The International Conference on Soil Mechanics and Foundation Engineering in 1936 was perhaps the first international forum which brought unsaturated soil problems to the attention of geotechnical engineers. Since then, the understanding of unsaturated soil behaviour has been improved considerably. The theory for the volume change and shear strength behaviour of unsaturated soils has now developed to the point of potential application in geotechnical practice. A complete understanding of the volume change behaviour of an unsaturated soil requires a knowledge of volumetric deformation moduli on four state planes. These moduli must be determined in either a direct or indirect manner in order to solve practical problems involving volume change, moisture movement, bearing capacity and slope stability analysis. The measurement of these moduli generally requires modification to conventional laboratory equipment. The solution of unsaturated soil problems would be greatly facilitated if the relationships between the various moduli were known. Then it would be possible for all moduli to be determined by a few established conventional soil tests. The main objective of this dissertation is to develop and measure the relationships between the various volume change moduli. The study began with a literature review on the volume change constitutive relations for the soil structure and water phase of an unsaturated soil. Attempts were made to gather information pertinent to the relationships between different moduli. The theory chapter started with an examination of the most acceptable form for the soil structure and water phase constitutive surfaces on both arithmetic and semi-logarithaic scales. Approximate semi-logarithmic constitutive surfaces were then proposed. The geometry of the approximate semi-logarithmic constitutive surfaces is used to relate the moduli associated with a particular phase (i.e., the soil structure or water phase). When a soil. is saturated, the soil structure and water phase moduli with respect to the logarithm of net total stress are related by the relative density, Gs' of the soil. The inter-relationship of the three remaining moduli was then studied. A laboratory test program was designed to obtain experimental data showing the characteristic form of the semi-logarithmic constitutive surfaces on the net total stress and matric suction planes. Two soils, a uniform silt and a glacial till were tested. Specimens were formed by static compaction at half standard Proctor compaction effort with either dry of optimum or at optimum initial water contents. The investigation included specimens being loaded and unloaded under Ko and isotropic conditions. The results were analyzed and used to evaluate the relationships between the moduli. The knowledge of four moduli is needed to completely describe the volume change behaviour of an unsaturated soil in a monotonic volume change process. Special tests are required to determine these four moduli in the laboratory. For instance, the one-dimensional or isotropic compression test, the suction and unconfined shrinkage tests are necessary for solving settlement problems. The use of an approximate semi-logarithmic constitutive surface as a means to relate moduli for the same phase appears to be viable only for the soil structure. The geometry of the approximate soil structure constitutive surfaces is identifiable by two characteristic stress states namely the corrected swelling pressure (i.e., Pś) and the initial stress state translated to the matric suction plane e following a constant volume stress path (i.e., (ua - uw)e/i). Relationships between soil structure moduli can be written e in terms of log (Pś) and log(ua - uw)e/i. The experimental data has revealed empirical relationships between moduli for the water phase. As a whole, six relationships for the eight moduli associated with monotonic volume decrease and increase are suggested. The compressive and swelling indices with respect to the net total stress (i.e., Ct and Cts respectively) can be measured using conventional oedometer or triaxial equipment. These two are regarded as "basic" moduli. The remaining moduli can be estimated from the proposed relationships with the knowledge of the basic moduli and the characteristic stress states, Pś and (ua - uw)e/i.

No / This paper presents results of the relationship between the degree of saturation and the matric suction head at static equilibrium and during dynamic flow of water using a Buchner funnel and a fully instrumented two-dimensional tank, respectively. The major influences of the dynamic flow on the relationships between the suction head and the degree of saturation are highlighted and discussed. The experimental results show that dynamic flow of water strongly affects the volume of entrapped air. The results also reveal that any scanning curve can be described as two parts, namely, transition and coinciding. The transition curve starts from the recent reversal degree of saturation and continues up to the previous reversal degree of saturation. The shape of the transition curve and the amount of hysteresis are not only a function of the reversal degree of saturation but are also a function of the saturation path history. The experimental results are used to examine the validity of the proposed analytical model by Parker and Lenhard in 1987 for describing the relationships between the degree of saturation and the matric suction head. It was found that Parker and Lenhard¿s model provides a good prediction of the relations provided that care should be taken for the value of the reversal degree of saturation at zero suction head.

