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इंटरनेट मानक Disclosure to Promote the Right To Information Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public. “जान1 का अ+धकार, जी1 का अ+धकार” “प0रा1 को छोड न’ 5 तरफ” Mazdoor Kisan Shakti Sangathan Jawaharlal Nehru “The Right to Information, The Right to Live” “Step Out From the Old to the New” IS 15026 (2002): Tunneling Methods in Rock Masses -- Guidelines [CED 48: Rock Mechanics] “!ान $ एक न’ भारत का +नम-ण” Satyanarayan Gangaram Pitroda ““IInnvveenntt aa NNeeww IInnddiiaa UUssiinngg KKnnoowwlleeddggee”” “!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता हहहहै””ै” Bhartṛhari—Nītiśatakam “Knowledge is such a treasure which cannot be stolen” IS 15026:2002 (Reaffirmed - 2012) IndianStandard TUNNELING METHODS IN ROCK MASSES — GUIDELINES ICS 93.060 0 BIS 2002 BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002 June 2002 Price Group 10 Rock Mechanics SectionaI Committee, CED 48 FOREWORD This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the Rock Mechanics Sectional Committee had been approved by the Civil Engineering Division Council. Tunneling is an art practized by all engineers, geologists, planners and people. Failures should be regarded as challenges and opportunities for generating new vital knowledge and thereby increasing self-reliance in the tunneling. The key to success is team spirit and love for rocks and nature. The most challenging construction problem is the squeezing ground condition which is encountered in weak rock masses under high rock cover. Further the shear zones are met frequently in lower Himalayan region. Special treatment is necessary to support shear zones in the tunnels. The design of underground excavations is, to a large extent, the design of underground support system. These can range from no support in the case of a temporary excavation in good rock to the use of fully grouted and tensioned bolts or cables with mesh; and sprayed concrete of Steel Fibre Reinforced Shotcrete (SFRS) or steel rib with concrete for the support of a large permanent civil engineering excavation. The philosophy of design of any underground excavation should be to utilise the rock mass itself as the principal structural materials, creating as little disturbance as possible during the excavation process and adding as little as possible in the way of shotcrete or steel supports. The extent to which this design aim can be met depends upon the geological conditions which exist atsite and the extent towhich the designer isaware ofthese conditions. There are many difficult geological conditions and extraordinary geological occurrences such as intra-thrust zones, very wide shear zones, geothermal zones of high temperature, cokllhot water springs, water charged rock masses, intrusions, etc. These are very difficult to forecast. Innovative methods of tunneling will have to be invented. Experts must be consulted. The composition ofthe technical Committee responsible for the formulation ofthis standard isgiven in Annex A. For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result ofatest oranalysis, shall be rounded off inaccordance with IS 2:1960 ‘Rules for rounding off numerical values (revi.re~’. The number of significant places retained inthe rounded off value should be the same as that of the specified value in this standard. & 1S 15026:2002 IndianStandard TUNNELING METHODS IN ROCK MASSES — GUIDELINES 1 SCOPE [S No. Title Part 2 Rock mass quality for predic- This standard provides guidelines for rock tunneling tion of support pressure in under- in Himalayan and other geological regions in India. ground openings In view of the difficulties in forecasting geological formations along deep and long tunnels particularly 3 PROBE HOLES in complex geological environment, the suggested Long tunnels, sometime pass through complex strategy of tunneling is such that tunneling could be geological conditions particularly in case of deep done smoothly in usually all ground conditions. This tunnel. Geological predictions in deep tunnel are hard standard recommends strongly adoption of the steel to make merely on the basis of surface observations. fibre reinforced shotcrete to cope up with even If the site conditions require, probe holes may be squeezing ground conditions. The use of steel ribs drilled at the face of the tunnel for about 20 m length should be restricted to highly squeezing or swelling along the tunnel alignment. These probe holes will rock conditions only. give reliable geological and geotechnical information in advance of tunneling. It will help in suggesting 2 REFERENCES the strategy of tunneling. The Indian Standards given below contain provisions which through reference in this text, constitute 4 EFFECT OF SEISMICITY provision of this standard. At the time of publication, A tunnel in aseismic area is likely to be affected near the editions indicated were valid. Afl standards are the portals and inneighbourhood of faults and thrusts. subject to revision, and parties to agreements