Rock - SRMEG · Rock Klima, Schubert Texture-Coefficient (Howarth & Rowlands 1987) Considers: Grain...

1

INSTITUTE FOR ROCK MECHANICS AND TUNNELING

1

Short Course Singapore 2011

Rock

Klima, Schubert

Rock


2


Rock

Klima, Schubert

The Rock Cycle

drawing: USCShttp://3dparks.wr.usgs.gov/nyc/images/fig6.jpg

2


3


Rock

Klima, Schubert

Graph: USCShttp://3dparks.wr.usgs.gov/nyc/images/fig6.jpg

The Rock Cycle


4


Rock

Klima, Schubert

GraniteIgneous (magamatic) rock, plutonic rock

3


5


Rock

Klima, Schubert

BasaltIgneous (magamatic) rock, vulcanic rock


6


Rock

Klima, Schubert

Sediments(“soil”) over consolidated silt / clay

4


7


Rock

Klima, Schubert

Sandstonesedimentary rock


8


Rock

Klima, Schubert

Limestonesedimentary rock

5


9


Rock

Klima, Schubert

Metamorphic RocksMineral Assemblage Change: Shale to Schist


10


Rock

Klima, Schubert

Slate very low grade metamorphic rock

6


11


Rock

Klima, Schubert

Phyllitelow grade metamorphic rock


12


Rock

Klima, Schubert

Dolomite – marblemedium grade metamorphic rock / carbonatic rock

7


13


Rock

Klima, Schubert

Mica Shistmedium grade metamorphic rock


14


Rock

Klima, Schubert

Gneishigh grade metamorphic rock

8


15


Rock

Klima, Schubert

How to name rocks

• Mineral constituents

• Chemical composition (magmatic rocks)

• Texture / structure / microtexture

• Grain size (sedimentary rocks)

• Geological position (magmatic rocks: plutonite– vulcanite)

• Genesis of rocks Recommendations by the IUGS Subcommissions on the

Systematics of Igneous Rocks and Metamorphic Rocks


16


Rock

Klima, Schubert

How to name rocks

• main constituent: constituent (mineral) present in modal content ≥50%.

• major mineral constituents: constituent (mineral) present in modal content ≥5%.

• minor constituents: constituent (mineral) present in modal content <5%.

• essential constituent: constituent (mineral) that must be present in a rock in a certain minimum amount to satisfy the definition of a rock

• critical constituent: constituent (mineral) indicating by its presence or absence distinctive conditions for the formation of a rock and/or a distinctive chemical composition of a rock.

• Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: Web version 01/02/07

9


17


Rock

Klima, Schubert

Composition

Fabric

Origin

XRD analysis, optical microscopic scanning, chemical analysis

Optical macro – microscopical inspection, XR texture analysis, microspicalautomated interactive image analysis

Fabric elements, mineral paragenesis, geological considerations

A proper rock name is derived from:


18


Rock

Klima, Schubert

Microscope

Thin Section

10


19


Rock

Klima, Schubert

X-RAY Diffractometer


20


Rock

Klima, Schubert

Principle of X-Ray Diffraction

Bragg's LawThe layers of a crystal act like weak reflecting mirrors for the X-

rays. Only if the path difference of the reflected X-rays is a whole number of wavelengths does constructive interference occur. This is described by Bragg's Law:

nλ = 2dsinθ

λ: wavelength of the X-raysd : the spacing of the layersθ: the incident angle of the photons

11


21


Rock

Klima, Schubert

Principle of X-Ray Diffraction

XRD Pattern of a mixture of Minerals


22


Rock

Klima, Schubert

Properties appointed by:

• mineral composition

• texture / structure / microtexture

• history of origin / genesis

• condition / weathering / alteration

ROCK (Intact rock)

12


23


Rock

Klima, Schubert

Example: Serpentinite


24


Rock

Klima, Schubert

Rock Fabric:Texture and Structure

13


25


Rock

Klima, Schubert

Fabric:The complete spatial and geometrical configuration

of all components (penetrative fabric elements, scale dependent) that make up a rock

Texture:Geometrical aspects of the

component particles of a rock, including size, shape and

arrangement;

Also:

Degree of crystallographic lattice-(or shape-) preferred orientation of

components

Structure:The presence of compositional

layering, folds, foliation, fractures, lineation . .

