[pt] Muitos autores concordam que areias em estado fofo, sob carregamento não drenado crescente e granulometria favorável à liquefação, necessariamente liquefazem em algum momento. Este trabalho tem como objetivo principal avaliar se duas amostras de areia, com características muito distintas uma da outra, submetidas às mesmas condições descritas acima, entram em liquefação. A primeira amostra é uma areia limpa que foi extraída de um aterro hidráulico localizado em Camboinhas, Niterói, RJ, Brasil. A segunda é um rejeito arenoso de ferro extraído de uma barragem de rejeitos localizada em Mariana, MG, Brasil. As avalições foram feitas através de ensaios de compressão triaxial com deformação controlada. Avaliou-se o comportamento desses materiais em condições de baixa compacidade e sob diferentes tensões de confinamento, com a finalidade de observar se ocorreria a liquefação. Em caso de não ocorrência da liquefação, o objetivo era compreender os motivos de tal resposta e no caso de ocorrência, avaliar a influência da tensão de confinamento, assim como delimitar as zonas de instabilidade não drenada. Verificou-se que a areia de Camboinhas entrou em liquefação total apenas para tensões de confinamento baixas, e apresenta comportamento oposto ao comportamento normal de solos arenosos fofos, tendo baixa resistência à liquefação em baixa tensão de confinamento e alta resistência à liquefação em grandes tensões de confinamento. O rejeito arenoso de Mariana entrou em liquefação total em tensões de confinamento baixas e altas. O rejeito apresentou comportamento diferente da areia de Camboinhas e semelhante ao comportamento normalmente obtido em solos arenosos fofos sob condições não drenadas. / [en] Many authors agree that loose sands, under increasing undrained loading and liquefaction favorable granulometry, necessarily liquefy at some moment. This work has as main objective to evaluate if two sand specimens, with characteristics very different from each other, under the same conditions as described above, enter into liquefaction. The first specimen is a clean sand that was extracted from a hydraulic embankment located in Camboinhas, Niterói, RJ, Brazil. The second is a sandy tailing of iron extracted from a tailing dam located in Mariana, MG, Brazil. The evaluations were made through triaxial compression tests with controlled deformation. The behavior of these materials was evaluated under conditions of low compactness and under different confininig pressure, in order to observe if liquefaction would occur. In case of no liquefaction, the objective was understand the reasons for such response and in case of occurrence, evaluate the influence of the confining pressure, as well as mark the zones of instability undrained. It was verified that the Camboinhas sand entered in total liquefaction only for low confining pressure, and it has the opposite behavior to the normal behavior of loose granular soils, having low strength to liquefaction in low confining pressure and high strength to liquefaction in large confining pressure. The Mariana granular tailing also entered in total liquefaction for low and higth confinig pressure. The tailing showed different behavior of the Camboinhas sand and similar to the behavior normally obtained in loose granular soils under undrained conditions.

Auf den Innenkippen nehmen mit dem Anstieg des Grundwassers die Zahl der Verflüssigungsereignisse und auch die Größe der verflüssigten Bereiche zu. Besonders davon betroffen ist der sogenannte Nordraum der Lausitz südlich von Lübbenau. Dort wurden deshalb Böschungskonturen vor und nach den Verflüssigungsereignissen über Jahre systematisch erfasst. Die erfassten Konturen wurden geokinematisch analysiert, um charakteristische Bewegungsmuster erkennen und beschreiben zu können. Das Ergebnis ermöglicht eine neue Klassifizierung der auf Innenkippen auftretenden Verformungsvorgänge. Darauf aufbauend, entstand eine neue Methodik zur Berechnung der Standsicherheit verflüssigungsgefährdeter Innenkippenflächen deren Basis die Theorien des Erddrucks und Hydromechanik sind. Für den Nachweis des horizontalen Gleichgewichts einer Böschung wird ein Kräfte-, für das der vertikalen, ein Momentenvergleich hergeleitet. Mit einem hydromechanischen Ansatz ist es auch möglich, zusätzlich die Endgeometrie der sich nach der Verflüssigung einstellenden Böschung zu berechnen. Die Ergebnisse der Standsicherheitsberechnungen und der geometrischen Endkonturen zeigen überraschende Übereinstimmungen mit den erfassten gegangenen Böschungsbewegungen.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20684号 / 工博第4381号 / 新制||工||1681(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 澤田 純男, 教授 清野 純史, 准教授 後藤 浩之 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Characterization of the seismic hazard and ground-failure hazard of a site using traditional empirical lateral spread displacement models requires consideration of uncertainties in seismic loading, site conditions, and model prediction. Researchers have developed performance-based design methods to simultaneously account for these sources of uncertainty through the incorporation of a probabilistic analytical framework. While these methods can effectively handle the various sources of uncertainty associated with empirical lateral spread displacement prediction, they can be difficult for engineers to perform in a practical manner without the use of specialized numerical tools. To make the benefits of a performance-based approach accessible to a broader audience of geotechnical engineers, a simplified performance-based procedure is introduced in this paper. This map-based procedure utilizes a reference soil profile to provide hazard-targeted reference displacements across a geographic area. Equations are provided for engineers to correct those reference displacements for site-specific soil conditions and surface geometry to produce site-specific, hazard-targeted estimates of lateral spread displacement. The simplified performance-based procedure is validated through a comparative study assessing probabilistic lateral spread displacements across several cities in the United States. Results show that the simplified procedure closely approximates the results from the full performance-based model for all sites. Comparison with deterministic analyses are presented, and the place for both in engineering practice are discussed.

