Geoscience Reference
In-Depth Information
•
the type of the foundation system (for example, isolated footings, mat foundation,
box-type foundation, piles, caissons),
•
the flexural and axial rigidity of the foundation system (thickness of mat foundation
cross-sectionand length of tiebeams, etc.),
•
theload of thesuperstructure and the foundation,
•
the stiffness of the superstructure (cross section of structural members, spacing of
columns, presence or not of shear walls),and
•
thelocation Sfromthe foundation corner to thefree-field outcrop.
However, a detailed investigation of the role of all the above parameters is beyond the
scope of this chapter. Reference is made to Anastasopoulos (2005) and Anastasopoulos
and Gazetas (2007b) for such a parameter study. Here we only outline a few characteris-
tic results pertaining to a 20m wide rigid mat foundation, supporting a 2-storey building
frame.Thesoillayeriseitherloose
(
D
r
≈
45%
)
ordense
(
D
r
≈
80%
)
sandoftotalthick-
ness H
40m. Three locations of the foundation with respect to the free-field outcrop
are considered: S
=
4, 10, and 16m, i.e. near the left edge, in the middle, and near the
right edge of the foundation, respectively.
=
Figures9.3-9.5 portray the response of the soil-foundation-structure system for each
location S and each of the two soil densities, for a parametrically variable ratio of base
dislocation over layer thickness: h
/
H
=
1-5%.
Shownineachfigurearethedeformedmesh,thedistributionofplasticstrains,thediver-
sion of the rupture D, the vertical displacement profile
, and
the contact pressures p
ν
along the soil-foundation interface. In all cases the results are
compared with the corresponding free-field results to visualize the effects of FR-SFSI.
The contact stresses are compared to their initial distribution (i.e. for h
y
, the distortion angle
β
0, before
thebedrockdisplacementisapplied)torevealwhichpartsofthestructurearelosingcon-
tact with the bearing soil, and hence foundation uplifting takes place. The left part of the
buildingthatupliftswillbedenotedasu
L
,therightu
R
,andu
C
iftheupliftingtakesplace
aroundthecentre.Insimilarfashion,thepartofthefoundationthatmaintainscontactwill
be denoted as b
L
,b
R
and b
C
, if it is located at the left side, the right side, or the middle,
respectively.
/
H
=
The following trends areworthy of note:
(1) Forthefaultemerging(withoutSFSI)neartheleftedge(s
=
4m,orS
/
B
=
0
.
20),
this lightly loaded foundation for a relative base dislocation h
5% would
causeonlyaminordiversionoftherupturepath,easilynoticeableonlyintheloose
soil(about2mtowardsthehangingwall,totheleftofthebuilding).Thedifferential
settlement is higher on loose sand. The main difference between the two soils is in
the uplifting of the foundation. In dense sand the building loses contact at both
/
H
=
