Geoscience Reference
In-Depth Information
8.2.2. A subway station in Tokyo (partially quoted from Yokota et al., 2001)
Near Kitasenjyu Station of the Chiyoda subway line in Tokyo, the uplift of an under-
ground tunnel due to liquefaction was a concern. Thus, high pressure jet grouting was
applied through the floor of the tunnel to make soil cement underground lattice walls, as
illustrated in Figure16.10(2). Two effects on liquefaction-induced uplift were expected:
(i) prevention of the movement of liquefied soil from surrounding ground to the bottom
of the tunnel, and (ii)a decrease of shear deformation of thesoil inthe lattice.
9. Remediation methods for existing structures affected by ground flow
9.1. PRINCIPLE OFREMEDIATION
In the Japanese Geotechnical Society, the probabilities of several kinds of countermea-
sures against liquefaction-induced flow were discussed by the “Technical Committee on
Liquefaction-inducedFlowandPermanentDeformationoftheGroundsandEarthStruc-
tures during Earthquakes” from 1995 to 1998. Table16.2 shows the ideas of the coun-
termeasures summarized by the committee (JGS, 1998; Kanatani et al., 2000). There are
threecategoriesofcountermeasuresagainstthedamagetostructuresduetoliquefaction-
associated ground flow. The most reliable measure is to improve the ground in the entire
area to prevent the occurrence of liquefaction. However this measure is uneconomical
and cannot be applied under or near existing structures.
The second measure is to strengthen a sea wall to prevent ground flow, if the ground
behind the sea wall is liquefied. Strengthening the ground with a wall, sand piles or den-
sificationofasmallareaofthegroundalsopreventsordecreasesgroundfloweventhough
liquefactionoccursintheground.Thethirdmeasureistostrengthenstructures,forexam-
ple,strengtheningapilefoundationwithadditionalpiles,topreventdamageeventhough
liquefaction and associated flow of the ground occurs. Among these countermeasures,
several methods have been applied to quay walls and express highways in Tokyo, Kobe,
and Osaka.
9.2. EXAMPLE OF TREATED STRUCTURES
9.2.1. Metropolitan Expressway in Tokyo (partially quoted from Yasuda and
Ogasawara, 2004; Yasuda, 2005a)
OntheMetropolitanExpresswayinTokyo,theBayShoreRouteandseveralotherroutes
run along or cross coasts, canals, and rivers. There was concern that the foundations of
bridgesontheseroadsmightbedamagedbyliquefaction-inducedflow.Thus,atechnical
committeewasorganizedtostudythepossibilityofdamage,appropriatecountermeasures
and design of the measures, from 1995 to 1997, after the Kobe earthquake. In the study,
severalkindsofcountermeasuresagainstliquefaction-inducedflowwerelistedandcom-
pared by focusing on their effectiveness, adaptability, and cost. The installation of steel
pipes to make a preventing wall between bridge foundations and sea walls was selected
because this method is economic. The effectiveness of this method was confirmed by
