Local Collapse in Soft Rock Bank Cavities

This paper examines an interesting problem of soil engineering: the collapse of blocks from the ceiling of cavities in soft rock banks. The Mohr-Coulomb yield state with the associated flow rule is assumed for the soil. The kinematic theorem of limit analysis based on the choice of paraboloidal collapse surface supplies the total dissipation function; the equilibrium equations and a solving procedure based on Kuhn\-Tucker conditions yield a closed form for the solution. This solution is applied to common soils in southern Italy and it agrees with the real situation in cavities known to the writers. Several examples are listed reporting the dimensions and the weight of the collapsing block depending on the variability of mechanical properties of different soils. Finally a method for the design of the reinforcement of the cavities roof based on the proposed calculation is reported.