Environmental Engineering Reference
In-Depth Information
3.
The piezometric head reached an unprecedented value during the rainstorm.
Terzaghi was hesitant to accept this as the only cause, since he considered it
unlikely that in the entire geologic history of the region, there had not been a
more severe storm. Therefore, he concluded that the slide resulted from two or
more changing conditions.
Gros Ventre, Wyoming
On June 23, 1925, following heavy rains and melting snow, approximately 50 million yd
3
slid in a few minutes down the mountainside along the Gros Ventre River near Grand
Teton National Park in Wyoming. The debris formed a natural dam as high as 250 ft
which blocked the river, and resulted in a lake 3 mi long. Almost 2 years later, in May
1927, water from heavy rains and melting snow filled the reservoir, over-topped the nat-
ural dam, eroded a large channel, and released flood waters which resulted in a number
of deaths.
The slide scar which is still evident in 1977, 52 years later, is illustrated in Figure 9.17. A
geologic section is given in
Figure 9.18.
Failure occurred along clay layers in the carbona-
ceous Amsden formation, dipping downslope. It appears that water entered the joints and
pores of the Tensleep sandstone saturated the clay seams, and reduced or eliminated the
normal stresses.
Vaiont, Italy
On October 9, 1963, the worst dam disaster in history occurred when more than 300 mil-
lion m
3
of rock slid into the reservoir formed by the world's highest thin-arch concrete
dam causing a tremendous flood which overtopped the dam and flowed into the Piave
River valley, taking some 2600 lives. The slide involved an area on the south side of the
valley roughly 2.3 km in width and 1.3 km in length, as shown in
Figure 9.19.
The natural
slope was of the order of 20 to 30°.
A geologic section is given in
Figure 9.20.
The valley had formed in the trough of a syn-
cline, and the beds forming the limbs dipped downslope at inclinations a few degrees
steeper than the slope. The south slope consisted of Jurassic sedimentary rocks, primarily
limestones and marls occasionally interbedded with clay seams (bentonite clay at residual
strength; Patton, F. D. and Hendron, A. J., unpublished). Tectonic activity had caused
regional folding, faulting, and fracturing of strata, and some of the tectonic stresses
Spur of
Sheep mt.
S
A
About 1½ miles
N
Lake level
C
FIGURE 9.18
Section showing geologic conditions after the Gros Ventre landslide. The landslide dammed the Gros Ventre
River. (From Alden, W.C., in
Focus on Environmental Geology
, Tank, R., Ed., Oxford University Press, New York
(1973), 1928, pp. 146-153. With permission.)
