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ABSTRACT The permanent displacement of earth slopes during earthquake shaking is a key indicator for landslide hazard assessment. Previous studies mostly attempt to evaluate the earthquake‐induced displacement of dry or saturated soil slopes, while it is less common to deal with partially saturated soils. In the present study, a simplified procedure is proposed to account for the seismic‐induced excess pore pressure in slopes with partially saturated sandy soils. The effect of matric suction, suction stress, and excess pore pressure on the yield acceleration of partially saturated sandy slopes is investigated, and the coupled Newmark sliding block method, known as the flexible soil columns with dynamic shear modulus and damping ratio, is modified to estimate the seismic slope displacement. Detailed discussions are made about the effect of different degrees of saturation on the excess pore pressure ratio, yield acceleration, and slope displacement. The numerical results show that the excess pore pressure ratio tends to exponentially increase with saturation, and the change of yield acceleration and displacement with saturation can be divided into suction stress dominant and excess pore water pressure dominant stages. [ABSTRACT FROM AUTHOR]

The conventional methods follow in designing piles adopt the assumption of saturated condition of soil depending on soil parameters at saturated condition while at most cases the whole piles or part of them lays in unsaturated soil zone, thus the estimated pile capacity will be far of the real. This issue made the need to study the pile capacity at unsaturated condition and compare it with saturated condition. This study is performed to investigate the behavior of single pile inserted in clay soil at different degrees of saturation. The test was performed under axial compression loads by using different degrees of saturation (100,80,60,40%). A pile of 14x14 mm cross section with different slenderness ratios (L/D) (24,30,36) employed in the study. The impact of saturation degree, matric suction and slenderness ratio on pile load capacity is examined. The results illustrate that pile capacity influenced considerably by the saturation degree, matric suction, and slenderness ratio. The results showed that when saturation degree reduced from 100% to (80,60,40%), bearing capacity of pile increased for all L/D used. An example ultimate capacity of pile with L/D (24) increased (380, 512, 63%) by de-creasing degree of saturation from 100 % to(80 ,60 ,40%) respectively, this means the pile capacity increased about four times by decreasing Sr. from 100 % to 80 % , five times by decrease Sr. from 100% to 60 % and little increase (63 %) in pile capacity by decreasing Sr. to 40 %.A close results had been observed at L/D 30 and 36. The effect of increasing slenderness ratio had been studied at different saturation degrees, an ex-ample by increasing L/D from 24 to 30 pile capacity increased (11.45, 10.2, 25, 32.5%) at Sr.(100 ,80 ,60 ,40%) respectively.

This paper presents a quantitative framework to optimise embedded footing performance subjected to extreme historical climate events with respect to the uncertainties associated with site-specific soil and climatic parameters. The proposed framework is developed based on partially saturated soil mechanics principles in conjunction with a multi-objective optimisation algorithm called Non-dominated Sorting Genetic Algorithm (NSGA-II) to develop a robust optimised design procedure. The proposed method was applied to two semi-arid climate sites, Riverside and Victorville, both situated in California, United States. The results show that the proposed method generally improves the embedded footing design compared to conventional methods in terms of cost and performance. Based on the findings, under the extreme climate conditions, the proposed method estimates the average soil degree of saturation within the footing influence zone between 52% and 95%, with a mean value of 63.1% for the Victorville site, and 57% and 90% with a mean value of 81.6% for the site in Riverside. It is also found that the optimal design from the proposed method shows a lower total construction cost, 44% and 19%, for the Victorville and Riverside sites, respectively, compared to the ones designed by the conventional methods. [ABSTRACT FROM AUTHOR]

The recent surge in the availability of sensor data and computational resources has fostered the development of technologies for optimization, control, and monitoring of large infrastructures, integrating data and numerical modeling. The major bottleneck in this type of technologies is the model response time, since repetitive solutions are typically required. To reduce the computational time, reduced order models (ROMs) are used as surrogates for expensive finite element (FE) simulations enabling the use of complex models in this type of applications. In this work, ROMs are explored for the solution of the fully coupled hydro‐mechanical system of equations that governs the water flow through partially saturated soil. The POD‐based Reduced Basis Method and the Discrete Empirical Interpolation Method (DEIM), as well as its localized version (LDEIM), are examined in solving a parametrized problem simulating the mechanical loading of an embankment dam. Hydraulic and mechanical soil properties are considered as parameters. It is shown that the combination of these methods results in simulations that require 1/10 to 1/100 of the FE response time. Moreover, the method is shown to yield scaling efficiency gains with increasing problem size. [ABSTRACT FROM AUTHOR]

