Apresenta-se um estudo paramétrico acerca da infiltração de água e sua repercussão no Fator de Segurança de talude em solos não saturados. Na análise adota-se um talude de referência com geometria fixada conforme a inclinação típica para taludes em areia argilo siltosa, característica do Centro-Oeste do estado de São Paulo. A análise paramétrica foi desenvolvida a partir de uma simulação de fluxo em regime transiente utilizando o programa SEEP/W, que utiliza o método de elementos finitos, e posteriormente uma análise de estabilidade do talude de referência utilizando o método de Bishop simplificado conforme apresentado no programa SLOPE/W. Foram analisados taludes homogêneos compostos por três diferentes tipos de solo, uma areia, um silte argiloso e uma areia argilo siltosa. Os parâmetros analisados compreendem a curva de retenção de água, a função condutividade hidráulica do solo e a intensidade de precipitação. Verificou-se que a função condutividade hidráulica e a pressão de entrada de ar são os principais determinantes do comportamento da infiltração e conseqüentemente da estabilidade do talude. As simulações de fluxo evidenciaram que os taludes em solos mais arenosos apresentam taxas de infiltração maiores que as apresentadas pelos taludes compostos por solos siltosos. Consequentemente, os escorregamentos ocasionados pela perda da contribuição da sucção para a resistência ao cisalhamento ocorrem primeiramente nos taludes compostos por solos arenosos e posteriormente naqueles compostos por solos siltosos, fato este que pôde ser confirmado pelas análises de estabilidade do talude de referência. / A parametric study is presented about water infiltration and its repercussion in the safety factor of unsaturated soil slopes. In the analysis it is adopted a reference slope with determined geometry according to the typical inclination for slopes in silty clayey sand, characteristic of the mid-western region of São Paulo State, in Brazil. The parametric analysis was developed from a flux simulation in transient regime using the SEEP/W software, which uses the finite elements method, and thereafter, a stability analysis of the reference slope using simplified Bishop method, as presented in the SLOPE/W software. Homogeneous slopes composed by three different types of soil (sand, clayey silt and silty clayey sand) were considered. The analyzed parameters include the water retention curve, the hydraulic conductivity function and the precipitation intensity. It was verified that the hydraulic conductivity function and the air entry value are the main determinants of the infiltration behavior and, subsequently, of the slope stability. The flux simulations have evidenced that coarser soils slopes show higher infiltration rates than the ones presented in finer soil slopes. Consequently, the slides caused by the loss of the suction\'s contribution to shear strength occur primarily in coarser soil slopes than in fine soil slopes, what could be verified in the stability analysis of the reference slope.

Shallow foundations rested on Leda clay that are widely distributed in Eastern Canada exhibit shrinkage characteristics and are prone to differential settlements. Due to this reason, significant repairs are necessary to the foundations and basements of residential structures constructed in Leda clay deposits. Differential settlements are commonly attributed to the changes in the natural water content of soils associated with water infiltration, evaporation or plant transpiration (i.e., tree-roots-suction). Various research studies have been undertaken to estimate the possible settlements of shallow foundations associated with the water infiltration or evaporation. Several thumb rules have been proposed through research studies, providing recommendations with respect to the distance at which trees must be planted as a function of their heights at maturity such that differential settlements can be avoided. However, limited studies have been carried out to estimate or model the settlements of shallow foundations taking into account the influence of tree-roots-suction. In the present research program, a comprehensive experimental study regarding the deformation characteristics of a sandy loam soil from Ottawa due to tree-root-suction is undertaken, using specially designed equipment. The study has been undertaken using a sandy loam soil so that the testing program can be conducted in a shorter period of time. An artificial rooting system (ARS) was designed and placed in a specially designed tank at the University of Ottawa to simulate tree-roots-suction and measure soil surface settlements associated with a decrease in natural water content (or increase in soil suction) using particle image velocimetry (PIV) technique. The ARS consists of an artificial root, suction generator, matric suction and volumetric water content monitoring devices. The variation of matric suction and volumetric water content are monitored at various depths using the instrumentation of the ARS. Based on the results of the experimental studies, a methodology is proposed to model the settlement behaviour of sandy loam soils due to suction from ARS, using commercial finite element software, SEEP/W and SIGMA/W (i.e. software package of GeoStudio 2007). The study offers a reasonably good comparison between the measured surface settlements and those estimated using the finite element modelling analysis. The modelling methodology presented in this thesis is promising and may be extended for estimating the settlement behaviour associated with the tree roots suction of Leda clay deposits and to other soils.

