The soil water retention curve (SWRC) is the relationship between the volumetric water content and the matric suction of an unsaturated soil. One key parameter of the SWRC is the air-entry value (AEV), which defines the minimum matric suction at which air starts to enter the largest pores in the soil as it desaturates. The volumetric water content at the AEV can also be identified from the evolution of the volumetric shrinkage characteristic curve (VSCC). The VSCC is the relationship between the void ratio and volumetric water content of an unsaturated soil as it dries towards the shrinkage limit. Fine-grained materials, such as dredged materials and mine tailings comprising clay minerals and natural clays, show a marked volume change with variation of the water content. In this study, the AEVs of three fine-grained materials (dredged material, red mud and kaolin) were measured from SWRCs and compared with the shrinkage limit values obtained from the corresponding VSCCs. The SWRC was measured by utilizing full-range polymer tensiometers. The polymer tensiometer is filled with polymer solution instead of water, diminishing the effect of soil salinity, and can measure the matric suction up to -1500 kPa. The SWRC and VSCC results were compared and discussed in terms of their applicability to providing an understanding of unsaturated soils that undergoing large volume change.

Results of plate load tests performed on saturated and unsaturated silty sand samples are presented. Very little is known about how to interpret the plate load test when performed on unsaturated soils comprising silt-sand mixtures, as the few published studies have been limited to either unsaturated clean sands or clays. The new plate load test results are interpreted using a bearing capacity equation, applicable when non-uniform χs profiles prevail in the soil, where χs is the contribution of suction to the effective stress. The interrelation between χs, strength and bearing capacity is shown. There is a good agreement between measured and computed bearing capacities. Assuming χs remains constant during a plate load test, compared to assumptions of constant suction or constant moisture content, simplifies interpretation without significant loss of accuracy. For a particular soil density, the bearing capacity for an unsaturated condition is found to be much larger than that for a fully saturated condition. It is also shown that the effect of suction on the bearing capacity is dependent on the initial location of the hydraulic state on the soil-water characteristic curve. Failing to account for suction and the hydraulic loading history may lead to incorrect interpretations. It is also demonstrated how plate load tests may be used to infer the value of χs at the soil surface.

Sand migration in gas hydrate-bearing reservoir poses a serious problem for a successful long-term gas production. Because gas production is achieved through hydrate dissociation, often driven by depressurization, the process of sand migration involves highly coupled multiphysics behavior. For example, hydrate dissociation causes sediment deformation and may increase the potential of sand migration but hydrate dissociation can also increase permeability, which may lower hydraulic gradient at a given flow rate, leading to reduction in sand migration. Other factors include that sand inflow (or outflow) would cause the increase (or decrease) in pore pressure due to void volume change and thus may halt (or accelerate) hydrate dissociation. An analytical thermo-hydro-mechanical sand migration model to incorporate these interacting features requires a number of parameters and it is important to quantify the significance of each parameter to this complex process of sand migration in gas hydrate-bearing reservoir. This study, therefore, conducts a series of sand migration analyses in field-scale homogeneous gas hydrate-bearing reservoir subjected to depressurization and presents the relative importance of each parameter to the volume of produced sand from a production zone. It is found that the volume of produced sand is mostly dominated by the parameter converting shearing deformation to sand detachment potential and by the parameter increasing critical hydraulic gradient for sand detachment with hydrate saturation.

Natural disasters including earthquakes, typhoons and heavy rainfalls induce various risks such as slope failures. The conventional unsaturated soils hydrological properties mainly the Soil Water Characteristics Curve (SWCC) and the Hydraulic Conductivity Function (HCF) determination techniques are limited due to the complexity and prolonged time required. Thus a simple method that considers short time and high accuracy under the drying and the wetting phases considering remolded and undisturbed samples is lacking. Through this paper, a novel systematic testing setup utilizing the Continuous Pressurization Method (CPM) that allows rapid, concurrent, continuous, direct determination of the SWCC and the HCF considering both remolded and undisturbed samples was developed. It was found that the air pressurizing rate influence on the obtained SWCC using the developed system can be neglected. It was confirmed that remolded samples do not properly represent the in-situ conditions with significant error that should be carefully considered. It must be noted that applying low air pressurizing rate induces almost linear suction profile, however, it changes into higher order non-linear profile when applying high air pressurizing rates or achieving low degrees of saturation. A correction function based on Van Genuchten (VG) model was proposed which has finally led to obtaining accurate reliable HCFs. Finally, it was concluded that the developed system is rapid, direct, reliable, continuous with accurate repeatability that allows concurrent determination of both the SWCC and the HCF under the drying and wetting phases. Where the system allows concurrent determination of the SWCC and HCF in less than 7% of the testing time required using the conventional methods and considers testing both remolded and undisturbed soil samples.

