Pile Design and Construction Practice, Fifth edition

Types of pile 29

give a sufficiently thick coating to prevent the piles from occasionally ‘locking-in’to the

moulds, in spite of a 1 in 10 taper on the sides. The oil also contaminated the prestressing strand.

When piles are cast within wooden side forms the latter should be removed as soon as

possible, and wet curing by water spray and hessian maintained for a seven-day period. As

soon as crushing tests on cubes indicate that the piles are strong enough to be lifted they

should be slightly canted by careful levering with a bar and packing with wedges to release

the suction between the pile and the bed. The lifting slings or bolt inserts may then be fixed

and the pile lifted for transporting to the stacking area. This operation of first canting and

lifting must be undertaken with great care since the piles have still only a comparatively

immature strength and any cracks or incipient cracks formed at this stage will open under

driving stresses.

The piles should be clearly marked with a reference number, length, and date of casting

at or before the time of lifting, to ensure that they are driven in the correct sequence.

Spacer bolts Bearer

Piles already

cast

Spacer blocks

Concrete casting bed

Bottom

boards

Sheathing

Figure 2.9Casting precast concrete piles in tiers.

108 394

(^19

-^4

99 )

(1^9

-^2

99 )

(8

99 )

102 394

356

102 108394

1

10

Heating

elements

114 114444 444

406

203

(4 4199 ) (1 9 – 3 2199 )(1(4 99 )(4 9 – 3 1299 )(1 99 ) 9 – 3 2199 ) (4^1299 ) (1 9 – 5 2199 )(1(4 2199 ) 9 – 5 1299 ) (4^1499 )

Figure 2.10Heated concrete moulds for prestressed concrete piles.