To address the technical challenges in widening existing embankment due to terrain constraints, a new composite supporting structure termed as adjacent composite pile-sheet wall (ACPSW) is proposed, i.e., the new pile-sheet walls are installed side-by-side in the middle of the old pile-sheet walls. Based on the Lanzhou Hub project of Zhongwei to Lanzhou Railway, this paper investigates the pile horizontal deformation, pile bending moment, soil pressure behind the pile and sheet, as well as load-sharing ratio between the old and new pile of ACPSW at different construction stages through field tests and numerical simulations. The results obtained from the field tests were compared with that obtained from the numerical simulation to validate the reliability of the numerical model. Moreover, a serviceability assessment on old pile of ACPSW is also conducted. The results indicate that the new pile-sheet wall and the old pile-sheet wall can deform synergistically and bear the external loads together under new widening embankment loads and train loads, and the load-sharing ratio between old and new pile is 0.62:1.0. The research results can provide a reference for the design and construction of existing line reconstruction and new projects adjacent to existing lines.

Geosynthetic-reinforced pile-supported (GRPS) embankments are a primary method for mitigating subgrade settlement. However, the load transfer mechanism between piles and soil remains incompletely understood, with the load sharing ratio (LSR) between piles and soil serving as a critical indicator for this mechanism. This study conducted a model test at a similarity ratio of 1:10 to investigate the effects of load amplitude, load frequency, number of geogrid layers, and pile types on the LSRs of piles and soil in GRPS embankments. The test results show that the pile's LSR increases with rising values of these parameters, while the corresponding LSR of the soil decreases. Among these parameters, the number of geogrid layers has the least effect on the LSRs of both piles and soil. Furthermore, the rigid long pile demonstrates a higher LSR than the flexible short pile, attributed to its greater stiffness. The influence of load frequency on the LSRs of the rigid long pile is also less significant compared to the flexible short pile. Variations of LSR increment can be predicted using a formula that incorporates the number of loading cycles. These findings provide deeper insights into the load transfer mechanism in the pile-soil system, contribute to the optimization of GRPS embankments design practice, and ultimately enhance performance and reliability of the GRPS embankments in geotechnical engineering applications.