Aside from common general types of extensometers, used in applications as diverse as civil engineering and material testing, some manufacturers also make specific types of extensometers for mining use. A good example of this type of extensometer is the SMART MPBX from Mine Design Technologies (MDT).
Purpose-built extensometers for mining applications are especially popular in underground mines where they are used to measure compression, consolidation, movement, settlement, spread, subsidence and other factors within the mine and its surrounding topography.
Originally the types of extensometers used in mining were mostly of the rod type, with measurements being taken by a person using a caliper and then recording the results. Although it does generate some data and is better than not measuring at all, this way of working is slow, cumbersome and carries with it a high risk of user error.
Fortunately, technological developments over the last few decades have made positive changes to many industries, including mining. In the specific example of using extensometers for mine monitoring and control, there has been a move away from manually read, rod-type extensometers to flexible extensometers with digital readout heads.
A common practice is for purpose-built extensometers for mining use to be fitted into a narrow borehole (leading to them often being referred to as “borehole extensometers”), with the entire instrument grouted firmly in place, and the digital readout head fitted flush with a surface, or slightly recessed, to reduce the risk of damage. In some cases, the head is then shotcreted over for extra protection, leaving only the wires from the readout head exposed.
These wires are then connected to a cable-based or wireless network that gathers all of the data and moves it to a central point where it can be easily accessed by mine engineers and used to make decisions and take action in response to any potential risks.