As slope failures induced by rainfall are universal problems, especially in areas covered by residual soils, slope preventive system is necessary to avoid casualties. One effectively-proven alternative method is capillary barrier system (CBS) which utilizes the principles of unsaturated soil mechanics to minimize rainwater infiltration into soil layer. Previous studies indicated that the efficiency of CBS could be enhanced further by incorporating different hydraulic conductivities in two different directions. This study investigated hydraulic anisotropy by using two different types of soil layering, horizontal-layering (HL) and vertical-layering (VL), with two main soil compositions such as sandy silt and silty sand. The hydraulic anisotropy ratio observed in this study was then correlated with various soil properties, such as percentages of fines, dry density, plastic limit and liquid limit in order to find the relationship between hydraulic anisotropy ratio and soil properties. This study showed that percentages of fines and dry density of soils exhibit non-linear relationship with hydraulic anisotropy ratio, while plastic limit and liquid limit of soils exhibit linear relationship with hydraulic anisotropy ratio.

Soil is a porous material which consists of a collection of soil particles with voids. The soil particles have different sizes with certain statistical distribution which are commonly described using grain-size distribution curve (GSD). The characteristic of GSD has significant effects on the engineering properties of the soil (especially for coarse-grained soil). On the other hand, the geometrical pore space in soil can be described by the pore-size distribution function (PSD). There are limited studies on the effect of PSD on the engineering properties of soil. For the soil with insignificant volume change, the soil-water characteristic curve (SWCC) is considered to be analogous to the PSD. In this paper, the soil skeleton is assumed to be rigid and the roles of PSD on the air/water flow in the unsaturated soil and on the unsaturated shear strength are explained. The proposed theories utilizing different PSDs are able to estimate the saturated hydraulic conductivities of different soil types. The proposed theories and equations are verified with experimental data from literatures.

Concerning on the liquefaction behavior of a type of bulk cargoes, iron ore fines (IOF), during maritime time transportation, systematic experimental and numerical programs were conducted. In this study, as an important parameter for seepage analysis, permeability of saturated and unsaturated typical IOF were evaluated in a triaxial system. As a comparison, similar tests were also conducted on a widely used laboratory material, Toyoura sand. The tests were conducted very carefully considering effects of system head loss and filter clogging issues on the hydraulic gradient applied to specimens. It was revealed that coefficient of permeability (k) of the typical IOF with compaction degree of 91-93% was about 1×10-5m/s for saturated condition (Sr=100%) and 2×10-7 m/s for Sr=84%. In addition, k of IOF-B in a full Sr range was estimated based on water retention data and k of unsaturated Toyoura sand in the past studied were summarized, which suggested that the testing system performed reasonably well.

This work develops a constitutive model for unsaturated nature loess considering the loss of structure upon wetting. the proposed model is an unsaturated kinematic hardening structure model (UKHSM) in the framework of Bishop's effective stress approach. The UKHSM is characterized by isotropic and kinematic hardening law in the bounding surface formulation, as earlier proposed by Muir et al. The UKHSM incorporates measuring structure degradation caused by moisture variation and describes the essential phenomena of pre-failure behavior of natural loess, including load&wetting induced collapse behaviors. CU, CD and CW triaxial tests on Henan loess have been modeled to validate good capability of the UKHSM.

Most residential houses in Loess Plateau of Northwest China have been built five decades ago. The wheat straw retrieved after crop harvesting has always been mixed with the loess to construct house walls. In spite that the extreme climate has already caused a series of extensive natural hazards (e.g., earthquake), the residential houses are well functioned until nowadays. This unique phenomenon drives this study to investigate the mechanical behaviour of the mixture of loess and wheat straw. Thus, uniaxial compressive strength tests and strain-controlled and stress-controlled direct shear tests are implemented on the loess-wheat straw mixture specimens. By adding the wheat straw to the specimens, the failure mode is transfers from the "shear failure" to the "ductile (barrel-shaped) failure" under uniaxial compression loading conditions. Compared to the loess specimens, the loess-wheat straw mixture specimens demonstrate its superior ability of withstanding larger shearing stresses as subjected to similar shear displacements. The gained insights guide the design of upcoming sustainable infrastructures.

Geosynthetic Clay Liner (GCL) has become an important component of waste containment system. The GCL is laid at the as-rolled moisture condition in the field and hydrates through absorbing water from the underlying soils or compacted clay liner. The degree of hydration or saturation of the GCL is important as it can affect the performance of the GCL. Thus, the water retention curve (WRC) of GCL is important for understanding the saturation process of the GCL. The GCL consists of a layer of granular sodium bentonite clay sandwiched in between a nonwoven geotextile and a woven geotextile. Test results showed that the geotextiles are fully desaturated when the suction is greater than 2 kPa. Thus, the WRC of GCL over the larger suction range is governed by the bentonite. In this paper, the water retention of commercially available powder bentonite and granular bentonite used in the GCL are determined by direct measurement using tensiometer and indirect measurement using chilled-mirror hygrometer. The implications of the water retention characteristics of the bentonites in a GCL are discussed.

An experimental study using kaolinitic clay was performed in order to understand the unsaturated behavior of soils with high organic matter content (OMC). Reconstituted samples of kaolinitic clay were prepared with different OMC. Soil Water Retention Curves (SWRC) were obtained after drying and wetting processes and volume changes were also measured. Matrix suction was measured by the filter paper technique. Results show that for a constant value of suction, the higher the OMC the higher the water content. The Higher the OMC, the lower the Air Entry Value and the slope of the SWRC. OMC showed to have a different influence in the Volume Change behaviour (VC) in the drying and wetting process. Experimental results suggest possible engineering applications for the evaluation of volume change due to suction changes on kaolinitic soils with relatively high OMC.

