Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Sadrekarimi, Abouzar

Abstract

This series of studies explores the liquefaction behaviour of cohesionless mine tailings and a natural sand and examines the effectiveness of a bio-mediated treatment for the mitigation of liquefaction. The first study investigates the flow liquefaction failure of the Fundão tailings dam (2015) by analytically assessing the stability of the breached abutment, accounting for the specific triggering mechanism and subsequent strength loss that led to its collapse. The second study evaluates the static liquefaction behaviour of gold mine tailings and its correlations with shear-wave velocity through an experimental program comprised of direct simple-shear and bender element tests. The last study investigates the static and cyclic liquefaction behaviour of Fraser River sand and assesses the efficiency of a Microbially Induced Calcite Precipitation treatment in improving the sand’s resistance to liquefaction. Overall, liquefaction is shown to produce substantial strength loss, and bio-mediation is proven to successfully mitigate it in the natural sand.

Summary for Lay Audience

Soil liquefaction is a phenomenon in which soils exhibit great loss of strength and subsequently seem to behave and flow like liquids. Wet granular soils such as saturated sands and silts are particularly susceptible to liquefaction and exhibit such a strength loss when loaded without allowing their volume to change. In this series of studies, the liquefied behaviours of granular mine waste materials, known as tailings, and a natural sand are explored. Additionally, the effectiveness of a soil strengthening treatment that relies on a particular metabolic process of certain types of bacteria is evaluated for the reduction of strength-loss caused by liquefaction.

The first study in the series investigates the flow failure of the Fundão tailings dam (2015), reported to have failed as consequence of liquefied tailings. The stability of the failing section of the dam is assessed by accounting for typical site conditions and the specific mechanism believed to have generated liquefaction of the tailings that ultimately led to the dam’s collapse.

The second study evaluates the liquefied behaviour of gold mine tailings when subjected to consistently increasing loading without allowing any changes in volume to occur, in an experimental program comprised of direct simple-shear and bender-element tests. The results obtained are associated with the velocity at which small-displacement shear waves travel through the samples (known as shear-wave velocity), in order to establish trends to estimate strength and determine liquefaction susceptibility from these velocity values.

The third and last study investigates the liquefied behaviour of a natural sand from the Fraser River delta when subjected to consistent and cyclic loads without allowing changes in volume to occur. This study subsequently explores the efficiency of a strengthening treatment involving the by-products of a particular metabolic process of certain types of bacteria in improving the sand’s resistance to strength loss by means of carbonate bonding of the soil particles.

Succinctly, this series provides insights into the nature of soil liquefaction, explores the various loading mechanisms that generate it, applies an innovative analysis method in evaluating dam stability against liquefaction flow failure, and proposes a soil improvement technique for liquefiable natural sands.

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