(scale dependent!)


26


Rock

Klima, Schubert

Rock (Micro-) Fabric:Elements, Terms Symmetry

different types of voids (microcracks, pores), their size, orientation and distribution

disturbance of crystallites (free space in the solid matrix)

voids

vector data (shape preferred orientation); scalar data (grain shape, grain size)

geometry (morphology) of crystallites (related to the solid matrix)

microstructure

crystallographic preferred orientation (e.g., quartz c-axes etc.)

preferred orientation of lattice of crystallites (related to the solid matrix)

texture

ExampleAspect of materialElements of rock fabric

14


27


Rock

Klima, Schubert

Rock Section displayingcomposition and microfabric elements of thematerial

(Shape, Size, Interlocking, arrangement of grains)

Original Photograph

Line Drawing

ExplodedDiagram


28


Rock

Klima, Schubert

Scope O: outlines of porphyroclasts and ribbons

Scope I: elongate parent grains, transgranular and grain-boundary microcracks

Scope II: recrystallised grain mosaique, subgrain boundaries and complete microcrack pattern

Example „scopes“ of fabrics:

15


29


Rock

Klima, Schubert

Some Microstructural Indices

Perimeter LP is the length of all edge pixels outlining an object

Shape Factor SF is an expression of the circularity of an object. SF is calculated as:

A = area of grain

LP = perimeter of grain

SFA

LP

=4

2

π


30


Rock

Klima, Schubert


Compactness is a numeric expression of the shape of an object as it moves from a circle to a line. Compactness is calculated as:

A = area of grain

LP = perimeter of grain

CompactnessLAP=

2

16


31


Rock

Klima, Schubert


Aspect ratio AR is a numeric expression of grain elipticity. AR is calculated as:

Dmax = major axis length

Dmin = minor axis length

ARDD

= max

min


32


Rock

Klima, Schubert


Index of grain size homogeneity : t (index of “textural”homogeneity introduced by Dreyer 1973. t is calculated as:

Aavg = average grain area

Ai = area of individual grain

[ ]t

A

A A

avg

i avg

=−∑ ( )2

12

17


33


Rock

Klima, Schubert


Feret’s diameter: Feret's diameter is the greatest distance possible between any two points along

the boundary of a region of interest. Dequiv is calculated as:

A = grain area

DA

equiv =⎛⎝⎜

⎞⎠⎟

412

πminimumFeret‘s diameter

maximumFeret‘s diameter

ΘL, ΘB = angle


34


Rock

Klima, Schubert


Index of interlocking: g (Dreyer1973) calculates the complexity of grain-grain relationships. g is calculated as:

n : number of grain considered

Ai : area of exposed grain section

LPi: portion of the grain perimeter which contacts neighboring grains

gn

=⎛

⎝⎜⎜

⎞

⎠⎟⎟∑1

12

L

AP

i

i

18


35


Rock

Klima, Schubert


Foliation index: F (Tsidzi 1986) is calculated as:

Mi : content of phase i

Si : shape factor (aspect ratio)

F M Si in i

n

=⎛⎝⎜

⎞⎠⎟

=∑1

100


36


Rock

Klima, Schubert

Texture-Coefficient (Howarth & Rowlands 1987)

Considers:Grain ShapeGrain OrientationGrain Interlocking

AW Weighting factor for packing densityN0 Number of grains with aspect ration <2.0N1 Number of grains with aspect ration >2.0FF0 Mean value of the Form Factors of all grains with aspect ratio <2.0; FF describes the deviation of grains from circular shape and the

roughness of the grain boundary respectivelyAR1 Mean value of all aspect ratios >2.0

AF1 Angle factor, a measure of the degree of constant grain orientation and the deviation of the max Feret’s diameter from a reference direction

19


37


Rock

Klima, Schubert



38


Rock

Klima, Schubert


Relationship between texturecoefficient and UCS

Relationship between texture coefficient and TBM performance

20


39


Rock

Klima, Schubert


Texture coefficient of igneous and sedimentary rocks


40


Rock

Klima, Schubert


Relationship between texture coefficient and UCS of 9 different metamorphicrock types (50 samples): no correlation for metamorphic rocks!

