Pile Foundations - Elements of Soil Mechanics - page 304

obtained by one of three approaches: from static load tests, from ground tests results or from dynamic
tests results.
Considering Design Approach 1, the following partial factor sets (see Section 5.7.1) are used for the
design of axially loaded piles:

Combination 1: A1 + M1 + R1
Combination 2: A2 + (M1 or M2)* + R4

* M1 is used for calculating pile resistance; M2 is used for calculating unfavourable actions on piles.

10.6.1 Note on the UK National Annex, NA EN 1997-1:2004

As mentioned in Chapter 5 , the National Annex allows each nation to provide Nationally Determined
Parameters (NDPs) that should be used in place of the values published in the main Eurocode document.
For Eurocode 7 Part 1, NDPs include partial factors and rules for use where national choice is permitted
in the main Eurocode. The partial factors for the GEO limit state in the UK National Annex are the same
as those listed in Eurocode 7 Part 1, with the exception of the partial resistance factors ( γ R ) and the cor-
relation factors ( ξ ) for pile foundations. It is important to note therefore that during pile foundation design
in the UK, the values provided in the National Annex must be used, rather than the values published in
the main Eurocode document. In the following sections, both sets of values are provided.

10.6.2 Ultimate compressive resistance from static load tests

The characteristic value of the compressive ground resistance, R c;k , is obtained by combining the measured
value from the pile load tests with a correlation factor, ξ (related to the number of piles tested). More
explicitly, R c;k is taken as the lesser value of:

( R ) ( R )

c m mean ; c m ; min

R = and R = c k ; c k ;

ξ ξ

1 2

Where

(R c;m ) mean = the mean measured resistance
(R c;m ) min = the minimum measured resistance
ξ 1 , ξ 2 = correlation factors obtained from Table 10.2A (Eurocode 7, Part 1) or Table 10.2B (UK National

Annex).

It may be that the characteristic compressive resistance of the ground is more appropriately determined
from the characteristic values of the base resistance, R b;k and the shaft resistance, R s;k :

R = R + R

c k ; b k ; s k ;

Table 10.2A Correlation factors - static load tests
results (from EN1997-1:2004, Table A9).

Number of piles tested

1 2 3 4 ≥ 5

ξ 1 1.4 1.3 1.2 1.1 1.0

ξ 2 1.4 1.2 1.05 1.0 1.0