After foundation pile construction, the top section of the pile is usually removed. During concrete casting, air bubbles, laitance, and other impurities tend to rise to the pile top, so the upper zone often contains a mixture of laitance and slurry. This reduces the strength of the pile-head segment. To ensure the required concrete strength of the entire pile, the upper defective segment must be chipped off.
Pile-head removal technology is now relatively mature. Depending on the equipment used, common methods include mechanical impact breaking, manual pneumatic air-pick breaking, ring-cutting, mechanical extrusion crushing, and expansive static splitting. The final choice should be based on pile diameter, number of piles, schedule, and cost.
Overview of Pile-Head Removal Methods
1. Mechanical Impact Breaking
An excavator is equipped with a hydraulic breaker at the end of the boom. The pile-head segment is broken and removed by repeated impact from the breaker.
2. Manual Pneumatic Air-Pick Breaking
A pneumatic air pick (a hand-held tool powered by compressed air, mainly used for breaking hard materials) is used for manual demolition.
For small-diameter piles, full direct breaking is typically adopted.
For large-diameter piles, the outer main reinforcement bars are first exposed, then horizontal holes are drilled at the cut-off level. Steel wedges are inserted, and impact from the air pick is applied to create a continuous horizontal crack through the drilled line. Finally, the pile head is lifted out as a whole, usually with a crane.
3. Ring-Cutting Method
A cut-off line is marked around the outside of the pile. An attached cutting machine is used to cut along this line, with cutting depth controlled by the measured concrete cover thickness. After cutting, an annular groove about 10 cm wide is chipped out with an air pick. The cover concrete is then removed as a whole and the main reinforcement is exposed. Subsequent steps are similar to the manual pneumatic air-pick method.
4. Mechanical Extrusion Crushing
Specialized crushing equipment is selected according to pile diameter, typically a matching circumferential hydraulic crushing device. Inside its rigid ring are multiple hydraulic jacks with crushing teeth. The device is installed at the pile cut-off level, and the jacks apply lateral pressure from multiple points to crush and remove the pile-head segment.
5. Expansive Static Splitting
When fabricating the reinforcement cage, isolation sleeves are installed around bars within the pile-head removal segment before cage lowering, isolating the reinforcement and eliminating bond grip between concrete and steel in that segment after hardening. A horizontal pipe is also pre-embedded at the cut-off level. In the later stage, one end is sealed and expansive agent is injected from the other end until full. The pile head is separated from the pile shaft by expansive static force.
