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The classical shotcrete design approaches often ignore the effect of suction, which enables higher strength and, accordingly, a cost-effective temporary support. This paper addresses a numerical approach to design an economic tunnel temporary support considering suction effect on the mechanical characteristics of a simulated soil and shotcrete. Various suction profiles at: fully saturated, high degrees of saturation, transition zone and residual saturated zone, at various shotcrete thicknesses (t), strength (cc) and cohesion values were analysed. Nonlinear stability–suction relationships were obtained. The role of suction on (t) for the simulated soil was more significant in the transition zone and then in the zone of high degrees of saturation. Reduction in (t) increased with suction increase until beyond the residual saturation. An increase of suction from 58.86 to 78.48 kPa (in the transition zone) at cc = 400 kPa was sufficient to cause a reduction of 61.4% in (t). [ABSTRACT FROM AUTHOR]

Biochar, a type of soil amendment, is widely used in heavy metal–polluted soil. It is also effective in enhancing plant performance. However, how biochar affects the soil heavy metal toxicity considering the plant–soil interactions is not well summarized. Therefore, this paper aims to review and summarize the effects of biochar on heavy metal availability in vegetated unsaturated soil. First, this review summarizes the effects of biochar on key parameters of unsaturated soil, including pore size distribution, water permeability, water retention curve, nutrient cycling and soil biota. Then, the mechanism of biochar for managing heavy metals in soil with vegetation is discussed, with a focus on both physical and biochemical aspects. Additionally, the impact of biochar-induced plant growth on the availability of heavy metals in the plant–soil system is explored. Finally, suggestions for future research and applications of biochar are provided. This paper supplies novel outlooks for further study and practice. [ABSTRACT FROM AUTHOR]

Geotechnical projects are typically initiated with an unsupported vertical trench (UVT) in unsaturated soils. In this case, it is fundamental to consider the contribution of soil suction toward the shear strength and hydraulic conductivity of soils when analyzing the stability of UVTs. The soil–water characteristic curve (SWCC) is a vital tool for estimating the variations of shear strength and hydraulic conductivity of soils with soil suction. In this study, numerical analyses were conducted to investigate the influence of SWCC on the safe height and stand-up time of UVTs in sandy and glacial till materials. SWCCs were established using three SWCC fitting models based on experimental data. The analysis results demonstrate that it is essential to understand the critical differences between the SWCCs obtained using different fitting models and their influence on the safe height and stand-up time of UVTs, rather than simply comparing the estimates. [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.)

The Global Digital Systems Ltd. (GDS) unsaturated soil triaxial test system is used to determine the shear strength of unsaturated undisturbed silty clay soil and obtain the soil-water characteristic curve. The van Genuchten (VG) and Gardner (GD) models are used to fit the soil-water characteristic curve to predict and verify the shear strength of the soil. The results show a better fit for the GD than the VG model. The shear strength of the soil increases with an increase in the matric suction, but the rate of increase is relatively low. The most significant influence of the matric suction on the soil strength is observed at less than 150 kPa. The influence of the matric suction on the shear strength of unsaturated silty clay mainly depends on the total cohesion. The soil shear strength value predicted by the GD model is conservative, but the predicted value tends to approach the measured value with an increase in the matric suction. [ABSTRACT FROM AUTHOR]

Since unsaturated soil conditions are normally experienced above the groundwater table, most treated or stabilised soils for roadworks, earth dams' embankments, landfill sites, hydraulic barriers etc. could be regarded as existing in this region. The soil–water characteristic (or retention) curve (SWCC) is a useful conceptual tool by which an evaluation of unsaturated soil's property functions and corresponding macro-scale behaviour (strength, volume change, hydraulic conductivity, fluid flow, diffusivity, etc.) can be carried out. Hence, an examination of some of the various factors that could affect the hydraulic or water retention property of the stabilised soil is very vital both for laboratory studies and field practice. However, a thorough assessment of the water retention behaviour of stabilised soils can be understandably limited sometimes. This could be partly due to some of the perculiar conditions associated with soil preparation methods, soil type, soil-stabiliser mix proportion used, curing conditions, method of compaction, durability assessment modalities and other logistical issues surrounding either laboratory instrumentation or in-situ application. This article presents a critical and comprehensive review of these factors on the stabilised soil's water retention behaviour and also provides a systematic understanding of the mechanisms of stabilisation occurring at the micro- and macro-mechanical levels. Recommendations are also made to stimulate further discussions on the synthesis of SWCC of stabilised soils vis-à-vis factors influencing them with possible interpreted engineering behaviours such as shear strength and soil consolidation. [ABSTRACT FROM AUTHOR]

