RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD · tunnelling method, the knowledge of...

RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD

Y. H. CHO.

Shin Sung Engineering Co. Ltd. Seoul, South Korea

RESEARCH OF ROCK CLASSIFICATION

USING KOREA METHOD

2008. 5.

Y. H. CHO.



Y. H. CHO.


Lists

1. Preface.

2. Rock Classification.

3. Classification method in practice

4. Character of KOREA method.

5. Application of KOREA method.

6. Numerical Analysis.

7. Conclusion.

Reference


Y. H. CHO.


1. Preface.

These days, after the construction of crude oil cavern in 1980's, the construction of tunnelling

methods are increasing in so many types as railways, roads and storage caverns in Korea. In

tunnelling method, the knowledge of subsurface distribution of Rock and soil are the most

important to perform a project successfully.

Therefore, we have classified the rock conditions by using of foreignner's rock classification

methods till now.

As the result of using foreigner's rock classification method, there are some personal

misunderstanding data and ignored in origin and filling materials of rock.

Above all, the calculations of rock classification are different and having some erros by each

engineer. Therefore in classifying the Rocks identically we can use the KOREA (Korea Rock

Estimation and Analysis) method in accordance with geological conditions and the rock

engineering characteristics.

In KOREA method, we use the more items to classify the rock conditions than other

classification methods including RMR, Q-system etc.

2. Rock Classification

2.1 general

The purpose of rock classification is to know the rock properties and engineering

characteristics in accordance with the properly design and construction of subsurface civil

structures as slopes, tunnels, dams, nuclear power plant etc. The values are different from their

strength, deformability, permeability and so on.

To get the detailed characteristics of physical and mechanical behaviors as for the bed rock, the

feasibilities of the structures in terms of engineering prospect are decided. The last stage, it can

be possible to compare the rock classification result, field test data and laboratory test data.

The results of compared data are used to judge the decision of reinforcement or not, and it

could be decided the range of reinforcement. Generally in tunnels and slopes, the main

advantages are to decide the standard design pattern to lead the safety and economic

construction fee. Rock classification method should be simple and objective and the items

shoud contain geological origin, strength, discontinuities, weathering grade, frequency of

discontinuity, direction of discontinuity, alterating, groundwater that are be correctly divided by

rock distribution statement.


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2.2 Classification factor

The most important factors to classify are character of composing mineral and geological origin.

Intact rocks are to be strong, interactive, and non permeable if not weathered. But because of

the possible discontinuities, the strength balance of bed rock should be failed and the failures

are increasing to the rupture.

Therefore intact rocks should be classified by the frequency and character of discontinuities,

progressing weathered rocks by discontinuities are preliminary considered the inverrals,

weathering statements, and filling materials of discontinuities. Rock classification by the

intervals of discontinuities are as below tabe 2.1

Classification interval of discantinuity

Massive very wide spacing

Blocky Equidimensional spacing

Tabular one dimension is shorter than others(two)

Columnar one dimension is longer than others(two)

Irregular wide variation(spacing)

Crushed heavily jointed

<Table 2.1> classification by the interval of discontinuity.

The statements of discontinuities are to be polished, slickensided, smooth, rough(by ANON),

and plannar, undulating, stepped, irregular (by Barton) respectivelly. Barton's theory are


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considerd the deformability theory with shear strength added by filling materials. The

discontinuities should firstly divided by open or close.

The result of dividing by aperture is as below table 2.2

Discontinuity width of aperture

Close

very tight less than 0.1mm

tight 0.1 ~ 0.25mm

partly open 0.25 ~ 0.5mm

Grapped

open 0.5 ~ 2.5mm

moderate wide 2.5 ~ 10mm

wide more than 10mm

Open

very wide 10 ~ 100mm

Extremely wide 100 ~ 1000mm

Cavernous over 1m

Table 2.2. Classification by the aperture

2.3 Classification in civil structure.

There are dam, tunnel, slope, bridge in civil structure.

when classification, it should be considered the bedrock condition and discontinuities

and groundwater etc.

2.3.1. Classification in Dam.

In Dam project, it should be considered cut off walls.

The stabilities of main dam, saddle dam and diversion tunnel considered,

mostly the conditions of rock and residual soils are important.

In case of Japan, they are divided


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3 Groups by hammering in strong, medium, weak.

