Environmental Engineering Reference
In-Depth Information
Table 14.3
Updated mean and COV of the bearing capacity ratio
based on SPT (Meyerhof 1976) and verified by proof tests
Total number
of tests
Number of
positive tests
Mean
COV
β
at FOS
=
2.0
4
4
1.77
0.38
2.67
3
1.19
0.24
2.38
2
1.04
0.24
2.00
1
0.91
0.24
1.57
0
0.69
0.30
0.60
3
3
1.74
0.38
2.58
2
1.14
0.25
2.21
1
0.96
0.25
1.70
0
0.72
0.31
0.67
2
2
1.68
0.39
2.45
1
1.06
0.26
1.91
0
0.75
0.32
0.77
1
1
1.59
0.41
2.23
0
0.82
0.34
0.95
the target reliability marked by the shaded zone can still be satisfied even if some of the tests
are not positive.
The FOS that will result in a sufficient level of reliability is of interest to engineers.
Figure
14.4
shows the calculated FOS values required to achieve a β value of 2.0 for the pile foun-
dation verified by proof tests with different outcomes. It can be seen that an FOS of 2.0 is
sufficient for piles that are verified by one or more consecutive positive tests, or by three or
four tests in which no more than one test is not positive. However, larger FOS values should
be used if the only proof test or one out of two tests is not positive.
3.0
Target reliability zone b
TS
=
1.7 - 2.5
2.5
2.0
1.5
1.0
All tests positive
Number of positive tests out of 4 tests
Number of positive tests out of 3 tests
Number of positive tests out of 2 tests
Number of positive test out of 1 test
0.5
0.0
0
1
2
3
4
5
Number of positive tests
Figure 14.3
The reliability of single driven piles designed with an FOS of 2.0 and verified by conventional
proof tests of different outcomes.
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