The osmotic technique in geotechnical testing of unsaturated soils is a promising technique to control soil-water potential. This technique is an alternative to the axis-translation technique. In this technique an aqueous polyethylene glycol (PEG) solution is interfaced with a selectively permeable membrane. The geotechnical literature has regularly referred to membrane effects which tend to reduce the achieved matric suction in relation to that theoretically attainable by consideration of the osmotic pressure of the bulk PEG solution. In this review, the literature on membrane science is studied in order to identify potential causes for these membrane effects. Concentration polarisation, membrane fouling and reverse solute draw are the underlying causes of these membrane effects and should be given consideration in the geotechnical osmotic testing literature. A better understanding of membrane science and its application to geotechnical osmotic testing can aid in the optimisation of osmotic testing and the systematic improvement of the technique. [ABSTRACT FROM AUTHOR]

According to the actual situation oflandfill site, it is assuming a three-layered system of compacted clay liner, unsaturated aquifer underlain the landfill, and one-dimensional governing equations for leachate transport in each layer of three-layered system are established. The governing equation are solved by numerical methods, which taken into account the effects of equilibrium nonlinear sorption of compacted clay liner and nonlinear sorption of unsaturated soil. The numerical simulation are carried out by varied the parameters, and the results show that the nonlinear sorption of unsaturated soil is more sensitive to pollutant transport than nonlinear sorption in compacted clay liner, and it became the controlling factor of pollutant transport in unsaturated soil. The nonlinear sorption parameter bu effects on the pollutant transport are more obviously than the nonlinear sorption parameter Sml· In the meantime, degree of saturation of unsaturated soil is the controlling factor of pollutant transport. [ABSTRACT FROM AUTHOR]

An extension of slip line theory to unsaturated soils is presented in this research and applied to the problem of stability of slopes in unsaturated soils. The matric suction was then introduced and applied to governing equations based on the well-known Bishop effective stress concept. In this regard, the van Genuchten model was utilized to estimate the effective stress parameter required for measuring effective stress. The influence of the soil matric suction on the stability of slopes was investigated for a variety of soils under steady-state evaporation and infiltration, i.e., distribution of the matric suction was assumed to remain constant with time. In addition, a measure of stability in terms of some stability factors was introduced. [ABSTRACT FROM AUTHOR]

In the current paper, we explore the effect of temperature changes in seasonal frozen areas on the strength parameters of unsaturated soil under low matric suction, as well as the impact of the parameters under different temperatures on an overwintering deep foundation pit in unsaturated soil under low matric suction. In particular, we take unsaturated silty clay in its original state as the research object and Global Digital Systems Ltd. (GDS) unsaturated silty soil as the triaxial tester to perform triaxial shear tests on unsaturated silty clay under several temperatures. The strength parameters obtained from the laboratory tests are then combined with Abaqus numerical simulations to analyze the stress and deformation of the overwintering deep foundation pit supporting structure in unsaturated soil within seasonal frozen areas. Experimental results under low matric suction demonstrate that temperature variations have a greater effect on the total cohesive force of unsaturated silty clay, yet their impact on the effective internal friction angle is relatively small. The influence of the frost heaving force produced by the freezing of the unsaturated soil on supporting structures is observed to be greater than the earth pressure during the freeze-thaw process. When the unsaturated soil is frozen, the horizontal frost heaving force of the retaining structure at the top and bottom of the foundation pit is relatively large. Furthermore, the selection of strength parameters for unsaturated soil during the freeze-thaw process has a great influence on the surrounding environment of the deep foundation pit, as well as the stress and the deformation of the supporting structure. Numerical simulations using strength parameters under different temperatures (20°C, - 15°C, 20°C -15°C--20°C) resulted in the following general trend for the horizontal displacement of the retaining structure, the horizontal force of the pile side and the displacement of the top of the deep foundation: simulation results of frozen soil parameters > simulation results of dynamic changes of parameters with temperature > simulation results of normal temperature soil parameters. [ABSTRACT FROM AUTHOR]

