Geoscience Reference
In-Depth Information
conducting several analyses and centrifuge tests. Then, this method was applied to Ake-
bono, Ariake, Katsushima, and Ayasegawa sites. In the design procedure decided by the
technical committee, the deformation of pile foundations is estimated by the seismic
deformationmethod,inwhichgrounddisplacementisestimatedfirst,andthenhorizontal
force is applied to piles through soil springs. The ground displacement is estimated by
residual deformation analysis in which the reduction of shear modulus due to lique-
faction is considered. The reduction of the soil springs due to liquefaction is also con-
sidered. Allowable displacement of the top of the pile foundation was defined as twice
the displacement which causes the pile to yield. At the Akebono site, a liquefiable sandy
layer is deposited from the ground surface to a depth of about 10m. Two bridge foun-
dations founded on 18 cast-in place concrete piles are located about 20m behind a sea
wall, as shown in Figure16.11. The sea wall is a sheet-pile wall and is estimated to
be unstable during future earthquakes. Figure16.12 shows the analyzed deformation of
the ground due to liquefaction. The estimated displacement of the surface of the ground
surrounding the bridge foundations was 1.2m. If the surrounding ground moves 1.2m,
Exisisting sheet
pile wall
12.24m
Exisisting sea
wall (sheet pile)
New
retaining
wall
New steel-pipe sheet
pile wall L=29.0m
Exisisting pile
foundation L=59.0m
< Side view >
Exisisting sheet
pile wall
New retaining
wall
< Plane view >
Fig. 16.11. Countermeasure method applied totheTokyo Metropolitan Express
Highway inthe Akebono district
