盾构直接切除大直径桩基的试验与工程实践

为研究盾构直接切削大直径桩基的可行性、评价滚刀和切刀的切桩性能、获取盾构切桩的关键掘进控制参数，进行盾构直接切削大直径桩基的模型试验。研究结果表明： 1)盾构切除大直径桩基宜采用“低推进速度，高转速”的磨桩方式，刀盘推进速度建议取3~5 mm/min，刀盘转速建议取1.0~1.2 r/min； 2)滚刀对混凝土的切削效果较好，切刀对钢筋的切削效果较好； 3)混凝土强度越高，滚刀对钢筋的切割效应越好； 4)滚刀切桩时，刀盘轴向振动作用明显，在低推进速度和低转速下，其刀盘的振动小于切刀切桩时刀盘的振动; 5)切刀切桩时，刀盘环向振动强烈，在高推进速度下刀盘易卡顿，提高转速可减少刀盘卡顿。

Experiment and Engineering Practice of Directly Removing Large diameter Pile Foundations by Shield

In order to improve construction efficiency, it is necessary to study the feasibility of directly cutting large diameter pile foundation by shield and the performance of hob and cutter and to obtain the key driving parameters of shield. A model experiment of directly cutting large diameter pile foundation by shield is carried out. The results show that: (1) Grinding method, "low propelling speed and high rotational speed", should be adopted for shield to cut pile foundation of large diameter, and the propelling speed of cutter head is suggested to be 3~5 mm/min, the rotational speed to be 1.0~1.2 r/min. (2) The hob is more favorable to concrete, while the cutter is more favorable to steel bars. (3) The higher the concrete strength, the better cutting effect of hob on the steel bar. (4) The axial vibration of cutter head is obvious when the hob cutting piles, but it is less obvious than that when the cutter cutting pile foundations at low propulsion speed and rotation speed. (5) The hoop vibrationg of cutter head is strong as cutting pile foundations, and it is easy to be jamed under high propelling speed, while increasing rotational speed can effectively reduce the stuck times of cutterhead.