Geoscience Reference
In-Depth Information
Table 10.10
Effect of distribution type on statistical values ((Look and Griffiths, 2004).
Rock
Distribution applied to point load index test results
Type
Weathering
Normal
Lognormal
Weibul
5%
Mean
95%
5%
Mean
95%
5%
Mean
95%
Argillite/
DW
−
0.4
1.0
2.4
0.1
1.0
2.6
0.2
1.1
3.1
Greywacke
SW
0.8
2.0
4.8
0.2
2.0
5.2
0.3
2.1
6.3
−
Sandstone/
DW
−
0.3
0.6
1.5
0.1
0.6
1.7
0.1
0.7
2.1
Siltstone
SW
1.1
1.1
3.2
0.0
1.1
3.3
0.1
1.1
3.1
−
Tuff
DW
0.1
0.4
0.8
0.1
0.4
0.9
0.1
0.4
1.2
−
SW
−
1.5
3.3
8.0
0.3
3.3
8.5
0.6
3.2
8.7
Phyllites
DW
0.3
0.9
2.0
0.1
0.9
2.2
0.1
0.9
2.7
−
SW
0.4
1.0
2.5
0.1
1.0
2.6
0.2
1.0
2.8
−
10.11 Variability in design and construction process
•
Section 5 provided comment on the errors involved in the measurement of soil
properties.
•
The table shows the variation in the design and construction process.
Table 10.11
Variations in Design and construction process
based on fundamentals only (Kay, 1993).
Variability component
Coefficient of variation
Design model uncertainty
0-25%
Design decision uncertainty
15-45%
Prototype test variability
0-15%
Construction variability
0-15%
Unknown unknowns
0-15%
•
Natural Variation over site (state of nature) is 5 to 15% typically.
•
Sufficient statistical samples should be obtained to asses the variability in ground
conditions.
•
Ground profiling tools (boreholes, CPT) provide only spatial variability. Use of
broad strength classification systems (Chapters 2 and 3) are of limited use in an
analytical probability model.
•
Socially acceptable risk is outside the scope of this text, but the user must be aware
that voluntary risks (Deaths from smoking and alcohol) are more acceptable than
involuntary risks (eg death from travelling; on a construction project), and the fol-
lowing probability of failures should not be compared with non engineering risks.
10.12 Prediction variability for experts compared with
industry practice
•
This is an example of the variability in prediction in practice.
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