FOUNDATION PERFORMANCE OF GARDINER DAM

Gardiner Dam is founded on a highly overconsolidated clay shale that had a profound influence on embankment design and performance. The shale contains preconstruction shear zones whose specific location, extent, and strength characteristics were virtually impossible to determine from test samples and soil logs. Analyses of slumped valley slopes and of shallow excavation slopes that moved during early stages of construction overestimated the strength of dormant shear zones that were activated during subsequent embankment construction. Major design modifications consisting of extensive slope flattening and toe-berm loading were undertaken to compensate for the weakness of the shear zones. About 2 m of foundation settlement and over 2 m of lateral displacement occurred under the central section of the 64 m high embankment during construction, but virtually none happened at the toe. Annual post construction increments of lateral displacement are related mainly to the yearly cyclic reservoir load. Refs.