Abstract: The techniques that can penetrate the gravelly soil with large size boulders and maintain the stabilities of bore holes are key factors for the success of the castinplace reinforced concrete pile installation. This paper presents a new allflight auger drilling method with special drill bit and a shallow displacement auger. With the secondary drilling, the majority of the boulder and large size gravel soils can be pushed into the adjacent soils so that the displacement type of the cast-in-place reinforced concrete piles can be successfully formed. The concrete pile integrity and static loading test indicated that the concrete pile installed with the new method had good installation quality. Due to the compaction effect, higher axial pile capacity can be obtained.

Key words: Rounded Gravel Soils, Auger Cast Piles, Compaction Effect, Secondary Drilling