Abstract:When the cast-in-place pile with a diameter of that is not less than 2000mm enters the hard rock stratum, in case of inclined rock surface or poor integrity of rock mass, development cracks and fracture zones, two new types of bits of upper centralization and lower centralization are researched . By adding upper centralization and lower centralization structures on the rotary drilling bit, guided and step-by-step reaming drilling is conducted, so that the bit as a whole is restrained by lateral support, so as to accurately locate the bit drilled in hard rock.The perpendicularity of the borehole is ensured, and the problem of eccentric hole caused by broken rock mass or inclined rock surface is effectively overcome, so as to reduce the cost and difficulty of problem solving.