Soil Liquefaction. Recently deposited (geologically) and
geotechnical investigations for a facility at a selected site,
relatively unconsolidated soils and artificial fills without
supplemental investigations may be conducted as needed
significant cohesion and located below the water table, are
to define the geologic hazards in more detail and/or
susceptible to liquefaction. Sands and silty sands are
develop mitigating measures. The scope and complexity of
particularly susceptible. Potential consequences of
a geologic hazard investigation depends on the economics
liquefaction include foundation bearing capacity failure,
of the project and the level of acceptable risk. In general,
differential settlement, lateral spreading and flow sliding,
major new building complexes, high-rise buildings, and
flotation of lightweight embedded structures, and
other high value or critical facilities shall have thorough
increased lateral pressures on retaining walls. The
geologic hazard investigations. Small, isolated buildings
investigation shall consider these consequences in
need not have elaborate investigations.
determining the size of the area and the depth below the
Surface Fault Rupture. For purposes of new building
surface to be studied. An investigation for liquefaction
construction, a fault is considered to be an active fault and
may take many forms. One acceptable method is to use
a potential location of surface rupture if the fault exhibits
blow count data from the standard penetration test
any of the following characteristics:
conducted in soil borings. This method is described in
publications by H. B. Seed and I. M. Idriss, (1982), Ground
Has had documented historical macroseismic
Motions and Soil Liquefaction During Earthquakes:
events or is associated with a well-defined pattern of
Earthquake Engineering Research Institute, Oakland, CA,
microseismicity.
Monograph Series, 134 p. and H.B. Seed et al, (1985) "The
Is associated with well-defined geomorphic features
Influence of SPT Procedures in Soil Liquefaction
suggestive of recent faulting.
Resistance Evaluations": Journal of Geotechnical
Has experienced surface rupture (including fault creep)
Engineering, ASCE 111(12): pp. 1425-1445.
during approximately the past 10,000 years (Holocene
time).
Landsliding. New construction shall not be sited where it
may be within a zone of seismically induced slope failure
Fault investigations shall be directed at locating any
or located below a slope whose failure may send soil and
existing faults traversing the site and determining the
debris into the structure. Factors which affect slope
recency of their activity. If an active fault is found to exist
stability include slope angle, soil type, bedding, ground
at a site and the construction cannot reasonably be
water conditions, and evidence of past instability. The
located elsewhere, investigations shall be conducted to
geologic hazard investigation shall address the potential
evaluate the appropriate set-back distance from the fault
for seismically induced slope deformations large enough
and/or design values for displacements associated with
to adversely affect the structure.
surface fault rupture.
351
SUBMISSION
REQUIREMENTS
A.5
Surveys and Geotechnical Reports Geologic Hazard Report
Revised March 2005 PBS-P100
Previous Page
