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

Accurate knowledge of hydraulic properties of unsaturated soil is vital to modelling water and solute transport process and addressing soil salinisation problems. Due to the defect that the van Genuchten (VG) model cannot represent soil water characteristics (SWC) during the drying stage, we have introduced a modified model, which combines capillary flow with film flow models to describe the unsaturated hydraulic conductivity. The capillary SWC is obtained by assuming the specific water capacity function with lognormal distribution. The film SWC is modified using the logarithmic nonlinear expression by introducing a modification coefficient into the Campbell equation, and the film relative hydraulic conductivity (RHC) is obtained based on the logarithmic nonlinear relationship. The calculated modification coefficient values range from 0.99 to 2.49. Finally, the proposed model's rationality and applicability are validated through root mean square error (RMSE) analysis with measured values and comparison with the VG model. While the calculation RMSEs of SWC in the two models are basically consistent, the RMSEs of RHC in the proposed model are around 1–10 times smaller than those of the VG model, indicating its superiority in calculating the hydraulic conductivities over the entire matric head. Highlights: A modified model describing the variably saturated hydraulic conductivity is presented combining the capillary with film flow model. A logarithmic nonlinear expression with a modification coefficient is introduced in the film soil water characteristic model. The fitting parameters for relative hydraulic conductivity are determined and root mean square errors are chosen for evaluating the modified model. [ABSTRACT FROM AUTHOR]

When remediating contamination in the vadose zone, which is a potential source of continuous groundwater and surface water pollution, technical challenges are often encountered. In this study, the feasibility of delivering sodium persulfate (SPS) oxidant to unsaturated soils was explored by integrating porous pipes, commonly used in agriculture, with in-situ chemical oxidation (ISCO). An evaluation of the operating characteristics of the pipe determined a recommended influent rate of < 0.1 L min−1 and an initial influent water pressure < 20 kPa to prevent percolation pore enlargement. Two-dimensional sandbox experiments revealed that pulse infiltration at an influent rate of 0.05 L min−1 was effective in creating matrix flow and lateral movement, minimizing preferential flow induced by continuous infiltration. Application of SPS (10% by wt.) under these conditions resulted in approximately 90% wetting of the sandbox area SPS flow at the experimental time that infiltrated from the pipe. After a 14-d post infiltration resting state, residual SPS concentrations ranged from 6,000 -12,000 mg/kg in soil, with soil pH levels of 3–4, ORP around 600 mV, and 40–60% decreases in soil organic carbon. This developed method helps retain the oxidant and promote chemical reactions, making ISCO a viable option for remediating unsaturated soil contamination. [ABSTRACT FROM AUTHOR]

AbstractExcess pore water pressure (EPWP) induced by shield tunneling has a significant influence on the stability of the tunnel face, post-construction settlement, and the mechanical behavior of the tunnel lining. However, the three-dimensional and unsaturated property of the soil field is seldom considered in current research. Considering the non-uniform radial convergence model, a modified three-dimensional displacement solution induced by shield tunneling was established first. Then based on unsaturated EPWP elastic theory, a reliable and efficient method is developed to expedite the evaluation of EPWP distribution in three-dimensional saturated and unsaturated clay soil. The validity of the method is confirmed through comparison with field test and numerical outcomes. The analysis examples demonstrate that negative and positive EPWP are generated above the tunnel crown and beneath the tunnel invert, respectively. In the vertical direction, the negative EPWP exhibits a decreasing trend ahead of the heading face and an increasing trend behind it. Along the longitudinal direction, the influence zone of EPWP extends to 1D ahead of and 6D behind the heading face. With the decrease of soil saturation, the EPWP values tend to diminish. The maximum EPWP values observed in saturated conditions can be 16.13 times higher than those under unsaturated conditions. [ABSTRACT FROM AUTHOR]

