58 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSESfor every site and will be organized into an overall database. The data will provide the basis for a detailed quantitative assessment of current design criteria of emergency spillways and will assist in the development of any needed revisions. I believe that Dr. Kirsten's idea of applying his erodibility index (expressed as N) to a rock mass that forms an excavated spillway channel should be explored in our (SCS) assessment. Once the data base is established from the spillway performance reports it would be productive to determine an empirical relationship between J, and the relative dip angle and block shape for hydraulic erosion of spillway channel beds. The analysis should be useful in our assessment of design criteria for excavated rock emergency spillways. Nick Barton' Rock Mass Classification and Tunnel Reinforcement Selection Using the Q-System REFERENCE: Barton, N., "Rock Mass Classification and Tunnel Reinforcement Selection Using the Q-System," Rock Classification Systems for Engineering Purposes, ASTM STP 984, Louis Kirkaldie, Ed., American Society for Testing and Materials, Philadelphia, 1988, pp. 59-88. ABSTRACT: This paper provides an overview of the Q-system and documents the scope of case records used in its development. A description of the rock mass classification method is given using the following six parameters: core recovery (RQD), number of joint sets, roughness and alteration of the least favorable discontinuities, water inflow, and stress-strength relationships. Examples of field mapping are given as an illustration of the practical application of the method in the tunneling environment, where the rock may already be partly covered by a temporary layer of shotcrete. The method is briefly compared with other classification methods, and the advantages of the method are emphasized. KEY WORDS: rock mass, classification, tunnels, rock support, shotcrete, rock bolts jointing This paper provides an analysis of the Q-system of rockmass characterization and tunnel support selection. The 212 case records utilized in developing the Q-system (Barton et al, 1974) are reviewed in detail, so that application to new projects can be related to the extensive range of rock mass qualities, tunnel sizes, and tunnel depths that constitute the Q-system data base. Ultimately, a potential user of a classification method will be persuaded of the value of a particular system by the degree to which he can identify his site in the case records used to develop the given method. The most comprehensive data base of the seven or eight classification systems reviewed is utilized in the Q-system. This body of engineering experience ensures that support designs will be realistic rather than theoretical, and more objective than can be the case when few previous experiences are utilized to develop a support recommendation. Classification Systems Currently in Use Table I is an abbreviated listing of most of the rock mass classification systems currently in use internationally in the field of tunneling. These are: Terzhagi (1946) Rock Load Classification — This has been used extensively in the United States for some 40 years. It is used primarily to select steel supports for rock tunnels. However, it is unsuitable for modem tunnelling methods in which rock bolts and shotcrete are used. Lauffer (1958) Stand - Up Time Classification — This introduced the concept of an unsupported span and its equivalent stand-up time, which was a function of rock mass quality. It appears excessively conservative when compared with present-day tunneling methods. ' Norwegian Geotechnical Institute, Oslo 8, Norway. 59 Bieniawski (1976) rates the following six parameters in his RMR system: I. and may be overly sensitive to orientation effects. which has extended the data base considerably. 1975. tunnelling RSR Concept Wickham et al (1972) USA tunnels with steel supports Geomechanics (RMR System) Q-System Bieniawski (1973) S. and Lunde (1974) Q-System—This classification system was developed independently of the Wickham et al (1972) and Bieniawski (1973) methods. but highly ductile. which could present technical and economic problems for any tunneling method. 6. so use by others on other projects may be difficult.60 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES BARTON ON Q-SYSTEM 61 TABLE 1—Major rock mass classification systems. the amount of water. which was developed by Rabcewicz. though details of these cases with their relation to support recommendations have not been published. Updating Case Records Some of the support methods recommended by the above classification methods are quite labor intensive and will need updating as new support methods become more generally available. excavation dimensions. and swelling. Orientation of joints. but pointed out that the details of jointing. In contrast. NATM One further tunnel support concept which should be mentioned here is the New Austrian Tunneling Method (NATM). Wickham. The NATM relies on performance monitoring for prediction and classification of ground conditions. by utilizing light temporary support. For example. Stress factor. These two systems are therefore compared in some detail here. The NATM is essentially a design method in which the rock mass is allowed to yield only enough to mobilize its optimum strength. Bieniawski (1973) RMR Geomechanics Classification—This evolved from several earlier systems and has undergone several changes (1974. Joint alteration. it must be understood that the method is principally utilized in squeezing ground conditions. Comparison of RMR and Q Systems The two classification systems that appear to be in widest use in tunneling that do not rely on performance monitoring (though they can be used in conjunction with monitoring) are the RMR and Q systems. On occasion. the joint roughness and alteration (filling). and Skinner (1972) Rock Structure Rating (RSR)—This concept introduced numerical ratings and weightings to relate rock mass quality. and numerous economic and technical failures in past years demonstrate the amount of confusion that prevails in this field. Full details of these cases are given later in this paper. Bieniawski (1975) appears to have favored the mean rating for spacing and orientation of the . introducing five additional parameters to modify the RQD value to account for the number of joint sets. has resulted in loss of ground control and severe damage to final concrete linings and bolt arrays (Barton. RQD. The extra strength of this product removes the need for mesh in shotcrete. it fails to account for the condition of joint surfaces and filling materials. The method was an immediate forerunner to the two methods now used most frequently on an international basis (the RMR and Q systems). and steel support requirements. almost everyone using this method has a different conception of it. the development of high strength. this initial yielding is arrested in time to prevent loss of strength. Barton et al (1974) Norway tunnels. and groundwater should also be taken into account when selecting support. squeezing. The method was eventually based on 49 case records. Packer. Recent applications of the RMR system have been made in mining. Spacing of joints. Lien. Uniaxial compressive strength of rock material. large chambers tunnels with steel supports " Sec Bibliography for details. It can be applied by one robot operator and one back-up person right at the tunnel face. and the various adverse features associated with loosening. 1974) rates the following six parameters: I. Africa tunnels. Number of joint sets. It has been successfully adopted as part of subsequent classification systems. A particular classification is therefore only applicable to the one case for which it was developed and modified. Condition of joints. while the Q-system considers the number of joint sets. 1982). The common parameter used in both systems is Deere's RQD. As acknowledged by Milner (Salzburg). Fourteen case records were utilized in developing these recommendations. mines. With correct timing of final support. In NATM's defense. and steel ribs with sliding joints. 