Dissertations / Theses on the topic 'Critical state soil mechanics'

One of the greatest breakthroughs in soil mechanics was the development of Critical State Soil Mechanics (CSSM) in the 1950s and 1960s and the derivation of a continuum elasto-plastic constitutive model, namely Cam clay, which was the foundation for other continuum models for clays, and much later for sands. However, as yet there has been no micro mechanical analysis which explains the existence of such continuum models; such a micro perspective must take into account the discontinuous nature of soil. Without such insight, the engineer cannot understand which micro parameters affect soil behaviour. This work uses the discrete element method (DEM) to model a silica sand as a sample of discrete particles, with properties which have been calibrated against experimental data in previous work, to build up a micro mechanical picture of the behaviour of sand under different loading conditions. The simplest of loading conditions is the one dimensional or oedometer test and has been modelled to check whether this agrees with previously published research. The simulated sample has then been subjected to isotropic compression to establish a normal compression line in log voids ratio – log stress space, and which turns out to be parallel to the one-dimensional normal compression line, in agreement with CSSM. The evolution of the isotropic normal compression line is due to local shear stresses within the sample, and the origin of the existence of both lines lies in the evolution of a fractal distribution of particles with a fractal dimension of 2.5. The effect of boundary particles has then been minimised by choosing an appropriate aspect ratio and a smaller number of particles in the sample to give a computational time which is acceptable for subsequent shearing to critical states. Isotropically normally compressed samples have been unloaded to different stress levels and sheared to critical states. A unique critical state line (CSL) exists at high stress levels, which is parallel to the normal compression lines, in agreement with CSSM. At low stress levels, the CSL is not linear and is non-unique; that is to say it is a function of preconsolidation pressure because the fractal distribution of sizes has not fully evolved. Samples sheared on the dense side of critical dilate and have a peak strength whilst loose samples exhibit ductile contraction, in agreement with CSSM. At a critical state, the work shows that crushing continues in the formation of ‘fines’, small particles with smaller than 0.1mm dimensions, which plays no part in the mechanical behaviour, which is reflected in the average mechanical co-ordination number and which means that plastic hardening can be assumed to have ceased at a critical state. For the isotropically overconsolidated samples sheared to critical states, a number of different definitions of yield have been used to establish a yield surface in stress space. The work shows that a previously published yield surface for sand (Yu, 1998; McDowell, 2002) gives a good representation of the behaviour, and it has therefore been shown that the sample of discrete particles has been shown to give rise to observed continuum behaviour. The work is, to the author’s knowledge, the first that has shown a DEM soil to show many of the desirable features of sand, in that the sample qualitatively gives normal compression lines and a CSL of the correct slope, which obeys CSSM and which gives a Cam Clay type yield surface in stress space. The work means that the established model can be used in the study of other micro mechanics problems such as particle shape and time effects and the application of DEM to boundary value problems directly.

The critical state soil mechanics (CSSM) framework originally proposed by Schofield & Wroth (1968) has been shown to capture the mechanical behaviour of soils effectively. The particulate implementation of the discrete element method (DEM) can replicate many of the complex mechanical characteristics associated with sand. This research firstly shows that the CSSM framework is useful to assess whether a DEM simulation gives a response that is representative of a real soil. The research then explores the capacity of DEM to extend understanding of soil behaviour within the CSSM framework. The influence of sample size on the critical-state response observed in DEM simulations that use rigid-wall boundaries was examined. The observed sensitivity was shown to be caused by higher void ratios and lower contact densities adjacent to the boundaries. When the void ratio (e) and mean stress (p’) of the homogeneous interior regions were considered, the influence of sample size on the position of the critical state line (CSL) in e-log(p’) space diminished. A parametric study on the influence of the interparticle friction (μ) on the load-deformation response was carried out. The macro-scale stress-deformation characteristics were nonlinearly related to μ and the particle-scale measures (fabric, contact force distribution, etc.) varied systematically with μ. The limited effect of increases in μ on the overall strength at high μ values (μ>0.5) is attributable to transition from sliding-dominant to rolling-dominant contact behaviour. A μ value higher than 0.5 leads to a CSL in e-log(p’) space that does not capture real soil response. True-triaxial simulations with different intermediate stress ratios (b) were performed. The dependency of strength on b agreed with empirical failure criteria for sands and was related to a change of buckling modes of the strong force chains as b increased. DEM simulations showed that the position of the CSL in e-log(p’) space depends on the intermediate stress ratio b. This sensitivity seems to be related to the dependency of the directional fabric anisotropy on b. The link between the state parameter and both soil strength and dilatancy proposed by Jefferies & Been (2006) was reproduced in DEM simulations. A new rotational resistance model was proposed and it was shown that the new model can qualitatively capture the influence of particle shape on the mechanical behaviour of sand. However, it was shown that the effect of rotational resistance is limited and to quantitatively compare the DEM simulation results with laboratory testing data, e.g., the critical-state loci, it is necessary to use non-spherical particles.
published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy

With the increased availability of computers of various sizes, it is becoming more common to predict the responses of geotechnical structures using numerical analyses which incorporate more realistic models of soil behaviour. The main objective of this research is to develop and evaluate a series of unified critical state models. These models are then used to solve some typical boundary value problems in geotechnical engineering. The new models are based on a critical state model called CASM which was formulated based on both the state parameter concept and a non associated flow rule. The main feature of CASM is that a single set of yield and plastic potential functions is used to model the behaviour of clay and sand under both drained and undrained loading conditions. These models are developed by incorporating a new non-linear elasticity rule, the combined hardening concept and the bounding surface plasticity theory. A new non-linear elasticity rule for clay materials is introduced into CASM, this gives a better prediction on the behaviour of soil. The new combined volumetric-deviatoric hardening model is named CASM-d and provides a better prediction of the behaviour of lightly overconsolidated clays and loose sands. The new bounding surface model is named CASM-b and provides a more realistic prediction of soil behaviour inside the state boundary surface. The new cyclic bounding surface model is named CASM-c and provides a good prediction of soil behaviour under cyclic loading conditions. To evaluate their adequacy, CASM and its extensions are implemented into a finite element package called CRISP. This program was specifically developed to incorporate the critical state type of constitutive models. The analyses of a variety of typical geotechnical engineering problems are carried out to further check the validity of the new constitutive models. The models prove themselves to be very robust and useful tools for solving a wide range of practical geotechnical problems under different loading conditions.

An embankment has been constructed to a maximum height of approximately twelve metres at Beckton, east London. The embankment is underlain by up to eight metres of alluvium and made ground. The embankment was monitored during construction. Centreline settlements of the order of O.6m and horizontal movements at the embankment toe of up to O.1Sm were measured. The excess pore pressures generated during construction were found to dissipate rapidly. Soil samples recovered from the site have been tested at city University. The alluvial clay is shown to have extremely variable compression characteristics and it is not possible to determine a single set of critical state soil parameters from the "undisturbed" soil samples. The use in design of parameters derived from reconstituted soil samples is investigated. Laboratory test results indicate that a small quantity'of organic matter in the soil has a large effect on the engineering properties of the alluvial clay. The importance of not dry~ng soils which contain organic matter is highlighted. It is shown that, despite the effects of the organic matter, critical state concepts and in particular the modified Cam clay soil model can be used to predict the behaviour of the alluvial clay in a wide variety of laboratory tests. standard methods of determining the yield stress or preconsolidation pressure are shown to be inadequate when used to analyse the results of compression tests performed at a constant rate of loading. An alternative method, the Lambda construction, is proposed and this is shown to be both reliable and objective. Two distinct testing methods have been used to probe the state boundary surface of the reconstituted alluvial clay samples. The results of these tests appear to indicate the existence of a single state boundary surface for both Ko and isotropically compressed samples. This surface has a shape similar to that predicted by the modified Cam clay soil model. This result conflicts with the findings of many other investigators. Finite element modelling of the embankment construction has been carried out. A single set of soil parameters derived from tests on the reconstituted clay were used to represent the alluvial stratum. The construction of the embankment was modelled as a drained event. The results are shown to compare favourably with the actual field data.