Lateral spread is a seismic hazard associated with soil liquefaction in which permanent deformations are developed within the soil profile due to cyclic mobility. Lateral spread has historically been one of the largest causes of earthquake-related damage to infrastructure. One of the infrastructure components most at risk from lateral spread is that of deep foundations. Because performance-based engineering is increasingly becoming adopted in earthquake engineering practice, it would be beneficial for engineers and researchers to have a performance-based methodology for computing pile performance during a lateral spread event. This study utilizes the probabilistic performance-based framework developed by the Pacific Earthquake Engineering Research Center to develop a methodology for computing probabilistic estimates of kinematic pile response. The methodology combines procedures familiar to most practicing engineers such as probabilistic seismic hazard analysis, empirical compution of lateral spread displacement, and kinematic pile response using p-y soil spring models (i.e. LPILE). The performance-based kinematic pile response model is applied to a series of lateral spread case histories from the earthquake that struck the Limon province of Costa Rica on April 22, 1991. The M7.6 earthquake killed 53 people, injured another 193 people, and disrupted an estimated 30-percent of the highway pavement and railways in the region due to fissures, scarps, and soil settlements resulting from liquefaction. Significant lateral spread was observed at bridge sites throughout the eastern part of Costa Rica near Limon, and the observed structural damage ranged from moderate to severe. This study identified five such bridges where damage due to lateral spread was observed following the earthquake. A geotechnical investigation is performed at each of these five bridges in an attempt to back-analyze the soil conditions leading to the liquefaction and lateral spread observed during the 1991 earthquake, and each of the five resulting case histories is developed and summarized. The results of this study should make a valuable contribution to the field of earthquake hazard reduction because they will introduce a procedure which will allow engineers and owners to objectively evaluate the performance of their deep foundation systems exposed to kinematic lateral spread loads corresponding to a given level of risk.

Stone columns are an established method of liquefaction mitigation in clean sands (fines content <15%). Although stone columns are considered less effective in silty soils, an increase in the area replacement ratio or the addition of wick drains may still produce improvement in the normalized blow count. Limited case histories are available with a direct comparison of the use of stone columns with and without wick drains at one location. The Salmon Lake Dam Modification project provided such a scenario. Two test sections were completed at the site prior to construction to determine the area replacement ratio for the final design as well as to compare the application of stone columns with and without wick drains. Visual observations of water and air escaping from wick drains within a distance of 15 ft of the stone column construction confirmed that drains aided in pore pressure dissipation. Test results indicated that stone column treatment with wick drains produced greater improvement in blow count than stone column treatment without drains. For the overall site, there was an increase in improvement ranging from 3 to 8 SPT blow counts. When compared to the results of a similar evaluation of a site in Ogden, Utah, which had a comparable fines content and an area replacement ratio of 26%, the increase in stone column effectiveness produced by adding wick drains was lower at the Salmon Lake Dam site. The increase in improvement at the Ogden, Utah site ranged from 12 to 18 SPT blow counts. At the Ogden site, wick drains were placed between every stone column while they were only placed between vertical rows of columns at Salmon Lake dam. Despite the beneficial effects provided by using wick drains with stone column treatment in silty soils, the performance was below what would be expected for stone column treatment without wick drains in clean sands with less than 15% fines. Stone column treatment also proved less effective in layers of sandy silt than in layers of silty sand, which was indicated by lower average improvement and more points of negative improvement in layers of sandy silt. Although several different area replacement ratios were analyzed (23, 27, 31, and 35%), no consistent trend towards greater improvement in blow count was seen as the replacement ratio increased beyond 23%.

