivity higher than the underlying soil horizons. This significantly affects hillslope hydrology by promoting lateral diversion of rainwater. This paper presents a case study in Scotland where the rhizosphere is demonstrated to play a major role in controlling shallow landslides. Field investigation and laboratory testing were carried out to characterise the hydraulic conductivity of the rhizosphere and deeper horizons. In turn, this formed the basis for the development of a physically based model for the slope. The model was first validated against its capability to simulate failure of two historical landslides and then exploited to demonstrate the beneficial effect of the rhizosphere. The lesson learned from this study is that shallow landslide hazard can be mitigated by enhancing the capacity of the rhizosphere to act as a natural lateral drainage. This implies that plants with root-system architecture that enhances lateral subsurface flow should be privileged when designing vegetation-based remedial measures. [ABSTRACT FROM AUTHOR]

Purpose: Loess landslides induced by irrigation are common geological disasters in the Loess Plateau, China. Long-term watering decreases the matric suction and soil strength of loess, thus causing the frequent occurrence of landslides. Therefore, studying the strength characteristics of unsaturated loess is of great significance for knowing how such landslides occur and, a step further, preventing them. Materials and methods: Undisturbed loess samples in Heifangtai Platform were collected to measure their soil water characteristic curves (SWCC) and a series of direct shear tests and triaxial shear tests were carried out with unsaturated loess. Moreover, the strength characteristics of the loess were discussed. Results and discussion: The results showed that in the direct shear test, the cohesion (c) increased linearly with increasing matric suction whereas the suction internal friction angle (φb) was approximately constant. In the triaxial shear test, c increased nonlinearly with increasing matric suction. The value of φb was a constant when matric suction was 0–100 kPa, but decreased as matric suction increased within the range of 100–200 kPa. The effective stress parameter (χ) lay in the range from 0.5 to 0.8. When the matric suction was small, the shear strength calculated by Lu's suction theory was almost the same as that obtained by Fredlund's theory. With the increase of matric suction, the shear strength calculated by Fredlund's theory gradually outperformed that of Lu's suction theory. The shear strength calculated by the curve of moisture desorption was slightly larger than that of moisture absorption. Conclusions: The variation trends of strength parameters with matric suction under the two tests were similar. The effective internal friction angles obtained by the triaxial shear test are slightly larger than those by the direct shear test. The suction internal friction angle (φb) was approximately a constant and smaller than φ´. The φb obtained by the direct shear test was slightly larger than that obtained by the triaxial test. Lu's theory can be used to evaluate the stability of unsaturated soils on some loess slopes with high soil moisture content. [ABSTRACT FROM AUTHOR]

Stability of trenches in vadose zone primarily depends on matric suction distribution with depth. The depth of ground water table, type of soils, and local climate conditions such as rainfall are major contributing factors to the matric suction distribution, and thus the stability of unsupported trenches. Trench failures are labelled as the cause of many work-related injuries and deaths in the construction industry. Hence, the design of unsupported trenches should be done with utmost caution. The focus of this study is directed towards investigating the influence of rainfall infiltration on the stand-up time of unsupported vertical trenches excavated in unsaturated coarse- and fine-grained soils. For this, a series of numerical analyses were carried out to estimate stand-up time of unsupported vertical trenches considering possible practical scenarios such as various rainfall intensities and groundwater table depths, impermeable membranes on the ground surface, and tension cracks. The commercial geotechnical modelling software, GeoStudio was used in this study to simulate excavation, redistribution of pore-water pressure due to excavation, rainfall infiltration, and slope stability analysis. [ABSTRACT FROM AUTHOR]

