Quasi-static Test on Mechanical Behaviors of Pre-hole Isolation Pile-soil Interaction

The heads of reinforced concrete (RC) piles are extremely easily damaged owing to the longitudinal deformations induced by the superstructures in integral abutment bridges (IABs) under temperature variations and seismic actions. The pre-hole isolation piles can be obtained by predrilling oversized holes (pre-holes) filled with damping materials. This can improve the seismic performance of RC piles in IABs. A pile beneath an abutment in an IAB was chosen as a case study. Quasi-static tests considering different pre-hole diameters and damping materials (rubber particles and foam) were carried out to analyze the mechanical behaviors of pre-hole isolation pile-soil interaction. When the loads reached the peak values, pile-sand separation was observed in the specimen without a pre-holes. Pile-damping material and damping material-sand separations were found in the specimens when the pre-holes diameter was two times the pile diameter. The horizontal displacement of the pile was completely absorbed by the deformation of rubber particles in the specimen with a pre-holes filled by rubber particles when the pre-holes diameter was three times the pile diameter. Therefore, the pre-holes diameter can be considered the parameter with the most influence on the transmission mode of pile horizontal displacement to the damping materials. Compared with the specimen without a pre-holes, the hysteresis loops of the pre-holes isolation specimens were larger, as were the equivalent viscous damping ratios. It can be concluded that the energy of the damping materials can be dissipated in the pre-holes isolation piles. The energy dissipation of the specimen with a pre-holes filled by rubber particles is stronger than that of one filled by foam. This is because the deformation capacity and automatic reset characteristics of the loose rubber particles can help energy dissipation; however, the viscosity and damping characteristics of the foam are influenced by its integrity. The stiffness of the p-y curves of the pre-holes isolation specimens within the pre-holes depth were significantly lower than those of the specimen without a pre-holes (maximum decrement of 45.1%). With an increase in the pre-holes diameter or a decrease in the stiffness of the damping materials, the soil modulus coefficients decrease. Compared with the specimen without a pre-holes, the ultimate load-bearing capacities of the pre-holes isolation specimens were slightly larger, and the initial stiffness and maximum bending moments along the piles were slightly smaller.