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World Tunnel Congress 2008 - Underground Facilities for Better Environment and Safety - India

Evaluation of TBM performance in a Himalayan tunnel

R.K. Goel Central Institute of Mining and Fuel Research, Roorkee, India

SYNOPSIS: An estimation of excavation rate is needed for time planning, cost control and choice ofexcavation method in order to make tunnel boring economic in comparison with the conventional drill and blast method. As a consequence, efforts have been made to correlate TBM performance in terms ofpenetration and advance rates with rock mass and machine parameters, either through empirical approach or physically based theories. The TBM performance has been evaluated using the QTBM and rock mass excavability (RME) index in the head race tunnel (HRT) of a hydroelectric project in the Himalayas and presented in the paper alongwith thedescription of QTBM and RME index. Keywords: TBM; Himalayan tunnelling; QTBM; RME index; Quartzites.

1. INTRODUCTION Tunnel boring was originally attempted over 150 years ago. The original attempts are generally considered failures, except for the 1.5km Shakespeare tunnel in Dover, a part of original Channel tunnel, bored over 100 years ago [1]. Another major attempt to establish tunnel boring was made in the United States during the early 1950s and continuing into the 1960s with some success in soft rocks. The use of tunnel boring machines (TBMs) increased into the 1960s and 1970s with technological advances that allowed successful tunnel boring in harder as well as less competent rocks at higher advance rates. Since then, the development of TBM has made a great progress. Rapid development in technology improves the capacities of thrust and torque of TBM. Different TBM types, such as gripper, open face, earth pressure balance (EPB), slurry, single and double shield, mixed shield and convertible shield are designed to suit for the different ground conditions [2]. TBM technology practically has now reached a stage of development where a tunnel can be bored in any rock and ground.

Todays TBMs can reach extremes of 1000m/month [3] but advance rates of less than 50m/month or even less may be experienced in adverse geological conditions or when support measures fail to maintain tunnel stability until the final lining [4]. The Lotschberg base tunnel in

Switzerland with an overburden depth of up to 2000m was partially excavated by a gripper rock TBM with diameter of 9.4m. It achieved 40.5m advancement in 20 hours in hard rock of 160-280MPa. Tunnelling requiring TBMs with larger diameter than ever before challenges TBM technology constantly. A TBM with diameter of 11.74m was used for Pinglin tunnel in Taiwan [5] and a TBM with diameter of 12.84m was used for Hida tunnel in Japan [6]. At the Kuala Lumpur SMART tunnel in Malaysia, the TBM has a diameter of 13.20m. The largest rock TBM at moment is 14.4m in diameter to be used for the excavation of the Niagara tunnel in Canada in limestone, sandstone and shale with strength up to 180MPa [2].

TBM excavation represents a big investment in an unflexible but potentially very fast method of excavation and supporting a rock tunnel. When unfavourable conditions are encountered without warning, time schedule and practical consequences are often far greater in a TBM driven tunnel than in a drill and blast tunnel [4]. The unfavourable conditions can be produced by either a rock mass of very poor quality causing instability of the tunnel or a rock mass of very good quality (i.e. strong and massive rock mass) determining very low penetration rates.

A reliable estimation of excavation rates is needed for time planning, cost control and choice of excavation method in order to make tunnel boring

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economic in comparison with the classical drill and blasting method. Performance of a TBM is measured in terms of both the penetration rate and the advance rate. Penetration rate (PR) is defined as the distance excavated divided by the operating time during a continuous excavation phase, while advance rate (AR) is the actual distance mined and supported divided by the total time and it includes the downtime for TBM maintenance, machine breakdown, and tunnel failure [7]. Even in a stable rock, the rate of advance AR is considerably lower than the net rate of penetration PR, and utilization coefficient (U = AR/PR) in the order of 30-50% have been reported mainly due to TBM daily maintenance [8]. In low quality rock, the penetration rate can be potentially very high but the support needs, rock jams and gripper bearing failure result in slow advance rate, with utilization coefficient as low as 5 10% or less [4].

