Extension of RMR and Q-system in Taiwan

Extension of RMR and Q-system in Taiwan
C. T. Chang 1 , P. C. Hou 2 , M. C. Lee 3 , Y. T. Lee 3 , P. H. Chang 3
1 Vice President of Sinotech Engineering Consultants, LTD. Taipei R.O.C.
2 Technical Manager of Sinotech Engineering Consultants, LTD. Taipei R.O.C.
3 Engineer of Sinotech Engineering Consultants, LTD. Taipei R.O.C.
ABSTRACT
The mechanism of mountainous tunnel engineering is quite complicated. At present, empirical
methods are basically used in tunnelling design and analytical or numerical methods are adopted as a
supplementation. While using empirical methods, rock mass classification is a vital tool because it
embraces many factors that affect the stability of a tunnel. It also provides a simple and fast means of
evaluation to design tunnel supports. Since 1970’s, New Austrian Tunnelling Method (NATM) has
been widely used in Taiwan. Moreover, Q-system of Barton et al. and RMR-system of Bieniawski are
commonly used to classify the rock mass. However, local geologic characteristics have never been
taken into considerations in these systems. It is necessary to review the suitability of these systems and
extend them on the basis of the domestic experience accumulated in last several decades.
This paper will begin at discussing the applicability of existent rock mass classifications in Taiwan,
including the applicability in rock tunnels and poor-cemented weak ground tunnels. Moreover, this
paper will develop a new classification system, which classifies rock formations in Taiwan into four
types: A, B, C and D. The above system is on the basis of local geologic material properties, geologic
age, sensitivity to water and relevant strength characteristics. It also formulates the criteria, which are
regarded as the bases of designing tunnel-support systems, for rating various rock types in Taiwan.
Keywords: rock mass classification, tunnel engineering
1. INTRODUCTION
RMR-system of South Africa and Q-system of Norway have been introduced from abroad for many
years. In Taiwan, they have been the most commonly used rock mass classifications and adopted in
numerous tunnels. Nevertheless, due to its young geologic age and the location among the zone of
plate collision, there are still some imperfections during the application of these classifications in
Taiwan. There is much difference between the original environment of existent classifications and
Taiwan in rock types, rock strength, cover and span of tunnels, groundwater, etc. Besides, gravel
layers, sandstone and mudstone in the western foothills exceed the applicable extent of existent
classifications. Therefore, it is necessary to establish the local rock mass classification system for
Taiwan.
The contents in this paper are cited from the research and development of Public Construction
Commission’s project “The establishment of rock mass classification system and tunnel engineering
databases in Taiwan” – “The establishment of rock mass classification and tunnel-support system in
Taiwan.”
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2. THE APPLICATION OF EXISTENT ROCK MASS CLASSIFICATION SYSTEMS
By making a comprehensive survey of major rock mass classifications worldwide, it can be traced
back to the middle of 1940’s that Terzaghi proposed the rock load method. Nevertheless, in Taiwan,
rock mass classifications weren’t adopted to design tunnel supports until late 1950’s. The above
method was mainly used at that period of time and it could classify the rock mass around tunnels into
nine rock load classes by using qualitative method. And it could be possible to design the so-called
rigid support system by using the conventional, semi-empirical, and structural analysis model. General
speaking, rock load method is more suitable for shallow cover tunnels. As our understanding of
tunnelling behavior improved, the construction concept of NATM was introduced into Taiwan in late
1970’s and has become the mainstream nowadays.
Rock mass classification systems adopted in mountainous tunnel engineering in Taiwan can be
roughly divided into two groups: qualitative and quantitative. For qualitative methods, rock load
method of Terzaghi and rock mass classification of Austrian are the common ones; while the RMRsystem
and Q-system are mainstream for quantitative methods. Nevertheless, the rock mass
classifications or classes nowadays used in Taiwan are quite different from the original system
because of technological innovation and accumulated experience these years. Take the corresponding
RMR rating of the third rock mass class for instance: Mu-Zha Tunnel of Northern Second Freeway is
56~65 and new water channel of Wu-Jie is 44~56. Those were both not the proposed value of RMRsystem
as 40~60. Besides, the rock mass classes adopted in tunnel groups of Northern Second
Freeway had increased by five classes to six. (Class I ~ Class VI)
Furthermore, as the economical development grows up in Taiwan these years, the cases of tunnels
along the western foothills increase. For example, Lan-Tan Tunnel and Zhong-Liao Tunnel of
Southern Second Freeway, Pakuashan Tunnel of Hanbao-Tsaotuen Expressway, tunnel groups of
High Speed Railway Project, etc. were all constructed along this area. The rock formations of this area
are chiefly composed of gravel layers, sandstone, and mudstone. As a result of uncompleted
lithification and geologic material compositions, there are usually some characteristics in this kind of
formation such as: (a) the ground is approximately intact and has few joints, (b) the strength of this
ground tends to be lower, (c) weaken easily with infiltration by water. Therefore, it is unsuitable to
adopt RMR-system and Q-system, which lay great emphasis on weak planes of rock mass structures,
to classify the above formation. At present in Taiwan, qualitative rock mass classification systems are
often used to classify this formation and the result of execution is quite good in general. However, the
geologic material properties encountered in tunnels differ from case by case and the classification
can’t always be adopted with each other.
