盾构隧道管片及接头耐火试验

盾构隧道衬砌由预制钢筋混凝土管片通过螺栓连接拼装而成，存在很多薄弱接头，这使其在火灾高温条件下会呈现出更加复杂的力学响应。因此，为了获取盾构隧道管片及接头高温下力学性能，对7组足尺管片试件进行了火灾试验，研究了火灾类型(ISO834、HC及RABT标准升温曲线)、管片类型(标准块、标准块接头及封顶块接头)和密封设置对盾构隧道管片在火灾高温下力学性能的影响。试验结果表明：①在较快的升温速率和较高的温度下，管片受火面混凝土发生严重剥落，导致大量钢筋外露，影响盾构管片高温下承载力，威胁盾构隧道衬砌结构安全；②当各试验距受火面25 mm处混凝土温度均超过《建筑设计防火规范》规定的耐火极限判断标准时，试验管片变形较小且未出现破坏现象，可知仅将温度作为隧道内承重结构体耐火极限判定依据较片面和保守；③管片接头处手孔密封设置及接缝密封设置分别对连接螺栓螺母和螺杆起到了很好的保护作用，但对止水条的温度变化趋势和特征影响不大；④混凝土严重剥落导致的管片厚度减少、大量裂缝产生造成的管片完整性下降以及混凝土水分受热蒸发留下的与外界贯通的毛细孔道均严重降低管片的抗渗性能。

Fire Experiments of Shield Tunnel Segments and Joints

A shield tunnel lining is composed of precast reinforced concrete segments connected by bolts. Many weak joints exist that present a more complex mechanical response under high temperatures. Therefore, fire tests were conducted on seven sets of full-scale segments to study the effects of fire types (ISO834, HC, and RABT standard heating curve), segment type (standard segment, standard segment joint, and capping segment joint), and filling settings on the mechanical performance of shield tunnel segments at high temperatures. The experimental results proved that ① under the fast heating rate and high temperatures, the concrete on the fired surface of the segment spalls, resulting in a large number of exposed steel bars, which affects the safety of the tunnel lining structure; ② when the concrete at 25 mm from the fired surface in each test exceeds the fire resistance limit judgment standard stipulated in the “Code for Fire Protection Design of Buildings,” the test segment deformation was small and no damage phenomena appeared. It is unreasonable and conservative to assess the fire resistance limit of the load-bearing structure in a tunnel based only on the temperature; ③ the hand hole and joint filling settings are essential in protecting the nuts and screws of connecting bolts; however, they have a small effect on the temperature trends and characteristics of the watertight rubber; ④ the thickness reduction of segments caused by severe concrete spalling, integrity reduction of segments caused by a large number of cracks, and perforated capillary channel left by the evaporation of concrete moisture significantly reduces the impermeability of segments, which affects the safety of the tunnel lining structure.