(1. Guangzhou Institute of Building Science Limited Company，Guangzhou，Guangdong 510440，China； 2. Guangzhou Everbright Real Estate Limited Company，Guangzhou，Guangdong 510250，China)
Abstract：When different weathered sandstones and mudstones are inter-embedded at different buried depths，and the weathered rock maximum strength is smaller than 14.4 MPa，it is difficult to find a suitable pile-end depth according to technical code for building pile foundations. Under-reamed uplift piles are constructed by rotary rig in different weathered sandstone and mudstone in South China. Rock-embededembedded under-reamed uplift piles are instrumented with strain gauges to measure the axial load distribution at all load increments. Based on the testing data，the crack and the deformation of shaft are discussed. The results show that the ultimate uplift capacity of pile is effected affected by pile friction and enlarged base of pile. The pile friction could be calculated considering that it is variable with pile length. The ultimate uplift capacity of pile is mainly effected affected by enlarged base of pile. Testing data show that the ultimate uplift capacity of pile is also decided by the critical displacement which is limited by the above building structure. To get larger ultimate load capacity of pile，it is useful to decrease the cracks and the deformation of pile under the pulling force such as constructing a short and large-diameter pile. Some methods such as vertical prestressed anchor are suggested to reduce the crack of shafts.