As a country with rich mineral resources, Australia, is amongst the top five world's leading exporter of minerals. As such, coal tailings, one of the by-products of mineral exploration, pose ample challenge for its handling, management and disposal in tailings dams. These usually are encountered with high moisture content. In order to avert the risk of fluidization and associated failures of coal tailing dams, dewatering is necessary to be applied for reducing their water content. With this in mind, some laboratory experiments based on a local coal tailings sample has been presented in this manuscript. The coal tailing sample has been characterized by conducting the liquid limit test, plastic limit test and shrinkage limit test. Sieve analysis and hydrometer test have been conducted to establish the gradational property of the material. Modified compaction test and one-dimension consolidation test have been performed and the load-deformation response of the material is described in detail. Also, the vane shear test has been conducted to figure out the relationship between gravimetric moisture content and shear strength. Furthermore, hydraulic and volume change response of the sample subjected to changing moisture content have been studied through soil-water retention curve (SWRC) and soil shrinkage characteristic curve (SSCC).

A fully coupled algorithm based on a recently developed meshfree method, called smoothed point interpolation method, is introduced for hydro-mechanical analysis of unsaturated porous media considering hydraulic hysteresis and material nonlinearity. A simple node selection scheme is adopted which ensures the non-singularity of the moment matrix in constructing the polynomial point interpolation shape functions. An effective stress based framework based on the work of Khalili et al. (2008) is followed in this study, and a hysteretic water retention model is taken into account which enables the evolution of water retention curve (WRC) with volumetric changes (Pasha et al., 2017). An elastoplastic constitutive model is employed within the context of bounding surface plasticity theory for predicting the nonlinear behavior of soil skeleton in unsaturated porous media. The applicability of the model is verified through several numerical examples.

A new explicit and rigorous analytical solution is presented to study the axisymmetric consolidation of a vertical drain inserted in a finite unsaturated soil layer. In the derivation, the decoupling process is employed to convert the governing equations of excess pore-air and pore-water pressures into essentially the same homogeneous partial differential equations (PDEs). Later, the explicit analytical solution with time is obtained by employing the separation variable method. Additionally, validation exercise is conducted to confirm the proposed solution is correct. Finally, the changing regularity of excess pore-air pressure, excess pore-water pressure and normalized settlement are studied against the ratios of air-water permeability, the ratios of radial-vertical permeability and depth. It is concluded that the solution presented in this paper is reliable and the research method has a reference to more complicated consolidation problems.

Maximum and minimum void ratios are two fundamental parameters for evaluating the packing efficiency of granular materials. For binary-sized granular materials composed of two size classes (coarse and fine), many packing models has been proposed for predicting their packing density (relating to void ratio). However, analytical packing models directly based on maximum and minimum void ratios are very limited in the field of geotechnical engineering. In this study, using a concept of dominant size class, a nonlinear packing model was developed for predicting the maximum and minimum void ratios with respect to fines content. Only two parameters (filling coefficient and embedment coefficient) were required in the proposed model and they were found to be closely related to the particle size ratios between the two size classes. The applicability and accuracy of the developed model were verified by experimental results of the crushed pellets of GMZ bentonite in this work and that of several other granular materials from literature. Furthermore, the relationship between the maximum and minimum void ratios was investigated. It appeared that the maximum void ratios were linearly related to the minimum void ratios with the same slope, regardless of the particle size ratio between the two size classes.

Bearing capacity of unsaturated soils can be interpreted extending either the modified effective stress approach (MESA) or the modified total stress approach (MTSA) depending on the type of soils and drainage conditions of pore-air and pore-water. However, the bearing capacity of unsaturated soils are typically estimated extending the MESA, rather than MTSA. In this study, an attempt was made to validate the MTSA by comparing the measured bearing capacity values from a series of model footing tests in an unsaturated cohesive soil with those estimated using a semi-empirical model and finite element analysis extending the MTSA. The commercial finite element software, SIGMA/W was used to numerically determine the bearing capacity values based on the vertical stress versus surface settlement behaviors of a model footing.

In this study, soil cement, as a method to enhance soil strength, was used as surface erosion protection. A series of erosion resistance tests were conducted to evaluate the resistance of soil cement to erosion due to rainfalls. In the experiments, two materials: DL clay (artificial silt) and normal Portland cement were used. The erosion model tests consisted of two layers of soils: 10 cm thick top layers treated with cement and 20 cm thick DL foundation layers. Three cases with different cement contents: Cc = 0, 3 and 5% in dry weight ratio were conducted under rainfall intensity 50 mm/h. The slope models were compacted in dry density:ρd = 1.3 g/cm3, the water content: w = 17 % and degree of compaction: D = 86%. The soil cement layers were cured for 7 days. The results of experiments show that in the case with Cc = 0%, the erosion developed from the lower to the middle part of the slope, and it was recognized as rill erosion. In the case with Cc = 3%, little erosion occurred and several spot splits, whose diameters were approximately 5 cm, were found on the surface. In the case with Cc = 5%, some small holes were only seen on the surface after the test. The bond due to cement hydration was sufficiently so strong that it prevented the surface layer treated with cement from strong detachment. The hydration of cement, DL clay and water formed the intra-aggregate pores inside the treated soil, which lead to increase the permeability and enhanced the infiltration of water into the soil. It reduced amounts of runoffs and soil loss. The overall results suggest clearly that the cemented DL clay layer effectively protects soil surface from erosion.