Simple performance correlations have been developed from data on conventional rock strength testing at the laboratory scale. These equations relate the penetration rate with intact rock parameters like the uniaxial compressive strength, the rock tensile strength or the rock fracture toughness, showing good predictive ability in the case of homogeneous low-fractured rocks. In jointed rocks the presence of discontinuities reduces the rock mass strength increasing the rate of penetration for a given TBM thrust [8]. Moreover, as studied by Zhao and Gong [2] the penetration rate is influenced by the joint orientation with respect to tunnel axis and the joint spacing. Hence, it is understood that the predictive equations should be based on rock mass properties rather than intact rock strength, for example, relating TBM performance with rock mass strength derived from the standard rock mass classifications.

Efforts have been made to correlate TBM performance with the rock mass and machine parameters. Two such approaches rock mass quality for TBM (QTBM) developed by Barton [9] and rock mass excavability (RME) index proposed by Bieniawski [10] have been briefly discussed in the paper. Subsequently, the TBM performance in a Himalayan tunnel has been evaluated using these two empirical approaches.

2. THE QTBM The QTBM method proposed by Barton [9] is based on an expanded Q-system of rock mass

classification, in which the average cutter force, abrasive nature of the rock, and rock stress level is accounted for. The new parameter QTBM is a function of 20 basic parameters, many of which can be simply estimated by an experienced engineering geologist [8]:

where RQD0 = RQD (%) interpreted in the

tunnelling direction. RQD0 is also used when evaluating the Q-value for rock mass strength estimation

Jn,Jr,Ja,Jw and SRF

= Ratings of Barton et al. [11] and are unchanged, except that Jr, Ja, should refer to the joint set that most assists (or hinders) boring

F = Average cutter load (tnf) through the same zone, normalized by 20 tnf,

Vcm or Vtm = Compressive and tensile rock mass strength estimates (MPa) in the same zone (the choice between Vcm and Vtm depend on the angle between tunnel axis and the major discontinuities or foliations of the rock mass to be bored),

Vcm = 5J (Qc)1/3 in MPa for unfaovurable orientation, where Qc = Q(Vc/100),

Vc = Uniaxial compressive strength of intact rock material in MPa,

Vtm = 5J (Qt)1/3 in MPa for favourable orientation, where Qt = Q(/I50/4),

I50 = Point load index on 50mm dia core in MPa,

J = Unit weight of the rock mass in g/cc, CLI = Cutter life index (e.g. 4 for

quartzites, 90 for limestone), q = Quartz content in percentage terms,

and VT = Induced biaxial stress on tunnel face

(approx. MPa) in the same zone, normalized to an approximate depth of 100m ( = 5MPa).

Major discontinuities would be faovourable or unfavourable depending upon the angle between the discontinuity and the tunnel axis or boring direction. In case the angle between the boring direction and the major discontinuity is more than 45+I/2, the condition is unfavourable other wise the condition is favourable. Here I is the angle of internal friction of the material [9].

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Figure 1. Suggested relation between PR, AR and QTBM [12]

Figure 1 is between QTBM and AR & PR. Penetration rate decreased with increase in QTBM value. The advance rate on the other hand increases up to QTBM = 1 and thereafter it decreases. There are three curves for AR for different time T. With increase in the TBM utilization time, the advance rate decreases. Conditions like tough, fair, very problematic, etc. at the top of the Fig. 1 suggest the ease or difficulty of boring.

2.1 Penetration and advance rates The ratio between advance rate (AR) and penetration rate (PR) is the utilization factor U,

AR = PR.U (2) The decelerating trend of all the data of PR and

AR may be expressed in an alternative format: AR = PR. Tm (3) where T is total time in hours and the negative

gradient (m) values are obtained using Fig. 1 and Eqn. (1).

2.2 Cutter wear The final gradient (-)m may be modified by the abrasiveness of the rock, which is based on a normalized value of CLI, the cutter life index. Values less than 20 give rapidly reducing cutter life, and values over 20 tend to give longer life. A typical value of CLI for quartzites might be 4 and for shale 80. Because of additional influence of

quartz content (q %) and porosity (n %), both of which may accentuate cutter wear, these are also included in Eq. 4 to give fine tuning to the gradient.

It has also been felt necessary to consider the tunnel size and support needs. Although large tunnels can be driven almost as fast (or even faster) as small tunnels in similar good rock conditions, more support-related delays occur if the rock is consistently poor in the larger tunnel [13]. Therefore, a normalized tunnel diameter (D) of 5m is used to slightly modify the gradient (m). (QTBM is already adjusted for tunnel size by the use of average rated cutter force.)

