RFI 10.03.2020 - Appendix C - Memorandum cooroibah waterway crossing · MCU16/0099.01

Rock Strength Classification
Strength      Symbol     Field Assessment                                       Uniaxial          Point Load
                                                                                Compressive       Index4
                                                                                Strength (Mpa)    Is(50) (MPa)
Very Low      VL         Material crumbles under firm blows with sharp end      0.6 to 2          0.03 to 0.1
                         of pick; can be peeled with knife; too hard to cut a
                         triaxial sample by hand. Pieces up to 30 mm thick
                         can be broken by finger pressure.
Low           L          Easily scored with a knife; indentations 1 mm to 3     2 to 6            0.1 to0.3
                         mm show in the specimen with firm blows of the
                         pick point; has dull sound under hammer. A piece
                         of core 150 mm long by 50 mm diameter may be
                         broken by hand. Sharp edges of core may be
                         friable and break during handling.
Medium        M          Readily scored with a knife; a piece of core 150       6 to 20           0.3 to 1.0
                         mm long by 50 mm diameter can be broken by
                         hand with difficulty.
High          H          A piece of core 150 mm long by 50 mm diameter          20 to 60          1.0 to 3.0
                         cannot be broken by hand but can be broken by a
                         pick with a single firm blow; rock rings under
                         hammer.
Very High     VH         Hand specimen breaks with pick after more than         60 to 200         3.0 to 10
                         one blow; rock rings under hammer.
Extremely     EH         Specimen requires many blows with geological           More than 200     > 10
High                     pick to break through intact material; rock rings
                         under hammer.


Notes on rock strength
1. Material with strength less than ‘Very Low’ shall be described using soil characteristics.
2. These items refer to the strength of the rock material and not to the strength of the rock mass
   which may be considerably weaker due to the effect of rock defects.
3. Anisotropy of rock material samples may affect the field assessment of strength
4. The unconfined compressive strength is typically about 20 x Is (50), but the multiplier may vary
   widely for different rock types.

Rock Defects
Defects are generally described using the following sequence of terms: [Defect Spacing]; [Depth
(metres from surface), Defect Type, Defect Angle (degrees from horizontal), Surface roughness, Infill,
Defect thickness (mm)]

Defect Description
Defect Type                   Surface Roughness            Surface shape                    Coating or Infill
Bp – Bedding Parting          Vr- Very Rough               St – Stepped                     cn – clean
Fp – Foliation Parting        Ro – Rough                   Cu – Curved                      sn – stained
Jo – Joint                    Sm – Smooth                  Un – Undulating                  vn – veneer
Su – Sheared Surface          Po – Polished                Ir – Irregular                   cg – coating
Sh – Sheared Zone             Sl – Slickensided            Pl – Planar
Se- Sheared Seam
Cs – Crushed Seam
Xs – Extremely weathered
seam
Is – Infilled Seam




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