明挖隧道衬砌结构拆模时间研究及可靠度分析

Mold Removal Time and Reliability of Open-Cut Tunnel Lining

为保证明挖隧道工程的施工进度和工程质量,避免衬砌结构拆模后产生温度裂缝,通过对咸阳机场预留高铁工程最大尺寸断面隧道衬砌进行有限元模拟和现场试验,综合考虑施工环境和衬砌混凝土的时变性,研究明挖隧道衬砌结构温度裂缝和最大主应力的位置及变化规律。通过将模拟结果与各龄期混凝土强度进行对比,确定了最大尺寸断面隧道衬砌结构在混凝土浇筑48 h后拆模可以避免温度裂缝的产生,拟合了不同尺寸断面隧道衬砌结构的拆模时间计算公式。最后,引入时变可靠度理论验证了最大尺寸断面隧道衬砌结构拆模时间的合理性,将均匀设计法与响应面法相结合确定了衬砌结构最不利截面的荷载效应和统计特征,并将其代入极限状态方程,运用一次二阶矩法编制MATLAB计算程序,计算出衬砌结构在混凝土浇筑后48 h拆模最不利截面的可靠度为6.61,高于规范规定的标准值,从而证明了混凝土浇筑后48 h拆模是可行的。

To ensure the construction progress and quality of open-cut tunnels while preventing temperature-induced cracks in the lining structure after mold removal,a case study is conducted on a reserved high-speed railway project at Xianyang Airport in Xi′an,China.The simulation involves the tunnel lining structure with the largest cross-sectional size,employing finite element simulation and field tests.The analysis considers the locations and variation patterns of temperature cracks and maximum principal stress in the open-cut tunnel lining structure.The comprehensive assessment considers the time variability of the construction environment and the lining concrete.The simulation results are then compared with the concrete strengths at different ages,indicating that temperature cracks in the tunnel lining structure do not occur within 48 h after concrete casting.A calculation formula for the mold removal time of tunnel lining structures of different sizes is developed based on the simulation results.Subsequently,time-varying reliability theory is introduced to validate the rationality of mold removal time.The load effect and statistical characteristics of the most unfavorable section of the lining structure are determined through a combination of uniform design and response surface methods.These parameters are then incorporated into the limit state equation,and the reliability of the most unfavorable section of the lining structure 48 h after mold removal is calculated using the MATLAB program.The calculation employs the first-order second-order moment method.The resulting reliability value is 6.61,surpassing the standard specified in the guidelines.This outcome demonstrates the feasibility of the proposed mold removal time.