Evaluation of TBM performance in a Himalayan tunnel

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 of excavation 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 of penetration 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 Q TBM 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 the description of Q TBM and RME index. Keywords: TBM; Himalayan tunnelling; Q TBM ; 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. Today s 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 1522

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 (Q TBM ) 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 Q TBM The Q TBM 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 Q TBM is a function of 20 basic parameters, many of which can be simply estimated by an experienced engineering geologist [8]: where RQD 0 = RQD (%) interpreted in the tunnelling direction. RQD 0 is also used when evaluating the Q-value for rock mass strength estimation J n,j r,j a,j w and SRF = Ratings of Barton et al. [11] and are unchanged, except that J r, J a, 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, σ cm or σ tm = Compressive and tensile rock mass strength estimates (MPa) in the same zone (the choice between σ cm and σ tm depend on the angle between tunnel axis and the major discontinuities or foliations of the rock mass to be bored), σ cm = 5γ (Q c ) 1/3 in MPa for unfaovurable orientation, where Q c = Q(σ c /100), σ c = Uniaxial compressive strength of intact rock material in MPa, σ tm = 5γ (Q t ) 1/3 in MPa for favourable orientation, where Q t = Q(/I 50 /4), I 50 = Point load index on 50mm dia core in MPa, γ = 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 σ θ = 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+φ/2, the condition is unfavourable other wise the condition is favourable. Here φ is the angle of internal friction of the material [9]. 1523

Figure 1 is between Q TBM and AR & PR. Penetration rate decreased with increase in Q TBM value. The advance rate on the other hand increases up to Q TBM = 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. 2.2 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 Figure 1. Suggested relation between PR, AR and Q TBM [12] 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. T m (3) where T is total time in hours and the negative gradient (m) values are obtained using Fig. 1 and Eqn. (1). 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). (Q TBM is already adjusted for tunnel size by the use of average rated cutter force.) 1524

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 Q TBM 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 (Q TBM ) -0.2 (5) From Eq. 3 one can therefore also estimate AR as follows: AR 5 (Q TBM ) -0.2. T m (6) One can also check the operative Q TBM value by back-calculation from penetration rate [12]: Table 1. Q TBM estimated from mean PR values, using Eq. 7 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 RMR TBM. 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 PR (m/hr) 0.1 0.5 1.0 5 10 Q TBM 3.1 x 10 8 10 5 3125 1 0.03 Q TBM (5/PR) 5 (7) A large range of Q TBM is obtained from Eq. 7 for different value of PR as shown in Table 1. The Q TBM approach can be used for used for performance prediction and back analysis. Barton [12] emphasized that improvements and corrections are possible in the suggested Q TBM 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 surrounding rock mass by the process of machine boring. Following correlation is available between the RMR D&B and RMR TBM based on the work by Alber [15]. RMR TBM = 0.8 x RMR D&B + 20 (8) Using RMR TBM 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 (ARA T ) in m/day of TBM [14]. ARA T = 0.422 x RME - 11.61 (9) 1525

Table 2. Input parameters rating for the RME index [10] Uniaxial Compressive Strength of intact rock [0-25 points] σ c (MPa) <5 5-30 30-90 90-180 >180 Rating 4 14 25 14 0 Drillability Drilling Rate Index [0-15 points] DRI <80 80-65 65-50 50-40 <40 Rating 15 10 7 3 0 Discontinuities in front of the tunnel face [0 30 points] Homogeneity Number of joints per meter Orientation with respect to tunnel axis Homogeneous Mixed 0-4 4-8 8-15 15-30 >30 perpendicular Oblique Parallel Rating 10 0 2 7 15 10 0 5 3 0 Stand up time for TBM excavated tunnels [0-25 points] Hours <5 5-24 24-96 96-192 >192 Rating 0 2 10 15 25 Groundwater inflow [0 5 points] Litre/sec >100 70-100 30-70 10-30 <10 Rating 0 1 2 4 5 Figure 2. Stand-up time vs. roof span for various rock massclasses as per RMR (RMR in the figure is RMR TBM ) [16] Subsequently, to get real average rate of advance (ARA R ) of TBM from theoretical average rate of advance, Bieniawski [10] suggested three adjustment factors as follows: (i) Influence of the TBM crew (F E ): It is experienced that the TBM crew who handles the tunnelling machine every day have an important influence on the performance achieved. The influence of TBM crew is as give in Table 3 [10]. Table 3. Adjustment factor for the influence of TBM crew (F E ) on TBM advance rate [10] Effectiveness of the crew handling TBM and terrain Crew Factor (F E ) Less than efficient 0.88 Efficient 1.0 Very efficient 1.15 (ii) Influence of the excavated length (F A ): It has been seen that as the tunnel excavation increases the TBM performance is increased. This is believed to be because of the adaptation of the machine and the quantitative effect of this adjustment adaptation factor (F A ) is given in Table 4. (iii) Influence of tunnel diameter (F D ): Equation 9 was derived for tunnels with diameter close to 10m. In order to take into account the influence of different tunnel diameters, D (in meters), on the advance rate of TBM, a coefficient F D is proposed as given in Eq. 10 (Bieniawski, 2007). F D = 0.007D 3 + 0.1637D 2 1.2859D + 4.5158 (10) Therefore, for D=10m, F D = 1.0, while for D=8m, F D = 1.2 but for D=12m, F D = 0.5, that is, one-half of the coefficient for D=10m. Combining the effect of the three adjustment factors, the real average rate of advance (ARA R ) can be estimated from Eq. 11. ARA R = ARA T. F E. F A. F D (11) 1526

