Post on 27-Mar-2020
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.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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.
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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.
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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)
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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.
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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)
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
(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%
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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).
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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)
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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.
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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.
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
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
RESEARCH OF ROCK CLASSIFICATION USING KOREA METHOD
Y. H. CHO.
Shin Sung Engineering Co. Ltd. Seoul, South Korea
- 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)