And by the intervals of discontinuity, with 3 groups in over 50cm, 15-50cm, less than 15cm each.

2.3.2 Classification in Tunnel.

Tunnel structures are described in long and thin structure than others.

To classify the rock conditions, it should be arranged linear profile.

Generally by use of the method of geophysical prospecting and core drilling investigation,

classification of rock conditions are carried out.

In Japan, rock types, seismic velocity are most considered.

To define the classification index, it should be considered rock type, strength, weathering and

altering grade, hammering reaction, intervals and state of discontinuities, RQD, seismic velocity

etc.

The classification index of rock type are as below table 2.3

Name classification index

Terzaghi strength, interval of discontimuity

Deer RQD

Bieniawski RMR

Barton Q-system

<Table2.3 Rock classification index>

Bieniawski and Barton are considered RMR and Q-system by using of rock condition remarks in

accordance with rock strength, the state of discontinuities, and groundwater etc.

But they are ignored the geological origin of rock,

depree of weathering and altering, state of discontinuity and infilled materials. Above all, the

results are different with the investigator's subjective opinion. Therefore to mimimize the

imvestigator's subjective opinion, the index of classification should be subdivided.

In KOREA (Korea Rock Estimation and Analysis) method, it should be considered all of the rock

classification index subdivided and appropriate the characteristic of korean geological condition.

It should be useful in planning, design, construction of tunnelling project.


Y. H. CHO.


2.3.3. classification in slopes.

To define the inclined grade and to maintain the stability of slope, the classification of rock and

residual soil are to be concerned.

lt should be considered the strength, the direction of slope and discontinuity, the height of slope,

weathering state, groundwater etc.

In rock slopes, according to the state of discontiuities, the stability is much safer in rough and

irregular than smooth, plannar, slickensided. Of course the direction of dicontinuities are the

most important.

In case of soil slope and much weathering state, the effective stress should be much considered

decreased by the pore water pressure. Therefore the drain work should be important in soil to

stabilize the slopes.

Therefore to maintain the stabilities of slopes, it should be continuously observed the direction

of slopes and discontinuities, the state of discontiuities, weathering grade, especially the

groundwater condition in the area of soil and highly we athered rock.

Three Rock classification method in practice are several used method for rock classification.

The typical methods are as below.

3. Classification method in practice

3.1. Terzaghi classification.

Terzaghi was one of the first workers to attempt an engineering classification of rook

masses.(1946)

He recognized the significance of discontinuities, their spacing and their filling materials as well

as the influence of weathering.

However he tended to overlook the properties of the rock. He thought only the state of the rock

as intact, jointed, seamy, crushed, squeezing, swelling and so on.

At all the calculated loads are considered to be reinforced by steel ribs.

The rock loads are table 3.1


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Rock Condition Rock Load Hp

in Feet Remarks

1. Hard and intact. zero Light linging required only if

spalling or popping occurs

2. Hard stratified or

schistose 0 to 0.5 B Light support, mainly for

protection against spalls

Load may change erratically

from point to point

3. Massive, moderately

jointed 0 to 0.25 B

4. Moderately blocky and

seamy

0.25 to 0.35

(B+Ht) No side pressure

5. Very blocky and

seamy

(0.35 to 1.1)

(B+Ht) Little or no side pressure

6. Completely crushed but

chemically intact 1.10 (B+Ht)

Considerable side pressure

softening effectis of seepage

towards bottom tunnel requires

either continuous support for

lower ends of or circular ribs

7. Squeezing rock,

moderately depth

(1.10 to 2.1)

(B+Ht) Heavy side pressure, invert

struts required

Circular ribs are recommended 8. Squeezing rock, great

depth

(2.10 to 4.5)

(B+Ht)

9. Swelling rock

Up to 250 feet,

irrespective of

the value of

(1.10 to 2.1)

(B+Ht)

Circular ribs are required

In extreme cases use yielding

support

Table 3.1(Terzaghi Rock Load)


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3.2 classification by RQD

RQD method was designed by Deer in 1964.

In drilling investigation, the ratio of over 10cm sample length as to total length is considered

Rock Quality Designation.

If massive rocks, the RQD value is almost 100%, and the value is diminished by the

discontinuities and crushed zone.

The classification index is as table 3.2

RQD (%) Rock Quality

< 25 very poor

25 - 50 poor

50 - 75 moderate

75 - 90 good

90 - 100 very good

Table 3.2. RQD Index

If not drilled, the value is indirectly calculated by Q = 115 - 3.3 Jv.

