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The study of slope instability includes a detailed study of environmental conditions and soil's geotechnical and hydrological parameters. In the present study, a thorough understanding of rainfall-induced slope instability is achieved by doing real-time monitoring on an unstable slope located in Shillong, Meghalaya, India. The area selected is prone to landslides due to heavy rainfall and because it is located in the wettest place on earth. The real-time monitoring involves observation of groundwater table variation, intensity of rainfall, soil suction, and their effects on the instability of an unsaturated slope. Boring data show that even if the area is in a hilly region, the groundwater table is very high. The effects of antecedent rain on the matric suction, which indirectly affected the stability of the unsaturated soil slope were noticed. The location of the irrometers helped us in assessing that the slope stability is affected by both the matric suction developed in the unsaturated shallow soil during rainfall and that developed due to the presence of high groundwater level. The displacements along the slope are independent of each other. The results of the numerical analysis show that the slope displacement is positively correlated with the principal strain and maximum shear stress, indicating that the infiltration of rainfall has a significant effect on the stress and strain associated with displacement. [ABSTRACT FROM AUTHOR]

This paper presents laboratory experiments on the effect of matric suction on the compressibility of unsaturated gypsum sand soil. The samples were obtained from Al-Najaf city in Iraq with gypsum contents of 14%, 22%, and 29%. Two series of laboratory tests were conducted. The first one is loading-path likes when a building is constructed on these soils in a specific degree of saturation (specific matric suction). Four matric suctions were adopted; 100, 60, 30, and zero percentages of initial matric suction under two confining stresses; 100 kPa and 200 kPa. Also, two saturated tests (CD) were performed under the aforementioned confining stresses. The second method is wetting-path, likes when a structure has been constructed and the degree of saturation of a foundation soil increases (decreasing in matric suction). The results from both paths revealed that the volumetric strains were increased by decreasing the matric suction and increasing the gypsum content.. [ABSTRACT FROM AUTHOR]

The Global Digital Systems Ltd. (GDS) unsaturated soil triaxial test system is used to determine the shear strength of unsaturated undisturbed silty clay soil and obtain the soil-water characteristic curve. The van Genuchten (VG) and Gardner (GD) models are used to fit the soil-water characteristic curve to predict and verify the shear strength of the soil. The results show a better fit for the GD than the VG model. The shear strength of the soil increases with an increase in the matric suction, but the rate of increase is relatively low. The most significant influence of the matric suction on the soil strength is observed at less than 150 kPa. The influence of the matric suction on the shear strength of unsaturated silty clay mainly depends on the total cohesion. The soil shear strength value predicted by the GD model is conservative, but the predicted value tends to approach the measured value with an increase in the matric suction. [ABSTRACT FROM AUTHOR]

The osmotic technique in geotechnical testing of unsaturated soils is a promising technique to control soil-water potential. This technique is an alternative to the axis-translation technique. In this technique an aqueous polyethylene glycol (PEG) solution is interfaced with a selectively permeable membrane. The geotechnical literature has regularly referred to membrane effects which tend to reduce the achieved matric suction in relation to that theoretically attainable by consideration of the osmotic pressure of the bulk PEG solution. In this review, the literature on membrane science is studied in order to identify potential causes for these membrane effects. Concentration polarisation, membrane fouling and reverse solute draw are the underlying causes of these membrane effects and should be given consideration in the geotechnical osmotic testing literature. A better understanding of membrane science and its application to geotechnical osmotic testing can aid in the optimisation of osmotic testing and the systematic improvement of the technique. [ABSTRACT FROM AUTHOR]

