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 Nc 5.2, sc 1.05, dc 1.3 and ic 0.96.
It is evident from the preceding calculation to obtain qubthat the third term in equation 5.1
is small and can be neglected.
Characteristic unit base resistance 190 5.21.051.30.96 1294.7 kN/m^2.
Applying the R1 resistance factor of 1.0, design resistance Rcd 1294.713.0
3.1 52176 kN which is greater than the design action V'dof 30 000 kN.
For Design Approach DA1, combination 2 (sets A2M2R1)

Design actions, V'd 1.030 000 30 000 kN

and H'd 1.31 500 1950 kN

Eccentricity of loading 1950(35.013.7)/30 000 3.2 m

Width of equivalent block foundation 10.4 2 3.2 4.0 m

Dimensions of equivalent block foundation are 13.04.07.7 m deep

The material factor, cu, for set M2 is 1.4 and R1 is 1.0

Design unit resistance to bearing failure 1365.20.91.30.86 711.6 kN/m^2

Design resistance of foundation Rcd 711.613.04.0 37 000 kN which is

greater than V'dof 30 000 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 13.03.1 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
1.040.3 7657 kN which is greater than H'd 1.5 1500 2250 kN.
For DA1, combination 2, base area 13.04.0 52.0 m^2 , Rcd 1.0 136 52.0
7 072 kN which is greater than Hd 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 13.811.2 m. Therefore

overall base pressure beneath raft

Assume a value of Eufor the glacial clay of 80 mN/m^2 and a value of mvof 0.05 m^2 /kN.
From Figure 5.20 for L/B 13.8/11.2 1.2, H/Band D/B 7.7/11.2 0.69 (ignoring

30 000

13.8  11.2

194 kN/m^2

Piles to resist uplift and lateral loading 371