Esta tese tem por objetivo analisar o comportamento mecânico de um solo coluvionar de arenito não saturado (Solo AV) em condições indeformadas e remoldados. Sua localização é na divisa dos estados de Santa Catarina e Rio Grande do Sul. Os corpos de prova foram moldados com o mesmo índice de vazios na condição indeformada e na condição remoldada com o intuito de se avaliar o papel da estrutura deste solo. Para este estudo foi modificado o equipamento triaxial com sucção controlada, apresentado por Pereira (2006), inserindo os medidores de deslocamentos locais nos corpos de prova (sensores de efeito Hall). A partir dos medidores de deformação locais foi possível observar a influência da sucção nos módulos de deformabilidade do solo AV para a condição remoldada. Foram determinadas as envoltórias de resistência ao cisalhamento para os ensaios na condição não saturada para corpos de prova indeformados e remoldados. Na condição não saturada observou-se que o ângulo de atrito interno (’) é influenciado pelo nível de sucção e tensão normal líquida aplicada. As envoltórias no plano tensão cisalhante versus sucção são não lineares e resultam, para baixos valores de sucção, em valores de b sempre superiores a ’. Os resultados indicaram que os corpos de prova indeformados, na condição saturada, apresentaram parâmetros e resistência ao cisalhamento superiores aos corpos de prova remoldados. Entretanto, para a condição não saturada, os corpos de prova remoldados apresentaram resistência ao cisalhamento superiores a dos corpos de prova indeformados. Os resultados dos ensaios do hollow cylinder indicaram que a magnitude da tensão principal intermediária influencia na resistência ao cisalhamento obtida. Pela variação da direção da tensão principal maior observou-se um comportamento anisotrópico nos corpos de prova remoldados. Em termos de parâmetros de resistência ao cisalhamento os ensaios triaxiais e hollow cylinder apresentaram resultados consistentes, de acordo com a literatura. Os principais modelos de previsão de resistência ao cisalhamento existentes, baseados em dados básicos do Solo AV, não apresentaram um bom ajustes para as condições de moldagem. Baseado em análises estatísticas, foi possível obter duas equações de ajuste, sendo uma linear exponencial para a condição indeformada e uma parabólica para a condição remoldada. / This thesis aims to analyze the mechanical behavior of an unsaturated sandstone colluvium soil (Soil AV) in undisturbed and remolded conditions. The colluvium is located on the border of the states of Santa Catarina and Rio Grande do Sul. The specimens were prepared with the same void ratio for undisturbed and remolded conditions in order to evaluate the soil structure. For this study the triaxial apparatus with suction-controll, presented by Pereira (2006), was improved by inserting local displacement traducers (Hall effect sensors). These tranducers allowed the evaluation of the influence of the suction on the Young’s modulus for the soil AV in the remolded condition. Shear strength envelopes were determined based on tests on unsaturated condition on undisturbed and remolded specimens. For the unsaturated condition, it was noted that the internal friction angle ('’) is influenced by the level of suction and net normal stress applied. The shear envelopes on the shear stress versus suction plane are nonlinear and showed b higher than ’, for low suction values. The results showed that undisturbed specimens in saturated conditions presented shear strength parameters and shear strength higher than the remolded specimens. However, in the unsaturated condition the remolded specimens showed higher shear strength than undisturbed specimens. The Hollow Cylinder test results indicated that the intermediate principal stress has influence on shear strength of the soil. By varying the direction of major principal stress it was noticed an anisotropic behavior in the remolded specimens. In terms of shear strength parameters triaxial and hollow cylinder tests presented consistent results as it was observed in the literature. Some of the models used to predict the shear strength, based on basic parameters of the soil AV, have not shown good matches for both, undisturbed and remolded conditions. Based on statistical analysis, it was possible to obtain two adjustment equations being a linear exponential to the undisturbed conditions and a parabolic for the remolded condition.

No description available.

