Influence of Ground Densification with Drainage Control on the Performance of Structures on Liquefiable Ground

Olarte, Juan Carlos

Graduate Thesis Or Dissertation

Influence of Ground Densification with Drainage Control on the Performance of Structures on Liquefiable Ground Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/s4655g781

Abstract

Significant progress has been made in recent years toward a better understanding of liquefaction and its consequences on structures. Several techniques have been developed to reduce the liquefaction hazard. Among these techniques, densification is the most popular in practice, sometimes combined with a form of drainage control. Yet, the influence of ground densification with or without drainage control on the performance of structures and the key mechanisms of soil-structure interaction remains poorly understood. In this study, centrifuge experiments were designed and conducted at the University of Colorado Boulder’s 400 g-ton centrifuge facility to evaluate soil-foundation-structure interaction (SFSI) effects, considering 3- and 9-story structures placed on a layered liquefiable soil deposit. The response of these structures was first evaluated with and without ground densification. Subsequently, a flexible impermeable latex barrier and prefabricated vertical drains (PVDs) were placed around the densified zone, to inhibit or enhance drainage. The results show that ground densification reduces the foundation settlement, but amplifies seismic demands on the superstructure, with potentially drastic consequences if not considered in design. The influence of densification on foundation rotations was shown dependent on the properties of structure and ground motions. Inhibiting flow around the densified area may be useful when confinement limits the pore pressure generation under the structure. This can lead to a reduction in foundation’s permanent rotation and the seismic demand transferred to the superstructure compared to the case involving only densification. In cases when there is substantial excess pore pressures generated under the building, inhibiting flow can amplify the extent of softening, particularly near the edges of the structure, increasing its permanent foundation rotation and demand on the superstructure through rocking. In contrast, enhancing drainage around the densified zone notably reduced permanent foundation settlement and rotation, but amplified foundation accelerations, leading to additional seismic demands on the structure which should be considered in structure’s design. The results presented in this dissertation point to the importance of considering the structure’s dynamic properties and force-deformation behavior, as well as foundation and ground motion properties, when designing mitigation techniques, with the goal of improving the performance of the system holistically.

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