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• Develop fiber-reinforced steel slag-bentonite mixture to construct hydraulic barrier. • This new material reduces desiccation cracks and ensures a low water permeability. • Fiber content and length affect hydro-mechanical properties and crack behavior. • Optimal use 0.3 % 9 mm-fiber to reinforce steel slag (90 %) mixed with bentonite (10 %) Desiccation-induced cracks in a compacted clay liner significantly deteriorate the hydraulic barrier performance of landfill covers. The present study explores the effects of polypropylene (PP) fiber reinforcement on the hydrological response and crack resistance of compacted steel slag (SS; 90 wt%) – bentonite (10 wt%) mixtures under drying and wetting cycles. Comprehensive tests were conducted to explore the impact of different fiber lengths (6–12 mm) and contents (0–0.4 % wt.%), including hydraulic conductivity tests for measuring the saturated hydraulic conductivity (k s), unconfined-penetration tests for measuring the tensile strength, small-sized plate tests for quantifying crack development, and large-sized bucket tests for studying the hydrological response and crack characteristics. Higher fiber contents and longer fiber lengths increased the k s -value of the specimens. For a 0.3 % fiber content, the tensile strength peaked for the 9-mm fiber. Consistently, the specimen reinforced with the 9-mm fibers exhibited significantly fewer cracks than those reinforced with the 6-mm and 12-mm fibers. It was because the 6-mm fibers had a shorter anchorage length, while the 12-mm fibers tended to agglomerate. The large-sized bucket tests showed that fiber reinforcement limited crack development significantly under wetting and drying cycles, reducing the rainfall infiltration by 40 % and enhancing the soil water retention capacity. Finally, a 0.3 wt% of 9-mm PP was recommended to reinforce the compacted SS-bentonite mixtures. [ABSTRACT FROM AUTHOR]

The effective interaction mechanisms in the pullout resistance of reinforcements include skin friction mobilized at the soil-solid surface, soil-soil shear resistance, and compressive resistance created against transverse elements. The third component is obtained from passive lateral pressure (LPM) or bearing capacity (BCM) methods. An analytical solution is proposed to determine the pullout capacity of geocell, geogrid, and strengthened geogrids embedded in ordinary and unsaturated soils. For unsaturated soils, the effective stress approach was employed. The solution-predicted results were compared with those obtained from large-scale pullout tests reported in the literature. Results indicated that considering LPM for 2D and 3D reinforcements better agrees with experimental results. The mobilized frictional rib-soil interfaces and the soil-soil shear resistance components generally contribute more to the pullout capacity of the geocell and geogrid, respectively. For the extensibility represented by m p i and flexibility of geocell denoted by α p i , the values of m p i = 1, 0.7, and 0.3 for the first, second, and third row of geocell, α p i = 0.4 for the first row of geocell and 0.25 for the second and subsequent rows are suggested to be considered. Parametric studies showed that the optimum transverse rib spacing is over 50 times the equivalent rib thickness (B eq). • To develop a solution based on the lateral earth pressure and bearing capacity methods to determine the pullout resistance of three-dimensional (3D) reinforcement such as geocell and two-dimensional (2D) reinforcement like geogrid and strengthened geogrids. • Validating the proposed equation for reinforcement pullout resistance in unsaturated soil, based on effective stress. • Investigating the present solution outcomes with 162 pullout tests performed on 28 different types of reinforcement, extracted from 10 case studies. • Proposing a method to reduce the passive resistance of geocell transverse ribs, related to the effects of extensibility and flexibility. • Presenting an evaluation method considering the geocell geometry and soil matric suction on the pullout capacity of geocells and the effects of the transverse rib spacing and width on the pullout capacity of geogrids. [ABSTRACT FROM AUTHOR]

• The vertical kinematic response of a pipe pile in unsaturated soil under P-waves is studied theoretically. • Introducing the fractional standard linear solid (FSLS) model describes the flow-independent viscosity of soil skeleton. • The effects of soil parameters on the seismic response of pipe pile are evaluated with parametric analysis. • The effects of slenderness and radius ratios for pipe pile on its seismic response are investigated in detail. • The physical mechanism behind the theoretical results is stated and discussed. This work investigates the kinematic response of a pipe pile embedded in a fractional-order viscoelastic unsaturated soil stratum over a rigid base subjected to vertically-propagating seismic P-waves based on a continuum model. The fractional standard line solid model is introduced to the governing equation of unsaturated soil to refine the frequency-dependent viscoelastic behavior of the soil skeleton. The Rayleigh-Love rod theory is utilized to characterize the vertical motion of the pipe pile. A rigorous series form solution for the vertical kinematic response of the end-bearing pipe pile under vertically incident P-waves is yielded theoretically with boundary conditions of pile-soil system. The proposed solution is then verified by comparing with the numerical result of the reported solution. Based on the given rigorous analyzed solution, the effects of physical parameters in pile-soil system on the vertical kinematic response of the end-bearing pipe pile under harmonic P-waves are studied in both the frequency and time domains through calculation example and parametric analysis. Finally, relevant meaningful conclusions are included and indicate that soil parameters and pipe pile dimensions have significant effect on the vertical kinematic response of the pipe pile. [ABSTRACT FROM AUTHOR]

This study focuses on the evaluation of stability for a typical unsaturated Soil Nailing Wall System (SNWS), considering variations in soil shear strength, suction, and elasticity modulus. The Random Finite Element Method (RFEM) is employed to derive the reliability indices for stability modes, including Global Stability (GS), Lateral Displacement Stability (LDS), Tensile Strength Stability (TSS), and Pullout Resistance Stability (PRS), which serve as essential components of the SNWS. Finally, the Sequential Compounding Method (SCM) is utilized to combine these modes of stability and their direct influence on the system reliability index. The results show although the maximum Coefficient of Variation (COV) of the soil parameters was 11%, the COV of lateral displacements at the top of the wall was obtained as 19%, which shows the significant influence of considering the soil heterogeneity. Furthermore, uncertainties of elasticity modulus and matric suction lead to an increase in GS, LDS, and PRS. The calculated system reliability index was found to be lower than the lowest reliability index of the individual components. The findings indicate that while the inclusion of matric suction and elasticity modulus may enhance the mean values of stability modes, there is a possibility that the system reliability index could decrease. [ABSTRACT FROM AUTHOR]

A comprehensive consideration of the shear and tensile strengths offers a deeper perspective on slope stability. However, such consideration is rare for unsaturated slopes with cohesive soils owing to the difficulties of tensile strength testing and its representation in the unsaturated criterion. This study provides a feasible way to incorporate tensile strength into the unsaturated strength criterion and apply it to stability analysis. Based on the effective stress principle, a cut-off criterion with a tensile reduction coefficient was developed for unsaturated soils. Compared to the linear extrapolation approach, the proposed approach effectively avoids the overestimation of the tensile strength. An unsaturated triaxial experiment was conducted to establish the relationship between the reduction coefficient and matric suction for a typical cohesive soil. For practicality, a fitting equation was proposed for the theoretical analysis. For three-dimensional unsaturated slope analysis, an analytical model was built using the upper bound limit analysis method; it captures the influence of the tensile cut-off impact on the sliding surface and the effects of infiltration or evaporation, allowing for an explicit expression of the safety factor. Parametric analysis indicated that the tensile cut-off effect reduced stability and became more pronounced as the suction phenomenon intensified. • The tensile cut-off criterion is developed for unsaturated soils. • The stability of 3D unsaturated slopes is evaluated considering the tensile cut-off. • Effects of the tensile cut-off on stability increase from infiltration to evaporation. [ABSTRACT FROM AUTHOR]