Taking Bingham slurry as the research object, an infiltration diffusion model of Bingham slurry in unsaturated soil is established based on the seepage theory of unsaturated porous media, which takes into account the displacement effect and the viscosity time-varying characteristics of slurry. Combined with the seepage motion equation, relevant boundary conditions and interface conditions, the Bingham slurry diffusion equation considers grouting parameters and mechanical parameters is obtained. The research results are degraded to the saturated state and compared with the existing theoretical results. Numerical examples are used to study the influence of the above parameters on grouting pressure and slurry diffusion radius, then the diffusion mechanism of Bingham slurry is verified and analysed by model test. The above analysis and test results confirm the effectiveness and applicability of the research results, which can provide reliable theoretical support and technical reference for the design and construction of grouting engineering in unsaturated soil areas. [ABSTRACT FROM AUTHOR]

Stability analysis of retaining structures supporting variably saturated backfills is a topic of great significance in civil engineering. However, the backfill soil may be exposed to elevated temperature; this may result in changes of the saturation state, thus posing temperature-dependent effective stress, variable suction stress and different hydro-mechanical characteristics to partially saturated soils. In the present work, the significant impact of elevated temperature is incorporated into the soil-water retention curve and suction stress-based effective stress formulations. Accordingly, the lower bound theorems of limit analysis in conjunction with finite element and second-order cone programming are adopted so as to thoroughly examine the impact of elevated temperature on the coefficients of lateral earth pressure acting on a model retaining wall backfilled by two hypothetical partially saturated soils; a granular material (sand) and a cohesive material (clay). The effective stress-based formula for the strength of variably saturated soils is implemented to modify the conventional Mohr–Coulomb yield criterion. In general, it was shown that for unsaturated clay backfills, the active lateral earth pressure decreases while the passive lateral earth pressure increases with increasing the induced temperature; however these influences were observed to be small for the sand backfill. [ABSTRACT FROM AUTHOR]

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]

This study investigates the bearing capacity of strip footings resting on unsaturated soils subjected to combined loading using the lower-bound limit analysis coupled with the finite element discretization approach. In this regard, second-order cone programming (SOCP) is exploited to simulate the nonlinear form of the universal Mohr-Coulomb yield criterion during the process of stress field optimization. The significant influence of matric suction induced below the surface footing was accounted for by adopting the suction stress concept under the no-flow and steady-state infiltration/evaporation flow conditions. The eccentricity and inclination of the foundation loading are introduced into the equilibrium equations along the strip footing so as to render various combinations of moment (M), vertical (V) and shear (H) forces. The results stemming from the lower-bound finite element limit analysis are compared with several previous studies throughout the literature for verification of the model. The substantial contribution of suction stress to the evolution of failure loci and the distribution of subsurface stresses for the shallow foundation subjected to inclined and eccentric loadings is thoroughly discussed. A general three-dimensional failure envelope is presented for shallow foundations resting on partially saturated soils under combined vertical, horizontal and moment loadings. [ABSTRACT FROM AUTHOR]

This study presents a series of triaxial tests to highlight the effect of saturation degree ranging from 79.8% to 100% on the behavior of sand subjected to cyclic loading, the development of pore water pressure increment, the volumetric strain at liquefaction state, and the behavior of sand subjected to monotonic loading after liquefaction. The tested sand was Hostun RF sand, fine clear sand that has been widely used in laboratory testing in France. The results show that there is a difference between the behavior of samples having saturation degrees higher and lower than 95%. Besides, the development of pore water pressure increment is affected significantly by the value of cyclic stress ratio (CSR) and saturation degree. The Saturation degree also affects the appearance of criteria of liquefaction as Excess Pore-water Pressure (EPP) and Double Amplitude of axial strain (DA). The analysis of the effect of saturation degree on sample volumetric strain exhibits nonlinear liquefaction criteria for a given maximum value of CSR. The monotonic loading tests after liquefaction showed a small difference between the monotonic compressed behavior of the samples before and after liquefaction. [ABSTRACT FROM AUTHOR]