Tensile and shear behaviour of unsaturated soil have been investigated separately in the past. However, there is no comprehensive study on the transition from tensile to shear failure in compacted clayey soils. A series of uniaxial tensile, direct shear and triaxial compression tests were conducted on compacted Regina clay specimens to investigate the strength mobilisation and failure mode under different loading paths. It was observed that the matric suction increases the apparent cohesion and tensile strength of the material. At a given constant matric suction, the compacted clay displays a transition from tensile to shear failure with increasing confining stress which can be approximated by a bilinear failure envelope encompassing the transitional behaviour. The friction angles in tensile regime are greater than those in compressive regime, which can be explained by the transitional change in failure surface morphology from tensile ruptured to shear smoothened one. [ABSTRACT FROM AUTHOR]

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]

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]

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]

High intensity rainfall leads to slope failures that are initially unsaturated. Rainfall is the main triggering factor for the slope failure; however, the denseness of the soil with associated soil properties has not received adequate attention on the stability of the slopes. In this study, the finite difference analysis of transient water flow through unsaturated–saturated soil is carried out to study the effects of rainfall intensity and duration on pore pressure generation, degree of saturation, slope stability and shear strain increment during rainfall event. A parametric sensitivity analysis is performed considering three rainfall intensities applied over the soil slopes consisting of three different soil states namely loose, medium and dense. Results indicate that the rainfall affects the stability of loose and medium soil slopes much as compared to the dense soil slope. The rain-induced instability is much more in loose soil slope as compared to the medium soil slope. [ABSTRACT FROM AUTHOR]

The air-entry value and residual state suction are two critical variables obtained from the soil–water characteristic curve (SWCC). An accurate determination of these variables is essential for the prediction of unsaturated soil properties. Currently, these variables are obtained by a conventional graphical method, which is implemented to the fitted SWCC. The graphical method is associated with subjective uncertainty, leading to inconsistent results. This study presents a new method to determine the air-entry value and residual state suction. Explicit equations are established with respect to four common van Genuchten (vG) SWCC model classes. The relationships between the air-entry value and fitting parameters are analysed using a compiled database of varying soil textural classes. The proposed equations outperform the graphical method by avoiding subjective judgements. Finally, ANOVA and sensitivity analyses are conducted to compare the advantages of the existing model classes in determination of the air-entry value. [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.)

Copyright of Journal of Northeastern University (Social Science) / Dongbei Daxue Xuebao (Shehui Kexue Ban) is the property of Dongbei Daxue 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.)

Unsaturated soils are frequently encountered in various civil engineering projects; however, their dynamic behaviour is still unexplored. Present study evaluates the influence of matric suction, initial static loading, and load repetition on dynamic response of unsaturated cohesive soil (CH type). A series of cyclic triaxial tests have been performed on Ahmedabad-based cohesive soil under as-compacted conditions (unsaturated). Matric suction of soil is obtained using filter paper method at varying dry density and water content to characterise the behaviour of unsaturated soil. Application of initial static axial strain exhibited a unique stiffness response in loading and unloading phases of cyclic testing, and significantly impacted the cyclic strength response of unsaturated cohesive soil. The initial static axial strain in cyclic triaxial testing represents the conditions of a highway/railway embankment, where the embankment load on soil acts like initial static loading and passing vehicles like cyclic loading on soil. Load repetition exhibited significant degradation in shear modulus of cohesive soil under cyclic loading conditions. [ABSTRACT FROM AUTHOR]

Fluid infiltration into unsaturated soil is of vital significance from many perspectives. Mathematically, such transient infiltrations are described by Richards' equation: a nonlinear parabolic Partial Differential Equation (PDE) with limited analytical solutions in the literature. The current study uses separation of variables and Fourier series expansion techniques and presents new analytical solutions to the equation in one, two, and three dimensions subject to various boundary and initial conditions. Solutions for ID horizontal and vertical water infiltration are derived and compared to numerical finite-difference method solutions, whereby both solutions are shown to coincide well with one another. Solutions to 2 and 3D vertical water infiltration are derived for constant, no-flow, and sinusoidal boundary and initial conditions. The presented analytical solutions are such that both steady and unsteady solutions may be obtained from a single closed form solution. The solutions may be utilized to test numerical models that use different computational techniques. [ABSTRACT FROM AUTHOR]

