Laboratory tests were performed to investigate the liquefaction susceptibility of uncemented calcareous sands. A series of isotropically consolidated undrained monotonic and cyclic triaxial tests were performed using the Playa Santa sand from Porto Rico. Playa Santa sand is a poorly graded calcareous clean beach sand composed of angular particles with large intra-granular voids. A series of consolidated undrained triaxial tests were performed with the Playa Santa sand remolded to a variety of relative densities and consolidated under a range of confining pressures. In addition, cyclic triaxial tests were performed at a confining pressure of 100 kPa and three sets of relative densities (20%, 40% and 60%). Generation of excess pore pressure under different levels of cyclic loading was established. As a result, relationships were developed to relate the number of cycles required for triggering of liquefaction to cyclic stress ratio. It was seen that the Playa Santa sand was less susceptible liquefaction than quartzitic sands of the same relative density remolded and tested under similar conditions. / Master of Science

Liquefaction of soil is one of the major contributing factors for damages of infrastructures and utility services during earthquake. Liquefaction occurs when short strong shaking creates undrained loading condition in saturated soil deposit thereby increases pore water pressure, which eventually equals the effective confining pressure resulting in significant reduction in shear strength and bearing capacity of soil deposit. Several studies have been conducted to investigate the effect of polypropylene fiber on sand deposit as a measure to prevent liquefaction but most of them are based on static tests. Therefore, the present study, tries to understand liquefaction characteristics of sand reinforced with polypropylene fiber based on cyclic triaxial test. The main objectives of this study are (i) to explore the effect of polypropylene fiber on pore pressure generation and deformation characteristics of sand, and (ii) to observe the effect of confining pressure on liquefaction characteristics of sand-fiber mixture. A series of stress controlled cyclic triaxial tests were performed at 5 and 10 psi effective confining pressures. At 5 psi effective confining pressure, specimens of clean sand, and sand containing 0.05, 0.075, 0.1, and 0.3% polypropylene fiber by dry weight were tested at 0.2, 0.25, 0.3, and 0.4 Cyclic Stress Ratio (CSR). However, at 10 psi effective confining pressure, specimens were also tested for 0.5%, and 0.75% fiber in addition to those at 5 psi confining pressure at 0.2, 0.3, and 0.4 CSR. Based on the test results, it was observed that, cyclic shear stress increases with the increase in initial effective confining pressure. Also, for a given CSR, liquefaction resistance decreased with the increase in effective confining pressure. Furthermore, significant improvement in liquefaction resistance was observed when the fiber content exceeded beyond 0.075% at 5 psi confining stress. However, at 10 psi confining pressure, addition of fiber did not help in improvement of liquefaction resistance of sand except when cyclic shear stress was applied at 0.2 CSR. At 0.2 CSR, although the specimens did liquefy based on pore pressure generation criteria at all fiber contents, specimens containing 0.5% and 0.75% fiber did not ever reach 2.5% and 5% DA (Double Amplitude) deformation throughout 1000 loading cycles.

