Pile bottom ramming test of prestressed end-bearing pipe piles in weathered rock strata

This paper introduces a method for reinforcing the pile-end holding layer through the continuous impact of a rammer on the debris and weak rock layer at the bottom of the pipe pile under underwater conditions. The simulation tests on the ramming of rock-embedded precast pipe pile bottoms and inspections of the pile foundation post-reinforcement were conducted. Simultaneously, an analysis of vibration energy propagation in surrounding buildings and strata was performed. The field test results demonstrate that the presented tamping reinforcement method effectively crushes sediment and the weak rock layer at the pile bottom. It creates a hole with a certain enlargement effect at the bottom of the pipe pile, allowing concrete to replace the weak bearing layer and form a robust bond between the pile end and the simulated bedrock. Besides, a significant improvement in dynamic stiffness of the piles was presented, ranging from 67% to 175%, highlighting the efficacy of the reinforcement process. Vibration monitoring during the tamping process reveals that the height of the hammer and the water level in the hole play pivotal roles in tamping energy. Additionally, the adverse impact of vibration energy on adjacent structures can be mitigated by injecting water into the respective buildings.