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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]

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]

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]

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 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]

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]

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]

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]

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Abstract: The influence of climate change on rainfall patterns has the potential to alter stability of partially saturated soil slopes. Changes in rainfall patterns have a strong influence on stability of partially saturated soil slopes, which recently have resulted in shallow landslides. In this paper, slope stability is assessed using a monolithically-coupled finite element model for a deformable partially saturated soil subjected to surface infiltration of water. Numerical analysis solves for the matric suction distribution over a two-dimensional cross-section of a soil slope while varying permeability, and considering a surface layer of soil with different permeability. The formulation of hydraulic conductivity for a coupled analysis includes dependence on porosity and degree of saturation to illustrate the effects of water infiltration and deformation behavior in partially saturated soils. Numerical examples demonstrate that change in rainfall patterns may trigger slope instability earlier in the rainfall event than for rainfall events of the past. Assessment of these simulations can provide an indication of the potential influence of climate change on shallow landslides in many mountainous areas in South Korea. [Copyright &y& Elsevier]