Civil Engineering Reference
In-Depth Information
Figure 22.14
Drainage conditions in foundations.
with depth. Figure 22.15(b) is for radial consolidation where
c
r
t
R
2
T
r
=
(22.28)
R
r
n
=
(22.29)
As discussed in Chapter 15, these can be used to calculate either the settlement after a
given time or the time for a given settlement. Although, in theory, complete consoli-
dation will require infinite time a reasonable approximation is that
T
v
or
T
r
≈
1.0 at
U
t
=
1.0.
22.11 Heave and settlement of foundations due to
changes of groundwater
We have seen that in general loading a foundation causes it to settle and unloading will
cause it to heave. Foundation movements can be caused by changes other than load-
ing such as underground mining, nearby construction and changes of groundwater.
Groundwater can change for a number of reasons, including water extraction, dewa-
tering nearby excavations and changes in vegetation. Foundation movements due to
its loading are usually called settlement and those due to other changes are usually
called subsidence.