1963 and Rabcewicz and Packer. and Muller (Rabcewicz. weathering. Orientation is included implicitly in the Q-system by classifying the joint roughness and alteration of only the most unfavorably oriented joint sets or discontinuities. steel fiber reinforced microsilica shotcrete is a revolutionary advance in tunnel support. 1975). Joint water. Drill core quality RQD. high stress. On its own. the desire to allow deformation to occur by installing canals of deformable material within the shotcrete. Deere et al (1970) utilized RQD to develop support recommendations for 6 to 12 m span tunnels. 1976. 6. Tiedemann. but it builds extensively on the RQD method of Deere et al (1967). Deere et al (1967) Rock Quality Designation (RQD)—This is a simple description of the condition of recovered drill core. and 1979) since its first introduction in 1973. Groundwater conditions. The classification method and the associated support recommendations were based on an analysis of 212 case records. It is adapted to each new project based on previous experience. Bieniawski also includes joint spacing and orientation. and it has sufficient early strength to replace steel arches and cast concrete under a large range of tunnelling conditions. Name of Classification Originator and Date° Country of Origin Applications Rock Loads Terzhagi (1946) USA Stand-Up-Time Lauffer (1958) Austria tunneling RQD Deere et al (1967) and Deere et al (1970) USA core logging. the Q-system (Barton et al. Barton. Joint roughness. The classification is also adapted during a single project based on performance monitoring. etc. design engineers will come back to the basic question: "Is this bolt spacing. Bieniawski also includes joint roughness in his fourth parameter "condition of joints. The Einstein et al (1979) comparison of each method with Cecil's supported cases indicated that the Q-system support recommendations also agree well with the actual support./SRF) (1) where RQD = rock quality designation (Deere et al. Bieniawski's chart of stand-up time versus unsupported span is still seen to be very conservative compared with the Q-system. and . Such discrepancies reflect the important differences in support philosophies between Scandinavia. and relative orientation. and squeezing and swelling ground. J.. and rock burst problems can be quite accurately predicted in hard rocks. so support recommendations are tentative. consisting of systematic bolts at I m centers. The Bieniawski (1976) and Deere et al (1969) RQD method were more conservative. The very detailed treatment of joint roughness and alteration. The case records examined included 13 igneous rock types. It is important to observe that the values of J. in the RMR it is impossible to separately vary the degree of joint roughness and the degree of infilling. continuous gouge >5 mm. However. the ratio (o. where the design is based on precedent. or unsupported span width reasonable in the given rock mass?" At present we have to rely on engineering judgment. J. perhaps the strongest feature of the Q-system. J„ = joint set number. although data for all joint set and discontinuities are collected. minimum inter-block shear strength. since the rating is usually based on the presence of three sets of joints. not continuous up to continuous with gouge). The Q-system is more detailed than any of the other methods as regards the factors joint roughness (or degree of planarity). up to open >5 mm. Massachusetts. since Cecil's cases formed the backbone of the method. Five of the classification methods listed in Table I were compared in detail during several stages of the project and by several observers. and when the rock was exposed in the final excavation. shotcrete thickness.) (unconfined compression strength/major principal stress) is evaluated when treating rock stress problems. the Deere et al (1969) method even larger amounts of support. in Bieniawski's RMR method. Einstein et al (1979) compared each method's support estimates with Cecil's (1970) unsupported cases. most commonly the joints were unfilled and the joint walls were unaltered or only slightly altered. and 11 sedimentary rock types. stable conditions were established. Furthermore.. from very tight./SRF) represent block size. . For example. in other words. 1967). only the average data are incorporated in the numerical ratings. respectively. mapping an inspection shaft and a pilot tunnel. In his 1974 publication Bieniawski condensed these three terms to "condition of joints" which again had five ratings. More than 80 of the case records involved clay occurrences./.) • (J. The Q-system predicted no-support. as obviously may occur in practice. rock stress is not used specifically as a parameter though it is apparently when selecting support measures. a 168 by 14 by 21 m excavation located 20 to 30 m below the surface in argillite. Despite these later modifications. and J„ relate to the joint set or discontinuity most likely to allow failure to initiate. Design decisions are nevertheless required both before and during construction. and 40 to 60 cm of shotcrete.1J„) • (J„. These are fundamental geotechnical parameters. No matter how many sophisticated rock mechanics test programs and finite element analyses are performed. Careful monitoring using MPBX (multiple position borehole extensometers) and convergence measurements revealed maximum deformations of only 8 mm. In his 1975 paper Bieniawski gives support recommendation for a tunnel of 5 to 12 m span in which the vertical stress should be less than 30 MPa. which is now acknowledged to be excessively conservative. In the Q-system. The Q-system also accounts for loosening caused by shear zones and faults. and the United States. is not particularly emphasized in the RMR Geomechanics Classification.1. or on classification methods. with the vertical stress limited to 25 MPa.1 mm up to >5 mm) and continuity of joints (5 ratings.c/o. The range of possible Q values (approximately 0. and active stress. It also seems to be a factor that is virtually ignored in the other classification schemes. joint alteration (filling). Underground excavations can be supported with some confidence primarily because many others have been supported before them and have performed satisfactorily.1 mm. = joint alteration number (of least favorable discontinuity or joint set). The classification of "least favorable features" (for J.001 to 1000) encompasses the whole spectrum of rock mass qualities from heavy squeezing ground up to sound unjointed rock. and where a good classification method will allow us to extrapolate past designs to different rock masses and to different sizes and types of excavation. = joint water reduction factor. Bieniawski increased Lauffer's maximum unsupported span of 8 m (in his 1973 version) to 20 m (1975 version) and finally to 30 m (1979 version). separation of joints (5 ratings. Detailed descriptions of the six parameters and their numerical ratings are given in Table 2. 26 metamorphic rock types. Method for Estimating Rock Mass Quality (Q) The six parameters chosen to describe the rock mass quality (Q) are combined in the following way: Q= (RQD/J. and J„.1. the same support recommendations are given specifically for 10 m span tunnels. separation <0. 1979). <0. The onset of popping.. These differences appear to be narrowing gradually. The Geomechanics Classification was based initially on Lauffer (1958). not continuous. and SRF = stress reduction factor. very few case records could be utilized in the squeezing category. Category 32 support predicted by the Q-system. In his later publications (1976. He also indicates (1979) that when only two joint sets are present the average spacing will prove conservative." In the RMR system. BARTON ON 0-SYSTEM 63 Description of the Q-System Rationale The vast majority of the thousands of kilometers of tunnels constructed world-wide every year do not have the benefit of performance monitoring. In his 1976 version. was "practically identical to the actual support" used.62 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES different joint sets according to the example given in his paper. = joint roughness number (of least favorable discontinuity or joint set). The methods were compared while classifying drill core. J„. South Africa. In his original version Bieniawski (1973) considered the condition of joints under three descriptive terms: weathering (5 ratings). Only the Q-system was found to be applicable to the worst conditions encountered in the main excavation.) represents one of the strongest features of the method. In a detailed comparison of various classification methods. One of the most recent reports of comparisons between rock mass classification systems for tunneling was published by Einstein et al (1983) from work performed at the Porter Square Station. The important influence of orientation relative to the tunnel axis is implicit. However. slabbing. The three pairs of ratios (RQD/J„. in Cambridge. They showed that Bieniawski's (1976) method predicted considerable support in all cases. J. 1.25 25 ..5-10 0. 