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Table 1. QTBM estimated from mean PR values, using Eq. 7 PR (m/hr) 0.1 0.5 1.0 5 10 QTBM 3.1 x 108 105 3125 1 0.03

The fine tuned gradient (-)m is estimated as

follows: Where D is the diameter of tunnel in meters, q

is the quartz content in per cent and n is the porosity in per cent.

Sometimes, PR becomes too fast due to the logistics and muck handling. There may be a local increase in gradient from 1 hr to 1 day as a more rapid fall occurs in AR.

2.3 Penetration and advance rate Development of a workable relationship between penetration rate PR and QTBM was based on a process of trial and error using case records [9]. Striving for a simple relationship, and rounding decimal places, the following correlation was obtained:

PR | 5 (QTBM)-0.2 (5) From Eq. 3 one can therefore also estimate AR

as follows: AR | 5 (QTBM)-0.2. Tm (6) One can also check the operative QTBM value

by back-calculation from penetration rate [12]:

QTBM | (5/PR)5 (7) A large range of QTBM is obtained from Eq. 7

for different value of PR as shown in Table 1. The QTBM approach can be used for used for

performance prediction and back analysis. Barton [12] emphasized that improvements and corrections are possible in the suggested QTBM model as more and more case records are available and tested.

3. ROCK MASS EXCAVABILITY (RME) INDEX

Bieniawski [10] analyzed over 500 case histories to develop the rock mass excavability (RME) index to estimate the performance of double-shield and

open-type TBMs. Excavability is defined as the rate of excavation expressed in machine performance in meteres per day.

Bieniawski et al. [14] found that the parameters with stronger influence in the average rate of advance (ARA), expressed in m/day, are abrasivity (or drillability), discontinuity spacing and the stand-up time. In addition, it was decided to include the two basic rock mechanics parameters - uniaxial compressive strength of the rock material and water inflow because in some cases these two factors influence strongly the TBM advance. Once the five parameters were selected, a weighted distribution was performed. These weights have been statistically analyzed, minimizing the error in the ARA prediction and resulting in the ratings shown in Table 2. Thus the RME index is based on the five input parameters listed in Table 2, together with the ratings associated with each.

Out of the five parameters listed in Table 2, three parameters uniaxial crushing strength, discontinuities in front of tunnel and groundwater inflow can be easily obtained by an experienced engineering geologist. Stand up time for TBM excavated tunnels has been obtained from RMRTBM.

Construction by TBM generally results in higher RMR values than for the same tunnel section excavated by drilling and blasting because of the favourable circular shape and lesser damage to the

surrounding rock mass by the process of machine boring. Following correlation is available between the RMRD&B and RMRTBM based on the work by Alber [15].

RMRTBM = 0.8 x RMRD&B + 20 (8) Using RMRTBM and the roof span of the

tunnel, the stand up time is obtained from Fig. 2. The RME index is obtained from summation

of the five input parameters in Table 3 which tabulates the ratings appropriate for the ranges listed. Using the RME index in the following Eq. 9 one can estimate the theoretical average rate of advance (ARAT) in m/day of TBM [14].

ARAT = 0.422 x RME - 11.61 (9)

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Table 2. Input parameters rating for the RME index [10] Uniaxial Compressive Strength of intact rock [0-25 points] Vc (MPa) 180 Rating 4 14 25 14 0 Drillability Drilling Rate Index [0-15 points] DRI 100 70 - 100 30 - 70 10 - 30

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Further, Bieniawski [10] evaluated Eq. 11 and found that the equation gives reliable results for double-shield TBM in rock with strength less than 45 MPa and open type TBM in rock with strength more than 45MPa.

4. TBM TUNNELLING IN THE HIMALAYAS Past experience of TBM tunnelling in the Himalayas is not encouraging. This is due to varying geology and presence of folds, faults, shear zones, water charged formations, etc. Therefore, the designers were hesitant to use TBM for tunnel excavations in the Himalayas. But, with the development of more advanced TBMs which have capability of drilling probe holes, grouting the rock mass, etc. the use of TBMs is now picking up in the Himalayan projects also.