In this paper, a series of suction-controlled triaxial tests were conducted to investigate the hydromechanical behaviour of an unsaturated kaolin mixture. The studied variables included the mean net stress, suction, and initial dry density. The suction was controlled over a wide range – in the span of 0–390 MPa using the axis translation method and the vapour equilibrium technique, aiming to holistically study the mechanical response of unsaturated soils. The discussion focused on the critical state behaviour and dilatancy characteristics of the tested soil. The experimental results indicate that the ductility of the soil decreases and shifts towards brittleness with increasing suctions. The critical state stress ratio (M a) of the soil exhibits a significant increase with suction, and this increase becomes more pronounced with higher initial dry density. Conversely, the impact of suction on the critical state line in the specific volume-mean net stress plane (v -ln p net plane) diminishes with higher initial dry density. Furthermore, suction notably influences the stress-dilatancy relationship of kaolin mixtures, while the effect of confining pressure appears to be marginal. The influence of suction on the stress-dilatancy relationship primarily stems from its impact on the critical stress ratio (M a), which can be normalized by dividing the stress ratio by the critical state stress ratio. Lastly, the stress-dilatancy equation of the modified Cam-clay model is extended to capture the effect of suction on the dilatancy characteristics of unsaturated soils. • The mechanism of suction-induced over-consolidation is analysed. • As suction increases over a wide range, the critical state stress ratio (M a) notably rises. • The impact of suction on dilatancy is a result of its influence on M a. • The suction-induced friction angle is unaffected by initial dry density. [ABSTRACT FROM AUTHOR]

Soil curling, a natural phenomenon in thin soil fragments induced by desiccation cracks, exacerbates the potential threats of soil cracking. Analyzing soil curling, especially in conjunction with soil desiccation cracking, poses challenges in existing numerical investigations due to factors such as inadequate knowledge of the soil curling mechanism, complex soil characteristics with diverse parameters, moving boundary conditions during deformation, and crack initiation and growth. This study aims to uncover the soil curling mechanism using a fully coupled hygro-mechanical ordinary state-based peridynamic (OSB PD) model and its corresponding monolithic solutions. Specifically, the PD form of the moisture diffusion equations for saturated and unsaturated states are derived by employing the variational principle with nonconservative Lagrangian action and peridynamic differential operator (PDDO). Also, the PD bond force is derived by considering the energy equivalent principle for a fully coupled hygro-mechanical model. A model of soil strip desiccation deformation and curling is constructed while considering realistic moving boundaries of moisture and displacement with relevant parameters, and soil characteristics evolution from saturated to unsaturated states. It successfully captures the entire curling process, including concave-up and concave-down curling. Furthermore, this study explores the influencing factors of liquid limit, extra evaporation surface, and thickness on the curling performance. • Peridynamic form of moisture diffusion equation for saturated and unsaturated soil. • Coupled multi-dimensional hygro-mechanical ordinary state-based peridynamic model. • A monolithic implicit solution of coupled equations for soil desiccation analysis. • Complete curling behavior due to the consideration of unsaturated characteristics in soil. • Soil curling mechanism induced by differential shrinkage and multiple influence factors. [ABSTRACT FROM AUTHOR]

Analytical expressions are presented for the determination of the pore air and pore water pressure parameters in unsaturated soils under undrained conditions. The kinematic constraints governing the volumetric alterations of the soil skeleton and fluid phases, in conjunction with the effective stress principle, are utilised to derive the pore pressure parameters. The effect of hydraulic hysteresis on the effective stress parameter and the soil water characteristic curve is considered in the solutions. The expressions derived are validated against the experimental data available in the existing literature. It is demonstrated that: − with an increase in the degree of saturation of the soil, both pore pressure parameters increase and approach unity; − the change in the pore water pressure in an unsaturated soil under undrained compression is greater than the change in the pore air pressure; − the pore pressure parameters are strongly dependent on the compressibility of the soil skeleton; − the hydraulic hysteresis has a substantial influence on the pore water pressure parameter; − the pore air pressure parameter is slightly affected by the hydraulic hysteresis and it is mostly influenced by the compressibility of the air phase; − an increase in the degree of saturation leads to a reduction in the instantaneous settlement; and − the hydraulic state has a significant impact on the instantaneous settlement of unsaturated soil. [ABSTRACT FROM AUTHOR]

Based on the motion theory of three-phase poroelastic medium, the torsional vibration of a pile in unsaturated soil is investigated contemplating the impact of construction disturbance. The soil is segregated into a series of vertical annular zones, with the soil parameters of each zone varied to simulate its radial inhomogeneity. Subsequently, the governing equations for pile-soil interaction are formulated and solved, leading to the derivation of an analytical solution for torsional vibration in the frequency domain. Following a validation process, the proposed solution underwent parametric analysis to scrutinize the influence of soil saturation degree and construction disturbance on the torsional vibration characteristics of the pile. [ABSTRACT FROM AUTHOR]

The fate of volatile organic compounds (VOC) vapors in the unsaturated zone is the basis for evaluating the natural attenuation potential and vapor intrusion risk. Microcosm and column experiments were conducted to study the effects chemical speciation and soil types/properties on the fate of petroleum VOCs in unsaturated zone. The biodegradation and total attenuation rates of the seven VOCs obtained by microcosm experiments in black soil and yellow earth were also generally higher than those in floodplain soil, lateritic red earth, and quartz sand. The VOC vapors in floodplain soil, lateritic red earth, and quartz sand showed slow total attenuation rates (<0.3 d−1). N-pentane, methylcyclopentane, and methylcyclohexane showed lower biodegradation rates than octane and three monoaromatic hydrocarbons. Volatilization into the atmosphere and biodegradation are two important natural attenuation paths for VOCs in unsaturated soil columns. The volatilization loss fractions of different volatile hydrocarbons in all five unsaturated soils were generally in the order: n-pentane (93.5%–97.8%) > methylcyclopentane (77.2%–85.5%) > methylcyclohexane (53.5%–69.2%) > benzene (17.1%–73.3%) > toluene (0–45.7%) > octane (1.9%–34.2%) > m-xylene (0–5.7%). The fractions by volatilization into the atmosphere of all seven hydrocarbons in quartz sand, lateritic red earth, and floodplain soil were close and higher compared to the yellow earth and black soil. Overall, this study illustrated the important roles chemical speciation and soil properties in determining the vapor-phase transport and natural attenuation of VOCs in the unsaturated zone. [Display omitted] • Volatilization and biodegradation are two main vapor natural attenuation pathways. • Soil texture and SOM content affect vapor fate and attenuation in the vadose zone. • Hydrocarbons with less carbon atoms have stronger volatilization loss. • Strong sorption and biodegradation enhanced vapor mass loss. [ABSTRACT FROM AUTHOR]

Prefabricated vertical drains (PVDs) are an established ground improvement method. Mimicking drinking straws, PVDs are installed to convey vacuum pressure in the ground and lift groundwater. However, the dewatering performance is suboptimal in consolidating fine-grained layers. Practical applications have shown that better dewatering performance is achieved through aiding the vacuum dewatering with an air-booster. Air-boosters are installed in an alternating pattern adjoining PVDs, increasing pore pressures and unclogging pores. This study presented a numerical model for this vacuum and air-booster combined dewatering solution. Taking account of the large strain deformation, this model used the Lagrangian-convective coordinate to track the global and local deformation of the soil layer separately, thus enabling accurate determination of consolidation. This model also considered air-booster induced unsaturated conditions and the associated effects on water flow. The numerical model was verified against field test results and laboratory measurements. [ABSTRACT FROM AUTHOR]

