某铁路明洞拱部裂缝成因分析

某双线铁路明洞结构拱部产生纵向裂缝，为分析该明洞拱部裂缝产生的原因，对裂缝分布情况及裂缝形态进行分析，拱部裂缝宽度与回填土石厚度存在正相关性，裂缝宽度随回填土石厚度增加而增大；当回填土石厚度为15 m时，裂缝宽度为0.55~1.00 mm。通过对明洞施工数值计算分析认为： 当回填土石厚度小于5 m时，随着拱顶回填土石厚度的减小，拱顶拉应力增大，此时施工动载对明洞结构受力影响较大；边墙回填密实度对拱顶拉应力影响显著，密实度为60%时，拱顶拉应力值为完全密实时的1.44倍，且已超出结构极限强度。综合分析认为，回填土石施工时机不当及边墙回填不密实是导致该明洞拱部产生裂缝的主因； 提出明洞结构设计计算应纳入施工动载，施工应严格掌控回填土石施作的时机，同时应加强建设管理等。

Analysis of Causes of Arch Cracks of a Railway Tunnel

Some cracks occurred on arch of an open cut double track railway tunnel. Hence, the causes of cracks, their distribution and morphologies are analyzed. It is revealed that the width of arch crack is positively correlates to thickness of backfill rock; the width of arch crack ranges from 0.55 mm to 1.00 mm when the thickness of the backfill rock reaches 15 m. The results of numerical analysis of open cut tunnel construction show that: (1) When the thickness of the backfill rock is less than 5 m, the arch tensile stress increases with the thickness of the crown backfill rock decrease； and meanwhile the construction dynamic load has a greater impact on the structural stress of the open cut tunnel. (2) The arch tensile stress is significantly affected by the backfill compactness of sidewalls;when the compactness is up to 60%, the arch tensile stress is 1.44 times that of when reaches complete compactness, which beyond the ultimate strength of tunnel structure. The comprehensive analysis shows that the premature backfill construction and the uncompacted backfill are the main causes of cracks on tunnel arch. It is proposed that the construction dynamic load shall be incorporated into the design calculation of the open cut tunnel and the timing of backfill shall be strictly controlled during construction. In addition, the construction management measures shall be enhanced and the study results can provide reference for similar projects in the future.