TBM performance in the head race tunnel of Parbati Hydroelectric Project Stage II has been evaluated in the paper using the QTBM and RME index. The information of the Parbati Project Stage II, the head race tunnel and the TBM for this study has been extracted from the papers of Madan and Kumar [17] and Dodeja et al. [18].

4.1 The Project The Parbati Hydroelectric Project Stage II near Kullu in Himachal Pradesh has been utilizing TBM for the part excavation of head race tunnel (HRT) and the inclined penstock tunnels. The project envisages utilization of water from Parbati river to obtain a gross head of 862 m between dam site at Pulga and power house site on the right bank of river Sainj. Out of the total length of 31.5km head race tunnel (HRT), 9.05km was planned to excavate by TBM. TBM used for HRT excavation is an open-type Atlas Copco model TBM MK 27 of 6.8 m diameter.

4.2 Geology and other rock properties The area lies in lesser Himalaya between latitude 31q40N to32q15N and longitude 77q15E to 77q50E. The HRT passes through the upper section of the lesser Himalayas having the rocks from meta-sedimentary to crystalline type. Being very close to main central thrust (MCT), the rocks along HRT have undergone intense compression and thus are folded, faulted, foliated and jointed which is the typical characteristics of the Himalayan rocks.

The TBM section of HRT mostly comprises of granites/gneissose granites (RD19354 15700m) followed by quartzites (RD 15700 - 10300m). Bands of biotite schist, talc chlorite schist or metabasics can be expected along the entire length of the TBM drive. The granites are hard and massive exhibiting a well developed foliations in some areas [17]. The quartzites (locally known as Manikaran quartzites) are moderately to extremely hard. The schists, varying in thickness from one to tens of metres, are softer with altered clay observed at places. No exploratory drilling was done along the TBM section due to high rock cover. Numerous lineaments representing large joint fractures or faults crossing the HRT have been interpreted from satellite imagery and aerial photos. Total overburden along the TBM section varies from 100m at Hurla Nala (near Adit 2) to 1300m.

The orientation of the foliation planes in granite / gneissose granite is given as 060q/045q (dip direction / dip slope) and the foliation surfaces are described as very persistent (10-50m) and as rough/planar. The chlorite schist bands generally occur parallel to the foliation. With roughly north-south alignment of the HRT (N190q in drive direction) the schist bands will show an apparent dip transverse to the tunnel, which could have an unfavourable effect locally on wall stability, requiring immediate rock support.

Table 4. Adjustment factor for the influence of excavated length (FA) on TBM advance rate [10]

Tunnel length

excavated (km) Adaptation

Factor (FA)

0.5 0.68 1.0 0.80 2.0 0.90 4.0 1.00 6.0 1.08 8.0 1.12 10.0 1.16 12 0 1 20

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Table 5. Properties of joints of Manikaran quartzites[18] Set no.

Average Orientation

Persistence Aperture Spacing Condition

1 060o/052o to 055o/070o

1 to 10m Mostly tight, at places open 5 to 30mm

5 to 50cm at places open 5 to 30mm

Slightly rough/planar

2 225o/050o to 240o/040o

0.5 to 3m rarely exceed > 10m

Generally tight, at places open 1 to 5mm

Generally tight, at places open 1 to 5mm

Smooth/planar

3 310o/052o to 330o/070o

2 5m Tight to 5mm Tight to 5mm Slightly rough/smooth planar

4 135o/072o to 160o/040o

1 5m at places > 10m

Tight to 5mm Tight to 5mm Smooth planar

The Manikaran quartzites is exposed as thick litho-stratigraphic unit in the area. The quartzites are tectonically overlain by carbonaceous phyllite/phyllitic schist of Kullu formation and underlain by green bed member comprising of metabasics and chlorite schists of Banjar formation. The quartzites are folded into major overturned fold and the strike of unit is cutting obliquely to the tunnel alignment. The rock mass being fine grained, hard and compact in nature with high vertical cover is prone to create problems like rock bursting and popping. At places where sericitic mineral content has increased, the rock mass seems to be schistose in nature. Presence of chlorite schist bands in such rock with varying thickness from few centimeters to few meters was anticipated and observed also during tunnelling. There are four sets of joints with some random joints observed in the quartzites. The average orientation and properties of these joints is as under (Table 5).

