Geoscience Reference
In-Depth Information
10.15 Acceptable probability of slope failures
•
The acceptable probability depends on its effect on the environment, risk to life,
cost of repair, and cost to users.
Table 10.15
Slope Stability - acceptable probability of failure (Santamarina et al.,1992).
Conditions
Risk to life
Costs
Probability of
failure (P
f
)
Unacceptable in most cases
10
−
1
<
Temporary structures
No potential life loss
Low repair costs
10
−
1
Nil consequences of failure
No potential life loss
High cost to lower P
f
1to2
10
−
1
×
bench slope, open pit mine
Existing slope of riverbank at
No potential life loss
Repairs can be promptly
5
10
−
2
×
docks. Available alternative
done.
docks
Do - nothing attractive
idea.
10
−
2
To be constructed: same
<
5
×
condition
Slope of riverbanks at docks
No potential life loss
Pier shutdown threatens
1 to 2
10
−
2
×
no alternative docks
operations.
10
−
2
Low consequences of failure
No potential life loss
Repairs can be done when
time permits. Repair
costs
costs to lower P
f
.
<
Existing large cut - interstate
No potential life loss
Minor
1 to 2
10
−
2
×
highway
To Be constructed: same
No potential life loss
Minor
10
−
2
<
condition
Acceptable in most cases
No potential life loss
Some
10
−
3
Acceptable for all slopes
Potential life loss
Some
10
−
4
Unnecessarily low
10
−
5
<
10.16 Probabilities of failure based on lognormal distribution
•
The factor of safety can be related to the probability of failure based on different
coefficients of variations (COV).
•
A lognormal distribution is used.
•
The factor of safety is the most likely value.
•
For layered soils, different COVs are likely to apply to each layer.
Table 10.16
Probability of Failure based on lognormal distribution (Duncan and Wright, 2005).
Factor of
Probability of failures (%) based on COV
safety
COV
10%
20%
30%
40%
50%
=
1.2
3.8
21
32
39
44
1.3
0.5
11
23
31
37
1.4
0.04
5.5
16
25
32
1.5
10
−
3
2.6
11
20
27
∼
10
−
3
2.0
<
0.03
1.3
5
11
10
−
3
2.5
∼
0.15
1.4
4.4
10
−
3
3.0
<
0.02
0.39
1.8
Search WWH ::
Custom Search