Thesis Format
Monograph
Degree
Master of Engineering Science
Program
Civil and Environmental Engineering
Supervisor
Sadrekarimi, Abouzar
Abstract
Static liquefaction has caused the failure of many large, earthen structures, including the recent Feijão and Fundão tailings dam failures in Brazil. This thesis focused on developing an energy-based static liquefaction triggering method.
The energy capacity of various soils was calculated from triaxial and direct simple shear data. Relationships between energy capacity (Ec) and void ratio, state parameter, fines content, gravel content, shear wave velocity, normalized cone tip resistance, and preconsolidation stress were established. The effects of preparation method, shearing mode, stress path, principal stress direction, and intermediate principal stress were also investigated. Finite element models of the Feijão and Fundão dams were created to calculate the energy present during failure (Ea). Triggering was identified by comparing Ec and Ea. From these analyses, the displacement and time until instability of the two dams was further calculated.
Summary for Lay Audience
Certain soils used in the construction of large earthen structures can be subject to a phenomenon called liquefaction, which is when a soil rapidly loses most of its strength. There are two main types of liquefaction: cyclic and static. Cyclic liquefaction is typically caused by earthquakes, while static liquefaction can be caused by a wider variety of processes, making it more difficult to identify. In the past, static liquefaction was thought to be less hazardous than cyclic liquefaction. Recent research has refuted that idea, finding that many catastrophic failures of man-made structures was due to static liquefaction. Most recently, two major mine-waste dams in Brazil failed due to static liquefaction. These two events killing a combined 289 people, as well as polluting the nearby river systems used by thousands for drinking water. This thesis is focused on developing a method to determine static liquefaction triggering with the goal of promoting better design and maintenance of earthen structures.
The industry’s most common method to determine static liquefaction risk is to use field investigations. Field tests are quick and relatively inexpensive but rely heavily on engineering judgement to be accurately used. This means that the findings of these investigations can vary significantly depending on who interprets the data.
In this thesis, an energy method is developed. Energy measurements were determined from laboratory data and are less subject to interpretation. This method has been accurately applied to cyclic liquefaction but has not yet been applied to static liquefaction.
The energy capacity of a soil, (i.e., how much energy a soil can handle before liquefying) was calculated for a wide range of soils using laboratory data. Computer models of the two Brazilian dams were created to determine the energy present during failure. If the energy present during failure was greater than the capacity, the soil would liquefy.
This method was able to accurately find liquefiable soil, as well as identify key areas of the dams that led to the failures. Knowing where these areas are can lead to better rehabilitation of earthen structures and prevent more failures like those in Brazil.
Recommended Citation
O'Sullivan, Kaitlyn, "An Energy-Based Method For Static Liquefaction Assessment" (2024). Electronic Thesis and Dissertation Repository. 9950.
https://ir.lib.uwo.ca/etd/9950
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