岩溶隧道施工时，不可避免地会遇到多种介质充填的溶洞。隧道穿越这类型的溶洞时，采用何种施工工法以及施工过程中隧道支护的稳定性已成为设计、施工的一个难点。选取宜万铁路马鹿箐隧道Ⅰ线DK255+925～+976段大型淤泥质充填溶洞为研究对象，采用三维快速拉格朗日法，对隧道开挖与支护过程中的力学行为进行研究，获得隧道在分步开挖、支护情况下围岩位移、初期支护内力及位移等的分布规律，计算分析结果对该隧道设计、施工提供理论支持，可为类似隧道工程借鉴、参考。

When tunnel is constructed in karst cave zone, all kinds of filled caverns will be inevitably meet.The construction method and tunnel structure's stability becomes the key problem for the design and construction. The range of DK255+925~+976, filled with crushed rock and silt, forⅠline of Maluqing tunnel on Yichang-Wanzhou Railway is taken as an example. The mechanical responses of excavation and support are studied by using the three-dimensional fast Lagrangian analysis of continua method. The numerical simulation reveals the distribution characteristics of displacement for surrounding rock and displacement and interial stress for the shotcrete and the maximum axis force for locking anchor pipe under the condition of dynamic step excavation and support. The obtained conclusions offer a guideline for the design and construction of tunnels in similar underground projects.