English：

The project of the Industrialization Demonstration Base of the National Chengdu New Drug Safety Evaluation Center has complex geological conditions, such as small pile diameter, serious hole collapse in the process of hole forming, and great difficulty in construction. The construction of rotary drilling cast?in?place pile is easily affected by pile diameter, geological conditions, construction technology and other factors. After studying the existing approaches of rotary drilling bored pile, the three?stage hole formation pile construction technology of rotary drilling bored pile,was adopted to avoid the construction difficulties caused by shrinkage and hole collapse under complex geological conditions, ensure the quality and safety of pile foundation construction, and improve the construction efficiency and comprehensive benefits, obtaining unanimous recognition of both the employers and the participating units and creating good social benefits.