The decision tree that the project director will typically follow when confronted with potential mine subsidence issues is summarized in Figure 1. The first step in this mine subsidence investigation is whether or not there is (or has planned to be) any underground mining present which can impact the site. The question may be easily resolved from existing mine records and mine depth but in areas where records are scarce or incomplete or of low quality the subsurface mining conditions in the project site vicinity can be investigated. Probably the most effective method of assessing the presence of mine voids, or limits of coal mining in the vicinity of the site, is the use of the cross-hole radar technique (see Update 5). Where potential subsidence effects are confirmed due to known underground mining in the area, or where a mining impact may be possible, a subsidence engineering investigation can be undertaken which may be coincidentally done with the mine verification exploration.

Where it is confirmed that underground mining has the potential to impact important infrastructure, mine stability analyses are then performed to assess how sturdy the mine workings will be over the considered life span of the project. This is a very important determination to get correct as the outcome of this analysis will determine if there is anywhere from a negligible up to a very high risk of surface subsidence from mine collapse (See Updated 14).

With the risk of subsidence properly assessed, the mine subsidence engineering investigation should then further assess the nature, extent, and magnitude of the surface subsidence, as this is a vitally important step in predicting the potential damage to the structure. This is best presented in the form of the spectrum of the damage potentialities (see Update 40). The damage assessment is most important to the risk decision maker as it typically determines the direction the project will take. In other words, using this data by the project decision maker determines whether or not the project should continue with or without risk mitigation, or should be abandoned. Where the risk is not acceptable, the project will proceed only when the necessary subsidence mitigation measures at the site are considered viable. Subsidence mitigation measures can be taken on the surface and/or in the subjacent mine workings to lower risk to an acceptable threshold. The cost to employ risk mitigation measures, especially mine stabilization measures, can be significant (See Update 24). Therefore, the importance of high quality mine subsidence risk evaluation cannot be over emphasized.