Editing Underground hard-rock mining (section)

===Area ground support===
Area ground support is used to prevent major ground failure. Holes are drilled into the back (ceiling) and walls and a long steel rod (or [[rock bolt]]) is installed to hold the ground together. There are three categories of rock bolt, differentiated by how they engage the host rock.<ref name="Underground Drilling and Loading Handbook 4.0">{{cite book
  | last = Puhakka
  | first = Tulla
  | title = Underground Drilling and Loading Handbook
  | publisher = Tamrock Corporation
  | year = 1997
  | location = Finland
  | pages = 153–170
  }}</ref>  They are:

====Mechanical bolts====
*'''Point anchor bolts''' (or expansion shell bolts) are a common style of area ground support. A point anchor bolt is a metal bar between 20&nbsp;mm – 25&nbsp;mm in diameter, and between 1&nbsp;m – 4&nbsp;m long (the size is determined by the [[Mining engineering|mine's engineering]] department). There is an expansion shell at the end of the bolt which is inserted into the hole. As the bolt is tightened by the installation drill the expansion shell expands and the bolt tightens holding the rock together. Mechanical bolts are considered temporary support as their lifespan is reduced by corrosion as they are not [[grout]]ed.<ref name="Underground Drilling and Loading Handbook 4.0"/>

====Grouted bolts====
*'''Resin grouted rebar''' is used in areas which require more support than a point anchor bolt can give. The [[rebar]] used is of similar size as a point anchor bolt but does not have an expansion shell. Once the hole for the rebar is drilled, cartridges of [[polyester resin]] are installed in the hole. The rebar bolt is installed after the resin and spun by the installation drill. This opens the resin cartridge and mixes it. Once the resin hardens, the drill spinning tightens the rebar bolt holding the rock together. Resin grouted rebar is considered a permanent ground support with a lifespan of 20–30 years.<ref name="Underground Drilling and Loading Handbook 4.0"/>
*'''Cable bolts''' are used to bind large masses of rock in the hanging wall and around large excavations. Cable bolts are much larger than standard rock bolts and rebar, usually between 6 and 25 metres long. Cable bolts are grouted with a cement grout.<ref name="Underground Drilling and Loading Handbook 4.0"/>

====Friction bolts====
*'''Friction stabilizer''' (frequently called by the [[genericized trademark]] ''Split Set'') are much easier to install than mechanical bolts or grouted bolts. The bolt is hammered into the drill hole, which has a smaller diameter than the bolt. Pressure from the bolt on the wall holds the rock together.  Friction stabilizers are particularly susceptible to corrosion and rust from water unless they are grouted. Once grouted the friction increases by a factor of 3–4.<ref name="Underground Drilling and Loading Handbook 4.0"/>
*'''Swellex''' is similar to Friction stabilizers, except the bolt diameter is smaller than the hole diameter. High pressure water is injected into the bolt to expand the bolt diameter to hold the rock together. Like the friction stabilizer, swellex is poorly protected from corrosion and rust.<ref name="Underground Drilling and Loading Handbook 4.0"/>