Orientador: Caio Gorla Nogueira / Banca: Paulo Cesar Lodi / Banca: Jefferson Lins da Silva / Resumo: Devido às consequências negativas associadas à ruptura e deslizamentos de taludes, a análise de estabilidade desses assume uma parte primordial na área da engenharia geotécnica. A maioria dessas análises é realizada de maneira determinística, não incorporando as incertezas inerentes ao sistema. A constatação dessas incertezas em projetos de taludes associa-se a previsão de uma probabilidade de falha no desempenho de taludes quanto à segurança. Nesse contexto, esta dissertação busca avaliar a segurança de taludes através de uma abordagem probabilística, simulando taludes com geometrias e solos variados, verificando ainda a influência da elevação da posição do nível d'água. Para essa finalidade foram realizadas análises probabilísticas utilizando First Order Reliability Method (FORM) com base nos métodos de Equilíbrio Limite, através dos programas computacionais acadêmicos RASS (análises determinísticas) e RELgen (análises probabilísticas). Com base nos resultados, verificou-se que as superfícies críticas obtidas pelos métodos determinísticos podem não coincidir com as superfícies que apresentam a maior probabilidade de falha. Isto é verificado ainda na análise de inclinação da superfície do talude, em que inclinações apresentando fatores de segurança admissíveis, apresentaram probabilidades de falha não aceitáveis. Estas divergências são atribuídas às incertezas inerentes ao sistema. Sendo assim, as análises de estabilidade de talude baseadas apenas nos resultados de análises ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Due to the negative consequences associated with slope rupture and landslides, the stability analysis of these slopes plays an important role in geotechnical engineering. Most of these analyzes are carried out in a deterministic manner, not incorporating the uncertainties inherent to the system. The observation of these uncertainties in slope projects is associated with the forecast of a probability of failure in slope performance in terms of safety. In this context, this paper present research seeks to evaluate slope safety in a probabilistic manner, simulating slopes with varied geometries and soils, also verifying the influence of elevation of the water level position. For this purpose, were performed probabilistic analyzes using First Order Reliability Method (FORM), based on the Limit Equilibrium methods, RASS (deterministic analysis) and RELgen (probabilistic analyzes). Based on the results, it was found that the critical surfaces obtained by the deterministic methods may not coincide with the highest most probability surfaces to fail. This is still verified in surface slope analysis, where inclinations with acceptable safety factors presented probabilities of failure unacceptable. These divergences are attributed to the uncertainties inherent in the system. Therefore, slope stability analyzes based only on the results of deterministic analyzes do not present all the variables present in the project context. Finally, through the results obtained in this research it is p... (Complete abstract click electronic access below) / Mestre

Slope channel systems represent significant but highly variable deep-water stratigraphic features and reservoir targets. Variations in architecture and component facies can take place along strike, depositional dip and stratigraphically. A better understanding of these variations permits improved sedimentological and architectural models. By integrating two outcrops (San Clemente, California and Baja California, Mexico) and one subsurface example (offshore Nile Delta), this study provides an opportunity to investigate cross-channel asymmetry, stratigraphic evolution and variability, vertical facies trends, and controls of slope channel systems. This study demonstrates that cross-channel asymmetry in facies and architecture is a lithology- and scale-independent feature, and preferentially occurs at channel bends and in the upper part of slope channel systems. Facies and architectural asymmetry are generally expressed as amalgamated, coarser-grained deposits displaced to the steeper channel edge (outer bend), and finer-grained deposits dominate towards the gentler channel edge (inner bend). A comparison of the systems exposed in Mexico and buried in the subsurface reveals a similar evolutionary trend, from initial sediment erosion/bypass, through early-stage laterally amalgamated channels, late-stage sinuous channels with levees/terraces, and final abandonment. However, pronounced variations exist in the late stage (e.g., presence or absence of lobes), and abandonment stage (e.g., presence or absence of MTDs plugging and channel avulsion). Additionally, for the first time, this study quantitatively demonstrates that early-stage and late-stage architectural elements are characterized by distinct patterns in preferred vertical facies transitions, based on Markov chain analysis of vertical successions. This study also suggests that both extrabasinal factors (e.g., relative sea-level) induced flow energy cycles and intrabasinal factors (e.g., folding and faulting, MTDs, channel bends) can exert a significant control on the architecture and/or evolution of slope channel systems.

Time-dependent behavior of natural and excavated slopes in sedimentary rocks is a subject that is poorly understood at present but that is now an important consideration in the design, operation, and reclamation of energy-extraction facilities, in part because of the environmental considerations mandated by the Surface Mining Control and Reclamation Act of 1977 (Public Law 95-87). A slide in an abandoned, unreclaimed strip mine northwest of Sheridan, Wyoming, has been analyzed as an example of a long-term slope failure in the region. This slide occurred in early 1975, some 20 years after cessation of mining. This investigation used Spencer's limiting equilibrium method and an elastic-plastic finite element method incorporating the Drucker-Prager yield criterion. This slide was found to fit the model for time-dependent failure proposed by Nelson and Thompson (1977) in which the time to failure is related to Skempton's residual factor. The Nelson-Thompson hypothesis is extended for use with the three-dimensional Drucker-Prager yield criterion. The residual factor (R) may be computed from the factors of safety with respect to peak (F(p)) and residual (Fᵣ) material properties, using either the Mohr-Coulomb or Drucker-Prager criterion, by the relationship R = [(F(p) - 1)/(F(p)-Fᵣ)] At the present time, the Spencer limiting equilibrium analysis is a more usable tool for ordinary slope design than the elastic-plastic finite element analysis because of the speed, simplicity, and ease of including the effects of ground water in the Spencer analysis.

