Extension of RMR and Q-system in Taiwan

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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