Soils bear natural and artificial structures and sustain agricultural and biological activities. Understanding soil behaviour is the key to appropriating the benefits derivable from this material. Engineers are usually interested in the mechanical aspect of soil behaviour. This involves the study of volume change and shear response to applied stresses. In the past, soil shear and volume change behaviour were studied independently. But many practical problems involve shearing accompanied by volume change, therefore, it is desirable to consider this interaction in modelling soil behaviour. The critical state theory (Roscoe et al. 1958) was developed to combine both shear and volume change behaviour of soils. Early soil mechanics theories including the critical state theory, were developed for saturated soils. Because unsaturated soils are encountered in many situations, there is the need to adapt earlier theories or to formulate new ones for unsaturated soils. The major differences in the physical behaviour of saturated and unsaturated soils are due to an internal stress called matric suction formed at the air-water interface in the soil pores. Theories developed for unsaturated soil mechanics are based on the inclusion of the effect of matric suction on soil behaviour. In this study, the applicability of two major frameworks (i.e., critical state theory and unsaturated soil mechanics) to the study of agricultural soil behaviour was investigated. Soil behaviour was considered within a modified critical state framework that permits the application of critical state theories to an unsaturated soil. An experimental program involving tests in a modified state-of-the-art triaxial testing system was undertaken. Critical state soil parameters were obtained and state boundaries identified. The role of matric suction and soil structure on state parameters are presented. Changes in matric suction caused a shift (translation) in state boundaries, while changes in structure caused a rotation of the state boundaries. Results also showed that the assumption that matric suction is a constant variable depends on the stress level in the soil. Under low stress regimes, this assumption seems justifiable, however this is questionable under high stress regimes. This study also showed the importance of consideration of suction in the analysis of agricultural soil behaviour.

The design of pile foundations in conventional geotechnical engineering practice is based on the soil mechanics principles for saturated soils. These approaches are also extended to pile foundations that are placed totally or partially above the ground water table (i.e., vadose zone), where the soil is typically in a state of unsaturated condition. Such approaches lead to unrealistic estimations of the load carrying capacity and the settlement behavior of pile foundations. Some studies were undertaken in recent years to understand the influence of the matric suction towards the bearing capacity of model pile foundations placed in unsaturated fine-grained and coarse-grained soils. The conventional   and methods were modified to interpret the contribution of shaft carrying capacity of single piles in fine-grained soils (e.g., Vanapalli and Taylan 2011, Vanapalli and Taylan 2012). Also, the conventional method has been used to understand the contribution of matric suction towards the shaft resistance in unsaturated sands (Vanapalli et al. 2010). One of the key objectives of the present research study is directed to determine the contribution of matric suction towards the bearing capacity and settlement behavior of model single pile foundations in unsaturated sands. A series of single model pile load tests were performed in a laboratory environment to study the contribution of the matric suction towards the total, shaft, and base bearing capacity of the model piles with three different diameters (i.e., 38.30, 31.75, and 19.25 mm) in two unsaturated sands (i.e., a clean commercial sand and a super fine sand). Hanging column method (i.e., plexi glass water container) was used to control the matric suction values in the compacted sands in the test tank by varying the water table. The results of the testing programs indicate the significant contribution of the matric suction towards the bearing capacity of single model piles (i.e., 2 to 2.5 times of base bearing capacity and 5 times of shaft bearing capacity under unsaturated conditions in comparison with saturated condition). The test results were interpreted successfully by modifying the conventional methods for estimating the pile shaft bearing capacity (i.e., β method) and base bearing capacity (i.e., Terzaghi 1943, Hansen 1970 and Janbu 1976). In addition, semi-empirical methods were proposed for predicting the bearing capacity of single model piles using the effective shear strength parameters (i.e., c' and ϕ') and the soil-water characteristic curve (SWCC). There is a good agreement between the measured and the predicted bearing capacity of single model piles using the semi-empirical models proposed in this study. In addition, numerical investigations were undertaken using the commercial finite element analysis program SIGMA/W (Geostudio 2007) to simulate the load-displacement (i.e., p-δ) behavior of the single model piles for the two sands (i.e., clean commercial sand and super fine sand) under saturated and unsaturated conditions. An elastic-perfectly plastic Mohr-Coulomb model that takes into account the influence of the matric suction was used to simulate the load-displacement (i.e., p-δ) behavior. The numerical approach proposed in this thesis is simple and only requires the information of the effective shear strength parameters (i.e., c' and ϕ'), the elastic modulus (i.e., Esat) under saturated conditions, the soil-water characteristic curve (SWCC), and the distribution of the matric suction with respect to depth. The approaches proposed in this thesis can be extended to determine the in-situ load carrying capacity of single piles and also simulate the load-displacement (i.e., p-δ) behavior. The studies presented in this thesis are promising and encouraging to study their validity in-situ conditions. Such studies will be valuable to implement the mechanics of unsaturated soils into geotechnical engineering practice.