Table 4. Adjustment factor for the influence of excavated length (F A ) on TBM advance rate [10] Tunnel length Adaptation excavated (km) Factor (F A ) 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 Further, Bieniawski [10] evaluated Eq. 11 and 120 4.2 Geology and other rock properties found that the equation gives reliable results for The area lies in lesser Himalaya between latitude double-shield TBM in rock with strength less than 45 MPa and open type TBM in rock with strength 31 40 N to32 15 N and longitude 77 15 E to more than 45MPa. 77 50 E. The HRT passes through the upper section of the lesser Himalayas having the rocks from metasedimentary 4. TBM TUNNELLING IN THE HIMALAYAS to crystalline type. Being very close to main central thrust (MCT), the rocks along HRT Past experience of TBM tunnelling in the have undergone intense compression and thus are Himalayas is not encouraging. This is due to folded, faulted, foliated and jointed which is the varying geology and presence of folds, faults, shear typical characteristics of the Himalayan rocks. The TBM section of HRT mostly comprises of zones, water charged formations, etc. Therefore, the granites/gneissose granites (RD19354 15700m) designers were hesitant to use TBM for tunnel followed by quartzites (RD 15700-10300m). excavations in the Himalayas. But, with the Bands of biotite schist, talc chlorite schist or development of more advanced TBMs which have metabasics can be expected along the entire length capability of drilling probe holes, grouting the rock of the TBM drive. The granites are hard and mass, etc. the use of TBMs is now picking up in the massive exhibiting a well developed foliations in Himalayan projects also. some areas [17]. The quartzites (locally known as TBM performance in the head race tunnel of Manikaran quartzites) are moderately to extremely Parbati Hydroelectric Project Stage II has been evaluated in the paper using the Q TBM 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]. 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 4.1 The Project overburden along the TBM section varies from 100m at Hurla Nala (near Adit 2) to 1300m. 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 The orientation of the foliation planes in granite / gneissose granite is given as 060 /045 (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 northsouth alignment of the HRT (N190 in drive Pulga and power house site on the right bank of river Sainj. Out of the total length of 31.5km head direction) the schist bands will show an apparent race tunnel (HRT), 9.05km was planned to excavate dip transverse to the tunnel, which could have an by TBM. TBM used for HRT excavation is an unfavourable effect locally on wall stability, open-type Atlas Copco model TBM MK 27 of 6.8 requiring immediate rock support. m diameter. 1527

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). 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 Table 5. Properties of joints of Manikaran quartzites[18] Set Average Persistence Aperture Spacing Condition no. Orientation 1 060 o /052 o to 055 o /070 o 1 to 10m Mostly tight, at places open 5 to 30mm 5 to 50cm at places open 5 to 30mm Slightly rough/planar 2 225 o /050 o to 0.5 to 3m rarely Generally tight, at Generally tight, at Smooth/planar 240 o /040 o exceed > 10m places open 1 to 5mm places open 1 to 5mm 3 310 o /052 o to 330 o /070 o 2 5m Tight to 5mm Tight to 5mm Slightly rough/smooth planar 4 135 o /072 o to 160 o /040 o 1 5m at places > 10m Tight to 5mm Tight to 5mm Smooth planar 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 cutter head location. The machine is equipped with ring-mounted probe drilling equipment, which can cover 360 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. 1528

Table 6. Geotechnical properties of Manikaran quartzites [18] Properties Direction of Test with Respect Location of Samples to Foliation Surface samples Tunnel samples Unconfined compressive strength Parallel to foliation 121.45 80-150 (σ c ), MPa Perpendicular to foliation 267.2 Brazilian tensile strength, MPa Parallel to foliation 16.2 6-13 Perpendicular to foliation 24.6 Modulus of Elasticity, GPa -- 12.5 -- Poisson s 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 (γ), 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 5. TBM PERFORMANCE EVALUATION The performance of Atlas Copco Jarva MK 27 TBM in Manikaran quartzites has been evaluated using the Q TBM and RME index. Various details of actual TBM working in tunnel obtained from Dodeja et al. [18] in quartzites are as follows: Total excavation of TBM till October 2006-510m Total time in days - 218 days Total time in hours - 5232 hrs 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% Total cutting time in hours (@10.31%) - 539 hrs Advance Rate (Excavated length/total time in hrs) - 0.097m/hr Penetration Rate (Excavated length/cutting time in hrs) - 0.946m/hr per the geological and geotechnical information of Manikaran quartzites. Values of various parameters of Q TBM are listed in Table 7. The penetration rate from Eq. 5 for Q TBM = 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. 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 Q TBM Equation 1 is used for estimating Q TBM. The rating of all the parameters has been obtained/estimated as 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 m 1 = -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. 1529

