Pile Design and Construction Practice, Fifth edition

It is assumed that the shear strength/depth realtionships in Figure 4.43 were based on an
adequate number of boreholes and soil samples, and that the straight line graphs are a
cautions estimate derived from the plotted data. Hence Figure 4.43 represents characteristic
values and the correlation factors need not be applied.

Calculating the mean and minimum pile resistances:

Rck(mean) 9  148 0.710.4597.535.81

946  1572 2518 kN

Rck(min) 946 (135 / 148) 1572 2435 kN

Taking the minimum value and allowing for the stiffness of the building structure:

Design Rck 2435 1.1 2678 kN

For DA1 combination 1, the partial factor sets are A1M1R1; from Table 4.1 the
A1 factors are 1.35 (permanent unfavourable) and 1.5 (variable unfavourable). Therefore
design value of actions:

Fd 1.35 1100 1.5 300 1935 kN

From Table 4.2, the M1 factors are all unity and R1 for combined compression is 1.15.
Therefore design value of resistance:

Rcd 2678 / 1.01.15 2329 kN which is greater than Fdof 1935 kN

For DA1 combination 2 (sets A2M1R4), the factors for permanent and variable
actions are unity and 1.3 respectively. Therefore

Fd 1.0 1100 1.3 300 1490 kN

M1 (structural action) is unity and R4 is 1.6, therefore

Rcd 2678 / 1.01.6 1674 kN which is greater than Fdof 1490 kN

Checking from equation 4.39, taking the drained deformation modulus of the clay at pile
base level as 140cu(for long-term loading), we get

= 0.4 + 12.2

= 13 mm

Example 4.4

A precast concrete pile 450 mm square forming part of a jetty structure is driven into a
medium dense over-consolidated sand. Standard penetration tests made in the sand gave an



(413 2 987)8 000

2 0.7854 30  106

0.5^987 1 000

2  140  145

Resistance of piles to compressive loads 229