The mechanical characteristics of tunnel invert for high-speed railway are complex and crucial to the operation safety for high speed train.In-situ stress tests were performed on the concrete and rebar of Fuchuan tunnel invert after being reworked on the second double-track of Lanzhou-Xinjiang Railway.The mechanical characteristics and stress change rule of concrete and rebar in invert structure were analyzed.Results showed that under the action of the dead weight of tunnel secondary lining,the load of upper surrounding rock,the expansion of surrounding rock on tunnel base,track roadbed and train load,the reworked concrete in tunnel invert experienced a change process of compression,local tensile stress and stable tensile-compressive stress.The maximum tensile stress of concrete and rebar in invert structure appeared at the upper part of invert center.The maximum tensile stress and compressive stress of concrete was 1.9 MPa and 8 MPa respectively during the whole course from invert reconstruction to tunnel operation.After a large amount of groundwater was added,a large amount of load was released from the expansion of surrounding rock on tunnel base,which made the concrete stress,rebar stress and earth compressive stress increase rapidly.Based on geological conditions and monitoring results,the floor heave of Fuchuan tunnel invert was divided into 3 degrees:mild,moderate and severe.Corresponding control measures were given for each degree of floor heave.%针对高速铁路隧道仰拱受力状态复杂且对高速列车行车安全至关重要的特点,现场测试兰新第二双线福川隧道返工后仰拱混凝土和钢筋的应力,分析仰拱结构中混凝土和钢筋的受力特征及应力变化规律.结果表明:受隧道二衬自重及上部围岩荷载、隧道基底围岩膨胀、轨道道床及列车荷载的作用,返工后仰拱混凝土经历了受压、出现局部拉应力、拉压应力稳定的变化过程;仰拱中混凝土和钢筋的最大拉应力均出现在仰拱中心上部,从仰拱返工到隧道运营的整个过程中,混凝土的最大拉应力为1.9 MPa,最大压应力约为8 MPa;地下水大量补充后,隧底围岩膨胀释放大量荷载,使得混凝土应力、钢筋应力以及土压应力迅速增大.基于监测结果及地质条件,提出将福川隧道仰拱底鼓分为轻微、中度和严重3种程度,针对每种程度的底鼓给出相应的控制措施.
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