Abstract: 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.

Key words: cave roof, ultimate bearing capacity, limit analysis, experimental study, punching shear failure