Evaluation of Gardiner Dam’s ongoing movement
Jody Scammell
Water Security Agency, Moose Jaw, Saskatchewan, Canada
Jitendra Sharma
Department of Civil Engineering, York University, Toronto, Ontario, Canada
ABSTRACT
Gardiner Dam is an earth embankment located on the South Saskatchewan River approximately 100 km upstream of
Saskatoon, SK. The dam consists of three embankments with a total length of 5000 m, the slopes ranging from 1V:2H to
1V:85H and the maximum embankment height is 64 m above the river bed. The embankment is founded on
approximately 33 m of River Sand, 30 m of marine deposited shale, and unconsolidated sandstone. The foundation
shale was deposited in the late cretaceous is pre-sheared, has slickensides, and has bentonitic seams present
throughout.
Shortly after the start of construction, the River Embankment at Gardiner Dam experienced horizontal downstream
movement along a shear plane in the shale foundation. The continuing deformation of the foundation raises questions
regarding the long-term stability of the structure. A second concern is the effect of continuing deformation on the integrity
of the embankment, ancillary works and the potential maintenance measures required to maintain the works in operating
condition. The mechanism(s) responsible for the ongoing movements are were not fully understood. As such, prediction
of on-going deformation has had only a limited success.
Historic geotechnical instrumentation data was used to identify a potential mechanism of movement within the shale
foundation. The identified potential mechanism can be briefly described as a combination of elastic deformation and
consolidation. As the reservoir level rises, part of the increase in horizontal thrust is transferred to the shale. Since the
shale has a relatively low hydraulic conductivity, a portion of this increase in horizontal pressure is transferred to the
pore-water, resulting in generation of excess pore-water pressures in shale. During the reservoir increase and
subsequent elevated period, a portion of the excess pore-water pressure begins to dissipate. The total movement is then
developed initially from a portion of elastic deformation due to undrained loading as well as from a portion of horizontal
consolidation caused by dissipation of excess pore-water pressure within the shale. The combination of deformation and
consolidation is then measured as a horizontal moment along the observed shear zone.