Geosynthetic-reinforced soil (GRS) walls using marginal soils can operate under unsaturated conditions depending on climate conditions and drainage inside the reinforced zone. Geocomposite reinforcements have been suggested to act as internal drainage layers, but their hydraulic behavior can also be strongly affected by climate conditions. Numerical analyses were conducted to observe the impact of four distinct tropical climate conditions (arid, semi-arid, humid subtropical and humid tropical) on suction profiles and stability of reinforced soil walls constructed using geogrid and geocomposite reinforcements. The climate simulation involved the incorporation of a soil-atmosphere interaction on water balance and on the unsaturated transient infiltration. Results indicate the GRS walls can operate under relatively high suction levels under arid climates in which cumulative evaporation overcomes infiltration. Any climate that has rainy seasons with consecutive rainfalls with intensities close to the infiltration capacity of soil and/or monthly cumulative precipitation higher than 200 mm/day led to critical conditions in terms of soil water saturation and stability. Under unsaturated conditions of soil, the drainage effectiveness of geocomposites is significantly reduced and adverse capillary break effects become critical. • Evaporation has a significant effect on stability of geosynthetic reinforced soil structures. • Unsaturated condition was kept in climates which the monthly precipitation does not overcome the evaporation. • The critical FOS was reached in climates with monthly cumulative precipitation of 200 mm. • The pattern of rainy season has a significant effect on the FOS. • Under the real climate conditions, the effectiveness of draining geocomposite reinforcements is significantly reduced. [ABSTRACT FROM AUTHOR]

Woven geotextiles are often to be used in roadways for reinforcement purposes due to their higher tensile strengths. In the design of a woven geotextile for practical applications, the focus is mainly put on its reinforcing effect, while its hydraulic behaviors are not major design parameters and the influence of hydraulic properties on the reinforcing effect is often ignored. However, woven geotextiles are predominantly made of polypropylene and polyester, which are hydrophobic. This characteristic can result in a capillary break effect which it is equivalent to raise the ground water table to the location where the geotextile is installed. Numerous researchers have reported that the moisture storage from a capillary break effect can be detrimental to the long-term performance of a pavement structure. Until now, no method is available to effectively resolve this issue. Recently a new type of wicking geotextile is produced which has the capability to laterally drain excess water in a roadway under both saturated and unsaturated conditions. Several field applications demonstrated its potential in improving pavement performance. This paper attempted to investigate the working mechanism of the wicking geotextile through numerical studies and quantify the benefits of the wicking geotextile in term of drainage performance in a pavement structure. A numerical model was developed and validated using column test results from existing literature. After that the drainage performance of the wicking geotextile under different working conditions was simulated and evaluated. • The wicking geotextile is a dual-functional woven geotextile for reinforcement and drainage purposes. • The wicking geotextile is able to drain both free water and capillary water under saturated and unsaturated conditions. • The wicking geotextile works as a capillary barrier in the cross-plane direction and has lateral drainage ability in the in-plane direction. • Two air entry values (AEV) of the wicking geotextile ensure higher abilities to hold and transport water compared with non-wicking geotextiles. • The efficiency has been validated via laboratory tests, numerical simulations, and field observations. [ABSTRACT FROM AUTHOR]

• A thermo-hydro-mechanical (THM) model for unsaturated soil is proposed. • THM behaviour of energy tunnels in unsaturated conditions is numerically investigated. • The influences of the water table and soil type are investigated. • Settlements of ground and tunnel and lining stress changes highly depend on the water table. • THM responses are underestimated if soils above the water table are assumed to be dry. Soils surrounding energy tunnels are often unsaturated, particularly in areas with a low water table. All studies of the mechanical behaviour of energy tunnels focused on saturated or dry soils. Through numerical simulations using a coupled thermo-hydro-mechanical model for unsaturated soils, this study aims to improve the understanding of the interactions between energy tunnels and unsaturated ground. The influences of water table position and soil type on the mechanical behaviour of energy tunnels were investigated. Results show that the thermally-induced lining convergence of energy tunnels does not change much with the water table position. Nevertheless, the other mechanical responses (e.g., settlements of ground and tunnel and lining stress changes) highly depend on the water table position. These mechanical responses are more significant when the water table is higher than the tunnel center, except for the larger settlements at a lower water table in clay. Furthermore, the above responses are underestimated if soils above the water table are assumed to be completely dry. The degree of underestimation is most significant for the clay, followed by silt and sand, e.g., a maximum of 54%, 23% and 10% in the change of circumferential stress, respectively. These results highlight that the unsaturated soil model should be used to evaluate the thermo-hydro-mechanical responses of energy tunnels in unsaturated soils, particularly for the clay ground. [ABSTRACT FROM AUTHOR]

Large-diameter pipe piles are widely applied in various civil engineering fields due to their outstanding load-bearing capability. The unsaturated characteristics, anisotropy, and heterogeneity of the soil jointly affect the dynamic response of the pipe pile. However, most previous studies were limited to single-phase or two-phase soil. This paper develops an analytical model for the torsional vibration of a pipe pile in transversely isotropic unsaturated soils considering construction disturbance. Based on transversely isotropic unsaturated soil theory, a pipe pile-soil interaction model has been developed, while the effect of construction disturbance is simulated by the radial heterogeneity of the soil. The general solution for the unsaturated soil is obtained using the separation of variables method with the boundary conditions. Then, the solution for the whole pipe pile-soil system is derived by considering the pile-soil interface conditions. The accuracy of the proposed solution is verified through comparisons with previous research results. The results show that unsaturated characteristics, construction disturbance, and transverse isotropy of the soil have significant effects on the impedance of large-diameter pipe piles. Specifically, with a low degree of saturation, there will be significant prediction errors when using previous works based on single-phase or two-phase soil theory to predict the dynamic response of large-diameter pipe piles. • The unsaturation, anisotropy, and heterogeneity of soils are incorporated into pipe pile-soil system. • The vibration of piles is significantly influenced by the transverse isotropy and saturation degree of the soil. • Softening effect of soil is more sensitive to the vibration of pipe piles than hardening effect. [ABSTRACT FROM AUTHOR]

This paper presents numerical simulations of the deformation response of unsaturated embankments subjected to rainfall infiltration using a coupled hydro-mechanical constitutive model for unsaturated soils. The constitutive model accounts for the influence of degree of saturation on the stress–strain behavior and the influence of void ratio on the water retention behavior. The constitutive model was implemented in the finite difference program FLAC, calibrated using triaxial test data, and validated using measurements of wetting-induced deformations of embankment models from centrifuge tests. The validation demonstrates that the constitutive model can capture the coupled hydro-mechanical behavior of unsaturated soils under wetting conditions. Simulations of the hydro-mechanical response of unsaturated embankments subjected to rainfall infiltration indicate that the differential settlement across the top surface of the embankment between the centerline and shoulder increases significantly during rainfall infiltration, which could result in severe damage to overlying transportation infrastructure. As the rainfall infiltration increases, shear strains accumulate and form a potential failure surface at a shallow depth of approximately 2 m from the slope surface. Insights into the hydro-mechanical response of unsaturated embankments subjected to rainfall infiltration gained will be useful for considering climate change effects in design and construction of compacted embankments. [ABSTRACT FROM AUTHOR]

Cavity expansion theory in unsaturated soils has attracted considerable attention in recent years, but little progress has been made in understanding how initial hydraulic state (IHS) influences the behavior of surrounding soil during the expansion. A rigorous semi-analytical approach is developed in this paper to solve the cylindrical cavity expansion problem with different initial hydraulic conditions in unsaturated soils, based on a simple but practical extended Cam-clay model. The cylindrical expansion problem can be formulated as a system of first-order differential equations in the plastic zone. The hydraulic behavior and mechanical behavior of unsaturated soils are appropriately coupled in the process of deriving the governing equations. The governing differential equations can be solved as an initial value problem with initial conditions determined from the continuity condition and the yield function of the soil model. Extensive studies are conducted to investigate the effects of the IHS and parameters. The results indicate that the variations in the IHS significantly alter the hydraulic path, which in turn has a profound impact on the cavity responses. It is expected that the proposed solution provides a theoretical analysis solution for the pressure meter test and pile installation in unsaturated soils across various natural hydraulic environments. [ABSTRACT FROM AUTHOR]

