Investigation on the lateral performance of new piles in sand sites containing existing piles and shallow cement-treated backfill

Piles are extensively utilized as the foundation to support buildings, bridges, and other superstructures subjected to lateral loads. The lateral load-bearing performance of newly installed piles in sites with existing piles is inevitably influenced by the presence of existing piles due to the interactions between the new pile, soil, and existing piles. Conversely, the lateral capacity of new piles can be significantly enhanced by effectively regulating these interactions. This study quantified the effect of shallow cement improvement on laterally loaded new piles in sand sites containing existing piles and shallow cement-treated backfill for different variables. A numerical model of new pile-soil-existing pile interactions under lateral loads was initially validated against 40 g centrifuge tests in density sand. Subsequent analyses incorporating shallow cement-treated backfill explored the lateral bearing mechanism of new piles and the corresponding response of existing piles. The findings indicate that cement-treated backfill can substantially enhance the lateral capacity of new piles for ultimate limit state (ULS) design limit by two times, compared with the condition without cement-treated backfill. With the increase of the depth of the new pile embedded in the cap, the thickness and modulus of the cement-treated backfill, the lateral capacity of the new pile increases. However, the depth of the existing pile embedded in the backfill has a limited influence on new pile capacity. Finally, a practical method for assessing lateral new pile capacities in sand sites containing existing piles and shallow cement-treated backfill was developed, demonstrating considerable advantages in designing laterally loaded new piles considering shallow cement improvement.