based The effect is observed to be up to a distance along on this standard are encouraged to investigate the tunnel within + B on both sides of the faults/thrusts, possibility of applying the most recent editions of the where B is spanlsize of the opening. The design standards indicated below: support pressure in the affected length of tunnel may IS No. Title be taken as 1.25 times of ultimate support pressure 432 Mild steel and medium tensile steel [see IS 13365 (Part 2)]. bars and hard-drawn steel wire for concrete reinfor c ement: 5 TUNNEL INSTRUMENTATION (Part 1): 1982 Mild steel and me dium tensile steel 5.1 Instrumentation oftunnel openings should be done bars (third revision) where squeezing ground condition is expected. The (Part 2): 1982 Hard-drawn steel wire (third revi- survival rate of tunnel instruments is generally as low sion) as 30 percent. Therefore many sections of the tunnel 456:2000 Code of practice for plain and should be instrumented so that enough instruments reinforced concrete ~ourth revision) survive and reliable data are obtained. The post 800:1984 Code of practice for general monitoring of support system in squeezing ground construction in steel should also be carried out until support system has 4880 Code ofpractice for design oftunnels stabilized with time. In cases of squeezing ground (Part 6) :1971 conveying water: Part 6 Tunnel conditions, observed vertical and horizontal tunnel support closures should be less than four percent of tunnel 5878 Code of practice for construction of width and height, respectively. tunnels conveying wate~ 5.2 Instrumentation should also be done at other (Part 4): 1971 Tunnel supports locations as per needs of the site. (Part 6): 1975 Steel lining 9012:1978 Recommended practice for 6SELECTION OF TYPE OF SUPPORT SYSTEM shotcreting 9179:1979 Method for the preparation of rock 6.1 Table 1 classifies various ground conditions for specimen for laboratory testing tunneling. Rock bursts are rare in tunneling for civil 13365 Guidelines for the quantitative engineering projects. Table 2 suggests the method of (Part 2): 1992 classification systems of rock mass: excavation, type of supports and precautions for I ‘, & IS 15026:2002 Table 1Classification of Ground Conditions for Tunneling (Clause 6.1) S1 Ground sub-class Reek Behaviour No. 1) Competent self-supporting Massive rock mass requiring no support for tunnel stability i]) Incompetent non-squeezing — Jointed rock mass requiring support fortunnel stability Ill) Ravening Chunks or flakes of rock mass begin to drop out of the arch orwalls after the rock mass isexcavated Iv) Squeezing Mild Squeezing Rock mass squeezes plastically into the tunnel and the (da =I-3(%) phenomena is time dependent; rate ofsqueezing depends Moderate Squeezing upon the degree of overstrcss; occursatshallowdepths (rda =3-5%) in weak rock masses like shales, clay, etc. hard rock masses under high cover may experience slabbing/ High Squeezing popinglrock burst (u,Ja>5) v) Swelling Rock mass absorbs water, increases in volume tind expands slowly into the tunnel, forexample montmorill - onite clay — vi) Running Granular material becolmes unstable witbin steep shear zones vii) Flowing A mixture of soil like material and water flows into the tunnel. The material can flow from invert as well as from tbe face crown and wall and can flow for large distances completely filling the tunnel insome cases \li]) Rock burst Aviolent failure inhard and massive rock masses ofclass 11type (UCS test on class IItype rock shows reversal of strain after peak failure), when subjected to high overstress . where U. —— radial tunnel closure; u=tunnel radius; and IiAlo = normalized tunnel closure inpercentage. V:irjolls ground conditions. where the loads and deformation do not attain stable values, itisrecommended that pressure measurements ,--- NOTE —Squeezing isruled outiftheobserved in-situ maximum should be made by using flat jack or pressure cells. [angential strain (ratio ofdownward crown displacement tothe [unnel radius) is less than the critical strain (ratio of UCS to 6.1.3 In the absence of any data of instrumentation, n)odulus of elasticity of rock mate r ial) in case of properly rock load or support pressure may be estimated by Q Suppol-tedtLllllldS. system as given in IS 13365 (Part 2). 