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On September 14, 1981 a major slide was discovered in the upstream slope of San Luis Darn, located about 100 miles southeast of San Francisco, California. The slide occurred at the end of a period of rapid drawdown of the reservoir. Although this was the longest and fastest drawdown in the life of the dam, 180 feet in 120 days, there had been seven previous cycles of drawdown, some nearly as severe as the one that preceded the slide. Field measurements showed the slide was caused by the clayey slopewash material left in the foundation of the dam during construction. Although the slopewash was dry and extremely strong when the embankment was built, it apparently was weakened considerably when submerged beneath the reservoir and its strength was further degraded by cyclic loading effects as the reservoir level was raised and lowered during the 14 years preceding the slide. The objective of this research was to gain a better understanding of the mechanisms of strength loss in the slopewash that resulted in the 1981 slide at San Luis Dam. This was accomplished using laboratory tests on undisturbed samples of slopewash, analyses of seepage through the embankment and foundation, finite element analyses of stresses in the dam during construction and operation of the reservoir, and conventional equilibrium slope stability analyses. The laboratory tests showed that the shear strength of the slopewash decreases very quickly when the desiccated material is wetted. Wetting causes immediate reduction in shear strength to the fully softened value, and there is no lasting effect of consolidation by drying. After wetting the highly desiccated slopewash has the same strength as in the remolded, normally consolidated condition. Tests that simulated cyclic changes in normal stress and shear stress like those during drawdown and refilling of the reservoir showed that further strength loss results from cyclic loading of the slopewash. Cyclic loading at stress levels below the fully softened peak strength result in continual shear displacement, and eventually, when the cumulative horizontal displacement reaches approximately ten inches, the shear strength is reduced to its residual value. / Ph. D.

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published_or_final_version / Applied Geosciences / Master / Master of Science

Thesis (MEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Riprap is commonly used as an erosion protection measure around the world. In some cases, for example when constructing bed arrestors, riprap has to be designed to be stable on steep slopes. The literature shows that the problem of incipient motion is reasonably well understood, but existing hydraulic design methods are found to be largely unreliable. The main objective of this study is to improve the understanding of the different factors affecting incipient motion in order to furnish the prospective design engineer with a reliable method for sizing riprap on steep slopes adequately. Eight existing theories dealing with the threshold of incipient motion are reviewed, of which Liu’s work (1957) seems most promising. Naturally, the required median rock diameter of the riprap is reasonably large (due to the steep slopes), with high particle Reynolds numbers. However, little data is available for these flow conditions. Data collected from 12 large scale laboratory tests carried out for this research indicate that the dimensionless Movability Number is in fact constant for large particle Reynolds numbers. For design purposes, the recommended Movability Number which emerged from this study is 0.18, provided that the steep bed slope is taken into account, and that the theoretical settling velocity is calculated using an accurate drag coefficient and the d90 sieve size. A comparison of the laboratory data with design equations showed that a large variety of results are obtained, which supports the need for this study. Finally, it was shown that a calibrated one dimensional hydrodynamic model can be used by the practicing engineer to extract the hydraulic properties needed for applying Liu’s theory. It was found that the ratio ks/d90 = 0.81 may be applied to estimate the bed roughness for the grading used in this study. / AFRIKAANSE OPSOMMING: Stortklip is ‘n metode wat wêreldwyd gebruik word om erosie te voorkom. In sommige gevalle, byvoorbeeld vir die konstruksie van erosietrappe, moet stortklip teen steil hellings spesifiek ontwerp word om stabiliteit te verseker. Die literatuur beskryf die probleem van aanvanklike beweging redelik goed, maar dit is bevind dat die bestaande ontwerpmetodes grotendeels onbetroubaar is. Die hoofdoelwit van hierdie ondersoek was om die faktore wat beweging van stortklip veroorsaak, beter te verstaan en ‘n betroubare metode te ontwikkel wat ’n ingenieur kan aanwend om stortklipbeskerming wat op steil hellings geplaas word te ontwerp. Agt verskillende metodes wat die begin van beweging beskryf is bestudeer, en dit wil voorkom asof die Liu teorie van 1957 die grootste potensiaal het. As gevolg van die steil hellings wat ondersoek word, is die benodigde klipgroote redelik groot wat weereens die oorsaak is vir ‘n hoë deeltjie Reynolds getal is. In die literatuur kon geen data gevind word vir so ‘n vloeitoestand nie. Daarom is 12 laboratoriumtoetse gedoen en daar is gevind dat die Mobiliteitsgetal redelik konstant is vir groot deeltjie Reynoldsgetalle. Vir onwerpdoeleindes word ‘n Mobiliteitsgetal van 0.18 aanbeveel, met die voorwaarde dat die bodemhelling in ag geneem word, en dat die teoretiese valsnelheid bereken word met die d90 klipgroote en ‘n akkurate sleurkoëffisiënt. Verder is gevind dat die labaratorium data die voorspellings van die bestaande ontwerpvergelykings nie bevredigend pas nie. Dit ondersteun die behoefte vir hierdie studie. Om die bogenoemde bevindings vir praktiese probleme bruikbaar te maak, is daar gewys dat ‘n gekalibreerde een dimensionale hydrodinamiese rekenaarmodel gebruik kan word om die nodige hidrouliese eienskappe te verkry om die Liu teorie toe te pas. Dit is bevind dat die verhouding ks/d90 = 0.81 ‘n goeie benadering vir die hidrouliese ruheid kan voorsien.