Bottom-expanding drill method
The pile end resistance is directly proportional to the pile end bottom area in the same stratum. According to the premise of a constant pile diameter, increasing the bottom area of the pile end will greatly increase its end bearing capacity. In this way, the bottom-expanding drill bit is an effective technical method for improving the vertical bearing capacity and pullout resistance of a single pile.
In Japan, most rotary drill rigs are equipped with oil pipe trays underneath the power heads, which are related to the bottom-expanding drill bits, and the use of bottom-expanding piles can save 50% of concrete, so 95% of pile holes there are base-expanding piles.
Post-pressure method
The single pile bearing capacity can generally be increased by 30 to 90% using this method, as it eliminates the hidden problem of slag at its bottom, reinforces the pile body, compacts the soil around the pile, and enhances the soil-pile bond.
In the post-pressing process, pressed cement slurry is combined with pile bottom slag to form concrete, thus eliminating the influence of pile bottom slag.
“False tips” formed by segregation are filled with pressed cement slurry, which strengthens the concrete at the pile tip by filling “dry slag stones.”
As a result of the pile bottom pressure slurry compaction, the cement slurry penetrates the soil below the pile to form a solid body, which improves the strength of the soil at the bottom, thus increasing the pile end bearing capacity of the bored pile.
A high-pressure slurry injection can exert upward prestressing force on a pile’s bottom, which is beneficial to the pile’s bearing capacity.
On the pile side, the high-pressure pressurized slurry has an extrusion compacting effect on the soil around the pile and penetrates into the soil, forming bamboo-like bubbles of slurry, which improves pile side friction resistance.
After drilling the pile hole and installing the reinforcement cage, the slurry pipeline is pre-set, the pile concrete is filled, and the slurry is pressed after solidification. Before grouting, you should conduct a clear water injection test to verify that the pipeline is smooth. Piles should be stacked side-by-side, then bottom-by-bottom. Fill first, then grout afterward.
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