6.1. I Before taking up the design of supports, the rock 6.1.4 As the tunnels generally pass through different load and pressure likely to act on the supports shall be types of rock formations, it may be necessary to estimated. The determination of rock load is complex workout alternative cross-sections of the tunnel problem, This complcxit yis due to inherent difficulty depicting other acceptable types of support systems. of predicting the primary stress conditions in the rock These types may be selected to match the various mass (prior to excavation) and also due to the fact that methods of attack that may have to be employed to get the magnitude of the secondary pressure developing through the various kinds of rock formations likely to after the excavation of the cavity depends on a large be encountered. The ‘A’ and ‘B’ lines shall be shown number of variables, such as size and shape of cavity, on these sections. depth of cover, disposition of strike and dip of rock 6.1.5 The support system shall be strong enough to formation in relation to alignment of tunnel, method carry the ultimate loads. For a reinforced concrete of excavation, period of time elapsing between exca- lining itiseconomical to consider the steel supports as vation and the time when the rock is supported and an integral part of the permanent lining. the rigidity of support. These pressures may not 6.1.6 Temporary support system must be installed develop immediately after excavation but may take a within stand-up time for safety of workmen but not long period after excavation to develop due to too early. adjustnlents/displacctnents in the rock mass. 7 STEEL FIBRE REINFORCED SHOTCRETE 6.1.2 In tnajor tunnels it is recommended that as (SFRS) excavation proceeds, load cell measurements and diametrical change measurements are carried out so 7.1 Steel fibre reinforced shotcrete either alone or in that rock loads may be correctly estimated. In rock s 2 IS 15026:2002 Table 2 Method of Excavation, Type of Supports and Precautions to be Adopted for Different Ground Conditions (Clause 6.1) SI Groond Excavation Method Type of Support Precautions No. Classification i) Self-supporting Tunnel Boring Machines No support or spot bolting with a Look out for localised competent (TBM) or full face drill and thin layer of shotcrete to prevent wedge/shear zone. Past contra-blast widening ofjoints experience discourages use of TBM if geological conditions change frequently ii) Non-squeezing Full face drill and controlled Flexible supporc shotcrete and First layer of shotcrete competent blast by boomers pre-tensioned rock bolt supports should be applied atter some of required capacity. Steel tibre delay but within the stand-up reinforced shotcrete (SFRS) may time to release the strain ormay not berequired energy ofrock mass iii) Ravening Heading and bench; drill and Steel support with struts/pre- Expect heavy loads inclu- blast manually tensioned rock bolts with steel ding side pressure tibre reinforced shotcrete (SFRS) may ormay not berequired iv) Mild squeezing Heading and bench, drill and Full column grouted rock anchors [nstall support atler each blast and SFRS, floor to be shotcreted blast circular shape is ideal; tocomplete supporting side pressure is expected; do not have a long heading which delays completion of support ring v) Moderate squeezing Heading and bench, drill and Flexible supporu full column Install support afier each blast grouted highly ductile rock blast; increase the tunnel anchors and SFRS. Floor bolting diameter to absorb desirable to avoid floor heaving, to develop closure circular shape is areinforced rock frame. Incase of ideal; side pressure is steel ribs, these should be expected; instrumentation is installed and embedded in shot- essential crete to withstand the high support pressure vi) High squeezing Heading and bench in small Very flexible support, full column Increase the tunnel diameter tunnels highly method in grouted ductile rock anchors and to absorb desirable closure; large tunnels; use forepoling SFRS. Yielding steel ribs with provide invert support as ifstand-up time islow struts when shotcrete ,fails early as possible’ to mobilise repeatedly; steel ribs should be full support capacity long- embedded in sbotcrete to term instrumentation is withstand high support pressure; essential; circular shape is close ring by erecting invert ideal support; floor bolting to avoid floor heaving; sometimes steel ribs with loose backfill is also used to release the strain energy in controlled manner (tunnel closure more than 4 percent shall not bepermitted) vii) Swelling Full face or heading and Full column grouted rock anchors Increase the tunnel diameter bench: drill and blast with SFRS shall be used around to absorb the expected the tunnel; increase 30 percent closure; prevent exposure of thickness ofshotcrete due to weak swelling minerals to bond of the shotcrete with rock moisture monitor tunnel mass; erect invert strut. The tirst closure layer of shotcrete is sprayed immediately to prevent ingress of moisture into rock mass viii) Running and flowing Multiple drift method with Full column grouted rock anchors Progress is very slow. fore-poles; sometimes and SFRS, concrete lining up to Trained crew should be advance grouting of the face, steel liner in exceptional deployed ground is essential; shield cases with shield tunneling tunneling may be used insoil like condition ix) Rock burst Full face drill and blast Fibre reinforced shotcrete with Micro-seismic monitoring is full column resin anchors immediately afier excavation IS 15026:2002 combination with rock bolts (specially in large to meet the requirements of early strength. openings) provides a good and fast solution for both 7.4 Steel fibres make up