2.undulating Smooth.in that order. gypsum.continuous zones H. JOINT SET NUMBER (J ) JD) 3. or 8-12 (25-30') (16-24') (12-16') (6-12') (6-24') 5. i.no or few joints 0.non-softening.33 2. Softening or low friction clay mineral coatings.66 1 . 0.clay mineral fillings.hard.small clay fraction (non-softening) 0.or sandy-clay coatings.e.50 50 .graphite etc.gravelly or crushed zone thick enough to prevent rock wall contact 1.90.5 .undulating Rough or irregular.planar Slickensided.) E. i. Crushed rock.and access to water etc.1-0. Excellent 0 . 100. Non-softening mineral coatings. locally.0 (25-30') 3.J for description of clay condition) N. (b) Rock wall contact 10 .considerable outwash of joint fillings Exceptionally high inflow or water pressure at blasting. egrated or crushed rock and clay(see G.planar 4.0 (20-25') (8-16') before Sandy particles.0 Medium or low over-consolidation.0 (25-35') 2. 8. sandy particles.P. 8 .75 75 90 90 .clay-free disintegrated rock etc.surface staining only Slightly altered joint walls.random. (including 0) a nominal value of 10 is used to evaluate Q in equation (1).0 10' 13 ' (6-24') (c) No rock wall contact when sheared 5. quartz or epidote Unaltered joint walls. 15 J.05 >10 Note: (i) Factors C to F are crude estimates.100 Note: (i) Where RQD is reported or measured as 10. Medium inflow or pressure.0 TABLE 2.5 0.L.95.earthlike 20 Note: (1) For intersections use (3.5 1.0 One joint set 2 One joint set plus random Two joint sets 4 Two joint sets plus random 6 Three joint sets 9 Three joint sets plus random 12 Four or more joint sets. (iii) J r w0.1.) Tightly healed.0 <1 0.. JOINT ALTERATION NUMBER (Jr) 4 3 2 1.impermiable filling i.5 1.J for description of clay condition) 6. Large inflow or high pressure in competent rock with unfilled joints Large inflow or high pressure.5 can be used for planar slickensided joints having lineations. < 5 1/min. .5-10 0.0 Strongly over-consolidated non-softening clay mineral fillings (continuous. Also chlorite. 65 and 66). (ii) Special problems caused by ice formation are not considered..e."sugar cube" etc. are sufficiently accurate. heavily jointed. and small quantities of swelling clays. 4. etc. but <5mm thickness) Value of J a depends on percent of swelling clay-size particles.5 2. i. ROCK QUALITY DESIGNATION (RQD) Very poor Poor Fair Good E.2. clay-free disintegrated rock etc. or bands of clay(see G.2-0.75 ( .0 x Jn) Note: (ii) For portals use 12.provided the lineations are orientated for minimum strength Dry excavations or minor inflow. (ii) RQO intervals of 5. Thick.) (a) Rock wall contact (Or) (approx. montmorillonite (continuous. JOINT WATER REDUCTION FACTOR (Jw) Zone containing clay minerals thick enough to prevent rock wall contact J. Increase J w if drainage measures are installed.5 Note: (1) Descriptions refer to small scale features 13-20 and intermediate scale features.planar Smooth. small clay fraction (non-soft. H. Sandy. (J.kaolinite or mica.. Silty-.H.0 0.0 Note: (ii) Add 1.0 J.e. (continuous but <5mm thickness) 8.e.(continued).0 if the mean spacing of the relevInt joint set is greeter than 3m.0 1.) 1.decaying with time Exceptionally high inflow or water pressure continuing without noticeable decay 1. Swelling -clay fillings.12 (c) No rock wall contact when sheared K. Zones or bands of disint. i.talc.softening.but <5 mm thickness) 6. .ms shear Massive. occasional outwash of joint fillings.e. Zones or bands of siltyor sandy-clay. JOINT ROUGHNESS NUMBER Rock wall contact and Rock wall contact before 10 ems shear Discontinuous joints Rough or irregular.1 >10 0.undulating Slickensided. BARTON ON Q-SYSTEM 65 64 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES TABLE 2-Ratings for the six Q-system parameters (table continues on pp. and 0 1 and 0 3 are the major and minor principal str?.6 instead of 1. reduce a c and a t to 0. (b) Competent rock. the jointing. and the apparent stability.60c o c unconfined and 0.3. (any depth) 10 2.0 Note: (i) Reduce these values of SRF by 25 . who described numerous tunneling projects in Sweden and Norway. very loose surrounding rock (any depth) Single weakness zones containing clay or chemically disintegrated rock(depth of excavation 50m) Single weakness zones containing clay or chemically disintegrated rock (depth of excavation > 50m ) Multiple shear zones in competent rock (clay-free). very tight structure (usually favourable to stability.66-. 1 contain case records. 1.which may cause loosening of rock mass when tunnel is excavated. and a t = tensile strength (point load). Similarly. Heavy squeezing rock pressure 10 20 swelling rock:chermecal swelling activity depending on presence of water P. The trial-and-error adjustment and readjustment of parameter ratings necessary during the development of the Q-system was an important factor in reducing the need for subjective judgments on the part of the developers. near surface Medium stress High stress.6). 5 10 0. by using ESR = 1.SeS.loose surrounding rock (any depth) Single shear zones in competent rock (clay-free) (depth of excavation S 50m ) Single shear zones in competent rock (clay-free) (depth of excavation 50m I Loose open joints. Suggest SRF increase from 2. The use of ESR = 1.5 1. Roof support. followed by repeated . 3a and 3b is often on an individual basis. the process of support selection is organized and reasonably objective. 6. including detailed evaluations of the rock. the type of support. This convenient shorthand method can be used during tunnel mapping.0 2.10 10 15 Examples of some tunnel projects in which the Q-system has been used extensively in day-today follow-up mapping are shown in Figs.5 to 5 for such cases (see H). The minimal disturbance caused by TBM excavation makes it particularly important to map as close to the advancing face as possible (for optimal joint definition).0 10-5 0. 3a and 3b. Note that the alphabetic descriptions given in brackets in Table 5 can be checked directly against the same letters given in Table 2. The quality of the rock mass between the zones is a decisive factor in deciding between individual "stitching" and general support. is searched to try to find the most appropriate support measures for the given excavations and rock mass conditions. The support recommendations for cases that plot in these same boxes are listed in Table 4. assuming the occasional fall of small stones (from the walls) were acceptable. When 0 1 /0 3 > 10. which is itself based on earlier experience.5 0.80t. Figure 2 shows three examples of Cecil's cases. One of the examples (Fig.16 02.80 0 and 0. Further details of the use of these support recommendations are given by Barton. Examples of Tunnel Mapping Squeezing rock:plastic flow of incompetent rock under the influence of high rock pressure (OAF) M. Most of the 38 numbered "support boxes" shown in Fig. STRESS REDUCTION FACTOR (a) Weakness zones intersecting excavation. Lien. presence of machinery. in which the positive and negative aspects of a rock mass are assessed. E.33-. Increased safety can be selected at will by reducing the ESR value (e. Figure I shows that the tunnel or excavation span width and the rock mass quality (Q) are the decisive parameters for placing an excavation in a given support category (Boxes 1 to 38). as obviously required. The whole procedure is probably not dissimilar to the mental process occurring when a very experienced tunneling consultant is asked for his support recommendations. reflects construction practice in that the degree of safety and support demanded by an excavation is determined by the purpose. rock stress problems o c ia l of/al Low stress.5 5. 