Deformation Control Standards of CFG Pile Composite Foundation in Loess Region

The deformation control standard for composite foundation load tests was originally established for multi-story and low high-rise buildings. However, the standard continues to be applied to high-rise and Class A structures(above 30 stories) without accounting for the increase in foundation settlement under higher structural loads, raising concerns about its applicability. High-rise buildings with plain concrete pile composite foundations in loess regions often experience significant settlement, sometimes leading to settlement-related structural issues. It is necessary to discuss the deformation control standards from a design theoretical perspective.Firstly, the shear stress-shear displacement relationship is determined through interface shear tests and a mechanical model for the contact interface is derived. A numerical simulation model incorporating pile-soil interaction is then developed for both group-pile and single-pile composite foundations. The settlement ratio between composite foundations and load tests is calculated. The numerical results are validated by comparing the settlement ratios of the composite foundation in existing cases with those from the load tests. Finally, a revised deformation control standard for single-pile composite foundation load tests in loess regions is proposed, along with recommended values. The results show that: The settlement ratio increases significantly with structural load; Soil properties around the piles have minimal impact on settlement ratio; The settlement ratio is primarily governed by load, and as load increases, the settlement observed in load tests becomes less representative of the actual behavior of group-pile composite foundations; A recommended deformation control standard table for load tests on plain concrete pile composite foundations in loess regions is provided based on structural load considerations.