The development of infrastructure in an urban city, such as road widening and building work, will inevitably result in the removal of trees. Therefore, innovative solutions such as containerised tree in the manner of increasing the portability of trees would be necessary to facilitate efficient transplanting in order to maintain a sustainable green urban environment. Differences in soil hydraulic properties between soil mixture and in situ soil naturally occur in tree planting, but this difference becomes more important in the use of container due to the limited tree root movement. The objective of this research was to examine the effects of soil hydraulic properties between the soils inside and outside of the container with focus being placed on moisture infiltration both in and out of the container. Field instrumentation and laboratory tests were carried out together with parametric study using numerical model. The results suggested that the higher the ratio between the saturated permeability of the soils inside and outside the container, the lower was the ability of water to flow in and out of the container. [ABSTRACT FROM AUTHOR]

Geotechnical design for unsaturated soils requires an understanding of their fundamental characteristics. In this paper, in order to study the monotonic, cyclic and post-cyclic behaviour of an unsaturated clayey soil, monotonic and cyclic triaxial tests were carried out on Tehran oil refinery’s disturbed unsaturated clayey soil (CL). Tests were conducted on the specimens with different initial matric suctions and net confining pressures with the same dry density under constant pore-air pressure and undrained conditions for water. No reconsolidation was allowed after cyclic loading of specimens. Tests results showed that cyclic loading degrade the undrained shear strength and deformation modulus of specimens during the post-cyclic monotonic loading. It was observed that shear modulus degradation is more pronounced than that of the shear strength due to cyclic loading. Also, the shear strength and shear modulus of soil generally increased with increasing the net confining pressure and initial matric suction. [ABSTRACT FROM PUBLISHER]

New calculation method for determining Soil water characteristic curves (SWCC) according to soil particle analysis tests based on BP neural network algorithm and Arya-Paris model. BP Neural network algorithm was used to simulate parameter model of soil particle size distribution based on soil particle analysis tests, and used to simulate the function relationship between soil volumetric water content and matrix suction which were calculated based on Arya-Paris model. The function expression of SWCC can be obtained by BP neural network algorithm based on Arya-Paris model. The result show that this method was applicability and reliability. [ABSTRACT FROM AUTHOR]

A major concern resulting from the increased use and production of natural gas has been how to mitigate fugitive greenhouse gas emissions (predominantly methane) from natural gas infrastructure (e.g., leaky shallow pipelines). Subsurface migration and atmospheric loading of methane from pipeline leakage is controlled by source configurations and subsurface soil conditions (e.g., soil heterogeneity and soil moisture) and are further affected by atmospheric conditions (e.g., wind and temperature). However, the transport and attenuation of methane under varying subsurface and atmospheric conditions are poorly understood, making it difficult to estimate leakage fluxes from methane concentration measurements at and above the soil surface. Based on a series of controlled bench-scale experiments using a large porous media tank interfaced with an open-return wind tunnel, this study investigated multiphase processes controlling migration of methane from a point source representing a buried pipeline leaking at fixed flow rate (kg/s) under various saturation and soil-texture conditions. In addition, potential effects of atmospheric boundary controls, wind (0.5 and 2.0 m s −1 ) and temperature (22 and 35 °C), were also examined. Results showed the distinct effects of soil heterogeneity and, to a varying degree, of soil moisture on surface methane concentrations. In addition, results also showed the pronounced effects of wind and, to a lesser degree, of temperature on surface methane concentrations in the presence of varying soil and moisture conditions. The observed subsurface methane profiles were simulated using the multiphase transport simulator TOUGH2-EOS7CA. Observed agreement between measured and simulated data demonstrates that for the conditions studied, multiphase migration of a multicomponent gas mixture (including methane) under density-dependent flow can be adequately represented with a Fickian advection-diffusion (or dispersion) model (ADM) framework. The dominant effect of saturation over the soil texture, could also be inferred from numerical characterization. [ABSTRACT FROM AUTHOR]

The evaluation of riverbank stability is a fundamental problem in flood risk management, representing a critical task for engineering practice. Soil heterogeneity together with initial and boundary conditions are among the crucial issues that should be considered to obtain an accurate solution of the problem. Generally, attention and efforts are mostly devoted to the soil characterization, the hydrometric level forecasts and the estimation of the rainfall intensity, while in situ measurements usually receive less attention. Nevertheless, suction and soil water content have a strong influence on the reliability of seepage and stability analyses. A preliminary study aiming at the design of a monitoring system for the measurement of soil moisture and suction in the unsaturated silty soils of a river embankment has been carried out, with the purpose of linking the collected data to the boundary conditions and hence obtaining a more accurate estimate of the riverbank probability of failure. Furthermore, a general outline of the research project, its methodology and application are presented in the paper. [ABSTRACT FROM AUTHOR]