The design of pile foundations in conventional geotechnical engineering practice is based on the soil mechanics principles for saturated soils. These approaches are also extended to pile foundations that are placed totally or partially above the ground water table (i.e., vadose zone), where the soil is typically in a state of unsaturated condition. Such approaches lead to unrealistic estimations of the load carrying capacity and the settlement behavior of pile foundations. Some studies were undertaken in recent years to understand the influence of the matric suction towards the bearing capacity of model pile foundations placed in unsaturated fine-grained and coarse-grained soils. The conventional   and methods were modified to interpret the contribution of shaft carrying capacity of single piles in fine-grained soils (e.g., Vanapalli and Taylan 2011, Vanapalli and Taylan 2012). Also, the conventional method has been used to understand the contribution of matric suction towards the shaft resistance in unsaturated sands (Vanapalli et al. 2010). One of the key objectives of the present research study is directed to determine the contribution of matric suction towards the bearing capacity and settlement behavior of model single pile foundations in unsaturated sands. A series of single model pile load tests were performed in a laboratory environment to study the contribution of the matric suction towards the total, shaft, and base bearing capacity of the model piles with three different diameters (i.e., 38.30, 31.75, and 19.25 mm) in two unsaturated sands (i.e., a clean commercial sand and a super fine sand). Hanging column method (i.e., plexi glass water container) was used to control the matric suction values in the compacted sands in the test tank by varying the water table. The results of the testing programs indicate the significant contribution of the matric suction towards the bearing capacity of single model piles (i.e., 2 to 2.5 times of base bearing capacity and 5 times of shaft bearing capacity under unsaturated conditions in comparison with saturated condition). The test results were interpreted successfully by modifying the conventional methods for estimating the pile shaft bearing capacity (i.e., β method) and base bearing capacity (i.e., Terzaghi 1943, Hansen 1970 and Janbu 1976). In addition, semi-empirical methods were proposed for predicting the bearing capacity of single model piles using the effective shear strength parameters (i.e., c' and ϕ') and the soil-water characteristic curve (SWCC). There is a good agreement between the measured and the predicted bearing capacity of single model piles using the semi-empirical models proposed in this study. In addition, numerical investigations were undertaken using the commercial finite element analysis program SIGMA/W (Geostudio 2007) to simulate the load-displacement (i.e., p-δ) behavior of the single model piles for the two sands (i.e., clean commercial sand and super fine sand) under saturated and unsaturated conditions. An elastic-perfectly plastic Mohr-Coulomb model that takes into account the influence of the matric suction was used to simulate the load-displacement (i.e., p-δ) behavior. The numerical approach proposed in this thesis is simple and only requires the information of the effective shear strength parameters (i.e., c' and ϕ'), the elastic modulus (i.e., Esat) under saturated conditions, the soil-water characteristic curve (SWCC), and the distribution of the matric suction with respect to depth. The approaches proposed in this thesis can be extended to determine the in-situ load carrying capacity of single piles and also simulate the load-displacement (i.e., p-δ) behavior. The studies presented in this thesis are promising and encouraging to study their validity in-situ conditions. Such studies will be valuable to implement the mechanics of unsaturated soils into geotechnical engineering practice.

