为探究公路隧道通风竖井高落差溜管浇筑过程中二次衬砌混凝土的离析行为及其力学性能变化规律，以子母岩隧道通风竖井工程为背景，采用现场取样与室内试验相结合的方法，分析浇筑中期混凝土的力学性能与微观结构特征。通过在井上与井下同步采集混凝土试样，进行抗压强度测试与核磁共振（nuclear magnetic resonance，NMR）弛豫时间T2谱分析，揭示高落差自由落体过程对混凝土匀质性与孔隙结构的影响机制。试验结果表明： 1）浇筑前期和末期的混凝土均出现肉眼可见的骨料与浆体分离现象，而浇筑中期的混凝土抗压强度符合设计要求，未发生明显离析； 2）与浇筑前期、末期相比，浇筑中期的混凝土骨料分布更加均匀； 3）浇筑中期的混凝土e组试样浇筑后，微孔占比显著降低，而中孔占比明显增加（达约50%），反映出该阶段混凝土内部颗粒分布更均匀，浆体包裹性更佳。
Segregation behaviors of cast-in-place concrete in ventilation shaft secondary lining of the Zimuyan tunnel during high-drop chute pouring are investigated and its mechanical properties are examined. Field sampling and laboratory testing are implemented to analyze the mechanical properties and microstructural characteristics of concrete. The research involves simultaneous collection of concrete samples from both the top and bottom of the shaft, followed by compressive strength tests and nuclear magnetic resonance T2 spectrum analysis, revealing the evolution mechanism of the high-drop free-fall process on concrete homogeneity and pore structure. The experimental results indicate that: (1) Concrete from the initial and final pouring stages exhibits visible segregation between aggregate and paste, while the concrete from the middle pouring stage meet the design requirements for compressive strength and shows no distinct segregation. (2) Compared to the initial and final stages, the concrete from the middle pouring stage demonstrates more uniform aggregate distribution after pouring. (3) For the Group e specimens from the middle pouring stage, the proportion of medium and large pores significantly decreases after pouring, while the proportion of medium pores increases markedly (reaching approximately 50%), reflecting more uniform internal particle distribution and better paste encapsulation at this stage.
