Civil Engineering Reference
In-Depth Information
thickness of soft and liquefiable sediments. This thick deposit of soft soil caused an ampli-
fication of the peak ground acceleration and an increase in the duration of shaking.
3.
Construction of the port:
The area of the port was built almost entirely on fill and
reclaimed land. As previously mentioned, the fill and reclaimed land material often con-
sisted of decomposed granite soils that were loosely dumped into the water. The principal
factor in the damage at the Port of Kobe was attributed to liquefaction, which caused lat-
eral deformation (also known as lateral spreading) of the retaining walls. Figures 3.27 to
3.30 show examples of damage to the port area.
4.
Artificial islands:
On Rokko and Port Islands, retaining walls were constructed by
using caissons, which consisted of concrete box structures, up to 15 m wide and 20 m deep,
with two or more interior cells (Fig. 3.31). The first step was to prepare the seabed by
installing a sand layer. Then the caissons were towed to the site, submerged in position to
form the retaining wall, and the interior cells were backfilled with sand. Once in place, the area
behind the caisson retaining walls was filled in with soil in order to create the artificial islands.
During the Kobe earthquake, a large number of these caisson retaining walls rotated
and slid outward (lateral spreading). Figures 3.32 and 3.33 show examples of damage
caused by the outward movement of the retaining walls. This outward movement of the
retaining walls by as much as 3 m (10 ft) caused lateral displacement and failure of the load-
ing dock cranes, such as shown in Fig. 3.34.
5.
Buildings on deep foundations:
In some cases, the buildings adjacent to the retain-
ing walls had deep foundations consisting of piles or piers. Large differential movement
occurred between the relatively stable buildings having piles or piers and the port retaining
walls, which settled and deformed outward. An example of this condition is shown in
Fig. 3.35.
FIGURE 3.27
Ground cracks caused by lateral retaining wall movement due to liquefaction during the
Kobe earthquake on January 17, 1995. The site is near Nishinomiya Port and consists of reclaimed land.
(
Photograph from the Great Hanshin Bridge Collection, EERC, University of California, Berkeley.
)
