Seismic Response of Shallow Underground Structures in Dense Urban Environments

Gillis, Kenneth Miles

Graduate Thesis Or Dissertation

Seismic Response of Shallow Underground Structures in Dense Urban Environments Öffentlichkeit Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/zs25x866v

Abstract

Shallow underground structures used for public transportation are a key component of sustainable cities. In dense urban environments, underground structures are often built near tall buildings. Although such buildings have the potential to alter ground motions in their vicinity and transmit significant forces to adjacent underground structures during earthquakes, these impacts are not well understood. Centrifuge tests were performed to evaluate seismic interactions between an underground structure, soil, and an adjacent mid- to high-rise building. The seismic response of a braced, temporary excavation and a permanent, cut-and-cover box structure in medium dense, dry sand is measured independently first and then when adjacent to mid and highrise buildings. The data from these tests serve two purposes: first, to better understand seismic soil-structure-underground structure-interaction (SSUSI), and second, to calibrate and improve numerical models. In each centrifuge experiment, the seismic performance of the underground structure was investigated in terms of key design parameters, such as seismic lateral earth pressures, racking displacements, and bending moments using tactile pressure sensors, linear potentiometers, accelerometers, and strain gauges. Centrifuge measurements indicate that both tunnel and excavation racking versus flexibility ratios followed the expected patterns when compared to the available design procedures for an isolated underground structure (e.g., NCHRP 611). The experimental results also indicate that the presence of an adjacent mid to highrise building slightly reduces racking displacements of the underground structure, but increases seismic lateral earth pressures. Bending moments along the excavation walls and axial forces on the struts are also shown to notably increase with the presence of an adjacent tall building. The dynamic lateral thrust acting on the sides of the underground structures is shown to roughly follow the adjacent building’s base shear in amplitude and frequency content. Based on the observed results, mechanisms of interaction among the tall building, soil, and an adjacent permanent or temporary underground structure are explored in terms of: 1) the tall building’s inertial forces, 2) the foundation’s kinematic constraints, and 3) the building’s added confinement.

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