Geoscience Reference
In-Depth Information
Additional
footing
Column
jet grout
Additional piles
High capacity
Micor pile
(2) High capacity micro pile
(1) Additional pile
(3) Soil improvement around
pile foundation
Fig. 16.4. Remediation methods for existing pile foundations
length to prevent erosion. By conducting detailed analyses, it was confirmed that forces
acting on the pileswere within the ultimate bearing capacity.
5.2.2. A bridge (partially quoted from JGS, 2004)
Thecolumnssupportinganotherbridgewerestrengthenedagainstliquefactionwithaddi-
tionalpiles.Highcapacitymicropiles,asshowninFigure16.4(2),wereselected,because
the bridge girders were not high enough to drive piles of normal length. Micropiles of
177.8mm in diameter were driven in a slightly inclined direction to bear some of the
horizontal force.
5.2.3. Elevated bridges in Kobe (partially quoted from Hanshin Express Way, 1997;
TC4, 2001)
Manyelevatedbridgeswithpilefoundationsweredamagedduetoliquefactioncausedby
the1995Hyogoken-nambu(Kobe)earthquake.Someofthedamagedpileswerestrength-
ened by methods to improve the surrounding ground. The column jet grout method was
applied to a pile foundation of the Hanshin Expressway, as shown in Figure16.4(3). For
theelevatedbridgeoftheRokkoLiner,thedeepmixingmethodwasselectedtoimprove
the ground surrounding damaged caisson foundations.
6. Remediation methods for existing embankments
6.1. PRINCIPLE OF REMEDIATION
If the soil of an embankment liquefies, it is necessary to prevent the flow of the liquefied
soil. Lowering the water level in the embankment by installing horizontal drain pipes
may prevent liquefaction. On the contrary, if the soil under an embankment liquefies,
large settlement of the embankment occurs due to horizontal movement of the ground
under the embankment, as schematically shown in Figure16.5. In this case, restricting
the movement by some technique, such as the installation of underground walls at the
toes of the embankment, can reduce the settlement, just as it prevents the settlement of
raft foundations.
6.2. EXAMPLE OF TREATED STRUCTURES
6.2.1. The Tokaido Shinkansen (partially quoted from Nasu, 1984; JGS, 1998)
The Tokaido Shinkansen Railway (Japanese Bullet Train) started business in 1964,
the same year of the 1964 Niigata earthquake. Some sections run over areas where
