This dissertation presents initial results from geotechnical centrifuge experiments on squat gravity caissons and monopiles under cyclic eccentric loading in soft clay under undrained conditions. These experiments were conducted in the 1-g laboratory at Texas A&M University and the 150g-ton centrifuge at Rensselaer Polytechnic Institute. All tested caissons had a length to diameter aspect ratios of two with four tested in the 1-g laboratory and four caissons tested in the centrifuge. Though this aspect ratio is a bit atypical, it could be a reasonable option for offshore renewable hydrokinetic systems or a component in tripod or tetrapod wind tower foundation systems. 1-g experimental results focus of the effect of caisson interior venting on capacity. Centrifuge experimental results focus on behavior arising from an unrestricted vertical coordinate, allowing self-weight to contribute to combined loading, the impact of depth of rotation on caisson resistance, and the global stiffness and damping ratio of the caissons. With the advent of high accuracy sensors and increased interest in geotechnical centrifuge testing simulating loading within serviceability limits a stronger understanding the strength and orientation of centrifuge gravity relative to the scale model is necessary. This dissertation presents a methodology for determining the 2-Dimensional centrifuge gravity within a model independent of centrifuge type or geometry. This can be used to recompose the gravity field from the direct measurement of single gravity vector, given angular velocity. Finally, the methodology is compared to the mechanics of drum and beam centrifuges to provide physical meaning to coordinate rotation variables. Microelectromechanical systems (MEMS) accelerometers are becoming more prevalent in geotechnical engineering and geotechnical centrifuge modeling. In geotechnical centrifuge experiments these sensors have shown much promise, but still exhibit some limitations. This dissertation proposes a new methodology for the use of single-axis low g, high accuracy, MEMS accelerometers to measure orientation of on object in a geotechnical centrifuge. The inclusion of the measured component of cross-axis in orientation calculations significantly improves measurements of absolute orientation, a 3.8º improvement in this study, and reduces errors in orientation measurement by allowing high accuracy low-g accelerometers to be used in the centrifuge.
|Qualification||Doctor of Philosophy|
|Award date||5 May 2016|
|Publication status||Unpublished - 2016|