Comparison among different criteria of RMR and Q-system for rock mass classification for tunnelling in Korea

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1 Tunnelling and Underground Space Technology 17 (2002) Comparison among different criteria of RMR and Q-system for rock mass classification for tunnelling in Korea S.Y. Choi, H.D. Park* School of Civil, Urban and Geosystem Engineering, Seoul National University, Shinlim-dong, Gwanak-gu, Seoul, , South Korea Received 4 March 2002; received in revised form 26 June 2002; accepted 8 July 2002 Abstract Recent increase in the number oftunneling projects in Korea resulted in a large amount ofgood quality data such as RMR and Q-value for the assessment of rock mass class. In addition, a new bidding system, so-called Turn-Key system, has also made the data quality better than ever before, due to the increase of the budget for site investigation. A conventional guideline for rock mass classification by KHC (Korea Highway Corporation) has been widely used in Korea but other forms of classification using different criteria of RMR or Q-value have been recently used. Since there have been few studies on the relationship among such different criteria on RMR or Q-value, this study mainly focuses on the comparison of the conventional guideline for rock mass classification with several individual classification schemes in Korea. Analysis of the coincidence among the different criteria using both RMR and Q-value showed that there is higher coincidence ifrock mass is in relatively good condition. It was also found that there is less consistency between RMR criteria and Q-value criteria in conventional KHC Guideline for rock mass classification than the recently adopted individual criteria Elsevier Science Ltd. All rights reserved. Keywords: RMR; Q-system; Tunnel design 1. Introduction In Korea, a new stage ofconstruction ofthe highway network has been planned to provide a good transportation system which is required by the increase of domestic consumer as well as the export industry. A total 2294 km ofhighway on 21 lines are in operation in November 2001 and the total length ofhighway is planned to be 3400 km up to 2004 (Fig. 1). Due to the high percentage ofmountainous area in Korea, up to 70%, tunneling work has been very frequently included in the construction of many roads and railways. In addition, such a big demand on the high speed railways and highways leads to more tunneling works recently because of the effort to keep the line as straight as possible. Total length ofhigh-speed railways is up to 412 km from Seoul to Busan and the first stage of the construction project for Seoul Daegu *Corresponding author. Tel.: q ; fax: q address: hpark@gong.snu.ac.kr (H.D. Park). section is in progress. The second stage ofthe construction project for Daegu Busan section is scheduled to start in All 46 tunnels (67 km long in total) in Seoul Daegu section have been completely excavated. There is also a tendency to construct long tunnels up to a few kilometers more and more (Table 1). In addition, a change ofbidding system for construction, i.e. a new system, so-called Turn-Key bidding system, which is based on the total quality ofthe construction plan, not merely on the minimum cost for construction, resulted in a significant change in site investigation process for the tunnel, which had to be conducted within a very restricted budget previously. It is not unusual to spend much more money than before for the site investigation of the ground condition. As a result, an enormous amount ofrelatively better quality data, when compared with the previous tunneling works in Korea, have been recently available to tunneling engineers. Better interpretation could be possible with the aid of many different techniques available, such as analysis ofremotely sensed imaging and a variety of geophysical survey methods. One ofthe most important /02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S Ž