The shear strength of soil-structure interfaces is relevant to the stability of energy piles. The thermo-hydro-mechanical processes can have a strong effect on the behaviour of interfaces between unsaturated soils and piles. Temperature changes lead to water movement in the soil. The moisture loss or gain in the soil causes drying or wetting. In addition, water movement influences the heat transfer properties of the soil. Temperature and moisture content changes affect the magnitude of soil suction in unsaturated soils. Changes in soil suction alter the strength and deformation characteristics of the soil mass and soil-structure interfaces. Similar to the effects of temperature changes, the mechanical loading and the changes in hydraulic conditions in the ground would cause changes in the void ratio, degree of saturation, suction, strength and deformation characteristics of soil. The interface behaviour under varying thermo-hydro-mechanical (THM) conditions is classified as a coupled problem and this is the subject of the present research. In the present investigation, laboratory studies and numerical analyses are carried out to evaluate the THM effect on the behaviour of interfaces between an energy pile material and an unsaturated soil. A 3D interface apparatus (Fakharian and Evgin 1996) has been modified (Fu et al. 2013) to allow the behaviour of an interface to be studied under thermo-mechanical loading conditions. In the present study, the experiments are conducted on soil samples with low degree of saturation and high degree of saturation. It is found that in interface tests using soil samples with low degree of saturation, the adhesion increased due to a positive effect of suction on strength than the negative effect of increasing temperatures. However, in interface tests on soil samples with high degree of saturation, the adhesion decreased with increasing temperatures while the positive effect of suction was not large enough to overcome the negative effect of increasing temperatures. This is a new finding that has not been reported anywhere in the literature. The friction angle for both soil samples (with different degrees of saturation) changed slightly with temperature change. Coupled finite element analyses conducted in the present study provide the following geotechnical information that would be useful for the design of energy piles: (a) Bearing capacity of the pile with and without the effect of temperature, (b) The effect of degree of saturation (or suction) on the strength and deformation characteristics of both the soil and the soil-structure interface, (c) Temperature effects on the amount of pile head movements (up or down), (d) Temperature induced stresses in the pile, (f) Amount of heat that can be stored or extracted from the ground as a function of time. At the initial stages of this study, THM effects on the behaviour of energy piles under saturated and unsaturated conditions are analyzed by using SIGMA/W and VADOSE/W finite element codes of GeoStudio 2012. Although these codes are not multi-physics FE codes, it is possible to use them sequentially to obtain results that will show the trends in pile behaviour. This numerical approach is used first to analyze the behaviour of an energy pile installed partially in unsaturated soil. The moisture content and temperature distributions around a 10 m long, bored pile are calculated using transient analyses. Changes taking place in the stress state along the pile shaft and the bearing capacity of the pile at different temperatures are calculated. In the second part of the numerical analysis of the present study, THM effects on the behaviour of energy piles under saturated and unsaturated conditions are analyzed by using PLAXIS 2D finite element code. PLAXIS is a fully couples finite element code. In order to enhance present understanding of the behaviour of energy piles and do the analysis correctly, a fully coupled analysis involving thermo-hydro-mechanical processes was carried out. Three simulations (mechanical loading only, thermo-mechanical coupling and thermo-hydro-mechanical coupling) are conducted using case studies that are available in the literature. In addition, the behaviour of a generic energy pile, which is installed in a kaolin-sand mixture, is studied by taking into consideration of thermo–hydro-mechanical processes. The coupled analysis provided the distributions of temperature, degree of saturation, suction and heat flux in the analysis domain. Numerical results of the fully-coupled method are compared with the results of sequential method of analysis.