This study focuses on the impact of relative density on the bearing capacity of unsaturated sand using both theoretical predictions and measurements from physical modeling tests. The theoretical predictions incorporate the effective stress, quantified using the suction stress concept and friction angles obtained from direct shear tests on unsaturated sand specimens at different relative densities and degrees of saturation, into conventional bearing capacity equations. The suction stress values inferred from the failure envelopes were found to match well with values predicted from the soil-water retention curves for sands with different relative densities. Moreover, the bearing capacity values measured in physical modeling experiments involving loading of a circular footing atop unsaturated silty sand layers having different initial degrees of saturation matched well with the predicted bearing capacity values from an effective-stress based model. As expected, the bearing capacity was greater for soils with increasing relative density, but an interesting observation is that a transition from general to local shear failure occurred at a certain combination of relative density and degree of saturation. For the silty sand tested, this transition occurred at a relative density of 0% for degrees of saturation between 4 and 16% and at a relative density of 40% for degrees of saturation between 30 and 90%. General shear failure was always observed at relative densities of 70 and 90%. [ABSTRACT FROM AUTHOR]

Periodic wave barriers have been widely used to mitigate ambient vibration. However, almost all the studies on the performance of periodic wave barriers are conducted under the assumption that soil is a single-phase or saturated medium. In fact, soil often consists of three phases: solid, liquid and gas, and it is more reasonable to be considered as an unsaturated soil. Existing research demonstrates that the dynamic properties of unsaturated soil have been significantly changed by gas phase, or the dynamic performance of unsaturated soil is completely different from that of single-phase soil and saturated soil. Especially, the dynamic performances of unsaturated soil cannot be approximated by the two extremes (saturated soil and single-phase soil). In this paper, the feasibility of vibration mitigation in unsaturated soil by periodic pile barriers is numerically validated. Firstly, based on the periodic theory, the complex band structures of P-SV waves in the periodic pile-unsaturated soil system are calculated. The influence of the saturation on the complex band structures is also investigated. Secondly, a numerical model for analyzing ambient vibration isolation is established. The responses of the numerical model are carried out in both frequency and time domains. The results indicate that periodic wave barriers in unsaturated soil can be designed with a wide attenuation zone covering the dominant frequencies of P1 waves, which is just a dream in saturated soil. Furthermore, S waves can also be greatly shielded in the target band. The present study removes the obstacles for the vibration mitigation in unsaturated soil by periodic pile barriers. [ABSTRACT FROM AUTHOR]

A multi-exponential function (ME) is proposed to depict the highly nonlinear soil water retention curve and hydraulic conductivity function. Then, semi-analytical solution of pore-water pressure in an unsaturated infinite slope at steady state is derived using ME to depict soil hydraulic properties. The solution is verified with experimental and numerical results. It is found that ME can better describe the highly nonlinear hydraulic properties of soil than the single exponential function (SE), which is commonly-used previously. At steady state, the adoption of SE results in overestimating negative pore-water pressure (PWP; i.e., matric suction) by about 25 kPa and slope's factor of safety (FOS) by 100% under rainfall, but underestimating negative PWP by about 50 kPa under evaporation. The difference between PWP and FOS calculated by using SE and ME becomes more significant for soil with bimodal hydraulic conductivity function than that with unimodal one. This difference reduces at a larger slope angle and deeper depth. Moreover, this difference generally increases at a lower S ME /S SE , where S ME and S SE represent the suction at which the unsaturated hydraulic conductivity expressed by ME and SE equals the applied rainfall intensity or evaporation rate, respectively. When S ME /S SE is greater than 0.1, the difference basically diminishes. [ABSTRACT FROM AUTHOR]

An effective contamination screening process is essential for mitigating the risk of overlooking pollution during site investigations. While Electrical resistivity tomography (ERT) and portable X-ray Fluorescence (XRF) offer quick assessments of contaminated areas, there is a notable gap in research regarding ERT's application in the unsaturated soil layer, and portable XRF's use for screening polluted samples in chromium-contaminated sites. This study gathered soil pollution and electrical resistivity data from a decommissioned chrome salt factory, employing drilling, sampling, XRF, and ERT methods. Predominantly, sulfate and chromium emerged as the pollutants, with concentrations ranging from 19.24 to 12700.00 mg/kg for sulfate, 0.65 to 3000.00 mg/kg for Cr(VI), and 12.00 to 27800.00 mg/kg for total Cr, respectively. Polluted hotspots were identified by lower apparent soil resistivity compared to the background levels at corresponding depth. Notably, a significant inverse correlation was observed between sulfate and Cr(VI) concentration and soil resistivity, particularly with sulfate (R2 = 0.48) demonstrated through a power function fit at depths ranging from −4 to 0 m. The XRF analysis for total Cr concentration exhibited a significant correlation (Pearson's r = 0.67) with chemical analysis, confirming 1000 mg/kg as an effective screening threshold. In light of these findings, this study proposes a scientific procedure that integrates drilling, sampling, ERT, and XRF for soil contamination investigation. This framework aims to support similar site assessments, reducing the risk of overlooking contamination. [Display omitted] • ERT's efficacy in screening inorganic pollution for unsaturated soil was confirmed. • Portable XRF could identify Cr-polluted samples with a threshold of 1000 mg/kg. • A procedure that integrates multi-methods for soil investigation was proposed. [ABSTRACT FROM AUTHOR]

