Environmental Engineering Reference
In-Depth Information
Figure 12.27.
Magnitude scaling factors (MSF). Earthquake use “range of recommended MSF from
NCEER workshop” for M
7.5 (Youd et al., 2001; from Youd
and Noble, 1997, reproduced with permission of ASCE).
7.5; and Idriss for M
It should be noted that there are no guidelines given in Youd et al. (2001) regarding an
acceptable factor of safety against cyclic liquefaction using Equation 12.24.
12.4.3.8
Corrections for high overburden stresses, static shear stresses and age
of deposits
The method of assessment of liquefaction potential described in Sections 12.4.3.2 to
12.4.3.7 is for horizontal or gently sloping ground and for depths less than about 15 m.
For assessments of liquefaction for embankment dams, the confining stresses may be
higher than this and the dam will impose static shear stresses, which may alter the lique-
faction potential.
Seed (1983) first proposed the factors K
to allow for the high overburden stresses
and static shear stress respectively. They are applied by extending equation 12.24 to:
and K
(12.25)
FS
(CRR
/CSR).MSF. K
.
K
7.5
K
and K
can be estimated as follows (Youd et al., 2001):
(a)
Overburden stress factor K
100 kPa in
clean and silty sands, and sandy gravels/gravelly sands can be estimated from
Figure
12.28
.
Note that the vertical stress is normalised to atmospheric pressure, so
The overburden stress factor K
for
vo
vo
3.
It should be noted that there is considerable scatter in the input data to derive these
curves. They have been described as “minimal, or conservative estimates” by Hynes
and Olsen (1999) and Youd et al. (2001), but considerable care should be taken in
their application.
(b)
Sloping ground correction factor K
300 kPa
The NCEER workshop participants concluded
that “although curves relating K
to
have been published (Harder and Boulanger,
