岩溶隧道底板以下既有溶洞对隧道施工安全及铁路运营有直接的影响，分析、评价岩溶隧道底板的稳定性是岩溶隧道施工的关键问题之一。采用荷载传递线的概念，提出了岩溶隧道底板最小安全厚度的半定量评价方法；采用弹性理论建立了在岩体按抗拉和抗剪强度准则基础上的岩溶隧道底板岩层的最小安全厚度的理论公式，为施工期岩溶隧道底板安全性评价提供了依据。

The existing karst caves below the floors of the karst tunnels have direct influence on the tunnel construction and railway operation. Therefore, the analysis and assessment on the stability of the floors of the karst tunnels is one of the critical issues for the karst tunnel construction. In the paper, a semiquantitative evaluation method is provided for the minimum safe thickness of the floors of the karst tunnels by means of the load transferring line concept; theoretical formulas are established for the minimum safe thickness of the floor rocks of the  karst tunnels based on the criteria of tension strength and shear strength of rocks by means of elastic theories. The paper can provide reference for the assessment on the safety of the floors of the karst tunnels during construction.