Granite residual soil is a special regional soil with special mineral composition and pore structure characteristics, which is easy to induce serious geological disasters or engineering problems, so it is particularly important to study its mechanical properties of unsaturated soil and its control mechanism. However, the effects of dry density and initial water content on soil–water characteristic curve (SWCC) and their mechanisms are still unclear. Therefore, samples with different dry densities (1.30 g/cm3, 1.50 g/cm3, 1.70 g/cm3) and initial water content (14 %, 20 %, 22 %) were set up in this paper. SWCC test was conducted on the two groups of samples under the humidification path and dehumidification path using filter paper method. Combined with scanning electron microscopy (SEM) test and pore-size distribution (PSD) test, the influence mechanism of different micro-pore structure on SWCC and hysteresis characteristics of granite residual soil was analyzed qualitatively and quantitatively. The results show that the samples with different dry densities basically coincide with each other in the high suction segment. The larger the dry density is, the smaller the range of transition zone in the low suction segment is. As the initial water content of the sample increases from 14 % to 22 %, SWCC changes from a single increase curve to a double increase curve, and the corresponding pore-size distribution curve (PSDC) changes from a trimodal curve to a bimodal curve. The SWCC of granite residual soil has obvious hysteresis effect, and the hysteresis area becomes smaller with the increase of dry density. The inflection point exists in the hysteresis area of SWCCS with higher initial water content. The distribution range of macropore is determined by dry density, and the distribution range of small pore is determined by initial water content. The transformation of SWCC from a single increase curve to a double increase curve is mainly controlled by the distribution range of small pores. The bottleneck effect in the migration process of pore water in the soil and the pore redistribution during water intake and water loss are the main reason for the hysteresis of SWCC. The results of this work provide some guidance for the study of unsaturated soil mechanical properties of granite residual soils. [ABSTRACT FROM AUTHOR]

This is a review of the papers written by the author with co-researchers, which have been published in Soils & Foundations and related publications. The contents of the papers are related to experimental and theoretical aspects of geomechanics, namely, the constitutive modeling of cohesive and sandy soils, the governing equations of three-phase materials, and analyses of the behavior of geomaterials and grounds. The following topics are included in the papers: effective stress, skeleton stress, constitutive models of clayey and sandy soils and soft rocks, material instability, strain localization, consolidation, bearing capacity, excavation problems, governing equations of multi-phase geomaterials, liquefaction, unsaturated soil, seepage-deformation coupled analysis, gas hydrate-contained soil, internal erosion, the material point method (MPM), and X-ray CT for geomaterials. [ABSTRACT FROM AUTHOR]

