Optimization of pile foundation for high-rise buildings in deep-covered karst areas

High-rise buildings, with a height over 150 m, commonly require high bearing capacity of the foundation and a pile-raft foundation is generally adopted. The pile foundation located in the deep-covered karst area should make full use of the bearing capacity of overlying strata and try to avoid the unstable section of the karst to optimize the use of pile foundation. Taking a 177 m-high building project in a deep-covered karst area as an example this paper presents the details of optimized design of pile foundation, large-scale construction and post-grouting at pile tips. Using the scheme of pile tip post-grouting and design of long- and short-piles, lengths of piles under the tower building is optimized from 40 m to 28 m under the core-tube zone and 23 m under the non-core-tube zone. Load tests and subsidence observations show that the vertical ultimate bearing capacity of single pile and foundation stiffness meet the designed requirement, and the differential settlement of foundation is very small, indicating that the post-grouting technology can effectively improve the bearing capacity of piles and the foundation stiffness. Adoption of long-short pile foundation can reduce differential settlement remarkably. Pile post-grouting technology can be recommended in high-rise building projects in deep-covered karst areas to make full use of the bearing capacity of overlying strata above the karstand reduce or avoid the risk of pile foundation across karst zones.