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Investigation of Softening Instability Phenomena Under Simulated Infinite Slope Conditions in Centrifuge Tilting Table Tests

Wolinsky, Eric
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
36.54%
Element test results reported in the literature under both triaxial and plane strain conditions indicate that loose saturated granular specimens can experience softening instability at stress ratios lower than what might otherwise be expected given the critical state friction angle of the soil. The region of potential softening instability in stress-space is often explained using the framework of the instability line. This phenomenon is particularly relevant to shallow slopes of 1 to 2 m depth. However, the practical realities of sample preparation for triaxial testing make performing tests below 20 to 30 kPa of confining stress exceptionally difficult. In this thesis, the development of a centrifuge tilt-table test device is described which aims to test the behaviour of loose granular slopes under stress paths of increasing slope inclination or increasing pore water pressure. A system of instrumentation including pore pressure transducers, inclinometers, displacement transducers, and high-resolution cameras was designed to monitor the behaviour of the slope model. The development of a system to provide a controlled groundwater level within the slope model proved to be particularly challenging. The results of two competing design concepts are presented for the water boundary condition and discussed. The centrifuge tilt-table is used to compare the physical response of a slope to the behaviour predicted by the infinite slope and softening instability models using scale model centrifuge testing. If softening instability is a rigorous concept...

Centrifuge Modelling of Instability in Granular Soils under Infinite Slope Conditions

Jacobs, EMILY
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
36.58%
Rainfall induced granular flow slides pose a significant risk in many areas of the world. These failures, characterized by the sudden release of material in a fluid-like manner, are the result of static liquefaction occurring in these slopes. The static liquefaction phenomenon has been linked to instability. Instability behaviour is primarily studied under undrained triaxial conditions, and although many instability theories have therefore been defined in this stress space, these have been shown to also extend into plane strain conditions. In order to further investigate this behaviour under these stress conditions, Wolinsky et al. (2013) developed a tilt-table soil box for use in a geotechnical centrifuge to analyze instability in infinite slope soil models. This testing apparatus has been used to simulate instability in plane strain under both dry and saturated soil conditions. Stress-controlled experiments were performed on dry infinite slope soil models to investigate the effects of both void ratio and effective stress on instability behaviour. By performing these tests dry, this test apparatus provides the ability to decouple the triggers of instability from the corresponding response in pore pressure and the consequences. The results of this testing confirmed that the instability line angle is a function of both void ratio and effective stress. As the void ratio decreases and effective stress in the soil model increases...