Environmental Engineering Reference
In-Depth Information
FIGURE 9.117
Shotcrete applied to retain loose blocks of granite gneiss in cut. Untreated rock exposed in lower right (Rio de
Janeiro).
Gravity walls
provide slope retention by either their weight alone, or their weight com-
bined with the weight of a soil mass acting on a portion of their base or by the weight of
a composite system. They are free to move at the top thereby mobilizing active earth pres-
sure. Included are rock-filled buttresses, gabion walls, crib walls, reinforced earth walls,
concrete gravity walls, cantilever walls, and counterfort walls. A series of reinforced earth
walls with a combined height of 100 ft is shown in
Figure 9.126.
Concrete walls are becom-
ing relatively uncommon due to costs, construction time, and the fact that the slope is
unsupported during construction.
Gebney and McKittrick (1975) report on a complex system of gravity walls installed to
correct a debris slide along Highway 39, Los Angeles County, California. The recon-
structed roadway was supported on a reinforced earth wall in turn supported by an
embankment and a buttress at the toe of the 360-ft-high slope. Horizontal and longitudi-
nal drains were installed to relieve hydrostatic pressures in that part of the slide debris
which was not totally removed.
Nongravity walls
are restrained at the top and not free to move. They include basement
walls, some bridge abutments, and anchored concrete curtain walls.
Anchored concrete cur-
tain walls
, such as the one illustrated in
Figure 9.127,
can be constructed to substantial
heights and have a very high retention capacity. They are constructed from the top down
by excavation of a series of benches into the slope and formation of a section of wall,
retained by anchors, in each bench along the slope. Since the slope is thus retained com-
pletely during the wall construction, the system is particularly suited to potentially unsta-
ble or unstable slopes. An example of an anchored curtain wall retaining a side-hill fill is
shown in
Figure 9.128.
A variation of the anchored curtain wall consists of anchored pre-
molded concrete panels. The advantage of the system is that the wall conforms readily to
the slope configuration, as shown in
Figure 9.129.
An alternate “top-down” procedure, common to the United States, is to install anchored
(tiebacks) soldier piles (
Figure 9.123)
.
As the excavation proceeds, breasting boards are
installed in the soldier pile flanges to support the slope.
