Pile Design and Construction Practice, Fifth edition

Bridge abutment
support piles
Embankment support piles
PF ash fill
Terram fabric reinforced with
‘Paraweb’ strapping
Cross section A-A
9.6 Piled foundations for over-water bridges
A
Reinforced fabric
A
Miscellaneous piling problems 463
PF ash fill
General fill
Reinforced concrete pile caps
Soft alluvium
Precast concrete piles
Transition piles
Figure 9.21 Arrangement of settlement reducing piles beneath bridge approach embankment (after
Reid and Buchanan (9.31) ).
9.6.1 Selection of pile type
Because of the desirability of avoiding different types of piling on the same bridge project
the piling used for piers constructed in over-water locations will usually dictate the type to
be used for the abutments. Driven piles are the favoured type for over-water piers. The
installation of bored piles is limited to work carried out either in a pumped-out cofferdam,
or in a permanent casing driven below river bed. In fast-flowing rivers the casing will have to
be taken down to a sufficient depth below the river bed to obtain fixity against overturning
particularly in conditions of bed scour. Tubular steel piles or precast concrete piles of cylindrical
section are preferred to H-sections in order to minimize current drag and eddies
causing bed scour. The need for raked piles for efficient resistance of lateral forces again
favours a driven type of pile. Where precast prestressed cylindrical piles are used in
deep-water locations or for deep penetrations below bed level there can be problems with
handling long heavy piles. Also, forming joints to extend partly driven piles can cause
difficulties and delays.
Attrition by soil particles of the exterior surface of piles at the sea or river bed can be
a factor influencing the material of the pile and its wall thickness. This is more likely to be a
problem where the bed level is constant or changing over a limited range rather than rivers
where seasonal floods cause wide variations in bed contours.