(when Jv is the number of joints per 1m )

3.3. RSR Method.

Wickham et al(1972) introduced the concept of rock structure rating(RSR) which refers to the

quality of rock structure in relation to ground support in tunnelling.

The RSR system rates several geological factors parameterA, parameterB, ParameterC.

If the values less than 27, there would be required heavy support, whilst those with ratings over

77 would probably stand unsupported.

The rates are tabe 3.3.


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Table 3.3 Rock structure rating (after Wickham et al. (1972))

Parameter A⑴ -Geological structure

Basic rock

type

Igneous

Sedimentary

Metamorphic

Massive

30

24

27

Slightly faulted

or folded

26

20

22

Moderately faulted

or folded

15

12

14

Intensely faulted

or folded

10

8

9

(Maximum value of parameter A is 30)

(2) Parameters B-Joint pattern and direction of drive

Average joint

spacing Strike perpendicular to axis Strike parallel to axis

Direction of drive

Both With dip Against dip Both

Dip of prominent joints

<20° 20-50° 50-90° 20-50° 50-90° <20° 20-50° 50-90°

<0.15m

Clearly jointed 14 17 20 16 18 14 15 12

0.15-0.3m

Moderately

jointed 24 26 30 20 24 24 24 20

0.3-0.6m

Moderate to

blocky 32 34 38 27 30 32 30 25

0.6-1.2m

Blocky to massive 40 42 44 36 39 40 37 30

>4.0m

Massive 45 48 50 42 45 45 42 36

(Maximum value of parameter B is 50)


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(3) Parameter C-Groundwater, joint condition

Anticipated water sum of parameters A + B

inflow

(1/s per 300m) 20-45 46-80

Joint condition*

1 2 3 1 2 3

None 18 15 10 20 18 14

Slight (<15) 17 12 7 19 15 10

Moderate (15-75) 12 9 6 18 12 8

Heavy (>75) 8 6 5 14 10 6

* I = tight or cemented; 2 = slightly weathered; 3 = severely weathered or open

(Maximum value of parameter C is 20)

3.4 RMR Method

Bieniawski(1973) proposed classifications of jointed rock masses which depended on various

weighed aspects of both the rock material and the rock mass.

Their objective was to obtain rock mass ratings which could be used for design purposes.

Excavation pattern and reinforcing types are mainly considered.

The parameters for classifications are uniaxial compressive strength, RQD, the spacing, state,

and direction of discontinuities, groundwater.

The standard rates are on table 3.4

Table 3.4 Engineering classification of jointed rock masses (after Bieniawski (1975a))

(a)Classification parameters and their ratings

1

Strength of Point load

intact rock strength index >8 4-8 2-4 1-2 use of unaxial

material (MPa) compressive test

preferred

Unaxial

compressive >200 100-200 50-100 25-50 <25

strength (MPa) Very high strength High strength Medium strength Low strength Very low strength

Rating 10 5 2 1 0

2 Drill core quality ROD 90-100% 75-90% 50-75% 25-50% <25%


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Rating 20 17 14 8 3

3

Spacing of discontinuities >3m 1-3m 0.3-1m 50-300mm

Very wide(solid) Wide(massive) Moderately close Close(fractured)

(blocky/seamy)