• We present a novel fiber-optic suction sensor for total suction measurement in unsaturated soils. • The measurement range (5–300 MPa), accuracy (±3.5 MPa), and response time (<10 mins) of the sensor were determined. • The changes in temperature, relative humidity, and total suction during evaporation can be effectively captured by sensors. • Fiber-optic suction sensor has potential for in-situ, long-term, and quasi-distributed suction monitoring. Measurement of the soil water suction is important for investigating geotechnical problems and mitigating associated risks; however, conventional high-range suction measurement techniques have some limitations for accurate, long-term, and quasi-distributed suction measurement in the field. Fiber-optic humidity sensors provide a viable solution due to their unique properties. Here, we present a novel microfabricated fiber-optic suction sensor for measuring the suction of water in unsaturated soils. We evaluated the performance of the sensor on four bentonite–sand mixtures by comparing it with two laboratory suction measurement methods (chill-mirror hygrometer, salt solution vapor equilibrium) and a capacitive relative humidity sensor. We determined that this sensor has a measurement range of 5–300 MPa with a root mean square error of less than 3.5 MPa, and a response time of 2–9 min over the tested suction variation range (6.5–80.5 MPa). The results of the evaporation model test showed that three fiber-optic sensors installed at different depths of bentonite could effectively capture changes in temperature, relative humidity in soil pores, and total suction during evaporation. Together, these results demonstrate the great potential of the fiber-optic suction sensor for in-situ, long-term, and quasi-distributed suction monitoring. [ABSTRACT FROM AUTHOR]

The settlement has been reported to regularly be a fundamental factor in controlling the stability of geotechnical structures. Because the theory of elasto-plasticity is widely employed to predict the settlement, the elastic modulus is a vital parameter that is regularly utilized for theoretical calculation. Moreover, thermomechanical behaviour of unsaturated soils has recently received considerable attention because its importance in various energy geostructures applications, as well as in relation to climate change. This paper presents a coupled thermo-hydro-mechanical model of the elastic modulus characteristic curve (EMCC) that was developed based on the effective stress theories of unsaturated soils. The proposed model uses the soil–water characteristic curve (SWCC) and the modulus of elasticity under saturated conditions to predict the variation of modulus of elasticity with matric suction for unsaturated soils. The successful prediction performance of the proposed model is demonstrated by the comparison of measured and predicted outcomes for various published data sets in the literature related to different soil types. The proposed method was then used to present a parametric study considering the coupled impact of some important parameters on SWCC and EMCC. The analysis results indicated that the normalized elastic modulus rate increases with increasing matric suction, hydraulic conductivity, soil density, and with decreasing flow rates, temperatures, and normal stresses. [ABSTRACT FROM AUTHOR]

Expansive soils exhibit excessive volume increases upon contact with water, which can pose a serious threat to stability of structures and foundations. Therefore, it is essential to determine the swelling properties, e.g. maximum swelling pressure, of these problematic soils. We employed a feed-forward neural network algorithm trained with Levenberg–Marquardt, Bayesian regularization, scaled conjugate gradient, and genetic algorithm to build a network model capable of determining the maximum swelling pressure of clayey soils over a wide range of conditions. The models were developed based on a sufficiently large experimental dataset that takes into account key factors that influence the soil swelling. The results show that the feed-forward neural network algorithm trained with Bayesian regularization has the highest overall accuracy, as its predictions agree well with the experimental data. Besides, a simplified network model was developed to be used in cases of limited data availability. The developed model provides accurate predictions over a wide range of conditions and can serve as a valuable tool for researchers and engineers dealing with expansive soils. [ABSTRACT FROM AUTHOR]

The bimodal characteristic of water retention curves of dual-porosity soils has been fully recognized, however, the excessive number of fitted parameters in the existing models limits their application. This study develops a simple water retention model for dual-porosity soils that considers the self-similar characteristics of the pore size distribution (PSD) between macropore and micropore regions. In the model, we simulate the macropore PSD by differential VG model, which is then shifted and scaled to capture micropore PSD. It is hypothesized that the bimodal PSD can be obtained by superimposing the PSDs of macropore and micropore regions to derive the bimodal water retention curve (BWRC). The mercury intrusion porosimetry (MIP) tests and water retention tests are conducted on Nanyang clay with three different dry densities to evaluate the proposed BWRC. The results show that the new parameter can be determined by the MIP dataset and then used to predict the water retention behavior of dual-porosity soils well. Finally, we also explore the application of the proposed BWRC in predicting the hydraulic conductivity of dual-porosity soils without adding any extra parameters. [ABSTRACT FROM AUTHOR]

