Stability of shallow caverns in blocky rock masses

The limiting relationship between underground opening span and required cover height for stability in blocky rock masses, characterized by a network of horizontal bedding planes and vertical joints, is explored here. Understanding this relationship is crucial for the design of mining excavations in karstic terrain as typically encountered in carbonate rock masses. We perform numerical analysis of multiple roof spans vs. cover height geometries using the DDA method to obtain the boundary curve between stable and unstable opening geometries. Our results indicate that for cavern spans of up to 18 meters a low cover height vs. opening span ratio of h/B = 0.33 is sufficient for stability. For spans greater than 18 meters the demand for cover height rapidly increases and it appears to stabilize at h/B = 1.0 for B = 26 meters and above.