Tar Island Dyke is a 92 m tailing dyke for retaining oil sand tailings
and has been operated by Suncor in Fort McMurray, Alberta. Constructi
on of the dyke began in the mid-1960's adjacent to the Athabasca river
. The foundation of the dyke consists of a layer of interbedded silts
and clay overlying a basal sand stratum. Stresses imposed by the dyke
on the foundation clay have been causing continuing movement of the st
ructure over 30 years. Movements of the dyke have been monitored for o
ver 25 years and show significant creep deformation of over 1 m in the
foundation clay. Pore pressure in the clay was monitored, with little
pore pressure change during this period. Therefore the movement was m
ostly due to creep rather than consolidation. The unique feature of th
is case is that the loading due to the dyke has been essentially const
ant for over 15 years but movement has continued. An effective stress
model for creep is adopted to simulate the construction of the Tar Isl
and Dyke. The model is based on critical state soil mechanics and uses
secondary consolidation and the Taylor Singh-Mitchell creep relations
hips. The model is able to capture the movement of the dyke and its fo
undation, and good agreement is obtained between the calculated and me
asured deformations. A sensitivity study has been carried out to study
the effect of varying the creep parameters on the results of the anal
ysis.