Field investigation of the influence of grouting pipe types and hole-forming methods on the response of post-grouted drilled shafts

This paper investigates the influence of grouting pipe types and hole-forming methods on the bearing characteristics of post-grouted drilled shafts (PGDSs) using field test data. It compares the percussion, auger, and rotary drilling methods, as well as straight and U-tube pipe types, analyzing their respective advantages. The bearing capacity enhancement coefficients of PGDSs with U-tube pipes are derived by comparing calculated and measured values, with the interaction mechanism of these factors are explored. The results show that auger drilling provides superior hole formation quality compared to rotary and percussion drilling, greatly improving shaft quality. The U-tube pipe outperforms the straight pipe in cement spreading and effectively controlling shaft tip settlement, thereby maximizing side resistance. Additionally, rotary-drilled shafts with U-tube pipes exceed the designed bearing capacity by 10%. Post-grouting technology is recommended for rotary drilling, with the economic benefits of rotary-drilled shafts requiring careful consideration. This study provides valuable insights into selecting the appropriate hole-forming method and grouting pipe type for engineering practice and offers guidance for improving design methods in existing specifications.