Geoscience Reference
In-Depth Information
developed. These techniques can be applied to existing structures. In this paper, these
recenttreatmentmethodsagainstliquefactionwhichcanbeappliedtoexistingstructures,
are introduced.
2. Remediation methods against liquefaction compiled in 1993
(partially quoted from Yasuda, 2005a)
As mentioned above, in 1993, the Japanese Geotechnical Society compiled remediation
methods against liquefaction (JGS, 1998). Table16.1 illustrates the compiled methods.
Thesemethodsareclassifiedintotwocategories:(i)thosethatimprovetheliquefiablesoil
to prevent liquefaction, and (ii) those that strengthen structures to prevent their collapse
if the ground should be liquefied. In the first category, ground is improved to increase
liquefaction strength by the following factors: (1) high density, (2) not-liquefiable grain
size, (3) stable skeleton or (4) low saturation. Other methods to prevent liquefaction are:
(5) immediate dissipation of increased excess pore pressure, (6) reduction of shear stress
byincreasingconfiningpressure,(7)reductionofshearstressbybuildinganunderground
wall.
Appropriate countermeasures in the second category differ by the type of structure. In
the countermeasures shown in Table16.1, the additional pile method has been applied to
bridge foundations, but other methods have been applied to only afew structures.
Among the measures, the sand compaction method has been most widely used because
ofitshighreliability.Intheoriginalmethod,acasingwaspusheddownandpulledupby
avibratinghammer.Therefore,themethodcouldnotbeappliedatsiteswithneighboring
structures because of the strong vibration. However, a new method to push down and
pull up the casings by static rotating force was developed recently. This “non-vibratory
sandcompactionpilemethod”hasbeenappliednearexistingstructures.Ofsolidification
methods,thedeepmixingmethodhasbeenappliedinmanycases,recently.Ofdissipation
andcontrolofporewaterpressuremethods,thegraveldrainmethodhasbeenappliedfor
many sites. These solidification and gravel drain methods can be applied at sites with
neighboring structures because of theirlow noise and vibration.
Recently, several new remediation techniques, which are not listed in Table16.1, have
beendevelopedinJapan.Inthefirstcategory,thecompactiongroutingmethodandseep-
age grouting method have been applied to several structures. In the second category, the
ringed type sheet-pile wall method has been developed. Details of these techniques are
described in the revised version of “Remedial Measures against Soil Liquefaction (JGS,
2004, inJapanese).”
3. Restrictions to be considered in remediation techniques for existing structures
Thoughmanyremediationtechniquesagainstliquefactionhavebeendeveloped,asshown
in Table16.1, several restrictions apply to these techniques when used for existing struc-
tures. Restrictionsto be considered are as follows:
(1) Unique techniques are necessary toimprove the ground under existing structures.
(2) Special machines without noiseand vibration mustbe used.