2 392 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) Table 2 Descriptive terms ofrock mass classes in Korea Rock mass class Class-I Glass-II Class-III Class-IV Class-V Descriptive terms Very good Good Fair Poor Very poor Fig. 1. Plan ofhighway network system (KHC, 2002). changes is that better assessment ofrock mass in terms ofrmr (Bieniawski, 1989) or Q-system (Barton et al., 1974), has been made possible by the extended coverage ofconventional data, e.g. enormous increases in the number ofdrillings, total drilling length, and the number oflaboratory tests ofrock specimens. Such an increasing demand for tunnel construction and change of bidding system provide a very good chance for the Korean tunneling industry to develop a higher level of technology. Recently, rock mass classification using both RMR and Q-system has been frequently used for tunnel design together with numerical analysis, in Korea. According to the most widely adopted procedure in Korea, rock mass is allocated into any of5 classes from Class-I (Very Good) to Class-V (Very Poor), based on the results either from one of the two rock classification systems or from both methods (Table 2). Each class is thus exclusively linked to each standard support pattern. The final suitability of each support pattern is examined through numerical analysis. Interpretation by geophysical technique is also used to confirm the result. KTA recommended that the rock mass would be divided into 5 classes using RMR, or into more detailed classes using Q-system (KTA, 1999). However, many other organizations have suggested different guidelines for rock mass classification and there was little consistency among these guidelines regarding the parameters used. Although a variety ofdata with relatively better quality have been produced in greater amounts than ever before, there have been few studies with regard to the relationship between RMR and Q-system, and the suitability ofthe judgement ofrock mass classes using RMR and Q in tunneling projects in Korea. Thus, this study focuses on the investigation of the relationship between RMR and Q-values obtained from three recent tunneling sites in Korea, which were designed according to the Turn-Key bidding system. 2. Preferential use of RMR and Q-system in Korea Although the rating methods ofrmr and Q-system are additive and multiplicative, respectively, the basic concepts ofboth schemes are similar. Both schemes allocate the ratings to the properties that influence the rock mass behavior and then quantitative figures such as total-rmr and Q-value are produced. These values would be used to judge the goodness ofrock mass for construction. Table 1 Highway tunnel length in Korea (KTA, 2002) Tunnel length In use Under construction Design completed (km) Number Total length Number Total length Number Total length (km) (km) (km) ) Sum

3 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) Table 3 General information on three tunnel sites Geology Tunnel features Length (km) Width (m) Usage Site A Precambrian biotite gneissy Road Precambrian banded gneiss Site B Cretaceous granite Road Site C Precambrian biotite gneissy Road Precambrian leucocratic gneiss Despite some differences between them, three important properties influencing the rock mass behavior are integrated in both RMR and Q-system, i.e. degree of fracturing, discontinuities conditions and groundwater. Milne (1988) pointed out the similarity ofeach ratio (RMR:Q-system) ofthe percentages ofthe rating regarding block size, discontinuity friction and strength are 32%: 44%, 30%: 39%, 15%: 0%, respectively. Later suggestions (Milne et al., 1998) show slightly different ratios, i.e. 54%: 44%, 27%: 39%, 16%: 19%. Other studies showed positive correlation between RMR and Q-system (Bieniawski, 1989; Rutledge and Preston, 1978; Moreno, 1982; Carmeron-Clarke and Budavari, 1981; Abad et al., 1984). Goel et al. (1996) suggested the correlation between the modifications of RMR and Q-system, i.e. RCR (Rock Condition Rating) and N (Rock Mass Number). Sometimes, these correlation approaches have been used on tunneling works in Korea. However, both schemes should be applied independently and a value ofone scheme should not be converted to the value ofthe other scheme (Palmstrom et al., 2001), and the correlation approach is not a purpose ofthis study. In Korea, it has been widely accepted that RMR is simpler than the Q-system and that variation ofrmr from subjectivity among different investigators could be smaller than that ofq-system. Because Q-system has been also widely used in Korea, it is necessary to follow a guideline for matching each class from RMR or Q- system into 5 classes ofstandard support pattern which is used as a kind ofuniversal system for describing the same engineering behavior ofrock mass, i.e. rating a rock mass as Class-I by Company A is equivalent to another Class-I rated by Company B. As pointed out in the above, each organization has its own guideline for matching such ratings to 5 classes ofstandard support pattern. Thus, it is necessary to compare such guidelines and to show how closely each guideline matches. 3. Comparison of RMR and Q-values based on 5 classes of standard support pattern 3.1. Data acquisition RMR and Q-data including ratings for each parameter were carefully selected from the site investigation reports for three different tunnel projects recently conducted in Korea. Geological information and tunnel features are summarized in Table 3. In this study, the comparisons ofrmr and Q-system were conducted according to three approaches. Approach ofso-called Total Judgement is not to observe that each data point would be classified into the same rock mass class by both RMR and Q-system ofeach criteria, i.e. approach ofso-called Coincidence Judgement, but to compare the results ofclassification regardless of coincidence. The relationship between the parameters included in RMR and Q-system was also investigated Comparison of several guidelines for rock mass classification Approach of total judgement From the guidelines of three different tunneling projects, so-called Individual Criteria, it can be easily noticed that different values have been used as criteria to be matched into 5 classes ofstandard support pattern (Table 4). However, KHC, which is responsible for Table 4 Individual criteria used for rock mass classification in three tunneling projects Rock mass class Site A Site B Site C RMR Q RMR Q RMR Q Class-I ) ) )150 Class-II Class-III Class-IV Class-V

