大直径盾构隧道中隔墙顶裂缝模式及扩展机制研究

Crack Mode and Propagation Mechanism of Diaphragm Wall Top in Large-Diameter Shield Tunnel

为揭示盾构隧道中隔墙顶部混凝土开裂机制,依托南京地铁某大直径盾构隧道区间,采用现场调研和扩展有限元分析相结合的方法,对隧道中隔墙顶部混凝土裂缝模式、分布特征以及开裂过程开展研究。结果表明:1)区间内中隔墙顶部出现96处裂缝,模式包括Ⅰ型、Ⅱ型、Ⅲ型、Y型和Z型,其中Y型和Z型裂缝是Ⅰ型裂缝的亚类型。2)裂缝起裂于烟道板水平向差异位移施加的对侧,Ⅰ型和Ⅱ型裂缝的长度和末端宽度发展曲线呈现3阶段变化特征;裂缝末端宽度与长度之间为非线性关系,250 mm和225 mm是Ⅰ型和Ⅱ型裂缝末端宽度快速增长的临界裂缝长度。3)Ⅱ型裂缝中,同一工况下2条裂缝的扩展曲线基本吻合,板缝间距对曲线各阶段长度与斜率影响较大;Ⅲ型裂缝中,首条裂缝扩展过程与Ⅰ型和Ⅱ型裂缝基本一致,其余2条裂缝的扩展均具有明显的脆性特征。

To investigate the cracking mechanism of concrete on the top of diaphragm walls, a case study is conducted on a large-diameter shield tunnel section of the Nanjing metro. By field investigation and extended finite element analysis,the crack mode, distribution characteristics, and cracking process of the concrete on the top of the diaphragm wall in the tunnel are studied. The results reveal the following:(1) There are 96 cracks on the top of the diaphragm wall, and the crack modes are types Ⅰ, Ⅱ, Ⅲ, Y, and Z, among which types Y and Z cracks are subtypes of type Ⅰ cracks.(2) The cracks start at the opposite side of the horizontal differential displacement of the flue plate;the development curves of the length and end width of types Ⅰ and Ⅱ cracks show a three-stage characteristic;the end width and length of the cracks are nonlinearly related;250 and 225 mm are the critical crack lengths with the rapid growth of the end width of types Ⅰ and Ⅱ cracks, respectively.(3) In type Ⅱ cracks, the propagation curves of two cracks under the same working condition are consistent, and the space of plate joints significantly influences the length and slope of each stage of the curve;the first crack propagation process in type Ⅲ cracks is consistent with that in types Ⅰ and Ⅱ cracks, and the propagation of the other two cracks have obvious brittle characteristics.