In 2010 and 2011 Christchurch, New Zealand experienced a series of earthquakes that caused extensive damage across the city, but primarily to the Central Business District (CBD) and eastern suburbs. A major feature of the observed damage was extensive and severe soil liquefaction and associated ground damage, affecting buildings and infrastructure. The behaviour of soil during earthquake loading is a complex phenomena that can be most comprehensively analysed through advanced numerical simulations to aid engineers in the design of important buildings and critical facilities. These numerical simulations are highly dependent on the capabilities of the constitutive soil model to replicate the salient features of sand behaviour during cyclic loading, including liquefaction and cyclic mobility, such as the Stress-Density model. For robust analyses advanced soil models require extensive testing to derive engineering parameters under varying loading conditions for calibration. Prior to this research project little testing on Christchurch sands had been completed, and none from natural samples containing important features such as fabric and structure of the sand that may be influenced by the unique stress-history of the deposit. This research programme is focussed on the characterisation of Christchurch sands, as typically found in the CBD, to facilitate advanced soil modelling in both res earch and engineering practice - to simulate earthquake loading on proposed foundation design solutions including expensive ground improvement treatments. This has involved the use of a new Gel Push (GP) sampler to obtain undisturbed samples from below the ground-water table. Due to the variable nature of fluvial deposition, samples with a wide range of soil gradations, and accordingly soil index properties, were obtained from the sampling sites. The quality of the samples is comprehensively examined using available data from the ground investigation and laboratory testing. A meta-quality assessment was considered whereby a each method of evaluation contributed to the final quality index assigned to the specimen. The sampling sites were characterised with available geotechnical field-based test data, primarily the Cone Penetrometer Test (CPT), supported by borehole sampling and shear-wave velocity testing. This characterisation provides a geo- logical context to the sampling sites and samples obtained for element testing. It also facilitated the evaluation of sample quality. The sampling sites were evaluated for liquefaction hazard using the industry standard empirical procedures, and showed good correlation to observations made following the 22 February 2011 earthquake. However, the empirical method over-predicted liquefaction occurrence during the preceding 4 September 2010 event, and under-predicted for the subsequent 13 June 2011 event. The reasons for these discrepancies are discussed. The response of the GP samples to monotonic and cyclic loading was measured in the laboratory through triaxial testing at the University of Canterbury geomechanics laboratory. The undisturbed samples were compared to reconstituted specimens formed in the lab in an attempt to quantify the effect of fabric and structure in the Christchurch sands. Further testing of moist tamped re- constituted specimens (MT) was conducted to define important state parameters and state-dependent properties including the Critical State Line (CSL), and the stress-strain curve for varying state index. To account for the wide-ranging soil gradations, selected representative specimens were used to define four distinct CSL. The input parameters for the Stress-Density Model (S-D) were derived from a suite of tests performed on each representative soil, and with reference to available GP sample data. The results of testing were scrutinised by comparing the data against expected trends. The influence of fabric and structure of the GP samples was observed to result in similar cyclic strength curves at 5 % Double Amplitude (DA) strain criteria, however on close inspection of the test data, clear differences emerged. The natural samples exhibited higher compressibility during initial loading cycles, but thereafter typically exhibited steady growth of plastic strain and excess pore water pressure towards and beyond the strain criteria and initial liquefaction, and no flow was observed. By contrast the reconstituted specimens exhibited a stiffer response during initial loading cycles, but exponential growth in strains and associated excess pore water pressure beyond phase-transformation, and particularly after initial liquefaction where large strains were mobilised in subsequent cycles. These behavioural differences were not well characterised by the cyclic strength curve at 5 % DA strain level, which showed a similar strength for both GP samples and MT specimens. A preliminary calibration of the S-D model for a range of soil gradations is derived from the suite of laboratory test data. Issues encountered include the influence of natural structure on the peak-strength–state index relationship, resulting in much higher peak strengths than typically observed for sands in the literature. For the S-D model this resulted in excessive stiffness to be modelled during cyclic mobility, when the state index becomes large momentarily, causing strain development to halt. This behaviour prevented modelling the observed re- sponse of silty sands to large strains, synonymous with “liquefaction”. Efforts to reduce this effect within the current formulation are proposed as well as future research to address this issue.

Weakening and liquefaction of sands with increasing excess pore water pressures under repeated loads is well-known. Occurrence of extensive damage to the built environment also at the sites underlain by fine soils during earthquakes have led the researchers to focus on the seismic response of such soils more recently. The primary objective of this study is to investigate the factors affecting cyclic behavior of saturated low-plastic fine soils through laboratory testing. An extensive laboratory testing program including conventional soil mechanics tests, consolidation tests, reconstituted sample preparation, monotonic and cyclic triaxial tests was carried out for this purpose. Laboratory program was conducted within two parts, one of which includes the tests performed with the silt specimens reconstituted in the laboratory and the other consisting of the tests performed with the undisturbed soil samples retrieved from Adapazari. The effects of the inherent soil properties and the effects of loading characteristics on the cyclic response of saturated low plastic silty soils were examined separately. Based on the test results, models were introduced (i) to predict the relationship between excess pore pressure ratio (ru), number of cycles (N) and cyclic stress ratio (CSRtx), (ii) to estimate the effect of initial shear stress on cyclic response, and (iii) to show the effects of initial void ratio (ei), initial shear stress ratio (