Salt expansion is one of the major problems of subgrade involving saline soils. Salt expansion is induced by the crystallization of salt when the soil water content or temperature decreases. A case of salt expansion in subgrade composed by saline soil is introduced. It is located in G314 Road, which is one of the national highways in China, from Urumqi to Khunjerab. There is 3.40 ∼5.91% salt within 1.0 depth in the ground surface of the G314 (K587 + 035), which belongs to strong sulphate salty soil. The maximum salt expansion is up to 20 cm in G314 Road, which has a serious impact on the road. Salt expansion is majorly controlled by the salt crystallization and the transmission of water and salt. Based on the solute transport theory in porous media, the water flow theory and thermal conduction theory, the govern differential equations of coupled salt crystallization, salt transmission and water flow are established in this paper. The coupled water and salt transfer problem of saline soil is solved by a software named as COMSOL with the use of a secondary development module. To verify the method for simulating the coupled water and salt transmission process, the water and salt transfer process in a 1D soil column is simulated and the results are compared with the theoretical solution. The results show that coupled model of water and salt established in this paper can accurately predict salt migration and crystallization of saline soil. [ABSTRACT FROM AUTHOR]

In thin flexible pavements, unbound aggregate layers and subgrade, contribute largely to the rut formation of the pavement system. Therefore, realistic prediction of surface rutting requires models that can reliably capture the cumulative plastic deformation of pavement unbound materials under repeated loads. Here four models were evaluated to capture the accumulation of permanent deformation of two fine grained subgrade materials. The models were modified based on the time hardening concept allowing them to be used in a multistage repeated load triaxial (RLT) test procedure, in which a single specimen is exposed to a series of consecutive stress paths of varying magnitudes. The RLT tests were conducted on two non-plastic silty sand subgrade soils with different fines content and at four different moisture contents. The used triaxial testing system was capable of controlling the pore-air and pore-water pressures of the specimen and therefore the permanent deformation tests were carried out with controlled matric suction of the soil samples throughout the test. An effective stress approach was therefore used in the modelling. Using the test data, the model parameters were determined using a parameter optimisation algorithm and the qualities of fits achieved was analysed and compared through goodness-of-fit statistics. In general, the four permanent deformation models were found to work satisfactorily in capturing the accumulation of the permanent deformation of the tested subgrade materials. It was concluded that the multistage RLT test procedure has the potentials to be used for characterizing the permanent deformation behaviour of subgrade soils. This can considerably reduce the effort and time required for permanent deformation characterization of subgrade materials. [ABSTRACT FROM AUTHOR]

This paper evaluates the synergistic effects of water content and fine fraction on shear behavior of unsaturated fouled ballast by performing a series of triaxial compression tests and water retention tests on fresh and fouled ballasts in unsaturated conditions. As the results, it was revealed that soil-water characteristic curves and relationships between degree of saturation and peak shear strength were seriously affected by intrusion of fouling materials into fresh ballast, and that the decreasing trend of peak strength becomes more remarkable in such a case where both water content and fine fraction increase. These results indicate that for the precise prediction of the long-term performance of transportation infrastructures and the evaluation for mechanical property of railroad ballast under repeated train passages, it is important to take into account the synergistic effects of water content and fine fraction on the deformation-strength characteristics of ballast in accordance with the degree of ballast fouling. [ABSTRACT FROM AUTHOR]

Paper approaches the problem of considering the unsaturation of soils above water table in the slope stability analysis, condition for obtaining realistic results in both cases of rainfall infiltrating into the soil mass and drainage for improving soil stability. It presents in its first part a brief review methods related to unsaturated stress analysis applied for slope stability analysis, such as Unsaturated phi-b, Unsaturated Fredlund, Unsaturated Vanapalli, Unsaturated Khalili and Unsaturated Vilar model. These methods are estimating in different manners the shear strength depending on soil unsaturated conditions. These methods are applied in the second part of the paper in a case study, presenting a site affected by landslides located in Cluj-Napoca, Romania. For the slope stabilization a siphon drain system has been proposed and installed. An experimental program started and is ongoing on site, compromising site monitoring of suction using jet fill tensiometers and laboratory testing. Site measurement of suction in presence of drainage system was used for perform slope stability analysis using SVSlope software and the embedded methods for estimating the increase in soil shear strength when passing from saturated to unsaturated state. [ABSTRACT FROM AUTHOR]

