Environmental Engineering Reference
In-Depth Information
FIGURE 9.26
Stereo-pair of aerial photos showing
slump failure landform
(scale 1:8000). (See also
Figure 2.12,
which shows a
stereo-pair of aerial photos of the general area at a scale of 1:40,000.) (From Hunt, R.E. and Santiago, W.B.,
proceedings of the 1st Congress Brasileiro de Geologia de Engenharia
, Rio de Janeiro, August, Vol. 1, 1976, pp. 79-98.
With permission.)
lateral strains causing the strength along certain planes to be reduced to residual values.
Water entering the mass through open tension cracks and fractures assists in the develop-
ment of failure conditions.
Marine Shale: Forest City Landslide
The Forest City Landslide, located on the banks of the Oahe Reservoir in South Dakota,
includes an area of about 700 acres (Hunt et al., 1993). The hummocky landform, typical of
marine shales and a large head scarp, is shown in the aerial oblique of
Figure 9.32.
Movements toward the reservoir, of the order of several inches or more per year, were caus-
ing distress in a large bridge structure. Investigations, including test borings and incli-
nometer data, identified the main failure surface at depths of the order of 100 ft, extending
upslope to the head scarp, a distance of 2200 ft. The approach roadway embankment was
moving laterally on shallower failure surfaces. A geologic section is given in
Figure 9.33.