In many situations, the upper layers of soil above the ground water table are in a state of unsaturated condition. Although unsaturated soils are found throughout the world, they are predominant in arid or semi-arid regions. In these areas, the soil water characteristic curve (SWCC) which relates the water content to the matric suction could be used as key tool to implement the mechanics of unsaturated soils into the designs of geotechnical structures such as dams, embankments, pavements, canals, and foundations. Several experimental techniques are available for determining the SWCC in a laboratory environment. However, these experimental techniques are expensive, time consuming typically requiring days or weeks, depending on the soil type, and demanding intricate testing equipment. Due to these reasons, there has been a growing interest to find other means for estimating SWCC and encourage the adoption of unsaturated soils mechanics in geotechnical engineering practice. Several methods exist to indirectly estimate the SWCC from basic soil properties. Some may include statistical estimation of the water content at selected matric suction values, correlation of soil properties with the fitting parameters of an analytical equation that represents the SWCC, estimation of the SWCC using a physics-based conceptual model, and artificial intelligence methods such as neural networks or genetic programming. However, many studies have shown that environmental effects such as temperature, soil structure, initial water content, void ratio, stress history, compaction method, etc. can also affect the SWCC. This means that the estimation SWCC from set of conditions may not reliably predict the SWCC in other conditions. Due to this reason, it is crucial for engineers involved with unsaturated soils to take into account all the factors that influence the SWCC. The two key objectives of the present thesis are the development of a method based on first principles, using the capillary rise theory, to predict the variation of the SWCC as a function of temperature, as well as developing a technique for the prediction of the fixed parameters of a well-known function representing the SWCC based on basic soil properties together with the moisture profile of a soil column subjected to a known temperature gradient. A rational approach using capillary rise theory and the effect of temperature on surface tension and liquid density is developed to study the relation between temperature and the parameters of the Fredlund and Xing (1994) equation. Several tests, using a Tempe cell submerged in a controlled temperature bath, were performed to determine the SWCC of two coarse-grained soils at different temperatures. A good comparison between the predicted SWCC at different temperatures using the proposed model and the measured values from the Tempe cell test results is achieved. Within the scope of this thesis, a separate testing program was undertaken to indirectly estimate the SWCC of the same two coarse-grained soils from the measurement of their steady state soil-moisture profile while subjected to a fixed temperature differences. The water potential equation in the liquid and vapor phases is used to analyses the steady state flow conditions in the unsaturated soil. A good comparison is obtained for the SWCC estimated using this technique with the SWCC measured used a Tempe cell submerged in a controlled temperature bath. The results of this study indicate that knowledge of the moisture content of a soil specimen under a constant thermal gradient and basic soil properties can be used to estimate the SWCC of the soil at the desired temperature.

The aim of the research is to investigate the effect of increased axle loading on saturated and unsaturated railway foundation materials for heavy haul applications. The research methodology comprises of a literature review to identify the lacuna in the scientific knowledge, finite element modelling for characterisation of railway cyclic loading, development of a cyclic triaxial apparatus for laboratory testing and experimental work, followed by analysis, interpretation and discussion of results and lastly the formulation of conclusions and recommendations. The axle loading of interest start with a base load of 20 tonnes per axle for general freight followed by increased axle loading of 26, 30, 32.5 and 40 tonnes per axle for heavy haul. The test materials used in the experimental work are representative of the subballast and subgrade layers in a railway substructure. As a reproduction of the climatic conditions in the field and the loading from passing trains, experimental testing was carried out on saturated samples under undrained conditions and unsaturated samples under constant water content. Unsaturated samples were prepared to matric suctions of 50, 100 and 225 kPa via axis translation. Monotonic and cyclic tests were conducted to investigate the behaviour of railway foundation materials. Critical state theory for saturated and unsaturated soils is used as a method of analysis in establishing the failure criterion and the failure envelope. Various parameters, such as stress states, strains, resilient modulus, pore water pressure and matric suction are also utilised in investigating trends and behaviours. Based on the monotonic test results, the shear strength of unsaturated samples was found to be greater than that of saturated samples, attributed mainly to strain hardening caused by the unsaturated soil conditions, with the presence of a peak deviator stress when plotted on the stress-strain graph. However, unsaturated samples were also found to be prone to load-collapse during monotonic shear, even when the water content and confining stress remained constant, which resulted in brittle behaviour with the sudden rupture and formation of multiple bifurcation shear bands and slip planes. Based on the cyclic tests on saturated materials, it was discovered that increased axle loading can result in phase-transition in soil behaviour, based on the stress states in the soil relative to the critical state line plotted in the effective stress space. Stress states below the critical state line resulted in a no-phase transition with dilation behaviour. Stress states on the critical state line resulted in a single-phase transition from dilation to contraction. Stress states above the critical state line resulted in a double-phase transition from dilation to contraction behaviour and then strain-softening. It is therefore concluded that increased axle loading can only be sustained by materials which presented dilation and no phase-transition