subsurface soil conditions.
This information
CHAPTER 9
includes:
FOUNDATIONS
Foundation type: spread footings, mat
9-1.
Introduction.
foundation, piles, drilled shafts.
Foundation dimensions: plan dimensions
Chapter 7 in FEMA 302 provides conventional
and locations.
For piles, tip elevations, vertical
foundation design provisions that are adequate for
variations (tapered sections of piles or belled
most military buildings.
This chapter provides
caissons).
guidance in the implementation of those provisions,
and also provides guidance in the use of load
Material composition/construction.
For
deformation
characteristics,
for
soil/structure
piles, type (concrete/steel/wood), and installation
interaction, in the form of simplified soil springs.
method (cast-in-place, open/closed-end driving).
The determination of appropriate soil springs and
the structural systems for which they provide a better
(2) Subsurface soil conditions. The capacity
representation of seismic response are discussed in
of the foundation soil in bearing or the capacity of
Paragraph 9-2b.
the soil interface between pile, pier, or caisson and
the soil will be determined by a geotechnical
investigation and shall be sufficient to support the
9-2.
Site Characterization.
structure with all prescribed loads, without seismic
Site characterization consists of the compilation of
forces, taking due account of the settlement that the
information on the site subsurface soil conditions,
structure can withstand. For the load combination
and the configuration and loading of the proposed
including earthquake, the soil capacities must be
foundations. The evaluation of the ground-shaking
sufficient to resist loads at acceptable strains
hazard and site geologic hazards is discussed in
considering both the short duration of loading and
Chapter 3.
the dynamic properties of the soil.
If load-
deformation characterization for the foundations are
a.
Site Foundation Conditions. Subsurface soil
to be considered (i.e., Paragraph 9-2b), the soil unit
conditions must be defined in sufficient detail to
,
assess the ultimate capacity of the foundation, and to
φ soil compressibility characteristics, soil shear
,
determine if the site is susceptible to seismic-
modulus, G, and Poisson' ratio, ν, need to be
s
geologic hazards.
determined for each soil type. Additionally, the shear
wave
velocity,
<s,
the
standard
penetration
(1) Structural foundation type. Information
regarding the structural foundation type, dimensions,
need to be determined to define the site classification
and material are required irrespective of the
9-1
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