In the current state of the study regarding passive earth pressure, the majority of literature was limited in scope to dry or saturated cases. However, most soils in practical engineering are unsaturated. Based on the log-spiral failure mechanism, this paper develops a limit equilibrium (LE) analysis to evaluate the passive earth pressure under the effect of steady unsaturated seepage conditions. For assessing the effect of suction stress on passive earth pressure, a suction stress-based effective stress representation is incorporated into a limit equilibrium analysis. The analytical formula of passive earth pressure coefficient is derived using the moment equilibrium equation for the backfill defined by a log-spiral slip surface. An optimization procedure is developed to search for the minimum passive earth pressure coefficient and the critical failure surface via MATLAB. A parametric analysis is performed to investigate the effects of some key parameters on passive thrust. Besides, examples of two different cases are given to verify the effectiveness of theoretical results. Results indicate that suction stress can increase the magnitude of the passive earth pressure coefficient and the suction-induced effect highly depends on the seepage conditions and soil types. [ABSTRACT FROM AUTHOR]

In current study, a test program is designed to observe the influence of wetting stress paths on behavior and instability of unsaturated soil in stress state space. The mechanical behavior was studied by performing three test series in constant matric suction plane. In first series, water infiltration was performed together with shearing starting from zero (0 kPa) deviatoric stress. In second series, first water was infiltrated at zero (0 kPa) deviatoric stress then samples were sheared in drained pore water pressure conditions. In third series, water was first infiltrated at zero deviatoric stress then specimens were sheared in undrained pore water pressure conditions. Instability was studied in constant shear stress plane by first shearing soil up to predefined level of deviatoric stress then infiltrating water keeping deviatoric stress constant on the specimen. This research also describes how unsaturated soil behavior and instability is varied with variation in net confining stresses when suction is decreased from initial measured value to start water infiltration with different wetting stress paths and their effect on shear state and failure surface in stress state space. The test results revealed that the movement of stress paths was independent of net confining stress, matric suction and shearing conditions employed in the study. [ABSTRACT FROM AUTHOR]

The soil deposits for general constructions and mining are often under both saturated and unsaturated conditions at different overconsolidation ratios. Within the frameworks of the unified hardening unsaturated model, in this paper, a constitutive model is proposed for the unsaturated overconsolidated soil under drained and undrained conditions. This model is validated against the unsaturated experimental results, and the hydromechanical behavior of soil is thoroughly investigated considering the dilation behaviour under a high overconsolidation ratio. It is found that the prediction results for the volume change, deviator stress, and suction behavior determined by the proposed model agree well with the experimental results, particularly for the dilation behaviour. It can be concluded that this model can predict the hydromechanical behavior of the unsaturated overconsolidated soil under both the drained and undrained conditions. [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]

In the current study, three Ng tests were performed to simulate the LNAPL contaminants' transport and fate in the porous media. Through the tests, the efficacy of the soil–cement vertical barriers with a low permeability, which is among the most-used techniques in site remediations in practical projects, was assessed, and the results were compared to that of free field condition. Furthermore, extensive insight was achieved into the migration pattern of the LNAPL in unsaturated soil. All of the Ng tests were implemented at 40 g to simulate a voluminous spill of LNAPL in various timeframes. Consecutive imaging through the transparent front was used to gather data, and the LRV image processing technique was utilized to analyze these data. Reliable and effective performance of the barriers for containing the LNAPL spread was confirmed. Groundwater depression was observed in all three tests, particularly in the tests with using barriers. Nevertheless, using barriers restrained the contaminated soil and groundwater to the zones between the two barriers. Based on the observed LNAPL plume, the minimum depth of these barriers was recommended to account for the preferential flow. Three different methods were used for the validation of the image processing results. All in all, the accuracy of image processing was satisfactorily high. [ABSTRACT FROM AUTHOR]

