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.