Pile Design and Construction Practice, Fifth edition

Resistance of piles to compressive loads 147
or parameters derived from in-situ tests. They are shown in Table 4.6. As described below
when Rck is obtained from static pile loading tests the factors are �1 and �2 (Table 4.7) and
when Rck is derived from dynamic impact tests the factors �5 and �6 are used.
The design action Fd in equation 4.2 and the design values of base and shaft resistance
are obtained by dividing the characteristic values of Rbk and Rsk obtained from equations 4.3a
and 4.3b by the partial factors �b and �s respectively. These factors are
for actions (A series): � G permanent and � Q variable from Table 4.1;
for ground properties (M series): � M from Table 4.2;
for ground resistances (R series): � R from Table 4.3 to 4.5; and
correlation factors from Table 4.6.
The above partial factors are selected by adopting one or all of three design approaches
each with a different combination or set of the A, M, and R series. Thus
Design approach 1 (DA1), Combination 1: A1 � M1 � R1
Design approach 1 (DA1), Combination 2: A2 � (M1 or M2) � R4
Design approach 2 (DA2), A1 � M1 � R2
Design approach 3 (DA3), A1 (or A2) � M1 � R3.
The plus sign in the above list denotes ‘combined with’. As design approach DA1 will be
adopted for pile design by the British National Annex when published. DA2 and DA3 are
not considered in this text.
Taking the case of a pile loaded axially in compression and considering the limit states
STR or GEO, for DA1 Tables 4.2 and 4.3 show that the partial factors for ground properties
and ground resistances are unity. Therefore to ensure that F d is equal to or not greater than
R cd the partial factors are applied to the actions. Accordingly, it is essential that the field
operations and laboratory testing techniques should be undertaken in a thorough manner
with the appropriate standard of quality.
Approach DA1, Combination 2 provides for alternative material factors M1 or M2. The
former is used for structural actions while the latter is applied to geotechnical actions caused
by ground movements. Similarly, when approach DA3 is used the action factor A1 refers to
Table 4.1 Partial factors on actions (� F)
Action Symbol Set
A1 A2
Permanent
Unfavourable � G 1.35 1.0
Favourable 1.0 1.0
Variable
Unfavourable � G 1.5 1.3
Favourable 0 0
Notes
The partial factors shown in Tables 4.1 to 4.8 are those
provided in Annex A of EC7.The mandatory factors to be
applied under the British National Annex are due to be
published in 2008, and should be consulted prior to undertaking
design to EC7 rules.
Different factors will apply to bridges in Table 4.1