This is a construction of pile cap.
First of all, the level of the pile cap need to be determined and complied to the drawing. Excavate a pit until the required level and sufficient pit size for formwork erection.
Usually cut pile, people will use hammer to knock it down at the required cut off level. Hence, the edge or the head of the pile is always in odd shape or broken pieces.
The better solution will be like this.. Mark the level and use grinder to cut it off at the level. It provides a better accuracy of cut off and flat surface of the pile head.
After cut along the perimeter of the pile, the upper portion (waste length) will be knocked off by hammer. Then, manually push it and break the joint. It also prevent the head portion being knocked down into broken pieces and affect the strength at the pile head.
After that, the cut portion will be remove. The lean concrete will be laid as per drawing and size of the pile cap.
It follow up by formwork with strutting, usually, it is in box shape and guided with 2"x3" timber to prevent bulging. The prefabricated reinforcement steel cage will be installed together with the column stump rebar. It is guided and tighthen into position with a cross timber 1"x2".
When everything is ready, concreting will take place and concrete will be pour into the box and pile cap is formed. tTereafter, the next element of structural work will continue like column stump, backfiling, etc.
An example of pile cap is shown at the above.