Petrographical analysis shows that the quartzites are fine grained and compact, essentially consisting of quartz (92 - 95%) with accessory minerals muscovite (2 - 4%) and chlorite (2 3%). The per cent of strained quartz is 68 75%. At places the quartz grains are thrusted into each other indicating a penetrative deformation. It is observed that fine flakes of mica and chlorite are present as clusters along with fine grained crushed quartz [18]. Other properties of Manikaran quartzites are given in Table 6.

4.3 TBM for HRT The TBM being used for HRT is Atlas Copco Jarva MK 27 of 6.8m diameter. The main structure of TBM consists of the main body, torque tube with

front and rear bearing housing, together with the drive shaft and bearings. It is a refurbished machine. The maximum machine thrust is 18,550 kN and considered suitable for hard rocks. The machine is open type high performance with six 525kW main drive motors. There are 49 cutters of 432mm (17) diameter; maximum recommended operating load per cutter is 267 kN. Nominal cutter spacing is 65mm, the installed cutter head capacity is 3159kW and stroke length is 2.05m. Cutter-head drive includes six variable speed drive motors (VFD). Maximum cutter-head rotating speed is 5.77rpm. Maximum total gripping force is 55600kN carried over 4 gripper pads with 3.6m height and 1.4m width resulting in maximum rock pressure of 3.22MPa. TBM conveyor of 1000mm width has normal capacity of 875cum per hour. The conveyor has a straight alignment without the down dip in the

cutter head location. The machine is equipped with ring-mounted probe drilling equipment, which can cover 360q of tunnel. The machine also has two number probe drills. Maximum probe length is about 120m. The probe drilling is found to be quite useful in Himalayan tunnels to ascertain the geology ahead of the working face. The probe drills are also intended for use in the installation of drain holes and for rock grouting. TBM has arrangement of rock bolting, wet and dry shotcreting and ring beam erector for erection of heavy steel arches. The high performance injection grouting plant is also equipped with the machine.

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Table 6. Geotechnical properties of Manikaran quartzites [18]Location of Samples Properties Direction of Test with Respect

to Foliation Surface samples Tunnel samples Parallel to foliation 121.45 Unconfined compressive strength

(Vc), MPa Perpendicular to foliation 267.2 80-150

Parallel to foliation 16.2 Brazilian tensile strength, MPa Perpendicular to foliation 24.6

6-13

Modulus of Elasticity, GPa -- 12.5 -- Poissons ratio -- 0.21 -- Porosity (n), % -- 1.74 2.75 0.4 7 (say 2.0) Water absorption, % -- 0.89 1.31 0.1 0.9 Density (J), g/cc -- 2.68 2.74 2.5 2.7 (2.6) Schmidt hardness number -- 45 49 50 60 Chercher abrasivity index (CAI) -- 4.02 5.00 4.96 5.13 Brittleness index (BI) -- 74* 77 Siever j value (Sj) -- 9.15 10.50 7.1 Drilling rate index (DRI) -- 71 73 78 * BI value assumed to determine DRI value for surface samples

x Total excavation of TBM till October 2006 - 510m x Total time in days - 218 days x Total time in hours - 5232 hrs x TBM Utilization for different activities

(i) Cutting time - 10.31% (ii) Rock support time - 2.95% (iii) Extra rock support time - 11.48% (iv) Shotcrete/Backfill - 11.14% (v) Cutter change - 7.11% (vi) Cutter inspection - 3.55% (vii) Maintenance time - 13.26% (viii) Probing time - 1.27% (ix) Delays - 38.93%

x Total cutting time in hours (@10.31%) - 539 hrs x Advance Rate (Excavated length/total time in hrs) - 0.097m/hr x Penetration Rate (Excavated length/cutting time in hrs) - 0.946m/hr

5. TBM PERFORMANCE EVALUATION The performance of Atlas Copco Jarva MK 27 TBM in Manikaran quartzites has been evaluated using the QTBM and RME index. Various details of actual TBM working in tunnel obtained from Dodeja et al. [18] in quartzites are as follows:

It may be seen in the above that maximum TBM utilization time has gone in to delays and then in maintenance. Out of total time of 5232 hours, only 539 hours the TBM was actually used. 5.1 Estimation of advance rate by QTBM Equation 1 is used for estimating QTBM. The rating of all the parameters has been obtained/estimated as

per the geological and geotechnical information of Manikaran quartzites. Values of various parameters of QTBM are listed in Table 7.

