Civil Engineering Reference
In-Depth Information
(a)
(b)
Jointed
rock
Porous
rock
(c)
Fault
(high conductivity)
Fault
(low conductivity)
Figure 5.11
Relationship between geology and ground water in slopes: (a) variation in water pressure in joints
related to persistence; (b) comparison of water tables in slopes excavated in porous and jointed rock; (c) faults
as low conductivity ground water barrier, and high conductivity sub-surface drain (Patton and Deere, 1971).
are related to geology as follows:
However, any improvement in slope stability
due to the increase in conductivity is prob-
ably out-weighed by the decrease in stability
resulting from blast damage to the rock.
(a)
Low persistence joints that are not connected
to the slope face may develop high tran-
sient water pressures, compared to joints
with greater persistence that are connected
to the face and allow water to drain at the
face (Figure 5.11(a)). It should be noted that
blast damage is one of the causes of per-
sistent joints and fractures close to the face.
(b)
The porosity of the rock mass will affect
the level of the transient water table in
response to the same precipitation event
(Figure 5.11(b)). In a porous rock mass the
infiltrating water will be contained within
the rock with the result that there will be