3. THE ESTABLISHMENT OF THE ROCK MASS CLASSIFICATION SYSTEM IN TAIWAN
3.1 Considered factors of the skeleton
According to the application of existent rock mass classification systems in Taiwan, the skeleton and
considered reasons of the rock mass classification system in Taiwan are described as follows:
(1) At present in Taiwan, quantitative classifications such as RMR-system and Q-system are generally
used while qualitative methods are adopted in the gravel layers, sandstone and mudstone. The
skeleton of the rock mass classification system in Taiwan is established by following the above
concept. In addition, because the influence of cover differs from case by case, this factor is not
embraced as the evaluation factor and will be properly considered in the tunnel-support suggestion
if it is necessary.
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(2) For quantitative classifications, with comparison between RMR-system and Q-system, it is simpler
to evaluate and calculate by using RMR-system. Moreover, while different people evaluate the
same rock mass, there is less difference by using RMR-system in general. Therefore, the rock mass
classification system in Taiwan is mainly on the basis of RMR-system and takes Q-system as a
complementary approach.
(3) The selection of quantitative or qualitative classifications is based on the geologic material
properties encountered in tunnels. Consequently, basing on the geologic material properties first
and then with reference to geologic age and relevant strength parameters, we classified the
geologic formations in Taiwan into different rock types. The purpose is to distinguish those rock
formations, which are suitable for quantitative classifications or qualitative ones. Rock mass
classes of various rock types can be decided by quantitative or qualitative rock mass rating method.
(4) The above rock mass classification and rating method, based on the consideration of geologic
factors, can be applied in tunnels such as highways, railways, and water resource tunnels in
Taiwan in the future. In addition, according to the rating of rock mass along the tunnel, we can
design tunnel supports with consideration of the span, cover, and other engineering factors
simultaneously in that case.
(5) Due to the special geologic background, tunnel engineering in Taiwan have encountered special
geologic condition several times in past twenty years such as faults, water egression, squeezing,
swelling, high tendency to rock burst, high ground temperature and hazardous gas. The
applicability of existent rock mass classifications under above conditions is frequently doubted. By
evaluating these special geologic conditions encountered in tunnels, we suppose it is impossible to
be solved basically by rock mass classifications. It is necessary to develop special corresponding
excavation technology and tunnel-support systems. Consequently, the rock mass classification
system in Taiwan proposed in this paper is suitable for rock mass in general condition, exclusive of
special geologic conditions. In the case of special geologic conditions, it is necessary to consider
especially about the excavation technology and support design because they differ from case by
case.
3.2 The establishment of the classification system
3.2.1 Principles of the rock mass classification
According to the skeleton of the rock mass classification mentioned in the previous section, first of all
we classify all the geologic formations in Taiwan into different rock types. The purpose is to
distinguish those formations, which are suitable for quantitative or qualitative classifications.
General speaking, without the consideration of faults, fold structures and weathering, it is possible to
estimate the rock properties, strength and other engineering geologic characteristics of a single layer.
Therefore, under the condition for lack of detailed geologic investigation and experimental data in the
plan stage, the strata along the tunnel may be the only geologic information by data collecting in
advance. Consequently, stratum is the basic unit to classify rock types while utilising our classification
system.