The state of a soil illustrated in the spaces of voids ratio and shear stress versus mean effective stress is known to control the soil behaviour through reflecting the impacts of initial density, stress level, static and cyclic stress ratios, and stress reversal condition. The multiplicity of the variables has led to confusing observations in studies of failure modes and cyclic strength. This research develops a better understanding of the effects of the state variables on the undrained cyclic response through conducting cyclic and monotonic triaxial tests on iso and anisotropically consolidated samples of Sydney sand, and using relevant experimental data published in the literature. The results indicate the major role of the degree of cyclic stress reversal in determining the cyclic failure mode. A “reversal ratio” is introduced, to quantify the reversal level, and a hybrid failure mechanism, referred to here as “plastic strain accumulation followed by cyclic mobility”, is analysed in detail. It is shown that the reversal ratio captures the combined impacts of the static and cyclic stress ratios on the behaviour. “Threshold reversal ratio” which is associated with the boundaries between different modes of failure is discussed and estimated. A state parameter approach is employed to investigate the impacts of static and cyclic stress ratios on the cyclic strength. The number of cycles to failure, Nf, and the cyclic resistance ratios, CRR15, CRR100 and CRR500, were found to correlate with the state parameter. However, these correlations become more sensitive to the state parameter as the static stress ratio increases. The results suggest that the interconnection between Nf and CRRn is not largely influenced by the static stress ratio and can be an alternative to the state parameter approach. Furthermore, the states causing failure are depicted on a unified state diagram that combines the roles of density, stress level, static stress ratio and cyclic stress ratio.

The railway track foundation of fine-grained soil subgrade, under repeated loading of cyclic nature, can gradually build up excess pore pressure and result in progressive shear failure at a stress level much lower than the monotonic loading strength of the soil. It is widely accepted that a threshold stress exists, above which, the induced stress generates large shear deformation and; below which, the soil deformation become stabilized irrespective of the number of loading applications. Previous studies into the behaviour of fine-grained subgrade under cyclic loading had mainly involved slow loading rate. The advance in transportation technology and the required efficiency of transporting goods and commuting passengers demands higher train speed and heavier loads. Consequently, better understanding on the behaviour of fine-grained subgrade under higher rate of loading (i.e. cyclic frequency) will be necessary as it influences the build-up of excess pore water pressure and strain accumulation of subgrade soil, hence the stability of the railway track. In addition, current design approaches to the railway tracks foundation of fine-grained subgrade have largely been empirical or semi-empirical unique to a range of geological characteristic, operating and traffic condition. The rationalization and reformulation of design approach may be required if general design means will to be devised.In this research, an in-depth study of undrained triaxial testing on the behaviour of a typical fine-grained reconstituted kaolinite clay soil, simulating the characteristic subgrade responses exhibit under the passing axles / wheel load of the contemporary train speed was performed and discussed. Four series of both static and cyclic undrained triaxial test were conducted. The static undrained triaxial test provides the behavioural benchmark and a prior indication on the maximum stress level from which the cyclic stress level can be apportioned. The cyclic undrained triaxial test simulates the behaviour of clay subgrade under a large number of passing axles/wheel load. The results of the testing described and characterized the stress / strain behaviour for saturated kaolinite clay of various consolidated state and stress history. In particular, it described the general concept of cyclic stress equilibrium state and resilient state, and detailed the characteristic pattern of the line of cyclic stress equilibrium state which dictates the way in identifying the threshold stress (or critical level of cyclic stress). The study demonstrated that, using effective stress analysis, the threshold stress can be obtained for clay under high cyclic loading rate. In conjunction with the stress response, the deformation and resilient characteristics of various series of cyclic undrained triaxial tests carried out on the saturated clay was described. Apart from highlighting and confirming the influence of consolidated state and stress history on the threshold stress and deformation characteristics, influence of the cyclic loading frequency simulating higher train travelling speed was also investigated and examined.Using the framework of critical state soil mechanics, the study described the existence of cyclic stress equilibrium state surface CSESS within the stress state boundary surface SSBS for saturated clay under cyclic undrained compression. A form of analytical / theoretical model was established which enables threshold stress to be ascertained without resort to lengthy laboratory testing at the preliminary design stage of railway track foundation design. Developed from the “original Cam-clay” model and validated by the cyclic triaxial test data on reconstituted kaolin clay, the theoretical model which described the CSESS enables the prediction of threshold stress (or critical level of cyclic stress) of general saturated clay soil under undrained cyclic compression to be made from the fundamental properties of the soil, based on the designed consolidated state and the stress history of subgrade soil.In addition, this study proposed a new approach which rationalized and reformulated the current state of design and management process of railway track substructure involved clay subgrade. The rational approach was developed based on the comprehension of “lower-bound threshold stress” and potential strengthening and densification of fine-grained subgrade soil through progressive and deliberate incremental loading of the track foundation. Concept of “Managing current lower-bound threshold stress” for clay subgrade was elaborated. The readily use of the developed theoretical model and design charts for predicting the threshold stress could offer a key advantage for the new approach over current practices.

