Failure rock bolts

Figure 7.67 shows an extremely irregular attack of the external surface of a longitudinal section of rock bolt. The presence of the oxide layer in Figure 7.67 and the dispersion of a metallic piece in Figure 7.68 support the analysis that, for this particular rock bolt, corrosion attack was rigorous and probably contributed in the failure of the rock bolt. 

Failure of Rock Bolts A typical Swellex rock bolt shown in Figure 5.57 has the following modes of support (i) beam building (ii) suspension (iii) pressure arch (iv) support of discrete bolts. 

E Gamboa, A Atrens, Material influence on the stress corrosion cracking of rock bolts, Engineering Failure Analysis, 2005, 12, 201. 

Skin failures are those that do not involve failure of the roof support elements, but result from rock spalHng from between roof bolts, around ATRS systems, or from ribs. They are of particular concern because they cause injuries and fataUties to workers who should have been protected by supports. In 1997, 98% of the 810 roof and rib injuries suffered by mine workers were attributed to skin failures... 

Roof skin failures almost always involve pieces of rock that are less than 0.6 m (2 ft) thick. About 40% of the 669 roof skin injuries in 1997 involved roof bolt operators and occurred beneath the ATRS. The other roof skin injuries occurred beneath permanent support and involved workers in a wide variety of activities. Common roof skin control techniques include oversized plates, header boards, wood planks, steel straps, meshing, and (in rare instances) spray coatings (sealants). 

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