Rock Bolts 2009.ppt 47114c

ROCK BOLTING Rock and Soils 2009 Don 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

Ta

Na

io s n te

n

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

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

 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 ROCKBOLTS B. Friction Anchored Rock Bolts (heavily ted 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 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

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

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

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

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

ive reinforcement - non-tensioned

i slid

ear h s ng

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

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 bolts Rock bolts and cables can incorporate; • mechanical anchorage • grout

Rock bolts and cables may be posttensioned (active) or rely on the rock mass to do the work (ive)