• A laboratory experiment on the energy pile in unsaturated soils is conducted. • A model considering the coupled heat and moisture transfer is established. • The impacts of thermal imbalance on long-term performance are discussed. • A complete case study is carried out for practical engineering. • The economic and technical feasibility is analyzed for design optimization. The operation of energy piles in unsaturated soils involves coupled heat and moisture transfer, demanding further detailed investigation. In this paper, laboratory tests were conducted to validate a numerical model that incorporated vapor and liquid migration, convection, and latent heat transfer in unsaturated soils. Moreover, this model captured the dynamic variation in characteristic parameters of unsaturated soils. Building upon this observation, this study delved into the thermal performance of the energy pile under ten-year cooling and heating cycles, specifically focusing on the temperature, heat exchange rate, volumetric water content, and thermal conductivity. It is demonstrated that the imbalanced cooling and heating load adversely affects the long-term operation. In particular, the cooling power experiences a reduction of 15.1% after ten years of operation. The results indicate that higher soil temperatures positively impact the heat exchange rate in heating mode, while rainfall facilitates heat transfer in both seasons. Furthermore, a case study of an energy pile system was carried out, encompassing load calculation, pile group simulation, economic analysis, and design optimization. A comprehensive evaluation of the technical and economic feasibility demonstrates that the system exhibits excellent performance, particularly when the ratio of cooling and heating loads ranges from 1.1 to 1.3. [ABSTRACT FROM AUTHOR]

An analytical solution for investigating the torsional dynamic response of a pipe pile in unsaturated poroelastic transversely isotropic soil under time-harmonic load is proposed. By employing the Biot's type three-phase porous media model and the three-dimensional continuum theory, taking into account the transversely isotropic characteristics of the soil skeleton, as well as the viscosity and inertial coupling between different phases, distinct dynamic governing equations are derived for the soils surrounding and inside the pipe pile. By considering the boundary and continuity conditions at the interface between the pipe pile and the soils surrounding and inside the pipe pile in the frequency domain, a mathematical expression is derived to describe the torsional dynamic behavior of the pipe pile. A parametric study aimed to investigate how the anisotropy of the soils surrounding and inside the pipe pile (soil plug) impacts its torsional complex impedance, twist angle, and torque was conducted. The parametric study also considered variations in saturation, pile lengths, porosity, the height of the soil plug and excitation frequencies to explore the effects of these parameters on the torsional behavior of the pipe pile. • An analytical solution for the torsional impedance of pile pile in unsaturated transversely isotropic is proposed. • The proposed model considering the soil anisotropy, viscous and inertial coupling of soil skeleton, pore-water and pore-air. • The solution can be both reduced to saturated and single phase transversely isotropic medium and solid pile. [ABSTRACT FROM AUTHOR]

Understanding and predicting dune erosion is crucial for coastal hazards mitigation, ecosystem preservation, as well as the protection of human settlements and infrastructure along sandy coastlines. However, our knowledge regarding the influence and potential importance of internal sand moisture content on wave-driven dune face erosion processes remains limited. This paper presents the findings from an extensive series of controlled wave flume experiments of eroding, unvegetated dunes, combining a range of wave conditions and water levels. A further variable that is studied directly for the first time is the internal moisture content of the dune. The initial moisture content and its evolving dynamics within the eroding dune face are quantified, revealing this to be a determining factor of the observed erosion rates, the final horizontal erosion distance, and the dune face failure type. Importantly, infiltration into the dune with each wave was not a driving mechanism of observed failures, but rather the rapid increase and then decrease of the phreatic surface within the dune, resulting in excess pore pressures and destabilization of the sediment matrix. Based on these observations two distinct mechanisms of shear failure and resulting dune face slumping are identified for unsaturated dunes corresponding to 'minimum' and 'field capacity' internal moisture content: Type 1 is associated with a circular failure surface in the absence of notching at the base of the dune, while for Type 2, notching is present and the failure surface is vertical. Under fully saturated conditions, the phreatic surface is observed to decouple from the wave runup, with excess water continuously exiting the dune face near the base. This results in rapid shear failure with no notching (Type 3). Significantly, dunes with saturated initial pore moisture content above the capillary fringe are observed to have up to 35 % greater erosion potential, consistently receding further landward than the two unsaturated counterparts as well as undergoing slumping in the absence of wave impact. A new conceptual framework is presented, comprising of a three-phase erosion sequence that directly links dune face failure mechanisms to wave runup and prevailing groundwater conditions. • A series of controlled wave flume experiments is conducted to examine dune erosion processes. • Internal dune moisture shown to affect the rate and magnitude of dune erosion • Internal dune moisture determines the failure mechanics of the dune face. • Saturated dunes observed to erode faster and to a further landward extent by 20–35 % • A conceptual framework incorporating hydrodynamic forcing and internal moisture dynamics is presented. [ABSTRACT FROM AUTHOR]

Band gaps or attenuation zones existing in periodic structures can filter out elastic waves propagating in both single-phase soils and saturated soils in specific frequency regions, which opens a window for designing new wave barriers to attenuate ambient vibration. However, vibration mitigation in unsaturated soil remains a significant challenge due to soil's constitutive relation strongly relying on saturation, especially by periodic wave barriers. Based on local resonance mechanism, the performance of a periodic in-filled barrier for isolating low-frequency ambient vibration is studied. The periodic in-filled barrier is filled with a viscous material. Investigations found that the attenuation zones of the periodic wave barrier are robust to saturation and the viscosity of the in-filled material can broaden the frequency range for vibration reduction. More interestingly, periodic wave barriers in unsaturated soils can produce attenuation zones for P1 waves, which is impossible in saturated soils. Therefore, this investigation provides a promising insight for the application of periodic wave barriers to unsaturated soils. • The complex band structures of bulk waves in an in-filled periodic barrier are obtained. • This periodic barrier provides a precise low-frequency attenuation zone which is robust to saturation. • The viscosity of the in-filled material can improve the mitigation performance outside the attenuation zone at the expense of weakening it inside the attenuation zone. [ABSTRACT FROM AUTHOR]

• Fiber-optic sensing technique is innovatively applied in the field of hydrology and geotechnical engineering. • Fiber Bragg grating (FBG) is utilized to continuously monitor soil water potential. • FBG-suction method can measure a wide range of total suction accurately and efficiently. • The geophysical method holds significant potential for characterizing dynamic surface processes. Accurate measurement of soil water potential or suction is crucial for hydrology and geotechnical engineering. Inspired by recent advances in fiber-optic sensing techniques, we develop an innovative geophysical method for measuring the soil suction by using fiber Bragg grating (FBG), named FBG-suction method. In this study, working principles and theoretical background associated with the FBG-suction method are discussed. For verification purposes, a series of laboratory-scale tests including calibration, suction measurement, and evaporation monitoring are performed on two clayey soils of low to high plasticity under different degrees of saturation. The calibration and measurement results demonstrate the efficacy and accuracy of the developed method for measuring a wide range of soil suction. The curves of soil saturation with suction obtained by WP4C and FBG-suction method are comparable and reflect the difference in the water retention capacity of the tested soils. Additionally, the evaporation monitoring results show that the FBG-suction method can measure the low suction during the drying process and accurately obtain the high suction above the measuring range of the PST-55 psychrometer. The findings affirm the scientific viability of the fiber-optic sensing technique for acquiring the spatial distribution of water potential or suction in unsaturated soils and provide a novel perspective for future investigations into the spatiotemporal evolution characteristics of in-situ unsaturated soil under climate change. As interdisciplinary collaborations continue to advance, it becomes increasingly apparent that methods based on fiber-optic sensing have the potential to revolutionize traditional approaches to characterizing dynamic subsurface processes. [ABSTRACT FROM AUTHOR]

