Analysis of foundation deformations beneath the Syncrude tailings dyke

Abstract

The paper presents the results obtained in the finite element simulation of 8 years of construction of a section of Syncrude's tailings dyke, which is located in northern Alberta and has been used to store oil sand mining waste. The site investigation for the construction of this dyke indicated that a region of the foundation contained a presheared, overconsolidated clay shale lying practically horizontal at about 20 m depth. Significant horizontal displacements have occurred along this layer. The section analyzed in this work is the one which showed the largest horizontal movements in the foundation. High pore pressures have been measured along this section, and the lateral displacements measured in the foundation have reached values over 25 cm. The major purposes of the finite element analyses were to identify the factors that have significantly influenced the deformation mechanisms and to determine a combination of parameters, within the acceptable range of values for each material, that would reproduce satisfactorily the field observations. Linear, nonlinear, and effective stresses analyses were carried out. The total stress analyses underestimated the displacements measured in the field very significantly. The displacements calculated by the effective stress analyses are in very good agreement with the measured values, and the combination of parameters necessary to reach those results are within the acceptable range of variability for each material involved, based on laboratory test results. The interpolation of the pore pressures based on the piezometer measurements and their incorporation into the analyses as known quantities at each stage of the loading process was found to be relatively simple and efficient, causing a substantial improvement of the results compared with the total stress analyses. Key words : tailing dyke, deformation analysis, shear zone, effective stress modelling, history matching.