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Automated monitoring and inverse analysis of a deep excavation in Seattle

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Performance monitoring of deep excavations typically includes slope inclinometers, optical surveying of soil deformation, tiltmeters and strain gages. Current monitoring data collection and processing requires time consuming site visits and manual data reduction by project engineers. Development of robotic and remote access geotechnical instrumentation conceptually allows processed data to be made available to project engineers and contractors in “real time.” Deep excavation design methods usually employ empirical methods and 2- dimensional (plane strain) finite element analysis, based on soil characteristics determined by in-situ and laboratory tests. Inaccurate predictions are often produced when the soil input parameters are not correctly evaluated and when changes in soil stress, due to ancillary activities, are not taken into account. A number of case histories and numerical analysis have also demonstrated that deep excavation deflections are greatly influenced by excavation sequence and 3-dimensional corner restraint (Finno et al. 2007). Inverse analysis methods can be implemented in finite element analyses for deep excavations support design to help minimize uncertainties associated with the soil constitutive model parameters. The inverse problem employs iterative algorithms to update selected soil parameters based on the observed soil response and support system performance in early excavation stages. The updated soil parameters are applied to iii simulations of future excavation stages to provide better soil response predictions. Effective use of inverse analysis in finite element models requires timely collection of soil response and excavation support system data to ensure that support design may be updated, if needed, without causing construction delays. This thesis focuses on the installation and performance of an automated surveying system, a relatively new and still developing monitoring technique, at the construction of the Olive 8 Towers in Seattle, WA. It summarizes the philosophy behind the real time instrumentation and shows how the total station data can complement the conventional inclinometer data. In addition, it is illustrated how soil stress changes due to ancillary activities prior to the excavation and careful design can be used to great effect in finite element simulations. Lastly, the observed responses from the inclinometers were used for inverse analysis to find parameters that resulted in a good agreement with observed data and to evaluate whether the soil stiffness input parameters had been accurately defined in the design stage of the project

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  • 08/14/2017
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