Geoscience Reference
In-Depth Information
Void of
coarse grains
n
c
n
f
Void of fines
n
c
n
c
-n
c
n
f
CF
c
Solid of fines
1-n
c
n
f
Solid of
coarse grains
1-CF
c
1-n
c
Fig. 8.21. Schematic diagram forcritical fines content
CFc
Table8.2. CriticalfinescontentcalculatedbysimplemodelforRS1andRS3withdifferentrelative
density
D
r
Relative density
Porosity
n
c
Porosity
Criticlefines
D
r
(%)
n
f
content
CFc
(%)
RS1
RS3
Fines
RS1
RS2
0
0.519
0.406
0.642
27.9
19.6
30
0.491
0.363
0.595
28.1
18.8
50
0.471
0.332
0.557
28.3
18.0
70
0.449
0.298
0.510
28.5
17.2
100
0.412
0.238
0.419
28.9
15.4
larger than
Fc
corresponding to the peak values of the maximum density both for RS1
and RS3. It is probably because the actual particle gradations are not so distinctly gap-
gradedandthefinesmatrixstartstooverflowbeforecompletelyfillingthevoidsofcoarse
soils. Nevertheless the value of
Fc
for the peak of the maximum density in Figure 8.14
is evidently smaller for well-graded RS3 than poorly-graded RS1 because
CFc
for RS3
is smaller than RS1. Accordingly, most of the strength decrease tends to occur due to
smaller increase of
Fc
inwell-graded soils(RS3) than inpoorly-graded sand (RS1).
Figure 8.20 clearly indicates that increasing fines tend to decrease liquefaction strength
irrespective of particle gradation. In the current liquefaction potential evaluation, based
on liquefaction case histories, higher liquefaction strength is given to a soil deposit con-
tainingmorefines,ifthepenetrationresistanceisthesame.Ifthesamepenetrationresis-
tancemeansthesamerelativedensityunderthesameoverburden,thepresenttestresults
seem quite contradictory to the current practice, implying that the penetration resistance
willdecreasewithincreasingfinescontentmoredrasticallythantheliquefactionstrength.
Further research for the effect of fines content on penetration resistance and liquefaction
strength is needed (e.g., Kokusho et al., 2005).