Several studies were undertaken by various investigators during the last five decades to better understand the engineering behaviour of unsaturated soils. These studies are justified as more than 33% of soils worldwide are found in either arid or semi-arid regions with evaporation losses exceeding water infiltration. Due to this reason, the natural ground water table in these regions is typically at a greater depth and the soil above it is in a state of unsaturated conditions. Foundations of structures such as the housing subdivisions, multi-storey buildings, bridges, retaining walls, silos, and other infrastructure constructed in these regions in sandy soils are usually built within the unsaturated zone (i.e., vadose zone). Limited studies are reported in the literature to understand the influence of capillary stresses (i.e., matric suction) on the bearing capacity, settlement and liquefaction potential of unsaturated sands. The influence of matric suction in the unsaturated zone of the sandy soils is ignored while estimating or evaluating bearing capacity, settlement and liquefaction resistance in conventional engineering practice. The focus of the research presented in the thesis has been directed towards better understanding of these aspects and providing rational and yet simple tools for the design of shallow foundations (i.e., footings) in sands under both static and dynamic loading conditions. Terzaghi (1943) or Meyerhof (1951) equations for bearing capacity and Schmertmann et al. (1978) equation for settlement are routinely used by practicing engineers for sandy soils based on saturated soil properties. The assumption of saturated conditions leads to conservative estimates for bearing capacity; however, neglecting the influence of capillary stresses contributes to unreliable estimates of settlement or differential settlement of footings in unsaturated sands. There are no studies reported in the literature on how capillary stresses influence liquefaction, bearing capacity and settlement behavior in earthquake prone regions under dynamic loading conditions. An extensive experimental program has been undertaken to study these parameters using several specially designed and constructed equipment at the University of Ottawa. The influence of matric suction, confinement and dilation on the bearing capacity of model footings in unsaturated sand was determined using the University of Ottawa Bearing Capacity Equipment (UOBCE-2011). Several series of plate load tests (PLTs) were carried out on a sandy soil both under saturated and unsaturated conditions. Based on these studies, a semi-empirical equation has been proposed for estimating the variation of bearing capacity with respect to matric suction. The saturated shear strength parameters and the soil water characteristic curve (SWCC) are required for using the proposed equation. This equation is consistent with the bearing capacity equation originally proposed by Terzaghi (1943) and later extended by Meyerhof (1951) for saturated soils. Chapter 2 provides the details of these studies. The cone penetration test (CPT) is conventionally used for estimating the bearing capacity of foundations because it is simple and quick, while providing continuous records with depth. In this research program, a cone penetrometer was specially designed to investigate the influence of matric suction on the cone resistance in a controlled laboratory environment. Several series of CPTs were conducted in sand under both saturated and unsaturated conditions. Simple correlations were proposed from CPTs data to relate the bearing capacity of shallow foundations to cone resistance in saturated and unsaturated sands. The details of these studies are presented and summarized in Chapter 3. Standard penetration tests (SPTs) and PLTs were conducted in-situ sand deposit at Carp region in Ottawa under both saturated and unsaturated conditions. The test results from the SPTs and PLTs at Carp were used along with other data from the literature for developing correlations for estimating the bearing capacity of both saturated and unsaturated sands. The proposed SPT-CPT-based technique is simple and reliable for estimation of the bearing capacity of footings in sands. Chapter 4 summarizes the details of these investigations. Empirical relationships were proposed using the CPTs data to estimate the modulus of elasticity of sands for settlement estimation of footings in both saturated and unsaturated sands. This was achieved by modifying the Schmertmann et al. (1978) equation, which is conventionally used for settlement estimations in practice. Comparisons are provided between the three CPT-based methods that are commonly used for settlement estimations in practice and the proposed method for seven large scale footings in sandy soils. The results of the comparisons show that the proposed method