Design of triple-row pile foundation pit support combined with CFG piles under shallow to deep process

In a construction project in Beijing, a high-rise residential building is adjacent to an underground garage, with a foundation height difference of 7.6 m. According to the construction schedule, the shallow residential building must be completed before the garage excavation. The design of the garage’s foundation pit support must consider the most critical scenario: the residential structure is topped out while the backfill space of the garage pit remains unfilled. To effectively control deformation in the deep foundation pit and the shallow residential building, a triple-row pile support system is adopted, integrating the adjacent CFG piles of the residential building. Numerical simulations and field monitoring demonstrate that deformations in the deep pit, settlement, and inclination of the residential building are within controllable limits. The load from the residential building is primarily transferred to deeper strata via the CFG piles, exerting minimal impact on the deep excavation. In this scheme, CFG piles serve dual functions: vertical load-bearing and lateral resistance. Their lateral stiffness is enhanced through a combination of diameter expansion and reinforcement. Additionally, uniformity in the bearing capacity and stiffness of the composite foundation must be rigorously controlled.