Geoscience Reference
In-Depth Information
0.15
0.1
0.0
0.05
0.5
0.2
F
drained = 0.8
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
V/V
uo
0.15
0.1
F
drained = 0.0
0.05
0.2
0.5
0.8
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
V/V
uo
Fig. 10.6. Drained sections of theEC8 bearing strength withincreasing level ofseismic
acceleration
plane, whilst the bottom part of the figure gives
V
0 plane
throughthesurface.ComparisonofFigures10.5and10.6showsthatthedrainedresponse
isverymuchmor
e
sensitivetoinertialoadingthantheundrainedresponse.Notealsothat
the definition of
F
drained
is such that there is no suggestion of a size effect on drained
response sothe inertiaeffect will be important forshallow foundations of any size.
−
M
boundaries in the
H
=
Figures 10.4, 10.5 and 10.6 are presented simply to clarify the workings of the EC8
bearing strength surface. They are not needed in making calculations of the response
of shallow foundations to earthquake loading, that is taken care off by Equation (10.3),
in which sense Equation (10.3) is operated as a “black-box”. Examples of the use of
Equation (10.3) are given by Fardis et al. (2005).
An attractive feature of Equation (10.3) is that it does not focus on the vertical bear-
ing strength of the shallow foundation in the manner of the more usual ultimate limit
state methods, even when shear and moment loading are involved (Pender, 2006). Equa-
tion (10.3) simply checks that the state point does not lie beyond the bearing strength
surface.
3. Serviceability limit state design of shallow foundations
for earthquake loading
In evaluating shallow foundation deformations during earthquake excitation it is neces-
sary consider the stiffness and damping properties of the soil and also the effect that
the structure-foundation system has on the earthquake motions. This is usually divided
into two steps - kinematic and inertial interaction, which is explained by Mylonakis
et al. (2006). Dynamic stiffness and damping values for shallow foundations are given
by Gazetas (1991) and Mylonakis et al.(2006).