66 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES TABLE 2—(continued). may be unfavourable for wall stability) Mild rock burst (massive rock) Heavy rock burst (massive rock) BARTON ON Q-SYSTEM 67 (SRF) >200 '00-10 >13 13-0.0 for power station chambers and major road tunnels ensures a high factor of safety.33 0. The list of ESR values in Table 3 was developed through exhaustive trial and error.g.5 <0. and Table 5 gives the abbreviated descriptions of the key rock mass parameters and describes the support actually used. It will be noticed that the treatment of crushed zones and major discontinuities shown in Figs. Examples of Case Records 10-20 Note: (ii) For strongly anisotropic virgin stress field (if measured): when 55 0 1 /0 3 5 10. wall support.66 2.heavily jointed or "sugar cube" etc. The large number of case records made it possible to generate the support recommendations quite objectively. A store of experience (case records). and temporary support can be selected as required. While the assessment of most of the parameters is admittedly subjective. support for oil storage caverns could be selected by using ESR = 1.60 t . (SRF) Multiple occurrences of weakness zones containing clay or chemically disintegrated rock. Mild swelling rock pressure Heavy swelling rock pressure 5 . A considerable data base for developing the Q-system was provided by Cecil (1970). when writing conditions are unfavorable.reduce o c and a t to 0.50% if the relevant shear zones only influence but do not intersect the excavation.3 for an important permanent mine opening in place of 1. where compression strength. and Lunde (1975). However. personnel.5 5. which reduces the effective span in Fig. R.5-2 5-2. 3b) is a tunnel excavated by a full-face tunnel boring machine (TBM). and seems to be the most workable solution to the problem of variable safety requirements. etc. there is an important user requirement for different degrees of safety.5 7. (iii) Few case records available where depth of crown below surface is less than span width. Mild squeezing rock pressure . The excavation support ratio (ESR).16 5-10 Method of Selecting Suitable Support The Q-system is essentially a weighting process. access tunnels. L 3.5 m+ S 5 cm (B = bolting. R I — 1.m.5 m c/c. minor road and railway tunnels. Figure 4 illustrates ten parallel (100 m long) sewage treatment caverns constructed near Oslo.0 79 ca. Table 1). etc.1 1111111111MMII MUM 11 ••n• 1111n 1111111∎ 111 In11111111 CC VI 2 MIMI • 1.5 m + S (mr) 12-15 cm Nodular limestone: B 1.8? 2 mapping before permanent support is chosen. Power stations.I:mr•61 '••=a0MMINIIIMMIIIII .1•1=111111119. A limited number of pillars in one of the mines were instrumented as a precaution.25 in c/c. water tunnels for hydro power (excluding high pressure penstocks). "1:=. PI Alnn•n••••••111MIINIM 00 Ili ). Detailed analysis of the available case records reveals the following requirements: . There were in fact limited areas in the mines where fall-out occurred from the pillars or walls. respectively. L= 3. mr = mesh reinforced) a .. drifts and headings for large openings Storage caverns.. 0 it 11 al TABLE 3—Excavation Support Ratio (ESR)pr a variety of underground gveavations. 1. By comparing these qualities with the permanently unsupported cases (Fig. civil defense chambers.. the quality of the limestone varied as follows: OMIS—n1•IMIN UCIN=M11•=1 UM. pilot tunnels. Underground nuclear power stations. support decisions were also guided by the method outlined. L = length.1111=NIMIIIIIIIIIMIIIMI Ma IIIIIMEM 11 MOINE 111111nn min MOE 111111 MI x 2 gamma .1 aatt "MI a Temporary mine openings etc. IMEMINON Q = INEMIEMEMII Unnn 0 1111111 essiuminn UMW 11111 UOMM•MMIN Z V 111111 nn1 R. 80 0 7 0. During construction. black circles) it was possible to demonstrate satisfactory conditions for the great majority of the excavations. The general improvement in rock conditions as the parallel caverns advanced from the shale into the nodular limestone were clearly reflected in the six parameters and support was reduced accordingly: Shale: B 1.. 0. n••nnnnnnnn N1118111111•1111MINM IN11611111111111111111=11 11111111101•11M=MMI 11•6•1•11•11111•1111111 228•1==MMI IMIIIIIIIIIMMEMIII nnnMEMIN 8 11E111nn 11111111 INIMIIIM=IMOMMOOMI nnn •=1•1=111•11n11.n 111•0111•1==n11n111n11•MIIMMIIINn 1611•11111•111/1/ sumwoommossoessammiss 11•11 8 BONIFIIIMIIMIIIn12••••nnn IIMMIINIMINMEMENIMOMMINI=M111 IN•mill1111111111111311111•1111M1111111111111 12. I. factories Number of Cases ca. The relationship between the maximum unsupported span and the Q-value is clearly seen in Fig. stability was apparently nearer the "temporary mine openings" category (ESR = 3-5. However. ESR Type of Excavation 11111111111111111M1 1111111111011011=1 1111111111111111111111111. There will then be improved possibilities for observing the character of narrow clay-bearing discontinuities. water treatment plants..10=1=M11=1. The effective RQD of the zone of rock around a TBM excavated tunnel will generally be higher than that around a blasted tunnel owing to the relatively slight disturbance of incipient joints and tight structures. . portals. c/c = spacing..—_cam The Q-system has also been used in the area of mine stability. railway stations. sports and public facilities..5 4 — 9 1 — 2 1 = 4 — 38 (fair -..1. surface mapping and drill core analysis were interpreted in terms of the Q-system parameters. S = shotcrete..6 83 1.3 25 1.1111 8 MI• O in . major road and railway tunnels. intersections E.1.1111111ONIMMIIII n )1-4 g I sr 0 0 BARTON ON 0-SYSTEM 69 1— 0. surge chambers. Permanent mine openings.rx====:::=E= mow se MOO :. At the feasibility and planning stage. in places.good) 1 In the great majority of the drifts the quality was "good" (Q = 18 — 38).68 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES 00 0 el . 3-5? 2 1..n 1 9. In a recent assessment of stability in two limestone mines with 13 to 15 m span rooms or drifts. Support requirements were predicted on this basis. 1n 0 0 11111111111n1 —0 11 80 — 100 Rock Mass Requirements for Permanently Unsupported Excavations 0 e) VS3 / NINS An important area of application for the Q-system is the recognition of rock mass characteristics required for safe operation of permanently unsupported openings.. S(mr) 10-20 cm - B(utg) 1 m +5 2-3 cm S 2.020. . J.5-2 in 01.5 - <10 13 I - Blutg) 1. VI I.5-2 m - <30 elm - shorty) I '1. V.5 m - >5 +clm I >5 - <10 m Blutg) 1-1. IV.5-2 ID <1. VI B(tg) 1.1„ ESR - .5-2 in >10 +clm 15 I. VIII. I (see Barton et al. Smooth wall blasting and thorough barring-down may remove the need for suppon.5 m + S(mr) 15-30 cm <30 m B(tg) 1-1. IV Bag) 1. Ill _010 m B(tg) 1-1.75 >1.5-2 m <1. XI I.12. II.31g) I - - 13(utg) 1-1. IX I. \ k<30 / . II.5 cm B(utg) 1 m +S 2. II.. IX VIII.5 010 I Bang) 1.5 m - <10 +S 2-3 cm I - <6 ni S 2-3 cm <10 I. XI VIII. III <15 Biutg) 1. - Conditional factors Ro.10-15 cm B(utg) I m -- + no or elm --B(utg) 1 rn +S(mr) 5 cm 130g) I m - +S(mr) 5 cm - BItg) 1 m + S1mr) 5-7.sblutg)) - 020 9 Biutg) 2. VII I. IX I. SPAN =- ____ - 1. .11 Bitg) 1.5 m + S 2-3 cm 19 -- 20' See note XII - - 21 22 - -.5 m 05 '110 in - +S 2-3 cm I 5 - <10 m B(utg) 1-1. IV I I I 1 I I 1 I. especially where the excavation height is >25 m Future cast records should differentiate categories I to 8. IX I. - - - - - 4' - 5 • - 6• . III B0g) 1-1. XI - .support Notes sblutg) sblutg) sblutg) sblutg) sblutg) sblutg) sblutg) - - 7' - g' sblutg) - Note.5 • 10 1 - filing) 1. IV - - 130g) 1.5-5 cm - B(utg) 1 m - - 13tutg) I in +clm - S 2.5 - - - - - - - - - - 25 26 27 - See note XII - - - - >5 >0. IV I.5 in 17 1 . V.5 m +clm 10 I. XI I. II 130g) 1.5-2 m <30 - - + clm 13002-3 in - - 030 II" .-6 m B(utg) 1-1. 