Civil engineers face significant challenges in the safe design and construction of durable road infrastructure in the presence of expansive soils. These problematic soils exacerbate undesirable serviceability concerns induced by pavement distress. Soil stabilisation has been recognised as a sustainable approach to alleviate the problematic nature of expansive subgrades. Road pavements constructed on top of expansive subgrade soils are generally under unsaturated conditions, where the moisture variations can significantly impact the pavement response. However, current pavement design and modelling frameworks overlook unsaturated soil behaviour by adopting simplified approaches. This study examines the hydraulic behaviour of expansive clayey soils stabilised with non-traditional and traditional chemical based additive. Tests were conducted to determine the state variation and stabilisation influence on the soil water characteristic curve using the dewpoint potentiometer for an expansive subgrade commonly found in Melbourne geology. Results show that the stabilisation has strong influence on soil hydraulic characteristics at various initial state conditions tested. Experimental data have been applied to illustrate the significance of incorporating realistic hydraulic response using a simulated practical application in road pavements. The research highlights the significance of incorporating accurate hydraulic characteristics for simulating and assessing the response of pavement constructed with stabilised unsaturated subgrade soils. [ABSTRACT FROM AUTHOR]

The combined effects of transient, surface and subsurface flows and infiltration govern the rainfall-induced potential failure of unsaturated soil slopes stabilised by matric suction. In this paper, it is shown how fundamental fluid dynamics can be employed to closely model the above flow effects than the empirical Richard's approach. The fluid dynamics-based Navier-Stokes formulation also facilitates the integration of the three modes of flow: (1) surface, (2) subsurface and (3) infiltration water flows, into a unified analytical model. Therefore, in contrast to previous studies, this fundamental approach can seamlessly incorporate the effects of continuous interplay between surface and subsurface water flows and the inertial terms of flow on the reduction of matric suction in unsaturated soils. Transient flow effects have been combined with geomechanics of unsaturated soil to demonstrate their impact on the stability of an embankment under a more realistic non-uniform rainfall. The innovative use of the laboratory-evaluated soil properties such as the hydraulic conductivity and porosity to express the drag force in the Navier-Stokes equations facilitates the examination of the sensitivity of slope stability to the relevant soil classification parameters. [ABSTRACT FROM AUTHOR]

Weather changes induce wetting and drying cycles in soil and consequently affect the matric suction and may create residual effects in soil, which is referred to as hydraulic hysteresis. The results of some researches in the literature indicate that effective stress parameter is changed under the influence of hydraulic hysteresis. In this regard, it is important to study the simultaneous effect of void ratio and hydraulic hysteresis on effective stress parameter in a wide range of suction. Therefore, in this research an experimental approach involving suction-controlled triaxial experiments was used to investigate the variations of effective stress parameter and degree of saturation versus suction at different initial void ratios along drying and wetting paths. The results of the experiments show that hydraulic hysteresis due to suction variation affects the effective stress parameter and changes the value of this parameter value during wetting and drying paths. Furthermore, the value of this parameter cannot be taken equal to the degree of saturation. In addition, effective stress parameter at a given value of suction depends on void ratio. The variation of effective stress parameter obtained from the experiments was compared with available models and their capabilities in predicting the soil behaviour were evaluated. [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]

The importance of the hydraulic properties of unsaturated soil for geotechnical designs has been well understood. Many studies on the soil water retention curve (SWRC) and the relative coefficient of permeability under drying and wetting cycles have been performed. However, most of the previous investigations of hydraulic properties are limited to a single drying and wetting cycle or are based on multiple drying–wetting cycles with limited soil experiments. This might be because the measurement of both the SWRC and the coefficient of permeability of unsaturated soil is complex and time consuming. In this study, the hydraulic properties of silicon micropowder (SMP) and Guangxi Guiping clay (GGC) were studied for the same soil specimen under five cycles of drying and wetting in multistep outflow experiments. Significant hysteresis of SWRCs was observed under the first drying and wetting cycle for both soils. However, the hysteresis effect decreased as the number of drying and wetting cycles increased. Furthermore, the coefficient of permeability was estimated using the van Genuchten–Mualem (VGM) model. Results also show that hysteresis plays an important role in the coefficient of permeability for both soils subjected to multiple drying and wetting cycles. [ABSTRACT FROM AUTHOR]