South Africa is cut-across an arid and semi-arid zone, this implies that 95% of its roadbed is under unsaturated condition. In this context, resilient performance of subgrades is determined considering matric suction ( ψ) and traffic loading parameters for resilient modulus (MR) analysis through the application of unsaturated soil mechanics. Expansive natural subgrade soil sample collected from Northern Cape in South Africa is selected for this study. Series of MR tests, Free swell index tests, Zero swelling tests, suction tests, X-Ray Diffraction and Scanning Electron Microscopy tests were conducted to investigate the unsaturated response of expansive subgrade stabilized with varying percentages 4%, 6%, 8% and 10% of activated fly ash (AFA). The suction components of the representative subgrade soils were determined through filter paper method. The soil-water retention curve (SWRC) was also analysed using Fredlund and Xing, and Seki's models. The results showed that inclusions of 6%, 8% and 10% AFA caused some considerable increase in MR and suction values to a limiting values 6% AFA content, below which resilient modulus values were reduced. The low MR values are recorded in 4% AFA stabilized specimen, as a result of insufficient free reactive calcium oxide. This resulted to incomplete pozzolanic reaction with the clay minerals. Significant changes were observed in the soil pore structure, based on microstructure analysis of the stabilized subgrade soils. Inter-cluster cemented bonds, were noted on the surface structure of the stabilized subgrade compared to unstabilized subgrade soil, due to increase in MR. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tensile and shear behaviour of unsaturated soil have been investigated separately in the past. However, there is no comprehensive study on the transition from tensile to shear failure in compacted clayey soils. A series of uniaxial tensile, direct shear and triaxial compression tests were conducted on compacted Regina clay specimens to investigate the strength mobilisation and failure mode under different loading paths. It was observed that the matric suction increases the apparent cohesion and tensile strength of the material. At a given constant matric suction, the compacted clay displays a transition from tensile to shear failure with increasing confining stress which can be approximated by a bilinear failure envelope encompassing the transitional behaviour. The friction angles in tensile regime are greater than those in compressive regime, which can be explained by the transitional change in failure surface morphology from tensile ruptured to shear smoothened one. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Collapse of soil skeleton due to variation in its loading and boundary conditions impacts the strength and stability of soil in its unsaturated state. The present study is focused on the influence of matric suction on collapsible behaviour and stiffness degradation of compacted unsaturated cohesive soil. Collapse characteristic of unsaturated soil is assessed under sudden inundation and varying vertical stress application. A series of dynamic triaxial, double oedometer and filter paper tests were conducted on unsaturated Ahmedabad cohesive soil under as-compacted conditions at varying dry density and water content to determine cyclic degradation index (δ), collapse potential and matric suction (ua – uw), respectively. Significant influence of matric suction was observed on collapse potential and stiffness degradation of unsaturated cohesive soil. Larger collapse potential at higher matric suction clarified the meta-stable state of compacted unsaturated cohesive soil under dry conditions. Cyclic degradation index (δ) with number of loading cycles was found to be decreasing with increase in matric suction representing brittle nature of soil possessing higher matric suction signifying soil skeleton to be highly volatile and unsafe under dynamic loading conditions. [ABSTRACT FROM AUTHOR]

To study the influence of matric suction on the strength characteristics of soil, consolidated and drained triaxial shear tests on undisturbed silty clay were conducted using GDS unsaturated soil triaxial apparatus under different matric suction conditions. The results show that the peak strength of soil increases with the increase of matric suction, and the rate of increase increases first and then decreases. With increased matric suction, the total cohesion increases and the extent of this increase gradually decreases, while the effective internal friction angle decreases slightly and then tends to be stable. The effect of matric suction on shear strength is mainly reflected in the total cohesion. Matric suction has the most significant influence on soil strength at 50 kPa to 100 kPa. In the presence of matric suction, the area of action of water film on soil particles determines the change of total cohesion, and the pore air pressure and pore water determine the change in effective internal friction angle. The angle used to describe the increase in the shear strength of soil with an increase in matric suction is φb=28.2°. According to Fredlund's strength theory, the formula of shear strength parameters of unsaturated silty clay in the study area under consolidation and drainage conditions was given, and the relationship between strength parameters and matric suction was fitted. [ABSTRACT FROM AUTHOR]

