Pile Design and Construction Practice, Fifth edition

224 Resistance of piles to compressive loads
For cu���vo � 110�98 � 1.1, Figure 4.6 gives �p � 0.5, and for L/B � 10/0.35 � 29, the
length factor � 1.0, giving � � 0.5.
Ultimate shaft resistance � 0.5 � 110 � 4 � 0.35 � 10 � 770 kN.
Total pile resistance � 770 � 91 � 861 kN.
Factor of safety on compression load � 861/(240 � 110) � 2.5 which is satisfactory.
Factor of safety on uplift load � 770 � 200 � 3.8 (satisfactory).
The above calculations using permissible stress methods can be checked for compliance
with the EC7 recommendations. Considering first the actions using the factors in Table 4.1:
Set A1, design value of actions � F d � 1.35 � 240 � 1.5 � 110 � 489 kN.
Set A2, design value of actions � F d � 1.0 � 240 � 1.3 � 110 � 383 kN.
The pile resistances are calculated from equation 4.10 for each borehole as follows:
BH1: R cal � 9 � 75 � 0.35 � 0.5 � 85 � 4 � 0.35 � 10 � 83 � 595 � 678 kN.
BH2: R cal � 83 � 80/75 � 595 � 115/85 � 893 kN.
BH3: R cal � 83 � 95/75 � 595 � 130/85 � 1015 kN.
The mean and minimum values of R cal are
R cal (mean) � (687 � 893 � 1015)/3 � 862 kN.
R cal (min) � 678 kN (BH1).
The above values are divided by correction factors 1.33 (mean) and 1.23 (min) for three
boreholes (Table 4.6) to give the characteristic values:
R ck (mean) � 862/1.33 � 648 kN, and
R ck (min) � 672/1.23 � 551 kN.
The least value of Rck is taken as 551 kN to calculate the design value Rcd. Because the
jetty structure is relatively flexible Rck is not multiplied by the factor of 1.1.
Using design approach DA1 and combination 1 (sets A1 � M1 � R1), for a driven pile
in compression, the factors and for M1 and R1 sets are unity (Tables 4.2 and 4.3).
� b
� s
Therefore design R cd � (83 � 595) / 1.23 � 551 kN which is greater than F d for the A1 set.
For DA1 and combination 2 (sets A2 � M1 � R4), M1 (structural actions) is unity and
R4 is 1.4. Hence design R cd � (83 � 595) / 1.23 � 1.4 � 393 kN, whcih is greater than F d
for the A2 set.
From the above check it can be concluded that the required penetration depth of 10 m into
the stiff clay as calculated by permissible stress methods with a safety factor of 2.5 complies
with the recommendations of EC7.
Example 4.2
A steel tubular pile 1.220 m in outside diameter forming part of a berthing structure is required
to carry a working load in compression of 16 MN and a uplift of 8 MN. The pile is driven with