High Walls

At surface mines, high walls are unexcavated faces of exposed overburden that can range from a height of 20 feet to over 100 feet, depending on the geological characteristics of the mine and the material being mined. The slope and condition of the high wall also vary depending on the type or nature of the stone or sediment particular to that surface mine. For example, high walls of consolidated stone may be nearly vertical, while high walls of unconsolidated materials and sediments may possess the slope of the material as it naturally comes to rest. This slope is called the angle of repose, and it varies depending on the nature of the material being used. Understanding the angle of repose is important in assessing and determining the safety of high walls and piles of unconsolidated materials. If a high wall rests at an angle greater than its angle of repose or is undercut, the resulting instability can create dangerous landslides.

To learn more about MSHA Part 48 training requirements visit our MSHA Part 48 Subpart B Surface Mining Online Training web page.