The penetration rate from Eq. 5 for QTBM = 290 works out to be equal to 1.6m/hr. The advance rate for ideal conditions from Fig. 1 is approximately 1.0 m/hr for T=24 hrs.

For estimating the advance rate using Eq. 6, gradient m is estimated using Eq. 4 and the tunnel diameter D = 6.8m, quartz content of 93.5%, porosity n = 0.4% and m1 = -0.5 for Q = 0.176 from Table 1. Accordingly m = -0.73.

Using the value m = -0.73 and PR = 1.6m/hr, the advance rate of TBM is estimated using Eq. 6 for different time T in hours as given in Table 8.

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Table 8. Advance rate for different time T and PR = 1.6m/hr Period PR 1 shift 1 day Time (T) Hours 1 8 24 AR (m/hr) 1.6 0.35 0.157

Table 7. Estimation of QTBM Parameter Description Rating/value RQD0 60% (Evaluated as per above details and using details

collected by the author; tunnel axis orientation in TBM length is N10E- S10W)

60

Jn Four plus random joints 15 Jr Slightly rough planar to smooth 1 Ja Unaltered to slightly altered chloritic coating 1 Jw Moist 0.66 SRF Rock strength 80-150MPa, rock cover around 1000m,

rock bursting is experienced 15

Q (RQD/Jn)(Jr/Jn)(Jw/SRF) 0.176 Vc (MPa) 80-150, average 115 (Table 6) 115 J (g/cc) From Table 6 2.6 Vcm(MPa) 5J(Q. Vc /100)1/3 7.63 F (tnf) Assumed as 15 15 CLI Quartzites is mainly composed of quartz 4 q 92-95%; average 93.5% 93.5 VT (MPa) 2J*rock cover in meters (rock cover is assumed as

1000m) 52

QTBM Eq. 1 289.85 (290)

It may be seen that the advance rate obtained from Fig.1 and from Eq. 6 is different. This is because of the time-dependent fine tuning suggested by Barton [12] considering the effect of the size of the tunnel, the hardness of the rock to be bored and the porosity.

5.2 Estimation of Advance Rate by RME Index Out of the five parameters for estimating the RME index (Table 3), the stand-up time is to obtained from the RMRTBM and the Fig. 2. Accordingly, first of all RMRD&B is estimated to get RMRTBM from Eq. 8. Subsequently, the rating of RME index parameters is obtained as indicated in Table 9.

The real average rate of advance (ARAR) for the TBM as estimated by the RME index is 0.45 m/hr (Table 9).

6. COMPARISON OF TBM PERFORMANCE The actual penetration and advance rates of TBM in the 510m length through the Manikaran quartzites in the HRT of Parbati stage II Project are reported as 0.956 m/ hr and 0.097 m/hr respectively [18]. The penetration rate and the advance rate as obtained by QTBM are 1.6m/hr and 0.157 m/hr for 24 hrs (Table 9) respectively. The advance rate, on the other hand, by RME index is 0.45m/hr.

In fact more than 50 % of the TBM utilization time is consumed in the delays because of some or the other reasons and in the maintenance, which has also adversely affected the advance rate. In case the time because of the delays (39%) only is discarded, the advance rate can be increased to 0.16m/hr. This is incidentally almost matching with the advance rate estimated by QTBM for 24 hrs.

The actual penetration rate is 40% less than the estimated value obtained from QTBM. As highlighted by Dodeja et al. [18], following are some of the reasons for low values of penetration and advance rates of TBM. x High cutter consumption due to abrasive and

compact nature of the rock mass x Frequent detachment of rock mass in the zone

inaccessible for rock supporting, i.e. in face and above cutter head

x Rock bursting/ Popping x Occurrence of heavy water ingress x Absence of detailed geological exploration and

therefore occurrence of unfavourable conditions without warning.

