Geoscience Reference
In-Depth Information
inclined towards the bay. This layer was compacted by the compaction grouting method,
which can be applied inside a room as shown in Figure16.2(2). Bore holes were drilled
and cement mortar was pushed intothe holes todensify the liquefiable layer.
4.2.4. An oil tank in Kawasaki (partially quoted from Nikkei Construction, 2005)
In Japan, liquefaction was taken into consideration in the design code for oil tanks in
1978. Old tanks constructed before then were not treated against liquefaction. In 1994,
the design code was revised to treat the existing old tanks against liquefaction. About
8000 old tanks had to be treated against liquefaction. In Kawasaki City, an old tank was
treated by the injection method. The capacity of the tank was 4843kl. The depth of the
liquefiablelayerwasabout10m.AsshowninFigure16.2(3),thegroundjustoutsidethe
tankwasexcavated1.3mdeep.Theninclinedboreholesweredrilledfromthedigintothe
ground under the tank. Then, multi-permeation grouting was injected through the drilled
holes. Silica type grouting material with durability and high permeability was injected
to make improvement balls with diameters of 2m. In total 139 improvement balls were
constructed under the tank.
4.2.5. An oil tank (partially quoted from Sawauchi et al., 1992)
Another old tank was treated by the sheet-pile-ring method. A steel sheet pile was
installed around the tank, and the top of the wall was connected to foundation gravel
with a concrete ringas shown in Figure16.2(4).
4.2.6. A timber house
A timber house settled and tilted due to liquefaction during the 2004 Tokachi-oki earth-
quake (Yasuda et al., 2004). After the earthquake, piles were installed just outside the
houseandthepileheadswereconnectedwithconcretebeamsextendedfromthefooting,
as shown in Figure16.2(5).
4.3. OTHERRELATED STUDIES
The effectiveness of several kinds of countermeasures for existing power transmission
towers with four footings was studied by centrifuge tests and analyses (Yasuda et al.,
2001).Intheanalyses,acomputerprogram“ALID(Yasudaetal.,1999)”wasused.Five
cases withand without countermeasures were tested and analyzed:
Case 1: without countermeasure,
Case 2: connecting tops of four footings withaconcrete slab,
Case 3: connecting tops of four footings with a concrete slab, and replacing the ground
under theslabwithgravel,
Case4:connectingtopsoffourfootingswithaconcreteslab,andsurroundingthemwith
sheet piles, and
Case 5: connecting tops of four footings with a concrete slab, and improving the ground
under the footings by densification method.
