盾构直接切削大直径群桩的刀具配置研究

Study on cutter configuration for directly shield cutting of large-diameter piles

以苏州地铁盾构切削穿越大直径桥梁群桩工程为依托,先从理论上探究切桩刀具的选型、适应性设计和布置方法,然后开展盾构直接切削Φ1200桩基现场试验,分析刀具损伤规律和切桩效果,对刀刃细部设计、刀间距取值、刀具立体布局等进行探讨和优化,并估算连续切削7根桩基的可行性。研究表明:切桩宜采用零后角负前角、双面刃的贝壳刀;贝壳刀以剪切切削与侧向挤碎的方式破除混凝土,以剪切切削的方式切筋,其磨损系数约为1.891mm/km;刀间距和刀身宽度的确定应能满足全覆盖面切削桩身混凝土;钢筋是否受周边混凝土的包裹固定是其能否被有效切断的关键,为此提出超前贝壳刀的立体布局方案以及分次切筋的切削理念;合金刀刃上应避免存在尖锐棱角,切削侧部桩对刀具的损伤要大于切削中部桩。研究成果成功应用于工程实践,并表明盾构连续切削多根大直径桩基是可行的。

Based on the project for shield cutting of large-diameter bridge piles in Suzhou subway, the type selection, adaptability design and layout method for pile cutters were studied firstly from the theoretical perspective, and then the field test on shield cutting of qbl200 diameter piles was carried out to analyze the damage law of cutter as well as its cutting performance. According to the test, the detail design of blade, cutter spacing and spatial layout of cutters were discussed and optimized, and furthermore the feasibility of cutting 7 piles continuously was evaluated. The results show that the shell cutter with double-side blade as well as zero back angle and negative front angle was recommended for cutting piles. The shell cutters broke concrete in the way of shear cutting and lateral crushing, and the steel rebar was cut by shear cutting with the coefficient of wear for cutter as 1. 891mm/km. The determination of cutter spacing and cutter width should cover the entire cutting plane of pile concrete. The wrapped and fixed conditions of rebar by surrounding concrete is a key factor of determining whether rebar could be cut off effectively, and consequently a spatial layout scheme of advancing shell cutter and the concept of cutting rebar in multiple times were presented. In addition, sharp corner should be avoided on the alloy blade, and cutting side piles may produce more damage on cutters compared to cutting central piles. The success of applying research results to engineering practice indicates that shield cutting of large-diameter piles continuously with adequate cutter configuration is feasible.