provides better estimations for both saturated and unsaturated sands. Chapter 5 summarizes the details of these studies. A Flexible Laminar Shear Box (FLSB of 800-mm3 in size) was specially designed and constructed to simulate and better understand the behaviour of model surface footing under seismic loads taking account of the influence of matric suction in an unsaturated sandy soil. The main purpose of using the FLSB is to simulate realistic in-situ soils behaviour during earthquake ground shaking. The FLSB test setup with model footing was placed on unidirectional 1-g shake table (aluminum platform of 1000-mm2 in size) during testing. The resistance of unsaturated sand to deformations and liquefaction under seismic loads was investigated. The results of the study show that matric suction offers significant resistance to liquefaction and settlement of footings in sand. Details of the equipment setup, test procedure and results of this study are presented in Chapter 6. Simple techniques are provided in this thesis for estimating the bearing capacity and settlement behaviour of sandy soils taking account of the influence of capillary stresses (i.e., matric suction). These techniques are consistent with the methods used in conventional geotechnical engineering practice. The studies show that even low values of capillary stresses (i.e., 0 to 5 kPa) increases the bearing capacity by two to four folds, and the settlement of footings not only decreases significantly but also offers resistance to liquefaction in sands. These studies are promising and encouraging to use ground improvement techniques; such as capillary barrier techniques to maintain capillary stresses within the zone of influence below shallow foundations. Such techniques, not only contribute to the increase of bearing capacity, they reduce settlement and alleviate problems associated with earthquake effects in sandy soils.

The Mechanistic-Empirical Pavement Design Guide (MEPDG) which is widely used for the rational design of pavements has three different design levels (i.e., Level 1, Level 2, and Level 3) that are typically based on the resources and the level of risk associated for a given project. Specifically, Level 2 design requires the estimation of the resilient modulus, MR (which is the key parameter in the mechanistic design procedures) from simple experiments such as the California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS) and R-value tests. In this study, a technique is proposed for estimation of MR from CBR that can be used in Level 2 designs of pavements. The California Bearing Ratio (CBR) is a relatively inexpensive laboratory test which provides a measure of the strength of a soil. The CBR test can easily be performed as the experimental procedure is relatively straightforward to execute. The CBR test procedure widely used and is simple, however the fundamental engineering principles governing CBR tests do not realistically describe the mechanical behavior of pavements. Due to this reason, there has been a significant interest to design pavements using a mechanistic approach such as the resilient modulus (MR). The MR test method provides an indication of the stiffness of pavement materials under cyclic loads, which closely represents the typical loading conditions that are experienced by pavements. MR is a reliable method as it considers the cyclic loading (i.e., resilient response) of pavements. However, it has one major drawback as the triaxial testing equipment used for measurement of the MR is relatively costly, testing is complex and requires trained professional to perform them. The CBR and MR are both used in present day practice to evaluate the strength of pavement materials. However, the CBR is widely used because of its relatively low cost and the vast experience with its use in the design of pavements. The common trend in today’s practice is to estimate the MR from CBR as evident in most pavement design procedures used around the world. For instance, the Mechanistic-Empirical Pavement Design Guide (AASHTO 2008) suggests that the MR may be estimated from standard tests like the CBR for design of Level 2 pavements. Numerous studies in the literature propose relationships between CBR and MR, but only a hand full of these studies takes account of the effect of matric suction, 𝜓 which is a key stress state variable that describes the rational behavior of unsaturated soils. This thesis document includes the explanation of a modified CBR test equipment capable of measuring unsaturated properties (𝜓 and water content) of specimens subjected to wetting and drying. In addition, some correlations were developed using the measured CBR data and the data of MR from other studies. The results provide useful information for Level 2 mechanistic-empirical design of pavement structures for various soils in the province of Ontario.

