软土地区盾构隧道管片开裂特性实测分析及影响因素研究

基于某软土地区城市地铁1号线的实测数据，统计分析该地铁线路整体与典型区间的病害情况与裂缝分布特点，结果表明: 管片裂缝的分布密度与隧道收敛位移具有明显关联性，区间隧道病害以密布于隧道拱顶的纵向裂缝为主，且分布规律与管环旋转角度相关。在此基础上，为探明软弱地层条件对盾构隧道带来的不利影响，基于断裂力学的非线性数值分析方法建立地层结构法有限元模型，模型中管片采用弥散开裂本构并嵌入简化的钢筋网单元，纵向接头通过考虑张开的间隙接触模型模拟。计算结果阐明了管片开裂的特性与影响因素，结果表明： 1)随着地层土体弹性模量和侧压力系数的减小，在地应力条件下隧道损伤区域明显增加； 2)随着埋深增加，当前主要开裂区与预测开裂区深度在原有基础上进一步扩展，从而引起隧道整体开裂率的上升； 3)参数分析探明了实测拱顶裂纹分布规律的成因为封顶块位置的差异。

Analysis on Cracking Characteristic of TBM Tunnel Lining in Soft Soil Area and Its Influencing Factors

Based on the field measuring data of metro line 1 of a city in soft soil area, the disease state and crack patterns of the whole line and a typical section in soft soil area are statistically analyzed. The statistical results show that the distribution of the cracks is demonstrably related to the convergence displacement of the tunnel, and the longitudinal cracks are the main disease in metro section, while they is densely distributed on the tunnel crown and related to the rotation angle of the segment ring. On this basis, a layer structure numerical model is established using nonlinear numerical analysis method of fracture mechanics so as to analyze the adverse effects of weak ground conditions on tunnel rings. The smeared crack model and simplified reinforcement grid elements are used in model segment, while the longitudinal joint is simulated by the gap contact model considering the joint opening. The calculating results illustrate the cracking characteristics of the segment and its influencing factors. The results show the following. (1) The tunnel damage area increases significantly under in situ stress condition with decreasing elastic modulus and lateral pressure coefficient of surrounding soil. (2) The depth of current crack zone and predicted crack zone further expands on the original basis with increasing burial depth, resulting in an increase in overall crack rate. (3) The parameter analysis reveals that the main cause for the crack pattern on the tunnel crown is the position of the key segment.