Table 7. Estimation of Q TBM Parameter Description Rating/value RQD 0 60% (Evaluated as per above details and using details 60 collected by the author; tunnel axis orientation in TBM length is N10E- S10W) J n Four plus random joints 15 J r Slightly rough planar to smooth 1 J a Unaltered to slightly altered chloritic coating 1 J w Moist 0.66 SRF Rock strength 80-150MPa, rock cover around 1000m, 15 rock bursting is experienced Q (RQD/J n )(J r /J n )(J w /SRF) 0.176 σ c (MPa) 80-150, average 115 (Table 6) 115 γ (g/cc) From Table 6 2.6 σ cm (MPa) 5γ(Q. σ c /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 σ θ (MPa) 2γ*rock cover in meters (rock cover is assumed as 52 1000m) Q TBM 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 RMR TBM and the Fig. 2. Accordingly, first of all RMR D&B is estimated to get RMR TBM from Eq. 8. Subsequently, the rating of RME index parameters is obtained as indicated in Table 9. The real average rate of advance (ARA R ) 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 Q TBM 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 Q TBM for 24 hrs. 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 The actual penetration rate is 40% less than the estimated value obtained from Q TBM. As highlighted by Dodeja et al. [18], following are some of the reasons for low values of penetration and advance rates of TBM. High cutter consumption due to abrasive and compact nature of the rock mass Frequent detachment of rock mass in the zone inaccessible for rock supporting, i.e. in face and above cutter head Rock bursting/ Popping Occurrence of heavy water ingress Absence of detailed geological exploration and therefore occurrence of unfavourable conditions without warning. 1530

Table 9. Estimation of RME index Parameter Description Rating/value RQD 60% 13 Uniaxial compressive strength (UCS) Strong to very strong (80 150 MPa) 7 for RMR Spacing of discontinuities Moderate to close 8-10 Condition of discontinuities Rough and slightly weathered, wall rock separation 25 <1mm Water condition Moist 10 Joint orientation with respect to tunnel Fair -5 axis RMR D&B Total of all above 6 ratings 58 60 (59) RMR TBM Eq. 8 67 Stand-up time 9000 hrs 25 UCS rating for RME 80 150 MPa 14 DRI 78 (Table 6) 10 Ground water <10 ltrs / sec 5 Discontinuities in front of face 4 to 8 joints per meter 7 RME 61 ARA T (m/day) Eq. 9 14.13 m/day or 0.587m/hr F D Eq. 10 for D = 6.8m 1.14 F E Table 3 1.0 F A Tunnel length excavated = 510 m, using Table 4 0.68 Real Average Rate of Advance Eq. 11 0.45 (ARA R ), m/hr The above may not be covering all the reasons for not getting the TBM performance as per the estimated values. In addition, there may be the possibility of improving the Q TBM and RME index for estimating the TBM performance in the Himalayan tunnels. More data from TBM tunnels in the Himalayas will help in identifying the real problem and developing a reliable TBM performance estimation technique for Himalayan tunnels. 7. CONCLUSIONS Following conclusions are drawn from the study. Experience of TBM excavation from a Himalayan tunnel in quartzites is not encouraging. More than 50 per cent of the TBM utilization time is consumed in the delays and in the maintenance. The actual penetration and the advance rates of TBM worked out were 0.956 m/ hr and 0.097 m/ hr respectively for 510m long excavation. Performance of TBM has been estimated by using the empirical approaches of Q TBM and RME index. The results show that the actual penetration and the advance rates are less than the estimated values. More and more Himalayan TBM tunnelling data is required to evaluate the empirical approaches of estimating TBM performance and, if required, to suggest some modifications. ACKNOWLEDGEMENTS Author is thankful to all the researches, academicians and publishers whose work is referred in the paper. He is also thankful to Central Board of Irrigation and Power for accepting the paper for publication in WTC 2008 Proceedings. The views expressed in the paper are of the author and not necessarily of the Organization to which the he belongs. REFERENCES 1. Tarkoy P. J. and Byram, J. E. (1991). The advantages of tunnel boring: a qualitative/quantitative comparison of D&B and TBM excavation, Hongkong Engineering, January. 1531

2. Zhao, J. and Gong, Q.M. (2006). Rock mechanics and excavation by tunnel boring machine Issues and challenges, Proc 4 th 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 China s 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 Eurock 96, 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). 1532