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Table 1 . Rock classification based on unconfined compressive <br /> strength. <br /> No. Description Uniaxial mmpr wive strength Zzmple: <br /> IbrO WCO Wa <br /> S 1 VERY SOFT SOIL-easily molded <5 4.4 m.04 <br /> with fingers,shows distinct <br /> heel marks. <br /> S2 SOFT SOIL-molds with strong 5-10 0.4-0.9 0.04-0.09 <br /> pmsmm from f ages,shows <br /> faint heel marks. <br /> S3 FIRM SOIL-very difficult to 10-20 0.9-1.5 0.09-0-15 <br /> mold with fingers,indented <br /> with finger nail,difficult to <br /> art with hand spade. <br /> S4 STIFF SOIL-cannot be molded 20-80 1.54.0 0.15-0-00 <br /> with fingas,cannot be art <br /> with hand spade,requires hand <br /> picking for excavation <br /> S5 VERY STIFF SOIL-very tough W150 6-10 0.6-1.0 <br /> difficult to move with hand <br /> pick.pneumatic spade required <br /> for excavation. <br /> RI VERY WEAK ROCK-Bumbles under M3500 10-250 1-25 Chalk.rocksalt <br /> sharp,blows with geological <br /> pick point.can be cut with <br /> pocket knife. <br /> R2 MODERATELY WEAK ROCK-shallow 3500-7500 250-SW 25-50 Coal,schist, <br /> arts or scraping with pocket siltstone <br /> knife with difficulty.pick <br /> point indents deeply with firm <br /> blow. <br /> R3 MODERATELY STRONG ROCK-knife 7500- S00-1000 50-100 Sandstone,slate, <br /> cannot be used to serape or 15000 shale <br /> peel surface.shallow indents- <br /> lions under firm blow from pick <br /> point. <br /> R4 . " STRONG ROCK-hand-held sample 15000- 1000-2000 100-200 Marble,granite, <br /> breaks with one firm blow from 30000 gneiss <br /> hammer end of geological pick. <br /> R5 VERY ST:ONG ROCK-requires >30000 >2000 >200 Quartzite.dolerite, <br /> many blows from geological pick gabbro,basalt <br /> .to bmak intact sample. <br /> From: Hoek dt Bray, 1981;Deem&Miller, 1966; <br /> Piteau, 1971 and Robertson, 1971 <br />