Rating 30 25 20 10 5

4

Orientations of discontinuities Very Favourable Fair Unfavourble Very

favourable unfavourable

Rating 15 13 10 6 3

5

Extremely tight Very tight Tight Open slickensided Very open

Very rough surfaces Slightly rough Slightly rough surfaces Soft gouge>5mm

Condition of Not continuous surfaces surface or thick

discontinuities No separation Separation Separation < 1mm Gouge<5mm thick or

Hard joint wall <0.1mm No gouge or Joints open>5mm

rock Hard joint wall soft joint wall Joints open 1-5mm Continuous joints

rock rock Continuous joints

Not continuous

Rating 20 15 10 5 10

Inflow per 10mm

tunnel length

or

None

>25 1/min

or

25-125 1/min

or

>125 1/min

or

joint

water

pressure

Ground 0 0.0-0.2 0.2-0.5 >0.5

water

Ratio


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major principal stress

or or or or

General

conditions Completely dry Moist only water under severe water

(interstitial water) moderate pressure problems

Rating 10 8 5 2

(b) Rock mass classes and their ratings

Class No. I II III IV V

Description Very good rock Good rock Fair rock Poor rock Very poor rock

Rating 100-90 90-70 70-50 50-25 <25

(C) Meaning of rock mass classes

Class No. I II III IV V

Average stand up

time

10 years for 5m

span

6 months for 4m

span

I week for 3 m

span

5 hours for 1.5m

span

10 minutes for

0.5m

span

Cohesion of the

rock mass >300 kPa 200-300 kPa 150-200 kPa 100-150 kPa <100 kPa

Friction angle of

the rock mass <45° 40-45° 35-40° 30-35° <30°

Caveability of ore Very poor

Will not cave

readily

Large fragments.

Fair

Will cave readily.

Good

fragmentation

Very good

3.5 Q - system

Q - system was considered by Norwegian Geotechnical Institute in 1974

with Barton, Lien, and Lunde.

It was classified by the data of 200 tunnelling construction.

Accordig to the Q-value, unsupportable span width, supporting patterns, excavation length etc

are suggested. The Q � value is calculated by RQD, the number of joint(Jn), Joint

alternatives(Ja), Joint roughness(Jr), joint water leakage(Jw), Stress Reduction factor(SRF).


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Q=RQD/Jn×Jr/Ja×Jw/SRF

The first parameter RQD/Jn means the block size, and second Jr/Ja is relate to the shear

strength, Jw/SRF means active stress.

If swelling rock and much ground water bearing zones, Jw/SRF value is the range of

0.0025~0.01, while the value is 1.0/0.5=2 when very tight rocks and dry condition. The value for

Q-system is as below table 3-5

1. ROCK QUALITY DESIGNATION (RQD) Note

Where RQD is reported ⒤

or measured as

10(including 0) a nominal

value of 10 is used to

evaluate Q in Eq. (3.2)

(ii) RQD intervals of 5, I.c.

100, 95, 90, etc. are

sufficiently accurate

A. Very poor 0-25

B. Poor 25-50

C. Fair 50-75

D. Good 75-90

E. Excellent 90-100

2. JOINT SET NUMBER (Jn) Note

A. Massive, no or few joints 0.5-1.0

For intersections ⒤

use(3.0×J )

(ii) For portals use(2.0×J )

B. One joint set 2

C. One joint set plus random 3

D. Two joint sets 4

E. Two joints sets plus random 6

F. Three joint sets 9

G. Three joint sets plus random 12

H. Four or more joint sets. random, heavily jointed, 'sugar cube', etc 15

J. Crushed rock, earthlike 20

3. JOINT ROUGHNESS NUMBER Note

Rock wa⒜ ll contact and

Rock wall contact before 10cms shear⒝

A. Discontinuous joints 47 Add 1.0 if the mean ⒤

spacing of the relevant joint B. Rough or irregular, undulating 3


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C. Smooth, undulating 2 set is greater than 3m

(ii) J =0.5 can be used for

planar slickensided joints

having lincations, provided

the lincations are favourably

orientated

D. Slickensided, undulating 1.5

F. Smooth, planar 1.5

G. Slikensided planar 1.0

⒞ No rock wall contact when sheared 0.5

H.Zone containing clay minerals thick enough to prevent rock wall

contact

1.0

(nominal)

J. Sandy, gravelly or crushed zone thick enough to prevent rock wall

contact

1.0

(nominal)

4. JOINT ALTERATION NUMBER �r(approx) Note

Rock wall contact ⒜

Values of (⒤ �)r. are

intended as an approximate

guide to the mineralogical

pro

A. Tightly healed, hard, non-softening, impermeable filling

I.c. quartz or epidote 0.75 (-)

B. Unaltered joint walls, surface staining only 1.0 (25-35°)

C. Slightly altered join walls. Non-softening mineral

coatings, sandy particles, clay-free disintegrated rock etc. 2.0 (25-30°)

D. Slity or sandy-clay coatings, small clay-fraction (non-

softening) 3.0 (20-25°)

E. Softening or low friction clay mineral coating, I.c.

Kaolinite, mica. Also chlorite, taic, gypsum and graphite

etc. and small quantities of swelling clays. (Discontinuous

coatings, 1-2mm or less in thickness)

4.0 (8-16°)

Rock wall contact before 10cm shear ⒝ 4.0 (25-30°)

F. Sandy particles, clay-free disintegrated rock etc. 6.0 (16-24°)

G. Strongly over-consolidated, non-softening, clay mineral

fillings. (Contituous, <5mm in thickness) 8.0 (12-16°)

J. Swelling clay fillings, I.e. montmorillonite(Continuous,

<5mm in thickness). Value of ja depends on percent of

swelling clay-size particles, and access to water etc.