• A conceptual model is proposed to categorize soil pore water types. • Quantitative analysis on pore water redistribution during soil dry-wet processes. • The SWCC can be predicted using the NMR cumulative pore water distribution curve. The pore water distribution (PWD) of soil provides key information about soil shear strength, hydraulic conductivity, and water-retention ability. The PWD characteristics of the soil depend on the specimen preparation conditions (i.e., the variations in initial water content or compaction degree) and drying-wetting processes, which were investigated by using the nuclear magnetic resonance (NMR) technique. The NMR T 2 spectrum is mathematically transformed into the PWD curve to more accurately quantify the variations in pore water content stored with pores of different radii. The pore water in silty clay can be categorized into strongly bound water, intra-aggregate pore water, and inter-aggregate pore water, which are identified by the pore radius of <0.05 μm, 0.05-1.0 μm and >1.0 μm, respectively. The effects of compaction degree and initial water content on the PWD of the soil exhibit distinctions. For unsaturated compacted specimens, the PWDs remain unaffected by changes in compaction degree, while an increase in initial water content promotes the formation of clay aggregates, thereby increasing the maximum water-holding pore radius and the intra-aggregate pore water content. For saturated compacted specimens, the inter-aggregate and intra-aggregate pore water content increases with a decrease in the compaction degree, while the changes in the PWD shape from unimodal to bimodal with an increase in the initial water content. During the soil drying process, inter-aggregate pore water is rapidly drained, the intra-aggregate dominant pore water content increases first and then decreases, and the strongly bound water content remains constant. The relationship between the cumulative pore water distribution curve and the soil-water characteristic curve (SWCC) can be established through the Young-Laplace theory. The SWCC can be well predicted by using the envelope of the cumulative pore water distribution curves during soil drying. [ABSTRACT FROM AUTHOR]

Post-wildfire mass wasting is a major problem throughout many regions worldwide. Recent dramatic increases in global wildfire activities coupled with a shift in wildfire-prone elevation to higher altitudes raise the need to better predict post-fire rainfall-triggered landslides. Despite its importance, only a limited number of studies have investigated landslide susceptibility in areas hit by wildfires using hydromechanical models. However, most of these studies follow either qualitative or semi-quantitative approaches without explicitly considering the fire's effects on the impacted area's physical behavior. This study aims to develop and employ a physics-based framework to generate susceptibility maps of rainfall-triggered shallow landslides in areas disturbed by wildfire. A coupled hydromechanical model considering unsaturated flow and root reinforcement is integrated into an infinite slope stability model to simulate the triggering of shallow landslides from rainfall. The impact of fire is considered through its effects on soil and land cover properties, near-surface processes, and canopy interception. The developed model is then integrated into a geographic information system (GIS) to characterize the regional distribution of landslide potential and its variability considering topography, geology, land cover, and burn severity. The proposed framework was tested for a study site in Southern California. The site was burned in the San Gabriel Complex Fire in June 2016 and experienced widespread landsliding almost three years later following an extreme rainstorm in January 2019. The proposed framework could successfully model the location of observed shallow landslides. The model also revealed a significantly higher likelihood for slope failure in areas burned at moderate to high severities as opposed to unburned and low-burn severity areas. The findings of this study can be employed to predict the timing and general locations of rainfall-triggered shallow landslides following wildfires. • Novel physics-based framework developed to predict post-fire rainfall-triggered landslides. • Integration of hydromechanical and infinite slope stability models considering fire effects. • Successful modeling of observed shallow landslides in a Southern California study site. • Higher likelihood of slope failure in areas burned at moderate to high severities revealed. [ABSTRACT FROM AUTHOR]

Cohesive soils in nature are created under anisotropic stress and have various stress histories. Embankments generate greater vertical loads underground. Moreover, associated excavation activities can exacerbate the extensional stress state. This study investigated the effects of induced anisotropy on the shear modulus in saturated and unsaturated cohesive soils. A triaxial testing apparatus, equipped with local small strain (LSS) measurement devices and bender elements (BEs), was used to measure the small strain shear modulus. Two series of tests were conducted: (1) LSS and BE tests used specimens normally consolidated under a constant mean effective stress of p' = 300 kPa or net mean stress p net = 300 kPa with different stress ratios to investigate the effects of anisotropic consolidation. The values of the applied stress ratios, represented as K = σ ' h / σ ' v for the saturated soil and K net = (σ h – u a)/(σ v – u a) for the unsaturated soil, were 0.35, 0.43, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0, and 3.5. (2) BE tests used specimens consolidated under various mean effective stresses in the order of p' = 50, 100, 200, 300, 400, 500, and 600 kPa, and swollen in reverse order under K of 0.35, 0.43, 0.6, and 1.0, to elucidate p' and the effects of the overconsolidation ratio (OCR). The results demonstrated that K -consolidation under constant p' produces large differences in initial shear modulus G 0 in saturated cohesive soil, but K net produces only slight differences in unsaturated cohesive soil because of the influence of strong matric suction. Finally, G 0 was normalized successfully considering the effects of void ratio e , K , and OCR. [ABSTRACT FROM AUTHOR]

The horizontal drainage layer is widely used in blow-filling and road foundation-filling projects. Due to the change in the groundwater table and horizontal drainage layer, the double-layer ground sometimes shows two states of unsaturated and saturated. Meanwhile, the two-layered unsaturated–saturated soil system ground is very widely distributed in nature. In this paper, based on the soil consolidation theory, semi-analytical solutions of excess pore pressures and the settlement of a two-layered unsaturated–saturated soil system containing a horizontal drainage layer under different drainage layer boundary are obtained by using the Laplace transform technique and decoupling method. And the model in this paper can be well degraded to two classic soil consolidation ones and presents an excellent agreement with references, showing excellent accuracy and reliability of the solutions obtained in this paper. Further, by selecting parameters to analyze their effects on the consolidation of the modelling in this paper. The results show that the horizontal drainage layer can provide additional drainage channels to accelerate the consolidation of two-layered ground in an unsaturated–saturated soil system, while the location of the horizontal drainage layer at 0.3 H -0.5 H can most efficiently accelerate the ground consolidation process. When drainage conditions are poor, the settlement completion time is prolonged. [ABSTRACT FROM AUTHOR]

Considering the soil skeleton to be statically transversely isotropic, the viscous and inertial coupling among three phases, along with the capillary pressure, the torsional dynamic response of an end-bearing pile in homogeneous unsaturated transversely isotropic soil under time-harmonic torsional load is investigated. The separation of variables method is employed to derive the torsional dynamic governing equations of unsaturated transversely isotropic soil in a cylindrical coordinate system, and pile is modeled as a 1D elastic theory. By combining the boundary conditions of the pile and soil, as well as the continuity conditions at the pile-soil interface, further employing the inverse Fourier transform and convolution theorem, fundamental analytical solutions for the torsional behavior of the pile are derived in both the frequency domain and time domain. Comparisons between the proposed solution and the two existing solutions indicate that the presented model exhibits stronger applicability, as it can simultaneously transition to both saturated transversely isotropic soil and unsaturated isotropic soil. Eventually, a parametric study is conducted to examine the influence of soil anisotropy, degree of saturation, pile-soil shear modulus ratio and pile length on the torsional dynamic response of end-bearing pile. • The viscous and inertial coupling among soil skeleton, pore-water and pore-air is considered in proposed model. • An analytical solution for the torsional response of end-bearing pile in unsaturated transversely isotropic is proposed. • The proposed solution can be completely reduced to a saturated and single phase transversely isotropic medium. [ABSTRACT FROM AUTHOR]

Rainfall-induced soil slope failures are among the most frequent and widespread landslides in the world. The infiltration of water plays a critical role in the instability of slopes under rainfall conditions. By employing the physical models, field monitoring data becomes instrumental for the back analysis of soil parameters, providing critical insights into the mechanisms of slope instability. In this review, the initial section investigates the hydraulic characteristics of unsaturated soils, encompassing the soil-water characteristic curve, permeability function, and their variability nature. Subsequently, a comprehensive overview of infiltration models for unsaturated soil, coupled with their numerical and analytical solutions, is provided. The subsequent section systematically introduces physical model-based Bayesian parameter inference, with a particular emphasis on the formulations of likelihood functions. The exploration then shifts towards investigating the impacts of prior knowledge, likelihood, model structure, and assimilation approach on an unsaturated soil slope monitoring case. Finally, the limitations of the current approaches and future outlooks in this field are presented. [ABSTRACT FROM AUTHOR]

