manifested at the ground surface as settlement. An
and for sloping ground conditions:
approach to estimate the magnitude of such ground
settlement that is analogous to the simplified empirical
LOG(DH+0.01) = - 15.787 + 1.178 M
procedure for liquefaction potential evaluation (i.e.,
-0.927 LOG R - 0.013 R + 0.429 LOG S
using SPT blowcount data and cyclic stress ratio) has
+ 0.348 LOG T15 + 4.527 LOG (100-F15)
been presented by Tokimatsu and Seed (1987) and is
- 0.922 D5015
suggested herein to the user. The relationships
presented by Tokimatsu and Seed (1987) are shown on
in which:
Figure F-13. An example illustrating the estimation of
DH
=
Displacement (m)
liquefaction-related ground settlement using the
M
=
Earthquake moment magnitude
Tokimatsu and Seed (1987) procedure is provided in
R
=
Horizontal distance from the seismic
Appendix G. Relationships presented by Ishihara and
energy source, (km).
Yoshimine (1992) are also available for assessing
settlement.
W
=
100 x (height (H) of the free face /
distance (L) from the free face).
(9) Consequences of liquefaction -- bearing
S
=
Ground slope (%).
capacity reduction. Shaking-induced strength
T15
=
Cumulative thickness of saturated
reductions in liquefiable materials that are associated
granular layers with (N1)60 < 15, (m).
with the generation and accumulation of excess pore
F15
=
Average fines content of saturated
water pressure can have effects on the support capacity
granular layers included in T15, (%).
of foundation elements. For spread-type footings, these
D5015 =
Average mean grain size in layers
effects may be substantial where the groundwater and
included in T15, (mm).
liquefiable materials are situated at shallow depths
relative to the size of the footing and when liquefaction
(b) This set of relationships is considered to be
or high levels of excess pore water pressure occur (i.e.,
adequate for most applications to obtain an order of
when the factor of safety against liquefaction is less
magnitude (i.e., generally within a factor of 2) of the
than about 1.5; see, for example Figure 27 of Marcuson
et al., 1990). Figure F-14 illustrates the relative effects
lateral spreading hazard for a site. More site-specific
that high excess pore water pressure or liquefaction
relationships may be developed based on slope stability
may have on the calculated ultimate bearing capacity of
and deformation analysis for lateral spreading
a spread footing. The effects illustrated in Figure F-14
conditions using undrained residual strengths for
were developed considering representative density and
liquefied sand (Seed and Harder, 1990; Stark and
strength properties for non-liquefied soil (i.e., friction
Mesri, 1992) along with simplified Newmark-type
angle) and liquefied soil (i.e., undrained residual
(1965) and Makdisi and Seed (1978) displacement
strength [e.g., Seed and Harder, 1990; Stark and Mesri,
approaches, or using more detailed displacement
1992]), the Marcuson et al. (1990) relationship
analysis approaches.
between excess pore water pressure and factor of safety
against liquefaction, and static ultimate bearing
(7) Consequences of liquefaction -- flow slides.
capacity formulations for layered systems (e.g.,
Flow slides generally occur in liquefied materials
Meyerhof, 1974; Hanna and Meyerhof, 1980; Hanna,
located on steeper slopes and may involve ground
1981). Meyerhof (1974) and Hanna and Meyerhof
movements of hundreds of meters. As a result, flow
(1980) address footings in sand overlying clay, which
slides can be the most catastrophic of the liquefaction-
can be used for evaluation of a liquefaction condition,
treating the liquefied material as a clay with strength
related ground-failure phenomena. Fortunately, flow
characterized by undrained residual strength, whereas
slides are much less common occurrences than lateral
Hanna (1981) addresses footings in strong sand
spreads. Whereas lateral spreading requires
overlying weak sand, which can be used for either
earthquake inertia forces to create instability for
liquefaction or high excess pore pressure.
movement to occur, flow movements occur when the
gravitational forces acting on a ground slope exceed the
strength of the liquefied materials within the slope.
(8) Consequences of liquefaction -- settlement.
With time following the occurrence of liquefaction, the
excess pore water pressures built up in the soil will
dissipate, drainage will occur, and consolidation or
compaction of the soil will occur that will be
F-26
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