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Rock mass versus intact rock

Short answer

Intact rock is the solid, unjointed material between discontinuities, tested in the lab. Rock mass is the in-situ rock with its joints, faults and bedding planes; its strength is lower, deformbility larger, and behaviour anisotropic, governed by the discontinuties.

Define rock mass and intact rock. Differentiate between them.

Intact rock is the unfractured block of rock between discontinuities, small enough to be tested as a laboratory core specimen. Rock mass is the in-situ rock together with all its discontinuities (joints, bedding, faults, shear zones), i.e. the intact rock blocks plus the structural planes between them.

BasisIntact rockRock mass
DefinitionRock material between discontinuitiesIntact rock plus discontinuities in the field
SizeCore or hand specimenWhole outcrop, slope or tunnel section
DiscontinuitiesAbsentPresent, control behaviour
StrengthHigh; given by UCSMuch lower; governed by joints
DeformabilitySmall, nearly elasticLarge, includes slip along joints
PermeabilityPrimary (very low)Secondary through joints (higher)
BehaviourHomogeneous, isotropicHeterogeneous, anisotropic
Scale effectNoneStrength falls as volume grows
TestLaboratory (UCS, point load)In-situ tests, classification (RMR, Q)

✓ Answer checked by Claude Opus 5.5 (high effort)

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