Unsaturated soils are frequently encountered in various civil engineering projects; however, their dynamic behaviour is still unexplored. Present study evaluates the influence of matric suction, initial static loading, and load repetition on dynamic response of unsaturated cohesive soil (CH type). A series of cyclic triaxial tests have been performed on Ahmedabad-based cohesive soil under as-compacted conditions (unsaturated). Matric suction of soil is obtained using filter paper method at varying dry density and water content to characterise the behaviour of unsaturated soil. Application of initial static axial strain exhibited a unique stiffness response in loading and unloading phases of cyclic testing, and significantly impacted the cyclic strength response of unsaturated cohesive soil. The initial static axial strain in cyclic triaxial testing represents the conditions of a highway/railway embankment, where the embankment load on soil acts like initial static loading and passing vehicles like cyclic loading on soil. Load repetition exhibited significant degradation in shear modulus of cohesive soil under cyclic loading conditions. [ABSTRACT FROM AUTHOR]

In the last decade, sediment replenishment forming cohesionless sandy banks below dams has become an increasingly common practice in Japan to compensate for sediment deficits downstream. The erosion process of the placed cohesionless sediment is a combination of lateral toe-erosion and the following mass failure. To explore cohesionless bank failure mechanisms, a series of experiments was done in a soil tank using a compacted sandy soil mass exposed to an increasing water level. Two types of uniform sand ( D 50 = 0.40 mm and 0.17 mm) and two bank heights (50 cm and 25 cm) were used under the condition of a constant bank slope of 75°. The three dimensional (3D) geometry of the bank after failure was measured using a handheld 3D scanner. The motion of bank failure was captured using the particle image velocimetry (PIV) technique, and the matric suction was measured by tensiometers. The compacted sandy soil was eroded by loss of matric suction accompanying the rise in water level which subsequently caused rotational slide and cantilever toppling failure due to destabilization of the bank. The effect of erosion protection resulting from the slumped blocks after these failures is discussed in the light of different failure mechanisms. Tensile strength is analyzed by inverse calculation of cantilever toppling failure events. The tensile strength had non-linear relation with degree of saturation and showed a peak. The findings of the study show that it is important to incorporate the non-linear relation of tensile strength into stability analysis of cantilever toppling failure and prediction of tension crack depth within unsaturated cohesionless banks. [ABSTRACT FROM AUTHOR]

Geotechnical design for unsaturated soils requires an understanding of their fundamental characteristics. In this paper, in order to study the monotonic, cyclic and post-cyclic behaviour of an unsaturated clayey soil, monotonic and cyclic triaxial tests were carried out on Tehran oil refinery’s disturbed unsaturated clayey soil (CL). Tests were conducted on the specimens with different initial matric suctions and net confining pressures with the same dry density under constant pore-air pressure and undrained conditions for water. No reconsolidation was allowed after cyclic loading of specimens. Tests results showed that cyclic loading degrade the undrained shear strength and deformation modulus of specimens during the post-cyclic monotonic loading. It was observed that shear modulus degradation is more pronounced than that of the shear strength due to cyclic loading. Also, the shear strength and shear modulus of soil generally increased with increasing the net confining pressure and initial matric suction. [ABSTRACT FROM PUBLISHER]

Compaction of aggregates is an important part of the design, construction and research of pavement geotechnics projects. An important application of compaction is sample preparation for pavement design studies. Conventionally, the impact method of compaction is used for studies on pavement materials. However, recently, some researchers have been using other methods of compaction, such as static compaction, specifically for studying the unsaturated behavior of pavement materials. The objective of this study is to investigate the effect of compaction techniques on resilient behavior of compacted laboratory specimens. Studies show that the resilient behavior of unsaturated compacted road pavement materials is influenced by suction. In this regard, two types of recycled Construction and Demolition (C&D) material were selected and static and impact compaction methods were utilized for sample preparation. Further, accuracy of four predictive resilient modulus models with or without incorporation of suction was investigated. Test results show the impact of compaction method on particle breakage, matric suction and accordingly resilient behavior of C&D granular material. [ABSTRACT FROM AUTHOR]