This study focuses on the consolidation behavior and mathematical interpretation of partially-saturated ground improved by impervious column inclusion. The constitutive relations for soil skeleton, pore air and pore water for partially saturated soils are proposed in the context of partially-saturated ground improved by impervious column inclusion. Settlement equation and dissipation equations of excess pore air/water pressures for a partially saturated improved ground are then derived. The semi-analytical solutions for ground settlement and pore pressure dissipation are then obtained through the Laplace transform and validated by the existing solutions for two special cases in the literature and the numerical results obtained from the finite difference method. A series of parametric studies is finally conducted to investigate the influence of some key factors on consolidation of partially saturated ground improved by impervious column inclusion. Based on the parametric study, it can be found that a higher value of the area replacement ratio or modulus of the pile results in a longer dissipation time of excess pore air pressure (PAP), a shorter dissipation time of excess pore water pressure (PWP), and a lower normalized settlement.

A two‐phase velocity‐pressure stabilized formulation is proposed for the numerical analysis of mechanized excavations in partially saturated soft soils using the Particle Finite Element Method (PFEM). The fully coupled formulation is based on the theory of porous media in association with the Soil Water Characteristic Curve and the porosity‐dependent Kozeni‐Carman model for the realistic estimation of the soil permeability. The combination of the PFEM methodology, characterized by a global re‐meshing strategy equipped with a new adaptive mesh refinement scheme for the resolution of strain localization zones in the ground, with a hypoplastic constitutive model for the description of the non‐linear behavior of the deformable soil skeleton, allows for the modeling of very large deformations, as required for excavation simulations. The PFEM model is validated based on selected geotechnical benchmark problems concerned with fully and partially saturated soil specimens. The model is further applied to computational re‐analyses of excavation tests involving a single cutting tool moving in a sandbox. The reaction force‐tool displacement curve for the excavation tool as well as the evolution of the deformed topology of the sand including the formation of shear zones obtained from the computational model are compared with respective experimental observations. Parametric investigations aimed at elucidating the influence of selected geotechnical parameters on the excavation process are also carried out. Finally, the suitability of the proposed PFEM‐based numerical strategy for the modeling of 3D excavation problems is demonstrated by means of 3D PFEM simulations in fully saturated sand. [ABSTRACT FROM AUTHOR]

There are numerous examples in the literature where numerical modelling has been used as a valuable tool in the study of rainfall-induced landslides. While much attention has been paid to the influence of different rainfall characteristics and patterns, spatial variability or temporal patterns of rainfall intensity, very little attention has been paid to the influence of the temporal resolution of rainfall data used in numerical simulations of rainfall infiltration and slope stability analysis. This is particularly true for deep-seated landslides occurring on slopes composed of soils with relatively low hydraulic conductivity, as in the case of flysch deposits presented in this study. A recently developed 2D numerical model is used to investigate the results of transient infiltration and slope stability analysis for flux boundary conditions derived from three temporal resolutions of realistic rainfall data: (i) 10-min, (ii) hourly and (iii) daily rainfall measurements. The results obtained show that deriving the time-dependent flux boundary conditions using the coarse resolution rainfall data (e.g. daily rainfall measurements) can lead to a calculation of unrealistically high infiltrated volumes, a faster increase in water content and pore water pressure in a slope cross-section, and a reduction in the factor of safety at an unrealistically high rate, resulting in a conservative prediction of the time to slope failure. The results suggest hourly rainfall data as the optimal form of input data for the case study under investigation. [ABSTRACT FROM AUTHOR]

In the event of a rainfall, the contrast in hydraulic conductivity and shear strength properties of a layered soil can be significant in determining the stability of a slope. The main objectives of this study were to model 1-D infiltration into a two-layered soil formation and to understand the effect of contrast in the permeability characteristics of the two layers on failure depth, time, and mechanism, in the event of a shallow landslide. Two hypothetical soils-relatively coarse and fine soils-were assumed for the layered soil model. 1-D infiltration into a partially saturated soil was modelled through the development of a finite difference numerical scheme by solving the mixed form of Richard's equation. The stability analysis has been conducted for varying rainfall intensities and permeabilities using a pre-defined stability envelope based on the pressure head. For the case where fine soil overlies the coarse soil in a two-layered model, results showed that the failure depth is significantly reduced when the saturated permeability of coarse soil decreases relative to the fine soil. The only possible failure mechanism was identified as 'loss of suction'. When the coarse soil overlain by a fine soil, no significant effect on failure depth has been observed. Both 'loss of suction' and the development of a 'perched water table' were identified as possible mechanisms. In both cases, it was noticed that the failure time decreases as the saturated permeability of coarse soil increases. The results suggest that contrast in permeability characteristics in layered soil formations plays a vital role in influencing failure time, depth, and mechanism. [ABSTRACT FROM AUTHOR]

