Geologic Description of Roof Falls
Roof falls are potential hazards in underground mines. Aside from being hazards, they also lead to extra costs in clean up and in some cases, changes to mine plans. Any roof fall should be examined (as safety and regulations permit) to gather as much information as possible about the reason the roof fell at that location. Large roof falls provide glimpses of the rock strata above the mined coal that are not visible during normal mining. Geologic examination should look for information about (a) fall location in the mine and relative to overlying topography, (b) timing of the roof fall relative to mining and support, as well as time of the year, (c) the shape of the fall scar, (d) fall orientation (especially if the roof breaks along fractures or slips at angles to entry), (e) rock types and bedding in the fall scar, (f) rock types and bedding in the fall material, and (g) the nature of contacts exposed in the fall scar. It is also important to note if the fall occurred in a position where the mined coal exhibited change in thickness or character (partings, etc.). Pictures and sketches of the fall can be included to aid in future comparisons with other data or falls. If the roof fall had geologic causes, examination of rock types, bedding, fractures, and other features can be used to determine the reason for the fall so that similar conditions can be anticipated and planned for in other parts of the mine. Some of the geologic causes of roof falls in underground coal mine roofs are discussed in this website.
It is important to try to categorize roof falls by the geology of the fall. If all roof falls are plotted on a mine map simply as roof falls (one category), then trends related to multiple, superimposed causes will be masked. Different types of falls may have unique trends, and may require different types of support. Common trends of different types of roof falls in underground coal mines are discussed in this website.