Abstract: The subsurface conditions in Qianhai area of Shenzhen are special. Because of the reclamation of land in the previous years, the upper part is mostly formed by large-size riprap replacement of the silty soft soils, the rock-filling layer is deep, and the lower part is the Quaternary marine-terrestrial sedimentary layer, which makes the borehole forming of the cast-in-place concrete pile difficult. In order to resolve the construction problem of the rotary excavation of the cast-in-place concrete pile in this special rock and soil strata, a project case history in this area is introduced to analyze the geological conditions and compare the construction method. This paper introduces the preparation of high-quality slurry and the mechanical borehole cleaning method of the suspension slurry method. The major points of the operation through the improvement and optimization of the construction are provided. Key construction procedures, the problems and treatment methods that might be encountered during the construction are also discussed in the paper. These methods are of high practical value, which can effectively ensure the safety, quality, progress and construction efficiency of the pile, and have little impact on the surrounding environment.

Key words: Deep Rock-Fill Layer, Rotary Drilling Borehole, High-Quality Drilling Slurry,  , Suspension Slurry Method