Underground Mining and Sinkholes: How Subsurface Activities Cause Surface Subsidence | Practical Engineering

Overview

Grady from Practical Engineering explains how historic underground mining can trigger sinkholes and surface subsidence. He uses a garage model of a room‑and‑pillar coal mine and rainfall tests to visualize how removing underground support redistributes stresses, leading to surface deformation. The video links micro scale processes to large scale effects, discusses the social and regulatory challenges, and contrasts room‑and‑pillar with longwall mining to explain different subsidence risks. It also touches on insurance, reclamation, and policy measures intended to mitigate damage while supporting resource extraction.

Overview

This video from Practical Engineering explores the subsidence hazards created by underground mining, focusing on how surface ground can sink or crack when the underground supports are removed. The presenter, Grady, weaves together history, geology, and engineering to explain why sinkholes form, how subsidence propagates laterally, and what this means for roads, homes, and infrastructure.

Historical Context and Core Concepts

The narrative begins with the long history of mining access from the surface to underground resources, highlighting how early mines often left behind unstable pillars. It explains the concept of overburden and why engineers sometimes remove material above the mineral to access it, and how this can set long term stability challenges in motion. The concept of room and pillar, a dominant underground mining method, is introduced as a balancing act between extracting material and leaving enough support to prevent collapse. The video then contrasts this with longwall mining where large sections of roof are allowed to fail in a controlled way to harvest entire seams, which increases surface subsidence risk.

The Garage Mine Model and Subsurface Mechanics

Grady provides a hands on demonstration by building a simplified room and pillar model in his garage. He uses cardboard to represent a coal seam and adds a rainfall simulator to mimic water infiltration and redistribution of stresses. The model shows how surface settlement can occur gradually as the underground structure weakens, and how rainfall can accelerate deformation by saturating soils and facilitating erosion. The video emphasizes that subsidence is not always linear and can occur in fits and starts, with local roof failures and progressive weakening eventually leading to surface movement.

Consequences and Real World Examples

The discussion connects the model to real world events such as sinkholes in urban areas and at sports complexes where underground mines exist or existed. It addresses common surface impacts including structural damage, pipe failures, road misalignment, ponding, and even changes to river courses. The video notes that in many cases the responsible mining companies no longer exist to be held accountable, and insurance may not cover subsidence, which has led to public sector support in some states for reclamation and risk sharing.

Regulation, Mitigation, and Modern Mining

The narrative covers regulatory history and the evolution of mining practices. It outlines how modern mines employ methods to mitigate subsidence, including improving mapping, monitoring with inclinometers and extensometers, and adopting longwall or other modern techniques that control roof behavior. It also explains reclamation strategies such as backfilling, grouting, and engineered stabilization to reduce future risk and to restore land above former mines. The video ends with a broader reflection on balancing resource extraction with property protection and environmental stewardship, noting that mining has become safer over time but still presents unresolved challenges.