2. The elevation of pile top is designed as the elevation of pile cap bottom +50mm or directly indicated in the design.

3. The empty hole depth is the actual hole-forming depth, that is, the difference between the elevation of the orifice and the elevation of the bottom of the hole.

Extended data: drilling phase

(1) Install the drilling rig to make the centers of drill pipes coincide, and adjust its horizontal displacement and inclination error according to the specification requirements.

(2) When drilling with an impact drill, drilling can only be started after the concrete poured on the adjacent holes has solidified and reached a certain strength.

(3) In the drilling process, the positive circulation rotary drilling construction technology is adopted. In the clay layer, less mud is put, and drilling is used to make slurry, while in the sand layer, the mud concentration is increased to strengthen the wall. The drilling speed always adapts to the mud displacement.

(4) The hydrostatic pressure in the hole is always 0.2kg/cm2, and the water level in the casing is always higher than the reservoir. In loose strata, the relative density and consistency of mud should be appropriately increased to reduce the influence of flushing fluid on the hole wall, and at the same time, the rotation speed and WOB should be reduced to meet the requirements of construction quality control.

(5) When drilling, it is forbidden to drop foreign bodies such as drill bits and drill pipes into the hole. Always check the wear of the drill bit.

(6) Take slag samples at any time during drilling, with a density of not less than 1 group per meter. Within the range from design elevation 1.0 ~ 1.5m, take 1 group every 30cm, and each pile of slag samples shall be no less than 3 groups.

Reference source: Baidu Encyclopedia-Bored Pile