The performance of transportation networks is critically dependent on the performance of cutting and embankment slopes. An instrumented embankment has been established at Nafferton farm in North East England to investigate the response of an embankment to changing climatic conditions. Higher pore water pressures (near to hydrostatic) were observed during winter months (typically January) falling back to lower values in March. The pore water pressures showed generally positive values in the upper 3 m of the embankment although suctions existed at 4.5 m depth. Soil water retention curves (SWRC) are essential to understand the changes in water content and suction that can take place during seasonal cycles and during extreme weather events. SWRCs for the embankment soil have been measured in the laboratory using novel high suction tensiometer based equipment. The results confirm that wetting and drying paths for the soil show significant hysteresis. The major differences occur in the first cycle of drying and wetting and smaller differences are seen in subsequent scanning curve paths. [ABSTRACT FROM AUTHOR]

The paper presents stability and seepage analysis performed in unsaturated regime to take care of the infiltration through the dam. Seepage analysis is divided into two stages: steady state analysis and transient analysis. It will be determined the pore water pressure load, the ground water level, estimate the flow (path and quantity) and also, an advanced analysis considering rainfall and rapid drawdown. Van Genuchten model will be used for the unsaturated soil. [ABSTRACT FROM AUTHOR]

This study aimed at proper characterization of the microstructure and unsaturated properties of undisturbed red soil with white net-like veins from the Chenshan laterite section in Xuancheng City, China. The chemical composition and micromorphology of the white veins and red matrix were studied using a scanning electron microscope, an energy dispersive spectrometer, and digital image processing. Then a series of soil-water characteristic curves (SWCCs) and shear strength experiments were performed on undisturbed net-like red soils using triaxial stress path testing, and empirical expressions commonly adopted for geotechnical engineering applications were used to represent measured SWCCs. A detailed comparison of microstructures in undisturbed soils and on failure planes was undertaken. The results showed that the white veins and red matrix clearly appeared as distinct features at both macro and micro levels. More quartz amassed in the white vein, and more intense depletion of Fe oxide occurred in the red matrix. Measured SWCCs at drying and wetting behaved with hydraulic hysteresis. Change in the axial strain did not match that in the volumetric strain. The stress-strain curve obtained from the unsaturated triaxial shearing test showed the characteristic of strain softening; the peak deviator stress increased with increments of the confining pressure and suction. Pores less than 5 nm2 in size were much more common on the shear failure plane than in the undisturbed soil, whereas pores larger than 50 nm2 were fewer. The major axial angle of soil pores showed a dominant orientation after shearing. In addition, the roundness and fractal dimension of pore outlines on the shear failure plane were greater than those in the undisturbed soil. These results reveal that microstructure and suction play important roles in the unsaturated mechanical behaviors of net-like red soil. [ABSTRACT FROM AUTHOR]

In the present study the numerical model of the pile embedded in the unsaturated substrate was proposed and tested. The solutions complemented the state of knowledge of the single pile loaded by bending moment in its head, horizontal forces and the environmental influences. The investigated reliability problem was defined by the union of failure events defined such: the excessive horizontal displacement of the pile head, the rotation beyond the limit state and maximum tensile stress in a pile material. The analytical model of water flow in the unsaturated soil was used. The profile of suction allowed to estimate the complete description of layers above the groundwater table. Flac 3D was used for modelling presented task. The main part of problem is reliability analysis of a single pile in complex environment. Due to the lack of analytical solutions the computations were done by the method of response surface in conjunction with based on polynomials regression. The Ditlevsen's bounds were taken into account for the calculation of system's reliability. [ABSTRACT FROM AUTHOR]

In this study, the loading behaviour of a small scale, single pile in unsaturated clayey soil was examined through a series of laboratory pile load tests and numerical analysis. To estimate the maximum bearing load of the pile in an unsaturated soil, the pile load tests were carried out at different water contents. At the same time, a finite element model was developed to simulate nonlinear response of a small scale single pile under a static axial loading. All parameters used in numerical analysis were obtained in laboratory. The results of numerical analyses conducted by finite element method were compared with the results of the physical pile load tests. The general trends of settlement obtained by the numerical analysis are consistent with pile load test results. With increasing soil water content, the dilatancy angle decreases, resulting in a decrease in ultimate bearing capacity. [ABSTRACT FROM AUTHOR]

