heavy ground

"Heavy ground" is a mining term for weak or high-stress ground that repeatedly fails and requires support replacement. Dealing with it demands ingenuity, patience, and significant time and funding, often necessitating on-site development of special techniques.1

Examples include the Mont Blanc Vehicular Tunnel, where a pilot bore helped reduce rock bursts by relieving stress, and the El Colegio Penstock Tunnel, which required extensive replacement of supports as the ground squeezed inward. While ground arches can stabilize, knowledge is insufficient to distinguish between beneficial deformation and excessive deformation that weakens the ground. Field tests are crucial for improvement but are costly.1

Underground mining is employed when ore bodies are deep, making surface mining impractical due to the high cost of removing overlying waste material. However, underground mining is generally more expensive per ton than surface mining due to smaller equipment, limited access, and lower productivity. The choice of underground mining method depends on the ore body's characteristics, rock strength, and depth.234