Geoscience Reference
In-Depth Information
4
4
a
b
3
3
2
2
1
1
0
0
0
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
V
end
V
end
Fig. 10.4. Relationship between theseismicparameters
F
undrained
and
F
drained
and the
dimension-lessverticalloadattheapexofbearingstrengthsurface:(a)
φ
=
0,(b)
φ>
0
0.25
0.2
0.15
0.0
0.1
0.5
0.05
1.0
F
undrained
= 1.5
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
0.0
0.05
0.5
1.0
F
undrained
= 1.5
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. 10.5. Undrained sections of the EC8 bearing strengthwith increasing level of
seismicacceleration
2.2. UNDRAINED RESPONSE
Figure 10
.5
has plotted sections of the undrained bearin
g s
tre
ng
th surface for a r
an
ge of
values of
F
undrained
. The top part of the figure gi
ve
s t
he
V
−
H
boundary
in
the
M
=
0
plane, whilst the bottom part of the figure gives
V
−
M
boundaries in the
H
=
0 plane
through the surface. This figure shows that as long as
V
33 then values of
F
undrained
up to about 1.5 have very little effect on the foundation bearing strength, so an assess-
mentignoringtheeffectofhorizontalaccelerationwouldbeadequate.Thisisinlinewith
the observation of Auvinet et al. (1986) that shallow foundations in clay, with appropri-
ate static bearing strength factors of safety, perform well in earthquakes. Furthermore
<
0
.
