Civil Engineering Reference
In-Depth Information
water table for the following conditions:
(a)
Infiltration
Original ground surface
Original phreatic line
•
large infiltration, low hydraulic conduct-
ivity; and
•
small
infiltration,
high
hydraulic
Drawn-down phreatic line
conductivity.
C
On the cross-section in Figure 5.16(c) draw
the approximate positions of the ground
water table for the following conditions:
(b)
Infiltration
•
joints on slope face plugged with ice;
•
immediately following a heavy rainstorm;
•
wet season; and
Phreatic line for large
inflow low
k
value
•
dry season.
Phreatic line for small
inflow high
k
value
Solution
Figure 5.17(a), (b) and (c) show the positions
of the ground water table under the various
conditions shown in Figure 5.16.
In general, the rock near the slope face has
been disturbed by blasting and has undergone
stress relief so it will have a higher hydraulic con-
ductivity than the undisturbed rock. When the
hydraulic conductivity is high, the rock drains
readily and the ground water table has a relatively
flat gradient.
If the face freezes and the water cannot drain
from the slope, the ground water surface will rise
behind the face. The same situation arises when
heavy infiltration exceeds the rate at which the
rock will drain.
Infiltration
(c)
Higher
K
Lower
K
Arbitrary boundary
Joints plugged with ice
Heavy rainstorm
Dry season
Wet season
Figure 5.17
Positions of ground water surface for
conditions shown in Figure 5.16 for Example 5.1:
(a) position of the ground water surface before and
after excavation; (b) relative positions of ground
water table for variations of inflow and conductivity;
(c) hypothetical positions of the ground water surface
in jointed rock for variety of climatic conditions.