The analytical representation of the dynamic interaction between a strength composite (SC) pile and unsaturated soil under lateral excitations at the pile head is studied using three-dimensional continuum modelling. The fractional standard line solid (FSLS) model is utilized in the governing equation of unsaturated soil to characterize the flow-independent viscosity of the soil skeleton. Timoshenko beam theory is employed to describe the horizontal dynamic behaviour of SC piles composed of cement-soil mixing (CM) piles and precast high-strength concrete (PHC) pipe piles. A closed series form solution of the horizontal dynamic behaviour for an SC pile embedded in unsaturated soil under lateral excitation at the pile head is deduced theoretically. The solutions of the proposed model are compared with those captured from existing solutions. Finally, the effects of physical parameters in the SC pile-unsaturated soil system on the horizontal dynamic behaviour of the SC pile are evaluated with analytical examples and parametric study. The results indicate that the radius and elastic modulus of the SC pile have a critical influence on the horizontal dynamic behaviour of the SC pile, the FSLS model parameters are the key factors influencing the horizontal dynamic behaviour of the SC pile, and the horizontal dynamic behaviour of the SC pile varies with the change in liquid saturation of unsaturated soil. The research results provide theoretical references for the anti-vibration design and safe operation of SC piles. [ABSTRACT FROM AUTHOR]

Different types of soil water, such as bound water and capillary water, have distinct effects on the physicochemical and engineering properties of soils, particularly unsaturated clayey soils. Therefore, it is crucial to develop an accurate and physically meaningful experimental method for identifying and quantifying these components. This study pioneers the use of a multi-step kinetic model to identify and quantify different soil water components across a wide range of relative humidity (RH) using thermogravimetric analysis (TGA) data. To validate the determined kinetic parameters (i.e., activation energy, preexponential factor, and reaction model) and the identification and quantification results of soil water components, TGA with multiple heating rates, nitrogen adsorption method, cation exchange capacity measurement, and nuclear magnetic resonance (NMR) were performed on kaolin samples equilibrated under various RH conditions. These experimental results cross-validate the superior performance of the kinetic model in determining soil water components and predicting the thermal desorption behaviors of soil water. Based on the cross-validation results, the soil water components obtained from the kinetic analysis are further identified as tightly-bound, loosely-bound, and capillary water, which exhibit variations consistent with empirical soil water isotherm models. The T 2 cutoff value between bound and capillary water is determined to be 1.79 ms based on TGA and NMR results. The determined thermal kinetic parameters of different soil water components can exhibit their distinct retention mechanisms. The method and results in this study provide a new perspective on identifying different soil water components, as well as understanding the mechanism of soil-water interactions in unsaturated soils. • A method based on thermogravimetric and kinetic analysis is developed to identify and quantify soil water components. • Kinetic model can detect tightly-bound, loosely-bound, and capillary water in kaolin. • Different soil water components exhibit distinct kinetic triplets. • Bound water content increases with humidity regardless of capillary condensation. • NMR T 2 cutoff value between bound and capillary water is 1.79 ms. [ABSTRACT FROM AUTHOR]

Various electrochemical methods were used to understand the behavior of steel buried in unsaturated artificial soil in the presence of cathodic protection (CP) applied at polarization levels corresponding to correct CP or overprotection. Carbon steel coupons were buried for 90 days, and the steel/electrolyte interface was studied at various exposure times. The coupons remained at open circuit potential (OCP) for the first seven days before CP was applied at potentials of −1.0 and −1.2 V vs. Cu/CuSO4 for the remaining 83 days. Voltammetry revealed that the corrosion rate decreased from ~330 µm yr−1 at OCP to ~7 µm yr−1 for an applied potential of −1.0 V vs. Cu/CuSO4. CP effectiveness increased with time due to the formation of a protective layer on the steel surface. Raman spectroscopy revealed that this layer mainly consisted of magnetite. EIS confirmed the progressive increase of the protective ability of the magnetite-rich layer. At −1.2 V vs. Cu/CuSO4, the residual corrosion rate of steel fluctuated between 8 and 15 µm yr−1. EIS indicated that the protective ability of the magnetite-rich layer deteriorated after day 63. As water reduction proved significant at this potential, it is proposed that the released H2 bubbles damage the protective layer.