... 100 Exc Poor 10 Ext Poor Very Poor 32 35 38 31 34 30 37 28 27 24 23 20 Very Good Good 16 15 19 14 13 18 22 26 Fair Ext Good 12 11 10 Exc Good 17 21 25 29 33 Poor 36 0.1 0.001 0.1 0.10 1.0 10 100 ... = − 45 Upward α = +90◦ α = + 45 Horizontal α = 0◦ 10 20 30 40 50 60 0 0 0 – −8.8 −7.8 −6.6 5. 3 −4.0 3. 2 3. 4 3. 1 −2.7 −2.2 −1.7 −0.8 −0.9 −0.8 −0.7 −0.6 −0.4 – −6.9 −6.2 5. 3 −4 .3 3. 3 JCS0 ... 250 100 200 80 60 150 30 29 28 27 26 25 24 23 22 21 20 40 100 Unit Weight, kN/m3 Compressive Strength (σc) of Rock Surface, MPa 35 0 30 0 32 31 80 60 50 40 30 20 20 Hammer vertical downwards 15...