Rainfall-induced slope failure is a natural hazard that occurs in many parts of the world. To identify areas where rainfall-induced slope failure may potentially occur in Singapore, a slope susceptibility map of needs to be developed. Majority of the slope failures occurred in residual soils during or after torrential rainfall. In Singapore, residual soils are generally unsaturated because of the deep groundwater table. Hence, it is important to incorporate unsaturated soil properties (i.e. soil–water characteristic curve) in the development of slope susceptibility map in Singapore. In this study, spatial distributions of saturated and unsaturated soil properties were estimated using ordinary kriging. Seepage analysis of zonation in the residual soil from Bukit Timah Granite was carried out using Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Model (TRIGRS), a publicly available software. The resulting pore-water pressures from the seepage analyses were incorporated into Scoops3D for three-dimensional slope stability analyses. Most areas in the investigated zone were found to have high factors of safety. Only 0.054% of the investigated zonation was associated with very low factors of safety. [ABSTRACT FROM AUTHOR]

This paper proposes a permeability function to estimate the water permeability coefficient of unsaturated soil. It is derived on the basis of the equilibrium equation of the water phase. Only one parameter is required in the proposed function, which is similar to the Brooks–Corey model. However, this parameter can be more easily obtained by using permeability tests of saturated soil with different porosity values. A number of test results in the literature are employed to validate the proposed permeability function, and the model prediction exhibits good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

A simplified numerical approach to predict meteorologically induced changes in pore water pressure in soil slopes is discussed. A simplified flux boundary condition (representing the net effect of rainfall, runoff and evapotranspiration) is defined that avoids many of the difficult to deduce parameters commonly used in a soil-atmospheric boundary interaction analysis and is used as an input to numerical analysis. The capability of the modelling approach has been tested using field monitoring data from a comprehensively instrumented research site in Southern England. Three different approaches to approximate the soil water characteristics curve (one of the most critical input) have been discussed and their effectiveness has been tested. The analysis is then extended to predict the behaviour of the slope under two future climate extremes. [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]

Nitrate ( N O 3 − ) leaching is a leading process of nitrogen (N) loss in agricultural ecosystems. The present research focused on N O 3 − leaching and transport in soil from the packed soil columns at different depths (0–20, 0–40, 0–60 and 0–90 cm) under saturated or unsaturated conditions for a lateritic soil. The leached N O 3 − collected from the bottom of column was analyzed with colorimetric method and was assessed for its variance in concentration (mg/L) with variable depths (20–90 cm). The leaching of N O 3 − was more in saturated condition than in unsaturated conditions. The cumulative N O 3 − concentration detected were 23, and 17 mg/L in a saturated condition for two N applications 15 mg and 7.5 mg, respectively, and were 2.10, and 1.36 mg/L in an unsaturated condition for two N applications 19.5 mg and 9.5 mg, respectively. Depth-wise analysis of N O 3 − leached indicated that at a 20 cm depth leached 16, 29 and 43% higher N O 3 − in a saturated condition whereas 21, 38, 52% higher N O 3 − in the unsaturated condition in comparison to 40, 60 and 90 cm depths, respectively. The N O 3 − concentrations with variable depths for both conditions were analyzed with principal component analysis (PCA) and PC (Pearson correlation) scores of 99.93% and 76.41% for unsaturated and saturated conditions were obtained and clarified that N application with more water results in more N O 3 − being leached out. Further, the study suggests that N O 3 − leaching can be restricted even with limited amount of nutrient and water. [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]

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]

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]

