Evaluation of Gardiner Dam’s Ongoing Movement

Jody Scammell, Jitendrapal Sharma

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Infrastructure

ABSTRACT: Gardiner Dam is an earth embankment located on the South Saskatchewan River approximately 100 km upstream of Saskatoon, SK. The dam has a total length of 5000 m, and has a height of 64 m above the river bed. The embankment is founded on river sand, 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 embankment 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 and serviceability of the ancillary structures. The mechanism(s) responsible for these ongoing movements are not fully understood. As presented in this paper, historic geotechnical instrumentation data was used to identify a potential mechanism of movement within the shale foundation.

RÉSUMÉ: Le barrage Gardiner est un barrage en remblai situé sur la rivière Saskatchewan Sud, à environ 100 km en amont de Saskatoon, en Saskatchewan. Il mesure 5000 m de long et s™élève à 64 m au-dessus du lit fluvial. Le remblai repose sur du sable fluvial, des sédiments de schiste, et du grès meuble. La fondation schisteuse a été déposée à l™époque crétacée et est précisaillée, contient des surfaces de glissement et contient plusieurs couches bentonitiques. Peu après le début de la construction du barrage, le remblai a effectué un mouvement horizontal en aval le long du plan de cisaillement de la fondation schisteuse. La déformation constante de la fondation suscite l™incertitude quant à la stabilité à long terme du barrage et la fonctionnalité des structures connexes. Il n™est pas possible de comprendre complètement le(s) mécanisme(s) responsable(s) de ces mouvements continus. Tel qu™élaboré dans la présente étude, des données historiques obtenues à l™aide d™instruments géotechniques ont servi à établir un mécanisme potentiel du mouvement à même la fondation schisteuse. 1 BACKGROUND Gardiner Dam is located on the South Saskatchewan River approximately 100 km south of Saskatoon, SK as illustrated in Figure: 1. The structure was constructed for the Saskatchewan Provincial Government in the 1960s by the Prairie Farm Rehabilitation Administration (PFRA) and is currently owned and operated by the Water Security Agency. The facility consists of three-zoned earth filled embankments with a total crest length of 4960 m; the Main (River) Embankment; the Plateau Embankment; and, the Coteau Creek Embankment as illustrated on Figure: 2. This evaluation is focused on the River Embankment. The River Embankment will be the main focus of this work has a crest length of 2500 m and a maximum height of 64 m. The foundation conditions beneath the River Embankment consist of alluvial sand underlain by the pre-glacial Bearpaw Formation including the clay shale of the Snakebite member and poorly consolidated sandstone of the Ardkenneth member (Cladwell 1968). The Snakebite member is a massive clay with limited laminations, mid to dark grey, silty, brownish grey weathering, and bentonite seams. Several shear planes exist in the Snakebite shale and are thought to be caused by glacial loading, unloading or thrust (Sauer 1978; PFRA 1980). Figure: 3 illustrates the general geology below the River Embankment. Shortly after the start of construction, the River Embankment experienced downstream movement on a defined shear plane in the Snakebite shale of the 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 and ancillary works and the potential maintenance measures required to maintain the works in operating condition. The mechanism(s) responsible for the ongoing movements are not fully understood. As such, prediction of on-going deformation has had only a limited success. This paper will discuss the process undertaken to improve on the understanding of the ongoing deformation. The historic geotechnical instrumentation data will then be used to identify potential mechanism of movement. Finally an analytical model will be developed and tested against the potential mechanism identified by the historical instrumentation data. 2 EMBANKMENT DEFORMATION The deformation of a water retaining embankment is generally influenced by two major factors: the geotechnical characteristics of the foundation and

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