针对下伏溶洞顶板极限承载力问题，提出了两种顶板极限承载力计算方法；方法1：假定冲切体为圆锥台，由极限平衡法得出极限平衡状态下破坏面上拉应力与剪应力同时作用时的极限承载力；方法2：假定冲切体是以一个未知曲线为母线的旋转体，由极限分析法求出其母线形式以及极限承载力的表达式，通过求偏导获得了溶洞顶板的极限承载力。同时进行了下伏溶洞顶板极限承载力室内模型试验，得到了1～5倍桩径顶板厚度下溶洞顶板基岩的破坏模式以及相应的极限承载力，实测结果与理论吻合良好。研究表明：溶洞顶板厚度为1D至3D（D为桩径）时，发生冲切破坏，破坏模式是以曲线为母线的旋转体，4D时发生撕裂+冲切复合破坏，5D时基岩出现塑性破坏。在溶洞顶板厚度为1D～4D时，同一跨径比条件下，极限承载力随顶板厚度的增加呈线性增长，达到5D时，顶板承载力与基岩基本一致。

Two methods are proposed for the determination of the ultimate bearing capacity of cave roofs. Method 1: assuming that the punching body is a truncated cone, the ultimate bearing capacity of cave roofs can be determined by applying tensile stress and shear stress simultaneously on failure surface using limit bearing method. Method 2: assuming that the punching body is a rotating body with an unknown curve as the generatrix, the expression of the generatrix and the ultimate bearing capacity is obtained by the limit analysis method. The ultimate bearing capacity of the roof is obtained by partial derivatives. Laboratory model experiments of the ultimate bearing capacity of cave roofs are conducted. The failure modes and the corresponding ultimate bearing capacity are obtained when the roof’s thickness varies from 1D to 5D. The measured data is in good agreement with theoretical calculation result. The study shows that the punching shear failure mode happens when roof’s thickness varies from 1D to 3D, and the failure pattern has a surface of revolution with a curve shape. When roof’s thickness reaches 4D, a failure mode of tearing damage and punching shear failure occurs. Plastic failure develops when roof’s thickness reaches 5D. The ultimate bearing capacity increases linearly with the increase of roof’s thickness from 1D to 4D in the same span-diameter ratio. When roof’s thickness reaches 5D, the ultimate bearing capacity of the cave roof is close to the ultimate bearing capacity of bedrock.