Geoscience Reference
In-Depth Information
behindtheseawall,andthespacebetweentheseawallandthetemporarysheetpilewas
excavated. Then, sand mixed withcement was filled in theditch.
7.2.5. A quay wall in Tokyo (partially quoted from JGS, 1998)
Aquaywallwasconstructedin1969asarevetmentofacanalfacingTokyoBay.Seismic
inspection revealed a loose silty sand layer of 4m in thickness that was susceptible to
liquefaction.Acountermeasureagainstliquefaction,thequaywallwasstrengthenedwith
self-supporting steel pipe piles, as shown in Figure16.7(4). New steel pipe piles with a
length of 28.5m were installed, sandstone fill was placed in front of the pipe piles as
foot protection and thespace between the existingand newly driven piles was filledwith
gravel.
8. Remediation methods for existing buried structures
8.1. PRINCIPLE OFREMEDIATION
Yasudaetal.(1995)conductedseveralshakingtableteststodemonstratethemechanism
of uplift and factors which affect the uplift of buried pipes. In their tests, the movement
of soil grains during the uplift of a model pipe was observed in detail. The movement
was estimated by measuring the displacement of chips of noodles which were installed
between the soil and the front glass of the model container. The excess pore water pres-
sure increased gradually due to shaking. Then, when the excess pore water pressure at
the bottom of the pipe reached the initial overburden pressure, i.e., when liquefaction
occurred, the pipe started to rise gradually. Simultaneously, liquefied soils on both sides
of the pipe moved toward the bottom of the pipe as shown in Figure16.8. It was hypoth-
esized that liquefaction and the movement of the liquefied soil toward the bottom of the
pipe must continue for a long time to induce large uplift. Therefore, the installation of a
pairofundergroundwallsatbothsidesofaburiedstructuremustreducetheupliftofthe
structure.
90cm
Fig. 16.8. Movement of soil particles during uplift of a pipe (Yasuda et al.,1995)