Soft soils are deposited globally, especially in estuarine or coastal areas. In recent years, the land resource has lessened due to rapid urbanisation and population growth around the globe. It is crucial to develop land on poor ground conditions to solve the issue of land shortage due to urbanisation. South East Queensland is a particular region where soft soils are widely deposited. More construction is expected to be carried out on its soft soil deposits as the urbanisation continues. However, the existence of soft soils can cause construction complications because of the following reasons: having high compressibility and water content, accompanied by low shear strength and permeability. Therefore, the study of the mechanical behaviour of reconstituted and stabilised soft soils is significant in geotechnical engineering practice. There are limitations in previous research regarding the properties of soft soils. For example, the common particles in soft soils are clay, silt, and sand particles. The behaviour of clay and sand particles are unique and easy to identify. However, the behaviour of silt particles lies in between the behaviours of clay and sand. It is important that some previous studies found that the behaviour of silt is not in accordance with the critical-state framework adopted for clay and sand. It is suggested that the behaviour of silts is a transitional form between clay and sand. Some silts exhibit sand-like behaviour, while some exhibit clay-like behaviour. Consequently, it is important to understand silt’s physical, mineralogical, strength and microstructural behaviour, as it is presently recognised that gaps in understanding its fundamental behaviour exist. In addition, soft soils need to be stabilised by suitable ground improvement techniques before any structure can be safely constructed on it. It is widely known that in-situ soil mixing or stabilisation (e.g., mass mixing or deep soil mixing) has been proven to be an effective ground improvement technique in improving the engineering properties of soft soils. Cement is one of the commonly used cementitious materials which can be used to treat soft soil in the application of in-situ soil mixing. It can increase the soil mix strength and decrease the water content by triggering the hydration of cement and pozzolanic reactions. The use of cement to stabilise soft soils and the behaviour of cement-stabilised soils has been extensively investigated in many previous studies. However, the use of cement can cause environmental issues as the production of cement results in high emissions of carbon dioxide (CO2). Hence, it is essential also to consider other suitable types of stabilisation additives to reduce the amount of cement used in the stabilisation of soft soil. Fly ash and a commercially available additive DuraCrete, were investigated in this study as partial replacements of cement. The behaviour of specimens stabilised by cement, fly ash-blended cement, and DuraCreteblended cement under both unconfined compressive (UC) and consolidated isotropic undrained (CIU) conditions were investigated in this study. The experimental results proved that fly ash and DuraCrete can be used as partial replacements of cement to achieve more remarkable improvement results than just cement alone in stabilising soft soils. DuraCrete is more effective compared to fly ash because the addition of DuraCrete can reduce the amount of cement needed for the stabilisation while also improving the strength of stabilised specimens. This project seeks to investigate a) the mechanical behaviour of South East Queensland soft soil stabilised by cement with different cement content; b) the effect of the presence of silt particles on the mechanical behaviour of soft soils, such as evaluating the behaviour of silty soils within the critical-state framework; c) the effect of the presence of silt particles on the mechanical and microstructural of soft soils after stabilised by cement; and d) the use of fly ash and DuraCrete as partial replacements of cement in soft soil stabilisation. A series of laboratory tests consisting of consolidated isotropic undrained (CIU) triaxial tests, unconfined compressive strength (UCS) tests, and scanning electron microscope (SEM) tests were conducted in this study to achieve these objectives. South East Queensland soft soil was collected and stabilised by cement with varying initial soil water content and cement content. The mechanical and microstructural behaviour of natural and cement-stabilised South East Queensland soft soil was investigated. Some empirical equations were derived to estimate the strength of South East Queensland soft soil specimens with different cement content. The microstructure of cement-stabilised soil specimens was also analysed and interpreted. A series of triaxial compressive tests were conducted in this study on five types of soft soils with varying clay and silt contents, and therefore the effect of silt contents on the strength and critical state behaviours of soft soils were investigated. The empirical equations were proposed to evaluate the effect of silt content on the stress paths of reconstituted soft soils under consolidated isotropic undrained triaxial tests and the critical state parameters. Based on the observations from the CIU triaxial compression tests, it can be concluded that 1. For silty soils which have a plasticity index above 29%, even the soils are classified as silt by Atterberg limit testing results, but the soils show clay-like behaviour in the critical state framework, evidenced by the corresponding normally consolidated line (NCL) and critical state line (CSL) are parallel. 2. For silty soils, which have a plasticity index between 19% and 29%, the soils show a transitional behaviour between the clay-like and sand-like behaviour, as the corresponding normally consolidated line (NCL) and critical state line (CSL) are becoming non-parallel. 3. For silty soils, which have a plasticity index lower than 19%, it shows typical sand-like behaviour. These types of soft soils were then stabilised by cement with varying cement content. A further series of unconfined compression tests were conducted for each group of cement-stabilised soil specimens. As the silt content might exhibit a different influence on the strength of cement-stabilised samples, a varying dosage of cement content was considered in this study. The experimental results indicate that silt content plays a different role in soil stabilisation under different cement contents. The effect of cement content and silt content on the microstructure development of stabilised soils were also analysed by utilising the Scanning Electron Microscope (SEM) images. With the increase of cement dosage, the number of cementitious products, such as reticulated CSH and needle-shaped ettringite, was notably increased, resulting in a denser structure. This can be attributed to the hydration of cement and the pozzolanic reactions. As for the effect of silt content, since particle size plays a significant role in microstructure development, both cement and silt contents can dramatically affect the pore size distribution. When the cement content is lower than 10%, clay platelets can fill the pore spaces and the cementitious products can enhance the inter-cluster bond strength by aggregating clay and silt platelets together to form larger and denser aggregates responsible for the strength improvement. When the cement content is between 10% and 20%, the stabilised soil strengths increase with the increase of silt content and then decrease when silt contents are higher than 50%. This is because the strength gained from cementitious product enhancement was partially countered by the increment of pore size caused by the excessive cement and silt contents. When the cement content is higher than 20%, the strength shows a negative correlation with silt content, which can be attributed to the incomplete reaction of cement due to the reduction of clay content. Regarding the partial replacement of cement by adopting fly ash and DuraCrete, the UCS and CIU testing results show that both fly ash and DuraCrete are very effective as partial replacements of cement to reduce the cement content and CO2 emission. Fly ash can the provide the highest reduction in the cement replacement content, and it can also provide the highest reduction in CO2 emission. However, at the same mixture content (e.g., 25%), the UCS of the specimens stabilised by fly ash-blended cement is lower than that stabilised by cement only. Thus, more material is needed when using fly ash to partially replace cement to maintain the same UCS. Even though, the CO2 footprint can still be reduced because the CO2 emission rate of fly ash is much lesser than that of pure cement. Therefore, fly ash is effective as a partial replacement of cement to reduce the use of cement and CO2 emission. Compared to fly ash, DuraCrete is more effective as a partial replacement of cement in some circumstances. For example, the total mixture content is reduced to achieve a target strength of 500 kPa when using DuraCrete-blended cement instead of pure cement only. The reduction in total mixture content is an essential advantage by using DuraCrete compared to using fly ash. Comparing the proportional quantities of fly ash and DuraCrete required, the quantity of fly ash required is between 6.1 times and 9.7 times the proportional quantity of DuraCrete required. Even though the use of DuraCrete can reduce the amount of cement used and reduce the total mixture content, it cannot provide as much reduction in cement as fly ash does. This is because there is a ‘saturation point’ with the DuraCrete replacement ratio. If this saturation point is exceeded, DuraCrete will not be as effective anymore, being mainly a magnesiumbased additive. Therefore, when the maximum reduction in cement is the only factor under consideration, fly ash is more suitable than DuraCrete, as it facilitates a greater reduction in cement. However, suppose both reduction in cement and the total mixture content are considered. In that case, DuraCrete might be more appropriate, as it not only reduces the use of cement but also reduces the total mixture content required. Most importantly, unlike cement and fly ash, the production of DuraCrete is not carbon-intensive. The production of DuraCrete does not produce carbon emission as it does not require a furnace, nor is it a by-product of a carbon emitting process. These critical outcomes can help engineers reliably customise the soil stabilisation design to achieve optimal strength, environmental friendliness, and cost-saving. As such, engineers can have more design options to meet the strength requirement while having the opportunity to minimise the negative impact on the environment by reducing the use of cement. They can also achieve a balance between the reduction in cement and the budget, hence the important contribution of this study.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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O modelo cam-clay modificado foi aplicado aos resultados experimentais obtidos para um solo arenoso típico da cidade de São Carlos. Os ensaios de compressão triaxial foram conduzidos em equipamento moderno, com instrumentação interna, segundo distintas trajetórias de carregamento. Verificou-se que os resultados obtidos em termos de modelagem foram satisfatórios, principalmente quando a tensão octaédrica (p\') foi diminuida durante os carregamentos. Nesse caso, tanto em termos de modelagem como de resultados experimentais, houve expansão de volume do solo. Com o aumento da tensão octaédrica, verificou-se a ocorrência de compressão volumétrica do solo. Observou-se que o modelo apresenta uma previsão de deformações axiais maiores do que as observadas experimentalmente nas trajetórias de -30, -50, 30, 40, 50, 60, 120 graus e no ensaio triaxial convencional com \'sigma\' 3 = 100 kPa. Além disso, determinou-se a superfície inicial de plastificação do solo utilizando-se dois critérios que tenderam a fornecer valores de tensão de cedência aproximadamente iguais, notando-se que a condição de fluxo associado não é obedecida.
The modified cam-clay model was used to model experimental results of a sandy soil from São Carlos - SP. Triaxial compression tests were performed using Bishop - Wesley cell with internal transducers to measure axial and radial strains. It was observed that the model fairly fitted experimental results, specially when medium effective stress (p\') is reduced during loading. In this case, both the model and the experimental results, showed volume increase. When (p\') increases the model and the tests showed a tendency to give volumetric compression, although the values were differents. The model yielded strains larger than that measured in the tests when the stress-paths were of -30, -50, 30, 40, 50, 60, 120 degrees and in axial compression test with 100 kPa of confining pressure. Besides that, initial yield surface of soil was calculated from test results using two different criteria which gave about the same yield stress and it is show that normality rule was not satisfied in this soil.

