盾构直接切削大直径钢筋混凝土桩基试验研究

基于苏州地铁盾构切削穿越14根大直径桥桩工程需要，开展盾构直接切削两根直径 1 200 mm桩基的现场试验，分析切桩效果及机制、掘削参数特征、刀具损伤规律等，并探讨研究盾构直接切削大直径桩基的可行性及关键技术。试验表明：贝壳刀可适用于直接切削桩基，以剪切切削与侧向挤碎的方式破除混凝土，切筋机制为剪切切削；钢筋受周边混凝土的包裹固定情况是其能否被有效切断的关键因素；作用于桩身的推力值、扭矩值与切深近似成线性关系；切桩时推速的波动幅度较大，易造成刀具合金崩裂；切削侧部桩相比中部桩对刀具的损伤更大。根据试验结果，提出超前贝壳刀的配置方案以及分次切筋的切削理念，建议推速设定值不超过2 mm/min，刀盘转速宜用中档。试验成果成功应用于苏州切桩工程，试验与实践共同表明盾构直接切削大直径桩基是可行的。

TEST STUDY OF SHIELD CUTTING LARGE-DIAMETER REINFORCED CONCRETE PILES DIRECTLY

Based on the construction need of shield cutting 14 large-diameter bridge piles in Suzhou subway，the field test of shield cutting two 1 200 mm diameter piles was carried out；the effect and mechanism of cutting piles，characteristics of cutting parameters and damage law of cutting tools were analyzed. Then，the feasibility and key technology of cutting large-diameter piles were studied. The test results show that shell cutter can be fit for cutting pile directly；it breaks concrete by the way of shear cutting and laterally squeezing to fracture；and its working mechanism of cutting rebar is shear cutting. The wrapped condition of rebar by surrounding concrete is the key factor determining whether rebar could be cut off effectively. The thrust value and torque value which acting on the pile have an approximately linear relationship with penetration. The alloys of cutting tools are easily cracked because of great fluctuation amplitude of advancing speed. Cutting side pile produces more damage on cutting tools than cutting central pile. According to test results，the configuration scheme of advancing shell cutter and the concept of cutting rebar with different times were presented；the setting value of advancing speed was suggested against exceeding 2 mm/min，and the cutterhead should rotate with medium speed. The test results were successfully applied to the Suzhou cutting piles engineering；the test and engineering practice jointly indicate that shield cutting large-diameter piles directly is feasible.