Earthquakes and groundwater are pivotal factors affecting slope stability. However, the majority of previous studies have focused on these factors individually, neglecting their combined effects. Hence, this paper aims to develop a framework using the kinematic approach of limit analysis to investigate the stability of slopes in partially saturated soils under the combined effects of seismic force and pore-water pressure. The pseudo-dynamic method (PDM) was employed to capture the temporal-spatial effect of horizontal and vertical seismic waves. Variations in suction and effective unit weight profiles with moisture content under steady-state unsaturated flow were considered. External rates arising from both static pore-water pressure and earthquake-induced excess pore-water pressure were incorporated into the energy-balance equation. With the aid of gravity increase method (GIM), an explicit expression of safety factor (FS) was derived and optimized using a genetic algorithm (GA). The validity of this approach was verified through a comparison with existing solutions. Parametric analyses were conducted to explore the influence of varying groundwater level, seismic coefficients, suction, three-dimensional effects, excess pore water pressure, unsaturated flow types, and pseudo-dynamic parameters, on the FS and critical sliding surface of slopes in partially saturated slopes. This framework can provide a good reference for the safety design of reservoir slope under the combined effects of earthquakes and groundwater. • A framework for slope stability in partially saturated soils under earthquakes and pore water pressure is developed. • Steady-state flow in saturated/unsaturated regions with varying water levels is considered. • Effects of earthquake-induced excess pore water pressure are incorporated into limit analysis. • Dynamic responses of slopes are discussed under combined effects of earthquake and pore water pressure. [ABSTRACT FROM AUTHOR]

Considered that the gas content of partially saturated soil would decrease under a shock load, which would cause volumetric plastic deformation, Lyakhov's constitutive model is improved. The P-α state equation is used to describe the volume compression relationship of partially saturated soil. Numerical and experimental results are compared to validate the material model. The peak stress and duration of shock wave are crucial to study the dynamic response of underground structures. Considered the saturation of partially saturated soils under natural conditions increases with depth and both peak stress and duration change when shock waves propagate in inhomogeneous media, several partially saturated soil models with linearly decreasing air content in the depth direction are developed. The propagation law of shock waves with various peak stresses and durations in partially saturated soils is studied. The results show that the peak stress caused by the incident load in partially saturated soil first decreases and then increases under incident loads with a shorter duration, and it increases monotonically under incident loads with a longer duration. The rate of change in the incident peak stress is proportional to the air content at the top of the partially saturated soil. The peak free-field stress reaches its maximum, which is 2.2 to 5.5 times the peak stress of the incident load, in fully saturated soil. Long-duration incident loads such as nuclear explosions are more threatening to underground structures than short-duration incident loads. Underground structures buried in fully saturated soil or below fully saturated soil with higher air contents above are more at risk than underground structures buried in partially saturated soil with smaller air contents.

Partially saturated soils are common in arid or semi-arid zones. It is a common practice to assume soil as fully saturated for estimation of bearing capacity. With this assumption, estimated bearing capacity is expected to be on conservative side. But sometimes it may be misleading. The motive of this study is to examine the effect of wetting induced collapse on the bearing capacity of shallow foundations. This paper presents the application of improved Barcelona basic model to the simulation of shallow foundation using coupled approach. A boundary value problem of strip footing resting over fully and partially saturated soil is analysed. Different loading and wetting sequences are followed to capture the effect of water table fluctuation on bearing capacity in partially saturated soils. From comparison of numerical prediction with analytical values of ultimate bearing capacity, a relationship for apparent cohesion is suggested for moderate range of angle of internal friction. [ABSTRACT FROM AUTHOR]

Rainfall-induced slope instabilities are ubiquitous in nature, but simulation of this type of hazards with centrifuge modelling still poses difficulties. In this paper, we introduce a rainfall device for initiating slope failure in a medium-sized centrifuge. This rainfall system is simple, robust and affordable. An array of perforated hoses is placed close above the model slope surface to generate the raindrops. The rainfall intensity depends on the centrifuge acceleration and the flow rate of the water supply, which is controlled by the size and number of the tiny pinholes in the hose walls. The rainfall intensities that are tested range from 2.5–30 mm/h, covering the intensity range of moderate, heavy and torrential rainfall events. Our model test with rainfall-induced slope failure shows that this system is capable of generating relatively uniform rainfall of wide intensities and leads to various patterns of slope failure. [ABSTRACT FROM AUTHOR]

