大直径灌注桩硬岩旋挖导向分级扩孔施工技术

直径不小于2 000 mm的灌注桩钻进入硬岩地层遇存在倾斜岩面或岩体完整性差存在发育裂隙、破碎带等情况时，研究制作上扶正、下扶正两款新型钻头。通过在旋挖钻头上增加上扶正、下扶正结构，进行导向，逐级扩孔钻进，使钻头整体受到侧向支撑约束，从而对硬岩中钻进的钻头进行精准定位，确保了钻孔垂直度，有效克服岩体破碎或倾斜岩面出现的偏孔问题，减少问题解决成本，降低问题处理难度。

Construction Technology of Large Diameter Cast-in-place Pile with Hard Rock Rotary Excavation Guidance and Graded Reaming

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.