Authors: Mark Bancroft¹, Salina Yong¹
Conference: 6th International ITASCA Symposium on Applied Numerical Modeling in Geomechanics
Date: June 3–6, 2024

¹ Knight Piésold Ltd., Vancouver, BC, Canada
 

INTRODUCTION

A currently operating tailings storage facility (TSF) was constructed on foundations consisting of, in de-scending stratigraphical order, a 3 m clay unit, a 5 to 10 m thick permeable gravel unit, a 1.5 m sand and silt unit, and a medium plastic clay unit (Lower Clay) that extends over 100 m in depth to bedrock. The TSF embankment is approximately 20 m tall and was constructed by raising annually. Slope inclinometers were installed at multiple locations along the embankment once construction neared the final crest elevation and during subsequent periodic site investigations. These inclinometers are currently showing constant-rate creep deformations within the Lower Clay.

Creep can occur in three stages. Primary creep occurs when the strain rate decreases with time, secondary creep occurs when the strain rate becomes constant, and tertiary creep occurs when the strain rate begins increasing exponentially resulting in failure known as creep rupture (Lacasse & Berre 2005). The potential for creep rupture can be evaluated by comparing shear stress within the foundations to the upper yield strength, which is defined as the shear strength associated with the minimum strain rate at which creep rupture occurs (Finn & Shead 1973). A FLAC model was constructed to estimate the shear stress distribution within the Lower Clay. The clay was modeled using the Burgers-creep viscoplastic constitutive model, and the FLAC model was calibrated against the slope inclinometer data. The modeled shear stress distribution will be compared to the upper yield strength of the material on completion of the laboratory testing underway to evaluate the potential for creep rupture. This abstract describes the construction of the FLAC model and calibration of the Burgers model viscous properties.

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