SEEPAGE
INDUCED SLOPE FAILURES ON SANDBARS IN GRAND CANYON
by
Muniram Budhu, M. ASCE and Roger Gobin
ABSTRACT:
The effect of fluctuating discharge from Glen Canyon Dam on downstream sandbars
is of significant concern to dam operators, environmentalists and the public.
In this contribution, the observations of seepage related erosion caused
by fluctuations in dam discharge are presented. A finite element model embracing
Biot's coupled stress - pore water pressure theory is used to study seepage
induced slope failures of sandbars in Grand Canyon. In addition, a simple
model based on seepage parallel to slope in an infinite, homogeneous, cohesionless
soil was used to determine the limiting stable seepage slope. In this paper,
it is shown that this limiting stable seepage slope becomes a predefined
failure plane. Sand deposited above this stable seepage slope will eventually
fail along the predefined plane from gravitational forces, high pore water
pressure and seepage forces. Field data from an instrumented sandbar in
Grand Canyon subjected to the fluctuating discharge from Glen Canyon Dam
are compared with the predictions from the simple model, the finite element
model and conventional slope stability analyses.