深覆盖岩溶地区高层建筑桩基优化实践

高度超过150 m的高层建筑，对地基基础的承载力要求较高，一般采用桩筏基础型式。位于深覆盖岩溶地区的桩基础，应充分发挥岩溶上覆地层的承载力，避开岩溶发育的不利地段，达到桩基优化的目的。文章结合深覆盖岩溶地区一高度为177 m的高层建筑项目，详细介绍了桩基优化设计、大面积工程桩施工以及桩端后注浆施工情况。项目采用桩端后注浆工艺并运用长短桩设计理念，将桩长由原设计的40 m优化至核心筒区域28 m及非核心筒区域23 m，试桩检测结果和塔楼沉降观测结果表明，单桩竖向极限抗压承载力和基础刚度均能够满足设计要求，且基础差异沉降较小，说明桩端后注浆技术能有效提高桩基承载力和基础刚度，采用长短桩设计理念可显著控制差异沉降，深覆盖岩溶地区可利用后注浆技术，充分发挥灰岩上覆地层的承载力，来规避穿越岩溶区域的桩基施工风险。 

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.