This paper presents the results of centrifuge tests on rainfall-induced instabilities in variably saturated slopes. The roles of rainfall intensity and initial conditions, such as slope angle, porosity and degree of saturation of the soil, in the failure initiation and postfailure kinematics are considered. The failure patterns, infiltration profile and deformation at prefailure and postfailure stages are characterized. The results indicate that rainfall-induced slope failures usually follow one of the following two failure modes, i.e. slide-to-flow and flowslide failure modes. The former pattern is characterized by soil mass flow after initial failure along a continuous shear surface, while the latter is more relevant to the rapid increase in the saturation at the slope surface, resulting in surface erosion channels followed by the acceleration of the soil mass. The flowslide failure pattern usually gives rise to several superficial shear surfaces and longer run-out distances. The rainfall intensity and profiles of the degree of saturation play the key roles in initiating the slope failure at the prefailure stage and subsequently in mobilizing the soil mass at the postfailure stage. Our test data, together with the data from the literature, are presented in two threshold curves to define the critical condition of slope failure under rainfall infiltration. [ABSTRACT FROM AUTHOR]

Partially saturated soils below the groundwater table usually exist because of decomposition of organics within the soil deposit or soil desaturation technologies for liquefaction mitigation. Therefore, the cyclic responses of partially saturated soils should be paid more attention to and it is necessary to establish a practical model to evaluate the liquefaction resistance improvement LRR 20 (the ratio of liquefaction resistance of partially saturated soil to that of fully saturated soil) due to the decrease of saturation. Some researchers have tried to quantify the liquefaction resistance of partially saturated soil using the P-wave velocity V p. However, whether the LRR 20 - V p relationship is influenced by initial states such as relative density, structure or fabric of soil, and fines content, is not clear yet. For this purpose, an experimental programme comprising undrained cyclic triaxial and bender elements tests was performed on partially saturated soils under various conditions. Results show that the cyclic shear behaviors of partially saturated sands with different B -values are significantly different from those of fully saturated sands. For partially saturated sands, as excess pore water pressure (EPWP) accumulates to a certain proportion of initial effective confining pressure, it suddenly develops with a significant increase followed by the occurrence of more than 5 % of axial strain. Based on the test results including those from independent literature, a unique experimental LRR 20 - V p relationship is proposed for different relative densities, sample preparation methods, initial effective confining pressures, and fines contents. • Undrained cyclic triaxial and bender elements tests are performed on partially saturated soils. • When reaching the transitional point, EPWP quickly accumulates and about 5% of ε a suddenly occurs. • A unique LRR 20 - V p relationship is proposed for different D r , SPMs, σ 0 ', and FCs. [ABSTRACT FROM AUTHOR]

A flume test was conducted to evaluate the failure mechanism of a rainfall-induced landslide and to develop a physically based warning system. The test was performed at full scale to prevent scale effects, and the flume was a rectangular channel that was 20 m long, 4 m wide, and 2.5 m deep. The volumetric water content and the matric suction were measured at various depths to determine the rainfall infiltration into partially saturated soil. The displacement and tilt were measured at the slope surface, and a video camera was installed to record the slope failure. The results showed that the rainfall infiltration caused the volumetric water content to gradually increase and the matric suction to decrease. The resulting decrease in the soil strength caused soil deformation. Thus, the rainfall induced a landslide. The matric suction and the degree of saturation were used to calculate the generalized effective stress of the solid skeleton to develop a warning system. The stress paths were calculated using the effective mean stress and the deviatoric shear stress. The inflection point of the stress paths can be used to define a threshold for a rainfall-induced landslide warning system. [ABSTRACT FROM AUTHOR]

Soil liquefaction during large earthquakes causes serious damage to structures built on foundations. In recent years, artificially injecting small amounts of air into liquefaction-susceptible soils has been proposed as a newly developed and cost-effective liquefaction mitigation method. Nevertheless, the liquefaction response of piles through this method has not been investigated so far. A series of 1g shaking table tests were conducted in this research to evaluate the liquefaction response of pile and pile group in air-injected partially saturated soils. The results have shown that air injection effectively reduces the liquefaction-induced settlements of pile and pile group. Also, this method has relatively reduced the excess pore pressure ratio. According to visual results and bending moments in piles, the depth of a liquefied soil layer decreases in air-injected partially saturated soils. Also, the deformation of soil structure is observed to decrease by injecting air into the samples. Despite these effects, larger accelerations are transmitted to the surface of the soil and consequently to the structure, and larger bending moments are applied to the piles in air-injected partially saturated samples. It was observed that at the low confining pressure, the effectiveness of this method is not a function of air injection duration. [ABSTRACT FROM AUTHOR]