Analisa-se a influência da sucção matricial e da dimensão de sapatas na capacidade de carga e nos recalques de fundações rasas, assentes em areia não-saturada. Na primeira parte da pesquisa foram analisadas 14 provas de carga estática em placas metálicas rígidas assentes a 1,5 m de profundidade, com diâmetros de 0,20, 0,40 e 0,80m e em uma sapata circular de concreto com diâmetro de 1,50 m, no campo experimental de fundações da USP/São Carlos. Devido ao caráter colapsível do solo, a sucção matricial foi monitorada por meio de tensiômetros instalados no fundo da cava. Na segunda parte da pesquisa, foram realizados ensaios em centrífuga, na Universidade do Colorado em Boulder, utilizando-se placas metálicas de 30 mm, 50 mm e 100 mm, ensaiadas a 1 g, 5 g, 10 g, 15 g, 25 g, 50 g e 100 g. As placas foram assentes em maciço de areia em três condições de umidade: seca, inundada e não-inundada. A partir dos resultados obtidos, procedeu-se a análise da capacidade de carga levando-se em conta tanto o efeito da dimensão como o da sucção matricial. A influência da dimensão nos recalques também foi analisada. Ratificou-se que o aumento da sução matricial provoca um aumento substancial na capacidade de carga do sistema placa-solo e uma diminuição considerável nos recalques. Em relação à influência da dimensão no comportamento de fundações rasas, demonstrou-se que tanto a variação da capacidade de carga como a dos recalques não ocorre de forma linear e crescente como apresentado pelos métodos teóricos. Para pequenas dimensões da sapata, os valores de capacidade de carga e recalque aumentam / The influence of matric suction and size of footings in the bearing capacity and settlement of shallow foundations in unsaturated sandy soils are analyzed. Fourteen plate load tests were performed in the first part of the research. Rigid metallic plates with diameters 0,20, 0,40, 0,80 m and one concrete circular footing with 1,50 m were used in the tests. All plates and footing were positioned at 1,50 m depth. The tests were performed in the foundation experimental field of USP/São Carlos. Due to the soil collapsible character, the tests were performed with the monitoring of matric suction pressure through tensiometers installed in the bottom of the holes. Centrifuge tests were carried out at the University of Colorado at Boulder in the second part of the research. Metallic plates with 30 mm, 50 mm and 10 mm were used and the gravity levels were 1 g, 5 g, 10 g, 15 g, 25 g, 50 g e 100 g. The plates were positioned on top of a sandy soil with three moisture conditions: dry, flooded and non-flooded. Thus, the capacity will be analyzed taking into consideration both the geometry of the tested plates and the influence of the matric suction pressure. The footing size influence in the settlement was also analyzed. A substantial increase of the plate-soil system bearing capacity and a considerable decrease in the settlements, caused by matric suction increase, was confirmed. It was also demonstrated that the bearing capacity and settlements variations are not a linearly increasing function of the size as theoretical methods suggest. For small footings, the bearing capacity and settlement increase as the footing size decreases

Analisa-se a influência da sucção matricial e da dimensão de sapatas na capacidade de carga e nos recalques de fundações rasas, assentes em areia não-saturada. Na primeira parte da pesquisa foram analisadas 14 provas de carga estática em placas metálicas rígidas assentes a 1,5 m de profundidade, com diâmetros de 0,20, 0,40 e 0,80m e em uma sapata circular de concreto com diâmetro de 1,50 m, no campo experimental de fundações da USP/São Carlos. Devido ao caráter colapsível do solo, a sucção matricial foi monitorada por meio de tensiômetros instalados no fundo da cava. Na segunda parte da pesquisa, foram realizados ensaios em centrífuga, na Universidade do Colorado em Boulder, utilizando-se placas metálicas de 30 mm, 50 mm e 100 mm, ensaiadas a 1 g, 5 g, 10 g, 15 g, 25 g, 50 g e 100 g. As placas foram assentes em maciço de areia em três condições de umidade: seca, inundada e não-inundada. A partir dos resultados obtidos, procedeu-se a análise da capacidade de carga levando-se em conta tanto o efeito da dimensão como o da sucção matricial. A influência da dimensão nos recalques também foi analisada. Ratificou-se que o aumento da sução matricial provoca um aumento substancial