4 394 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) Table 5 Guidelines for rock mass classification for the selection of standard support pattern by KHC (KHC, 1996; Kim and Kim, 2000) Rock Rock RMR Q RQD P wave velocity UCS TCR b mass condition (%) (kmys) (MPa) a (%) Class-I Hard )40 )70 )4.5 )122 )90 rock Class-II Medium rock Class-III Soft rock Class-IV Weathered rock Class-V Weathered -20 rock or c N )100: IV earth-like N-100: V a 2 b c Remarks: Original unit (kgfycm ) has been converted; TCR: Total Core Recovery; N: SPT (Standard Penetration Test) value. highway construction and maintenance, has its own criteria as a form of guideline (Table 5), which does not coincide with the recent tendency on the tunneling in Korea. Recently in Korea, while RMR and Q-system are major rock mass classification schemes, RQD, UCS (Uniaxial Compressive Strength) and P-wave velocity, etc., have been used as just additional reference for classification. For final rock mass classification, working cycle and efficiency during construction are also considered. Class-I judged by Q-system with KHC Criteria exactly matches with the range from Exceptionally Good to Very Good for Q-system. Class-II matches with Good, Class-III with Fair, Class-IV with Poor and Class-V with the range from Very Poor to Exceptionally Poor in Q-system, respectively. The RMR criteria ofkhc and Sites B and C are exactly the same as those ofbieniawski (1989), on the other hand, the RMR criteria ofsite A is slightly different, especially for Class-I. However, KHC Criteria and Individual Criteria using RMR are generally similar. In general, Individual Criteria are less conservative than KHC Criteria, for the classification of rock mass in poor condition using Q-system, i.e. Class-IV or V (see Table 4 and Table 5). To compare the distribution ofrock mass class, each raw data has been re-classified according to the criteria suggested by KHC. The proportion ofdata at each class is shown as KHC Criteria, and the original criteria for each site is shown as Individual Criteria in Table 6. Frequencies ofrock mass classes determined by KHC and Individual Criteria are plotted (Fig. 2). Although general trend shows that Class-I and Class-II dominate in all three sites, there are significant differences in both results from RMR and Q-system. According to the KHC Criteria (Fig. 2 a,b,c), the proportion ofclass-v by Q- system is larger than RMR in all three sites. On the other hand, the smaller proportions ofclass-v from Q- system by Individual Criteria (Fig. 2e,f, Table 6) are similar to those ofclass-v from RMR by KHC Criteria (Fig. 2b,c, Table 6), except for Site A where the number ofclass-v judged by RMR is zero in KHC and Individual Criteria (Fig. 2a,d). From the comparison between proportions ofclass-v from RMR by KHC Criteria and those ofclass-v from Q-system by Individual Criteria, it can be observed that both values are Table 6 Proportion ofeach rock mass class for three tunnel sites (unit:%) Rock Site A Site B Site C mass class KHC Individual KHC Individual KHC Individual Q Q RMR Q RMR Q RMR Q RMR Q Class-I Class-II Class-III Class-IV Class-V Sum ofproportion Total number ofdata

5 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) Fig. 2. Frequencies of each rock mass class determined by different criteria from three tunneling projects.

6 396 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) Fig. 3. Distributions of RMR and Q-values with different criteria for 5 classes standard rock mass classification (bold line represents each rock mass class zone and regression line is also plotted). more similar than proportions ofclass-v determined by the same criteria. Such a similar tendency could be observed for Class-IV. As seen in Table 4 and Table 5, the ranges ofclass-v and Class-IV from RMR in the KHC and Individual Criteria are almost similar. The ranges ofclass-v and Class-IV from Q-system in the KHC and Individual Criteria are different. However, the ranges ofclass-v and Class-IV from Q-system in Individual Criteria are exactly the same. Thus, it could be said that this tendency might be caused by the change ofranges for Class-V and Class-IV in Individual Criteria and that there might be consensus for rock mass grades belonging to Class-V and Class-IV at least in Korea. Apparent feature was not observed for Class-III, Class- II and Class-I. However, it does not mean that poor rock mass can be classified into same rock grade by Individual Criteria. The degree ofcoincidence will be discussed in the next section. The number ofeach rock mass class judged by RMR and Q-system in Individual Criteria shows similar ten-