Sinkhole accidents bring various damages to the society and the infrastructures. Some of the accidents are induced by internal erosion with the seepages. Concretely, soil is drained to cracks and breakages of sewer pipes in urban areas with rainfalls. The underground cavities are expanded by soil drainages and finally it causes sinkholes. Recent studies simulated these phenomena but there are some differences between experimental conditions and actual ones. For examples, practical ground containing fines is not uniform, having lower permeability than of the model ground. This study aims to make connection of the knowledges indicated by the previous researches using simulations by the model ground, and actual phenomena happening in the ground. Firstly, we performed the model tests using a backfill soil. Obvious collapse and cavity expansion hardly occurred because of the very low permeability. It is suggested that two specific conditions are required to promote the cavity expansion; one is the strong seepage close to the cavity, and which directly flow into there. Another is repetitions of drying-wetting in the ground. After the end of infiltration, cone penetration test was performed to evaluate the stiffness vicinity of the cavities. We proposed the new evaluation method based on the fines contents.

Slope protection works are often used on the surface of slopes of road and railway embankments, in order to prevent from seepage of rainfall and erosion. However, the effect for the reduction about water content has not been clarified by experimental and numerical studies. In this paper, the measurement of the water content in the test embankment with the leaking isolation sheet was conducted. From the comparison of the measurements with the presence and absence of slope protection works, it was revealed that the slope protection works played a role for prevention from seepage of rainfall.

Desaturation is an effective ground improvement for mitigating liquefaction-induced ground failures. This paper aims to discuss numerical capabilities for simulating the undrained cyclic behavior of desaturated silica sands. The laboratory experiments were initially conducted to investigate desaturation effects on medium dense desaturated silica sand behavior (Dr=60-65%, Sr=91-100%) under undrained triaxial loading conditions. Desaturation was achieved by injecting micro-bubbled water. The experimental results showed an increase of the angle of a phase transformation line, ϕpl, in 4-5˚, no desaturation effects on the angle of a critical state line, ϕcl, and less degradation of Young modulus comparing to the saturated condition. The numerical analysis was secondarily performed to simulate the experimental results using LIQCA2D17. The comparisons to the preliminary experimental result showed that failure criteria were critical on stress-strain behaviors, and the Yasufuku criterion was suitable for both saturated and desaturated conditions. The desaturation effects were further discussed. The desaturation critically affected the stress-strain behavior after the stress path reached the phase transformation. The desaturated silica sands exhibited continuous modulus reduction although the specimens were fully liquefied (i.e., EPWP ratio nearly equaled to 1.0). Liquefaction of those desaturated silica sands was characterized as "slowly flow deformation."

Many research works have been conducted on saturated soils under cyclic loadings. Most embankments such as fill dams, road and railway embankments are constructed by compacted unsaturated geo-materials. Nowadays, it has been more important to study the dynamic properties of unsaturated soils in geotechnical engineering. However, there have been few research works on the unsaturated soils under cyclic loadings. The main purposes of this paper are to investigate cyclic deformation properties of an unsaturated silt named DL clay, and to obtain stress-dilatancy relationships under unsaturated conditions. The stress-dilatancy relationships are expressed as the relationships between plastic strain increment ratio: dԑvp/dγp and stress ratio: q/p'. Triaxial cyclic loading tests were conducted for isotropically consolidated and unsaturated-state silt specimens under a constant net confining pressure and different suctions with three different types of cyclic shear loading applied. The stiffness of the soil increased with an increase in suctions and cyclic times. Total amount of volume reductions of the specimens decreased with an increase in suction. As the numbers of cyclic loadings and suction values increased, the amount of dilations also increased. The stress-dilatancy relationships could be formulated as linear lines and the relationships were valid under loading and unloading processes for all specimens.

The deformation of the unsaturated granular material under the action of large number of cycles can be interpreted by several ways. The various changes on the soil properties by the application of the cyclic loading creates an unique response to the applied external forces. A change in any one of the several properties of the soil will create a response which will be different from the responses created by altering other properties. One of the parameter influencing the soil response under the application of cyclic load is soil suction. For development of the realistic coupled model which takes the account of different nonlinear behavior coupled intrinsically in the model, needs a general experimental overview beforehand the model development process is undertaken. In this regard, this study is performed for the response of the rigid footing coupled by the multidimensional nonlinearity in the domain of the unsaturated soil and the angular loading. The coupled phenomenon is furthermore studied in detail by performing the experiment in one domain by keeping the parameters in the other domain constant. The evolution of the displacement in each cycle which leads to the unique accumulated cyclic strain in the system is studied for the unsaturated domain at a constant angle. The comparative study of the accumulation behavior of plastic strain within the imposed cycle for the saturated, dry and two unsaturated condition of Hostun sand is performed and presented.

