Why pile chipping is required before the pile cap works
Piles were cast with high slump concrete, during the concreting of piles, there is a chance that fines from concrete might accumulate at the top and also if there is any slush in the bored pile, it will also come up during concreting. So the concreting of the pile is overflowed to take out all impurities. After casting of the piles, the top portion of the pile is chipped out till the pile cap.
Excavation is done around the pile area to facilitate removal of the extra pile portion by chipping. Pile Chipping is the extra pile that is above the cutoff level, which provided for good and sound concrete. The main purpose of chipping is to remove the surplus slushy concrete (a mixture of concrete, slurry, and mud) over the cutoff level. When concreting is going on, the black slush comes out from the borehole. Black slush represents the mud which produced at the time of boring.
Pile Cut-off level is the actual level at which the piles below pier are made to be of the same level. The concrete of pile is cut-off at the specified level (given in the specifications or drawings usually around 75 mm) while the steel is kept projected in-to the pile cap to make an effective bond.
The pile cap usually forms part of the foundation of a building, typically a multi-story building, structure or support base for heavy equipment. The cast concrete pile cap distributes the load of the building into the piles. A similar structure to a pile cap is a “raft”, which is a concrete foundation floor resting directly onto soft soil which may be liable to subsidence.