Summary: In this study, a linear poroviscoelastic model based on the Biot theory is proposed to analyze the dynamic response of partially saturated soil. Both the flow‐dependent and flow‐independent poroviscoelastic behaviors are described in the proposed model. The compressibilities of both the constituents, including the skeleton material and porefluid, are considered, and the effective skeleton stress is determined using the linear viscoelasticity law based on the generalized spring‐dashpot model. The soil surface is subjected to two types of harmonic loading, namely, vertical compressive loading and lateral shear loading. The influences of the relaxation time, saturation degree, and soil permeability on the surface and interior dynamic responses of the soil layer are investigated. It is revealed that the amplification factor, effective stress, and pore pressure decrease as the viscous damping increases, indicating that neglecting the viscoelastic property of solid skeleton could overestimate the induced dynamic responses. Furthermore, in comparison with the viscous damping of the solid skeleton, the viscous coupling involving the viscous resisting forces between the solid skeleton and pore fluid has limited effect on the dynamic behavior of the soil layer. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study to investigate the load carrying capacity of piled raft foundation embedded within partially saturated sandy soil. The effect of matric suction on the bearing capacity of the foundation system was investigated. The experimental work consists of two models of foundation, circular raft foundation and circular piled raft foundation. The circular raft foundation has dimensions of 10cm in diameter, and 2.5cm thickness, while the piled raft foundation has the same dimensions of the circular raft model but with a single pile of 2.0cm in diameter and 40.0cm in length fixed at the center of the raft. Both models are loaded and tested under both fully saturated condition and unsaturated conditions, which are achieved by, predetermined lowering of water table. The lowering of water table below the soil surface was achieved in to two different depths to get different values of matric suction and the relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil water characteristic curve (SWCC) estimated by applying fitting methods through the software (SoilVision). A validation process then was carried out for the case of circular piled raft foundation with lowering the water table 45cm bellow soil surface in the aid of a sufficient finite element computer program ABAQUS 6.12. An eight-node axisymmetric quadrilateral element CAX8RP and CAX8R were used to simulate the soil continuum and piled raft respectively. The interaction method used to simulate the intersect surfaces of the system (pile-raft-soil) is a surface-to-surface discretization method under the concept of master and slave theory. The behavior of piled raft material is simulated by using a linear elastic model while the behavior of soil is simulated by an elasto-plastic model by the use of the Mohr-Coulomb failure criterion. The results of the experimental work demonstrate that the matric suction has a significant role on the bearing capacity of all tested models. It shows that the ultimate bearing capacity of circular raft foundation under a partially saturated condition is increases by about (7.0-8.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. While the ultimate bearing of circular piled raft foundation under partially saturated condition increases by about (8.0-9.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. The results of the ultimate bearing capacity of piled raft foundation that obtained from the experimental model and from the numerical modelling for the same soil condition and same matric suction indicate that a successful validation is achieved for the simulation process.

This investigation aims to increase the slope of the downstream slope in an earth dam 30 meters high, homogeneous and made up of various combinations in curtain-foundation with soils of the Mariel and Toledo formations, in saturated and partially saturated states, by incorporating the hydraulic conductivity curves and the characteristic curves of the soils. The analysis for mattress and drainage prism are performed using the SIGMA / W, SEEP / W and SLOPE / W programs and the Morgestern-Price method to estimate the safety factor of the slope downstream. It is obtained as a result that it is possible to have steeper slopes by including the laws of unsaturated soil mechanics in the analysis of the stability of slopes in earth dams. [ABSTRACT FROM AUTHOR]

