Rock bolts

The properties and design of rock bolts are available in the literature.1 A Swellex rock bolt is shown in Figure 7.62. The modes of support for rock bolts can be ... 

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. 

When a horizontal opening is created in a solid or fissured rock formation, tensile stresses are generated in the roofs of these openings. In a solid formation, the opening may remain stable for various lengths of time. In a fissured formation, or even in a solid formation of weak rock, the opening may cave immediately, or in a short period of time. Rock bolts are widely used in mine tunnels drifts) as a major means of roof support. 

Mechanical rock bolts are steel rods fitted with expanding end pieces which are anchored into a drilled hole. The exposed end of the rod is threaded, and fitted with a large plate (which acts as an oversized washer), and a heavy nut with which tension is applied to the bolt. The applied tension then compresses the rock, reducing or eliminating the tendency to spall or cave. Mechanical rock bolts come in a number of different configuration and lengths, but they all function in the same manner. They must be spaced so that the zones of compression of adjacent bolts overlap. Rock bolts have a long history of use, particularly in coal mines. 

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. 

The corrosion modes of rock bolts are (i) uniform corrosion (ii) pitting or crevice corrosion (iii) galvanic corrosion. 

Figure 5.57 Swellex rock bolt (Figure originally published in Reference 31. Reproduced with permission of the Canadian Institute of Mining, Metallurgy and Petroleum. www.cim.org.)...

Figure 5.58 Visual examination of the fracture of a rock bolt (19).

J Hadjigeorgiou, F Charette, Rock Bolting for Underground Excavations, Chap. 63, Hus-trilid, Bullock (eds). Society of Mining Engineers, pp. 547-554, 2001. 

E. ViUalba, A. Atrens, Metallurgical aspects of rock bolt stress corrosion cracking. Mater. Sci. Eng. A 491A (2008) 8-18. 

E. Camboa, A. Atrens, Material influence on the stress corrosion cracking of rock bolts, Eng. Fad. Anal. 12 (2005) 201-235. 

Sun, Xiaoyun Cheng, Jiulong. 2008. Application of Information Processing Technology on Nondestructive Detecting of Rock Bolts, China Mining Magazine ll(135) 87-90. 

II mainly, some III-IV J2, J1 toppling J3 planar(10- 30°) J1-J3 wedge (21°) Major rock bolting Major toppling hazard, adjacent to condominium... 

Controlled blasting, followed by major rock bolting program. 

XV) Ammunition Depot, Tg. Gelang, Kuantan, Pahang Storage tunnels Phyllitte/Quartzite, complex folding faults Heavy tunnel supports steel arches + resin grouted rock bolts. 

Resin bonded systems employing the larger bar diameters and lengths of several metres have also proved popular for rock bolting and ground anchor systems for example as shown in Fig. 7.6. Three basic systems are available ... 

The final shaft diameter after shotcrete and grouted rock bolts will be 06.0 m. 

Measures to control rockfall include catch fences, benches, wire mesh and rock traps. Restraining structures control landslides by increasing the resistance to movement. They include, for example, retaining walls, reinforced earth structures, shotcrete, cribs, gabions, buttresses, piling, dowels, rock bolts and rock anchors (see Chapter 9). The following minimum information is required to determine the type and size of a restraining structure ... 

Gunite or shotcrete frequently is used to preserve the integrity of a rock face by sealing the surface and inhibiting the action of weathering (Fig. 9.7). They are pneumatically applied mortar or concrete, respectively. Coatings may be reinforced with wire mesh and used in combination with rock bolts. Heavily fractured rocks may be grouted in order to stabilize them. 

Rock mass class Mainly rock bolts (20 mm diameter, length half of tunnel width, resin bonded) Mainly shotcrete Mainly steel ribs... 

II Generally no support required Rock bolts spaced 1.5-2 m. Shotcrete 50 mm Uneconomic... 

III plus occasional wire mesh Rock bolts spaced 1.0-1.5 m in crown. Shotcrete 100 mm in Light sets spaced... 

IV and 30 mm shotcrete in crown where required Rock bolts spaced 0.5-1.0 m sides, plus occasional wire mesh and rock bolts where required Shotcrete 150 mm in Medium sets spaced... 

---