Quantitative Classification of Rock Mass Description of Joints: - - PowerPoint PPT Presentation

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Quantitative Classification of Rock Mass Description of Joints: - - PowerPoint PPT Presentation

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Quantitative Classification of Rock Mass Description of Joints: Description of Joints: Orientation, Persistence, Roughness, Wall Strength Aperture Filling Seepage Strength, Aperture, Filling, Seepage, Number of sets, Block size, spacing.

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Quantitative Classification of Rock Mass

  • Description of Joints:

Description of Joints: Orientation, Persistence, Roughness, Wall Strength Aperture Filling Seepage Strength, Aperture, Filling, Seepage, Number of sets, Block size, spacing. ISRM i i ’ t ISRM commission’s report Classification of Rock Material Based on Uniaxial Compressive Strength

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Point Load Index

  • Quick evaluation for uniaxial strength

(field or lab setup) (field or lab setup)

  • ASTM D 5731 procedures
  • Little sample preparation (cores,

pieces)

  • Measure force (P) to crunch intact rock

specimen

  • Point Load Index: Is = P/de

2 where de

= equivalent core diameter equivalent core diameter

Fig.8-1

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Point Load Index

GCTS Device Roctest Equipment

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Uniaxial Compressive Ranges for some Uniaxial Compressive Strength Ranges for some Common Rock Material Term Kg/cm2 Schist, Silt stone VW-W, Sand Very Weak- VW < 70 Stone, Lime stone –VW-M,Granite, Basalt Gneiss y Weak- W Medium Strong-MS 70-200 200-700 Basalt, Gneiss, Quartzite, Marble –MS-VS Medium Strong MS Strong- S Very Strong- VS 200 700 700-1400 > 1400 MS VS | Very Strong VS > 1400 |

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Classification for Rock Material Strength Strength

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Rock Quality Designation (RQD) M difi d C R

  • r Modified Core Recovery

x RQD

i

Σ = L Q

xi = lengths of individual pieces of core ≥ 10 cm

i

g p L is the total length of the drill run

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Indirect Methods of determination f RQF

  • f RQF

Seismic Method - Seismic Method RQD= (Vf / Vl )2 * 100 R ti f l it i th fi ld t th t i th l b Ratio of velocity in the field to that in the lab Volumetric Count - RQD = 115- 3.3* Jv where J is a measure of number of joints where Jv is a measure of number of joints within a unit volume of rock mass

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RQD RQD

RQD

  • A. Very poor

0 – 25

  • B. Poor

25 – 50 C.Fair 50 – 75 D.Good 75 – 90 E Excellent 90 100

  • E. Excellent

90 - 100

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ROCK STRUCTURE RATING (RSR) (RSR)

  • Wickham et. al. (1972) suggested this based on

( ) gg

  • bservation of small tunnels supported by steel ribs.
  • RSR = A + B + C

Parameter A Geology: General appraisal of geological Parameter A, Geology: General appraisal of geological structure on the basis of:

  • a. Rock type origin (igneous, metamorphic,

di t ) sedimentary).

  • b. Rock hardness (hard, medium, soft, decomposed).
  • c. Geologic structure (massive, slightly faulted/folded,
  • c. Geologic structure (massive, slightly faulted/folded,

moderately faulted/folded,

  • intensely faulted/folded).
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  • Parameter B, Geometry: Effect of discontinuity pattern

ith t t th di ti f th t l d i th with respect to the direction of the tunnel drive on the basis of:

  • a. Joint spacing.
  • b. Joint orientation (strike and dip).
  • c. Direction of tunnel drive
  • Parameter C: Effect of groundwater inflow and joint

Parameter C: Effect of groundwater inflow and joint condition on the basis of:

  • a. Overall rock mass quality on the basis of A and B

combined.

  • b. Joint condition (good, fair, poor).
  • c. Amount of water inflow (in gallons per minute per 1000

feet of tunnel).. feet of tunnel)..

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RMR or ‘Geomechanics Cl ifi i ’ Classification’

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Guideline properties of Rock Mass Cl Classes

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Evaluation of Tunnels b d RMR

Example: 10 m span RMR = 80 Stand up time > 4 years

based on RMR

Stand up time > 4 years RMR = 50 Stand up time ≈ 2 days

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RMR modified for slopes or tunnels RMR modified for slopes or tunnels

Additional factors applied to RMRbasic

  • Accounts for excavation method
  • Accounts for excavation method

BUT moreover,

  • Accounts for joint orientation wrt the excavation

– Unfavourable conditions, deduct points from , p RMRbasic – refer section F of Table refer section F of Table

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Slopes - unfavourable Slopes unfavourable

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Slopes - favourable

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Tunnels - unfavourable

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Tunnels - favourable

  • Widely spaced joints?

Widely spaced joints?

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RMR & Tunnels RMR & Tunnels

  • “Stand up time” for various tunnel spans

based on RMR

  • Unreinforced tunnels

─ no advice re support e.g. shotcrete or rockbolts/anchors Shotcrete = sprayed concrete, lightly reinforced p y , g y

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NGI Q-System Rating for Rock Masses

(Barton, Lien, & Lunde, 1974)

Norwegian Classification for Rock Masses

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = SRF J J J J RQD Q

w a r n

Q - Value Quality of Rock Mass

< 0.01 Exceptionally Poor

  • 4. Discontinuity Condition & Infilling

= Ja 0.01 to 0.1 Extremely Poor 4.1 Unfilled Cases 0.1 to 1 Very Poor Healed 0.75 1 to 4 Poor Stained, no alteration 1 4 to 10 Fair Silty or Sandy Coating 3 10 t 40 G d Cl ti 4 10 to 40 Good Clay coating 4 40 to 100 Very Good 4.2 Filled Discontinuities 100 to 400 Extremely Good Sand or crushed rock infill 4 < 400 Exceptionally Good Stiff clay infilling < 5 mm 6 Soft clay infill < 5 mm thick 8 PARAMETERS FOR THE Q-Rating of Rock Masses Swelling clay < 5 mm 12 Stiff clay infill > 5 mm thick 10 Stiff clay infill > 5 mm thick 10