[pt] Apresenta-se, neste trabalho, resultados de um extenso estudo experimental de laboratório, cujos objetivos eram: obter informações do comportamento tensão-deformação em condições não drenadas, e verificar a susceptibilidade à liquefação de um resíduo oriundo da lavra do itabirito silicoso da Mina de Fernandinho, que situa-se no Quadrilátero Ferrífero (Minas Gerais ), região com grande concentração de minério de ferro. Para realizar o estudo de susceptibilidade à liquefação do resíduo, foi necessário projetar e construir um equipamento que é constituído de: uma célual triaxial, servo-motores, válvulas para regulagem de pressão, um microcomputador AT486, conversor D/A, um sistema de aquisição de dados da National Instruments e alguns acessórios que foram desenvolvidos para facilitar a execução dos ensaios. Durante a fase de projeto e montagem deste equipamento foi implementado um programa na linguagem de programação C para gerenciar os ensaios. Este equipamento possibilitou a execução dos ensaios triaxiais cíclicos e monotônicos com trajetórias de tensões servo controladas. Na primeira fase deste estudo foram realizados ensaios de caracterização completa, análise mineralógica e de microscopia eletrônica. Após a caracterização física do material, passou-se ao estudo do comportamento tensão- deformação e resistência com a execução de ensaios triaxiais. Nesta fase foram executados ensaios monotônicos e cíclicos em corpos de prova adensados isotropicamente e anisotropicamente. Com as análises dos resultados e entendimento do comportamento tensão deformação deste material em condições de laboratório, concluiu-se que este é susceptível à liquefação devido ao comportamento colapsível e desenvolvimento elevado de poropressões. Finalmente, propõe-se uma nova metodologia experimental para estudar os mecanismos que levam o solo a desenvolver o fenômeno de liquefação, tendo em vista que as metodologias apresentadas na literatura corrente não são adequadas para estudar este fenômeno. / [en] This work presents results of na experimental research programme executed in the laboratory at PUC-Rio, Brazil. The aim of this research was investigated the stress-strain behaviour and the evaluation of the susceptibility of fine grained tailing material from Fernandinho Mine to liquefaction. This mine is at Quadrilatero Ferrífero (Minas Gerais - Brazil), region with one of the largest sources of iron ore in Brazil.In order to study the susceptibility to liquefaction of tailing material an servocontrolled triaxial device was developed. This device were composed by: triaxial cell, servo-motors,pressure regulators, microcomputer, one digital analogy convert of, one analogy digital convert developed in the laboratory at PUC-Rio and other accessories. During the development of the device, one software to control all the trajetories was implemented. Using this device some cyclic and monotonic triaxial tests were carried out.Complete characterization, mineralogical and eletronic microscope analysis were carried out in the preliminary steps of this research. After this, an extensive programme of triaxial tests were carried out in order to determine the failure envelope, stress-strain behaviour and liquifiction resitance of the tailing material.A colapsive behavior of the tested material was observed at small strain and stress conditions. Another important observation was the high level of poropressure development,suggesting that this material is susceptible to liquefaction in special conditions.Finally, based on the test results, a new methodology is proposed to investigate soils when submitted to undrained conditions.

The presence of silt and clay particles has long been thought to affect the behavior of a sand under cyclic loading. Unfortunately, a review of studies published in the literature reveals that no clear conclusions can be drawn as to how altering fines content and plasticity actually affects the liquefaction resistance of a sand. In fact, the literature contains what appears to be contradictory evidence. There is a need to clarify the effects of fines content and plasticity on the liquefaction resistance of sandy soils, and to determine methods for accounting for these effects in engineering practice. In order to help answer these questions, a program of research in the form of a laboratory parametric study intended to clarify the effects which varying fines content and plasticity have upon the liquefaction resistance of sandy sands was undertaken. The program of research consisted of a large number of cyclic triaxial tests performed on two sands with varying quantities of plastic and non-plastic fines. The program of research also examined the applicability of plasticity based liquefaction criteria and the effects of fines content and plasticity on pore pressure generation. Lastly, a review of how the findings of this study may affect the manner in which simplified analyses are performed in engineering practice was made. The results of the study performed are used to clarify the effects of non-plastic fines content and resolve the majority of the inconsistencies in the literature. The effects of plastic fines content and fines plasticity are shown to be different than has been previously reported. The validity of plasticity based liquefaction criteria is established, the mechanism responsible for their validity is explained, and a new simplified criteria proposed. The effects of fines content and plasticity on pore pressure generation are discussed, and several recommendations are made for implementing the findings of this study into engineering practice. / Ph. D.