71 and 72).0 030 - - 23 - - 24 • See note XII - - - - >10 >0. II. IX IV. Rough-wall blasting may result in the need for single applications of shotcrete. \ B(tg) 1 in k<30 nil +S(mr) 20-30 cm <20m B(tg) I m +S(mr) 15-20 cm CCA)sr) 30-100 cm + B(tg) I m B(utg) I m - +S 2-3 cm B(utg) 1 m - +S(mr) 5 cm - B0g) I m +S(mr) 5 cm Notes I. Support rate- gory I" Cottilatonal factors Ro J.0 >1.5 (>10.5-2 m 015 - note + S(an) 10-/5 cm XII I sblutg) - - >30 (. 1974.5-10 cm <I2m B(utg) 1 m +S(mr) 5-7.5-5 cm -12m B(tg) I m +S(mr) 7.5-2 in >15 - - 16' +clm See I. II.70 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES BARTON ON Q-SYSTEM 71 TABLE 4-Support recommendations for the 38 categories shown in Fig.5-2 in 015 010 - +clm I.5-2 in - - +clm I.5-7.0. IX 1._ 13(tg) I 5-2 in <30 + clm BItg) 2-3 m - 030 12' 130g) 1. V. VI I.5 m +S (me) 10-15 cm <15 m B(utg) 1-1. SPAN 1.75 >0. IV.5 IP + S( mr) 5-10 cm '30 ni B0g) 1-1.0 '1.10 <30 00.25 - -=_0.5 '--0. X.5-5 cm B(utg) 1 m 15 m B(tg) 1-1.5 in + S(mr). 11. X. X. II.5-2 m 015 <10 - Id +S(mr) 5-10 cm I.25 5 >0.. V. 1a ESR Support cute- gory Tvpe of . 1975 TABLE 4-(continued). for notes: table continues on pp.5 cm - B(utg) I m +S(mr) 2. VI Bug) 1.25 -_ 020 in Type of support B(tg) 1-2 m + SAO 10-15 cm <20 mBItg) 1-1.5 cm 0-40 cm >I2m CCA + Im <I 2m S(mr) 10-20 cm + B(tg) I m 0-30m B(tg) I m +S(mr) 30-40 cm (.75 <l2.5-3 m - <20 Blutg) 2-3 in - - 030 10 Biutg) 1. The type of suppon to be used in categories I to 0 will depend on the blasting technique. IV I 1 1 VIII. X.5 - 00. IV.5 m +S(mr) 5-10 cm 035 in Bag) 1-2 m + S(mr) 20-25 cm <35 in 130g) 1-2 m -.5-2 in --10 + S(mr) 5-10 cm I. II.5 <10 + S 2-3 cm 1. II I. V.5 010 >0. X. III IX VIII. X1 B0g) I ni + S(mr) 5-7.5 — <1.1.5-15 cm — 36 • — 37 Notes Type of support B(tg) I in +S 2.20nt — <20m — — 02 — — <2 — — — — — 02 0--0. XI IX IV. X. XI VIII.'. XI IX S(mr) 10-20 ent S(mr) 10-20 cm + B(tg) 0.0 m 38 See note XIII IX Bttg) I m +S(mr) 2.5 cm S(mr) 7. grouted post-tensioned in very poor quality rock masses. XI IX IX IX. XI — — — — 010m 010m — --- — — <10m <10m CCA(sr)100-300 cm CCA(sr)100-300 cm +130g) I m S(mr) 70-200 cm S(mr) 70-200 cm + B(tg) 1 m IX VIII.. !UM- 80ry 30 31 14 ESR — <5 — — — >4 — — 04. III. VIII.5-15 cm S(mr) 15-25 cm CCA(sr) 20-60 cm +130g) 1 rn IX Blig) I m + S(mr) 30-100 cm CCAIsr) 60-2(0 cm + Bttg) I m B(tg) I m + S(mr) 20-75 cm CCAtst) 40-150 cm + B(tg) I m cr) III.25 — — — — — 35 See note XII — <5 32 See note XII 33• — . :_-_-'15m -0"15m — — <15m <15in B(tg) I m +S(mr) 5-12. XI. Conditional factors RQD 1. -- spot bolting = systematic bolting = untensioned.5-10 m IX VIII.5-5 cm S(rnri 5-7. XI Key to Support Tables.25 <0. XI IX VIII.5-25 cm CCA 20-40 cm + Bag) I m CCA(sr) 30-50 cm + B0g) I in B0g) I m + Simr) 40 60 cm Bug) I m + Stmr) 20-40 cm CCAlsr) 40-120 on +B(tg) I in - IX VIII. IX. X. X. X. XI II. X1 VIII. XI — — — — Slmr) 20-60 cm Slot') 20-60 cm + B(tg) 0.1.5 — — — — — — — . X • Authors' estimates of support.5 cm O -0 IX IX VIII. . IV.72 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES BARTON ON Q-SYSTEM 73 TABLE 4—(continued). (expanding shell type for competent rock masses. X. see Note XI) S = shotcretc (mr) = mesh reinforced clm = chain link mesh CCA = cast concrete arch (sr) = steel reinforced B (utg) (tg) w 0 IX VIII. X. Insufficient case records available for reliable estimation of support requirements. grouted = tensioned. SPAN 5 "PP. sh If) 0. IX. XI VIII. XI II.5-5 cm S(mr) 5-10 cm Slim) 7. II. III. X. IV.5-1. '" — 1. XI.25 — <2 — — 00. O O .5 cm 13(tg) 1 m +S(nu) 5-7.5 cm S(mr) 7. X. X. II IX. w . massive gneiss.1 Category 0.5 18 1E ( -) 2A 3E ( --) 4B 5A (--) 6H 200 1. Case No.Sweden (ref. rough-surfaced.0 1.6 50 spot bolts in about 300 a of 100 chamber 1.6 6.Sweden (ref._1.8 Category 31 . Headrace tunnel.5 =None or sb 5 1.5 7. Wine and liquor storage rooms. Stockholm (ref. N.5 SA ( 6C.TABLE 5-Comparison of support used and support recommended for three case records described b y Cecil (1970).0 5 (SA) 68 0.0 10 (IA) 2B (3H) 40 10 20 24. 5-30 cm spacing. wire mesh and shotcrete RQD L. Cecil 1970) 300 m length. slickensided graphitecoated joint surfaces.10 1. Purpose of excavation.5 ( m ) 6. 5-30 cm Insignificant spacing. Vietas Hydro. 3. 60 Wedge shaped roof fall.5-5 cm 1. plus random. RQD = 10 water inflow.5 50 Rock bolts. Minor water inflows (<31/min). Chrushed mylonite and non-softening clay seams and joint fillings. zone was 50-100 cm wide and contained smooth.) 1. 100 water inflow. Cecil 1970). unaltered Joints. few joints.0 2.3 2. location. 1 joint set.3 J SRF n (Code :Tables 1 to 6) 60 1. Tailrace tunnel. . 15 m length. including a 1 m wide shear zone in mylonite. Planar.3 1. Minor overbreak.3 15. 3. Hydro. Cecil 1970).0 6 6 31 ( 4K ) 2E Q ESR Category 22 =13 1 m +S(mr) 2.5 4. overthrust shear zone in schist. N. Intersecting 2 joint sets joint set. reference 60 m length.8 1 m +S(mr) 5 cm 1. in which there was a 3 cm thick clay (non softening) Shear and graphite seam.0 SPAN Estimate of ESR permanent roof support 4. SPAN Height Depth Support used (m ) 12. 24 48 77 DESCRIPTION OF ROCK MASS Nature of instability 3. RQD .4 . Bergvattnet.5 ( m) 60 Rock bolts. wire mesh and two shotcrete applications 2 1. 3. no falls or slides.r. Wedge-shaped roof fall. 3 m spacing. Insignificant RQD . . . 10..4 ..2 .. ...5 t.--- I'.SYSTEM 77 . r/ t' '-'" zt .76 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES BARTON ON Q ..•.c. = 6 '-' --' ROCK NOTES Gneiss 810 ..-sr z .44 r..9• .817 TUNNEL crushed Orginally elo .. RECOMMENDED SUPPORT crushed clay fitting MAPPING ....k t 'C . z . r SUPPORT DESCRIPTION ": RECOMMENDED „ 1.. -_-1 C3 --n . thickness 50cm Crushed zone.. ..100 Slmr) 15cm 1070- - a1... weathered with clay Grouted bolts Strike/dip Shotcrete Dikes and sills S (mr) .2 . with 10 cm clay filling with large 1050 - 111 Lz'e —...FORRE z Lo aN. Mesh reinforced shotcrete with grouted bolts Cast concrete arch FIG.. +• .• . . _r l... .. a -' a ET.. L.•-n lf. .ROCK MASS ic TEMPORARY .111. V. 10cm !. . .-. • t 60 or or . . 7 '``.0.='n 7( 2 NOTES- 1060-1075 Fault 20 cm .. 815 810 10cm 11111111111111 -I- .c-.. L3 Z .. lb. . _ S Im I 1111. l'. • 825 • 4.SUPPORT LOCALITY HOL ME N (right I s2.0 ° . vert ••... -r4 (0. - ntictine ritlip e0.Are Like o -H .. 830 I - o o°. o o .-_-... : .. 3b—Example of tunnel mapping using the Q-system: 3. -.1...-- ! Jy eo E . 2.. .._o - . ULLA . L---" . . SIm 1 11111114 I 1 . 10cm . • .4ir ..v iv 4a (clay sample (C/C I .” ° c .. w C C"' I 1080 ROCK SiON oar[ 25 3 SO et) PROJEC T 71610 NO 5NEE T NO Nodular lime stone and shale TUNNEL Fault 3m crushed zone 2 m crushed zone Discontinuity with 5cm 1090 1100 ' -_C-—% .411.-.. .-.5'.51C/C) • 1441% 1080- ....1041. -L'--.a . • '. ti. • •• 8 1. . .' - 805 t. .. ‘". without clay 80 SUPPORT B L°0 o fi Expansion bolts Bolts with bands Crushed zone. o .. I i .830 Heavily jointed .." z i.?. S 5cm 1 • • PI I.-... ng ROCK MASS -It TEMPORARY DESCRIPTION `I SUPPORT SUPPORT . .. t 0'. . I .!. cO ° . Z 1 ice . 3a—Example of tunnel mapping using the Q-system: 160 m 2 headrace tunnel. m 4 40 'c' l • .! )..i. .' .. ri0 0 o . - 1060 e-. IIt I ... .•. 1090 • ." . FIG. to in. KS 4. o . partly a little c lay Crushed waterie akage zone with clay MAPPING .. 1 a...3 m diameter TBM driven sewage tunnel. ..4 ..: 17...x..1 401. ."... + Simi.. . °A TI 80 PROJECT NO 50000 NO 716 28 NO ROCK MASS Discontinuity.SUPPORT LOCALITY HYLLEN .. z i o ..T.. z .1 .. O . • ? 820 A40 . \ . need J. % 1. If SPAN > 20 m. unjointed rock and completely crushed. consequently there were some 40 cases of large caverns with spans in the range of 15 to 30 m and wall heights in the range of 30 to 60 m. Histograms of the principal parameters used to codify the 212 case records used in the Q-system have been developed.2 to 100 m.0. or whether he would be relying on few. The shorthand in No. A significant body of the case records came from hydroelectric projects. J„-. Existing natural and man-made openings indicate that very large unsupported spans can be safely built and utilized. 1. need J. If J„ = 9.e. poured The number of joint sets was most commonly in the range of one set (plus random) to three sets (plus random). The predominant tunnel dimensions (span or diameter) were 5 to 10 m (78 cases) and 10 to 15 m (59 cases). or combinations of rockbolts and shotcrete. 