L'incorporation d'échangeurs de chaleur dans des géostructures conventionnelles comme les pieux peut extraire la chaleur du sol à des fins de chauffage et l'injecter dans le sol à des fins de refroidissement. Ces dernières années, des recherches ont été menées à l'échelle réelle et en laboratoire pour étudier l'effet de la température sur le comportement géotechnique de ces géostructures énergétiques ainsi que sur le sol environnant. En effet, ces géostructures énergétiques peuvent être soumises à des charges mécaniques cycliques et a des variations thermiques tout au long de leur durée de vie. L'objectif de cette étude était d'approfondir la compréhension du comportement du contact sable/argile-structure sous des charges thermomécaniques complexes. Un dispositif de cisaillement direct à température contrôlée permettant d'effectuer des essais monotones et cycliques à charge normale constante ou à rigidité normale constante a été mis au point. La réponse de l'interface aux effets thermiques sur le comportement mécanique des sols et l'interface sol-structure a été étudiée. Le sable de Fontainebleau et l'argile kaolin ont été utilisés comme substituts pour les sols sableux et argileux. Les résultats ont montré que les variations thermiques appliquées ont un effet négligeable sur la résistance au cisaillement de l'interface entre le sable et la structure du sol. Dans les échantillons d'argile, l'augmentation de la température a augmenté la cohésion et par conséquent la résistance au cisaillement, en raison de la contraction thermique pendant le chauffage. L'adhérence de l'interface argile-structure était inférieure à la cohésion des échantillons d'argile. Pour étudier les effets de la charge mécanique cyclique sur l'interface argile-structure à différentes températures, des essais de cisaillement direct monotone et cyclique à volume équivalent non drainé ont été réalisés sur l'interface argile-argile et argile-structure à différentes températures. Les résultats ont montré que le nombre de cycles jusqu'à la rupture pour l'essai d'interface argile-structure était inférieur à celui du cas argile-argile dans la même gamme de rapports de contraintes de cisaillement cycliques et moyennes. L'augmentation de la température a réduit le taux d'accumulation des contraintes et le nombre de cycles jusqu'à la rupture a été multiplié par 2 ou 3. Le taux de dégradation (paramètre de dégradation, t) a diminué de 16% avec un chauffage de 22 à 60 °C pour les différents rapports de contrainte cyclique testés. Un modèle d'interface sol-structure non isotherme basé sur la théorie de l'état critique a ensuite été développé. Le modèle non isotherme prend en compte l'effet de la température sur le taux de vide de l'interface avant le cisaillement. Le modèle est capable de saisir l'effet de la température sur l'interface sol-structure dans des conditions de charge normale constante et de rigidité normale constante pour les interfaces sableuses et argileuses. Les paramètres supplémentaires ont des significations physiques et peuvent être déterminés à partir d'essais classiques en laboratoire. La formulation est en bon accord avec les résultats expérimentaux et les principales tendances sont correctement reproduites
Incorporation of heat exchangers in conventional geostructures like piles can extract the heat from the soil for heating purposes and inject it to the soil for cooling purposes. In recent years, research has been conducted at full and laboratory scale to investigate the effect of temperature on the geotechnical behavior of these energy geostructures as well as on the surrounding soil. Indeed, these energy geostructures can be subjected to cyclic mechanical loads and thermal variations throughout their lifetime. The aim of this study was to deepen the understanding regarding the behavior of sand/clay-structure contact under complex thermo-mechanical loads. A temperature-controlled direct shear device to perform monotonic and cyclic constant normal load or constant normal stiffness tests was developed. The response of the interface to the thermal effects on the mechanical behaviour of soils and soil-structure interface was investigated. Fontainebleau sand and kaolin clay were used as proxies for sandy and clayey soils. The results showed that the applied thermal variations have a negligible effect on the shear strength of the sand and sand-structure interface. In clay samples the temperature increase, increased the cohesion and consequently the shear strength, due to thermal contraction during heating. The adhesion of the clay-structure interface, was less than the cohesion of the clay samples. To investigate the mechanical cyclic load effects on the clay-structure interface at different temperatures, monotonic and cyclic constant-volume equivalent-undrained direct shear tests were performed on clay-clay and clay-structure interface at different temperatures. The results showed that, the number of cycles to failure for the clay-structure interface test was lower than that for the clay-clay case in the same range of cyclic and average shear stress ratios. Increasing the temperature, decreased the rate of strain accumulation and the number of cycles to failure increased by 2-3 times. The rate of degradation (degradation parameter, t) decreased by 16% with heating from 22 to 60oC for the different cyclic stress ratios tested. A non-isothermal soil-structure interface model based on critical state theory was then developed. The non-isothermal model takes into account the effect of temperature on the void ratio of interface prior to shearing. The model is capable to capture the effect of temperature on soil-structure interface under constant normal load and constant normal stiffness conditions for both sandy and clayey interfaces. The additional parameters have physical meanings and can be determined from classical laboratory tests. The formulation is in good agreement with the experimental results and the main trends are properly reproduced

Thesis (M.S. in civil engineering)--Washington State University, August 2009.
Title from PDF title page (viewed on Aug. 10, 2009). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 45-46).

The existing creep constitutive models do not include directly shear stiffness of the soil that can be easily obtained by standard geotechnical tests. These models do not account for high shear stiffness of the soil at small mobilisation degree. In this respect, they do not distinguish between soil elements that undergo lower mobilisation in the far field and the ones that undergo higher mobilisation close to the embankment. This may result in overprediction of horizontal displacements under the field and the result of the finite element analysis is sensitive to the extension of the model boundary. To address this model deficiency, a new critical state soft soil creep model with shear stiffness (CS-SSCG) is implemented. In the CS-SSCG model, shear stiffness of the soil will be explicitly given by the engineer instead of commonly used Poisson's ratio. Results from the simulation of the MIT-MDPW embankment show that horizontal displacement has been improved significantly using the CS-SSCG model compared to Plaxis Soft Soil Creep (SSC) standard model.

