Bored Cast in-situ Piles
In this system, a hole is bored within the ground, reinforcement, if needed lowered and concreting done. Boring is commonly carried out through rotary or percussion kind drilling rigs. Kelly mounted hydraulically operated grabs are also used.
If the soil is such in which the walls of the bore would cave in, casing tubes have to be used that is consequently extracted although concreting. Sometimes the casing is left in the ground and the concreting completed within the casing. Such piles are called as cased piles. Another method to remain the sides of the hole in position is through pumping bentonite slurry within the borehole as the soil is erased. Bentonite is clay of the montmorillonite group. Its slurry forms a membrane along the walls of the bore hole and also acts hydrostatically to retain the stability of the sides of the hole. After the needed depth of the bore is reached a high slump concrete is placed through means of a tremic.
For piles of little diameter and depths upto 10 m, the minimum cement content of the concrete should be 3.5 kN/m3 although for larger diameter and deeper piles it should be 4 kN/m3. Slump of concrete should range among 100 to 180 mm depending on the manner of concreting.
Whereas drilling mud is used before concreting, the bottom of the hole should be flushed within fresh bentonite slurry. All through the boring operation, it has to be ensured which the drilling mud suspension is of the needed consistency.