Bored Precast Piles
Bored precast concrete piles are constructed in a casting yard and subsequently lowered into prebored holes and the space grouted.
As far as possible, in-situ extensions shall be avoided.The casting yard should be well drained. As far as possible, longitudinal reinforcement shall be in one length. In case joints are needed, they should be staggered.The hoops and links for reinforcement shall fit tightly against the longitudinal bars and be bound to them by welding or by tying with binding wire, the free ends of which should be turned into the interior of the pile. The longitudinal bars may be held apart by temporary or permanent spreader forks not more than 1.5 m apart. The reinforcement shall be checked for tightness and position immediately before concreting. After casting the piles, they shall be stored as described in
Bored precast piles shall be .constructed by suitable choice of boring and installation techniques depending on detailed information about the subsoil conditions. The bottom end of the pile shall have proper arrangements for cleaning and grouting.
Piles shall be installed as vertically as possible according to the drawings, or to the specified batter.The deviation from specified alignment shall be as permitted for under-reamed piles.
Cement and sand (1 : 2) grout mixed with water in a high speed colloidal mixer is fed to the pile with grout pump of suitable capacity to the central duct through a manifold. Temporary casing used here shall be removed in stages with the rise of level of grout. The grout should be levelled off at the top. The strength of the grout shall be at least equal to the strength of the surrounding soil.
Where a pile is to have another length cast on to it before or during placing, the longitudinal reinforcement should be welded with full penetration butt welding, after the concrete at the top of the pile should be cut-off to expose not less than 200 mm of the bars. Bars may be lapped if it is not possible to undertake butt welding with an overlap of 40 times the dia of bar.