Unsaturated soil shear strength can be determined using e ective stress relation that depends on the effective stress parameter. Several models have been developed in the past few years to estimate this parameter. In this research, the Gene Expression Programming (GEP) is used as an Artificial Intelligence (AI) method for developing a model to predict the e ective stress parameter, using effcient parameters. The principal advantage of the GEP approach is its ability to generate powerful prediction equations without any prior assumption on the possible form of the functional relationship. The input terminal set consists of net confining pressure, suction, Soil Water Characteristic Curve (SWCC) fitting parameter, bubbling pressure, residual and saturated volumetric water content. The output terminal set has one member, which is the effective stress parameter. An experimental database obtained from the literature is employed to develop the model. Comparison of the model prediction with the actual data, as well as other investigators, indicates a very good performance and ability of model. Sensitivity and parametric analyses are conducted to verify the results. It is also shown that soil suction is the most inuential parameter in the effective stress parameter of unsaturated soils. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the difference of influencing factors on soil-water characteristic curve (SWCC). Tested are four reconstructed specimens based on the moist tamping technology. Test results indicate that SWCC should be made up of the average in the disorder stage while the Fredlund and Xing model has been found suitable for testing.

PCSiWaPro® is a software tool developed by the TU Dresden which simulates water flow and contaminant transport in the unsaturated soil zone. Due to the increasing demand in computational efficiency for large numerical meshes, simulation runs needed to be accelerated. This acceleration was carried out by manual parallelization of parts of the software's simulation kernel. After identifying the most time-consuming sections of the code several numerical equation solver libraries were implemented and tested. Different concepts of software parallelization as well as different types of mathematical solving strategies were tested for their suitability for PCSiWaPro®. With the SAMG software, a multigrid solver developed by the Fraunhofer Institute for Algorithms and Scientific Computing, the largest reduction of simulation time could be achieved. [ABSTRACT FROM AUTHOR]

The landfill site was idealized as three-layer stratum composed of a compacted clay liner (CCL), a underlying layer and a layer of aquifer below the landfill. Based on Richards equation, the analytical solutions of volumetric water content in both CCL and underlying layer were obtained under steady-state seepage. According to the contaminant migration mechanism in the porous media, the one-dimensional computing model was established for contaminant migration in the three-layer strata including two unsaturated soil layers. The model considered nonlinear sorption of CCL and bio- degradation of contaminant migration process and bio-degradation of waste. The established mathematical model was used for carrying on the concrete computation on some hypothesis landfill sites. The studies on the calculation and analysis of variable parameters were conducted to examine the effect of all the related factors on the contaminant migration. The calculated results show that the sorption and bio-degradation of unsaturated soil have remarkable effect on the contaminant migration process, especially when the sorption and degradation of CCL are important controlling factors for contaminant migration process. When volumetric water content of unsaturated soil is large, the variation of volumetric water content has negligible influence on contaminant migration. [ABSTRACT FROM AUTHOR]

A simple model was proposed by Oh et al. (2009) to predict the variation of modulus of elasticity with respect to matric suction for unsaturated coarse-grained soils (i.e., sandy soils with plasticity index, Ip = 0). This model requires the modulus of elasticity under saturated condition (Esat) and the Soil-Water Characteristic Curve (SWCC) along with two fitting parameters (α and β). In the present study, this model has been extended and a general model has been proposed such that the modulus of elasticity can be estimated for all soils (i.e., both coarse- and fine-grained soils). The proposed model is developed using model footing and in-situ plate load test results of six different unsaturated soils. The study shows that there is a good comparison between the measured and the predicted modulus of elasticity with respect to matric suction for all the six soils whose plasticity index, Ip values are in the range of 0 to 16%. [ABSTRACT FROM AUTHOR]

