G-4.
Example 4 Landslide Hazard Screening
This example presents the steps involved in screening a
site for potential earthquake-induced landsliding
hazards. The example problem is illustrated in Figure
G-13.
a.
Review of available information
(1) Site development and soil conditions. A
barracks building is located 20 feet (6.1 m) back from
the crest of a 40 feet (12 m) high slope (Figure G-13).
The ratio of the slope width to the slope height is
approximately 1.5:1. The building is to be supported
on a shallow foundation system. Soil conditions at the
site consist of clay with a uniform undrained shear
strength (cohesion) of approximately 1150 psf (55.2
kPa) and a unit weight of 115 pcf (18.0 kN/m3).
Bedrock is located approximately 60 feet (18 m) below
the building and groundwater is not present at the site.
(2) Historic earthquake effects and postulated
earthquake parameters. This site has been shaken by
several moderate earthquakes. However, no known
historic information indicates that earthquake-induced
landsliding occurred. Inspection of the building site
shows that the slope is stable under static conditions.
No cracking above the slope crest or other evidence of
present instability were observed. Seismic landslide
hazard maps have not been developed for this area. Site
specific analyses determined the MCE to have a
moment magnitude of approximately 6.5 and a peak
horizontal acceleration of 0.40 g. The predominant
estimated to be 0.3 seconds.
b.
Earthquake-induced landslide screening
(1) Susceptibility. To conclude that a landsliding
hazard does not, each of the landslide screening criteria
presented in paragraph F-3 must be satisfied. The
stability of the slope during past earthquakes and
present site conditions indicate no significant
susceptibility to landsliding. The site is not adjacent to
a shoreline. The building is located approximately 20
feet (6.1 m) from the top of the slope and a horizontal
distance of 80 feet (24 m) from the toe of the slope
(Figure G-13). According to the screening criteria, the
building cannot be located closer than the distance of
the slope height (40 feet or 12 m) from the top of the
slope or closer than three times the slope height (120
feet or 37 m) from the toe of the slope. This criterion is
not satisfied indicating further evaluation is required.
G-19
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