Unsaturated soil shows complex mechanical behaviours compared to saturated soil. A number of constitutive models for unsaturated soil have been proposed. However, these models suffer limitations. In this paper, a new constitutive model has been proposed in terms of effective stress and degree of saturation based on the modelling assumption about the relationship between hardening effect and degree of saturation. The proposed volume change equation gives a new explanation for the volume change of unsaturated soil. Then, an alternative approach to simulate coupled hydraulic hysteresis and the influence of the volume change on soil–water characteristic curves is suggested. Finally, this paper presents comparisons between the model simulations and experimental data. It is shown that the proposed model represents great ability to reproduce the mechanical and hydraulic response of unsaturated soil. [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]

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]

Most structures are subjected to more cyclic loads during their life time than static loads. These cyclic action could be a result of either natural or man-made activities and may lead to soil failure. In order to understand the response of the foundation and its interaction with these complex cyclic loadings, various researchers have over the years developed different constitutive models. Although a lot of research is being carried out on these relatively new models, little or no details exist in literature about the model-based identification of the cyclic constitutive parameters which to a large extent govern the quality of the model output. This could be attributed to the difficulties and complexities of the inverse modeling of such complex phenomena. A variety of optimisation strategies are available for the solution of the sum of least-squares problems as usually done in the field of model calibration. However, for the back analysis (calibration) of the soil response to oscillatory load functions, this article gives insight into the model calibration challenges and also puts forward a method for the inverse modeling of cyclic loaded foundation response such that high-quality solutions are obtained with minimum computational effort. [ABSTRACT FROM AUTHOR]

This article presents the results of the volumetric behaviour of an Algiers clayey soil. An experimental work was carried out bothin situ(core drilling; pressuremeter testing) and in the laboratory (drying–wetting and oedometric tests). Drying–wetting paths of soil samples were obtained using vapour equilibrium method and osmotic technique. These suction-controlled methods have gained widespread acceptance as reliable methods for imposing suction on soil specimens. They allowed for tests to be performed in the range of suction comprised between 0 and 300 MPa. The ability to impose suction on soil specimens allows for drying and wetting stress paths to be imposed to evaluate resulting changes in void ratio, degree of saturation and water content. These paths were explored at different initial states of clay. Slurries of soil were used to characterise the reference behaviour, whereas undisturbed soil samples allow characterising the material underin situconditions. [ABSTRACT FROM PUBLISHER]

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]

The development ofin situvapour sampling methods to measure δ2H and δ18O in pore water of deep, unsaturated soil profiles, including mine tailings and waste rock, is required to improve our ability to track water migration through these deposits. To develop appropriate field sampling methods, a laboratory study was first undertaken to evaluate potential materials and sampling methods to collect and analyse vapour samples from unsaturated mine waste. Field methods were developed based on these findings and tested at two mine sites using either on-site analyses with a portable isotope laser spectrometer or sample collection and storage prior to laboratory analyses. The field sites included a series of deep (>50 m) multiport profiles within a coal waste rock dump and open wells installed in a sand tailings dyke at an oil sands mine. Laboratory results show that memory effects in sample bags and tubing require 3–5 pore volumes of vapour flushing prior to sample collection and sample storage times are limited to 24 h. Field sampling highlighted a number of challenges including the need to correct for sample humidity andin situtemperature. Best results were obtained when a portable laser spectrometer was used to measure vapour samplesin situ. [ABSTRACT FROM AUTHOR]

The interfaces between saturated/unsaturated and structure are common to many offshore and on-shore civil engineering structures, but their behavior is not well understood. The shearing behavior of the interface plays a significant role in the stability and serviceability of the associated structures. With this in view, to study the influence of matric suction on interface (a stainless steel plate), a suction-controlled direct shear apparatus was modified. The main modifications included the fabrication of the shear box base/test cell for interface testing, along with some other important features and modifications that are described in this paper. By utilizing the modified direct shear apparatus, several suction-controlled direct shear tests were conducted on both the soil and the soil-steel plate interface. The main aim of this study was to develop laboratory testing equipment that can be used to determine shear strength of unsaturated soil-steel interfaces, at different shearing planes. The typical test results obtained from the study are presented and discussed in this paper, and it has been observed that the modified apparatus is suitable for testing the unsaturated soil-steel plate interfaces. [ABSTRACT FROM AUTHOR]

