Geoscience Reference
In-Depth Information
Fig. 11.22. Charts forthe evaluation of liquefaction settlements of stripfoundations
resting on a cohesive (clay) crust - “weak” seismicexcitations
(ρ
o
/
B
=
0
.
01
)
seismic scenarios (“weak” and “strong” motion) defined previously. The average con-
tact pressure was kept constant at
q
100kPa, bearing in mind that lower values
would probably guide the designer to alternative means of foundation, involving ground
improvement or the use of pilefoundation.
=
This figure makes clear that, when the thickness and the shearing resistance of the clay
crust increase, seismic settlements
ρ
dyn
are drastically reduced and degraded factors of
safety
FS
deg
increase. Moreover, an acceptable foundation performance is possible for
undrained shear strength values and thicknesses of the clay crust which are commonly
met in practice. For instance, for a reinforced concrete building where the allowable set-
tlement is of the order of 0.05m, the average bearing pressure would be safely sustained
by a clay crust with
C
u
=
40kPa and the following values of normalized thickness:
-
H
/
B
=
0
.
80
[
FS
deg
=
1
.
00
,ρ
dyn
=
3
.
0cm
<
5
.
00cm
]
, for “weak” seismic shak-
ing, and