This study is focused on developing a method to predict the dynamic behavior of mine tailings dams under earthquake loading. Tailings dams are a by-product of coal mining and processing activities. Mine tailings impoundments are prone to instability and failure under seismic loading as a result of the mechanical behavior of the tailings. Due to the existence of potential seismic sources in close proximity to the coal mining regions in the United States, it is necessary to assess the post-earthquake stability of these tailings dams. To develop the aforementioned methodology, 34 cyclic triaxial tests along with vane shear tests were performed on undisturbed mine tailings specimens from two impoundments in Kentucky. Therefore, the liquefaction resistance and the residual shear strength of the specimens were measured. The laboratory cyclic strength curves for the coal mine specimens were produced, and the relationship between plasticity, density, cyclic stress ratio, and number of cycles to liquefaction were identified. The samples from the Big Branch impoundment were generally loose samples, while the Abner Fork specimens were dense samples, older and slightly cemented. The data suggest that the number of loading cycles required to initiate liquefaction in mine tailings, NL, decreases with increasing CSR and with decreasing density. This trend is similar to what is typically observed in soil. For a number of selected specimens, using the results of a series of small-strain cyclic triaxial tests, the shear modulus reduction curves and damping ratio plots were created. The data obtained from laboratory experiments were correlated to the previously recorded geotechnical field data from the two impoundments. The field parameters including the SPT blow counts (N1)60, corrected CPT cone tip resistance (qt), and shear wave velocity (vs), were correlated to the laboratory measured cyclic resistance ratio (CRR). The results indicate that in general, the higher the (N1)60 and the tip resistance (qt), the higher the CSR was. Ultimately, practitioners will be able to use these correlations along with common state-of-practice geotechnical field methods to predict cyclic resistance in fine tailings to assess the liquefaction potential and post-earthquake stability of the impoundment structures.

The liquefaction resistance of undisturbed soil samples collected from a selected location in Carbondale, Southern Illinois was evaluated by conducting cyclic triaxial tests. Index property tests were carried out on the sample for identification and classification of the soil. Cyclic triaxial tests were conducted on undisturbed sample after saturation, undisturbed sample at natural water content and remolded samples prepared by compaction in the lab. The results were used to evaluate the effect of saturation and remolding on liquefaction resistance of the local soil. Effect of effective confining pressure on dynamic properties of soil (Young's Modulus and Damping ratio) was also studied. Forty five stress controlled cyclic triaxial tests were performed. Three different values of initial effective confining pressure (5 psi, 10 psi and 15 psi) were used and cyclic stress ratio was varied from 0.1 to 0.5 in order to apply different cyclic shear stresses. The results show that the cyclic load resistance of soil decreases as a result of remolding. Saturated undisturbed samples show increase in resistance to liquefaction with increase in initial confining pressure. Remolded samples were prepared by compaction in the lab keeping unit weight and water content equal to that of undisturbed samples. Remolded samples show increase in liquefaction resistance with increase in confining pressure. Undisturbed samples at natural water content show increase in resistance to develop axial strain with increase in confining pressure. Both the rate of excess pressure development and axial strain development increase significantly as a result of remolding. While investigating the effect of saturation of undisturbed samples on liquefaction resistance of soil, interesting observations were made. The excess pressure buildup rate was faster in case of saturated undisturbed samples compared to that in samples with natural water content. On the other hand, rate of strain development was significantly high in case of sample with natural water content compared to that in saturated sample. Also, results obtained from cyclic triaxial tests on saturated undisturbed samples were compared with results obtained from similar tests on Ottawa Sand (Lama 2014) sample. The comparison shows that the saturated undisturbed soil samples of the selected local soil have very high resistance to liquefaction both in terms of initial liquefaction and development of 2.5% and 5% axial strain. Modulus of Elasticity and damping ratio were studied as important dynamic properties of soil. Young's Modulus was observed to decrease significantly at higher strain levels for all three types of samples. Young's modulus increased with increase in effective confining pressure, the effect of confining pressure being large at low strain level and almost insignificant at higher strain level. Damping ratio was highest in undisturbed sample at natural water content and smallest in remolded sample and damping ratio for saturated undisturbed sample falls in between. The damping ratio did not show any definite correlation with strain and confining pressure at lower strain level. But, for strain higher than 1% double amplitude axial strain, damping ratio significantly decreases with increase in strain. Damping ratio increases with increase in confining pressure as observed at high strain for all samples.