7 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) Fig. 4. Procedure ofcalculation ofcoincidence percentage. dency and frequency (see Fig. 2). Therefore, it may be necessary to modify the KHC Criteria for Q-system, at least for Class-V and Class-IV Approach of coincidence judgement Distributions ofrmr and Q-values from three sites are plotted with KHC Criteria and Individual Criteria used in rock mass classification for 5 classes of standard support pattern (Fig. 3). Boxes with bold line represent the zones where the rock mass classes judged by RMR and Q-system are the same. The location above the boxes means that RMR represents the rock mass higher grade than Q-system does and the location under the boxes means the opposite. It is shown that rock mass from RMR has been classified into better grade than Q in Site A and B for both KHC Criteria and Individual Criteria. In Site C, opposite tendency is generally observed. Because the number ofpoints within the boxes is increasing as RMR and Q-values increase, the degree ofconsistency of judgement between RMR and Q-system can be said to be higher in the case ofgood rock mass. For the case ofindividual Criteria, it can be observed that more points fall within the boxes than for the case of KHC Criteria. This is caused by the difference between ranges ofclass-v, Class-IV, Class-III and Class-II ofq-system in Individual Criteria and those in KHC Criteria (see Fig. 3). From Table 4 and Table 5, it is found that the lower boundaries ofrmr and Q-system for Class-II used in Site B and C are exactly the same as those for Good grade in normal RMR and Q-system. But such tendency is not observed in Site A. This means that there is a higher coincidence in relatively good rock mass than in poor rock mass (see Fig. 3). As Fig. 3 shows, the junctions between boxes representing rock mass class zone from Individual Criteria lie more closely to the regression lines, plotted in the data points, than those ofkhc Criteria do. This observation could be an explanation for the preference of Korean geological engineers who tend to set the criteria for rock mass classes by taking account of results of regression analysis. In order to determine such a degree ofcoincidence quantitatively, Coincidence Percentage and Cumulative Coincidence Percentage, which are calculated in the procedure shown in Fig. 4, are introduced in this study. These calculation methods are suggested because a number ofdata for poor rock condition are relatively less than that for good rock condition. Example ofcalculation: For Site A, Coincidence percentage ofclass-i for RMRs20y (0q0q3q7q20) Cumulative coincidence percentage ofclass-iii for RMRs(2q0q11)y(2q0q0q12q0q0q0q17q 11) Table 7 Coincidence Percentage from RMR and Q-system (unit:%) Rock Site A Site B Site C mass class KHC Individual KHC Individual KHC Individual RMR Q RMR Q RMR Q RMR Q RMR Q RMR Q Class-I Class-II Class-III Class-IV Class-V Total Coincidence a a These are the ratio oftotal number ofdata judged as same rock class by RMR and Q-system to total number ofdata. Plots ofthese data are found as the points of Class-I in Fig. 5.

8 398 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) The results are shown in Table 7 and Fig. 5. Although the coincidence percentages do not show the uniform tendency regarding the degree ofcoincidence, the coincidence percentages ofclass-i and Class-II are higher than those ofclass-iii, Class-IV and Class-V, in general. It is also observed that the coincidence percentages of Individual Criteria are higher than those ofkhc Criteria. It was also observed that cumulative percentages of Individual Criteria are higher than those ofkhc Criteria. Because RMR and Q-system are applied independently, rock mass classes judged by both schemes need not coincide. However, through observed tendency regarding coincidence, it is deduced that there is less confusion between judgements by RMR and Q-system in good rock condition and therefore applicability and characterization ofboth schemes are better in good rock condition in Korea. Barton (1995) indicated that Q- system has higher applicability in softer rocks and RMR is relatively unreliable in very poor rock masses (Singh and Goel, 1999). However, according to the current result, poor rock mass has much more uncertainties, i.e. there may be much larger differences between the characterizations by RMR and Q-system. Thus, merely based on this study, it cannot be concluded which scheme is more suitable for poor rock mass in Korea, although both RMR and Q-system have good applicability for good rock mass in Korea. In practice, if the type and size of tunnels are different, tunnel support patterns should not be the same although the tunneling works are conducted in same rock condition or rock mass class. This is the reason why a slight difference is found between standard support patterns from KHC Criteria and Individual Criteria at Site C. More conservative design has been adopted in the support patterns ofsite C (Table 8). This could be attributed from the difference in both the KHC criteria and the Individual Criteria in Site C, e.g. rock masses with different Q-values are classified in the same class in certain range. However, both criteria using RMR are the same in this case. Thus, there could be some confusion for practical use of rock mass classification system in Korea, due to a variety ofindividual criteria modified by each company s experience Relationship between block size and joint shear strength Important properties influencing rock mass behavior are commonly integrated in both RMR and Q-system as Milne (1988), Milne et al. (1998) pointed out. Thus, several common parameters ofrmr and Q-system were considered together in this study. Among the parameters in Q-system, RQDyJn can be used as an indicator for block size and JryJ a, as an indicator for joint shear strength (Barton et al., 1974). J n, Jr and Ja are the Fig. 5. Comparison ofeach cumulative coincidence percentage.

