明挖法隧道衬砌开裂原因分析与预防措施研究

Research on the Cracking Causes and Prevention Measures of the Tunnel Lining by Open Excavation Method

研究目的:混凝土开裂问题一直被人们所关注。某铁路隧道采用明挖法施工,部分工程完成后,衬砌产生开裂现象。通过分析裂缝数量与裂缝形状、裂缝长度、裂缝宽度和裂缝深度的关系,研究发生开裂的原因,从而制定预防措施。研究结论:(1)明挖法隧道衬砌开裂主要是由温差应力、混凝土收缩和施工工艺控制所引起;(2)针对明挖法隧道,通过采取"三时机、三措施、两加强"的综合预防措施,基本上控制了衬砌裂缝的产生;(3)明挖法隧道衬砌施工应选择合理的时机,混凝土浇筑宜选择在每天16:00开盘,至次日8:00前完成;外模、内模拆除宜分别选择在混凝土浇筑完成后12 h、36 h左右完成;外侧拱脚4 m高度范围混凝土回填宜选择在混凝土浇筑完成后7 d内完成;(4)明挖法隧道衬砌施工宜采取外模浇筑、多开窗口、快速浇筑措施,一般情况下混凝土浇筑时间应控制在12 h以内;(5)明挖法隧道衬砌施工应加强振捣、加强养护,确保混凝土质量;(6)本研究成果可在明挖法隧道衬砌施工中借鉴应用。

Research purposes:The problem of concrete cracking has been paid attention to.A railway tunnel was constructed by open excavation method.After some of the projects were completed,the lining produced cracking phenomenon.By analyzing the relationship between the number of cracks and the shape,length,width and depth of cracks,the causes of cracking were studied,and the preventive measures were formulated.Research conclusions:(1) The cracking of the tunnel lining by open excavation method is mainly caused by the temperature difference stress,concrete contraction and construction process control.(2) For the open-cut tunnel,the creation of lining cracks was basically controlled by adopting comprehensive preventive measures of "three timing,three measures,and two enhancements".(3) The construction of the tunnel lining of the open excavation method should be chosen at a reasonable time.Concrete pouring should be opened at 16:00 every day and be completed before 8:00 the next day;The external mold and internal mold removal should be selected to complete about 12 h and 36 h after the concrete pouring is completed;Concrete backfill in the 4m height range of the lateral arch foot should be selected to be completed within 7 d after concrete pouring is completed.(4) In the construction of tunnel lining by open excavation method,it is appropriate to adopt external mold casting,multiple open windows,and rapid pouring measures.Under normal circumstances,the concrete casting time should be controlled within 12 h.(5) The construction of tunnel lining by open excavation method should strengthen vibration and strengthen maintenance to ensure the quality of concrete.(6) The research results can be used for reference in open-cut tunnel lining construction.