between 0.5 to 2 percent of initial and permanent rock support. Being ductile, it the total volume ofthe mix (1.5to 6percent by weight). can absorb considerable deformation before failure. Shotcrete mixes with fibre contents greater than 7.2 Controlled blasting should be used preferably. The 2 percent are difficult to prepare and shoot. advantage of fibre reinforced shotcrete is that smaller 7.5 The steel fibres are manufactured by cutting cold thickness of shotcrete is needed, in comparison to that drawn wires as per IS 432 (Parts 1and 2). of conventional shotcrete. Fibre reinforced shotcrete is required, specially in rock conditions where support 7.6 Some of the impoctant parameters of steel fibres pressure ishigh. Use of tibre-reinforced shotcrete along shall be: with resin anchors isalso recommended for controlling a) Geometrical shape — as shown in Fig. 2. rock burst conditions because ofhigh fracture toughness Length of the fibres may be 20 to 40 mm. of shotcrete due to specially long steel tibres. This can Recommended sizes of the tibres are 25 to also be used effectively in highly squeezing ground 35 mm X0.40 mm $ conditions. It ensures better bond with rock surface. b) Aspect ratio (length/equivalent diameter) = With mesh, voids and pockets might form behind the 60 to 75. mesh thus causing poor bond and formation of water seepage channels as indicated in Fig. 1. c) Ultimate ten~ile strength > 1000 MPa d) Shear strength of SFRS = 8 to 10 MPa 7.3 The major draw-back of normal shotcrete isthat it israther weak intensile, flexural and impact resistance 7.7 Shotcrete Ingredients strength. These mechanical properties are improved 7.7.1 Shotcrete ingredients infibre reinforced shotcrete by the addition of steel fibres. Steel fibres are comm- are : only made into various shapes to increase their bond- ing intimacy with the shotcrete (see Fig. 2). Itisfound a) Cement that hooked ends type of steel fibres behave more b) Micro silica fumes (8-15 percent by mass of favorably than other types of steel fibres in flexural cement) for improving pumpability and strength and toughness. Accelerators play a key role strength and to reduce rebound . REINFORCED -S HOT CRETE 1 \ FIG. 1DIFFERENCE IN SHOTCRETE CONSUMPTION WHEN WIRE MESH OR STEEL FIBRES A Es045mm --lr ().5mm + & 0.53mm (A) TYPICAL FIBRE WITH RECTANGULAR CROSS-SECTION (B) TYPICAL FIBRE WITH CIRCULAR CROSS-SECTION FIG. 2 TYPICAL FIBRES USED IN SHOTCRETE WORK 4 ?$ IS 15026:2002 ,, $ ,. c) Aggregates 7.8 Capacity of Fibre Reinforced Shotcrete d) Water 7.8.1 It is assumed that the fibre reinforced shotcrete e) Hydration control agent (wet mix) I is intimately in contact with the rock mass and having f) Super plasticizers (3-6 l/m3) for slump in- the tendency to fail by shearing. crease and improvement in strength 7.8.2 Capacity of tibre reinforced shotcrete isgiven by g) Accelerators (2-5 percent by mass of cement) I h) Curing agent Ufs, tfsc I I) Steel fibres P=fsyc ,..(1.1) fsc Shotcrete ingredients and properties are listed in where f Table 3. shear strength of fibre reinforced 9fsc = Table 3 Typical Steel Fibre Reinforced shotcrete (550 t/m2), Shotcrete Mix t = thickness of fibre reinforced shot- kc I crete (m), S1 Material Mean Aggregate Mean Aggregate No. Size 6.35 mm Size 10mm B= size of opening (m), I Quantity Quantity BFf,c = distance between vertical planes ofmaxi- kg/m’ kglm~ mum shear stress in SFRS (m), i) Cement 446-558 >445 F,,c = 0.6 * 0.05, and ii) Blended sand 6,35 mm maximum size 1483-1679 697-880 Pr,c = support capacity of fibre reinforced iii) 10mmaggregate 700-875 shotcrete lining (t/mz). iv) Steel tibre 39-157 39-150 v) Accelerator Vanes Varies 7.8.3 The thickness of fibre reinforced shotcrete lining I vi) Water/cement 0.40-0.45 0.40-0.45 may be estimated by substituting ultimate support (byweight) pressure (p,OOf)in Equation 1.1 in place of pf,c. Additional layers of shotcrete should be sprayed to 7.7.2 Key to successful SFRS construction isthe use of arrest tunnel closure if needed. aWCIItrained and experienced shotcrete application crew. 7.8.4 Proper equipment should be used to avoid 7.7.3 Prc-construction and post-construction testing bunching of steel fibres and to ensure homogeneous of shotcrete shall be done for quality assurance as per mixing of fibres in the shotcrete. IS 9012. 7.7.4 To increase the standup time, for a full front 7.9 Drainage System in Road/Rail Approach tunnel profile in poor rock quality condition (or Tunnels Within Water-Charged Rock Mass squeezing rock conditions), spiling dowels are provided (see Fig. 3). 7.9.1 Strips of about 50 cm width along the side walls and roof should not be shotcreted to allow free seepage 7.7.5 To stabilize the broken zone insqueezing ground of ground water otherwise shotcrete is likely to crack conciitions more than one layers of SFRS is provided due tobuilding up of seepage pressure behind shotcrete (.SCVFig. 4). in heavily water-charged formations. /r ROCK BOLTS WITH FIBRE FIG. 3 ARRANGEMENTOFSptL[NGDOWELWITHTHEADVANCEMENTOFTUNNELFACE 5