9. If SPAN > 10 m.5) and one needs RQD = 90 (i. extreme conditions called for extreme varieties of support (e. Forty (40) cases lay in the "very poor" category (0 to 25%) and fifty-three (53) cases in the "excellent" category (90 to 100%). 6. = 1.0 'At 0 --116m 60 U.1. The following brief summary describes the extreme values and the most common values of the various factors affecting tunnel stability in the case records considered. % 1. J„. In this section.g.1. though most were commonly in the range of 50 to 250 m. Oslofjord.) at least equivalent to rough-planar or smooth-undulating (J. had exactly three joint sets. need J. need J. Note that the other case records contribute most of the data on the deeper-seated excavations.0. Analysis of Q .6 m long bolts on overlapped 0.. need 4 and SRF 1. including numerous hydropower caverns.. extreme value cases.. 7. need J„ 2.system arc analyzed by means of histograms. Depths Excavation depths ranged from 5 to 2500 m. The Scandinavian bias caused predominantly by Cecil's (1970) case records is shown in Fig. Dimensions The cases studied ranged from unsupported 1. if the rock mass is of sufficiently high quality. 3 gives the following recommendations: 3.System Case Records 1 0 FIG. disintegrated rock. Excavation heights ranged from extreme values of 1. Conditional requirements for permanently unsupported openings: If RQD 40. If there are as many as three joint sets (J„ = 9).e. The predominant form of support in the case records was rockbolts.9 m centers together with 14. it is preferable that): 20 J„ 9. If SRF > 1. If f. RQD Support Method Number of Joint Sets (. Only 32 cases were permanently unsupported.= 1.0.) The large majority (180) of the 212 case records were supported excavations. then one needs joint roughness (J. "excellent").1. J.• BARTON ON 0-SYSTEM 79 78 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES SPAN OR DIAMETER 60m 60 m 40m 40m 1-5 5-10 10-15 15-20 (m) 20-30 30-100 NODULAR LIMESTONE AND SHALE 20m =CY T--)-5 --CM77:nF 0 ==n==r-)==r-)==n 0 BO 20m 1.5 and RQD 90. CO 2 ♦0 General requirements for permanently unsupported openings (i. in multiple arch and wall drifts.. often mesh reinforced. which would inherently reduce the reliability of associated support recommendations.9 m centers) and mesh-reinforced gunite. .5 (see Table 2). the largest group. Support ranged from spot bolting (as little as 50 bolts over a roof area of 6000 m 2 ) to very heavy rib-and-rock-bolt-reinforced concrete of 2 to 3 m thickness. 4—Vertical section through the VEAS sewage treatment plant. Occasionally.8 to 100 m.. 0 FIG. Extreme cases consisted of massive. Fifty-two (52) cases. Ultimately. 5—Histogram of tunnel spans.8 m long rockbolts on 0.0. SRF 2. a potential user of a classification method will be persuaded of the value of a particular system by the degree to which he can identify his site in the case records used to develop the given method. the characteristics of the 212 case records used to develop the Q . The potential user can evaluate to what extent his site fits with the data base. < 4. < 9.5. The "rock quality designation" (RQD) ranged in a quite uniform manner from 0 up to 100%.2 m wide pilot tunnels to unsupported 100 m wide mine caverns (Fig. 5). Our case records describe unsupported man-made excavations having spans from 1. respectively.kr.lcr. data plotted in Fig. 7—Histogram of stress/strength ratios. these included twelve (12) swelling clay occurrences. (range) = 1. = 0. slabbing. The mean and extreme values of the a. and smooth-undulating surfaces. or rock burst problems numbered only twenty (20). the majority of cases with these features were classed as "weakness zones causing loosening or fall-out . 1970) Stress Reduce Factor (SRF) ME OTHER CASES FIG. which is neither too high nor too low. (b) rock stress problems in competent rock. Thirteen (13) cases consisted of healed joints. Thirty-two (32) cases were classified as having rock stress problems (group (b)) with ratios of cr. 0 SCANDINAVIAN CASES (CECIL. Eighty-one percent (81%) of the cases fell in this category. 10 shown in Fig./cr. The data for this histogram were obtained from the case records in which stress and strength data were specifically described.80 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES BARTON ON Q-SYSTEM TUNNEL DEPTH (meters) 0-25 81 O f /ac RATIO (STRESS /STRENGTH) 25-50 60-100 100-260 250-500 600-250 1. thin clay fillings. occasional outwash of joint fillings" (J.66 to 0. swelling clay. > 10).." In other words. . = 0. (mean) = 112 MPa • cr.0 MILD ROCK BURST HIGH STRESS MEDIUM STRESS MOST OF THE 212 CASE RECORDS PLOT IN THIS CATEGORY FIG." or "exceptionally high inflow decaying with time" (J." or "thick clay fillings. Seventy-three (73) cases fell in group (a) in which clay fillings were the direct cause of loosening and fall-out. Joint Water (.) .5-2. (mean) = 15. These ranges.g. Eleven (II) of the cases were found to have satisfactory ratios of cr. (i. Joint Roughness (sr) The joint roughness numbers most commonly found in the 212 case records were 1. equal to 120 to 200 MPa). less than 10. and their extreme value ratios. (unconfined compression strength/major principal stress) in the moderate range of 10 to 200. 6—Histogram of tunnel depths. /( T . 10 - . These are divided into four broad groups: (a) weakness zones causing loosening or fall-out. O HEAVY ROCK BURST 10 6-10 16 - 30 20 2. a.1w) The joint water reduction factor describing the degree of water inflow was strongly biased in the direction of "dry excavations or minor inflow" (<5 L/min locally).0 to 62 • a.1 MPa o.L) The joint alteration parameter most commonly seen in the case records was represented by the number 1./a. ./o. (c) squeezing (flow of incompetent rock). The actual case records describing high stress." or "considerable outwash of joint fillings.e.0-1.0. (range) = 3. " Eighty-one (81) cases were classified as having moderate stress in essentially competent rock. The stress reduction factor has sixteen (16) classes. rough-planar. in which eighty-one (81) cases were identified as having "mineral coatings.e. Joint Alteration (.5 501- ♦0 -10 . However.. with ur ic'. which represent smooth-planar. 7. more than eighty (80) of the case records involved clay mineral joint fillings of various kinds. This can be compared with the statistic for J. which are obviously very favorable for stability and for their inherently low permeability. Twelve (12) cases were classed as "large inflow in competent rock. 7 can be summarized by the following values: u. Twenty-four (24) cases had "medium inflow.66).8 (It should be noted that several of the case records with et. 7. Use of the extreme values expanded this data base to the 32 cases with a. (range) = 7 to 300 MPa • a..33). were plotted in Fig. 7. and (d) swelling (chemical effect due to water uptake). ( mean) = 8. and a data gave ranges for at least one of these parameters (e.0 (unaltered or unweathered). One hundred and three (103) cases were in this class. Extreme values consisted of discontinuous joints in massive rock (16 cases) and plane slickensided surfaces (17 cases) typically seen in faulted rock with clay fillings.0-2..6-6.. This statistic is shown in Fig.5 to 50 MPa o.. i. EXC.1 (very poor) to 40 (good). provided that any special characteristics of the new rock type are adequately represented in the six parameters. massive rock).0-4 4-10 10-40 4 i 00 I.0 (two joint sets—two plus random). and the mean J. quartzite (13). Metamorphic 83 1 Amphibolite 8 Chalk 1 4 2 1 I Anorthosite (meta-) Arkose Arkose (meta-) Claystone (meta-) 1 Limestone 3 I 3 2 1 Marly Limestone Mudstone Calcareous Mudstone 1 2 46 I 1 2 2 2 Dolomite Gneiss Biotite Gneiss Granitic Gneiss Schistose Gneiss Graywacke Grecnstone Schistose meta Graywacke Quartz Hornblende Leptite Marble Mylonite Pegmatite Syenite Phyllite Quartzite Schist Biotite Schist Mica Schist Limestone Schist Sparag mite 14 1 4 2 I Sandstone Shale Clay Shale Siltstone Marl Opalinus Clay 4 2 2 2 I 4 2 1 1 13 17 1 2 1 2 Conclusions I.0 to 4). and stress-strength ratios. "poor" (Q = I. The predominant rockmass characteristic in the cases with popping. Q-Value The whole spectrum of rock mass qualities exhibited by the case records is shown in Fig.0). or rockbursting was relatively massive