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Identification and Classification of rock

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Title: Identification and Classification of rock


1
Identification and Classification of rock
  • Part 1
  • Rock Identification and Description

2
Classification and Engineering Description of
Rock
  • Introduction Eurocode 7 EN ISO 14689
    and BS5930
  • Primary concept Rock Material v Rock Mass
  • Identification of Rock type (lithology)
  • What should be included in a rock description
  • Discontinuities and structure

3
Definitions
  • Rock
  • - Eurocode 7 naturally occurring assemblage
    of
  • minerals, consolidated, cemented or bonded
    so as to
  • form material of generally greater
    strength or
  • stiffness than soils
  • Geoguide 3 (HK) any naturally formed earth
    material which cannot be broken down by hand into
    its constituent grains, or may only be partially
    broken down by hand depending on its weathering
    condition
  • Our definition Cannot be worked with hand tools

4
Definitions
  • Rock material (part a)
  • the rock which makes up the blocks within the
    framework of discontinuities
  • Rock Mass (part b)
  • the rock together with its discontinuities and
    weathering profile

5
Rock Material and Rock Mass
  • Describe the material and identify rock type
    this can be done from hand specimens or in the
    field
  • Describe the rock mass characteristics - this
    includes the orientation, nature and condition of
    the discontinuities which separate the rock
    blocks. Best done in the field but some
    quantification can be made from rock core
    extracted from a borehole

6
The Engineering Description
  • Formal system of rock description
  • Conveys a sense rock strength, condition and
    possible susceptibility to future changes
  • Provides a set of terms with defined meaning
  • Comprehensive,
  • meaningful concise
  • Its good news

7
Identification and Description of Rock
  • Description of rock
  • A statement describing the physical nature,
    composition
  • and state of the rock
  • Visual examination
  • Simple tests in the field
  • in situ or hand specimen
  • Observation of site conditions, geological
    history.
  • Classification (Identification of rock type)
  • Assigning the correct petrological name (see
    Table A.1 )
  • Usually from hand specimen, but may require thin
    section for specialist engineering applications
    (e.g. tunnelling)

8
Petrological Classification of Rock
  • ROCK NAME always in CAPITALS
  • (Refer Simplified Classifications and Table A.1)
  • Based on geological origin, mineralogy and grain
    size
  • Often of some engineering significance e.g.
  • -SLATE cleavage imparts strength anisotropy
  • -GRANITE strong when fresh but weathers to a
    residual soil
  • -LIMESTONE soluble in water, may contain karst
    features

9
Rock Identification (rock name)
  • See Aide memoirs for identification
  • Genetic group Igneous plutonic volcanic
    Metamorphic
  • Sedimentary clastic, chemical, organic
  • Grain size
  • Minerals composition
  • Texture and Fabric
  • Other (voids )

10
General Description Description of Rock Material
  • Description of Rock Material
  • Colour
  • Grain size
  • Matrix
  • ROCK NAME (in CAPITALS)
  • Weathering or alteration
  • Carbonate content
  • Stability when exposed to a new water or
    atmospheric environment
  • Strength
  • Eurocode 7 BS5930

11
Description of Rock colour
  • Systematic approach to colour descriptions
  • Colour charts are useful as everyone sees colours
    differently

12
Description of Grain Size
  • Key parameter in petrological classifications
  • (See Table A.1 Aid to rock Identification)
  • Grain size influences engineering behaviour
  • Predominant grain size of the minerals or rock
    fragments
  • May be necessary to describe both the clasts
    (grains)
  • and the matrix (ground mass)

13
Description of Grain Size
  • Grain size
  • very coarse grained
  • 63mm ----------------------------------
  • coarse grained
  • 2mm ----------------------------------
  • Medium grained
  • 0.063mm ----------------------------
  • Fine grained
  • 0.002mm ---------------------------
  • Very fine grained

14
Description of Rock Material texture
  • Texture refers to individual grains and
  • their relationship or arrangement