8.0-12.0 (6-12°)

No rock wall contact when sheared ⒞

K. Zones or bands of disintegrated or crushed rock 6.0

L. and clay(see G, H, J for description of clay M. condition) 8.0


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M. condition) 8.0-12.0

N. Zones or bands of silty or sandy clay, small clay fraction(non-

softening) 5.0 (6-24°)

O. Thick, conrinuous zones or bands of clay(see G, 10.0, 13.0 or (6-24°)

P. H, J for description of clay condition) 13.0-20.0

R.

5. JOINT WATER REDUCTION FACTOR (Jw)

A. Dry excavations or minor inflow, I.e. <5 / min locally> 1.0

B. Medium inflow or pressure occasional outwash of joint fillings 0.66

C. Large inflow or high pressure in competent rock with unfilled joints 0.5

D. Large inflow or high pressure, considerable outwash of joint fillings 0.33

E. Exceptionally high inflow or water pressure at blasting, decaying

with time 0.2-0.1

F. Exceptionally high injlow or water pressure continuing without

noticeable decay 0.1-0.05

6. STRESS REDUCTION FACTOR

Weakness zones inersection excavation, which may cause ⒜

loosening of rock mass when tunnel is excavated

A. Multiple occurrences of weakness zones containing clay or

chemically disintegrated rock, very loose surrounding rock(any depth)

B. Single weakness zones containing clay, or chemically disintegrated

rock(depth of excavation 50m)

C. Large inflow or high pressure in competent rock with unfilled joints

D. Multiple shear zones in competent rock(clay free), loose

surrounding rock(any depth)

E. Single shear zones in competent rock(clay free) (depth of

excavation 50m)

F. Single shear zones in competent rock(clay free) (depth of

excavation 50m)


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G. Loose oen joints, heavily jointed or 'sugar tube' etc. (any depth)

Competent rock, rock stress problems ⒝

H. Low stress. near surface

J. Medium stress

K. High stress, very tight structure (usually favourable to stability)

L. Mild rock burst (massive rock)

M. Heavy rock burst (massive rock)

Squeezing rock, plastic ⒞ flow of incompetent rock under influence of

high rockpressure

N. Mild Squeezing rock, chemical swelling activity depending on

presence of water

P. Mild swelling rock pressure

R. Heavy swelling rock pressure

Table 3-5 values for Q-system

3.6 Flanklian method

This method was considered. by the uniaxial compressive strength and the Joinjt spacing in

earth working.

Three methods of digging, ripping, blasting are considered by the strength and the Joint spacing


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4. Character of KOREA Method

To analysis the stabilities of rock foundation, it should be considered origin and history of the

rock mass. The former classification methods are usually applied in design and construction of

rock foundation as tunnels, slopes dams and other facilities.

The object of considering KOREA method in classification of rock mass is to carry out the safe

and econonical construction by the appropriate

analysis of rock mass and useful reinforcing design.

Actually the analysis of rockmass was somewhat different lead to the excessive reinforcing

works.

Therefore by using KOREA method, it is possible to design and perform the successful

engineering works for brief analyzing of rock mass.

The principal check points as to the foremer classification method are as belows.

1) Terzaghi method

This method was considering all the loads over tunnels are eftective in tunnelling safety But

these days, New Austrian Tunnelling Method was developed and by the rock bolt and shoterete

works, the loads to be effected are mostly dimimished and the loads are mimimumized.

Therefore this method should be reconsidered, and only used in linited area like very dangerous

zones.

2) RQD method

RQD means Rock Quality Designation during drilling work.

It should be analyzed only by the length of cores while the strength of the rocks be overlooked.

3) RSR method

RSR means Rock Structure Rating. RSR method was considering origin of rocks, fault and

folds, the direction of joints, groundwater etc.

Nearly all of the parameters are checked in RSR method, but the range of calculated remarks

are somewhat wide, therefore the results are sometimes subjetively.

To obtain objective results, the more items should be analyzed.