The proportions of the Critical State surfaces of a given soil depend on its stress and moisture history, its current moisture status and soil type. The influence of these factors on the geometry of the state surfaces, and their bearing on the mechanical behaviour of the soil itself, cannot be readily perceived because of the very large number of interacting effects present in the model. The use of sophisticated computer graphics for the three-dimensional visualization of critical state surfaces would therefore provide a ready means for obtaining an insight into the complex changes taking place in critical state space. The initial part of the thesis deals with the formulation of mathematical models and computer software for integrating numerical computations, data reduction and visualization techniques for analysing critical state surfaces. The programmes developed were used for interpreting the influence of moisture status on the key behavioural patterns of three different British Soils. Systematic changes to state space due to the combined influence of moisture content variations and soil type were readily traced. It is well known that collating data for the above analysis is difficult and requires advanced measuring techniques. An attempt was therefore made to establish a connection between the data obtained from a simple field measuring device, such as a cone penetrometer, with the volume-change behaviour of soil, as modelled by its critical state surfaces. This is attempted in two stages. The first stage presented in the thesis assumes the soil to be a rigid-plastic Mohr-Coulomb material and deals with the formulation of a mathematical model to predict cone index as a function of cone geometry, penetration depth, c, cp and soil-to-metal parameters cQ and S. This model is based on the extension of the basic two-dimensional Sokolovski solution to the three-dimensional slip-line field developed during the deep penetration phase of a cone. Shallow penetration depths, at which the standard Sokolovski rupture surface interacts with the soil surface, cannot be dealt with by this approach. The second stage of the investigation attempts to connect cone index with the stress (p, q) and pore space (v) parameters of the soil on the cone surface. The model developed in the thesis is based on identifying a state parameter yr (defined by Been and Jefferies for dry sands). This establishes the position, within critical state space, of the cone surface stress and pore space parameter (p, q and v) relative to the critical state wall. The state parameter yr is then associated with soil type and moisture 2 content by a two-parameter linear function. Once these two parameters are found experimentally, cone index can be readily translated into pore-space estimates. The thesis presents the mathematical analysis which provides the basis for this correlation. The thesis describes the experimental investigations carried out to verify the performance of the theoretical models developed. The validation of the state parameter concept required the design and development of a special calibration chamber which could apply controlled boundary stresses to a cylindrical soil sample into which the penetrometer is advanced. Ideally very large sample diameters are required to minimise boundary interference, but a compromise had to be made by using miniature penetrometers and a realistic sample diameter of 100 mm. The cone penetrometer performance model was tested under laboratory conditions in an indoor soil tank. Both these investigations required tedious back-up laboratory experimentation to establish the basic Mohr-Coulomb and critical state parameters of the test soil over a wide range of moisture contents. All the soils were dealt with in a remoulded state as consistently reproducible stress and moisture histories for this case can be easily maintained in each of the very large number of samples required in the experimental programmes. The experimental work shows very clearly that the state parameter concept is applicable to partly saturated c-Sp soils over a wide range of moisture contents and that it is possible to quantify the systematic changes in the state parameter y' with soil moisture content. The predictive performance of the cone penetrometer model, within the specified penetration range, was also good. Data reduction charts for interlinking these two models are presented and the use of these charts for the derivation of pore space particulars from cone index data predicted satisfactory trends. However, this procedure appears to over-predict dry bulk density by a considerable margin. The validation presented in this study is for a single sandy loam soil. Even though the overall predictive performance of the mathematical models in this particular soil is most encouraging, it should be borne in mind that the models developed are bound to be influenced by the drastic simplifications required to interlink two disparate models, one which ignores volume change with one which does not. Further work is required to remove any detrimental consequences of these compromises and to introduce confidence in extending the findings to other soil types.

The objectives of this dissertation are to measure and calculate surface free energies of soil particles, to understand the mechanical behavior of unsaturated silty sand through first studying the stress-strain relationship, the effects of matric suction and pore water chemistry and second to interpret the behavior by the critical state frame work, to develop a method to predict cone tip resistance in unsaturated soils, and to present the concept of pseudo strain and dissipated pseudo strain energy. Universal Sorption Device (USD) is developed to measure surface free energies of soil particles. The test results on a soil sample shows that specific surface area increased with decreasing particle size. The components of surface free energies and the work of adhesion increased with decreasing particle size. A servo controlled triaxial testing device is developed to test 15.24 cm in height and 7.62 cm in diameter, recompacted specimens of unsaturated soil under varying matric suction and different pore chemistry. During the test, the matric suction is maintained constant. Results from the triaxial drained tests are used for validation of the constitutive models proposed by Alonso et al. (1990). Predictions from the model are in good agreement with experimental results. The critical state model for unsaturated soil is used to calculate cone tip resistance in unsaturated silty sand. The calculated cone tip resistance is used to evaluate the liquefaction potential of unsaturated soils. The results from the stress based liquefaction potential analysis reveal that even in an unsaturated condition soil is susceptible to liquefaction. By applying the pseudo strain concept, it is possible to account for the viscous resistance of water during cyclic loading. The results of undrained cyclic triaxial tests are used to calculate pseudo-strain and dissipated pseudo strain energy. The results of calculated dissipated pseudo strain energy suggest that the effect of initial matric suction is evident. On the other hand, the effect of surface tension increase or decrease due to existence of chemical on the pore water is negligible.

Traditionally, void ratio, e has been used as a state variable for predicting the liquefaction behaviour of soils under the Critical State (Steady State) framework. Recent publications show that void ratio, e may not be a good parameter for characterizing sand with fines as the steady state, SS data points move downward in e-log(p) space up to certain fines content termed as threshold fines content, TFC. Thus, it was difficult to apply SS concept on sand with fines as a small variation of fines content may lead to different SS line. Many researchers proposed to used equivalent granular void ratio, e* as an alternative state variable (i.e. in lieu of void ratio, e) in attempt to obtain a narrow trend line for SS data points irrespective of fc provided fc  TFC. The e* is obtained from e. For the conversion from e to e*, one need a parameter b which presents the active fraction of fines in overall force structure of sand. However, predicting the b is problematic. Most, if not all, of the b reported were determined by case-specific back-analysis, that is, the b-value was selected so that the test results for a given sand-fines type could be correlated with the equivalent granular void ratio, e* irrespective of fines content. This thesis examines the factors that affecting the b value by examining published work on binary packing. This leads to a simple semi-empirical equation for predicting the value of b based onparticle size ratio,  and fines content, fc. Published data and experimental results on Sydney sand appears to be in support of the proposed equation. The single relation of SS data points in e*-log(p) space for sand with fines is referred as Equivalent Granular Steady State Line, EG-SSL. The EG-SSL is then used to define the equivalent granular state parameter,*. A good correlation observed between * and q-p, q- q responses in undrained shearing. The e* and * are also used to modified a state dependent constitutive model. Seven model input parameters are needed in addition four to critical state input parameters. These parameters are obtained from drained test. The model is used to predict q-pand q- q responses for flow, non-flow and limited flow behaviour for 0% to 30% fines contents. The model predictions are in good agreement with experimental results. The effect of fines types (in terms of plasticity and angularity) on the prediction equation of b are also examined with four different types of fines. A negligible effect of fines type on the prediction equation of b is observed. The link between monotonic and cyclic loading behaviour for sand with fines are also examined with emphasis on cyclic instability and strain hardening behaviour after quasi steady state, QSS for a range of fines contents (provided that fc < TFC). It is found that a single set of rules could be used to correlate monotonic and cyclic behaviour for a range of fines contents at same *.