rock. although a total of twelve cases were listed as rock containing swelling clay such as montmorillonite. The whole spectrum of case records utilized in the Q-system ranges from qualities of 0. EXTREM. leptite (11). and rock mass qualities.0). III. Their characteristics are quantified in such a manner that the individuality exhibited by many rock types is carried all the way through to support selection. Sedimentary 100-1000 40 - 0 II. Sedimentary rocks are relatively poorly represented with only 19 cases. Squeezing or swelling problems (groups (c) and (d)) were encountered in only nine of the case records. Jointing ranged from three widely spaced sets (J„ = 9) to massive intact rock (J„ = 1. The mean RQD for these cases was 91% (range 70 to 100%).BARTON ON 0-SYSTEM I 82 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES TABLE 6—Frequency of occurrence of rock types in examined case ROCK MASS QUALITY (0) . Rock Types The distribution of rock types represented in the case records can be summarized as follows: igneous rock (13 types). Very poor rock qualities previously requiring . and rock bursting problems are represented in a sufficient number of case records for reliable determination of support requirements. depths. slabbing. As expected. The statistics are dominated by granite (48) and gneiss (21). slabbing. The environment expected under tunnel use must always be carefully considered.001-. Swelling. Application of the Q-system to other rock types than those described in the case records can be performed with confidence. However. Table 6 provides a complete breakdown on the rock types and the number of case record occurrences of each type. Detailed analysis of the case records has revealed the overall distribution of individual rock mass parameters such as joint roughness. General tunneling conditions are extremely well represented.1-1. with 160 case records in the range of Q-values from 0. the majority of cases (76%) fall in the central categories "very poor" (Q = 0. a revolutionary new material that is rapidly replacing labor-intensive mesh-reinforced shotcrete.0 1.01-0.001 (extreme squeezing) to 800 (essentially unjointed. there are significant numbers of case records involving schist (21). "fair" (Q = 4 to 10). 8 — Histogram of Q-value for all 212 case records. value was 5. The large number of case records utilized to develop the Q-system ensures that reliable support recommendations are provided for a very wide range of tunnel sizes. and "good" (Q = 10 to 40). types of excavation. alteration. and amphibolite (8).1 to 1.01 . metamorphic rock (26 types). with few joint sets and/or wide joint spacing. and sedimentary rock (II types). Squeezing ground is the only class of problems that is inadequately represented in the original data base. Fifty individual rock types are represented in the case records. The Q-system has been used for several years in conjunction with Norwegian tunnels supported with fiber-reinforced microsilica shotcrete. records. so that extreme value cases can be readily identified.1 0. GOOD FIG. Igneous - 30 - - 20 - - Basalt Diabase Diorite Granodiorite Quartzdiorite Dolerite Gabbro Granite Aplitic Granite Monzonitic Granite Quartz Monzonite Quartz Porphyry Tuff 1 EXCEPT. 8. VERY POOR POOR POOR POOR FAIR VERY 0000 0000 EXT. A case in point would be the susceptibility to alteration by exposure to moisture. Conference on Geomechanics. No.. Symposium Exploration for Rock Engineering. R. 414 pp.0 mm 0.. F." Rock Mechanics Discussion Meeting. Swedish Rock Mechanics Research Foundation.). Tiedernan. H. Befo. I. Joint walls do not come into contact at all upon shear. 111. Vol.Z. 4th International Congress on Rock Mechanics. N. Jg. slightly clayey non-cohesive tilling Non-softening strongly over-consolidated clay mineral tilling. E. pp. 4th Rapid Excavation Tunneling Conference. U.. 12. A. "Rock Defects and Loads on Tunnel Supports.0' 8. Barton. N. Parker. The respective relationships are given by the expressions TABLE D-1—Joint alteration number (1.." in Proceedings. non-softening. Vol. R. E. 2. Ch. E.. 1975. Johannesburg 2000. 1975. D. 553561. 18. N. and.D." Transactions of the South African Institution of Civil Engineering..0' 6.A. 26-33.0 5. 1972." Highway Research Record. These problems can be overcome by observing that. H. and Thompson. 1976." in Proceedings. Proctor and T. Ing. pp. 15. hard. 3rd International Congress on Rock Mechanics. F. South Africa.0 mm" mmb Larger than 5. International Conference on Sub-Surface Space. Box 8856. pp. Further difficulties arise in the case of homogeneous rockmasses with regard to assessing the degree of stressing. T. pp. non-cohesive rock mineral or crushed rock tilling Non-softening. non-homogeneous rockmasses [DI. Deere. "Rock Mass Classifications in Rock Engineering. and Cording. pp. S. 1963.-N. Z. 315.0 ° Joint walls effectively in contact. Figures added to original data to complete sequences. Lien. H.0 3." Rock Mechanics. Ohio.0' 6." in Proceedings. AIME. 1974. 597-620. B. u. Rabcewicz. Terzaghi. Geol. 683-706. H. Rapid Excavation and Tunneling Conference. Kirsten' (written discussion)—The table of Barton et al [DI. "Correlations of Rock Bolt-Shotcrete Support and Rock Quality Parameters in Scandinavian Tunnels.10) is quite complex and relatively open to interpretation.0' 10. to the field stress state relative to the rockmass strength. 3c. E. A. and Lunde.. A. ' Steffen. 27-32.. New York. G. 1979. Barton et al provide qualitative criteria for determining SRF for incompetent.0 2. I.0 4. "Application of the Q-System in Design Decisions Concerning Dimensions and Appropriate Support for Underground Installations.. Int. 1. Ed. Table 2] for the joint alteration number (. pp. "Estimation of Support Requirements for Underground Excavations.228. S.. H." in Rock Tunneling with Steel Supports. pp.. T." Ph. Q. India. University of Illinois. 234-241. 51-58. White.°° 10. Barton. D. with or without crushed rock Less than 1. "Design of Surface and Near-Surface Construction in Rock. pp. p. Commercial Shearing Co. 36-41.. Theme II. Fairhurst. pp. H. Z. A. The determination of SRF is open to interpretation.. R." in Proceedings. Denver. homogeneous rockmasses [Dl.. The criteria may be systematized and extended as shown in Table D-1 to overcome these problems to a large extent. 2. R..0' 10." in Proceedings. Youngstown. It is a parameter that characterizes the loosening of the rock around the excavation as a whole...0' 13.. p. The stress reduction factor (SRF) is not a geological property that varies for different regimes of rock around an excavation. Vol. 1982. pp. Colo. pp. pp. G. thesis...0 3. Vol. 339. 16th Symposium on Design Methods in Rock Mechanics.0 8. J. Johannesburg. D.. Jr. and Pacher. 4th IAEG Congress. and Skinner. 3/4. J. Die "Neue Osterreichische Bauweise" und ihr Einlluss auf Gebirgsdruckwirkungen und Dimensionierung. with or without crushed rock Shattered or micro-shattered (swelling) clay gouge.22I-V. "Ground Support Prediction Model (RSR Concept). J. Lauffer. J. "Characterizing Rock Masses to Improve Excavation Design. 61-94. 1977.. 1974. I. 36. Updating of the Q-system for use in countries with access to this new temporary and permanent support method is underway at NGI.. New Delhi. No. N. 2nd Aust. Australia. Monsees. Bibliography Barton. 1982. Balkema. in the case of non-homogeneous rock. T.. 24. Montreaux. "Assessment of Empirical Design Methods for Tunnels in Rocks. "Design of Tunnel Support Systems. Vol. 1970. bursting. 97-106. Loset... Einstein. R.. K. V. Bemessung von Hohlraurnbauten. Eds. Steiner. and Kirsten... Fourth Cong. 1970. "Case Studies: Prediction of Rock Mass Behavior by the Geomechanics Classification. L. Felsmech. "Engineering Classification of Jointed Rock Masses. pp.. ISRM. Palmstrom. Bieniawski." in Failure and Breakage of Rock. Vol. Table 3a1 and competent." Geologie und Bauwesen. 1967. ° Also applies when crushed rock is present in clay gouge and there is no rock wall contact.0' 4.. pp. Peck.0 4.. 189-236.84 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES cast concrete arches are being successfully supported by fiber-reinforced shotcrete and rock bolts. of Engineering Geology. 