This research consists of full-scale shake table tests to investigate liquefaction of sandy soils. Consideration of the potential and consequences of liquefaction is critical to the performance of any structure built in locations of high seismicity underlain by saturated granular materials as it is the leading cause of damage associated with ground failure. In certain cases the financial losses associated with liquefaction can significantly impact the financial future of an entire region. Most liquefaction triggering studies are performed in the field where liquefaction has been previously observed, or in tabletop laboratory testing. The study detailed herein is a controlled laboratory test performed at full scale to allow for the measurement of field-scale index testing before and after cyclic loading. Testing was performed at the Parson’s geotechnical and Earthquake Laboratory at Cal Poly San Luis Obispo on the 1-dimensional shake table with a mounted flexible walled testing apparatus. The testing apparatus, originally constructed for soil-structure interaction experiments utilizing soft clay was retrofitted for the purpose of studying liquefaction. This research works towards comparing large-scale simple-shear liquefaction testing to small-scale simple-shear liquefaction testing of a #2/16 Monterey sand specimen. The bucket top was modified in order to apply a vertical load to the soil skeleton to replicate overburden soil conditions. Access ports were fitted into the bucket top for instrument cable access and to allow cone penetration testing before and after cyclic loading. A shear-wave generator was created to propagate shear waves into the sample for embedded accelerometers to measure small strain stiffness of the sample. Pore-pressure transducers were embedded in the soil sample to capture excess pore water pressure produced during liquefaction. Displacement transducers were attached to the bucket in order to measure shear strains during cyclic testing and to measure post-liquefaction volumetric deformations. The results of this investigation provide an empirical basis to the behavior of excess pore water production, void re-distribution, shear wave velocity, shear strain and cone penetrometer tip resistance of #2/16 Monterey sand before, during, and after liquefaction in a controlled laboratory environment at full-scale.

Liquefaction-induced lateral spread displacements cause severe damage to infrastructure, resulting in large economic losses in affected regions. Predicting lateral spread displacements is an important aspect in any seismic analysis and design, and many different methods have been developed to accurately estimate these displacements. However, the inherent uncertainty in predicting seismic events, including the extent of liquefaction and its effects, makes it difficult to accurately estimate lateral spread displacements. Current conventional methods of predicting lateral spread displacements do not completely account for uncertainty, unlike a performance-based earthquake engineering (PBEE) approach that accounts for the all inherent uncertainty in seismic design. The PBEE approach incorporates complex probability theory throughout all aspects of estimating liquefaction-induced lateral spread displacements. A new fully-probabilistic PBEE method, based on results from the cone penetration test (CPT), was created for estimating lateral spread displacements using two different liquefaction triggering procedures. To accommodate the complexity of all probabilistic calculations, a new seismic hazard analysis tool, CPTLiquefY, was developed. Calculated lateral spread displacements using the new fully-probabilistic method were compared to estimated displacements using conventional methods. These comparisons were performed across 20 different CPT profiles and 10 cities of varying seismicity. The results of this comparison show that the conventional procedures of estimating lateral spread displacements are sufficient for areas of low seismicity and for lower return periods. However, by not accounting for all uncertainties, the conventional methods under-predict lateral spread displacements in areas of higher seismicity. This is cause for concern as it indicates that engineers in industry using the conventional methods are likely under-designing structures to resist lateral spread displacements for larger seismic events.

Liquefaction-induced lateral spread displacements cause severe damage to infrastructure, resulting in large economic losses in affected regions. Predicting lateral spread displacements is an important aspect in any seismic analysis and design, and many different methods have been developed to accurately estimate these displacements. However, the inherent uncertainty in predicting seismic events, including the extent of liquefaction and its effects, makes it difficult to accurately estimate lateral spread displacements. Current conventional methods of predicting lateral spread displacements do not completely account for uncertainty, unlike a performance-based earthquake engineering (PBEE) approach that accounts for the all inherent uncertainty in seismic design. The PBEE approach incorporates complex probability theory throughout all aspects of estimating liquefaction-induced lateral spread displacements. A new fully-probabilistic PBEE method, based on results from the cone penetration test (CPT), was created for estimating lateral spread displacements using two different liquefaction triggering procedures. To accommodate the complexity of all probabilistic calculations, a new seismic hazard analysis tool, CPTLiquefY, was developed. Calculated lateral spread displacements using the new fully-probabilistic method were compared to estimated displacements using conventional methods. These comparisons were performed across 20 different CPT profiles and 10 cities of varying seismicity. The results of this comparison show that the conventional procedures of estimating lateral spread displacements are sufficient for areas of low seismicity and for lower return periods. However, by not accounting for all uncertainties, the conventional methods under-predict lateral spread displacements in areas of higher seismicity. This is cause for concern as it indicates that engineers in industry using the conventional methods are likely under-designing structures to resist lateral spread displacements for larger seismic events.

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