Dynamic analysis of earthen embankments is a crucial aspect in geotechnical engineering. It has been difficult to properly analyze the embankments, as it is difficult to obtain any experimental or field data. Centrifuge experiments on embankments would help us to properly understand the behavior of embankment, if we could simulate the conditions in centrifuge as close as to field. This study aims to experimentally simulate the response of an earthen embankment which is usually used for agricultural purposes, in centrifuge. Water level in the embankment is controlled and drawdown of the water was induced using a custom developed in-flight control of water path during centrifugal rotation. LVDT is used to measure the surface settlements. We have simulated the phenomenon which make the embankment weak in strength, steady state and rapid drawdown, and give shaking to the model to observe how theses phenomenon would affect the strength of embankment. Time histories of acceleration and pore water pressure are shown in this paper. Even though both steady state and rapid drawdown are critical phenomenon of embankment, cracks and failure of upstream slope is seen only in rapid drawdown condition.

A fully coupled flow-deformation model is presented for the nonlinear cyclic analysis of multiphase unsaturated soils. The coupling between fluid flow and deformation fields is established using the effective stress parameters. The hydraulic hysteresis is accounted for in the model through the effective stress parameters and the soil water characteristic curve. The volume change dependency of the effective stress parameters and the soil water characteristic curve is addressed in the formulation. The elastic-plastic behaviour due to cyclic loading is captured using the bounding surface plasticity. Numerical examples are presented, demonstrating the application of the proposed approach.

Newly constructed earth-fill dams in a residual soil rich area have a high probability of failure occurrence in the first five years of operation. Monitoring a rate of the first impoundment of the dams is critical for monitoring the effectiveness and designed function of the dam over its service life. However, stability of the dams is uncertain under influential factors such as variability of soil properties of support foundations, simultaneous increases of water level in the upstream and infiltration in downstream dam surface from prolonged heavy rainfall event. In this study, failure mechanism for an earth-fill dam due to concurrent rises in water level upstream and rainfall infiltration was investigated using saturated-unsaturated soil principles. Seepage was analyzed using Finite Element Method and slope stability was analyzed using Limit Equilibrium Method. Results of the failure mechanism were compared and discussed with respect to varying stiffness of residual soil support foundation, coupled rising water reservoir and applied prolonged rainfall.

Rainfall-induced failure is common after intensive rainfall events in mountainous areas, particularly in areas covered by residual soils. The infiltration of the surface water can have a significant influence on the stability of slopes. The increase of infiltration into the soil reduces the matric suction of the soil and hence results in a reduction of the shear strength of the soil, which increases the potential for slope instability. The mountainous road slopes in Timor Leste are located on scarp nearby the ocean. Slope failures repeatedly happened at several locations in Timor Leste after the intensive rainstorm events during the wet season. At some locations, the failure of the slopes occurred again even after the repair of the slopes. A geotechnical investigation, a geological study, and a surface seismic geophysical survey were conducted at the site to obtain soil/bedrock profiles and properties for the numerical modeling in this study. Seepage and slope stability analyses were conducted to evaluate the increase of the pore water pressures during the wet season and the resulting reduction of the slope stability. The results of the seepage analyses demonstrated that the pore water pressure within the slopes was significantly increased due to the increase in infiltration during the wet season. The results of the slope stability analyses showed that the as-built fill slopes at the dry season had only an initial factor of safety of about 1.3. The factor of safety of the as-built slopes was further reduced to reach unity or less during the wet season. The results of the analyses concluded that the triggering mechanisms for the failures are the combinations of geotechnical and hydrological properties in addition to the physical properties of the slopes. Conceptual repair plans including (1) regrading of the existing slopes, (2) installation of tieback anchors, and (3) installation of geogrids were considered in this study. Recommendations for the design of roadway in an area that is susceptible to a rainfall-induced slope failure potential were provided in the paper.

The purpose of this paper is to develop a new earth reinforcement technology called "The SDPR method" having both functions of a single earth reinforcement to increases the embankment strength and a drainage pipe to lower a ground water level in embankment at the same time. This paper summarizes the effectiveness of the SDPR method by means of unsaturated-saturated seepage analysis and slope stability analysis in terms of the drainage effect, reinforcement effect and unsaturation effect of SDPRs.

Influences of rainfall infiltration on the settlement of shallow foundations in unsaturated soil were numerically investigated. A computer based finite element analysis using PLAXIS 2D is used to estimate the effects of rainfall infiltration and hysteresis on the settlement behavior of the shallow foundations by incorporating the hysteretic soil-water characteristic curve (SWCC) of unsaturated soils derived from laboratory. There is a good comparison between load-settlement responses and variations in matric suction calculated from the numerical model in the present study were in good agreement with the field measurements. The results of the parametric studies highlight the rainfall intensity played a significant role in the wetting-induced settlement of shallow foundations in unsaturated soil. The wetting-induced settlement during rainfall was also affected by the groundwater table position near the ground surface due to changes in matric suction. In addition, the analysis by a wetting SWCC produced a slight lager settlement up to 5% than that of a drying SWCC. Therefore, appropriate SWCCs (i.e., drying or wetting) is encouraged in the numerical analysis in accordance with the condition that the soils underneath shallow foundations experience.

