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 between pile cap and piles.
Why pile is trimmed or cut?
For Piles casted in dry bore holes while using temporary casing, piles heads shall be casted to a level a bit above the specified cut-off so that, after cutting or timming, a sound concrete connection can be made with the pile. While we cast the piles under water we use tremie method of concreting.
In this method the shaft of concrete pile is casted by using a tremie pipe which is lowered below the water level or the interfacing concrete and concrete is poured with pressure while the slurry and other raw concrete or weak concrete comes up. For tremie method slump mix should be greater than 175 mm. Pile cut-off level can be above or below the group. When it is above ground, Concrete should overflow from the pile head on completion.
Due to tremie method the upper part of pile consists of weak concrete as well as some contaminated boring debris. In case the pile cut-off below the ground, the concrete level should be raised to allow for around 1 m for trimming off the weak concrete.
Traditionally the cropping or trimming process to achieve the required cut off level is done using a jackhammer or hand-arm vibration syndrome (HAVS).
Source: iamcivilengineer.com
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