The study presents an experimental and numerical study on an unsaturated, non-plastic and poorly graded sand, originated from Fortaleza-CE, Brazil. The numerical analyses used the Finite Element Method (FEM), were performed using the UNSTRUCT software to simulate the curve stress versus strain, considering the effect of suction on soil stiffness. Characterization and determination of the retention curve were performed through filter paper tests, which were used to determine the stress versus strain curve in a double-oedometer test. Suction was considered constant along the entire test. From the numerical analyses done with UNSTRUCT software presented satisfactory results, especially in the presence of suction profiles, that show the variation of suction along of the depth. It can be concluded that higher suction values (and soil stiffness) generate lower settlements.

Resumo. Este trabalho tem como principal meta avaliar a influência da não saturação dos solos na estabilidade dos taludes durante o período de operação em barragens de terra. Para isto, foi realizado um estudo de estabilidade de taludes para a Barragem de Pesqueiro-CE para avaliar a segurança da obra durante o período de operação. Os parâmetros geotécnicos utilizados nas análises foram obtidos a partir da realização de ensaios de laboratório em amostras extraídas no maciço da barragem e da jazida de empréstimo. As condições de poro-pressão na barragem foram obtidas por simulações numérica transientes, simulando a operação da barragem num período de 6 anos. Após a definição da variação das poro-pressões durante o regime operação, foram realizadas as análises de estabilidade de taludes considerando a não saturação do solo por meio da influência da sucção mátrica na resistência ao cisalhamento do solo, e por meio das metodologias tradicionais, as quais a sucção mátrica não é levada em conta na resistência ao cisalhamento dos materiais. Os resultados mostraram que, para o talude de jusante, a estabilidade não ocorre alterações significativas em ambas as metodologias adotadas, devido ao sistema de drenagem interno, diferente do talude de montante, que por conta das grandes alterações de poro-pressões, apresenta grandes variações de estabilidade no período estudado. Avaliando a influência da sucção na estabilidade, é verificado uma diferença média de 13,8% para o talude de jusante e uma diferença de pico de 29,6% para o talude de montante para ambas as metodologias.

This work developed prediction models for maximum dry unit weight (γd,max) and optimum moisture content (OMC) for compacted soils in Ceará, Brazil, ba M Winnie the Pooh sed on index and physical properties. The methodology included data from soils used in the construction of 15 dams in Ceará, with available information regarding laboratory tests of interest. Correlations were developed using non-linear regression, from 169 laboratory results (83 for training and 86 for validating the models), which presented a R2 of 0,763 for MoPesm (prediction model for γd,max) and 0,761 for MoTuo (model for OMC). A posteriori, the same physical indexes used to train and validate MoPesm and MoTuo were used as inputs of other prediction models available in the literature, whose outputs differed considerably from laboratory results for the evaluated soils. MoPesm and MoTuo were able to satisfactorily predict compaction parameters, with outputs close to those obtained in the laboratory for tested soil samples. Their performance justifies their use for predicting compaction parameters in geotechnical structures that use compacted soils when there are financial restraints, short timeframes, or unavailability of test equipment, particularly in early design stages and preliminary studies, before appropriate soil sampling and field investigation can be conducted, thus saving substantial time and financial resources.

The present work intends to demonstrate the advantages of considering transient flow regime in the stability analysis of the upstream slope for the rapid drawdown situation of a homogeneous earth dam. Upstream slope stability evaluations were carried out, considering pore pressure and suction from transient flow analysis while simulating rapid drawdown of the reservoir. The evaluations comprised different geometries of the upstream slope (from 1V:1.1H to 1V:2.5H) and heights varying from 10 m to 50 m, as well as several low permeability materials (SM, SM-SC, SC, ML, ML-CL, CL, MH and CH). In addition, equations relating the safety factor to such slopes or dam height were adjusted to the analysis data, in order to define the minimum slope for a certain dam height or the maximum height for a given upstream slope. The results have shown that, considering the transient flow condition, including suction, within the slope stability analysis of the rapid drawdown situation, increases the safety factor in relation to the simplified analysis that is usually adopted. This also results in much steeper slopes (for a safety factor of 1.1) than the ones recommended by the U.S. Bureau of Reclamation (USBR), suggesting the importance of performing transient flow analysis for rapid drawdown situations and considering its results instability analysis.

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