Abstract: During the constructtion of drilled cast-in-place pile by normal circulation drilling, the time of the second clean-out hole must be controlled based on different soil properties. The time of clean-out hole is too short, the specific gravity of the mud and the thickness of the sediment at the bottom exceed standard value.The time is too long, the specific gravity is much small, the thickness of the sediment is bigger. In order to obtain the best values of the specific gravity and the thickness of sediment, it is necessary to control the time of the second clean-out Hole.