15
Description of matrix
  • Definition relatively fine grained material in
    which the coarser fragments or crystal are
    embedded
  • - describe particle size and mineralogical
    composition.
  • e.g. - Very fine grained argillaceous
  • - orangey brown ferruginous
  • - grey micritic calcareous
  • - siliceous

16
Carbonate Content
  • Carbonate content determined by reaction to
    dilute HCL
  • Carbonate free no effervescence
  • Calcareous clear, but not sustained
    effervescence
  • Highly Calcareous strong and sustained
    effervescence
  • Note Wet or moist surfaces delay the reaction
  • Dolomitic rocks will react when grains
    are crushed

17
Stability of rock material
  • Degradation of rock material when exposed to a
    new water or atmospheric environment
  • Stable no change
  • Fairly stable specimen surface crumbles
  • Unstable specimen disintegrates
  • This highlights the inter-grain bond strength.
    So friable
  • sandstones, sedimentary rocks with some clay
    content
  • and weathered igneous and metamorphic rocks may
    crumble.
  • Rocks containing swelling clay minerals may
    adsorb moisture
  • from the air and spall.

18
Stability of rock material in water
  • After soaking for 24 hours
  • Term Description Grade
  • Stable No Changes 1
  • Fairly stable A few fissures, surface crumbles
    slightly 2
  • Many fissures, breaks into small lumps, surface
    crumbles highly 3
  • Unstable Disintegrates ,or most of the surface
    crumbles 4
  • Whole specimen becomes muddy or disintegrates
    into sand 5

19
Description of Rock Material Strength
  • Unconfined Compressive
  • Strength (MPa)
  • Extremely weak Indented by thumb nail (soils)
    lt1
  • Very Weak crumbles under firm blows with point
    of geological hammer 1 5
  • Can be peeled by a pocket knife
  • Weak difficult to peel with a pocket knife,
    shallow indentations made by 5 - 25
  • firm blows with pointed end of geological
    hammer
  • Medium strong Cannot be peeled or scraoed by a
    pocket knife 25 50
  • Can be fractured by single firm hammer
    blow
  • Strong Requires more than one firm hammer blow
    to fracture 50 100
  • Very strong Requires many blows to fracture
    100 250

20
General Description General Information
  • Additional information and minor constituents
  • Abnormal minerals, vugs or voids with description
    of size and mode of origin
  • Fossils
  • Other
  • Geological Formation From geological maps or
    memoirs
  • Prefer to put this in brackets
  • May or may not indicate some engineering
    characteristics
  • Only use if confident
  • The Geological Formation or stratigraphic name
  • e.g. Sherwood Sandstone
  • Woolwich and Reading Formation

21
General Description Description of Rock Mass
  • Types of rock
  • Structure Larger scale interrelations of
    geological features and associations between
    rock types in-situ.
  • Discontinuities
  • Weathering
  • Fracture State
  • Groundwater
  • Eurocode 7 BS5930

22
Description of Rock Mass Structure
  • Descriptive terms for sedimentary rocks
  • Bedded (well, poorly)
  • Interbedded (with.)
  • Laminated
  • Graded
  • Massive (ambiguous term)
  • Folded (post-depositional)

23
Description of Rock Mass Structure
  • Descriptive terms for
  • Metamorphic rocks
  • Cleaved
  • Foliated
  • Schistose
  • Banded
  • Lineated
  • Gneissose
  • Folded

24
Description of Rock Mass Structure
  • Descriptive terms for intrusive and extrusive
    igneous rocks
  • - Massive
  • - Flow banded
  • - Lineated
  • - Layered
  • - Folded

25
Classification and Engineering Description of Rock
  • Examples material description
  • Very strong, light pinkish white, porphyritic,
    coarse grained, slightly weathered to fresh
    GRANITE, with feldspar phenocrysts gt6mm.
  • Strong, thickly bedded, dark grey, medium
    grained, crystalline, oolitic LIMESTONE with
    micritic matrix and occasional fossils.
    Burrington Oolite, Carboniferous.
  • Very weak to weak, orangey brown, medium grained,
    inequigranular, micaceous, friable SANDSTONE.
    Quartz grains sub-rounded.
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