Environmental Engineering Reference
In-Depth Information
100
5
80
4
1
3
60
40
2
20
Approximate bounds of fills susceptible to
static liquefaction and flow sliding
0
0.001
0.01
0.1
1
10
100
Clay
Gravel
Silt
Sand
Particle size (mm)
1- Coarse grained coal mine waste (Dawson et al., 1998; Taylor, 1984; Bishop et al., 1969; Hutchinson, 1986)
2- Loose silty sand fills, Hong Kong (upper and lower quartile of pre 1977 fills (HKIE, 1998))
3- Hydraulically placed mine tailings and fills in dam embankments (various published sources)
4- Sensitive clays (indicative limits from: Lefebvre, 1996; Bentley & Smalley, 1984; Mitchell & Markell, 1974; Hutchinson, 1961,1965)
5- Sub-aqueous slopes, natural and fill slopes (Koppejan et al., 1948; Kramer, 1988; Sladen & Hewitt 1989; Comforth et al., 1974)
Figure 12.17.
Particle size gradation of soils susceptible to flow liquefaction under static and earth-
quake loading (Hunter and Fell, 2003a,b).
Collins and Tjoumas (2003) point out that the original Wang (1979, 1981) criteria were
somewhat different, being that soils which satisfied the following criteria may liquefy:
1. w
c
0.9w
L
,
where w
c
is water content, w
L
is liquid limit;
2. I
L
0.75,
where I
L
is Liquidity index, (w
c
- w
P
)/I
p
;
3. q
u
50-70 kN/m
2
, where q
u
is unconfined compressive strength;
4. SPT N
4;
5. Sensitivity S
t
4.
They also point out that the Seed and Idriss (1982) type criteria should only apply to
shallow (less than 5 m) soils and, at higher stresses, the original criteria may be more mean-
ingful. They quote experience from Saluda dam where silty (ML) and sandy (SM) soils out-
side the criteria were shown to be liquefiable in laboratory tests. They recommend the
criteria not be applied to non-plastic ML or SM soils, and suggest that such soils, up to a
plasticity index of 7, may be susceptible to liquefaction.
Youd et al. (2001), quoting Robertson and Wride (1998) suggest additional criteria if
cone penetration tests are being used.
From the above data it is concluded that:
(a) Soils within the boundaries for flow liquefaction in Figure 12.17 are susceptible to
flow liquefaction;
(b) Finer soils, particularly mine tailings, which may have clay size particles which are not
clay minerals, and dredged fills may also be subject to liquefaction;
(c) Soils which meet all of the following criteria may be susceptible to liquefaction:
- The “clay” content (particles smaller than 0.005 mm) is
15% by weight;
- The liquid limit is
35%;
- The natural moisture content is
0.9 times the liquid limit.
(d) ML and SM soils, which have a plasticity index less than 7%, may be susceptible to
liquefaction, even if not all criteria in (c) are met;
