Pile Design and Construction Practice, Fifth edition

8.21GERWICK, B. C.Construction of Offshore Structures, Wiley, 1986.
8.22YA R O N, S. L. and SHIMONI, J. The Hadera offshore coal unloading terminal, Proceedings of the
Offshore Technology Conference, Paper OTC 4396, Houston, 1982.

8.5 Worked examples

Example 8.1

A breasting dolphin is constructed by linking at the head four 350350 mm reinforced
concrete piles which are driven through 2.5 m of soft clay into a stiff clay, to a total
penetration below sea bed of 9.0 m. Find the kinetic energy which can be absorbed by the
pile group for an impact at a point 8 m above the sea bed. The maximum energy absorption
value is to be taken as the figure which stresses the piles to their yield point.
The piles can be considered as fixed at the surface of the stiff clay stratum, and the
ultimate resistance moment of each pile at the yield point is 125 kN m. Therefore from
equation 8.4:

work done in deflecting piles to yield point

Example 8.2

A steel tubular pile having an outside diameter of 1300 mm and a wall thickness of 30 mm
forms part of a pile group in a breasting dolphin. The pile is fabricated from high-tensile alloy
steel to BS4360 Grade 55C. The piles are driven into a stiff over-consolidated clay (cu 150
kN/m^2 ). Calculate the maximum cyclic force which can be applied to the pile at a point 26 m
above the sea bed at the stage when the failure in the soil occurs at sea-bed level, the deflec-
tion of the pile head at this point, and the corresponding energy absorption value of the pile.
Steel to Grade 55C should have a minimum yield strength of 417 N/mm^2 and an elastic
modulus of 2 105 MN/m^2.

The first step is to establish the p–ycurves. In equations 6.36 and 6.37, the submerged
density of the soil is 1.2 Mg/m^3 , and a value of 0.25 can be taken for the factor J.
At sea-bed level

Nc 3  0  03

pu 3  150 1.3 585 kN per m depth

Critical depth xr 6 1.3

1.29.811.3

150

0.25

22.1 m

Moment of resistance of pile at yield point 417 0.024

0.65

15.4 MN m

Moment of inertia of pile(1.30^4 1.24^4 ) 64 0.024 m^4

4  1252 (82.5)

6  26  106 0.08330.35^4

3.37 kJ

Piling for marine structures 425