Heavy rainfall on the evening of January 9 and morning of January 10, 1983 triggered debris avalanches and debris torrents at Smith Creek, western Whatcom County, Washington, USA. Nine debris avalanches are back analyzed in detail. Conclusions are drawn concerning, 1) climatic controls on debris avalanches and debris torrents; 2) debris avalanche characteristics; 3) hillslope hydrology; 4) slope stability. Rainfall data show that the January 9-10, 1983 storm had a 71-year recurrence interval in the 12-hour duration, with less than 6-year recurrence intervals in 1, 2, and 3-hour durations. In contrast, rainfall during a torrent event on January 29-30, 1971 had recurrence intervals of less than 2 years in all durations, but snowmelt was a contributing factor. The types of debris torrents produced by these contrasting storms are discussed. Four distinct failure geometries are defined, based on avalanche descriptions: 1) wedges; 2) drainage depressions; 3) logging roads; 4) discontinuity surfaces. Three scour zones are also distinguished, based on slope segment types observed. To model storm water table levels a one-dimensional, vertical, transient, saturated-unsaturated finite difference infiltration program is linked to a kinematic wave equation. Rainfall duration and intensity, initial conditions, soil hydraulic conductivity, and soil depth are factors controlling vertical soil discharge rates. January, 1983 discharges are clearly distinguishable from comparison storm discharges at all avalanches. Kinematic wave results help differentiate Coulomb shear and washout type failures, and provide pore pressures for stability analyses. The modified Mohr-Coulomb strength equation is used to outline factors controlling debris avalanche initiation. The factors are: 1) slope angle; 2) soil depth; 3) soil density; 4) vegetative cover; 5) bedrock surface characteristics; 6) snow. These factors are quantitatively assessed. Infinite slope analyses show limiting slope angles of 29.7° for Group I vegetation, and 24.6° for Group III vegetation. Vegetative cover and soil depth are the two controlling factors that change significantly over the short term. A root cohesion parameter, Cr, is used to assess the shear strength provided by vegetation. Four vegetative covers are distinguished, three of which were logged between 1918 and 1950: Group I - relatively weak understory vegetation (Cr range: 1.6 -2.0 kPa); Group II - understory plus stunted trees (Cr range: 2.3 - 2.6 kPa); Group III - understory plus mixed, regenerating forest (Cr range: 2.6 - 3.0 kPa); Group IV - old-growth forest of higher root strength.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

This thesis focuses on proposing a novel comprehensively predictive modelling framework for granular materials which builds on the hydrodynamic procedure to satisfy the principles of thermodynamics, mass, momentum and energy conservations. In developing our physical arguments we recognise that complexity of the macroscopic mechanical response of granular media is mainly a result of kinematic degrees of freedom in granular scale. We therefore employ the original concept of two-stage irreversibility by Jiang and Liu (2009) and consider an energy sink from the mesoscopic granular entropy level to the microscopic thermal entropy level. In stark contrast from previous hydrodynamic formulations for granular materials, we establish a clear passage from the granular temperature to calibrate instead our model based on the measurable kinetic pressure. We introduce a novel coupling between the hydrodynamic formulation and plasticity theory by directly defining the evolution equations for state variables and imposing restrictions to ensure the non-negativity of the mechanical dissipation. Within our hydrodynamic-plastic framework, we construct two constitutive model variants. The first simpler model demonstrates remarkable capability to predict comprehensive rate-independent and rate-dependent phenomena, all while relying on only five previously defined mechanical constants. We enhanced the first model to capture particle breakage effects through integration with the breakage mechanics theory (Einav 2007). This more advanced model readily maintains all the rate-independent capabilities of the first one, and demonstrates remarkable agreement with elaborated experimental breakage data from monotonic and cyclic compression and shear tests. This thesis provides a foundation to explore and further model granular materials, as well as materials with complex internal heterogeneous mesoscopic structure, such as weakly cemented granular rocks, silts and clays.

The heavy precipitation event of November 3-8, 2006 dropped over 60 cm of rain onto the bare southern slopes of Mount St. Helens and generated debris flows in eight of the sixteen drainages outside the 1980 debris avalanche zone. Debris flows occurred on the upper catchments of the Muddy River, Shoestring Glacier, Pine Creek, June Lake, Butte Camp Dome, Blue Lake, Sheep Creek, and South Fork Toutle River. Debris flows were clustered on the west and south-east sides of the mountain. Of the eight debris flows, three were initiated by landslides, while five were initiated by headward or channel erosion. Six debris flows were initiated in deposits mapped as Holocene volcaniclastic deposits, while two were in 1980 pyroclastics on andesite flows. The largest (~975,000 m2) and longest (~8,900 m) debris flow was initiated by landslides in the upper South Fork Toutle River Drainage. The average debris flow initiation zone elevation was 1,750 m, with clusters around 1,700 m and 2,000 m elevation. The lower cluster is associated with basins that host modern or historic glaciers, while the upper is possibly associated with recent pyroclastic deposits. Upper drainages with debris flows averaged 41% slopes steeper than 33 degrees, while those without debris flows averaged 34%. The upper basins with debris flows averaged 6% snow and ice cover, 21% consolidated bedrock, and 74% unconsolidated deposits. Basins without debris flows averaged 3% snow and ice cover, 27% bedrock, and 67% unconsolidated deposits. Drainages with debris flows averaged an 89% loss of glacier area between 1998 and 2009, while those without debris flows lost 68%. Further comparing glacier coverage during that period found that only five of ten glaciers still existed in 2009. On average, the glaciers had reduced in area by 67%, decreased in length by 36%, and retreated by an average of 471 m during that period. Basin attributes were measured or calculated in order to construct a predictive debris flow model based on that of Pirot (2010) using multiple logistic regression. The most significant factors were the percentage of slopes steeper than 33 degrees, unconsolidated deposits in the upper basin, and average annual rainfall. These factors predicted the 2006 debris flows with an accuracy of 94% in a debris flow susceptibility map for Mount St. Helens.

A variety of conservation trends have gained and lost favor throughout the years in agriculture, with U.S. Farm Bills often influencing what conservation practices are implemented by farming communities throughout the U.S. This dissertation focuses on the unintended consequences of conservation management practices in the Fifteenmile Watershed of Wasco County, Oregon. Specifically, I seek to address how farmer enrollment in various conservation techniques, loosely defined as no-till agriculture, has affected soil and water quality through the increased use of herbicide, and subsequently rendered ecological and human health vulnerable. Using a critical physical geography framework, I address both the biophysical factors and social structures that have co-produced changes in soil and water quality in the study area of this research through intensive physical field data collection, spatial analysis, social surveys, and interviews. I also demonstrate how three neoliberal sets of processes: market-friendly reregulation; state rollback and deregulation; and the creation of self-sufficient individuals and communities, have transformed the human socio-environmental relationship to agriculture. These processes have had significant effects on the policies governing how soil and water quality are managed on both a state and national level, and have created a dependence on enrollment in conservation practices that may ultimately prove counterproductive for long term goals of environmental protection and sustainability.

