Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Shideh Dashti

Second Advisor

Abbie B. Liel

Third Advisor

Wil V. Srubar

Fourth Advisor

Ellen M. Rathje

Fifth Advisor

Scott J. Brandenberg

Abstract

Liquefaction mitigation techniques are often used in the field to alleviate liquefaction hazard to the built environment. However, the current practice of designing mitigation techniques ignores the presence of buildings, and depends solely on satisfying the settlement criteria, and constructability. This design practice is due to lack of understanding of the influence of different mitigation strategies on the performance of soil-foundation-structure systems.

In this dissertation, centrifuge experiments were designed and conducted to investigate soil-mitigation-foundation-structure systems, considering two potentially inelastic structures (3- and 9-story) placed on a layered liquefiable deposit (with and without a silt cap), with three different mitigation strategies: 1) enhanced drainage through prefabricated vertical drains (PVDs); 2) shear reinforcement using in-ground structural walls (SWs); and 3) enhanced drainage and damping, and shear reinforcement provided by an in-ground gravel-rubber panel wall system.

The first set of test results show that PVDs and SWs reduced total foundation settlement compared to the unmitigated case. However, they amplified accelerations on the foundations, which could increase flexural deformations and P-Δ effects, with potentially adverse effects on foundation tilt (particularly for the taller, heavier, more deeply embedded, and weaker 9-story structure). The presence of soil interlayering (due to a silt cap) affected the overall response of unmitigated and PVD-mitigated structures, particularly impacting foundation tilt.

Based on the insights gained from the tests with traditional mitigation techniques, we designed and tested a new mitigation strategy for shallow-founded structures: an in-ground gravel-rubber panel wall (GR) system. This system aims to reduce building settlements and tilts, while isolating the structure from the larger acceleration demands expected in mitigated ground. Test results showed that the GRs could be beneficial, roughly satisfying design objectives for the 3-story structure, but amplified tilt on the 9-story structure. Therefore, additional design considerations and shear reinforcement are required in the panel walls to improve total system response.

The results presented in this dissertation point to the importance of considering the structure’s dynamic and geometric properties, force-deformation behavior, soil interlayering, and the possible increase in shaking intensity level due to different mitigation strategies, when designing traditional or innovative techniques to mitigate consequences of liquefaction.

Share

COinS