4) RMR method

RMR means Rock Mass Rating. RMR method is the most useful one to analyze the rock mass

considering strength, RQD, the spacing and state of joints, groundwater etc.

Of course it is useful in domesic area but the items about roughness and infilled materials are

overlooked.


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To complement the items, it should be checked more particularly and objectively.

5) Q-system

In Q-system, block size, shear strength, and active stress are most inportant factors to be

applicated. In 1980, the underground crude oil storage project, Q-system was applicated in

tunnel design and reinforcing works. And as to the results, the reinforcing index are much

excessive in that project because of the difference from the rock origin between Korea and

Norway.

Therefore it should be necessary to be changed to modified Q-system.

The value of Rock quality is much wide ranges in 0.001~1000 lead to the erros much highly

sometimes. Actuallly these days the RMR method is much more applicated than Q-system

because Q-system should be reconsidered more objectively.

6) Flanklian Method

The approximate classificaion method was Flanklian method to apply for the earth works to

check the excall ation efficiency.

To analyze the tunneling project, much more items like state and direction of joints, infilled

maerials groundwater and other factors should be reconsidered.

5. Application of Korea method.

The object of the considering KOREA method to be applicated is to confirm the rock mass

quality correctly and with the appropriate reinforcing works more safe and economic tunnelling

works and other facilities refer to the rock mass quality value are-anticipated-

the subjective decisions. The final recheck for professional engineer should be applicated more

particalarly and objectively. The items to be applied are as belows.

1) The origin of rock

Rocks are classified with igneous, metamorphosed and sedimentary.

All the rocks are divided with massive and jointed.

rocks igneous metamorphosed sedimentary

state massive jointed massive jointed massive jointed

rank 5 4 4 3 4 3


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2) The strength of rock

The rank of strength are 10 at all because the strength of rock is much inportant in

classification. The state of rock are divided 4 groups

A(strong) is difticult for explosion.

B(medium) is easy for explosion.

C(weak) is somewhat weathered, ripping capable.

D(soil) is easily broken like soil

state of rock A(strong) B(medium) C(weak) D(soil)

rank a b a b a b a b

10 8 8 6 6 4 4 2

a: general state

b: crushed and like soil

3) RQD

In case of over 90% RQD, the rocks are mostly slightly weathered.

RQD over

90% over 50% under 50%

rank 5 a b a b

4 3 2 1

a: fresh

b: weathered

4) The frequency of joints

The state of rock mass were divided massive, blocky, tabular, columnar, irregular, crushed.

SPACING

Massive

over

10m

Massive

over

1m

Blocky Tabular columnar irregular crushed

over

1m

over

0.5m

over

10cm

less

10cm

over

10cm

less

10cmweathered soil

rank 10 9 8 7 6 5 5 4 3 2

remarks Tabular : One dimension shorter than others (two)

Columnar : One dimension longer than others (two)

5) Direction of Joints

Actually, the direction of joints are the most important in rock slope and tunnelling.


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It is more safe to excavate tunnel perpendicular to the exis than parallel

strike & Excavation perpendicular parallel

dip & Excavation Dip direction against dip high

dip

Low

dip high dip low dip high dip low dip

rank 10 8 6 4 2 0

6) Continuities of Joint

Accordig to the continuities of Joint, they are divided ino solid(over 2m) blocky(75mm~2m),

broken(less 75mm) crushed(less 20mm)

continuities

of Joint solid blocky broken crushed soil

rank 5 4 3 2 1

7) infilled materials.

The spacing of joints are divided into wide in over 200mm, narrow in 6~20mm And the infilled

materials such as clay are also important for the safety of rock foundation.

infilled

material

clay free clay contained

tight Narrow wide less

5mm

over

5mm slickensided

rank 5 4 3 2 1 0

8) Open, sand or clay minerals.

The seepage velocity of jonts are depend on the state of joint. Open joint is the best seepage

condition and next filled with sand.

It would be impermeable with clay minerals lead to decrease the shear strength owing to the

increasing of pore water pressure

minerals

open sand clay

air water less

5mm

over

5mm

less

5mm

oven

5mm

rank 5 4 3 2 2 1


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9) Joint roughness

Joint roughness are divided with rough(irregular) smooth, slickensided and particularly,

stepped, undulating, plannar.

