Environmental Engineering Reference
In-Depth Information
Analyses are performed to evaluate stable cut angles and sidehill fill stability, and the
necessity for drainage and retention. Consideration must be given to the possibility of a
number of failure forms and locations as shown in
Figure 9.130,
as well as to changing
groundwater and other environmental conditions.
9.5.4
Case Study
Background
A roadway was constructed during the early 1990s beginning on the western coastal plain
of Ecuador, crossing over the Andes Mountains, and terminating after 110 km at the city
of Cuenca. Landslides began at numerous locations where the roadway climbed the steep
mountain slopes, usually 35° or steeper. The general landform along a portion of the
roadway is illustrated on the 3D diagram in
Figure 9.131.
Slope failures increased signifi-
cantly during the El Niño years of 1997 and 1998.
Investigation
Initially, investigation included a number of trips along the roadway during which the
slope failures were photographed and cataloged. Pairs of aerial photos were examined
stereoscopically. Eventually a helicopter fly-over was made and the roadway continuously
photographed. Debris avalanches, occurring on the upslope side of the roadway, were the
most common form of slope failure (
Figure 8.6,
Figure 9.5,
and
Figure 9.132)
.
Over 125 fail-
ure locations were identified. The landslide debris was bulldozed from the roadway onto
the downslope side (Figure 9.132) further destabilizing the slopes and contributing to ero-
sion and choking of streams downslope (see
Section 8.2.2
and
Figure 8.8).
km 40
FIGURE 9.131
Three-dimensional diagram of a portion of roadway over the Andes Mountains in Ecuador. Sidehill failure at
km 62 is shown in
Figure 9.6.
Debris avalanche at km 88 shown in
Figure 9.132.
Large slump slide shown in