in soil behaviour, which occurred at axle loading of 20 and 26 tonnes per axle for the subballast and subgrade materials. Based on the cyclic tests on unsaturated materials, it was established that increased axle loading did not cause material failure for all load axle cases and materials. The stress states of all tests plotted well below the failure envelope in the net stress space, which is indicative of resilient and elastic behaviour. Increased axle loading instead resulted in decreased permanent strain, until the critical level of repeated deviator stress of 32.5 tonnes per axle was found, where the permanent strain increased. It is therefore concluded that, as a result of the increased shear strength from the strain hardening property of unsaturated materials, an increased axle loading of 32.5 tonnes per axle can be safely sustained by the tested materials provided the matric suction in the soil is greater than 50 kPa. / Thesis (PhD)--University of Pretoria, 2020. / Civil Engineering / PhD / Unrestricted

Soil is the most widely used material in the construction of various civil infrastructure. Various types of soils are extensively used in its natural or compacted form in the construction of dams, canals, road and railway subgrades, and waste containment structures such as soil covers and liners. These infrastructure and foundation soils are exposed to the influence of environmental factors. In the permafrost and seasonally frozen regions, soils can be in different states (e.g., saturated or unsaturated, frozen or thawed, or combinations of them) due to the variations in moisture content and temperature. The soil-water characteristic curve (SWCC), which is the relationship between soil water content and suction, is used in the interpretation and prediction of unsaturated soils behavior. Similarly, the soil-freezing characteristic curve (SFCC), which is the relationship between unfrozen water content and subzero temperature, is used in the prediction and interpretation of frozen soils behavior. In this thesis, the SWCC and SFCC of two Canadian soils (i.e. Toronto silty clay (TSC) and Toronto lean clay (TLC)) were extensively investigated for better understanding the fundamental relationship between SWCC and SFCC. The soil resilient modulus (MR) is a key material property used in the rational design of pavements. Experimental investigations were undertaken to determine the MR of five Canadian soils (i.e., TSC, TLC, Kincardine lean clay (KLC), Ottawa Leda clay (OLC), and Indian Head till (IHT)), considering the influence of moisture and temperature, with the aid of an advanced triaxial testing equipment. Two simple models were proposed for estimating the MR of frozen soils, in this thesis. In addition, an artificial neural network (ANN) model was developed for estimating the MR of the five Canadian soils considering various influencing factors. The conclusions from the various studies in this thesis are succinctly summarized below. (1) Four expressions (i.e. power relationship, exponential relationship, van Genuchten equation, and Fredlund and Xing equation) that are widely used for representing the SFCC were selected for providing comparisons between the measured and fitted SFCCs for different soils. The results suggest that the exponential relationship and van Genuchten equation are suitable for sandy soils. The power relationship reasonably fits the SFCC for soils with different particle sizes, but not for saline silts. The Fredlund and Xing equation is flexible and provides good fits for all the soils. (2) The SFCC and SWCC of TSC and TLC were experimentally determined, analyzed, and compared. Many factors influence the reliable measurement of SFCC, which include sensors’ resolution and stability, sensor calibration for each soil, and thermodynamic equilibrium condition. The hysteresis of SFCC for the two soils is mainly attributed to the supercooling of pore water. The quantitative dissimilarity in the measured SFCC and SWCC may be attributed to specimen structure variations during compaction and saturation, and during freezing / thawing processes, and cracks formation due to sensors insertion. In addition, some fundamental differences may exist between the drying / wetting and freezing / thawing processes, resulting in dissimilarity. (3) Two novel models were proposed for the estimation of MR of frozen soils. The semi-empirical model extends the mechanics of unsaturated soils and employs SFCC for prediction. Several coarse- and fine-grained saturated soils were used to validate this model. The empirical hyperbolic model was proposed considering that the frozen MR versus subzero temperature relationship resembles hyperbola. This model was validated on coarse- and fine-grained soils under saturated / unsaturated conditions. The hyperbolic model has wider application since it can be used for both saturated and unsaturated frozen soils. Both the models are simple and promising. (4) The MR of five Canadian soils subjected to wetting and freezing was determined by using the GDS ELDyn triaxial testing system. A freezing system was established for controlling the desired testing temperatures within the soil specimens. The results suggest: (i) The effect of subzero temperature on the MR is significant. (ii) For TLC, KLC, OLC, and IHT, the frozen MR versus subzero temperature relationship of the saturated specimen typically has steeper slope than specimen at the optimum water content, for the temperature range from 0 to -5 °C. (iii) The effect of stress levels on the frozen MR depends on soil type, water content, and subzero temperature. Lastly, (iv) Loading frequency does not show a significant influence on the frozen MR. (5) The MR of the five Canadian soils was determined considering wetting and freeze-thaw (F-T) conditions. The results suggest: (i) The F-T cycles result in weak soil structure due to reduction in suction, particles movement, loss of cohesion, and formation of cracks / channels. (ii) The critical numbers of F-T cycles were determined as 1, 1, 2, and 1 for TLC, KLC, OLC, and IHT at the optimum water content, respectively. (iii) The percentage of reduction in MR after the critical number of F-T cycles was strongly related to the plasticity index for specimens tested at the optimum water content. (iv) The wetting process results in the decrease in suction and enlargement of soil pores. Consequently, relatively low MR values were measured at high water contents, and the effect of F-T cycles becomes insignificant. Finally, (v) The effect of stress levels on the MR was dependent on the initial water content of the specimen and soil type.