The shear strength values are depend on the roughness.

roughness Rough smooth slickensided

undulating plannar stepped plannar stepped plannar

rank 5 4 3 2 1 0

10) Weathering grade

weathering Fr SW MW HW CW Rs

rank 5 4 3 2 1 0

11) Weathering in joints.

Joint compressive strength is decreased with the weathering grade in joint. The decreasing

ratio is up to 75% as low as uniaxial compressive strength.

weathering

Joint

One Direction over two direction

less

0.6cm 0.6-2cm 2-6cm 6-20cm

over

20cm

less

0.6cm0.6-2cm 2-6cm 6-20cm

over

20cm

rank 5 4 3 2 1 4 3 2 1 0

12) Stress

The induced stress in tunnel is increased with excavation quantities. If the strength of rock is

less than induced stress, it should be destroyed. Therefore it should be checked stress in tunnel

design for safe excavation.

The stress is effectcd with the overburden and the shape of tunnel.

Excavation Rock Soil(weathered rock)

overburden over

2D 2D-1D

less

1D

over

2D 2D-1D

less

1D

Rank a b a b a b a b a b a b

10 9 8 7 6 5 6 5 4 3 2 1

a: round section

b: angular section


Y. H. CHO.


13) Groundwater

Groundwater is affected with pore water pressure lead to decrease the shear strength

water good rock bad rock

dry damp leakage dry damp leakage

rank 5 4 3 3 2 1

14) Structural geology

Fault and folds are very harmful in tunnelling excavation. In tunnelling excavation, fault breccia,

fault clay means the structural unsafe condition like slickensided zone

Rock good bad

structural

zone no

less

5cm

over

5cm

over

2Direction

less

5cm

over

5cm

over

2Direction

rank 10 8 6 4 6 4 2

15) Check by professional engineer

Rock very

good good Moderate bad

very

bad

rank 8-10 6-8 4-6 2-4 0-2

The last check by professional engineer is also important for calculating correct results to

construct safe facilities.

6.Numerical Analysis

To check the applicability in tunnel design and construction with KOREA method. 2 projects

such as tunnel section for road were applied.

One is Song Jung Tunnel in Pusan-Ulsan highway project and the other is Shin hyun Tunnel in

A Ju-Sang Dong road construction project.

The Typical section is as below

items Rock RMR KOREA reinforcing type


Y. H. CHO.


S

O

N

G

J

U

N

G

T/L

STA1+600 Soil 21-40 20 T-5

STA1+640 W/R <20 24 T-5

STA1+700 W/R~S/R <20 35 T-5

S

H

I

H

Y

U

N

T/L

STA5+P01.4 S/R 69 64 T-2

STA6+352 S/R 51 64 T-2

STA5+822.2 H/R 68 79 T-2

STA6+321 H/R 81 85 T-1

7. Conclusion

These days RMR Method is generally applied in classification of rock mass for tunnel design

and construction. The RMR method is consist in 6 different parameters such as strength, RQD,

Joint spacing, Joint state, Groudwater and Joint direction. The ranks of each item are somewhat

resulted much erros in classification such as subjective data and overlooking some

characteristics. Therefore they lead to over reinforcing works and economical damage.

The object of suggesting KOREA method is to recognize the rock mass quality correctly.

Accordig to the KOREA Method, it is possible to apply correct reinforcing works and appropriate

construction schedule. To confirm the application effect, numerical analysis was performed in 2

of the road tunnels. After that analysis, it is proved that the KOREA method is useful to

determine the rock quality. The applied 15 items for KOREA method are as below

- Rock origin


Y. H. CHO.


- Rock strength

- RQD

- Joint Direction

- Infilled material

- Open, sand or clay

- Joint state

- Weathering grade

- Roughness

- Stress

- Groundwater

- Structural gelolgy

- Check by professional Engineer

Reference

[1] Numerical analysis report in A Ju-Sang Dong(2005.8)

[2] F.G.Bell Fundamentals of Engineering geology pp 165-210, pp 528-554

[3] MOCT technical reference 60.62

Rock and Rock Mass pp. 17-35

[4] ZARUBA MENCL Engineering geology pp310-341

[5] ZDENEK BAZANT Methods of foundation Engineering

pp 40-42

[6] Korea Expressway Corporation

Highway reference for tunnelling practice pp. 109-127

[7] Report on song Jung 2 Tunnel in safety(2003.7)

RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD · tunnelling method, the knowledge of...

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