Bearing capacity of rocky strata

Bearing capacity of rocks for foundation

1. SSTPP – Malwa - II Bearing Capacity of Soil with RMR Method By: Amardeep Singh

2. Team Person Responsible: Larsen & T oubro Ltd Package : Silo Foundation Description : The test was conducted to confirm the bearing capacity of soil for Silo Foundations. The testing was conducted as per IS: 13365(PART-1), IS: 12070-1987, IS: 516. In house calculation was done with client consents which was later verified by third party. The basic aim of sharing the methodology is to circulate information amongst the L&T Power-QMCC & other departments for reference purpose.

3. Scope Determining of the Class of Rock mass based on the geo-mechanics classification system Also known as the Rock Mass Rating(RMR). Cohesion, angle of internal friction and elastic modulus can be determined. Field Data Required Uniaxial Compressive Strength of Intact R ock Material Rock Quality Designation Spacing of Discontinuities Condition of Discontinuities Ground Water Condition Orientation of Discontinuities

4. Uniaxial Compressive Strength of Intact Rock Material Rock Quality Designation(RQD)

5. Spacing of Discontinuities Condition of Discontinuities

6. Ground Water Condition Orientation of Discontinuities

7. Boring at Silo Foundation for Rock Sample

8. Sample of the Rock Layer by Layer

9. Rock Mass Rating Location Ash Silo N-2267.686 Level -4 m to -7 m E-1057.873 s. no. description condition rating as per IS 13365 (part -1) ANNEX B 1 Strength Average 4 2 Rock Quality Description(RQD) 66.67 (fair) 13 3 Spacing of discontinuities close 8 4 condition of discontinuities 5 mm thick soft gauge 5 Groundwater condition dripping 4 6 Orientation of discontinuities favorable -2 RMR 27 RMR value is 27 therefore as per IS 12070-1987 Table no. 3 SBC is 78.210 t/ sqm at -4 m to -7 m level Rock Mass Rating Location Ash Silo N-2267.686 Level -7 m to -10 m E-1057.873 s. no. description condition rating as per IS 13365 (part -1) ANNEX B 1 Strength Average 4 2 Rock Quality Description(RQD) 75.33 (good) 17 3 Spacing of discontinuities close 8 4 condition of discontinuities 5 mm thick soft gauge 5 Groundwater condition dripping 4 6 Orientation of discontinuities favourable -2 RMR 31 RMR value is 31 therefore as per IS 12070-1987 Table no. 3 SBC is 92.89 t/ sqm at -7 m to -10 m level Rock Mass Rating Location Ash Silo N-2267.686 Level -10 m to -13 m E-1057.873 s. no. description condition rating as per IS 13365 (part -1) ANNEX B 1 Strength Average 4 2 Rock Quality Description(RQD) 91.5 (excellent) 20 3 Spacing of discontinuities close 8 4 condition of discontinuities slickensides wall rock surface of 1-5 mm thick 10 5 Groundwater condition dripping 4 6 Orientation of discontinuities favourable -2 RMR 44 RMR value is 44 therefore as per IS 12070-1987 Table no. 3 SBC is 171.37 t/ sqm at -10 m to -13 m level

10. Core Strength As per IS 516 H/D 2 1 Corr. Factor 1 0.89 Location: Ash Silo N-2267.686 E-1057.873 Date: 24-08-2016           S. no. Core height (H) Core Dia (D) H/D ratio Load Strength Correction factor as per IS 516 corrected strength   mm mm   KN N/sqmm   N/sqmm     level = -4 m to -7 m       1 95 50 1.90 95 48.36 0.989 47.83 2 86 50 1.72 100 50.91 0.969 49.34 3 92 50 1.84 100 50.91 0.982 50.01             Avg. 49.06       level = -7 m to -10 m       1 97 50 1.94 105 53.45 0.993 53.10 2 78 50 1.56 105 53.45 0.952 50.87 3 96 50 1.92 100 50.91 0.991 50.46             Avg. 51.48       level = -10 m to -13 m       1 96 50 1.92 110 56.00 0.991 55.51 2 75 50 1.50 105 53.45 0.945 50.51 3 94 50 1.88 100 50.91 0.987 50.24             Avg. 52.09

11. Rock Mass Rating Location Ash Silo N-2303.370 Level -4 m to -7 m E-1063.143 s. no. description condition rating as per IS 13365 (part -1) ANNEX B 1 Strength Weak 2 2 Rock Quality Description(RQD) 6.33 (very poor) 3 3 Spacing of discontinuities very close 5 4 condition of discontinuities 5 mm thick soft gauge 5 Groundwater condition dripping 4 6 Orientation of discontinuities fair -7 RMR 7 RMR value is 7 therefore as per IS 12070-1987 Table no. 3 SBC is 45.25 t/ sqm at -4 m to -7 m level Rock Mass Rating Location Ash Silo N-2303.370 Level -7 m to -10 m E-1063.143 s. no. Description Condition Rating as per IS 13365 (part -1) ANNEX B 1 Strength Weak 2 2 Rock Quality Description(RQD) 52 (fair) 13 3 Spacing of discontinuities close 8 4 condition of discontinuities 5 mm thick soft gauge 5 Groundwater condition dripping 4 6 Orientation of discontinuities favourable -2 RMR 25 RMR value is 25 therefore as per IS 12070-1987 Table no. 3 SBC is 71.47 t/ sqm at -7 m to -10 m level Rock Mass Rating Loacation Ash Silo N-2303.370 Level -10 m to -14 m E-1063.143 s. no. description condition rating as per IS 13365 (part -1) ANNEX B 1 Strength Strong 7 2 Rock Quality Description(RQD) 87.5 (good) 17 3 Spacing of discontinuities close 8 4 condition of discontinuities slickensided wall rock surface of 1-5 mm thick 10 5 Groundwater condition dripping 4 6 Orientation of discontinuities favourable -2 RMR 44 RMR value is 44 therefore as per IS 12070-1987 Table no. 3 SBC is 171.37 t/ sqm at -10 m to -13 m level

12. Core Strength As per IS 516 H/D 2 1 Corr. Factor 1 0.89 Location: Ash Silo N-2303.370 E-1063.143 Date: 26-08-2016           S. no. Core height (H) Core Dia (D) H/D ratio Load Strength Correction factor as per IS 516 corrected strength   mm mm   KN N/sqmm   N/sqmm     level = -4 m to -7 m       1 94 50 1.88 35 17.82 0.987 17.58 2 93 50 1.86 30 15.27 0.985 15.04 3 88 50 1.76 35 17.82 0.974 17.35             Avg. 16.66       level = -7 m to -10 m       1 96 50 1.92 35 17.82 0.991 17.66 2 88 50 1.76 35 17.82 0.974 17.35 3 86 50 1.72 40 20.36 0.969 19.74             Avg. 18.25       level = -10 m to -14 m       1 92 50 1.84 145 73.82 0.982 72.52 2 90 50 1.80 155 78.91 0.978 77.17 3 89 50 1.78 160 81.45 0.976 79.48             Avg. 76.39

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