The movements of salt and water, particularly in fairly dry soils or compacted shales, are important processes in both agronomic studies and hydraulics of deep ground water which is important in the location of oil.

Field compaction control is arguably the most common yet critical quality control procedure in geotechnical engineering. Since the early 1930s, the systematic process for performing quality control of compacted soils has often been performed by measuring the in-place dry unit weight (or density) and as-compacted soil moisture content after placement in a fill. However, the current practice overlooks several facts resulting from comparing soil prepared and compacted in the laboratory to soils placed and compacted in the field. These issues include comparing the compaction energy in the lab versus what is applied in the field, and the behavior of saturated soils in the laboratory to the performance of unsaturated soils in the field. To address some of these gaps, this study presents a new saturation-based framework for compaction quality control. The aim of this new framework is to reduce the uncertainties and assumptions of the compaction control process and provide practicing engineers with further insight into the key engineering attributes of compacted soils. The proposed saturation-based approach compares a degree of saturation difference to a normalized dry unit weight ratio, making saturation upon compaction the controlling diagnostic variable and the focus of the monitoring effort. In essence, the optimal compaction conditions will be referenced to a characteristic saturation state near 80%. Compared to the conventional quality control system for field compaction, the saturation-based approach is developed with the same field and reference data collected for most earth fill projects. The results of this approach enhance the engineering judgment required to match the laboratory reference values to the field conditions. For illustration purposes, the proposed saturation-based framework is applied to compaction control data of a large earth dam and compared against the conventional method side-by-side. The proposed framework builds on the unique physical features of the "family of curves" and expands the ability of the user to select the compaction criterion using that relationship to produce project design properties. Overall, the proposed approach enhances the knowledge of the physical behavior of compacted soils and provides a more comprehensive understanding of the long-term performance of compacted fills.

The shear stress in an unsaturated soil increases rapidly with limited shear strain to a peak value and then drops gradually with a further increase in the shear strain until a residual value is reached. In other words, there is a significant strain-softening behavior under large shear deformation. A variety of geotechnical structures (e.g., slopes, foundations, retaining walls and piles) associated with unsaturated soils typically undergo a large progressive deformation prior to reaching failure conditions due to the influence of environmental factors (e.g., rainfall infiltration and wetting-drying cycles). As a result, the shear strength of soils in sliding zones typically reduces from a peak to a residual value with the progressive development of large shear deformation, while the shear strength of soils in other zones are still at the peak level. In other words, in many scenarios the strain-softening behavior of unsaturated soils can significantly influence the mechanical behavior of geo-structures. Therefore, a thorough understanding of the shear strength behavior of unsaturated soils during strain-softening is required to reliably interpret the mechanical behavior of geo-structures that undergo large shear deformation. Significant advances have been made during the last thirty years to understand and model the strain-softening behavior of unsaturated soils. Most of these studies however focus on the strain-softening behavior within a relatively small shear deformation due to the limitations of the experimental apparatuses. Only limited experimental studies under large shear deformation were reported based on the modified suction-controlled ring shear apparatus. Therefore, more investigations are still required to provide a comprehensive understanding of the shear strength behavior of unsaturated soils during strain-softening under large shear deformation. Studies presented in this thesis are directed towards investigating the shear strength behavior of unsaturated soils during strain-softening and its application in geotechnical engineering practice. The following studies have been conducted: (i) A state-of-the-art review of the strain-softening behavior of unsaturated soils published in the literature during the past three decades is summarized. The physical mechanisms and modelling methods of the strain-softening behavior and the peak, critical and residual shear strength of unsaturated soils are investigated. (ii) A disturbed state concept model is proposed to predict the variation of shear stress in unsaturated soils during strain-softening process under drained