Highlights • Pore-scale investigations of soil by Voronoi cells and cubic subsets were conducted. • Distribution width of the degree of saturation was wider than that of the porosity. • Distribution of the pore volume is non-normal while that of porosity is normal. • 2D histograms of pore volume and degree of saturation are presented. • Each investigation has particular characteristics regarding water retention behavior. Abstract Partially water-saturated granular soils are mixtures of soil grains, pore water, and pore air. This study presents methodologies to obtain local quantities, such as porosity, degree of saturation, and pore volume, for partially water-saturated uniform sand at the pore scale. A sand specimen subjected to different water retention states was scanned using X-ray micro computed tomography. The obtained three-dimensional tomographic images were trinarized, i.e. segmented into soil grain, water, and air phases. The trinarized volumes were divided into Voronoi cells containing individual pores, and the volume and degree of saturation for the pores were calculated. Alternatively, the porosity and degree of saturation were quantified for cubical local subsets arranged regularly in the trinarized volumes. Pore characteristics and local water retention behavior are discussed using the results of these two investigations. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study to investigate the change of plug length for pipe pile under different state of saturation and investigate the effect of number of pipe piles on plug length. The influence of matric suction (i.e., capillary stresses) in unsaturated zone is typically considered on the plug length of pipe piles. The experimental work consist of testing 20 models of pipe piles, these models divided into 4 different configuration of pipe piles; single pipe pile, group of double pipe piles, group of triple pipe piles and group of six pipe piles. All these models are loaded and tested under three different states; dry condition, fully saturated condition (i.e., matric suction equals to 0 kPa) and unsaturated conditions with three different matric suction values (6, 8 and 10 kPa), which are achieved by predetermined lowering of water table. The relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil, water characteristic curve (SWCC) was estimated by applying fitting methods through the program (Soil Vision). The results of experimental work demonstrate that the values of plug length decreased with increase in value of matric suction for the same configuration of pipe piles, and the values of plug length decreased with increase in number of pipe piles.

This paper presents an experimental study conducted on model piled rafts in partially saturated sandy soil. The aim of the experimental program is to study the effect of matric suction on the load carrying capacity of piled rafts embedded within partially saturated sandy soil .The influence of number of piles are presented and discussed in this study. The piled raft is arranged in different configurations of piles (single, double and triple piled raft with spacing 3.5D c/c) with the same area ratio (raft area to the cross section area of piles) to avoid different contact pressure area and to show the effect of different piles number and its group action. The influence of matric suction (i.e., capillary stresses) in partially saturated zone is typically not taken into account in the conventional design of both shallow and deep foundations so that the present research study the determination and contribution of matric suction towards the load carrying capacity of piled raft. The experimental work consist of 3 models of footing "single piled raft (8.3 x 5) cm, double piled (16.6 x 5) cm and triple piled raft (25 x 5) cm". All these models are loaded and tested under both of fully saturated condition (i.e., matric suction equals to 0kPa) and unsaturated conditions (i.e., matric suction value equals to 6kPa , 8kPa and 10kPa), which are achieved by predetermined lowering of water table.

Occurrence of extreme hydrological events is frequent in recent years. These events impact the performance of many structures specially the foundations which transfer superstructure load to the ground. The shear strength and settlement of soils and foundations are influenced by the degree of saturation of the soil which varies with hydrological parameters such as rainfall, flood, and evapotranspiration. Therefore, the hydrological parameters must be incorporated in the design to obtain the optimum design for a particular location with specific geotechnical parameters. In this paper, a novel procedure, which considers the site specific hydrological parameters into the shallow foundation design, is presented with sample applications in the United States. The degree of saturation of the partially saturated soil within the influence zone of the foundation was modeled using the one-dimensional Richards' equation considering infiltration rate and water table location as the top and bottom boundary conditions, respectively. The historical rainfall data and water table locations for two study areas in Victorville, California and Levelland, Texas were obtained from the U.S. Geological Survey and National Climatic Data Center data repositories. The results from the Victorville site indicated a near 230% increase in the ultimate bearing capacity and a corresponding 80% decrease in the elastic settlement from those calculated assuming the fully saturated condition. On the other hand, there was only a small increase in bearing capacity at the Levelland site with a corresponding decrease in settlement of 40%. These significant differences in results are because of the inherent variation of the soil properties and hydrological parameters for both site locations. The results clearly indicate that shallow foundation design can be improved if the hydrological parameters are incorporated in the design procedure. [ABSTRACT FROM AUTHOR]

