Civil Engineering Reference
In-Depth Information
they can sever sewer pipelines and other utilities in the failure mass, and they can cause com-
pression or buckling of structures, such as bridges, founded at the toe of the failure mass.
Figure 3.42 shows lateral spreading caused by liquefaction during the Prince William Sound
earthquake in Alaska on March 27, 1964, that damaged a paved parking area.
9.5.2 Empirical Methods
Based on a regression analysis using 60 data sets, Hamada et al. (1986) developed the
following equation:
D
0.75
H
0.5
0.33
(9.5)
where
D
horizontal displacement due to lateral spreading (m)
H
total thickness of the liquefiable layers (m)
slope of the ground surface or the slope at the bottom of the liquefied layer,
whichever is greater, expressed as a percentage
Equation (9.5) should not be used for a level ground site adjacent a riverbank (i.e., a
free face condition), unless the underlying liquefiable layers are tilted. For a level ground
site adjacent a riverbank with horizontal underlying liquefiable layers,
0 and Eq. (9.5)
predicts zero horizontal displacement for this condition. However, during the earthquake,
the riverbank could fail first and then the lateral displacement and ground cracks could
progressively move inland across the flat ground.
Example problem.
A site has a ground surface inclination of 20:1 (horizontal:vertical)
and an underlying sand layer that is 4 m thick that will liquefy during the earthquake. The
liquefiable layer is approximately horizontal. Determine the horizontal displacement using
Eq. (9.5).
Solution:
For a 20:1 (horizontal:vertical) slope, the inclination is 1
20
0.05
5%.
Since the liquefiable layer is approximately horizontal, the ground surface inclination
governs and
5%. The thickness
H
of liquefiable soil is 4 m, and substituting these
values into Eq. (9.5):
0.75
H
0.5
0.33
(0.75)(4
0.5
)(5
0.33
)
2.6 m
D
This is a considerable amount of lateral movement and most roads, utilities, foundations,
etc. would be severely damaged by the lateral spreading.
Another commonly used method for predicting the amount of horizontal ground dis-
placement due to liquefaction-induced lateral spreading is to use the empirical method
developed by Bartlett and Youd (1995), with equations updated by Youd et al. (2002). As
stated in these papers, both U.S. and Japanese case histories of lateral spreading of liquefied
sand were used to develop the displacement equations. Based on the regression analysis,
two different equations were developed: (1) for lateral spreading toward a free face, such
as a riverbank, and (2) for lateral spreading of gently sloping ground where a free face is
absent. See Youd et al. (2002) for the updated equations.
The regression analyses described in this section will usually predict a significant
amount of horizontal ground displacement for the condition of liquefaction at a sloping
ground site. For example, using the previous example problem of a 5% slope, but with
only a 1 ft (0.3 m) thick layer of liquefiable soil, the calculated horizontal movement due
to lateral spreading is 2.3 ft (0.7 m). A steeper slope and/or thicker layer of liquefiable soil
will result in even greater values of horizontal movement due to lateral spreading. Since