A finite element code was used for investigating the effect of some relevant characteristics of a phytoremediation project (crop type and density, presence of an irrigation system, soil capping and root depth). The evolution of the plume of contamination of Cd2+, Pb2+, and Zn2+was simulated taking into account reactive transport and root processes. The plant contaminant uptake model was previously calibrated using data from greenhouse experiments. The simulations adopted pedological and climatological data representative of a sub-tropical environment. Although the results obtained were specific for the proposed scenario, it was observed that, for more mobile contaminants, poor water conditions favor stabilization but inhibit plant extraction. Otherwise an irrigation system that decreases crop water stress had an opposite effect. For less mobile contaminants, the remediation process did not have appreciable advantages. Despite its simplifying assumptions, particularly about contaminant sorption in the soil and plant system, the numerical analysis provided useful insight for the phytoextraction process important in view of field experiments. [ABSTRACT FROM AUTHOR]

Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressure and increasing the shear strength by induced matric suction. This paper describes the way vegetation influences soil matric suction, shrinkage and ground settlement in the vadose zone through transpiration. A mathematical model for the rate of root water uptake, including the root growth rate considering ground conditions, type of vegetation and climatic parameters, has been developed. A finite element approach is employed to solve the transient coupled flow-deformation equations. The finite element mesh is built using partially saturated soil elements capable of representing the salient aspects of unsaturated permeability and the soil water characteristic curve. The model formulation is based on the effective stress theory of unsaturated soils. Based on this proposed model, the distribution of the ground matric suction profile adjacent to the tree is numerically analysed. Current field measurements of soil matric suction and moisture content collected from Miram site located in Victoria State, Australia by the authors are compared with the numerical predictions. The results indicate that the proposed root water uptake model incorporated in the numerical analysis can be used for prediction of ground properties influenced by tree roots. [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]

This paper reports laboratory experiments and numerical simulations of river embankment failure due to overtopping flow for different sediment sizes and different saturation conditions of embankment body. The effects of saturation and sediment size of embankment materials on the erosion process are discussed based on the results of the laboratory experiments. A numerical model is proposed to simulate the erosion process of embankments by overtopping flows. The proposed model considered the effects of infiltration process and resisting shear stress due to suction of unsaturated sediment. To simulate the embankment erosion phenomenon, the numerical model consists of four modules: two-dimensional (2D) shallow-water flow, seepage flow, sediment transport using a non-equilibrium model framework, and 2D slope stability. The validity of the developed model is tested using experimental data on embankment erosion. The numerical results on progressive embankment erosion agree well with the results of the sandy river embankment experiments. [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]

This paper discusses the results of an investigation on the influence of rainfall intensity and duration on the suction distribution within a soil mass. A series of numerical analyses were conducted on an infinite slope model to simulate the responses of the slope consisting of typical soil types to various rainfall intensities and durations from selected locations in the Malaysian Peninsular. The study showed that the critical duration was governed by three major factors: the saturated permeability of the soil, the geographical location, and the depth of the slip plane. The critical rainfall duration for highly permeable soil was 1 day, while 30 days of antecedent rainfall were required for the stability analysis of a slope made of soil with low saturated permeability. The critical duration of antecedent rainfall in soils with intermediate saturated permeability was found to vary with the rainfall pattern. A chart is proposed to determine the critical duration, critical intensity and critical suction for each type of soil. [ABSTRACT FROM AUTHOR]

This paper deals with the application of a meshless method called element-free Galerkin method (EFGM) for modelling the contaminant transport through the unsaturated porous media with transient flow condition. In EFGM, an approximate solution is constructed entirely in terms of a set of nodes and no elements or characterization of the interrelationship of the nodes is needed to construct the discrete equations. For analysis, the one-dimensional form of advection-dispersion equation with linear first-order degradation is considered. The unknown concentration values are approximated by using moving least square approximants. The weak form of the governing equation is formulated and the Lagrange multiplier method is used for enforcing the essential boundary conditions. The van Genuchten model is used for describing the hydraulic properties of the unsaturated soil. MATLAB code is developed to obtain the numerical solution. Numerical examples representing various phenomena that occur during the migration of contaminants are presented to illustrate the applicability of the proposed method and the results are compared with those obtained from the finite element method and the analytical solution. [ABSTRACT FROM AUTHOR]