condition. Five sets of experimental data gathered from the literature on unsaturated soils varying from coarse- to fine-grained soils are used to verify the proposed model. The proposed model can provide reasonable predictions for the strain-softening stress-strain relationships of various types of unsaturated soils. The model is simple in concept and all the required parameters can be obtained from conventional saturated and unsaturated shearing tests and pressure plate tests. (iii) Two sets of suction-controlled multistage ring shear tests are conducted on unsaturated SP-SM soil and Indian Head till (IHT), respectively. The variation of the shear stress, void ratio, and water content of specimens during shearing (the shear displacement reaches 100 mm) under multi levels of net normal stress and matric suction are described and discussed. The influence of matric suction and net normal stress on the residual shear strength envelops of unsaturated soils are critically discussed. (iv) A model for predicting the residual shear strength for a wide range of unsaturated soils comprising coarse- to fine-grained soils is developed in terms of two stress state variables (i.e., the net normal stress and matric suction) by using the soil water characteristic curve as a tool. The model is formulated and validated based on experimental data in a series of suction-controlled ring shear tests using the axis-translation technique, including the two sets of tests (SP-SM and IHT) conducted in this research and another three sets of tests (SM, SC-SM and CH) gathered from the literature. The fitting parameters are related to the plasticity index (Iₚ); thus, only four basic parameters (i.e., cᵣ', φᵣ', Sᵣ and Iₚ) are included in this approach. (v) A series of slope stability analyses of a landslide in unsaturated condition are conducted using Geoslope software based on the peak and residual shear strength parameters. The analyses results highlight the role of residual shear strength in the slope stability of unsaturated soils. In summary, the mechanical behavior of unsaturated soils under large shear deformation is comprehensively investigated in this thesis. The experimental results of the suction-controlled ring shear tests reported in this research contribute towards understanding the fundamental shear strength behavior of unsaturated soils during strain-softening under large shear deformation. The models proposed in this research provide simple tools to predict the shear strength of unsaturated soils under different levels of shear deformation.

There has been an increasing interest in fundamental and applied research on emerging geotechnical and geoenvironmental engineering applications that pose multi-physics problems involving non-isothermal processes in unsaturated soils. Properly studying these problems requires the development of analytical models to describe the constitutive behavior of unsaturated soils under non-isothermal conditions. However, major gaps remain in the development of unified models that can properly represent the temperature dependency of unsaturated soil behavior. The effects of temperature on the stability of slopes, lateral earth pressure, and pile resistance in unsaturated soils are also not well understood. The main objective of this study is to provide new insight and robust tools to characterize and model the temperature-dependent behavior of unsaturated soils. For this purpose, novel unified models are developed for soil water retention curve, effective stress, thermal conductivity function, and small-strain shear modulus for unsaturated soils at elevated temperatures. The models are proposed by establishing or extending the unified model at isothermal conditions to nonisothermal conditions. The fundamental and main variable in all unified models is capillary pressure (also referred to as matric suction). The effect of temperature is considered on adsorption and capillarity as a function of water-air surface tension, soil-water contact angle, and enthalpy of immersion. The proposed models are verified by comparing them with experimental data reported in the literature and measurements made in this study. Overall results of the proposed models show an excellent predictive capability. Furthermore, the parametric study is conducted to understand the effect of different parameters such as soil type, temperature, drainage conditions, and among others on hydraulic and mechanical properties of unsaturated soil. Finally, the proposed models are incorporated into geotechnical applications such as slope stability, lateral earth pressure, and pile resistance involving unsaturated conditions and elevated temperatures. The variation of temperature in unsaturated soils for these applications can be notable and cannot be ignored in the design and analysis. The proposed formulations can also be readily incorporated into analytical solutions and numerical simulations of thermo-hydro-mechanical processes in unsaturated soils. The findings of the study can facilitate using numerical models to simulate various non-isothermal applications including geo-energy systems and soil-atmospheric interaction problems.