One of the most critical problems geotechnical engineers face with is the determination of the amount of consolidation settlement that will occur at a site as a result of the construction of a structure. The compressibility behavior of the soil is an important parameter in determining the amount of consolidation settlement. The goal of this study is to develop probabilistically based correlation between the compressibility behavior of soil and in-situ test data. Within the scope of this research effort, performed CPT tests and the recorded settlement case histories where consolidation settlements at the field under various surcharge loads were compiled from the Bursa East and West Waste Water Treatment Plant soil investigation projects. A database was composed of the results of 45 CPT and 57 settlement plate recordings. For the compilation of this database, a series of finite difference software FLAC-3D analyses were carried out to calculate the change in stress distribution under the settlement plates. A maximum likelihood framework was used for the development of compressibility behavior of soils. As a result of careful processing of available data, the cone tip resistance (qc), soil behavior type index (Ic) were selected as two important parameters effecting the value of the one-dimensional constraint modulus, M. The regression analysis which uses the settlement values recorded at the site and those computed using the change in the stress distribution, the thickness of the sublayers and the proposed one-dimensional constraint modulus were carried out to calculate the values of these model parameters. Two correlations based on the cone tip resistance and soil behavior type index were developed for the computation of the one-dimensional constraint modulus, M.

Procurando diminuir as incertezas a respeito do comportamento de estacas em perfis arenosos, desenvolveu-se um campo experimental localizado em Araquari-SC, conduzido pela Universidade Federal do Rio Grande do Sul, no qual foram executados (a) ensaios de campo para definir as condições geotécnicas do solo, (b) estacas escavadas e hélice continua e (c) provas de carga estática nos elementos estruturais. O presente trabalho tem como objetivo estudar as variáveis que intervêm no mecanismo de transferência de carga ao solo. Mediante ensaios de laboratório, caracterizou-se o solo presente no campo experimental, definiram-se os parâmetros de resistência, mineralogia, forma, distribuição e tamanho das partículas, para serem usadas na retro análise do coeficiente de pressão de solo (ks) das provas de carga. Para esta finalidade foram analisados os resultados medidos em estacas escavadas executadas com bentonita e polímero. A retro análise foi realizada através do método beta (β), abordagem que permite a obtenção da capacidade lateral das estacas construídas em perfis arenosos, baseado nas tensões verticais, no coeficiente de pressão de solo e no ângulo de atrito da interface solo-estaca. Devido à interação entre as partículas do solo e concreto da estaca, estas são mobilizadas a elevados níveis de deformações, o ângulo de atrito da interface é considerado próximo ao ângulo de atrito no estado crítico da areia. O solo presente no campo experimental corresponde a areia fina com lentes de silte. Assim, os parâmetros de resistência definidos foram o ângulo de atrito no estado crítico e de pico com valores de 33,0° e 33,4° respetivamente. O ângulo no estado crítico foi utilizado na retro análise das provas de carga e como resultado foi obtido o ks, para posteriormente ser comparado ao coeficiente de empuxo no repouso (k0). Os resultados mostraram que com a profundidade o valor ks aproxima-se ao valor de k0, apresentado uma relação de ks/k0 próxima a unidade. Conclui-se que, o mecanismo de transferência de carga entre o solo e a estaca pode ser avaliado em função das tensões iniciais do depósito, expressas a partir de k0 estimado com base nos ensaios de laboratório.
In order to reduce the uncertainties regarding the behavior of piles in sandy profiles, an experimental field was developed by the Federal University of Rio Grande do Sul in Araquari-SC, where were executed (a) field tests to define soil geotechnical conditions, (b) bored and continuous flight auger piles and (c) static load tests on the structural elements. The aim of this research was to study the variables that intervene in the soil load transfer mechanism. The soil at the experimental field was characterized by laboratory tests, and parameters of resistance, mineralogy, particle shape, distribution and size were obtained for use in the back analysis of the soil pressure coefficient (ks) of the load tests. For this purpose, were analyzed the results measured on bored piles executed with bentonite and polymer. The back analysis was made using the beta method (β), which allows to estimate the lateral capacity of the piles constructed in sandy profiles, based on vertical stresses, soil pressure coefficient and friction angle of the soil-pile interface. Due to the interaction between the soil particles and the pile concrete, the first are mobilized at high deformation levels, the friction angle of the interface is considered close to the friction angle in the sand critical state. The soil present in the experimental field corresponds to fine sand with silt lenses. Thus, the resistance parameters defined were the critical state and peak friction angle with values of 33.0 ° and 33.4 ° respectively. The critical state angle was used in the back analysis of the load tests, and as a result the ks was obtained, to be subsequently compared to the at rest lateral earth pressure coefficient (k0). The results showed that, with depth, the value ks approaches the value of k0, with a relation of ks / k0 close to unity. It is concluded that the load transfer mechanism between the soil and the pile can be evaluated as a function of the initial stresses of the deposit, expressed from an estimated k0 based on the laboratory tests.

Le développement de l’urbanisme privilégie de plus en plus souvent la solution souterraine. Le creusement d’environ 200km de tunnels est prévu dans les dix prochaines années en France seulement, en milieu urbain dense.L’excavation d’une cavité dans un terrain engendre des mouvements dans le massif. Le front de taille se déplace généralement instantanément vers l’excavation. A ce déplacement d’extrusion s’ajoute la convergence des parois du tunnel. A faible profondeur, ces mouvements risquent de se propager jusqu'à la surface du terrain constituant une cuvette de tassement qui peut conduire à des désordres importants voire de nature accidentelle (tassements différentiels, développement de fontis, effondrement de constructions, etc.). Plusieurs paramètres influencent la qualité des simulations et la prévision des déplacements induits par le creusement d’un tunnel. Le choix d’une loi de comportement est primordiale pour la modélisation des tunnels qui dépend de la réponse du sol en termes de déformations. La prédiction des déplacements engendrés requière un modèle de comportement du sol rigoureux qui puisse simuler le plus fidèlement possible la réponse du sol.Cette thèse propose un modèle de comportement adapté à la simulation du creusement de tunnel avec un mécanisme d’écrouissage déviatorique dans le cadre de la théorie de l’état critique. Ce modèle reproduit de manière satisfaisante la réponse non linéaire du sol à l’échelle des essais de laboratoire et présente une alternative sécuritaire pour les simulations à l’échelle de la structure.L’effet de l’influence de plusieurs paramètres sur la simulation des tunnels est étudié à travers des simulations 2D et 3D avec différentes configurations et en considérant le couplage hydromécanique. Le modèle proposé est aussi utilisé pour la reproduction de mesures in-situ d’une section de tunnel du Grand Paris
Tunnels construction is increasingly favored as a sustainable transportation and infrastructure development system. 200km are going to be excavated only in France in the next ten years in dense urban areas.During tunnel excavation, ground movements must be controlled and well predicted to avoid any damage on existing buildings. The tunnel face moves typically instantly toward the excavation. The tunnel wall convergence is added to theface extrusion. These movements may spread to the surface of shallow tunnels leading to significant disturbances or accidental damage (differential settlement, cave-in occurrence, buildings collapse, etc.).Different parameters influence the quality of tunnels simulation and induced displacements prediction. The quality of those predictions closely depends on the choice of soil constitutive model. In this context, some widely used soil models in engineering practice not only fail to reproduce some characteristics of soil behavior on the constitutive level but also lead to shallower settlement.This PhD thesis proposes an enhanced critical state model incorporating deviatoric and volumetric hardening mechanisms adapted for tunneling simulations. This model satisfactorily reproduces the nonlinear soil response to laboratory tests and enables a more conservative tunneling design.The impact of other modeling choices is studied through 2D and 3D tunneling simulations in different configurations with the proposed soil model. Furthermore, comparison with measurements obtained from a tunnel section of the Grand Paris Project highlight the performance of the proposed model in simulating tunneling induced displacement

