ROCK BOLTING

Rock and Soils 2009Don Cameron

CONTENT Introduction to rock bolting

Rock Bolts, Rock Anchors Tension bolt

mechanical bolt

friction bolt

grouted bolt or cable

Shear bolt (dowel action)

Long or relatively short?

Benefits of a Bolt

tension

Ta

Na

Tensile force in bolt produces greater normal force & hence joint friction and anti-sliding force, Ta

TYPES 0F ROCKBOLTSA. 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

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

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

Reference: Hoek, E., Ch 14 of Practical Rock Engineering, 2007

http://www.rocscience.com/hoek/pdf/14_Rockbolts_and_cables.pdf

TYPES 0F ROCKBOLTSB. 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/

TYPES 0F ROCKBOLTSB. 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

TYPES 0F ROCKBOLTSC. 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

http://www.rocscience.com/hoek/pdf/14_Rockbolts_and_cables.pdf

Reference: Hoek, E., Ch 14 of Practical Rock Engineering, 2007

TYPES 0F ROCKBOLTSD. 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

Passive reinforcement - non-tensioned

Tensile force develops as slide initiates: dilational joint only (rough, undulating)

sliding shear

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

Summary: Rock boltsRock 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)