9.4.3 Rock Bolts

Rock bolts are used for reinforcement of rock slope and strengthening closely jointed or highly fissured rocks in cut slopes (Figure19). These bolts are variable lengths, normally from 1.2m to over 12m, diameters vary from 10mm to 51mm. The use of wire mesh or straps complements the reinforcement achieved with a rock-bolt pattern. In areas of highly jointed or fractured rock, wire mesh can be used to hold the small blocks of rock between the face plates in place.

A general rule for rock-bolt spacing is that the distance between face plates should be approximately equal to three times the average spacing of the planes of weakness in the rock mass and the bolt length should be twice the bolt spacing (Hock and Wood, 1988). Rock bolts generally have heads that expand following installation and are classified according to their method of anchorage: expansion, wedge and grouted.

Figure 19: Rock bolting is using to transfer loads from the unstable zone at the rock face to the stronger interior mass (http://www.moretrench.com)

Fgirue 20: Application of rock bolt to prevent the rock fall (http://www.dywidag-systems.com)