无导洞法连拱隧道先行洞仰拱开裂及受力分析

Reason for Cracks of Double-arch Tunnel without Middle Drift and Analysis of Mechanical Characteristic

研究目的:为探明无导洞法连拱隧道先行洞仰拱衬砌开裂的原因,本文首先通过现场监测得到先行洞的受力规律,然后基于该受力特征提出一种考虑后行洞开挖的先行洞荷载-结构计算模型,进而结合现场监测和数值计算分析先行洞仰拱衬砌的开裂原因,最后评价先行洞二衬的安全性并给出相应的控制措施。研究结论:(1)当后行洞开挖前,先行洞二衬对称受力且各截面的安全系数大于2.4;当后行洞开挖后,先行洞二衬处于偏压受力状态,仰拱右侧的安全系数仅为1.25,其内表面恰是最大拉应力所在位置,与现场仰拱衬砌的开裂位置吻合;(2)先行洞仰拱衬砌开裂的原因是由于后行洞开挖导致的隧道偏压受力以及仰拱不均匀沉降;(3)提高支护抗力系数有助于改善衬砌结构的安全性,但支护抗力系数高于某值后安全系数变化不大;(4)本研究成果可为相关连拱隧道的设计和施工提供参考。

Research purposes:To reveal the reason for invert lining cracking in double-arch tunnels adopting the construction technology without middle drift,this paper first obtained the force patterns of the first tunnel by field monitoring.Based on the mechanism characteristics,this study put forward a load-structure calculation model for the first tunnel considering the excavation of the second tunnel.The results of numerical simulations combined with field monitoring were utilized to analyze the causes of the invert lining cracking.Finally,the safety of the secondary lining was evaluated and the corresponding control measures were suggested.Research conclusions:(1)Before the excavation of the second tunnel,the secondary lining of the first tunnel is in a symmetrical stress state and the safety factor of each section is greater than 2.4.After the excavation of the second tunnel,the first tunnel is under an unsymmetrical stress state,and the safety factor of the right side of invert is only 1.25.The inner surface of the right side of invert is exactly where the maximum tensile stress is located,which is consistent with the actual position of observed cracking.(2)The cracks of invert lining in the first tunnel is caused by uneven settlement and unsymmetrical pressure due to the excavation of the second tunnel.(3)Enhancing the support resistance factor could improve the safety of the lining structure,but the safety factor has little change when the support resistance factor is higher than a certain value.(4)The research results can provide guidance for the design and construction of similar double-arch tunnels.