This paper presents an innovative experimental approach for simultaneous measurements of the suction head, volumetric water content, and the acoustic admittance of unsaturated sands. Samples of unsaturated sands are tested under controlled laboratory conditions. Several types of uniform sand with a wide range of particle sizes are investigated. The reported experiments are based on a standard Buchner funnel setup and a standard acoustic impedance tube. It is a novel, nondestructive, and noninvasive technique that relates the key geotechnical parameters of sands such as volumetric water content, density, and grain-size distribution to the acoustic admittance and attenuation. The results show a very sensitive dependence of the acoustic admittance on the volumetric water content controlled by the value of suction head applied. Analysis of the obtained data demonstrates that the relationship between the volumetric water content and the real part of the surface admittance in the frequency range of 400–1,200 Hz can be represented using a logarithmic equation. It is found that the coefficients in the proposed equation are directly related to the uniformity coefficient and the acoustic admittance of the dry sample, which can easily be measured or predicted for a broad range of sands. A validation exercise is conducted to examine the accuracy of the proposed equation using a sand sample with markedly different properties. The results of the validation exercise demonstrate that the proposed relations can be used to determine very accurately the volumetric water content within the porous specimen from the acoustical data. The error in the acoustically measured volumetric water content is found to be ±2.0% over the full range of volumetric water contents ( 0≤θ≤n , where n is the sample porosity).

A mecânica dos solos não saturados tem se tornado um importante tema de pesquisas dedicadas a entender o comportamento dos solos não saturados e otimizar sua utilização em várias obras civis. A curva de retenção de água, definida como a relação entre a sucção e a quantidade de água presente no solo, é considerada um elemento chave na interpretação do comportamento e propriedades dos solos não saturados tais como a condutividade hidráulica e a resistência ao cisalhamento. Este trabalho apresenta a estrutura de um banco de dados projetado para armazenar informações de solos brasileiros com enfoque nas características de retenção de água. O banco de dados inclui a curva de retenção e os parâmetros de ajuste das equações de van Genuchten (1980) e Fredlund & Xing (1994), assim como informações das características dos solos como índices físicos, classificações dos solos, análises granulométricas, índices de consistência e localização e estado da amostra. Além da estimativa da função condutividade hidráulica, o banco de dados oferece duas ferramentas que permitem a pesquisa rápida ou detalhada das informações e os dados armazenados podem ser mostrados na tela ou em relatórios impressos / Unsaturated soil mechanics has become an important subject of research devoted to understand the behavior of unsaturated soils and optimize their use in several civil works. The soil-water characteristic curve, defined as the relationship between the suction and the amount of water present in the soil, is considered as the key in the interpretation of the behavior and properties of unsaturated soils, such as the hydraulic conductivity and the shear strength. This paper presents the structure of a database designed to store information of brazilian soils with focus in the characteristics of water retention. The database includes the retention curves and the parameters of adjusted van Genuchten and Fredlund & Xing equations and also information of soil characteristics such as physical indexes, soil classifications, particle-size analysis, consistency indexes and location and kind of used samples. Beyond the estimate of hydraulic conductivity, the database presents two search tools that allow for quick and detailed recovering of information and stored data can be displayed on screen or in printed reports

The primary objective of this thesis is to develop a model for quantification of weather-related railway embankments hazards. The model for quantification of embankment hazards constitutes an essential component of a decision support system that is required for the management of railway embankment hazards. A model for the deterministic and probabilistic assessment of weather-related geo-hazards (W-GHA model) is proposed based on concepts of unsaturated soil mechanics and hydrology. The model combines a system of two-dimensional partial differential equations governing the thermo-hydro-mechanical behaviour of saturated/unsaturated soils and soil-atmosphere coupling equations. A Dynamic Programming algorithm for slope stability analysis (Safe-DP) was developed and incorporated into the W-GHA model. Finally, an efficient probabilistic and sensitivity analysis framework based on an alternative point estimate method was proposed. According to the W-GHA model framework, railway embankment hazards are assessed based on factors of safety and probabilities of failures computed using soil property variability and case scenarios. <p> A comprehensive study of unsaturated property variability is presented. A methodology for the characterization and assessment of unsaturated soil property variability is proposed. Appropriate fitting equations and parameter were selected. Probability density functions adequate for representing the unsaturated soil parameters studied were determined. Typical central tendency measures, variability measures, and correlation coefficients were established for the unsaturated soil parameters. The inherent variability of the unsaturated soil properties can be addressed using the probabilistic analysis framework proposed herein. <p> A large number of hypothetical railway embankments were analysed using the proposed model. The embankment analyses were undertaken in order to demonstrate the application of the proposed model and in order to determine the sensitivity of the factor of safety to the uncertainty in several input variables. The conclusions drawn from the sensitivity analysis study resulted in important simplifications of the W-GHA model. It was shown how unsaturated soil mechanics can be applied for the assessment of near ground surface stability hazards. The approach proposed in this thesis forms a protocol for application of unsaturated soil mechanics into geotechnical engineering practice. This protocol is based on predicted unsaturated soil properties and based on the use of case scenarios for addressing soil property uncertainty. Other classes of unsaturated soil problems will benefit from the protocol presented in this thesis.