9 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) Table 8 Comparison ofstandard support patterns for each rock mass class Rock Advance RyB length SyC thickness Steel Rib e Concrete lining mass (m) (m) (cm) (m) (cm) class KHC Site C KHC Site C KHC Site C KHC Site C KHC Site C Class-I a 4 a 5 c 5 c Class-II b 4 b 5 d 8 d Class-III b 4 b 8 d 12 d f 40 Class-IV b 5 b 12 d 16 d f 40 f Class-V y1.0 4 b 5 b 16 d 16y20 d y f 40 f Remarks: a: random rock bolt, b: systematic rock bol; c: wire-mesh reinforced shotcrete, d: steel-fiber reinforced shotcrete; e: C.T.C (Center To Center); f: reinforced. KHC support patterns relate with approximately 10 m width tunnel. Fig. 6. Scatter diagrams between block size* and joint shear strength* ofeach rock mass class** (based on RMR*, and grouped by KHC Criteria**). Fig. 7. Scatter diagrams between block size* and joint shear strength* ofeach rock mass class** (based on Q-system*, and grouped by KHC Criteria**).

10 400 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) Fig. 8. Scatter diagrams between block size* and joint shear strength* ofeach rock mass class** (based on Q-system*, grouped by Individual Criteria**). ratings allocated to joint set number, joint roughness and joint alteration, respectively. Similar parameters can also be considered in RMR. The sum ofratings allocated to RQD and joint spacing might be considered as an indicator for block size. The ratings allocated to joint condition in which persistency, roughness, filling material, aperture, weathering are included, might be regarded as an indirect indicator for joint shear strength. Grounwater is the property closely related with stress. Thus, it could be regarded as non-intrinsic property ofrock mass (Milne, 1988). This is the reason why the JwySRF is an indicator for effective stress in Q-system (Barton et al., 1974) and why groundwater is not directly included in RMi (Palmstrom, 1996). Thus, the ratings for groundwater were excluded for further analysis. Compressive strength in RMR is not included either because it is not directly estimated in the Q-system. Figs. 6 8 show the relationships between block size and joint shear strength for three tunnel sites. Although there might be some variations between the different investigators and errors caused by the same investigator s misjudged, a certain tendency ofpositive relationship between the two factors, e.g. the relationship in Fig. 6 could be found. Each rock mass is clearly grouped considering both the block size and the joint shear strength, together comparing that grouping with Table 9 Correlation coefficients between block size and joint shear strength Site A Site B Site C RMR Q RMR Q RMR Q Correlation coefficient y either the block size or the joint shear strength only. The relationships between the block size and the joint shear strength ofthe RMR for all three tunnel sites show a higher apparent positive correlation than those ofq-system (Table 9). This shows that the grouping using RMR is more obvious than using Q-system, however, this does not necessarily mean that RMR is more suitable than Q-system in Korea. It could be also inferred from this observation that Q-system is much more sensitive to variations ofrock mass properties than RMR, possibly due to the different rating system. Especially it is found that the scatter of Class-V differ between KHC Criteria and Individual Criteria from Fig. 7 and Fig. 8. This is caused by different boundary setting for Class-V between two criteria (see Table 4 and Table 5) and the cases ofindividual Criteria seems to be more reasonable. Thus, it could be another reason why KHC Criteria for Class-V in Q-system need to be modified. 4. Conclusion It should be noted that there is a limitation in the current research. Due to the field monitoring data after installation ofthe support pattern which have not been retrieved yet, it is impossible to compare the current results with the real behavior ofthe rock mass in practice. However, the following conclusions could be drawn from the current study. 1. For poor rock condition Very Poor grade in RMR has been considered as the rock grade ranging from Extremely Poor to Exceptionally Poor in Q-system in tunneling practice in Korea. Poor grade in RMR

