Environmental Engineering Reference
In-Depth Information
Geology
The mountain is the limb of an anticline composed of limestone and shales as shown in
the section in
Figure 9.54a.
Failure was sudden, apparently beginning in bedding planes
in the lower shales (Krahn and Morgenstern, 1976) which are steeply inclined. The slide
scar is shown in Figure 9.54b.
Cause
Terzaghi (1950) postulated that the flow was caused by joint weathering and creeping of
the soft shales, accelerated by coal mining operations along the lower slopes.
9.2.11
Soil and Mud Flows
General
Soil and mud flows generally involve a saturated soil mass moving as a viscous fluid, but
at times can consist of a dry mass. Major causes include earthquakes causing high pore-air
pressures (loess) or high pore-water pressures; the leaching of salts from marine clays
increasing their sensitivity, followed by severe weather conditions; lateral spreading fol-
lowed by a sudden collapse of soil structure; and heavy rainfall on a thawing mass or the
sudden drawdown of a flooded water course.
Flows occur suddenly, without warning, and can affect large areas with disastrous con-
sequences.
Recognition
Occurrence is common in saturated or nearly saturated fine-grained soils, particularly sen-
sitive clays, and occasional in dry loess or sands (sand runs).
Profile before slide
Limestone
Shale
Rupture surface
Slide debris
Anticline
(a)
FIGURE 9.54
Turtle Mountain rock slide, Frank, Alberta in 1903. (a)
Geologic section (From Krahn, J. and Morgenstern, N.R.,
Proceedings of ASCE, Rock Engineering for Foundations and
Slopes
, Vol. 1, 1976, pp. 309-332. With permission.) (b) Photo
of scar (source unknown).
(b)