Bentonite and bentonite mixtures are used as buffer material for deep geological radioactive waste repositories. The proper determination of bentonite maximum swelling pressure is important as it influences the long-term stability and sealing characteristics of the barrier system. We developed a constrained machine learning model based on extreme gradient boosting (XGBoost) algorithm tuned with grey wolf optimization (GWO) to determine the maximum swelling pressure of bentonite and bentonite mixtures. We integrated a penalty term into the XGBoost algorithm's loss function to constrain the model during the training phase ensuring meaningful predictions. To this end, we compiled a dataset containing 305 experimental data of bentonite maximum swelling pressure and other relevant soil properties including montmorillonite content, liquid limit, plastic limit, plasticity index, initial water content, and soil dry density to develop the model. The performance of the hybrid GWO-XGBoost model was benchmarked against feed-forward and cascade-forward neural network models. The GWO-XGBoost model showed a better performance in estimating the experimental values comparing to the other models, thereby demonstrating its effectiveness and reliability in determining the maximum swelling pressure of bentonite and bentonite mixtures. [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]

Wicking geotextile has been increasingly utilized in field projects to mitigate water-related roadway problems. The previous studies showed that the wicking geotextile could provide mechanical stabilization, serve as capillary barrier, and enhance lateral drainage. The wicking geotextile differentiates itself from non-wicking geotextiles by providing capillary or wicking drainage in unsaturated conditions, whereas non-wicking geotextiles only provide gravitational drainage under saturated or near-saturated conditions. Although the previous studies have demonstrated the benefits of soil water content reduction by the wicking drainage, it is not well understood how the wicking geotextile stabilization improves overall performance of aggregate bases over subgrade under traffic or cyclic loading. This paper presents an experimental study where large-scale cyclic plate loading tests were conducted under different conditions: (1) non-stabilized base, (2) non-wicking geotextile-stabilized base, and (3) wicking geotextile-stabilized base, over soft and moderate subgrades. Rainfall simulation was carried out for each test section. After each rainfall simulation, a drainage period was designed to allow water to drain from the section. The amounts of water applied and exiting from the test section were recorded and are compared. Cyclic loading was applied after each drainage period. The test results show that the combined hydraulic and mechanical stabilization effect by the wicking geotextile reduced the permanent deformation of the aggregate base over the subgrade as compared with the non-stabilized and non-wicking geotextile-stabilized sections. ⁃ This paper presents an experimental study on the improved performance of wicking geotextile-stabilized bases over different subgrades over non-wicking geotextile-stabilized bases and control bases after simulated rainfalls. ⁃ Large box tests clearly demonstrate the benefits of the wicking geotextile to remove more water from the base courses by capillary drainage as compared with other test sections. ⁃ Large box tests also show that the wicking geotextile significantly reduced permanent deformations of the base courses under cyclic loading as compared with other test sections. [ABSTRACT FROM AUTHOR]

Considering unsaturated triaxial tests including a ceramic disk as initial and boundary value problems, a series of suction change, isotropic consolidation, and drained shearing processes was simulated using a soil-water-air coupled elastoplastic finite deformation analysis code. As a result, it was demonstrated that the delayed behavior of a wetting-induced collapse during the suction change and isotropic consolidation processes, as well as water-absorption behavior during the subsequent drained shearing process, were attributed not to the characteristics of the soil specimen, but to the permeability of the disk. Thus, it is important to take the ceramic disk into account in unsaturated triaxial tests regarded as initial and boundary value problems in order to understand the temporal change behavior of unsaturated soil specimens. Otherwise, there is a risk that the behavior appearing as the solution of an initial and boundary value problem may be modeled as a constitutive relation. [ABSTRACT FROM AUTHOR]

• Soil porosity has a strong impact on the thermal performance of SBTES. • Seasonal variation in surface pressure has no effect on SBTES performance. • Ignoring subsurface moisture content may lead to errors in SBTES performance estimation. The thermal performance of soil borehole thermal energy storage (SBTES) systems in unsaturated soils is investigated to address three primary objectives: (1) to explore the impact of subsurface moisture content condition on the SBTES thermal performance, (2) to assess the effect of seasonal surface pressure variation on the SBTES thermal performance, and (3) to examine the influence of soil porosity on the thermal performance of SBTES in homogeneous and layered soils. Results indicate that a higher subsurface moisture content leads to a lower average temperature in the thermal storage domain. Notable hydrodynamic fluctuations are observed in the shallow depth of SBTES domain because of seasonal surface pressure variations although the average temperature and heat storage in SBTES remain mostly unaffected. The results show that a low soil porosity leads to superior SBTES thermal performance, while high porosity soils experienced more pronounced hydrodynamic fluctuations under surface pressure variation conditions. The impact of soil porosity on SBTES thermal performance is minimal in layered soil, except when one soil layer dominates and has a high volume fraction. [ABSTRACT FROM AUTHOR]

The migration behavior of pollutants is affected by consolidation and temperature when using thermal desorption technology to clean contaminated sites. Based on a one-dimensional consolidation model for unsaturated soil and the traditional heat conduction equation, a pollutant transport model accounting for the combined effects of consolidation and temperature was established in this paper. An analytical solution was obtained by using the separation of variables method and the integral transformation method. In addition, the correctness of the proposed model was verified via a comparison between the existing analytical solution and the theoretical model. Finally, adopting benzene as the research object, the influence of different factors on pollutant migration was studied. It was found that the growth rate of the pollutant concentration increased with increasing consolidation pressure, and the final pollutant concentration decreased with increasing consolidation pressure. The pollutant concentration increment due to temperature first increased and then decreased with increasing migration distance. The higher the Soret coefficient and volumetric moisture content are, the higher the pollutant concentration. • The impact of consolidation on pollutant migration is mainly considered in saturated soil throughout the experimental and theoretical research results of scholars on pollutant migration, and this article mainly focuses on the influence of consolidation and temperature on pollutant migration in unsaturated soil. • Most scholars mainly focus on the relevant parameters involved in the migration process of pollutants due to temperature changes, while this article mainly explores the direct impact of temperature on pollutant migration.This article is based on the one-dimensional consolidation model of unsaturated soil proposed by Chen (1993). It is assumed that the temperature field distribution in the research domain conforms to the heat conduction equation, which convenient to reflect the direct impact of temperature field on pollutant migration field. Considering the thermal diffusion effect, establishing a mathematical model for the migration of unsaturated soil pollutants that simultaneously considers the consolidation effect and temperature effect. • The analytical solution of the model is obtained using the separation of variables method and integral transformation method. Through the analysis of the analytical solution, the consolidation effect, temperature, and The influence of retardation factors and volumetric moisture content on pollutant migration. [ABSTRACT FROM AUTHOR]

Hydropower resources have been developed to the cold regions in the west of China recently, wherein the dam will be subjected to high frequency of repeated freeze-thaw action during the construction process in winter, and thus will cause safety and stability problems of these projects. According to the actual construction situations of Lianghekou hydropower station located in Sichuan Province, one-side freezing and two-side thawing tests of unsaturated core-wall soil samples in a closed system are carried out, and the evolution of temperature, water and displacement as well as their interaction are tested and analyzed. The results show that with the increasing of freeze-thaw cycles, water migration results in a decrease of water content in the unfrozen zone and an increase in the frozen zone, and the water concentration area is formed in the soil column. Simultaneously, a deeper freezing depth accompanied with a shorter thawing duration after 10 freeze-thaw cycles is observed through the temperature field results, whereas a steady fluctuation of the deformation field is showed after the 7th freeze-thaw cycle. Moreover, based on the test results and exiting researches, a thermo-hydro-mechanical coupling model for unsaturated soils subjected to cyclic freeze-thaw action is proposed, in which both the permeability and compressibility are inextricably related to the void ratio, and vary in different calculated areas. Additionally, the effects of number of cycles on initial conditions and model parameters are also considered. Comparisons with the experimental data demonstrate the validity and adaptability of the proposed model in describing the freeze-thaw process of unsaturated soil. Through the combination of experiments and numerical simulation, the freeze-thaw process can be more clearly understood, and related engineering problems can be predicted with the help of the mathematical model in this paper. • One-side freezing and two-side thawing tests of unsaturated soil are carried out. • A thermo-hydro-mechanical coupling model in freeze-thaw process is proposed. • The thermo-hydro-mechanical coupling mechanism is revealed by simulations. [ABSTRACT FROM AUTHOR]

