SIMULATION OF CREEP DEFORMATION IN THE FOUNDATION OF TAR-ISLAND DYKE

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.