A semi-empirical model was proposed by for predicting the variation of the modulus of elasticity with respect to matric suction for soils with plasticity index Ip values lower than 16%. This model has been extended in this paper to predict the modulus of elasticity of unsaturated expansive soils. The information required for using the model include the soil-water characteristic curve (SWCC) and the modulus of elasticity of soil under saturated condition along with two fitting parameters. Experimental data of triaxial tests for three different expansive soils from the literature were used to examine the validity of the model. The results of the study suggest that the model can reasonably predict the modulus of elasticity of unsaturated expansive soils. The study results are encouraging in reliably using the modulus of elasticity based method proposed by for estimation of the volume change behavior of expansive soils. [ABSTRACT FROM AUTHOR]

The in situ bearing capacity of sandy soils is determined or estimated using plate load tests (PLTs), cone penetration tests (CPTs), or standard penetration tests (SPTs). The contribution of matric suction toward the bearing capacity of unsaturated sands is, however, not estimated from these tests. In this paper, SPTs and PLTs were conducted in situ on sandy soil in Ottawa, Canada under saturated and unsaturated conditions to demonstrate the contribution of matric suction on the bearing capacity results. In addition, relationships are proposed to estimate the bearing capacity of sands under both saturated and unsaturated conditions from the SPTs results. Comparisons are provided between the measured and estimated bearing capacity values for three different sands from the literature using the proposed relationships. The results of the study suggest that the proposed relationships can be used in the estimation of the bearing capacity of both saturated and unsaturated sands. [ABSTRACT FROM AUTHOR]

The paper describes instrumentation, testing, and detailed results of three 1-m high reinforced embankment models that were built in the laboratory at three different gravitational water contents (GWC). Each embankment model was subjected to a strip load near its crest until failure. The embankment models were constructed using lean clay at the GWC values ranging between OMC−2% and OMC+2% (OMC: optimum moisture content). Each embankment model included a single reinforcement layer which was placed 180 mm below the embankment surface. The location of the reinforcement layer was selected based on preliminary embankment tests and numerical simulations to ensure that it would intercept the failure surface that developed underneath the strip footing near the embankment slope. The embankments were instrumented with a total of 67 sensors to measure the soil GWC, matric suction and excess pore pressure, reinforcement strains, earth pressure and deformations of the embankment models, and the test box during the tests. The test setup and data described in this paper are part of a long-term study to validate a set of moisture reduction factors (MRF) introduced by the authors in their recent studies which involved pullout and interface shear tests on the same soil and reinforcement materials. Specifically, the data and discussions in this paper provide a basis for further in-depth analysis to verify or modify the authors' proposed MRF values for actual embankment configurations. Furthermore, the test descriptions and results in this study will be used to validate numerical models to examine the influence of the soil matric suction and moisture content on the soil-geotextile reinforcement interface strength and internal stability of reinforced soil structures. The ultimate goal of the study is to develop a better understanding of the influence of matric suction on the performance of reinforced earthen structures constructed with marginal soils, and improved methodologies for their design. [ABSTRACT FROM AUTHOR]

Copyright of Revista Internacional de Desastres Naturales, Accidentes e Infraestructura Civil is the property of University of Puerto Rico and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista Internacional de Desastres Naturales, Accidentes e Infraestructura Civil is the property of University of Puerto Rico and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A simple model was proposed by Oh et al. (2009) to predict the variation of modulus of elasticity with respect to matric suction for unsaturated coarse-grained soils (i.e., sandy soils with plasticity index, Ip = 0). This model requires the modulus of elasticity under saturated condition (Esat) and the Soil-Water Characteristic Curve (SWCC) along with two fitting parameters (α and β). In the present study, this model has been extended and a general model has been proposed such that the modulus of elasticity can be estimated for all soils (i.e., both coarse- and fine-grained soils). The proposed model is developed using model footing and in-situ plate load test results of six different unsaturated soils. The study shows that there is a good comparison between the measured and the predicted modulus of elasticity with respect to matric suction for all the six soils whose plasticity index, Ip values are in the range of 0 to 16%. [ABSTRACT FROM AUTHOR]