为探讨铁路隧道小角度斜交下穿公路隧道的设计难点，以贵广铁路四寨二号隧道下穿厦蓉高速公路瑞坡隧道为例，通过理论分析、数值模拟和现场监测的方法，选择了安全经济的设计方案。主要研究内容和结论如下： 1）破碎围岩条件下小角度立交隧道的特点决定了下穿段影响范围较大，可利用Peck公式理论分析其影响范围； 2）可由保证既有隧道结构安全来确定其沉降控制标准； 3）可通过数值分析对初步拟定设计措施进行模拟验证，针对性地优化施工方法及工程措施。

No. 2 Sizhai tunnel on GuiyangGuangzhou railway crosses underneath the existing Ruipo tunnel on XiamenChengdu expressway with a small angle. Theoretical analysis, numerical simulation and site monitoring are made to achieve a safe and economic design of the tunnel. Main study contents and conclusions drawn are as follows: 1) No. 2 Sizhai tunnel, which crosses underneath the existing tunnel with a small angle, is located in fractured rock mass, therefore the scope of the influence induced by the construction of No. 2 Sizhai tunnel is large. The influence scope can be analysed by means of Peck formula. 2) The settlement control standard of the existing tunnel can be defined on the prerequisite that the structural safety of the existing tunnel is guaranteed. 3) The preliminary design of the tunnel can be verified by means of numerical simulation, and therefore the construction methods and countermeasures can be optimized.