The most common approach for remediation of unsaturated soils contaminated with volatile organic compounds (VOCs) is soil vapor extraction. Contamination in low-permeability fine-grained soils poses a significant technical challenge to in situ remediation efforts. The main objective of this paper is to evaluate prefabricated vertical drains (PVDs) as a method of increasing the effectiveness of the soil vapor extraction (SVE) process. The equivalent diameter for PVDs used for SVE applications was determined, and the radius of influence for PVDs were determined so as to measure the gas permeability for fine grained soil under differing conditions including densities, water content, and flow rates. This paper presents the discussions with regarding on the experiments using PVDs for contaminant recovery in the pilot-scale testing. The toluene tracer solution which is one of the oil contaminant BTEX (benzene, toluene, ethylbenzene, xylene) was used to evaluate contaminant remediation efficiency. The concentration of toluene from the extracted samples was measured in a sampling port with the elapsed time and flow rates after operating a PVDs system. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of the pore air flow in the soil slope stability analysis, a water-air two-phase flow model, based on the multi-phase flow theory, is proposed and with the model, the water-phase and air-phase seepages of the soil slope in the stable seepage and rainfall situations are simulated. The soil slope safety coefficients are obtained according to the simulated pore air pressure and pore water pressure. The calculation results show that in the stable seepage situation, the influence of the pore air pressure on the soil slope stability can be neglected, while in the rainfall situation, the pore air pressure generated in the unsaturated zone will reduce the safety coefficient, and the larger the distance between the slip surface and the underground water level is, the greater the influence of the pore air pressure on the soil slope stability will be. [ABSTRACT FROM AUTHOR]

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Many types of chemical substances have been used as tracers to estimate the migration of contaminant in a porous media. Inorganic ionic compounds have been applied extensively as hydrogeologic tracers. Sodium chloride is generally used as a tracer since this common salt does not degrade or get removed from the system. Movement of tracer could be described as migration of a non-reactive constituent. A tracer transport numerical model was developed according to the advectivedispersive contaminant transport equation in unsaturated porous media. The governing equation was solved numerically and coded in MATLAB program. The objectives of this study were to develop a model for estimating the non-reactive constituent transport in the unsaturated porous media and to determine the impact of ionic strength of tracer and the effect of the thickness of porous media. The experiments were conducted with two different sodium chloride tracer concentrations (low strength-200 mg/L and high strength-500 mg/L) and for two different soil depths (5 and 20 cm). The observation and simulation data indicate that the interference from soil background concentration is significant, provided that the high strength tracer is applied. As expected, the tracer transport in the thick layer took longer elapse time than in the thin layer. The simulation results using the developed model corresponded very well with the observed data. [ABSTRACT FROM AUTHOR]

Hydraulic conductivity of unsaturated soils is often used in environmental engineering and geotechnical engineering, where stress usually exists. The compressive stress effect on unsaturated hydraulic conductivity was analyzed, and the expression of unsaturated hydraulic conductivity can be derived from the fractal model for the pore-size distribution. It is shown that the fractal dimension of the pore-size distribution does not change with compressive stress, and the variation of unsaturated hydraulic conductivity due to compressive stress occurs through changes in saturated hydraulic coductivity and the air-entry value. [ABSTRACT FROM AUTHOR]

Chemical oxidation has been applied to remove soil contaminants and thereby reduce human and ecological risks from contaminated sites. However, few studies have been conducted on the natural infiltration of oxidant solutions into unsaturated soil. Moreover, the infiltration capacity of oxidant solutions at various concentrations in unsaturated soil has not yet been studied. This study investigated the natural infiltration tendency of oxidant solutions like hydrogen peroxide (H 2 O 2), potassium permanganate (KMnO 4), and sodium persulfate (Na 2 S 2 O 8), in sand and sandy loam. Cumulative infiltration was recorded from a soil column equipped with a Mariotte reservoir. The infiltration rate, sorptivity, and unsaturated hydraulic conductivity were obtained from the cumulative infiltration results. Na 2 S 2 O 8 showed the highest infiltration rate in both sand and sandy loam, and the infiltration of Na 2 S 2 O 8 increased as the concentration was increased from 0.05 to 1%. However, the infiltration of KMnO 4 and H 2 O 2 solutions was governed more by chemical reaction behavior than by liquid physical properties or soil hydraulic properties. The production of oxides and gas due to reaction induced clogging in flow paths, resulting in less infiltration. Infiltration of H 2 O 2 at concentrations greater than 0.5% was not observed in sand or sandy loam due to gas formation and swelling. • Infiltration of oxidants in soil was affected by soil texture and reactivity with organic matter. • Infiltration of Na 2 S 2 O 8 was highest in both sand and sandy loam. • The chemical nature of H 2 O 2 and KMnO 4 reduces soil infiltration. [ABSTRACT FROM AUTHOR]