21


41


Rock

Klima, Schubert

Intergranular microcracks

(quartz, Biotite)

Intragranular microcracks

quartz, feldspar, biotite, chlorite

Microcracks


42


Rock

Klima, Schubert

Disintegration of rock by inter- und intragranular microcracks

QU quartz FSP feldspar

GR garnet BI biotite

CHL chlorite

GR

QU

FSP

BIBI

BI

FSP CHL

QU

Microcracks

22


43


Rock

Klima, Schubert

Example thin section photograph, traced grain boundaries and microcrack traces pattern.


44


Rock

Klima, Schubert

Rock (Micro-) Fabric:Elements, Terms Symmetry

transgranularcrack

intergrain, multigrain crack

multigrain microcrack

transecting one or more grains

intergranularcrack

grain-bounderymicrocrack

grain-bounderymicrocrack

between two grains

intragranularcrack

intragrain, cleavage, transgranularcrack

intragranularmicrocrack

inside one grain

Terms used in fractographicstudies (e.g., Monoto et al., 1981)

Terms used in geological studies (e.g., Richter and Simmons, 1976; Kranz1983)

Proposed termPosition of the microcrack

23


45


Rock

Klima, SchubertX

Y

Z

Schematic Microcrack Orientation and DistributionExample


46


Rock

Klima, Schubert

in particular the microcrack pattern is responsible for the regular divisibility of apparently massive rock, e. g. marbles for utilization as dimension stones

Microfabric,

24


47


Rock

Klima, Schubert

Pore size distribution of gneisses, cummulative [cm3/g]


48


Rock

Klima, Schubert

Pore size distribution of gneisses, -dV/dlogD [c3/g]

25


49


Rock

Klima, Schubert

Characterization of Intact Rock:

Abrasiveness


50


Rock

Klima, Schubert

Quartz Equivalent Proportion

0,1553Carbonate

31,05total

1,32334Phyllosilicate

5,581831Feldspar

24,0024100Quartz

Example:

Proportion [%]

Rosival-abrasion-hardness

Mineral

26


51


Rock

Klima, Schubert

Abrasiveness of Sedimentary rocks(FSCHIM )

[mm] mean diameter of quartz grains

V [%] Quartz equivalent proportion

[MPa] Brazilian tensile strength

Schimazek & Knatz 1970


52


Rock

Klima, Schubert

CERCHAR-Abrasiveness-Test

• The abrasiveness of intact rock or rock mass affects the wear behaviour of drilling, cutting and milling tools.

• Abrasiveness of rocks depends on different parameters (e.g. structure and texture, equivalent quartz content, Young’s modulus)

• CERCHAR-Abrasiveness-Test is a common testing procedure for the prediction of tool wear due to the fast measurement process and the cheapness.

• The only formal description of this test is the French Standard AFNOR, NF P94-430-1 (2000)

27


53


Rock

Klima, Schubert

CERCHAR-Abrasiveness-Test

„West-Apparatus“(1989) at Graz, University of Technology, Institute of Applied Geosciences, [1] weight, [2] steel pin, [3] vise, [4] rock sample, [5] hand crank

Sample-specimens

steel-styli


54


Rock

Klima, Schubert

CERCHAR-Abrasiveness-Index (CAI)

Worn steel stylus tip under the microscope (right picture: 90° rotated)

CAI = d*10

d : diameter of worn stylus dip [mm]

