Mine subsidence is the collapse or settlement of the ground surface from failure of an underlying mine. The most common mine subsidence events are from the extraction of coal. However, it also occurs from underground mining of other ores or natural resources as well. This would include mines in gold, iron, zinc, trona, salt, gypsum, limestone, etc. The nature of the mining and depth play a significant role in how the subsidence expresses itself on the ground surface. Based on essentially these two factors the mine subsidence can express itself on the ground surface as pothole sized to large sinkholes and small to very large trough to bowl-shaped depressions.
The mine subsidence movements can be very gradual to rapid depending on the type of mine failure. Example of larger and smaller sinkholes are shown in Figure 1 and 2. Examples of smaller to larger sag depressions of the ground surface are depicted in Figures 3 and 4.
For more information on mine subsidence see: Establishing Mine Subsidence Risk. In selecting a mine subsidence expert see: What to look for in a Geotechnical Engineering Expert.
FIGURE 1 SINKHOLE FROM MINE SUBSIDENCE
FIGURE 2 LARGE SINKHOLE
FIGURE 3 SMALLER SAG DEPRESSION FROM MINE SUBSIDENCE
FIGURE 4 LARGER SAG DEPRESSION FROM MINE SUBSIDENCE
The most appropriate mine subsidence expert for your case depends on the nature of the problem to be investigated. Mine subsidence investigations can require various expertise depending upon the focus of the problem. Some of the questions that may need answers are:
• Is the damage from mine subsidence?
• Will the underground mine result in subsidence in the future?
• If subsidence were to occur, what is the range of movement you would expect?
• If subsidence does occur, how severe could the resulting damage be?
• Was the mine designed properly so that mine subsidence would not result in the future?
• How can we mitigate the subsidence risk to a tolerable level?
• Can you stabilize the mine and how much would that cost?
As you can see from the above, the subject of mine subsidence can actually involve a number of expertise depending upon focus of the investigation. Also, there is the context of the expert mine subsidence investigation: Is it being done for existing or new construction, mine design, review of a mining permit application, or is it for tort litigation? Therefore, in addition to having the technical know-how, and expert with oratorical skills may also be necessary.
Karst subsidence are typically in the form of sinkhole to bowl-shaped depressions. They can occur unexpectedly and fairly abruptly and can cause significant damage. Because of their erratic geologic nature, karst it is often difficult to quantify the subsidence risk and associated damage potential. Therefore, the expert which is hired should be well versed in all the subsidence engineering aspects of interest. More common questions the karst subsidence expert will be asked to answer are: • What is the chance that there will be subsidence in the future? • If there is a subsidence(s), how severe will it be? • If there is subsidence, how much damage can we expect? • What are my options to reduce the risk of subsidence in the future? • A sinkhole has appeared, what do I do? • Is there any way to virtually eliminate the risk of subsidence in the future? Subsidence investigations in karst terrain are most commonly related to new construction or encountering unanticipated subsidence or other karst features which disrupt construction progress, insurance claims, or subsidence damage. Given the context of the investigation and the amount of risk which may be involved should determine the level of expertise that the subsidence engineer should have. If tort litigation is involved the karst subsidence expert should also be competent in this area. Also, with greater knowledge and experience in karst subsidence problems, the more cost effective the solution.