Resilient modulus (Mr), the ratio of the amplitude of cyclic axial stress to the amplitude of the resultant recoverable axial strain, is especially important in mechanistic pavement design procedure and it usually decreases in thaw season. This loss of stiffness was attributed to the change of moisture and the effect of freeze-thaw has not been considered completely. This paper proposed a new test method for resilient modulus of unsaturated unbound granular materials subjected to freeze-thaw action. By controlling the matric suction stable during freeze-thaw process, the water content before and after freeze-thaw is constant. As a result, the effect of freeze-thaw on resilient modulus could be studied. Test results illustrate that freeze-thaw process not only reduces resilient modulus greatly, but also weakens the influence of bulk stress, deviator stress, and matric suction on resilient modulus, even with same water content before and after freeze-thaw. Besides, a freeze-thaw process also leads to a smaller Secant Young's modulus and a larger permanent axial strain under repeated axial loads.

This study aims to reveal the effect of suction on the ice formation in unsaturated soil. Unfrozen water content was measured by a pulse NMR for the saturated and unsaturated silt prepared by vapor pressure technique. Based on the data, for the unsaturated frozen soil with the initial high water content, the unfrozen water content of the unsaturated soil has the same tendency as that of saturated soil. While, water rarely freezes in case of low water content. Water cannot freeze less than the water content corresponding to the beginning of residual water saturation for all conditions. Furthermore, the unfrozen water ratio of the unsaturated soil is higher than that of the saturated soil. Therefore, these results revealed that suction has strong influence on the ice formation in unsaturated soil.

A fully coupled flow-deformation model for describing time-dependent behaviour of unsaturated soil is presented. The proposed hydro-mechanical model is formulated based on the theory of multiphase mixtures using the effective stress approach and the bounding surface viscoplastic constitutive model. The governing equations for the flow model are derived using the conservation equations of mass and momentum. The deformation of the solid skeleton is described using the bounding surface viscoplasticity framework to capture the time-dependent stress-strain behaviour of geomaterials. The constitutive model is based on the viscoplastic consistency theory and the bounding surface plasticity model. The proposed viscoplasticity model allows a smooth transition from rate-independent plasticity to rate-dependent viscoplasticity. The hardening parameter representing the size of the bounding surface is defined as a function of viscoplastic strain, viscoplastic strain rate, and suction. For unsaturated soils, the suction hardening effect is described using the coupled influence approach where suction has a multiplicative effect to the viscoplastic volumetric hardening. The numerical results are then presented demonstrating the capability of the proposed model in describing time-dependent behaviour of unsaturated soils.

This paper focuses on the response of unsaturated granular soils under cyclic loading and the subsequent dissipation mechanism of excess air and water pressure which can result in the accumulation of water in the upper layer and increase of saturation degree in these zones. A problem that can be the source of structural instability and leading to problems such as capsizing the ships carrying unsaturated iron cargo and landslide failure. The employed numerical model is based on previous developments by the authors of a finite element (FE) approach that considers the hydraulic hysteresis of Soil Water Characteristic Curves (SWCCs) with a mechanical model based on two-surface plasticity to capture the cyclic mechanical response. We demonstrate that the accumulation of water in unsaturated soils subjected to cyclic motions happens during the consolidation stage and our chosen numerical framework can successfully capture this process. It is also shown that the problem can be explained by considering the difference between the dissipation speed of the water and the air phase and the settlement of the unsaturated soil during the consolidation stage.

In this paper, we propose a calculation method of pore size distribution which formed by soil having various soil particle sizes, assuming that soil particles and the pore between the soil particles are spherical. The pore spheres formed between the soil particles are defined as spheres that are inside four mutually contacting soil particle spheres and circumscribe all four soil particle spheres. The size distribution of the pore sphere is obtained from the probability of taking out 4 soil particle spheres based on the type and quantity of the soil particle sphere present. In addition, a calculation example of the pore radius distribution of the pore sphere formed by soil particle spheres having a particle size distribution similar to actual sandy soil is shown. By this method, it is expected that the suction stress acting between the soil particles of the unsaturated ground can be quantitatively evaluated and the suction stress in the unsaturated soil can be reflected in the design.

Gathering insights on materials at pore scale using digital imaging techniques, such as X-ray computed tomography (CT), gains more and more attention in various fields of engineering disciplines. The better understanding of material properties, internal structures, and material behaviour has generated many scientific and industrial advances. Investigations on porous materials, especially the visualisation of the pore space, allow the derivation of macroscopic material properties and provide a basis for numerical calculations, e. g. flow or contaminant transport through three-dimensional pore structures. The investigated porous material in this study is used in water-permeable road constructions as a novel pavement material aiming at instant drainage of rainfall into the subgrade and subsoil. Commonly used porous asphalt is made utilising bitumen-based binder materials. In this case, however, an innovative binder material based on polyurethane (PU) is used to form a flexible and porous pavement layer. The utilisation of this binder material not only increases the functionalities of the pavement layer but also increases rutting resistance and fatigue behaviour. This paper gives insights on the pore space obtained from CT-scans of two different pavement compositions of novel porous pavement material. The compositions vary in terms of particle size distribution of the utilised grains and the maximum grain diameter. The segmentation process of the obtained CT-images into the components of the multiphase media, i. e. grains, pore space, and binder material, as well as the reproduction of the three-dimensional models will be presented. Also results of investigations on the representative elementary volume for two volume-dependent properties will be demonstrated.