High Pressure and High Temperature (HPHT) oil and gas pipelines are commonly buried subsurface and the depth of burial is determined by upheaval buckling mitigation requirement or legislation requirement. The upheaval buckling mitigation design requires evaluation of uplift resistance of soil in which pipeline is buried. Conventional design guidelines and current analytical models for predicting the soil uplift resistance are based on either dry soil or fully saturated soil. However, onshore pipeline are buried in soils which are often partially saturated. Therefore, current analytical models do not capture the effects of soil saturation on the uplift resistance of buried pipeline. In partially saturated soils, the uplift resistance is greater than that under fully saturated conditions. This is because the water meniscus between soil particles creates an additional normal force due to suction, which in turn makes the soil behaviour stiffer and stronger. This paper presents full scale pipe-soil tests results and finite-element parametric studies conducted to investigate the effects of soil moisture content, dimensionless cover heights (soil cover height to diameter ratio) and soil relative density on the peak uplift resistance of pipes. The results demonstrate that the current available analytical models under-predict the soil peak uplift resistance in partially saturated conditions. Further, the analyzed results are presented as dimensionless design charts and non-linear regression models which can be used to quantify the partial saturation effect on uplift resistance of buried pipes. [ABSTRACT FROM AUTHOR]

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The paper describes a proposed unified hydro-elasto-plastic model with a solid–fluid transition. The model associates a hydro-elasto-plastic model for partially saturated geomaterials, a Bingham’s viscous law, and the transition criterion between solid and fluid states. The model describes both solid and fluid behaviours of partially saturated geomaterials in a unified framework. In addition, this paper describes a novel Finite Element Method with Lagrangian Integration Points (FEMLIP) formulation for solving hydro-mechanical problems. Based on the equilibrium equation of momentum and the continuity equation of water flow, the formulation was developed and implemented in a FEMLIP tool. Bishop’s effective stress expression and proper water retention diagrams were taken into account. A heuristic column and real rainfall-induced mudflows were also simulated and analysed in this study. The permeability effects of partially saturated soil and the effective cohesion were considered, which included consideration of the entire mudflow process. The results were proven satisfactorily in a qualitative fashion. [ABSTRACT FROM AUTHOR]

A proper assessment of the soil effective stress state is crucial in many cases to identify a potential geological/geotechnical hazard as shallow landslides or failure of levees that may have a significant impact on human activities and development. This paper is aimed at validating a methodology for the expeditious and economic determination of effective stress state in the vadose zone recently proposed by Lo Presti et al. in 2016. The method is based on the interpretation of cone penetration tests (CPTu). Its validation was carried out by comparing the CPTu predicted values of suction against the measured ones in a well-documented and monitored site. The comparison also includes the prediction of suction that was obtained by using the so-called Modified Kovacs model (MK). Moreover, additional data of water content and saturation degree from another site were used to predict the suction by using the MK model. These values of suction were compared with those inferred by the CPTu. [ABSTRACT FROM AUTHOR]

The mechanical behavior of partially saturated soils can be different from that of fully saturated soils. It has been found that for such soils, changes in suction do not have the same effect as changes in the applied stresses, and consequently the effective stress principles is not applicable. A finite element analysis was carried out on a single pile with a diameter (0.6 m) and (12) m length embedded in fully and partially saturated clayey Iraqi soils within Baghdad city. The partially saturated parameters were calculated using laboratory methods; the filter paper method was utilized to estimate the soil water characteristic curve (SWCC) from which the H-Modulus function was obtained. The program (SoilVision) was used to make a fit of the SWCC. The finite element programs SIGMA/W and SEEP/W are then used in the analysis. A parametric study is carried out and different parameters are changed to study their effects on the behavior of partially saturated clay. These parameters include the degree of saturation, depth of water table and shear strength of clay. The study reveals that when the soil becomes partially saturated by dropping water table at different depths with different degrees of saturation, the pile capacity increases. It is concluded that the change in the water table level and the degree of saturation has a great effect on the behavior of partially saturated clay. In this work, it is found that due to dropping of water table and contribution of matric suction (i.e. negative pore water pressure), the pile capacity in partially saturated soil is approximately (3-5) times higher than the capacity of piles in the same soil under saturated conditions

This paper investigates the drying and wetting soil water retention curves (SWRCs) of statically compacted lime-stabilised London Clay specimens. A series of tests were performed using the contact filter paper method, pressure plate apparatus and a suction-controlled triaxial system incorporating the axis translation technique. These investigated the water retention of the soil under different boundary and stress-state conditions and simultaneously determined the volume change in the soil during drying and wetting. Factors relevant to the lime treatment of soils, such as curing period and method (air vs. water curing), were also considered. Finally, the hysteresis of the SWRC of the chemically treated soil (for which there appears to be a lack of information in the international literature) was investigated. The results showed that the treatment with lime increased the volumetric stability but reduced the water retention ability due to a more open structure enabled by the flocculation and chemical bonding effects. Curing period and method effect appears to be small. Hysteresis was noted to some degree in all instances. [ABSTRACT FROM AUTHOR]

