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Properties of rock mass and discontinuities

Short answer

Rock mass properties include physical (density, porosity), mechanical (strength, modulus), lithological, structural, hydrogeological, in-situ stress, and time-dependent behaviour. Discontinuity properties for classification: orientation, spacing, persistence, roughness, wall strength, aperture, infilling, seepage, number of sets, block size, weathering.

List out the different properties of rock mass. Write down the properties of discontinuities used for rock mass classification.

Properties of rock mass

  1. Physical: density, porosity, water content, permeability.
  2. Mechanical (strength and deformation): compressive, tensile and shear strength, modulus of deformation, Poisson's ratio, cohesion and friction angle.
  3. Lithological/petrographic: rock type, mineral composition, grain size, texture, weathering and alteration.
  4. Structural: discontinuities, folds, faults and their geometry.
  5. Hydrogeological: groundwater level, seepage, secondary permeability.
  6. In-situ stress: magnitude and direction of stresses.
  7. Time-dependent behaviour: creep, swelling, slaking, stand-up time.

Properties of discontinuities (ISRM) used for classification

PropertyMeaning
OrientationDip and dip direction (strike)
SpacingDistance between adjacent joints of a set
PersistenceLength or extent of the trace
RoughnessWaviness and surface unevenness (JRC)
Wall strengthStrength of the joint wall (JCS)
ApertureOpening between the walls
InfillingMaterial in the gap (clay, calcite, sand)
SeepageWater flow through the joint
Number of setsJoint sets cutting the mass
Block sizeSize and shape of blocks formed
Weathering/alterationDegree of decay of walls

✓ Answer checked by Claude Opus 5.5 (high effort)

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