In the last years, X-ray computed tomography (CT) has been found to be a valuable tool to visualize and analyze structures in granular media from a microscopic point of view. With a sufficient resolution (voxel size) and a sequence of images over time, CT-images also allow to visualize processes in unsaturated soils, where microscopic features, such as the phase distribution (water-air-solid), the distribution of pores or air clusters as well as the interfaces between the phases, e. g. the interfacial area between the non-wetting and the wetting phase, can be studied. In the experimental program presented here, CT-imaging is applied to obtain 3D-data sets of two different soils in the unsaturated state. The hydro-mechanical behavior of free-standing unsaturated soil columns, only kept together by capillary cohesion, is investigated in two test series. In the first test series, soil columns, made of a coarse to medium coarse sand and of a packing of glass beads, are submitted to evaporation, while their macroscopic degree of saturation is monitored by weighing over time. The evaporation process is virtually stopped at selected time points by sealing the specimen from the outer atmosphere. Then, the specimens are placed in a micro CT-scanner to investigate the unsaturated state changed by evaporation from a microscopic point of view. The distribution of pore water, the change in interfacial area as well as the shape of capillary bridges can be analyzed with focus on the loss of capillary cohesion within the specimen on its way to collapse due to drying. In the second test series, a recently developed miniature compression device is used to perform uniaxial compression tests on free-standing cylindrical unsaturated sand and glass bead specimens. The compression device is also placed in a CT-scanner to obtain 3D-images for different compression stages, i. e. for different axial strain. The measured CT-data of the evaporation and compression tests are finally analyzed with the focus on differences between the hydraulic and mechanical behavior of irregular shaped sand packings and ideal glass bead packings. Furthermore, the microscopic and macroscopic behavior during a change in degree of saturation by evaporation and during mechanical compression can be compared.

It is known that unsaturated soil shows more brittle modes of failure with clearer shear band than fully saturated soil. Investigation of three-phase microstructural changes in shear band of unsaturated soil is important to clarify its mechanism. In the present study, x-ray micro computed tomography (CT) focusing on shear band was performed at different stages of deformation during a triaxial compression test for an unsaturated sand. Variations in the local void ratios, degrees of saturation, the number of grain contacts and the number of water menisci with development of shear band were revealed using image analysis techniques. The relationship between their microscopic behaviors and the macroscopic deviator stress of the unsaturated sand under triaxial compression is discussed.

To solve the energy shortage problem, transmission lines are widely built in the middle-west of China where the expansive soil is widely distributed. The transmission tower foundation may suffer wetting and shrinking load due to weathering. To solve this problem, consolidated undrained shear tests are conducted to obtain the mechanical behavior of expansive soil with different water content. The bearing behavior of pile foundation and plate foundation under uplift force are simulated by finite element method. The bearing capacity, axial force and lateral friction of pile foundation are analyzed. The bearing capacity of plate foundation is also investigated. These obtained numerical results can provide a good reference for the design of transmission line tower foundation when it is located in an expansive soil area.

Calibration chambers can provide a laboratory-controlled environment and have long been used to study, such as cone penetration tests and pressuremeter tests. However, the finite radial size of the sample that the chamber can accommodate may give rise to the boundary size effect which can influence the test results. When unsaturated soils, especially for soils where suction hardening is present, are concerned, the effect of suction on the boundary size effect is unknown. This study presents a new cavity expansion solution in unsaturated soils of finite radial extent, with which the boundary size effect can be quantified. The solution is formulated for spherical cavities subjected to two boundary conditions under the drainage condition where the contribution of suction to the effective stress is constant. It is found that samples with a higher suction value are under more influence of the boundary size effect and this is more obvious with higher mean net stress and higher void ratio.

The hydraulic states in dike are affected by external factors such as rainfall and river water level, and have direct relevance to the safety and stability of the structure. Unsteady unsaturated seepage flow analysis based on Richards equation for water mass balance is widely used to predict hydraulic states in dikes. However, previous trials suggest that this approach tends to reproduce much higher phreatic surface than observed in field during and after heavy rainfall. One factor explaining this problem is the potential effect of entrapped air in dike. In this study, a sandy river dike along Babame River in Akita, Japan, was chosen as a study site. Along with basic site investigation and long-term pore water pressure monitoring with tensiometers, 1- and 2-phase seepage flow analysis was performed to understand the role of air impedance in light of field monitoring results. 2-phase seepage flow analysis outputs more subdued pore water pressure responses than 1-phase analysis during and after extremely heavy rainfall (more than 100mm/day). For lesser rainfalls, however, the difference between the two analytical approaches was negligible.

