Page 97 - Rock Mechanics For Underground Mining

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for this low range, uniaxial compression test is preferred 1–5 5–25 1 2 < 25 3 < 0.06 5 soft gouge > 5 mm thick or separation > 5 mm. continuous joints 0 > 125 > 0.5 flowing 0 very unfavourable −12 −25 −60 < 20 V very poor rock V 30 minutes for 1.0 m span < 100 < 15 ◦

1–2 25–50 4 25–50 8 0.06–0.2 8 slickensided surfaces gouge < 5 mm thick separation 1–5 mm continuous joints 10 25–125 0.2–0.5 dripping 4 unfavourable −10 −15 −50 40 ← 21 IV poor rock IV 10 hours for 2.5 m 100–200 15 ◦ –25 ◦
Ranges of Values or or span

2–4 50–100 7 50–75 13 0.2–0.6 10 slightly rough surfaces, separation < 1 mm, higly weathered walls 20 10–25 0.1–0.2 wet 7 fair −5 −7 −25 60 ← 41 III fair rock III 1 week for 5 m span 200–300 25 ◦ –35 ◦

Geomechanics classification of jointed rock masses (after Bieniawski, 1989).
4–10 100–250 12 75–90 17 0.6–2 15 slightly rough surfaces, separation < 1 mm, highly weathered walls 25 < 10 < 0.1 damp 10 favourable −2 −2 −5 80 ← 61 II good rock II 1 year for 10 m span 300–400 35 ◦ –45 ◦

> 10 > 250 15 90–100 20 > 2 20 very rough surfaces, not continuous, no separation, unweathered joint wall rock 30 none 0 completely dry 15 very favourable 0 0 0 100 ← 81 I very good rock I 20 years for 15 m span > 400 45 ◦

(a) Classification parameters and their ratings Parameter ⎧ point–load–strength ⎪ index(MPa) ⎪ ⎪ ⎨ ⎪ ⎪uniaxial compressive ⎪ strength (MPa) ⎩ drill core quality RQD (1%) ⎧ inflow per 10 m tunnel ⎪ length ( min −1 ) ⎪ ⎪ ⎪ or ⎪ ⎨ joint water pressure ⎪ major principal stress ⎪ ⎪ ⎪ ⎪or ⎩ general conditions (b) Rating adjustment for joint orientations strike and dip orientations of joints ⎧ tunnels and micro ⎨ ⎩ foundations slopes (

Table 3.5 Strength of inftact 1 rock material rating 2 rating joint spacing (m) 3 rating condition of joints 4 rating 5 groundwater rating Rating Ratings Class no. Description (d) Meaning of rock classes Class no. average stand-up time

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