Environmental Engineering Reference
In-Depth Information
Table 10.5
Recommended correlation factors
ξ
1
and
ξ
2
in Eurocode 7 to derive characteristic resistances
from static pile lo
ad tests
Number of static pile load
tests (n)
1
2
3
4
≥
5
1.40
1.30
1.20
1.10
1.00
ξ
1
applied to mean of the
measured resistances
ξ
2
applied to lowest
measured resistances
1.40
1.20
1.05
1.00
1.00
the lowest value as R
c;k
:
(
R
)
;
(
R
)
Š
'
ccal mean
;
ccal min
;
R
=
in
(10.25)
ck
;
ξ
ξ
3
4
The ξ values for determining the characteristic pile resistance, taking into account the
number of pile load tests and number of test profiles, are similar to the ξ values in
Figure 10.5
for determining the characteristic values of soil parameters, taking into account the extent
of failure mechanism. As
Tables 10.5
and
10.6
show, the recommended ξ values decrease
toward unity as the number of static pile load tests and profiles of test results increase so
that the statistical uncertainty in the pile resistance is reduced and the reliability is increased.
Except for when there is only one pile load test and one profile of test results, the recom-
mended ξ
1
and ξ
2
values are all greater than the corresponding ξ
3
and ξ
4
values, reflecting
the greater uncertainty in the pile resistance calculated from a profile of test results, which
involves the use of a calculation model with certain assumptions about the soil behavior,
compared to bearing resistances that are measured directly in static pile load tests.
The recommended ξ values given in
Tables 10.5
and
10.6
have been determined so as to
provide characteristic pile resistance values with a confidence of 95% for soils with a range
of variabilities assuming that
• When the COV of the pile resistance is less than 10%, the characteristic resistance is
governed by the mean of the measured pile resistances from static pile load tests or the
mean of the pile resistances calculated from profiles of tests.
• When the COV of the pile resistance is greater than 10%, the characteristic resistance
is governed by the lowest measured pile resistance from static pile load tests or the low-
est pile resistance calculated from profiles of tests.
Bauduin (2001) has provided some theoretical background to the ξ values for the design
of piles.
Table 10.6
Recommended correlation factors
ξ
3
and
ξ
4
in Eurocode 7 to derive characteristic resistances
from profiles of tests
Number of profiles of tests (n)
1
2
3
4
5
7
10
1.40
1.35
1.33
1.31
1.29
1.27
1.25
ξ
3
applied to the mean of the calculated
resistances
1.40
1.27
1.23
1.20
1.15
1.12
1.08
ξ
4
applied to lowest calculated
resistance
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