na capacidade de carga do sistema placa-solo e uma diminuição considerável nos recalques. Em relação à influência da dimensão no comportamento de fundações rasas, demonstrou-se que tanto a variação da capacidade de carga como a dos recalques não ocorre de forma linear e crescente como apresentado pelos métodos teóricos. Para pequenas dimensões da sapata, os valores de capacidade de carga e recalque aumentam / The influence of matric suction and size of footings in the bearing capacity and settlement of shallow foundations in unsaturated sandy soils are analyzed. Fourteen plate load tests were performed in the first part of the research. Rigid metallic plates with diameters 0,20, 0,40, 0,80 m and one concrete circular footing with 1,50 m were used in the tests. All plates and footing were positioned at 1,50 m depth. The tests were performed in the foundation experimental field of USP/São Carlos. Due to the soil collapsible character, the tests were performed with the monitoring of matric suction pressure through tensiometers installed in the bottom of the holes. Centrifuge tests were carried out at the University of Colorado at Boulder in the second part of the research. Metallic plates with 30 mm, 50 mm and 10 mm were used and the gravity levels were 1 g, 5 g, 10 g, 15 g, 25 g, 50 g e 100 g. The plates were positioned on top of a sandy soil with three moisture conditions: dry, flooded and non-flooded. Thus, the capacity will be analyzed taking into consideration both the geometry of the tested plates and the influence of the matric suction pressure. The footing size influence in the settlement was also analyzed. A substantial increase of the plate-soil system bearing capacity and a considerable decrease in the settlements, caused by matric suction increase, was confirmed. It was also demonstrated that the bearing capacity and settlements variations are not a linearly increasing function of the size as theoretical methods suggest. For small footings, the bearing capacity and settlement increase as the footing size decreases

Mechanical behaviour of variably saturated clay fills VLADISLAVA KOSTKANOVÁ Ph.D. Thesis - English Abstract The excavated overburden from open-cast coal mines is end-dumped in fills. Clay type soil prevails among the filled soils in North-western Bohemia. As a consequence of the character and state of the soil, together with the mining and dumping technology, a typical lumpy structure of the clay fill is formed. The filled lumps range in size and vary in mechanical properties, but stiff to solid lumps up to 0.5 m in size are prevalent. Large and open macrovoids between the single lumps are a characteristic feature of the clay fills. Clay fills exhibit a double porosity structure, consisting of intergranular porosity between the lumps and intragranular porosity inside them. The total porosity of the freshly filled soils can reach 70%. This type of clay fill structure is metastable. This thesis focuses on the problematic behaviour of clay fill soils due to their metastable structure and their partly saturated state. Long-term monitoring of matric suction at depths up to 2 metres in two reclaimed clay fills revealed two different trends. Seasonally-dependent suction oscillations were recorded in the moderate slope of the clay fill in the Bílina mine, while no suction pointing to fully saturated conditions was...

Several hydraulic loadings impose earthen levees to time-dependent variably saturated seepage conditions. The main objective of this study is to improve the analysis of levees under transient seepage with the use of unsaturated soil mechanics. An extensive set of laboratory testing, field monitoring and numerical modeling are performed to analyze a silty sand setback levee located near Seattle, WA. In-situ data obtained from field monitoring are used to monitor suction and effective stress within the levee’s embankment and foundation over the past two years. Soil samples taken from the site are used to perform index, water retention, and unsaturated multi-stage triaxial tests in the laboratory. A finite element model of transient seepage under saturated-unsaturated conditions is then developed and calibrated to reasonably match the field data. The results highlight the need to consider unsaturated soil mechanics along with climatic variables and soil-atmosphere interaction when analyzing levees under transient seepage conditions.