Rock mechanics experimental data of important public engineering cases in Taiwan have been
collected. (2230 sets of uniaxial compression test and 250 sets of triaxial compression test are included)
By reviewing the rock mechanics properties of strata in Taiwan and furthermore with reference to
geologic age, geologic material formation, characteristics of weak plane in rock mass, etc., the strata in
Taiwan can be classified into A, B, C, and D four rock types. The distribution of these four rock types
in Taiwan is shown as Fig.3-1. The principles of classification are mentioned as follows:
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Ma-Zu Area
Jin-Men Area
Rock Type A
Rock Type B
Rock Type C
Rock Type D
Fig.3-1 The Distribution of Rock Type A, B, C and D in Taiwan
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(1) Rock Type A: The strength of this type can be approximately corresponded to higher or equal to
“moderate strength” in the geologic material strength rating of ISRM. This rock type is hard and
brittle. Due to tectonic stress, joints are easy to be developed in this type. The failure mechanism
of this rock type is structural failure controlled by weak planes such as joints and cleavage. In
Taiwan, all metamorphic rocks, sub-metamorphic rocks, igneous rocks, exclusive of volcanic
breccia, and sedimentary rock, whose degree of lithification and strength is high, are all included
in this rock type.
(2) Rock Type B: The strength of this type can be approximately corresponded to “low strength” in
the geologic material strength rating of ISRM. This rock type isn’t as hard and brittle as Rock
Type A. Under tectonic stress, joints aren’t easy to be developed in this type. Because of poor
cementation, the strength will decrease significantly as the water content goes up. The failure
mechanism of this rock type includes structural and material failure. In Taiwan, sedimentary rocks,
which are cemented but weaker and often distributed along the western foothills, are included in
this rock type.
(3) Rock Type C: The strength of this type can be approximately corresponded to lower or equal to
“very low strength” in the geologic material strength rating of ISRM. Besides, this rock type also
embraced complex materials, whose mechanics behavior is controlled by fine grains and the
content of coarse grains (grain size greater than sieve #4) is less than 50%. The degree of
cementation is extremely poorer than Rock Type A and B. The phenomenon of softening is quite
obvious with infiltration by water. There are few geologic weak planes in this rock type. The
failure mechanism is chiefly material failure. The determinate factor of rock mass strength is
mainly the properties of compositions, cementation and water content. The strata of late Pliocene
to Pleistocene in the south of Taiwan, and the poor-cemented sedimentary rocks or melanges in the
Eastern Coastal Mountain are included in this rock type.
(4) Rock Type D: This rock type is roughly supposed to be complex materials with fine grains. It is
mainly composed of coarse grains (the content is greater than 50%). Gravel layers, volcanic
breccia, volcanic agglomerate, etc. are included in this rock type. The variation of uniaxial
compression strength is considerable and it results in the amounts of weak planes. Moreover, the
rock mass strength, which is influenced by the amounts of water content, varies from case by case.
The failure mechanism of rock mass is mainly controlled by the cementation of fine grains while
the content of coarse grains is between 50% to 75%; the failure mechanism of rock mass is mainly
controlled by the coarse grains while the content of coarse grains is greater than 75%.
3.2.2 Criteria of rock mass rating
Quantitative rating criteria of RMR-system is proposed to rate the rock mass belongs to Rock Type A
and B. Furthermore, basing on the RMR rating, rock mass can be rated into different rock mass classes.
