Civil Engineering Reference
In-Depth Information
This becomes necessary because slope stability
conditions deteriorate over time, and it is not pos-
sible to re-rate every slope, every year, according
to the scoring system shown in Table 12.3. How-
ever, it is possible to inspect all the higher priority
slopes on an annual basis to assess stability, and
from this assessment determine whether stabiliza-
tion is required and within what time frame. This
involves assigning each slope an “Inspection Rat-
ing” and a corresponding “Required Action” (see
Table 12.5). The filled boxes in the table indic-
ate allowable Actions for each of the Ratings.
For example, for an Urgent slope the permissible
actions are to limit service and work at the site
within one month, or to carry out a follow-up
inspection to assess stability conditions in more
detail. However, for either an Urgent or Priority
slope it is not permissible to assign “No Action”
to the site.
The following are examples of criteria that
could be used to assign Inspection Ratings, using
a combination of measurement, the rating scores
given in Table 12.5, and subjective observations
of stability:
•
Observe
—Possible recent movement, but no
imminent instability. Check specific stability
conditions in next inspection.
•
OK
—no evidence of slope movement.
It has been found that there are two primary bene-
fits in assigning a Required Action for every slope.
First, this forces the inspector to make a decision
on the urgency for mitigation, and second, it auto-
matically draws up a list of work sites for the
current year and the next two years. This list
becomes the basic planning tool for the on-going
program.
12.3.6 Selection of stabilization measures
This section provides some guidelines on select-
ing the method, or methods, of stabilization
that are most appropriate for the topograph-
ical, geological and operational conditions at the
site. Methods of slope stabilization fall into three
categories:
(a)
Reinforcement;
(b)
Rock removal; and
(c)
Protection.
•
Urgent
—Obvious recent movement or rock
falls, kinematically feasible block with
dimensions large enough to be a hazard;
weather conditions are detrimental to stabil-
ity. Failure possible within next few months.
Figure 12.3 includes 16 of the more common sta-
bilization measures divided into these categories.
The following are examples of the factors that
will influence the selection of appropriate stabil-
ization methods. Where the slope is steep and
the toe is close to the highway or railway, there
will be no space to excavate a catch ditch or
•
Priority
—Likely movement since last inspec-
tion of block, large enough to be a hazard;
failure possible within next two years approx-
imately.
Table 12.5
Inspection ratings and corresponding actions
Required Actions
Limit
service;
work within
1 month
Inspection
Rating
Work in
current
year
Follow-up
inspection
Work in
1-2
years
No action
Urgent
×
×
Priority
×
×
×
Observe
×
Okay
×
