Pile Design and Construction Practice, Fifth edition

406 Piling for marine structures
permitting vessels to berth in any position along the face. Pairs of rakers resisting the ship
impact are spaced at intervals along the deck or are grouped to form ‘strong points’ with the
deck slab acting as a horizontal beam.
Breasting dolphins for the oil loading terminal of Abu Dhabi Marine Areas Ltd., at Das
Island, were designed by the British Petroleum Company to consist of groups of vertical steel
tubular piles. The main outer dolphins were formed from a group of seven piles, and the inner
secondary dolphins were in three-pile groups. The conditions at sea-bed level, which consisted
of a layer of shelly limestone cap-rock underlain by a stiff calcareous marl and then a dense
detrital limestone, favoured the adoption of vertical piles to absorb the berthing forces. The
36.6 m piles varied in outside diameter from 800 mm at the top to 1300 mm at the bottom,
the latter being closed by a full plate on which 15 roller cutters were mounted. The piles were
pitched through a reinforced concrete template placed on the sea bed and then drilled down
by rotating them by means of a hydraulically powered rotary table operated from a jack-up
platform. The cuttings were washed up the annular space between the outside of the pile and
the rock and this space was afterwards grouted with a sand–cement mix.
Broadhead (8.2) described a pulling test made on a mooring dolphin pile to confirm that the
lateral resistance of the weak rocks below the sea bed would not be exceeded at the working
load. The test pile had a bottom diameter of 1300 mm and the pull was applied at a point
24 m above the sea bed. The load/deflection curve obtained at a measuring point 22.86 m
above the sea bed is shown in Figure 8.9 and is compared with the theoretical deflection
curve assuming fixity at sea-bed level or support from an uncemented shell sand below sea
bed, using the elastic analysis of Reese and Matlock (see Section 6.3.4).
Horizontal movement at top of pile (mm)
1600
1400
1200
1000
800
600
400
200
0
10.4 m 24 m
ARRANGEMENT OF TEST PILE
Pull
Sea level
Theoretical curve for support
by uncemented shell sand
(Reese and Matlock)
100
1300 mm O.D.
steel tubular pile
Template
Sea bed
Variably cemented shell sand
Stiff clay
Limestone
Observed deflection
200 300 400 500 600 700
Horizontal pull at top of pile (kN)
Theoretical curve for
fixity at R.C. template
on sea bed
Figure 8.9 Load/deflection curve for 1300 mm O.D. steel tubular pile due to horizontal load at head
of pile (after Broadhead (8.2) ).