Land and groundwater pollution is increasingly threatening public health and ecological safety. Vertical drain is recognised as an effective solution to clean up contaminated lands. Clean-ups often involve complicated hydro-chemical transport processes and are difficult to manage. This study presents a consolidation–solute transport model to assist with clean-up management. The model can predict coupled consolidation and chemical transport in diverse ground conditions, e.g., fully or partially saturated, less to highly deformable, or permeable to impermeable layers. To factor in the varied ground conditions, the model integrates the unsaturated flow characteristics, finite deformation theory and finite difference method into a set of governing equations and numerical solutions. The model was experimentally verified and then applied to examine effects of soil saturation conditions, solute transport conditions, and consolidation efforts on solute transport. The results show that the dispersion process contributes to the chemical clean-up, whereas the contribution becomes less noticeable in unsaturated conditions. The solute sorption process counteracts the solute transport and delays the clean-up. The consolidation accelerates the transport of reactive chemicals but shows limited effects on transport of non-reactive chemicals. [ABSTRACT FROM AUTHOR]

Water level rise and fall can lead to changes in seepage flow in the bank slopes of reservoirs. Cyclic seepage flow can result in the redistribution and even loss of fine particles in the slope, which eventually influences the slope stability. In this study, numerical simulations were conducted based on a multispecies transport finite element method (FEM) to investigate the influence of periodic water level fluctuations on the reservoir bank slope. The unsaturated soil was treated as a five-constituent mixture, by which erosion and deposition behaviours were captured by phase transition between deposited and fluidized fines. A constitutive model for suffusion considering the hydraulic fluctuation effect was employed to quantify the erosion process. The change in the seepage field and the corresponding evolution of the erosion rate and fines eroded ratio in the slope during the fluctuation period were investigated. The influence of the water level fluctuation frequency on the fines redistribution in the slope was analysed. Furthermore, the evolution patterns of the slope stability under different fluctuation frequencies were compared. The numerical results indicated that a higher fluctuation frequency could promote fine particle loss in the zones near the slope surface, consequently inducing greater deterioration in the slope stability. [ABSTRACT FROM AUTHOR]

A generalized water retention curve (WRC) model in a wide suction range considering the initial void ratio is presented in this paper. Both capillary and adsorbed water in soil pores are considered. Based on the experimental results that the adsorbed water content w a is not dependent on the initial void ratio, a new degree of saturation equation of adsorbed water is established. Meanwhile, a new degree of saturation equation of capillary water at various initial void ratios is proposed with a void ratio-related expression of the air entry value. Compared to Lu's model, only one parameter b is introduced in the established model, which can be easily calibrated using WRCs under two initial void ratios. The measured WRC results of 5 soils are used to verify the proposed model in comparison with the other 3 widely used WRC models. The soil used in the model validation covers a wide range of soil types from sandy soil to clay soil, including clayey silty sand, sandy clay till, clayey silt, expansive soil and lateritic soil. The proposed model is well verified for its ability to describe soil water retention characteristics in a wide suction range at various initial void ratios. [ABSTRACT FROM AUTHOR]

Lateritic soils are associated with a high content of sesquioxides, which enhance the aggregation of fine particles. The formation of aggregates can induce significant changes in the pore size distribution (PSD) and consequently affect the hydro-mechanical behaviour of lateritic soils. The influence of mineral types on the extent of aggregation and the stress-dependent water retention behaviour of lateritic clays is not well understood. In this study, the stress-dependent water retention curves (SDSWRCs) of a compacted lateritic sandy fat clay with halloysite (i.e., GLH) obtained from Ghana were measured at different net vertical stresses using an improved stress-controlled pressure plate apparatus. The results were then compared with those of another lateritic sandy lean clay with goethite (NLG) obtained from Nigeria. Additionally, scanning electron microscopy (SEM) was employed to examine the microstructure associated with these soils. The experimental results show that GLH has a higher ability to retain water than NLG at any given suction, even though the former has a higher void ratio than the latter prior to the drying-wetting cycle. This is because of the presence of relatively small aggregates and small-size macropores in GLH, as revealed by SEM images. On the other hand, the water retention capacity of both soils reduces with elevated stress levels, except at net vertical stress of 120 kPa for GLH, with a corresponding decrease in the rate of desorption. Furthermore, the overall increase in the total degree of hysteresis measured is almost 2 times higher for NLG (i.e., 116%) than GLH (i.e., 72%) in the stress and suction range considered, contrary to the decreasing trends commonly reported in the literature. It was found that the sizes of aggregates in GLH reduced ('finer soil') as stress level increased and caused more water to be retained. Conversely to GLH, the aggregate size remained unchanged for NLG, as revealed by aggregate size analysis. This is mainly because of the differences in the strengths provided by the unique minerals in the two soils (i.e., halloysite for GLH and goethite for NLG) to the aggregates, due to the different parent rocks from which the soils were formed. • The water retention curves of a lateritic clay with halloysite (i.e., GLH) as predominant minerals was investigated. • The results were compared with those of another lateritic clay with goethite (NLG) as predominant mineral. • The sizes of aggregates in GLH reduced ('finer soil') as stress level increased and caused more water to be retained. [ABSTRACT FROM AUTHOR]

In this study, we used a probabilistic approach to evaluate the probability of failure of small diameter bored piles in unsaturated sandy soils. The prediction of the bearing capacity was based on the Cone Penetration Test (CPT). We assessed the seasonal influence by analyzing CPT data from dry and wet seasons. The LCPC and Aoki-Velloso semiempirical methods were deterministically applied, and the Aoki-Velloso method was examined using reliability theory. The first-order reliability method (FORM) was used to evaluate the probability of failure and calculate the reliability index based on random variables obtained from CPT data considering the effect of season when predicting bearing capacity. A total of 8.0 m long bored piles with diameters of 0.25, 0.30, and 0.35 m were used for both deterministic and probabilistic analyses. We also evaluated the influence of load ratio variation on the reliability index and determined the pile length required to reach a target reliability index value. Reliability analyses considering CPT campaigns conducted in different seasons showed the effect of season on the prediction of bearing capacity. For example, an 8.0 m long pile with a 0.30 m diameter and 100 kN vertical load had a probability of failure of 38.7 % in the wet season and 0.01 % in the dry season. The reliability analyses provided insights into the influence of seasonal variability on in situ tests for pile bearing capacity, affecting the design of foundation elements. • Reliability analyses showed the influence of seasonal variability on in situ tests. • Failure probability differ between CPTs conducted in the dry and the wet seasons. • Seasonal variability affects the design of foundations in unsaturated soils. • Analyzing data from both dry and wet season results in distinct pile lengths. [ABSTRACT FROM AUTHOR]

Pre-existing (open) cracks at slope crests, especially tension cracks, are a significant factor in the transition from shallow to deep-seated landslides in unsaturated soil slopes induced by rainfall. This paper presents an analytical framework to assess the stability of unsaturated soil slopes for deep-seated rotational failure considering arbitrary crack depths and unsteady infiltration, and its effectiveness is verified by previous literature and finite element analysis. A closed-form formula is proposed for the maximum depth of cracks in unsaturated soils by the stability of the vertical crack boundary. A parametric study is performed to investigate the impact of some key parameters on the stability of unsaturated soil slopes with cracks. Dimensionless stability charts are developed, which can calculate the factor of safety for the slopes with cracksof any depth and can reflect that the potential slip surfaces through or without passing through the crack tip. In addition, given the existence of a critical crack depth and maximum crack depth, with a ratio ranging from 0.5 to 0.6 based on the stability charts, deep-seated rotational failure is more likely to occur than failure caused by a crack boundary. [ABSTRACT FROM AUTHOR]