28


55


Rock

Klima, Schubert

Cerchar-Classification-Scheme(CERCHAR, 1986)

extremely abrasive4,0 - 6,0

very abrasive2,0 - 4,0

medium abrasiveness to abrasive1,0 - 2,0

slightly abrasive0,5 - 1,0

not very abrasive0,3 - 0,5

ClassificationCAI


56


Rock

Klima, Schubert

CAI of some rocks

29


57


Rock

Klima, Schubert

Abrasiveness 0.1 mm

Mohs‘scale

Relation between Mohs‘ hardness grade and steel point abrasiveness test value


58


Rock

Klima, Schubert

MLPC ABROY Abrasion Meter500 g of crushed rock in the grain size range of 4 - 6.3 mm is placed in the container and the vane is rotated at 4,500 rpm for 5 minutes.The vane suffers abrasion and resulting loss of mass. The quantity of abraded vane metal is then correlated to rock abrasiveness.

French Standard AFNOR, NF P18-579 (1990)

30


59


Rock

Klima, Schubert

Qualitatively estimate of the durability of weak rocksSlake Durability Test (ASTM D4644)

Type I: Retained specimen remain virtually unchanged

Type II: Retained specimen consist of large and small fragments.

Type III: Retained specimen is exclusively small fragments.

Calculating the slake durability Index 2nd circle):

B = mass of drum plus oven-dried specimen before 1st circle [g]

WF = mass of drum plus oven-dried specimen retained after the 2nd circle [g]

C = mass of drum [g]

Id(2) = [(WF – C) / (B – C)] x 100

Id(2) = [(WF – C) / (B – C)] x 100


60


Rock

Klima, Schubert

Qualitatively estimate of the durability of weak

rocks Slake Durability Test (ASTM D4644)

< 30< 60Very Low Durabiliy

30 – 6060 – 85Low Durability

60 – 8585 – 95Medium Durability

85 – 9595 – 98Medium High Durability

95 – 9898 – 99High Durability

> 98> 99Very High Durability

% retainedafter 2 cycles

% retainedafter 1 cycle

Group Name

Gambles´ Slake Durability Classification (Goodman 1980)

31


61


Rock

Klima, Schubert

Swelling

Swelling of the ground is a time dependant volume

increase, which is caused by physical-chemical

reactions of rock and water, leading to inward

movement of the tunnel perimeter.


62


Rock

Klima, Schubert

• Swelling by capillary adsorption

• Swelling by osmosis

• Swelling by hydration of interlayer cations

(swellable clay minerals, e.g., smectite)

• Swelling by formations of new crystal structures

(e.g., anhydrite + water = gypsum)

Stress-Relief - Physico-Chemical Effects Involving Water

Swelling

32


63


Rock

Klima, Schubert

• Stress relief leads to a modification of the inter- or

intra-particle stresses which in turn facilitates flow and

ad/absorption of water

• Stress relief causes fissures which in turn facilitate flow

of water

• Water addition causes modification (increase) of inter

(intra) particle distances and this in turn affects the

stresses

Swelling


64


Rock

Klima, Schubert

• Water content changes increase pore water pressure

from an originally negative to a smaller negative or to a

positive value

• Fissuring or breaking of diagenetic bonds during

shrinkage facilitates flow and modifies original stresses

which in turn facilitates interparticle or intraparticle

addition of water

• Indirect effect: Shearing (e.g. of faults) breaks

diagenetic bonds and increases the exposed surface

areas

Swelling

33


65


Rock

Klima, Schubert

Swelling


66


Rock

Klima, Schubert

Basic Elements of Silicate Structure

Swelling

34


67


Rock

Klima, Schubert

Swelling

Crystalline Structure of swellable Smectite


68


Rock

Klima, Schubert

Huder-Amberg-graph

Swelling

35


69


Rock

Klima, Schubert

Clay – content [%]

Swelling-pressure[MPa]

Swelling-pressure of clayey anhydrite depending on clay-content, after 600 days

Swelling


70


Rock

Klima, Schubert

Swelling

Rock - SRMEG · Rock Klima, Schubert Texture-Coefficient (Howarth & Rowlands 1987) Considers: Grain...

Documents

Transcript of Rock - SRMEG · Rock Klima, Schubert Texture-Coefficient (Howarth & Rowlands 1987) Considers: Grain...