A proper assessment of the soil effective stress state is crucial in many cases to identify a potential geological/geotechnical hazard as shallow landslides or failure of levees that may have a significant impact on human activities and development. This paper is aimed at validating a methodology for the expeditious and economic determination of effective stress state in the vadose zone recently proposed by Lo Presti et al. in 2016. The method is based on the interpretation of cone penetration tests (CPTu). Its validation was carried out by comparing the CPTu predicted values of suction against the measured ones in a well-documented and monitored site. The comparison also includes the prediction of suction that was obtained by using the so-called Modified Kovacs model (MK). Moreover, additional data of water content and saturation degree from another site were used to predict the suction by using the MK model. These values of suction were compared with those inferred by the CPTu.

Proper soil water retention curves (SWRCs) and hydraulic conductivity functions (HCFs) are necessary for a fair analysis of groundwater flow in unsaturated slopes. In principle SWRC is hysteretic; as a consequence, laboratory characterization may not be sufficient to determine the scanning curve and the hydraulic parameters operating in situ. In this paper some results obtained by tests at different scales (testing on laboratory specimens and physical prototype and measuring in an experimental field) are presented in order to explore the hydraulic behaviour of pyroclastic soils. As regards HCF, in the paper the comparison between the hydraulic conductivity functions obtained from inverse analysis of evaporation lab tests, and the conductivity values estimated on the basis of both in situ measurements and results of tests on the aforementioned physical model is proposed. From these results, the physical prototype size (medium scale) seems to be acceptable for determinations of both SWRC and HCF. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of suction and lime treatment on the volumetric and shear behaviour of a partially saturated high plasticity clay (London Clay). A series of triaxial tests were performed on statically compacted London Clay and lime-treated London Clay specimens. These were prepared at the same target void ratio and tested under partially saturated conditions. The tests concerned isotropic compression and two different types of shearing tests (a) shearing at constant suction and (b) shearing at constant water content, using the axis translation technique. Based on the results, the effects of suction and lime-induced bonding are evaluated and quantified within an elastoplastic partially saturated soil framework. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, a series of multimaterial benchmark problems in saturated and partially saturated two-phase and three-phase deforming porous media are addressed. To solve the process of fluid flow in partially saturated porous media, a fully coupled three-phase formulation is developed on the basis of available experimental relations for updating saturation and permeabilities during the analysis. The well-known element free Galerkin mesh-free method is adopted. The partition of unity property of MLS shape functions allows for the field variables to be extrinsically enriched by appropriate functions that introduce existing discontinuities in the solution field. Enrichment of the main unknowns including solid displacement, water phase pressure, and gas phase pressure are accounted for, and a suitable enrichment strategy for different discontinuity types are discussed. In the case of weak discontinuity, the enrichment technique previously used by Krongauz and Belytschko [ Int. J. Numer. Meth. Engng., 1998; 41:1215-1233] is selected. As these functions possess discontinuity in their first derivatives, they can be used for modeling material interfaces, generating only minor oscillations in derivative fields (strain and pressure gradients for multiphase porous media), as opposed to unenriched and constrained mesh-free methods. Different problems of multimaterial poro-elasticity including fully saturated, partially saturated one, and two-phase flows under the assumption of fully coupled extended formulation of Biot are examined. As a further development, problems involved with both material interface and impermeable discontinuities, where no fluid exchange is permitted across the discontinuity, are considered and numerically discussed. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Based on the mixture theory, considering the flow-independent viscosity related to solid skeleton, the present work investigates the propagation characteristics of Rayleigh wave in partially saturated viscoelastic soil. Firstly, the complex history-dependent viscoelastic behavior of solid skeleton is characterized by the fractional standard linear solid constitutive model. The generalized governing equations of motion for the partially saturated viscoelastic soil are established theoretically. Secondly, the analytical solution of Rayleigh wave fields in the partially saturated viscoelastic soil is obtained using the wave function expansion method. Finally, the influences of flow-independent viscosity characterized by fractional viscoelastic parameter on the propagation behaviors of Rayleigh wave are implemented analytically and then discussed in detail. The results show that the fractional index, stress relaxation time and strain relaxation time in the fractional standard linear solid constitutive model have significant influence on the phase velocity and attenuation coefficient of Rayleigh wave. The fractional index, stress relaxation time and strain relaxation time have similar effects on the P 1 and S waves included in body waves. Additionally, the influences of the fluid hydraulic conductivity and liquid saturation on the wave propagation cannot be ignored. [ABSTRACT FROM AUTHOR]