  • 1. RQD = Rock Quality Designation = sum of cored pieces

Soft clay infill > 5 mm thick 15 > 100 mm long, divided by total core run length Swelling clay > 5 mm 20

  • 2. Number of Sets of Discontinuities (joint sets)

= Jn

  • 5. Water Conditions

Massive 0.5 Dry 1 One set 2 Medium Water Inflow 0 66 One set 2 Medium Water Inflow 0.66 Two sets 4 Large inflow in unfilled joints 0.5 Three sets 9 Large inflow with filled joints Four or more sets 15 that wash out 0.33 Crushed rock 20 High transient flow

0.2 to 0.1

High continuous flow

0.1 to 0.05

  • 3. Roughness of Discontinuities*

= Jr g

r

Noncontinuous joints 4

  • 6. Stress Reduction Factor**

= SRF Rough, wavy 3 Loose rock with clay infill 10 Smooth, wavy 2 Loose rock with open joints 5 Rough, planar 1.5 Shallow rock with clay infill 2.5 Smooth, planar 1 Rock with unfilled joints 1 Slick and planar 0.5 Filled discontinuities 1 **Note: Additional SRF values given *Note: add +1 if mean joint spacing > 3 m for rocks prone to bursting, squeezing and swelling by Barton et al. (1974)

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Rock Tunnelling Quality Index, Q ( N i Q t ) B t t l 1974 (or Norwegian Q system), Barton et al., 1974

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = SRF Jw J Jr J RQD Q ⎟ ⎠ ⎜ ⎝ ⎟ ⎠ ⎜ ⎝ ⎟ ⎠ ⎜ ⎝ SRF Ja Jn Q

RQD = Rock Quality Designation 100 - 10 Jn = Joint set number 1 – 20 Jr = Joint roughness factor 4 -1 Ja = Joint alteration and clay fillings 1 – 20 Jw = Joint water inflow or pressure 1 – 0 1 Jw Joint water inflow or pressure 1 0.1 SRF = stress reduction factor 1 – 20 Typically: 0.01 < Q <100

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Q system Q system

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ = SRF Jw J Jr J RQD Q ⎠ ⎝ ⎠ ⎝ ⎠ ⎝ SRF Ja Jn

  • (RQD/Jn) = crude measure of block size
  • (Jr/Ja) = roughness/friction of surfaces

( /S ) f ( )

  • (Jw/SRF) = ratio of two stress parameters (active stress)
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Geological Strength Index, GSI GSI

  • Developed by Hoek, Kaiser, & Bawden

(1995) H k & B (1997) (1995), Hoek & Brown (1997).

  • GSI from Q-system:

44 log 9 + ⎥ ⎤ ⎢ ⎡ ⎟ ⎟ ⎞ ⎜ ⎜ ⎛ ⎟ ⎟ ⎞ ⎜ ⎜ ⎛ =

r

J RQD GSI

  • GSI from Geomechanics system where
  • g

9 ⎥ ⎦ ⎢ ⎣ ⎟ ⎟ ⎠ ⎜ ⎜ ⎝ ⎟ ⎟ ⎠ ⎜ ⎜ ⎝

a n

J J GS

GSI from Geomechanics system where RMR > 25:

( )

∑

+ =

4

10

i

R GSI

  • Chart approach based on structure &

f lit

∑

=1 i

surface quality

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Slope Mass Rating (SMR) Slope Mass Rating (SMR)

  • SMR = RMRb

i – ( F1 F2 F3 ) + F4

SMR = RMRbasic ( F1.F2.F3 ) + F4

  • F1, F2 and F3 are adjustment factors

related to joint orientation with respect to related to joint orientation with respect to slope orientation. F4 is the correction factor for method of excavation factor for method of excavation.

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Suggested Supports for Various SMR l SMR classes

SMR Classes SMR Values Suggested Supports SMR Classes SMR Values Suggested Supports I a 91-100 None I b 81-90 None, scaling is required II a 71-80 Spot Bolting II b 61-70 Spot or systematic bolting III a 51-60 Spot or systematic bolting, spot shotcrete III b 41-50 Systematic bolting and shotcrete, toe wall IV a 31-40 Anchors, systematic shotcrete, toe wall IV b 21 30 S t ti i f d h t t t ll IV b 21-30 Systematic reinforced shotcrete, toe wall, re-exacavation V 11-20 Gravity or anchored wall, re-excavation

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Rock Strength: mi parameter

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Strength of Rock Masses

mi

↓

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Strength of Rock Masses

c'/qu mi

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Equivalent Modulus of Rock Masses (Table 10 7) (Table 10-7)

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Allowable Bearing Stresses on Rock Masses

Foundations on Fractured Rock Formation

30

MPa)

Note: Use maximum qa < q u where qu = compressive strength

20 25

ress qa (M

where qu compressive strength

  • f intact rock specimens

15

earing Str

) 130 / ( 1 ) 16 / ( 1 ) ( RQD RQD MPa q ALLOWABLE − + ≈

NOTE: 1 MPa = 10 tsf

5 10

  • wable Be

Peck, et al. (1974)

NOTE: 1 MPa = 10 tsf 10 20 30 40 50 60 70 80 90 100

Allo

( ) Approximation

Rock Quality Designation, RQD

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