Rock bolts

1. ROCK BOLTING
Rock and Soils 2009
Don Cameron

2. CONTENT
 Introduction to rock bolting

3. Rock Bolts, Rock Anchors
 Tension bolt
 mechanical bolt
 friction bolt
 grouted bolt or cable
 Shear bolt (dowel action)
 Long or relatively short?

4. Benefits of a Bolt
Tensile force in bolt produces greater normal force &
hence joint friction and anti-sliding force, Ta

5. TYPES 0F ROCKBOLTS
A. Mechanically Anchored
 Cone forced into expanding shell @ base by
screwing nut to shank
 Voids subsequently grouted
 Moderately hard to hard rocks
 slipping likely in VERY hard rock
 Blast vibration may loosen anchor

6.  Digunakan untuk lubang bukaan pada
batuan terkekarkan
 Daerah yang berpotensi terjadinya
runtuhan baji atau blok
 Mudah dan cepat dalam
pemasangannya
 Dapat ditarik untuk memberi efek
kuncian pada potensial baji yang
tidak stabil

7. Terbagi menjadi ( berdasarkan
pengaplikasiaannya):
 Ungrouted mechanicals anchored bolt
• pada daerah non korosi
• Untuk penggunaan jangka pendek
dan menengah
 Grouted mechanicals anchored bolt
• Terdapat resiko korosi
• Penggunaan jangka panjang
• Grouted dilakukan setelah periode
tarikan

8. Reference: Hoek, E., Ch 14 of
Practical Rock Engineering, 2007
http://www.rocscience.com/hoek/pdf/14_Rockbolts_and_cables.pdf

9. TYPES 0F ROCKBOLTS
B. Friction Anchored Rock Bolts (heavily jointed
rock) perlu wire mesh/shotcrete
Split-set & Swellex
1. Swellex - collapsed tube, expanded in drillhole
with water pressure
 Pull-out resistance dependent on applied water
pressure
 Expensive and temporary
http://www.swellex.com/

10. TYPES 0F ROCKBOLTS
B. Friction Anchored Rock Bolts
2. Split-set - collapsed tube, expanded in drillhole
with water pressure
 borehole diameter crucial: must be slightly smaller than
split-set
 no tension
 bolt lengths < 3 m
www.splitset.com/rock-bolts.html

11. TYPES 0F ROCKBOLTS
C. Grouted Rock Bolts
 Cement or resin cartridge placed in drillhole
 Reobar ‘drilled’ through cartridges
 Top of the bolt not bonded to the grout (wrapped
in PVC tape)
 Nut tensioned against anchored end
 Versatile, high corrosion resistance

12. http://www.rocscience.com/hoek/pdf/14_Rockbolts_and_cables.pdf
Reference: Hoek, E., Ch 14 of
Practical Rock Engineering, 2007

13. TYPES 0F ROCKBOLTS
D. Grouted Cable Bolts
 Temporary support systems
 Untensioned fully grouted cables (used in the
mining industry)
 act as passive reinforcement
 the rock mass must be in a state of compression
during installation
 dilation upon shearing tensions the anchor

14. Passive reinforcement
- non-tensioned
Tensile force develops as slide initiates:
dilational joint only (rough, undulating)

15. Example of use of Cable Bolts
Windy Point Great Ocean Road
 instability of 200,000 tons of rock
 Sandstones, interbedded mudstones, 27° dip seaward
 Problems during installation; slide moving @ 2 cm per
day
 Slide stopped after first 7 anchors installed
 45 x 170 ton anchors, 18 to 43m long
 Estimated F of S = 1.07

17. Summary: Rock bolts
Rock bolts and cables can incorporate;
• mechanical anchorage
• grout
Rock bolts and cables may be post-
tensioned (active) or rely on the rock
mass to do the work (passive)