(Shown as Table 3-1) On the other hand, we propose to adopt qualitative rating criteria composed of
geologic compositions, the ratio of coarse grains, cementation and other characteristics to rate the rock
mass belongs to Rock Type C and D. (Shown as Table 3-2)
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Table 3-1 Criteria for rating Rock Type A and B
Rock mass class of
Rock Type A
RMR range of
Rock Type A
RMR range of
Rock Type B
Rock mass class of
Rock Type B
AⅠ RMR≧81 ---- ----
AⅡ RMR80~61 RMR≧81 BⅡ
AⅢ RMR60~41 RMR80~61 BⅢ
AⅣ RMR40~21 RMR60~41 BⅣ
AⅤ RMR20~11 RMR40~21 BⅤ
AⅥ RMR≦10 RMR≦20 BⅥ
Table 3-2 Criteria for rating Rock Type C and D
Rock mass class
Cementation
Standards of rating
Geologic material composition
Rock
Type
CⅠ(C)
CⅠ(MIX)
CⅠ(S)
Fair or good cementation
(can’t be dented by the thumb)
The content of silt and clay is greater than 50%
The content of sand, silt, clay or gravel
individually isn’t greater than 50%
The content of sand is greater than 50%
C
CⅡ(C)
Poor or loose cementation
CⅡ(MIX)
(can be dented by the thumb)
The content of silt and clay is greater than 50%
The content of sand, silt, clay or gravel
individually isn’t greater than 50%
CⅡ(S)
The content of sand is greater than 50%
The content of boulders and coarse grains (grain
DⅠ(G) Extremely good cementation size greater than sieve #4) is greater than 75 %;
(boulders or gravel need to be contact with each other
knocked off by geologic hammer The content of boulders and coarse grains (grain
DⅠ(M) with great power)
size greater than sieve #4) is between 50% ~
75%; don’t contact with each other
The content of boulders and coarse grains (grain
Rock
Type
D
DⅡ(G)
DⅡ(M)
size greater than sieve #4) is greater than 75 %;
Fair or good cementation
contact with each other
(boulders or gravel need to be
knocked off by geologic hammer)
The content of boulders and coarse grains (grain
size greater than sieve #4) is between 50% ~
75%; don’t contact with each other
The content of boulders and coarse grains (grain
DⅢ(G)
DⅢ(M)
Poor or loose cementation
(boulders or gravel need to be
knocked off by hand)
size greater than sieve #4) is greater than 75 %;
contact with each other
The content of boulders and coarse grains (grain
size greater than sieve #4) is between 50% ~
75%; don’t contact with each other
Notes: 1.Because the amount of water content affects the tunnel construction of Rock Type C and D
considerably, this table must be adopted based on drainage in advance.
2.Sand layers and gravel layers possibly appear simultaneously on the excavation face. The
location of sand layers on the excavation face has a determinate influence on the stability of
tunnels, and it should be considered carefully while designing tunnel supports.
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4. CONCLUSION
The establishment of the rock mass classification system in Taiwan is based on the design and
construction experience accumulated in past twenty years in Taiwan and moreover with consideration
of local geologic age, geologic structures, rock mass strength, the influence of groundwater in rock
mass, compositions of rock layers, etc. In the future, this system can be adopted in tunnel engineering
at the plan and design stage. According to the strata along the tunnel, rock mass can rapidly be
classified into Rock Type A, B, C or D. Furthermore, the corresponding rock mass rating criteria to
execute the rating task can be chosen. Basing on the above results, we can design tunnel supports. It is
equal to say that this rock mass classification system can be regarded as the bases of rock mass
characteristic evaluation and tunnel-support design.
ACKNOWLEDGEMENT
We would like to express our thanks to Public Construction Commission, Executive Yuan, which
supports the expenditure of this project. On-site verification was assisted by Directorate General of
Highways, MOTC, Water Resources Agency, Ministry of Economic Affairs, Taiwan Power Company,
Engineering Department of High Speed Rail System of Transportation Bureau, Taiwan Area National
Expressway Engineering Bureau, MOTC, Eastern Engineering Department of Railway Reconstruction
Bureau, etc. Furthermore, this project is also in co-operation with United Geotech, Inc., China
Engineering Consultants, Inc., Moh and Associates, Inc., Sinotech Engineering Consultants, Inc.,
National Taiwan University, National Central University, National Taiwan University of Science &
Technology, National Taipei University of Technology, etc. In addition, this project has been
examined several times by consultants invited by Public Construction Commission, Executive Yuan,
for example, J. J. Hung, C. H. Huang, J. Z. Lee, Z. X. Ye, Y. S. Xie, N. H. Huang et al. They also
provided many treasured suggestions.
REFERENCE
1.C. T. Chang, W. T. Wang, L. Z. Sun, N. H. Huang et al., 2000. The establishment of rock mass
classification system and tunnel engineering databases in Taiwan (Phase 1) – Work Item D: The
establishment of rock mass classification and tunnel-support system in Taiwan, Public Construction
Commission, Executive Yuan.
2.C. T. Chang, M. L. Lin, L. Z. Sun et al., 2001. The establishment of rock mass classification system
and tunnel engineering databases in Taiwan (Phase 2) – Work Item D: The establishment of rock mass
classification and tunnel-support system in Taiwan, Public Construction Commission, Executive Yuan.
3.C. T. Chang, P. C. Hou, M. C. Lee et al., 2002. The establishment of rock mass classification system
and tunnel engineering databases in Taiwan (Phase 3) – Work Item D: The establishment of rock mass
classification and tunnel-support system in Taiwan, Public Construction Commission, Executive Yuan.
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