At present, the common technical methods to improve the vertical bearing capacity of single pile in cast-in-place piles are foundation expansion method and post-grouting method.

In the same stratum, pile end resistance is proportional to the pile's end base area. When the pile diameter remains constant, increasing the base area significantly enhances the bearing capacity. Therefore, using an expanded base drill bit to enlarge the pile hole bottom creates a smaller-top and larger-bottom structure, which is an effective technique for improving vertical bearing capacity and uplift resistance. Most rotary drilling rigs in Japan are equipped with oil pipe racks under their power heads for expanded base drills. This method saves 50% of concrete usage, resulting in 95% of Japanese pile holes being expanded base piles.

The post-pouring method effectively addresses settlement issues at pile bases, strengthens the pile body, compacts surrounding soil, and enhances bonding between piles and surrounding soil, thereby increasing single-pile bearing capacity by 30-90%. The process creates a concrete composite through cement slurry injection that combines with settlement materials, eliminating their adverse effects. It also eliminates "hollow tips" and "dry debris" caused by segregation during filling, improving concrete strength at pile tips. Post-pouring compacts soil and forms consolidated structures through cement infiltration, significantly enhancing end-bearing capacity of bored piles.

High-pressure slurry injection generates upward prestress at pile bases, benefiting end-bearing piles. High-pressure grouting on pile sides compacts surrounding soil and forms bamboo-joint-like voids, creating a "bamboo-joint pile" effect that increases lateral friction resistance. After hole completion, pre-installed grouting pipes are used for concrete filling followed by post-curing. A water injection test confirms pipeline integrity before grouting. Grouting follows lateral reinforcement before foundation treatment, with batch pouring preceding batch grouting.