1976. and Lunde.." Panel Report. pp. Vol. 1958. and Schmidt." in Proceedings. Patton. Einstein." in Proceedings. D. H. 1st Rapid Excavation Tunneling Conference. and 34 The non-homogeneities provided for involve single or multiple clay filled weakness or clay free shear zones. SRF is related to the overall quality of the rock. Vol. "Rock Mass Classifications in Rock Engineering Applications. in the case of homogeneous rock. J.. Lien. E. 237-302. 0. "Engineering Classification of Rock Masses for the Design of Tunnel Support. 4. 1973. P. "Evaluation of Design and Performance—Porter Square Transit Station Chamber Lining.. New York. A. and Baecher. pp. 1980. Ing. Deere. New York. ISRM. 0. "Unsupported Underground Openings. . Vol. "Gebirgsklassifizierung far den Stollenbau. H. Robertson. non-softening impernieable tilling Unaltered joint walls.0° 13. 15-99. squeezing. 4651. B. published by ASCE. Lien. Stockholm. Tables 3b. Sub-Surface Space.0 6.. Z. A. N. McKown. 1983." in Proceedings. pp.. Society of Mining Engineers of AIME. Brisbane. Rockstore. R. Z. C. 1946.. Wickham. Minn." in Proceedings. 6.. T. Joint Alteration Number for Joint Separation of Description of Gouge Tightly healed. Vol. Barton. Barton. Hendron.75 1.. V. Z. Bieniawski.. W. B. IIA. with or without crushed rock Softening or low friction clay mineral coatings and small quantities of swelling clays Softening moderately over-consolidated clay mineral tilling.. V.. Azzouz.. W. L. Urbana. Chicago. DISCUSSION ON Q-SYSTEM 85 DISCUSSION H. and Lunde.0° 18. surface staining only Slightly altered. b Joint walls come into contact before 100 mm shear. because of the qualitative nature of the criteria and the difficulties that often arise in deciding whether the rockmass is homogeneous or not. 335-344.. Die Elemente der "Neuen Osterreichischen Tunnelbauweise" und ihre geschichtliche Entwicklung." Osterr. Assoc. Zschr. and swelling. Vol. "The Volumetric Joint Count—A Useful and Simple Measure of the Degree of Rock Mass Jointing. Bieniawski. Bieniawski.. F. New York. 1979. AIME. 224.'' in Proceedings. India. T. D.. U. discussion on pp. Cecil. F. J. Vol... H.. 1975. Rabcewicz.. No. Stockholm. Bieniawski. 43-64. "Geomechanics Classification of Rock Masses and Its Application in Tunnelling. Theme 2. 163-177. 1„ )(4)1 ..0 `o /00 F4 0 c r4 o R2 Cl.. 1 211112INIMEIMIIELEINIMI G END: AtIks /. 099 .. H.8090 0. . versus H/UCS for range of (RQD1l„)(.Z.1?':_. The proposed procedure for determining SRF replaces that given by Barton et al IDI] and is illustrated graphically in Fig. The proposed direct calculation of SRF from a limited number of geological parameters is the only quantification of the loosening potential or stress relaxational behavior of tunnelled ground available to date. 0 k— potential - 1. to Kirsten)l . D-2 confirm the proposed alternative determination of SRF.1.7C ‘/ illi (ROD/JII)(Jr /Jo) 41..J..329) 1 Q.0 /Op 05 MINIMAL FRACTURING SQUEEZING SWELLING I The ruling value for Q may be determined by calculation as the minimum of these two expressions.DISCUSSION ON Q-SYSTEM 87 86 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES /00 .se 2 E0 . . The fact that Terzaghi worked in tunnels which were generally of a squeezing nature and not self-supporting is confirmed in Fig.. The significance of the proposed alternative procedure is illustrated in Fig./-. fratOMIMM 11111111111 (after Barton et al (1)) 111MMIIIII=11111 ormdleiliiiikin_ irE + BA RTON TABLE 3(al ii ii .00e. The various case histories shown plotted in Fig.../ 13P° Lt° vo iC> t le g22/ TEFCAGHI I II IllibrAlill l .11„). imam. SRF„ = 1.3-.. TN.809 Q -0329 SRFh = 0. VO ?iii II 11111aN=1 Il roil .244 e346(H/UCS)1 322 + 0..JJ„)(J„/SRF)..00/ 0. The corresponding rockmass indices are given by the expressions Qn = I ( RQD/J. = 1. increasing increasing loosening -.0 ( H / UCS) 0.809 Q-°" 9 represents the squeezing behavior associated with shear or weakness zones in incompetent ground.. D-2—Plot of stress reduction factor versus rock mass quality.-4...-1. maximum-to-minimum principal field stress ratio.... It is also evident that tunnels in ground in which the loosening behavior is governed by shear or weakness zones or by compressible gouge on the joints are generally not self-supporting./... Barton and his co-authors should be congratulated for this contribution.006 MILD HEAVY ROCK BURST ROCK BURST SQUEEZING SOUSE ZING SWELLING SWELLING 1..48 SRF Contours of ---1 n in f n r n E o° 0 .. 0. and UCS applies. and UCS = unconfined compressive strength of rock.. .for P h / Q n .0 C 0 I PcPe ./„/0.. M 11111111•111•=11011LBINIIMINIMINIIMI 5 MEM Illiek --4‘111 CM III II IIIIMMOMMI __ mo o IN alimmo mmiumnImlommmannsm nNMI. D-1 for K = 1.e IIIIMIIIIMnleMMMINMENOIN=MO MMENEW ...•1n111•11111•11 Contours of SRF .244 K 0346 (H/UCS)' 722 + 0./0 1111111 IEEE".809)I"' .. D-1—Graphs of QhIQ. m. D-2.--e-bursting potential m ROCK MASS QUALITY 0 \ .7. K H = head of rock corresponding to maximum principal field stress. The behavioral characteristics of the ground surrounding a tunnel are detailed in Table D-2..176(UCS/H) 4 II L Stress Reduction Woll SRF . although they were not explicitly aware of the quantitative implications of their findings..176(UCS/H)' 413 where Q = (RQD/J„)(J.0 and J.C15' E .... The domain above the graph represents the loosening behavior of competent rock. The straight-line graph corresponding to SRF = 1.0/ FIG.o IP0/ 6.. D-2. In the event of this value corresponding to SRF h it may further be established which of the two terms in the expression for SRFh is the larger.)(Jr/. As such it represents the lower bound values for SRF.0.0 C C el 29 rErt a) (after Barton et d Mt I SELF SUPPORTED CASES (otter Barton et al (I)) R POOR POOR ii X 0. The corresponding value for SRF may also be determined. = (RQD/J„)(...0 0.: 1 . MPa.n5‘' * - Ci CECIL i $: ^ ..-: 6 1...„ l' III n10=113= 6./.0 r'ili) .4 q° /./„)1.. 0/ 4 /0 Z a IIIIII•11•111.. J w i z' 0. to which the expression for SRF in terms of K. These two terms represent respectively the stress and structurally controlled behavior of competent rock. NO FRACTURING SQUEEZING SWELLING III :". The correspondence between Barton's and Terzaghi's implied relationships between SRF and Q for incompetent ground is remarkable.1. —0.329 (applicable to incompetent rock) liMill 00 POOR 4 =lin V RY GOOD 40 /00 GOOD 1111 XC GOOD 400 1000 FIG." 4' Z -) S .0% ei)11. 6. or swelling Random block displacement Lowly stressed elastic arch 2.0-640 No fracturing.05-10() No fracturing. pp.001-25/ Heavy rock-burst0. or swelling Moderate elastic deformation Moderately stressed elastic arch 0.0) Controlling Criterion Stress in respect of competent rock/Shear or weakness zones in respect of incompetent ground Stress Reduction Factor Probable Rock Mass Quality (SRF) (0° Larger than 10 0." Rock Mechanics. squeezing. "Engineering Classification of Rock Masses for the Design of Tunnel Support.4-2. or swelling Block fall outs or Non-arching in runs of ground completely loosened ground 5-10 1-2.5-5 0.006-0. J.. or swelling Limited elastic deformation Lowly stressed elastic arch 0.05-0.4 Minimal fracturing. Vol. Discussion References [DI] Barton.. = K = 1. R.5-5 0. 1974. 88 ROCK CLASSIFICATION SYSTEMS FOR ENGINEERING PURPOSES TABLE D-2—Behavioral characteristics of tunnelled ground in terms of SRF (J.5 Geological structure in respect of competent rock ExcavationInduced Ground Condition The two probable ranges of Q correspond to the given controlling criteria. or swelling Terminating creep Partially plastic arch 2. squeezing.05 Mild rock-bursting. 4. squeezing. 189-236.4-250 No fracturing. or swelling Random block displacement Keystone arching by mechanical interlocking of blocks Larger than 5 0.. squeezing. No. or swelling Large elastic deformation Highly stressed elastic arch 0. squeezing.4-640/ 0.001-0.4-100 No facturing. Lien.05-100/ 0.006 ing.001-50 No fracturing.006-50/ 0. N.4–I 6. squeezing..5 0. or swelling Excavation-Nature of Induced GroundGround Supporting Displacement Action Indefinite creep Visco-plastic arch 0. . squeezing. and Lunde. squeezing.
Report "Rock Mass Classification and Tunnel Reinforcement Selection Using the q System Astm_Barton 1988_HAVE BETTER VERSION CHECK"