Experimental and finite element analyses of laterally loaded RC piles with pre-hole filled by various filling materials in IABs

Under seismic actions, reinforced concrete (RC) piles are considered the most vulnerable components of integral abutment bridges (IABs). This paper investigates the mechanical behavior of the pile with pre-hole seismic isolation system through pseudo-static low cycle tests and numerical analyses on scaled specimens with various filling materials. The ultimate goal of this technical solution is to improve the seismic performance of IABs. The experimental results proved that the pile specimens with pre-hole seismic isolation system exhibit higher energy dissipation than those without pre-hole. The equivalent viscous damping is 17.1 ∼ 49.3 % higher when the filling is rubber and 3 ∼ 12 % higher using foam. The influence of the pre-hole diameter and soil deformation is also significant. When the pre-hole diameter is large enough, the horizontal displacement of the pile specimen is entirely absorbed by the rubber particles. Nevertheless, the pre-hole seismic isolation system does not significantly influence the failure mode, skeleton curve, yield load and bearing capacity. Finite element models (FEMs) were implemented in ABAQUS and calibrated using the experimental results. The FEMs allowed extrapolating the experimental outcomes under different geometrical and mechanical configurations, considering the sand-pile interaction with various filling materials (rubber particles and foam), and pre-hole sizes. The numerical results showed that the subgrade modulus and the ultimate soil resistance decrease when the pile has a pre-hole seismic isolation system. Therefore, the lateral deformation of a pile with pre-hole seismic isolation system can be estimated by multiplying the subgrade modulus used for the pile by a specific reduction factor dependent on the pre-hole geometry and the mechanical parameters of the filling material. The paper proposes and discusses a novel definition of the p-y curves for predicting the response of the pile with pre-hole seismic isolation system modified from classical p-y curves.