Civil Engineering Reference
In-Depth Information
Figure 14.1
Groundwater conditions.
and swelling, is known as consolidation. This is covered in Sec. 6.9 and Chapter 15.
During consolidation, pore pressures are
t
he su
m
of the steady state pore pressures
u
0
=
γ
w
h
w0
and the ex
ce
ss pore pressure
u
=
γ
w
h
w
, as shown in Fig. 14.1(c). Graphs
of excess pore pressure
u
at given times are called isochrones. Remember consolidation
works both ways. If the excess pore pressure is positive water is squeezed out and the
soil compresses. If they are negative water is sucked in and the soil swells.
14.2 Practical problems of groundwater flow
Any child who has dug a hole in the beach or constructed a small soil dam across
a stream has soon recognized the importance of groundwater in ground engineer-
ing. It is impossible to excavate much below the groundwater table and dams soon
fail by downstream erosion, even if they are not overtopped first. The hole can only
be continued if water is pumped from the excavation, and possibly from the sur-
rounding ground as well, and engineers will need to determine the quantities of water