Se ha llevado a cabo:A) Un estudio de las propiedades básicas del suelo no saturado (tipo limo) a escala microestructural, incluyendo esqueleto sólido, fase liquida y fase gaseosa. B) Elaboración de un modelo conceptual discontinuo de comportamiento. La geometría interna esta construida por partículas, agua retenida en forma de meniscos alrededor de los contactos y aire ocupando los restantes poros. La interfase liquido gas esta gobernada por la succión y la tensión superficial. Los meniscos tienen un efecto rigidizador del esqueleto.Se observa la posible redistribución de la humedad y del aire, quedando acoplados en definitiva los aspectos mecánicos y de flujo.C) En base a lo anterior, implementación de un modelo numérico discontinuo de ensayo de comportamiento basado en ordenador. Se ha adaptado y modificado el D.E.M. de P.A. Cundall (diferencias finitas explicitas en el tiempo), indicado en el caso que se trata, con no-linealidades geométricas. Se han desarrollado importantes algoritmos de control geométrico. D) Verificación parcial del modelo y aplicación a casos típicos en suelo no saturado, especialmente el colapso.En conjunto es una herramienta útil para su estudio y permite apreciar algunos interesantes mecanismos de actuación de la succión a escala microscópica.

The primary objective of this thesis is to develop a model for quantification of weather-related railway embankments hazards. The model for quantification of embankment hazards constitutes an essential component of a decision support system that is required for the management of railway embankment hazards. A model for the deterministic and probabilistic assessment of weather-related geo-hazards (W-GHA model) is proposed based on concepts of unsaturated soil mechanics and hydrology. The model combines a system of two-dimensional partial differential equations governing the thermo-hydro-mechanical behaviour of saturated/unsaturated soils and soil-atmosphere coupling equations. A Dynamic Programming algorithm for slope stability analysis (Safe-DP) was developed and incorporated into the W-GHA model. Finally, an efficient probabilistic and sensitivity analysis framework based on an alternative point estimate method was proposed. According to the W-GHA model framework, railway embankment hazards are assessed based on factors of safety and probabilities of failures computed using soil property variability and case scenarios. <p> A comprehensive study of unsaturated property variability is presented. A methodology for the characterization and assessment of unsaturated soil property variability is proposed. Appropriate fitting equations and parameter were selected. Probability density functions adequate for representing the unsaturated soil parameters studied were determined. Typical central tendency measures, variability measures, and correlation coefficients were established for the unsaturated soil parameters. The inherent variability of the unsaturated soil properties can be addressed using the probabilistic analysis framework proposed herein. <p> A large number of hypothetical railway embankments were analysed using the proposed model. The embankment analyses were undertaken in order to demonstrate the application of the proposed model and in order to determine the sensitivity of the factor of safety to the uncertainty in several input variables. The conclusions drawn from the sensitivity analysis study resulted in important simplifications of the W-GHA model. It was shown how unsaturated soil mechanics can be applied for the assessment of near ground surface stability hazards. The approach proposed in this thesis forms a protocol for application of unsaturated soil mechanics into geotechnical engineering practice. This protocol is based on predicted unsaturated soil properties and based on the use of case scenarios for addressing soil property uncertainty. Other classes of unsaturated soil problems will benefit from the protocol presented in this thesis.