Issues related to the numerical simulation of moisture migration patterns in the unsaturated zone and in the vicinity of mature trees are explored in this paper. The research is based on the use of Richard's equation for unsaturated moisture flow incorporating a sink term. A numerical solution has been achieved via the finite-element method for spatial discretization along with a finite-difference time-marching scheme. An axisymmetric solution is developed to represent water uptake near an established tree. The approach adopted utilizes radial symmetry and assumes a linear distribution of water extraction rates with both depth and radius. The model has been validated by direct comparison with field measurements recorded (by others) for a mature lime tree located on a boulder clay subsoil. Non-linear hydraulic properties have been obtained from independent published data. A good correlation between field data and simulated results has been achieved. The simulation covers a full annual cycle starting from field capacity in winter, extending through a full spring-summer drying period and subsequent autumn recharge. It is believed that this is the first attempt to simulate the behaviour of an established tree over such a time-scale. This relatively straightforward approach is thought to be suitable for development and application to a range of geo-engineering problems (e.g. slope stability, shrinkage/heave prediction, etc). [ABSTRACT FROM AUTHOR]

Nature as described by classical mechanics is governed by a set of physical laws in the balanced film of various physical entities, including mass, linear and angular momenta, energy, and entropy (entropy inequality). These laws must be obeyed in the development of any theory of applied mechanics. In soil mechanics, one deals with porous material composed of solids and fluids strongly interacting with each other. Within the framework of continuum mechanics, materials are assumed to be infinitesimally continuous, which renders an unavoidable hypothesis for soil. That is, each of the solid, liquid, and gaseous phases can be treated as a 'smeared' medium superimposed by and interacting with other constituents at the same infinitesimal point. Such treatment, however, requires the fundamental balance laws be recast into more elaborative forms involving microstructural effects (inter-phase actions). This paper introduces such a continuum framework based on existing theories of immiscible mixtures. To accommodate the pre-flow response, in the present work, the energy terms attributable to shear deformation and spin, allied with a coupling effect, are included. In the framework, a set of extended effective stresses is defined; indicating that the still skeleton has an effective stiffness, which may still be positive-definite after failure. The framework is general and may pave a way for solving practical geotechnical problems covering both pre- and post-failure stages. [ABSTRACT FROM AUTHOR]

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a military explosive that is a common soil and groundwater contaminant at facilities that manufacture, handle, and dispose of munitions. One such facility isthe U.S. Department of Energy Pantex Plant, the focus of this research in which the feasibility of in situ bioremediation of contaminatedsoil in the vadose zone was assessed. A batch technique using14C-RDX was developed to investigate the degradation of RDX underaerobic, microaerobic, and anaerobic conditions. In addition, the effect of nutrients (organic carbon and phosphorus) on biodegradation rates was studied. The extent of mineralization was quantified by monitoring the production of 14CO2, and RDX biodegradation rates were estimated for each environmental condition. The results showed that RDX degraders were indigenous to the contaminated soil and degraded RDX to a significant extent under anaerobic conditions. Little biotransformation was observed under aerobic conditions. The addition of a biodegradable organic carbon source significantly increased the RDX biodegradation rate. Under appropriate environmental conditions, significant mineralization of RDX also was observed. The half-lives for the degradation of RDX under anaerobic conditions wereapproximately 60 days and decreased to approximately 40 days with nutrient addition. In contrast, the half-life for aerobic degradation was on the order of 1000 days, with an upper 95% confidence interval approaching infinity. [ABSTRACT FROM AUTHOR]