# When Abandoned Mines Collapse Channel: Practical Engineering Source: https://www.youtube.com/watch?v=RZg1zOKm5wk Recap page: https://rapidrecap.app/video/RZg1zOKm5wk Generated: 2025-07-15T21:38:48.213+00:00 --- ## Quick Overview Abandoned underground mines, particularly those using the "room and pillar" method, frequently collapse due to factors like water infiltration, material softening, and erosion, leading to surface sinkholes and widespread ground subsidence. These collapses, often stemming from mining practices over a century ago with little concern for long-term stability, cause significant damage to infrastructure and property, and are typically excluded from standard insurance, necessitating government-backed programs and modern regulations to mitigate ongoing risks. **Key Points:** - Sinkholes on I80 near Wharton, New Jersey, in late 2024 and early 2025 resulted from the collapse of underground iron mines established over a century ago. - Early underground mines, especially those using the "room and pillar" method, often left pillars "as small as the company thought they could get away with," leading to inherent instability. - Abandoned mines flood when companies stop pumping water, and this water dissolves minerals, softens materials, and causes erosion, significantly weakening the remaining supports. - Surface manifestations of mine collapse range from "well-defined sinkholes" (often sudden) to "generalized and broader sinking and settling over a large area." - Property insurance typically "specifically excludes damage from mine subsidance," leading to government-subsidized insurance programs in eight U.S. states where coal mining was extensive. - The 1977 Federal Mining Act mandated modern mines to prevent or control subsidence, with methods like "longwall mining" intentionally allowing roof collapse behind moving supports, making surface subsidence "practically inevitable." - Engineers predict subsidence using empirical data and numerical modeling, measure it with instruments like inclinometers, and repair damage through backfilling, grouting, or structural retrofits. **Context:** The video explores the complex and often delayed consequences of historical underground mining practices, particularly the collapse of abandoned mines leading to surface subsidence and sinkholes. It highlights how issues set in motion over a century ago, such as the extensive iron mining in areas like Wharton, New Jersey, continue to impact modern infrastructure and communities. The discussion delves into the evolution of mining techniques, the lack of foresight in early operations regarding long-term stability, and the subsequent challenges of property damage, accountability, and mitigation efforts in areas built over these forgotten subterranean voids. ## Detailed Analysis Abandoned underground mines pose a significant and often delayed threat of collapse, leading to surface sinkholes and widespread ground subsidence, as exemplified by recent incidents on I80 in New Jersey attributed to century-old iron mines. Early mining, particularly the "room and pillar" method common in soft rock mining like coal, prioritized extraction over long-term stability, leaving minimal support pillars and often failing to map or archive mine locations. Over time, these abandoned mines flood as water pumping ceases, and the water critically weakens the remaining pillars by dissolving soluble minerals, softening materials, and causing erosion, leading to eventual collapse. The surface impact can manifest as sudden, well-defined sinkholes or as a more gradual, generalized sinking over a broad area, with deeper mines potentially causing wider lateral subsidence. The consequences are severe, including damage to structures, infrastructure, and farmland, and property owners often lack recourse as standard insurance policies exclude mine subsidence damage, necessitating government-subsidized programs in affected states. While modern mining, regulated by acts like the 1977 Federal Mining Act, employs methods like longwall mining that intentionally cause controlled subsidence, engineers now focus on predicting, measuring, and mitigating these effects through advanced modeling, instrumentation, and reclamation techniques such as backfilling voids and structural retrofits. The video concludes that while historical mining practices were problematic, modern engineering strives to balance resource extraction with environmental and property protection. ### The Problem of Mine Collapse - Sinkholes on I80 in New Jersey are linked to century-old underground iron mines - This is a human-made issue with long-term consequences - The problem is complex and global, demonstrated with a garage model. ### Evolution of Mining Practices - Early mining focused on surface extraction, then moved underground for efficiency and deeper resources - Coal mining drove early underground expansion, often without detailed maps or concern for long-term stability - Information about abandoned mines was lost as companies dissolved or were acquired. ### Mechanics of Underground Mine Collapse - The "room and pillar" method leaves columns to support the roof, but these pillars are often minimally sized for maximum extraction - Water plays a critical role in collapse by flooding abandoned mines, dissolving soluble minerals, softening materials, and causing erosion - Stresses in surrounding soil and rock redistribute over time, leading to non-linear progression of collapse. ### Surface Manifestations and Consequences - Collapses near the surface often result in sudden, well-defined sinkholes, as seen in Alton, Illinois - Deeper mines or gradual processes can cause generalized and broader sinking over large areas - Subsidance can extend laterally from the mine, impacting areas not directly above it - Consequences include damaged structures, broken pipes, shifted foundations, ruined farmland, and disrupted habitats. ### Legal and Financial Implications - Property ownership can be split into surface and mineral rights, complicating accountability - Typical property insurance excludes mine subsidence damage, leading to government-subsidized insurance programs in eight U.S. states - The federal government collects fees from coal mines for reclamation of pre-1977 abandoned mines. ### Modern Mining and Mitigation - The 1977 Federal Mining Act mandated modern mines to prevent or control subsidence - Longwall mining intentionally allows roof collapse behind moving supports, making surface subsidence practically inevitable - Engineers predict subsidence using empirical data, geotechnical data, and numerical modeling - Mitigation involves measuring subsidence with instruments like inclinometers and extensometers, and reclamation through backfilling, grouting, or structural retrofits.