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Rock Mass Characterization
Geological and geotechnical data
collection
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Purpose
To obtain representative and
unbiased information:
Location of major geological
features
Discontinuity orientation,frequency, size, shear strength
Information to carry out a
rock mass classification
Intact rock strength
Ground water
Joint condition
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Concepts Rock mass can be thought of as an assembly of potential
blocks, which can be disaggregated by an excavationprocess
Geotechnical domains: regions of similar engineering
behaviour that can be delineated within a rock mass.
Structural domains: regions comprising similar sets of
geological structures that can be delineated within a rock
mass
Systematic collection of geotechnical information is
essential for accurate characterization
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Concepts
Rock mass behavior is controlled by the nature ofgeological discontinuities and the physical properties ofthe rock material bridges (intact rock bridges)
Large scale geological discontinuities are often low inshear strength and continuous, and can be seismicallyactive. They are often defined during orebody delineation
Minor scale jointing stochastic joint set characteristics,
sampling techniques required
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Types of Data Collected
Rock Name (Type)
Rock Material Properties Colour
Grain size and shape
Texture
Other textural features and fabric
State of weathering
State of alteration
Strength
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Types of Data Collected
Alteration & weathering Affects both rock & discontinuities
Alteration may enhance rock strength
Weathering will always reduce rock strength
Multiple weathering schemes have been suggested including
Dearman (1986) and Stapleton ,1976
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Types of Data Collected
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Types of Data Collected
Strength Via laboratory testing
Uniaxial Compressive Tests
Triaxial Tests
Field Tests Point load Index
Schmidt Hammer
Discontinuity wall strength Grades
See next slide
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Types of Data Collected
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Source of Data
Core Logging Borehole geophysical logging
Outcrop and spot mapping
Systematic face mapping
Scanline mapping
Window mapping
Photographic scanning
Steropsis
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Source of Data
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Geotechnical core log
Comprises:
Header (hole number, project, rig, core size, bit type, plunge andbearing of hole, collar coordinates)
Depth (from - to)
Rock material description
Degree of weathering
Field estimate of rock strength
Graphic log
Defect description and angle relative to core axis
Location of samples taken for testing
Rock Quality Designation
Core recovery
Water return Packer test results
Casing details
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Oriented Core Log
Augments data from the simple geotechnical log and
includes additional information on:
alpha and beta angles for the defect
defect roughness and planarity
infill characteristics (type and thickness)
actual fracture spacing
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