In the present study, seepage failure by upward flow is numerically simulated using a seepage-deformation coupled method in which the internal erosion of fine particles and the transport of these particles are considered. The field equations are derived in the framework of multiphase mixture theory, and the erosion process is modeled as the mass transfer from the solid phase to the fluidized soil phase. In addition, the particle size distribution of soil is considered in the erosion criteria and the rate equation of the mass transfer. Using the proposed method, one dimensional upward flow in a gap-graded sandy soil is simulated. From the simulations, it is found that the seepage failure occurs under relatively low average hydraulic gradient when the internal erosion is considered. This is due to the decrease in the total stress and the non-uniformity of hydraulic conductivity due to the erosion of fine particles.

Vegetation has been recognized as an environmentally friendly method for stabilizing soil slope. Whereas hydrological effects of vegetation are experimentally investigated by several researchers, the field studies are rarely conducted and gain less attention. In this research, a field study was carried out on unsaturated soil slopes. The field measurement consisted of two neighboring cut slopes, namely bare soil slope and grassed soil slope. Field measurement results reveal that grass has influences on reducing and stabilizing the soil water content, increasing matric suction, and lowering soil temperature in warm seasons. The approach of coupled nonisothermal-seepage numerical analysis for unsaturated soil slope considering impacts of grass is suggested. The good agreement in comparisons between simulation and field measurement indicates that the proposed approach is useful to consider the influences of grass on the soil behaviors against climate variations.

Preliminary results of a comprehensive microstructural investigation aimed at studying the influence of osmotic effects in Ashfield shale, a low permeability sedimentary rock from the Sydney Basin (Australia), are presented in the paper. Natural rock specimens were exposed to different brine solutions to assess their influence on rock microstructure. Qualitative as well as quantitative experimental techniques were used to evaluate changes in mineralogical composition (XRD analysis), Cation Exchange Capacity (CEC), cation/ion concentration (chromatographic analysis), specific surface, structural arrangement (Scanning Electron Microscopy) as well as pore size distribution (Mercury Intrusion Porosimetry). Test results show an important influence of the applied osmotic potential on specific surface, CEC and pore size distribution and to a lesser extend the structural arrangement assessed via SEM. These changes occur without important variations in the mineralogical composition of the rock.

Using molecular mechanics and molecular dynamics (MD) methods, Li-, Na-, K-, Ca- cations based montmorillonite models are built in materials studio software. Molecular dynamic simulations are carried out to investigate the influences of different cations on the swelling behavior of montmorillonite when absorbing water. Molecular dynamic simulations indicate that the montmorillonite's volume and layer spacing are increased by multi-steps, but the density is reduced by multi-steps. Water molecule concentration profiles in lithium-, sodium-, potassium- and calcium-montmorillonite adsorption models show that the montmorillonite can form one, two and three layers of water molecules. The radial distribution function of Li-, Na-, K-, Ca- cations based montmorillonite is obtained for absorbing 16 to 96 water molecules. The results indicate Li+ is easier to hydrate, follows by Na+, while K+ and Ca2+ are not easy to hydrate. Different types of cations between layers have different effects on the adsorption ability of montmorillonite.

This experimental study investigates the compaction behavior of Maryland clay with different pore water salinity. Maryland clay powder was prepared with deionized water and CalCl2 solutions prepared at two concentrations (0.1 M/L Ca2+ and 1.0 M/L Ca2+) and then statically compacted in an oedometer cell. The compaction tests were complemented by microstructural characterization using mercury intrusion porosimetry. The effect of pore water salinity on the compaction behavior of the ML clay is quantified at both micro and macro scales. Results show that the compression index from 1D compression tests and the pore size distribution inferred by MIP are highly dependent on both the water content and pore water salinity. The compression index increases with water content but is not uniquely correlated with pore water salinity at a given water content. At low water contents, pore water salinity mainly affects the macro pores, while it leads to a significant influence on the micro pores when increasing water content.

Fly ash is a by-product of thermal power plant generated due to the combustion of coal. The silt size hollow spherical particles of fly ash have low specific gravity and high crushability. Fly ash is used as a structural fill in highway/railway embankments that remain unsaturated during most of the year, and its behavior under unsaturated conditions has not been explored yet. The current research explains a procedure to determine unsaturated shear strength parameters of type-F fly ash by using conventional shear strength parameters and matric suction. A series of filter paper tests and consolidated undrained (CU) triaxial tests were conducted to obtain the soil water characteristic curve (SWCC) and effective shear strength parameters (c' & ϕ') of fly ash respectively. Unconfined compression (UC) test series at varying degree of saturation was performed to determine unsaturated shear strength (USS) of fly ash as a function of matric suction. USS of fly ash was observed to increase with matric suction until it reached the residual zone of unsaturation, after which it was observed to reduce. The angle of internal friction with respect to matric suction (ϕb) increased and stiffness decreased with the increment in degree of saturation. Additionally, the effect of crushability of fly ash particles on matric suction evolution was also analyzed using Scanning Electron Microscope (SEM) images to evaluate its microscopic behavior. The reduction in matric suction with increasing crushing cycles could be attributed to the breakage of cenospheres and deformation of plerospheres.