Pile Design and Construction Practice, Fifth edition

The Brinch Hansen bearing capacity factors for � � 0� are obtained in the same way as
shown above, giving N c � 5.2, s c � 1.05, d c � 1.3 and i c � 0.96.
It is evident from the preceding calculation to obtain q ub that the third term in equation 5.1
is small and can be neglected.
Characteristic unit base resistance � 190 � 5.2 � 1.05 � 1.3 � 0.96 � 1294.7 kN/m 2 .
Applying the R1 resistance factor of 1.0, design resistance � R cd � 1294.7 � 13.0 �
3.1 � 52176 kN which is greater than the design action V' d of 30 000 kN.
For Design Approach DA1, combination 2 (sets A2�M2�R1)
Design actions, V' d � 1.0 � 30000 � 30000 kN
and H' d � 1.3 � 1500 � 1950 kN
Eccentricity of loading � 1950(35.0 � 13.7)/30000 � 3.2 m
Width of equivalent block foundation � 10.4 � 2 � 3.2 � 4.0 m
Dimensions of equivalent block foundation are 13.0 � 4.0 � 7.7 m deep
The material factor, � cu, for set M2 is 1.4 and R1 is 1.0
Design unit resistance to bearing failure 136 � 5.2 � 0.9 � 1.3 � 0.86 � 711.6 kN/m 2
Design resistance of foundation � R cd � 711.6 � 13.0 � 4.0 � 37000 kN which is
greater than V' d of 30000 kN
DA1 is used to check compliance with EC7 with respect to sliding. In the following
calculations the passive resistance of the soil to horizontal movement of the piles has been
ignored.
For DA1, combination 1, the base area of the equivalent block using the factored values
of V' and H' is 13.0 � 3.1 � 40.3 m 2 . From Table 4.2, M1 is 1.0 and R1 for spread
foundations in respect of sliding is 1.0. Therefore design resistance to sliding � 190 � 1.0 �
1.0 � 40.3 � 7657 kN which is greater than H' d � 1.5 � 1500 � 2250 kN.
For DA1, combination 2, base area � 13.0 � 4.0 � 52.0 m 2 , R cd � 1.0 � 136 � 52.0 �
7072 kN which is greater than H� d � 1950 kN.
It is also necessary to confirm that the total settlements and tilting of the structure are
within safe limits. The following calculations are carried out using unfactored loadings to
verify the serviceability limit-state.
Calculating first the immediate and consolidation settlements under dead and imposed
load, but excluding the wind load. Because the piles have under-reamed bases which carry
the major proportion of the load, the base of the equivalent raft will be close to pile base
level. The approximate overall dimensions of the equivalent raft outside the toes of the pile
bases are 13.8 � 11.2 m. Therefore
overall base pressure beneath raft �
Piles to resist uplift and lateral loading 371
30 000
13.8 � 11.2 � 194 kN/m 2
Assume a value of E u for the glacial clay of 80 mN/m 2 and a value of m v of 0.05 m 2 /kN.
From Figure 5.20 for L/B � 13.8/11.2 � 1.2, H/B ��and D/B � 7.7/11.2 � 0.69 (ignoring