碩士
國立暨南國際大學
土木工程學系
97
Fines content has been recognized as an important factor that affects the critical state soil parameters of granular soils, but no consistent correlation has been established. Undrained simple shear tests were performed on sand-fine mixtures prepared by moisture tamping method to study the critical state behavior under conditions. The results show that the effective stress ratios on plane at critical state and quasi-steady state decrease as fines content increases from 0 to 10% but only slightly increases from 10 to 100%. Undrained shear strength decreases as fines content increases from 0 to 20% and the minimum undrained shear strength observes around 20 to 35% fines content, which is in the proximity of transitional fines content. The trend reverses as fines content exceeds 35%. Additionally, fines content will lower the position of critical state line on p’-e plane and reduce the slope. Quasi-steady lines are parallel to the corresponding critical steady lines with smaller void ratios.

碩士
國立成功大學
土木工程學系碩博士班
101
Critical state soil mechanics has been well recognized for prediction the behaviors of saturated soils. Although unsaturated critical state soil models have been proposed, the development is slow due to limited testing data and highly complexity of the testing procedure. This experimental study aims to verify the testing procedure of unsaturated triaxial tests up to the critical state. A miniature suction probe used to monitor the suction in the middle plane and an inner cell system for total volume measurement are integrated in a triaxial testing system for unsaturated triaxial and isotropic consolidation tests. The maximum ratio of excess suction during shearing is used to determine the testing strain rate. Unsaturated triaxial tests of a silty soil with constant suction in drained condition were performed. The testing result reveals that the silty soil reaches critical state at 30% axial strain with constant excess suction, volume, and deviator stress. The critical state parameters are determined from the critical state line (CSL) on p-q and p-v planes and the consistence of the results confirms the validation of the testing procedure in this study. This experimental study also finds that the normal consolidation line is not parallel with the CSL for unsaturated soils, while in saturated soils they are parallel with each other.

Although lymphatic vessel behavior is analogous to hearts (e.g. systole and diastole) and blood vessels (e.g. basal tone), hearts and blood vessels have fundamentally different contractile properties. While summation during contraction is minimized in the heart, summation is necessary for tonic contraction in blood vessels. Because lymphatic vessel behavior mimics cardiac and vascular behavior, we hypothesized that above a critical contraction frequency there is significant summation, evidenced by significantly increased diastolic active tension (i.e. basal tone). We used an isovolumic, controlled-flow preparation to examine the interaction of contraction cycle-time with contraction frequency. Using segments of isolated lymphatic vessels (~1 cm in length and 3-4 mm in diameter) from bovine mesentery, we measured transmural pressure and diameter for end-diastole and end-systole during spontaneous contractions for 10 volume steps. We found time between contractions (beat-to-beat period) decreases with increasing diameter, and total contraction time (vessel twitch length, 11.08 ± 1.54 s) slightly increases with increasing diameter. At the intersection of these relationships, there is a critical period, below which the vessel does not have time to fully relax. Above the diameter at the critical period, diastolic active tension (end-diastolic minus passive vessel tension) significantly increases with increases in diameter (309 to 562% change in slope, p<0.0001), and, below the critical period, diastolic active tension increases with decreases in beat-to-beat period (712 to 2208% change in slope, p<0.0014). Because this transition occurs within a physiological range, it suggests summation may be crucial for lymphatic vessel function as a pump and a conduit.

Dissertação de Mestrado em Mecânica dos Solos e Engenharia Geotécnica apresentada à Faculdade de Ciências e Tecnologia
A gestão e deposição de rejeitos de mineração tem-se mostrado um problema,sobretudo devido a procedimentos inadequados na deposição e a lacunas naabordagem aos mecanismos de rotura destas grandes estruturas geotécnicas.Eventos como de Mariana (2015) e Brumadinho (2019) intensificaram a discussãonos últimos anos na segurança e estabilidade dessas estruturas. Um desígniorecente para solucionar a debilidade estrutural das barragens e depósitos comrejeitos soltos e submersos suscetíveis instabilização frágil por liquefação, é adeposição em pilhas do rejeito enxugado e depositado com alguma compactação.Nesta dissertação, pretende-se estudar um rejeito proveniente de um grandeempreendimento em Minas Gerais no Brasil, partindo de um estudo decaracterização física e compactação Proctor de um material específico, realizado naUniversidade Federal de Viçosa (UFV). Estes foram confirmados no laboratório degeotecnia da FEUP, que conjuntamente estimaram o comportamento mecânicodeste material, através de ensaios triaxiais avançados que permitiram determinarparâmetros para modelos de cálculos, nomeadamente baseados na teoria dosestados críticos, com vista à identificação de estados contrácteis e dilatantes, quepossam identificar eventuais suscetibilidades à liquefação. Estas estruturas empilhas requerem a verificação de segurança para condições de carregamentodrenadas e não drenadas, para a qual foi estabelecida uma abordagem numéricapelo Método dos Elementos Finitos, com os programas Plaxis e RS2 utilizando oCritério de Mohr-Coulomb no Estado Plano de Deformação.Pretende-se que esta dissertação contribua para a avaliação da segurança destasolução de deposição de rejeitos, alinhada com alguns dos objetivos da Agenda2030 das Nações Unidas.
The management and deposition of mining waste has proved to be a problem, mainly due toinadequate deposition procedures and gaps in the approach to the rupture mechanisms of theselarge geotechnical structures. Events such as Mariana (2015) and Brumadinho (2019) haveintensified the discussion in recent years on the security and stability of these structures. Arecent project to solve the structural weakness of dams and deposits with loose and submergedtailings susceptible to fragile instability by liquefaction, is the deposition of the dried anddumped tailings with some compaction. In this dissertation, we intend to study a tailings froma large enterprise in Minas Gerais in Brazil, starting from a study of physical characterizationand Proctor compaction of a specific material, carried out at the Federal University of Viçosa(UFV). These were confirmed in FEUP's geotechnical laboratory, which together estimated themechanical behavior of this material, through advanced triaxial tests that allowed determiningparameters for calculation models, namely based on the theory of critical states, with a view tothe identification of contractile and expanding states , which can identify any susceptibility toliquefaction. These stacked structures require a safety check for drained and undrained loadingconditions, for which a numerical approach was established using the Finite Element Method,with the Plaxis and RS2 programs using the Mohr-Coulomb Criterion in the Deformation PlaneState .It is intended that this dissertation contributes to the evaluation of the safety of this tailingsdisposal solution, in line with some of the objectives of the United Nations Schedule 2030.