O objetivo deste trabalho é avaliar a influência da variação do teor de umidade no valor do módulo de resiliência (MR) de um solo argiloso de subleito, tendo em vista que este parâmetro é muito susceptível à variações climáticas ambientais. Foram realizados ensaios triaxiais cíclicos para se estimar o módulo de resiliência de corpos de prova ensaiados em diversas condições de umidade. Verificou-se que o MR é influenciado pela tensão desvio, de forma que aquele aumenta com o acréscimo desta. Constatou-se que os corpos de prova moldados na Wot e submetidos a trajetórias de secagem e umedecimento alcançaram valores de MR superiores e inferiores, respectivamente, ao se comparar com o MR de corpos de prova ensaiados na Wot. Este fato foi também observado para os corpos de prova moldados com massa específica seca máxima, em teores de umidade abaixo e acima do teor ótimo. Determinou-se, ainda, a sucção no solo através do método do papel filtro e levantou-se a sua curva característica. Verificou-se que à medida que a umidade aumenta, a sucção diminui. Observou-se que o valor do MR aumenta com o aumento da sucção no solo. Este crescimento é tanto maior quanto maior seja a tensão desvio aplicada. Foi possível determinar a relação entre o MR, a tensão desvio e o módulo tangente inicial (Eo), proveniente dos ensaios de compressão simples. Relacionou-se, também, o Eo e a sucção no solo. / The aim of this work is to evaluate the influence of moisture content variation in resilient modulus value (MR) of a subgrade clayey soil, considering that this parameter is very susceptible to environmental climatic variations. Cyclic triaxial tests were performed to acess resilient modulus of specimens tested in several moisture conditions. lt has been verified that MR is influenced by deviator stress, so that the former increases with the latter increases. lt has been confirmed that specimens molded in Wot and submited to a drying and moistening route reached MR values higher and lower, respectively, to compare with MR of specimens tested in Wot. This fact was also observed for the specimens molded with dry density, in moisture contents below and above of optimum moisture content. lt has been also determined the soil suction using filter paper method and it has been built its characteristic curve. lt has been verified that when moisture increases, the suction decreases. lt has been observed that MR value increases with the soil suction increase. This increase is as bigger as bigger the applied deviator stress be. lt was possible to determine the relationship between MR, deviator stress and parameters from compressive strength tests. lt has been related parameters from compressive strength tests and soil suction.

Na construção de rodovias, as condições de umidade e densidade observadas na compactação são, geralmente, próximas daquelas correspondentes ao pico da curva de compactação obtida no ensaio Proctor. É sabido que variações ambientais no decorrer da vida do pavimento podem alterar, de maneira significativa, a umidade do subleito e dos seus componentes e assim, as suas propriedades resilientes. O objetivo principal desta pesquisa é avaliar a influência da variação da umidade pós-compactação no módulo de resiliência de solos de rodovias do interior paulista a partir de resultados de ensaios de laboratório. Foram coletados e caracterizados setenta e três solos, e, dentre estes, selecionados trinta para a etapa de estudo da variação da umidade pós-compactação, após a realização de ensaios MCT, difração de raios-x, microscopia eletrônica de varredura e azul de metileno para determinação da gênese. Os solos selecionados apresentam características distintas quanto à gênese, sendo metade laterítico e metade não-laterítico. Os corpos-de-prova foram compactados na umidade ótima e submetidos a processos de secagem e umedecimento e, posteriormente, realizados ensaios triaxiais cíclicos. Os resultados permitiram a modelagem do 'M IND.R' em função do estado de tensão para diferentes umidades e a avaliação da competência de alguns modelos matemáticos nesta representação. Estudou-se a influência da gênese e da granulometria sobre o valor do 'M IND.R' e avaliou-se a conseqüência da variação da umidade sobre este para solos lateríticos e não-lateríticos. Determinou-se uma expressão para estimar a variação do 'M IND.R' com a variação da umidade a partir do parâmetro k1, independentemente do estado de tensão. Pesquisou-se a existência de relações entre os parâmetros de regressão do modelo composto e os resultados dos ensaios de compressão simples e as propriedades físicas dos solos, de forma a permitir a estimativa do módulo de resiliência a partir do resultado de ensaios mais simples. Investigou-se a possibilidade de se utilizar as relações entre a variação do módulo tangente inicial com a variação da umidade para estimar os efeitos sobre o 'M IND.R'. / On road construction, the field compaction conditions are usually close to those determined from Proctor tests. Environmental variations may lead to changes in the pavement moisture and also changing its resilient properties. The main objective of this research is to study the influence of post-compaction moisture content variation on the resilient modulus of soils from São Paulo state pavements, using laboratory tests. To accomplish this objective, seventy three soils samples were collected and characterized. Among them, thirty samples were selected, after four different tests were carried out to determine the soils genesis, to study the post-compaction moisture content variation. Half of these selected soils are lateritic ones, and the other half are non-lateritic soils. The specimens were compacted at optimum moisture content and submitted to drying and moistening processes prior cyclic triaxial test to be carried out. The results allowed the resilient modulus modeling as a function at the stress state and the performance evaluation of five different models. The genesis and grain size distribution influence on the resilient modulus values were studied. The effects of moisture content variations on lateritic and non-lateritic soils were investigated. An expression to estimate the resilient modulus variations with the moisture variations was determined, independently of the stress state. The existence of relations of the compound model regression parameters with the results of unconfined compressive strength and soil properties were studied. The possibility of using the initial tangent modulus variations with the moisture variations to estimate the effects on the resilient modulus were also investigated.