The objective of this research was to investigate the effects of thermal gradient and fines content and the interaction between these two factors on the frost heave characteristics of a typical Alaska base material. The laboratory frost heave testing involved one type of aggregate base material, three thermal gradients, and three fines contents in a full-factorial experimental design with two replicates. The aggregate was classified in the American Association of State Highway and Transportation Officials soil classification system as A-1-a; the thermal gradients were 0.15, 0.30, and 0.45 ºC/cm; and the fines contents were 6, 8, and 10 percent. After frost heave testing, a stepwise regression analysis was performed to identify significant independent variables for each of nine separate dependent variables, including frost heave, heave-uptake ratio, steady-state frost heave rate, gravimetric water ingress, and gravimetric water content in each of the five individual lifts tested following frost heave testing. Soil suction, specific gravity, salinity, and hydraulic conductivity testing were also performed on samples prepared at each of the three fines contents to support numerical modeling of the frost heave test results using the computer program ICE-1. The results of the stepwise regression analysis indicate that thermal gradient is a significant predictor of six of the nine dependent variables and that the square of thermal gradient is a significant predictor of five of these six dependent variables. As the thermal gradient increased, the samples experienced decreasing amounts of water ingress and frost heave. However, the data show that neither fines content nor the square of fines content is a significant predictor of any of the dependent variables. Thus, although previous research has shown that higher fines contents are generally associated with greater susceptibility to frost heave, this effect is not manifest in the comparatively small increases in fines contents evaluated in this research. The interaction between thermal gradient and fines content is a significant predictor of only one independent variable. Differences between the modeled and measured frost heave values ranged from 0.01 to 0.92 cm, with the larger differences typically associated with the lowest thermal gradient and the lowest fines content.

[pt] O propósito do trabalho é avaliar a viabilidade técnica do uso de sondas tipo TDR e tensiômetros no monitoramento de encostas não saturadas. Com tais instrumentos, objetiva-se monitorar a variação da sucção mátrica e da umidade no solo em períodos chuvosos, visando aperfeiçoar os sistemas de alerta usados em áreas de risco e, consequentemente, minimizar perdas materiais e humanas. Para as medições, foram instalados uma estação meteorológica (munida de um pluviômetro, um datalogger, uma placa solar e uma antena para a transmissão de dados via internet), quatro sensores de umidade tipo TDR e um tensiômetro de alta capacidade em uma encosta localizada a montante da Faculdade de Medicina de Petrópolis, cidade da região serrana do estado do Rio de Janeiro. Foram registrados cerca de três meses de dados das sondas tipo TDR e, por conta de uma pane elétrica, apenas treze dias de dados do tensiômetro. As sondas tipo TDR apresentaram tempos de resposta rápidos, com nítidos aumentos de umidade volumétrica com o início de um evento chuvoso. Elas também apresentaram sensibilidade adequada para serem utilizadas em sistemas de alerta, sendo capazes de registrar alterações de umidade volumétrica com pequenos volumes de chuva. As curvas características encontradas através de ensaios de papel filtro mostraram um bom paralelo entre as sucções medidas diretamente pelo tensiômetro e aquelas obtidas indiretamente pelas sondas tipo TDR, através da conversão das umidades volumétricas em sucção. / [en] The purpose of this work is to evaluate the technical feasibility of using TDR probes and tensiometers to monitor unsaturated slopes. The objective is to monitor with these instruments the variation of matric suction and soil moisture during rainy periods, aiming to improve the warning systems used in hazardous areas and, consequently, to minimize human and material loss. For the measurements, a meteorological station (equipped with a rain gauge, a datalogger, a solar panel and an antenna for data transmission via internet), four TDR-type humidity sensors and a high capacity tensiometer were installed in a slope located in the University of Medicine of Petrópolis, city of the mountainous region of the state of Rio de Janeiro. Approximately three months of data were collected from the TDR probes and only thirteen days of tensiometer data due to a power outage. TDR-type probes showed fast response time, with clear increases in volumetric humidity with the beginning of a rainfall event. They also showed adequate sensitivity to be used in warning systems, being able to register changes in volumetric humidity with small precipitation amounts. The characteristic curves found by the filter method showed a good correlation with the suctions measured directly by the tensiometer and those obtained indirectly by the TDR probes, by converting the volumetric humidity into suction.