Integrated Analysis of Optimization and Settlement Characteristics in Hybrid Pile Systems for Reused Foundations

Pile reuse is a common technique in bridge renovation projects. However, the interaction mechanisms between new and existing piles under a shared cap remain unclear, restricting the size setting and further optimization of new piles in existing pile foundation environments. This study analyzes the effects of key parameters for new piles on the settlement behavior of existing piles under a shared pile cap using field measurement data and simulation results. The findings indicate that, within one pile cap, the settlement of both new and existing piles exhibits a negative correlation with the increasing new pile length. With the different load distribution patterns, the settlement differences between new and existing piles tend to be more stable in a lateral arrangement compared to a symmetrical distribution. Additionally, the pile cap size has a boundary effect on the combined pile system, specifically, as the pile cap length/width ratio is 4:2, the settlement disparity between new and existing piles tends to stabilize. Settlement behavior is also significantly affected by soil properties, with stiffer soils (higher elastic modulus) showing smaller settlements. Introduce the existing pile efficiency parameter, the main factors influencing settlement behavior rank as follows: soil properties, load distribution, pile distribution, pile length, pile diameter, and pile cap size. Based on these findings, it is recommended that the length of new piles be controlled to 1.0–1.1 times the length of existing piles, and the diameter of new piles be 1.0–1.2 times the diameter of existing piles. The study explores the interaction effects between new and existing piles, aiming to optimize the performance of pile reuse.