This study focuses on investigating the shear behavior of the Shanghai clay-concrete interface under cyclic loading using a large-scale multifunctional shear apparatus. Considering that soil-structure interfaces are typically found in shallow soil layers or even above the ground surface, the interface zone is unsaturated in its natural state, the shear experiments were therefore conducted on the tested soil with different water contents. The corresponding matric suction of the tested soil under different water content and initial dry densities was determined by the filter paper method. The experimental findings indicate a substantial influence of matric suction on the interfacial strength, revealing a pronounced non-linear relationship. The interface exhibits the highest shear strength during the initial shear, which gradually decreases with an increasing number of shear cycles. This reduction can be attributed to the weakening of the bonding effect at the interface caused by cyclic shear. On the other hand, the matric suction decreases with water content increases, leading to a decrease in interface shear strength. Additionally, the vertical cumulative displacement of the soil increases with higher water content. • Cyclic shear experiments were conducted on the interface between unsaturated Shanghai clay and concrete. • The interface strength exhibits a non-linear relationship with the matric suction. • The contribution of matric suction to the interface strength is significantly influenced by the number of shear cycles. [ABSTRACT FROM AUTHOR]

• Develops a fractal thermal conductivity model of heterogeneous soils. • The model can predict the thermal properties of unsaturated fine-grained soils. • The model can capture the thermal conductivity evolution during soil deformation. • The developed fractal model performs better compared to other models. Accurately predicting the thermal conductivity of unsaturated soils is crucial for assessing and simulating the long-term environmental impact of subterranean engineering structures. This study presents a fractal thermal conductivity model for unsaturated soils that considers the influence of heterogeneous pore topology, water content and volumetric deformation. Based on the results from the scanning electron microscopy (SEM) and mercury intrusion-extrusion cyclic porosimetry (MIECP) tests on Shanghai clay and Kaolin, we introduce the pore-throat structure to describe the soil heterogeneity and deal with the coupling of solid-pore thermal properties through the mixing law at the pore scale. Together with the self-similar fractal law, the thermal conductivity model is upscaled from the pore scale to the representative element volume (REV) scale. During the process, heterogeneity factors are introduced to describe differences between local and bulk properties, such as porosity and saturation. Thermal property tests of Shanghai clay and Kaolin with varying porosities are then conducted to validate the proposed thermal conductivity model. Additionally, nineteen published datasets on thermal conductivity are also utilized to confirm the adaptability and robustness of the model. The results show that the proposed model predicts well the thermal conductivity of unsaturated soils. Moreover, when compared to existing models, the proposed model offers superior performance in describing the thermal properties of unsaturated soils. [ABSTRACT FROM AUTHOR]

Identification of water–air distribution at meso-scale in unsaturated soil is of great significance in the field of soil studies. In order to better understand the water–air distribution in soil pore, a meso-scale numerical model was developed: (1) a stochastic generation method was developed for the generation of mesoscopic soil structure, (2) the lattice Boltzmann method was selected for the numerical solutions of multiphase flow partial differential equation (PDE) in soil pore, (3) the water–air interface was tracked by using Shan–Chen model. The generation of soil structure and the solution of governing equations were completed by Open Source Lattice Boltzmann Code (OpenLB). The simulated water–air distribution shapes were almost the same with those reported in literature, indicating that the model developed in this study can be well used to evolve the water–air interface formation. Water–air​ distributions in soil pore at different porosities, wettabilities and saturations were detailed. [ABSTRACT FROM AUTHOR]

Triaxial tests and numerical simulations were conducted to determine the water absorption compression of unsaturated soil. In the triaxial tests, unsaturated silt specimens under the same initial condition were prepared and the processes of different suction reduction, isotropic consolidation, and exhausted-drained shearing were applied to the specimens. The numerical simulations used a soil-water-air coupled finite deformation analysis code with a newly incorporated elastoplastic constitutive model. The degree of saturation was introduced to the internal state variables of the yield function of the SYS Cam-clay model and a soil-water characteristic model with void ratio dependency. Then, the triaxial test was treated as an initial and boundary value problem, and the series of processes in the experiments were simulated using a single set of material constants and initial values. The new findings are as follows: 1) The loading criterion and the classification of loading conditions considering change in saturation degree can be specified in the elastoplastic constitutive model for unsaturated soil. 2) Water absorption compression behavior was observed in the experiments not only under suction reduction but also under constant suction condition. This water absorption compression under constant suction condition was explained as a saturation-increase behavior due to volume compression using the soil-water characteristic model with void ratio dependency. 3) By considering the triaxial test as an initial and boundary value problem, the temporal change in the volume and the amount of water absorption/drainage were able to be reproduced. [ABSTRACT FROM AUTHOR]

A method is presented for using DEM to find the pore pressure, total stress, and effective stress within a granular assembly during either undrained or drained conditions, by using poroelastic principles to directly determine the pore fluid pressure. The paper considers both the saturated and quasi-saturated conditions, the latter meaning a slightly unsaturated granular material, in which isolated gas bubbles reduce the compressibility of the pore fluid but do not form liquid bridges between the particles. The presence of air increases the pore fluid compressibility and is known to improve undrained strength and liquefaction resistance and has been considered for remediation of loose, susceptible soils. Past DEM studies have approximated undrained loading as a constant-volume condition, but this approximation does not allow the simulation of complex loading sequences, even with fully saturated materials. The paper's method allows the direct control and measurement of total stress, water pressure, and water influx. The method includes the effects of water compressibility, grain compressibility, pore air compressibility, surface tension, air solubility within the pore liquid, and vapor pressure of the water gas phase. These factors all affect the evolving sizes of the bubbles and the consequent compressibility of the air–water mixture. The resulting algorithm is applied in three examples: the laboratory saturation of a soil specimen by increasing chamber pressure and back pressure, the undrained triaxial compression of quasi-saturated specimens, and the cyclic undrained triaxial liquefaction of quasi-saturated specimens. Example simulations agree favorably with laboratory tests. [ABSTRACT FROM AUTHOR]

The assessment of the internal stability of geosynthetic-reinforced earth retaining walls has historically been investigated in previous studies assuming dry backfills. However, the majority of the failures of these structures are caused by the water presence. The studies including the water presence in the backfill are scarce and often consider saturated backfills. In reality, most soils are unsaturated in nature and the matric suction plays an important role in the wall's stability. This paper investigates the internal seismic stability of geosynthetic-reinforced unsaturated earth retaining walls. The groundwater level can be located at any reinforced backfill depth. Several nonlinear equations relating the unsaturated soil shear strength to the matric suction and different backfill type of soils are considered in this study. The log-spiral failure mechanism generated by the point-to-point method is considered. The upper-bound theorem of the limit analysis is used to evaluate the strength required to maintain the reinforced soil walls stability and the seismic loading are represented by the pseudo-dynamic approach. A parametric study showed that the required reinforcement strength is influenced by several parameters such as the soil friction angle, the horizontal seismic coefficient, the water table level, the matric suction distribution as well as the soil types and the unsaturated soils shear strength. [ABSTRACT FROM AUTHOR]

In the present note, constitutive equations for air-water-solid three-phase porous materials were formulated considering thermodynamics in the context of continuum mechanics. In the formulation, the complementary energy function was used and the internal variable was adopted that manifests the inelastic strain. Then, a linear three-phase elastic model was analyzed in detail and the material parameters were identified based on drained, unjacketed tests and the suction-saturation relation. It is well known that, for partially saturated soils, Bishop's effective stress, generalized Bishop's effective stress and the skeleton stress concepts, etc. are used. From the present study, it was found that the skeleton stress with Biot's coefficient can be reasonably derived for air-water-solid three-phase materials. In addition, a saturation-matric suction relation was obtained by the constitutive model that includes the interaction between the solid skeleton and the fluids. [ABSTRACT FROM AUTHOR]