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Table 9. Estimation of RME index Parameter Description Rating/value RQD 60% 13 Uniaxial compressive strength (UCS) for RMR

Strong to very strong (80 150 MPa) 7

Spacing of discontinuities Moderate to close 8 - 10 Condition of discontinuities Rough and slightly weathered, wall rock separation

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2. Zhao, J. and Gong, Q.M. (2006). Rock mechanics and excavation by tunnel boring machine Issues and challenges, Proc 4th ARMS and ISRM Int Symp 2006 on Rock Mech in underground construction, November, Singapore, pp. 83-96.

3. Wallis, S. (1999). Record settings TBMs on Chinas long yellow river drives, Tunnel 1999, Vol. 1, pp. 19-26.

4. Barla, G. and Pelizza, S. (2000). TBM tunnelling in difficult ground conditions, GeoEngineering 2000, Int Conf on Geotechnical and Geological Engineering, Melbourne, Australia.

5. 5Tseng, Y. Y., Wong, S. L. and Chu, B. (1998). The Pinglin mechanized tunnelling in difficult ground, 8th International IAEG Congress, A.A. Balkema, Rotterdam, pp. 3529-3536.

6. Miura, K., Kawakita, M., Yamada, T. and Sano, N. (2001). Study on the application of a large TBM to Hida highway tunnel, Modern Tunnelling Science and Technology, Adachi et al (eds), Swets and Zeitlinger, pp. 481- 486.

7. Alber, M. (1996). Prediction of penetration and utilization for hard rock TBMs, Proc ISRM International Symposium Eurock96, A. A. Balkema, Rotterdam, pp 721-725.

8. Sapigni, M., Berti, M., Bethaz, E., Busillo, A. and Gardone, G. (2002). TBM performance estimation using rock mass classification, Int J Rock Mech and Min Sci, Vol. 39, pp. 771-788.

9. Barton, N. (2000). TBM tunnelling in jointed and faulted rocks, A.A. Balkema, p. 173.

10. Bieniawski, Z. T. (2007). Predicting TBM excavability, Tunnels and Tunnelling International, September.

11. Barton, N., Lien, R., and Lunde, J. (1974). Engineering classification of rock masses for the design of tunnel support, Rock Mechanics, Vol. 6, No. 4, Pringer-Verlag, pp. 189-236.

12. Barton, N. (1999). TBM performance estimation in rock using QTBM, Tunnels and Tunnelling International, September, pp. 30-34.

13. Dalton, F.E., DeVita, L.R., Macaitis, W.A. (1993). TARP tunnel boring machine performance, Chicago, Proc. RETC Conf Boston, US, SME, Eds. Bowerman and Monsees, pp. 445-451.

14. Bieniawski, Z. T., Caleda, B., Galera, J. M. and Alvares, M.H. (2006). Rock mass excavability (RME) index, ITA World Tunnel Congress (Paper no. PITA06-254), April, Korea.

15. Alber, M. (2000). Advance rates for hard rock TBMs and their effects on project economics, Tunnelling and Underground Space Technology, Vol. 15, No. 1, pp. 55-64.

16. Bieniawski, Z. T. (1989). Engineering rock mass classification, Wiley & Sons, New York, p. 251.

17. Madan, M.M. and Kumar A. (2004). Tunnel boring machine (TBM) for construction of Parbati project yunnel Problem faced during commissioning and suggestions for future projects, Proc. Int Conf on Tunnelling Asia 2004, December, New Delhi, Inida, pp. VII45-VII61.

18. Dodeja, S.K., Mishra, A.K. and Virmani, R.G. (2007). Performance of tunnel boring machine in Manikaran quartzite with special reference to construction of HRT at Parbati hydroelectric project, Stage II, NHPC, Distt Kullu, H.P., India, Proc. Workshop on Rock Mech and Tunnelling Techniques, October, Gangtok, India, pp.153-168.

BIOGRAPHICAL DETAILS OF THE AUTHOR

Dr. R.K. Goel post-graduated in Applied Geology from University of Roorkee (now IIT Roorkee) in 1982. He obtained Ph.D. in Mining Engineering (Tunnelling Technique) at the VNIT, Nagpur. From 1982 he worked for Central Mining Research Institute (now Central Institute of

Mining and Fuel Research), specializing in the application of engineering geology and rock mechanics in the design of tunnels and underground space. Currently he hold the position of Scientist F (Deputy Director).