Orencio Monje Vilar, sem a colaboração de quem fatalmente não teria sido possível realizar esta pesquisa. Pela colaboração, pela amizade, pelo empenho, pelo constante estímulo e pela paciência na realização deste trabalho, o meu muito obrigado. A todos os professores do Departamento de Geotecnia da Escola de Engenharia de São Carlos (EESC) pelos conhecimentos transmitidos e pela amizade. Ao coordenador do Curso de Pós-Graduação em Geotecnia Lázaro Valentim Zuquette, por sua dedicação aos assuntos da pós-graduação e por sempre estar disposto a ajudar. Aos técnicos do Departamento de Geotecnia da EESC-USP, em especial a José Luís e Oscar. A todos os colegas de pós-graduação, pela amizade e pelos momentos de descontração. A CAPES pelo apoio financeiro.
This paper deals with the performance of a stress and suction-controlled cubical triaxial device developed to test 6-cm cubical soil specimens in saturated and unsaturated conditions. In saturated tests, saturation is achieved by back-pressure while matric suction during unsaturated tests is imposed to the specimen assuming valid the axis-translation technique. The paper describes details of the new device, the testing methodology, as well as presents a series of drained conventional triaxial compression tests on a young residual soil from gneiss performed with the new equipment. The developed apparatus works properly and is adequate to perform tests at different stress-paths that can be helpful to obtain soil parameters needed in the development or improvement of constitutive models for soils. Test results compare well with results from conventional triaxial tests and have showed that suction increased the initial stiffness and the shear strength of the soil, which is commanded by an increase of the cohesion intercept, since the friction angle remained approximately constant.
An alternative methodology for direct determination of the soil-water retention curve (SWRC) and evaluation the hydraulic conductivity of the unsaturated soil was developed using a commercially available small centrifuge with a swinging type rotor assembly without in-flight instrumentation. The testing procedure consists of spinning up four initially saturated soil specimens until constant water content is achieved for a given angular speed. The soil – suction relationship is determined by relating the respective water content to the suction magnitude induced by the ceramic plate at the specimen’s base. The hydraulic conductivity of the unsaturated soil is estimated by dividing the cumulative flow rate measured at each angular speed by the respective hydraulic gradient applied at specimen’s middle height. This methodology was applied for evaluating the SWRC of a residual gneissic soil profile using both, undisturbed and remolded soil specimens. The results show good agreement to other well established methodologies such as filter-paper method, porous plate funnel and suction plate extractor. The determined unsaturated hydraulic conductivities magnitudes were compared to the theoretical predicted values given by the Mualem – van Genuchten model (van Genuchten, 1980) indicating good agreement. Overall, it can be concluded that the methodology proposed ensures good agreement in determining the SWRC and the hydraulic conductivity of studied soils.
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