11 S.Y. Choi, H.D. Park / Tunnelling and Underground Space Technology 17 (2002) has been used as the same grade as the Very Poor grade in Q-system. By judging the terminology only, it can be said that RMR has been used more conservatively than Q-system in Korea. 2. By comparing the judgement ofrock mass classes according to KHC Criteria and Individual Criteria, the determination through Individual Criteria shows higher degree ofcoincidence ofrock mass classes between RMR and Q-system. This results from more conservative boundary settings ofkhc Criteria for Class-III, Class-IV and Class-V in Q-system. In addition, the Individual Criteria for three tunnel sites seems to be set, based on regression analysis, between RMR and Q-value estimated in each site. Thus, such criteria for classification should be reviewed using more field data. 3. The degree ofcoincidence ofrock mass classes between RMR and Q-system in good rock quality is higher than in poor rock mass, which means that the applicability ofrmr and Q-system is higher in better rock quality. 4. It was observed that rock mass classes could be more clearly grouped when both block size and joint shear strength were used together as criteria. 5. The result ofcurrent study confirms that it is necessary to revise the current KHC Criteria and it is also necessary to conduct further research on the relationship between RMR and Q-value and its links to the behavior of rock mass before and after excavation. Acknowledgments This study was supported by the Brain Korea 21 project in 2002 and was also supported by the Research Institute ofengineering Science (RIES), Seoul National University, Seoul, Korea. References Abad, J., Caleda, B., Chacon, E., Gutierrez, V. and Hidlgo, E., 1984, Application ofgeomechanical classification to predict the convergence ofcoal mine galleries and to design their supports, 5th Int. Congr. Rock Mech., Melbourne, pp Barton, N., Lien, R., Lunde, J., Engineering classification of rock masses for the design of tunnel support. Rock Mech. 6, Barton, N., 1995, Permanent support for tunnels using NMT, Special Lecture, Proc. Symp. ofkrms (Korea Rock Mechanics Society) and KSEG (Korea Society ofengineering Geolgoy), pp Bieniawski, Z.T., Engineering rock mass classifications. John Wiley and Sons, New York, pp Carmeron-Clarke, I.S., Budavari, S., Correlation ofrock mass classification parameters obtained from borecore and in situ observations. Eng. Geol. 17, Goel, R.K., Jethwa, J.L., Paithankar, A.G., Correlation between Barton s Q and Bieniawski s RMR-A new approach. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. 33, KHC (Korean Highway Corporation), 1996, Handbook for design of highway tunnel, p. 514 (in Korean). KHC (Korea Highway Corporation), 2002, Accessed 2002 March 15. Kim, S.H, Kim, N.Y., Present situation ofhighway in Korea. Tunnel. Technol. 2, (in Korean). KTA (Korean Tunneling Association), 1999, Standard for tunnel design, Goomi Press, p.133 (in Korean). KTA (Korean Tunneling Association), 2002, Accessed 2002 March 15. Milne, D., 1988, Suggestions for standardization of rock mass classification, MSc. Thesis, Imperial College of Science and Technology, University oflondon, p Milne, D., Hadjigeorgiou, J., Pakalnis, R., Rock mass characterization for underground hard rock mines. Tunnel. Underground Space Technol. 13, Moreno Tallon, E., 1982, Comparison and application ofthe geomechanics classification schemes in tunnel construction, Proc. Tunneling 1982, Institution ofmining and Metallurgy, London, pp Palmstrom, A., Charaterizing rock masses by the RMi for use in practical rock engineering: Part 1: The development ofthe rock mass index (RMi). Tunnel. Underground Space Technol. 11, Palmstrom, A., Milne, D., Peck, W., The Reliability ofrock mass classification used in underground excavation and support design. ISRM News J. 6, Rutledge, J.C. and Preston, R.L., 1978, Experience with engineering classifications of rock, Proc. Int. Tunnel. Symp., Tokyo, A3.1 A3.7 Singh, B, Goel, R.K., Rock mass classification: A practical approach in civil engineering. Elsevier, Amsterdam, pp. 267.