膨胀性围岩的吸水膨胀特性会对隧道支护结构产生不利影响，继而容易诱发各类工程灾害，影响工程进度和后期列车正常运营。因此，此类隧道的力学特性和支护方式的选择一直备受关注。以内蒙古某一穿过膨胀性泥岩的隧道为例，基于现场监测和数值计算方法，分析原支护条件下膨胀性泥岩隧道支护结构的变形破坏特性，进而从支护变形和力学特性方面研究双层初支在此类隧道的适用性，并提出相应的支护参数建议。结果表明：泥岩的膨胀特性引起原支护条件下（单层初支）支护结构变形达到309 mm，导致隧道施工现场出现支护严重侵限和被迫换拱等问题。相对单层初支，双层初支施工方法可以显著改善膨胀性泥岩隧道支护的变形和受力状况，且变形降幅达到63.88%以上。随着二次初支厚度的增加，初支变形和受力逐渐降低，最大变形降幅可达234.5 mm，各工况下的压应力降幅达到39%。因此，可考虑在膨胀性泥岩隧道中采用双层支护施工方法，并结合变形需求合理选择第二层初支厚度。研究成果可为今后类似工程提供重要参考。

The water absorption and expansion characteristics of the swelling surrounding rock can have adverse effects on the tunnel lining structure, which can easily lead to the induction of various engineering disasters, and impact the progress of the project, as well as the normal operation of the train in subsequent stages. Therefore, the mechanical characteristics and support method selection of such tunnels have always been of great concern. Taking a tunnel passing through expansive mudstone in Inner Mongolia as an example, based on field monitoring and numerical calculation methods, the deformation and failure characteristics of the tunnel lining structure in mudstone tunnel under the original lining conditions were analyzed. Subsequently, the applicability of double-layer preliminary lining in such tunnels was studied from the aspects of support deformation and mechanical properties, and corresponding lining parameter suggestions were proposed. The results indicate that the expansion of mudstone causes the deformation of the original lining structure (single-layer preliminary lining) to reach a magnitude of 309 mm. Such deformation leads to significant encroachment of the lining and necessitated forced arch replacement during the tunnel construction process. In comparison to the single-layer preliminary lining, the double-layer preliminary lining construction method has been found to significantly improve the deformation and stress state of the tunnel in expansive mudstone, achieving a deformation reduction rate that exceeds 63.88%. As the thickness of the secondary preliminary lining increases, the deformation and stress of the preliminary lining gradually decrease, achieving a maximum deformation reduction of 234.5 mm and a compressive stress reduction rate of up to 39% under various conditions. Consequently, the double-layer lining construction method can be considered for tunnels in expansive mudstone, with the thickness of the secondary preliminary lining being reasonably selected based on deformation requirements. The research findings can serve as a valuable reference for similar projects in the future.