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the landslide areas and minimize the damage and to protect thenational park.

REFERENCESBurrough, PA.,1986, Principles of Geographic Information System

and Land Resource Assessment, Claredon Press, Oxford,England,194p.

Capolongo D., Refice A., Mankelow J.,2002, Evaluating earthquake-triggered landslide hazard at the basin scale through GIS inthe Upper Sele river Valley. Surveys in Geophysics, v. 23(6), pp. 595–625.

Del Gaudio V., Pierri P., Wasowski J.,2003, An approach to time-probabilistic evaluation of seismically induced landslidehazard. Bulletin of The Seismological Society of America93: 2, pp. 557–569.

Del Gaudio V., Wasowski J.,2004, Time probabilistic evaluationof seismically induced landslide hazard in Irpinia (SouthernItaly). Soil Dynamics and Earthquake Engineering 24: 12,pp. 915–928.

Fleming, R.W. and Taylor, F.A. (1980) Estimating the costs oflandslide damage in the United States, U.S. Geol. SurveyCircular 832, 21 p.

Guzzetti F., Peruccacci S., Rossi M., Stark CP.,2007, Rainfallthresholds for the initiation of landslides in central andsouthern Europe. Meteorology and Atmospheric Physics98:3-4, pp. 239–267.

Hansen, A. and Franks, C.A.M.: 1991, Characterisation and Mappingof Earthquake Triggered Landslides for Seismic Zonation,Proceedings of the Fourth International Conference on SeismicZonation, Stanford, California, v. 1, pp. 149–195.

Ingles J., Darrozes J., Soula JC.,2006, Effects of the verticalcomponent of ground shaking on earthquake-induced landslidedisplacements using generalized Newmark analysis.Engineering Geology 86: 2-3, pp.134–147.

Keefer, D.K., 1984, Landslides Caused by Earthquakes, GeologicalSociety of America Bulletin, v. 95, 406–421.

Seed, H.B., 1968, Landslides During Earthquakes Due to SoilLiquefaction, American Society of Landslides for SeismicZonation, Proceedings of the Fourth International Conferenceon Seismic Zonation Stanford, California, vol. 1, pp. 149–195.

Varnes, D.J.,1984, Landslide Hazard Zonation: A View of Principlesand Practices,Commission in Landslides of the IAEG, Unesco,Natural Hazards, No.3 , 61p.

Wasowski J., Del Gaudio V., Pierri P., Capolongo D., 2002, Factorscontrolling seismic susceptibility of the Sele valley slopes:The case of the 1980 Irpinia earthquake re-examined. SurveyIn Geophysics 23:5 63–593

Fig. 3: (a) Map of Shivapuri National Park showing theslope aspect, (b) Map showing the different elevation rangeand the slope greater than 30°, and (c) Map showing theslope aspect and the slope angle greater than 30°.

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*Ujjwal Acharya, Madan Bhattari, Deepak Banjade, and Niraj Regmi

Sanima Hydropower Limited, Kathmandu, Nepal*Corresponding author: ujjwal.acharya@sanimahydro.com.np

ISSN 2676-1386 (Print); ISSN 2676-1394 (Online)

Study of stability of slopes of tunnel portals using modified SMR approach:A Case Study of Lower Likhu Hydropoer Project

INTRODUCTIONThe Lower Likhu Hydropower Project (28 Mw) is run-

off-the river type hydropower project located at Ramechhapand Okhaldhunga district. The studied slopes are five headracetunnel portals, namely Seti Outlet, Seti Inlet, Poku Outlet, PokuInlet, Main Outlet, and one surge shaft slope. Modified SMRapproach is used for the slope stability assessment of the area(Anbalagan et al., 1992). The general geology of the areacomprises of mainly two units: phyllite dominated andmetasandstone dominated rock units.

GEOLOGICAL SETTINGThe general geology of the area comprises of two rock

units. Thinly foliated, greenish grey, slightly to moderatelyweathered phyllite with intercalations of metasandstone andquartzite is present on the northern part of the study area (Fig.1). Fine to coarse grained, greenish grey to grey, fresh tomoderately weathered metasandstone with partings of phyllite,and few interbedding of coarse-grained meta-conglomerate ispresent on the southern part of the study area. The regionalgeological map published by DMG (1984) shows that the arealies in Seti Formation of Pokhara Sub-group, which comprisesof grey to greenish grey phyllites, gritty and quartzites withminor conglomeratic layer with some basic intrusions.

METHODSThe field data were collected using standard geological

instruments. Modified SMR approach (Anbalagan et al., 1992)was used for the slope analysis.

The stability of rock mass using SMR approach isobtained using the Bieniawski’s Rock Mass Rating (RMRbasic)and substraction of adjustment factors of the joint-sloperelationship and addition of a factor dependent to the methodof excavation.

ABSTRACTThe Slope Mass Rating (SMR) is widely used for stability assessment of rock slopes. The Modified SMR approach is used for thestability assessment of six rock slopes in tunnel portals and surge shaft area of Lower Likhu Hydropower Project (28.1Mw). The majorrock types of the study area are Phyllite and Metasandstone. The study shows some probability of wedge and planar failures at someslopes, whereas some slopes were found to be stable.

Key words: Likhu Khola Hydropower Project, Likhu Khola, Slope Mass Rating, Planar failure

SMR = RMRbasic – (F1.F2.F3) + F4, in which

RMRbasic is calculated according to Bieniawski (1979,1989) by adding the ratings of five parameters, whichare:

i. Uniaxial Compressive Strength of intact rock material,

ii. Rock Quality Designation (RQD),

iii. Joint or discontinuity spacing,

iv. Joint condition, and

v. Ground water condition.

F1 is dependent on parallelism between joints and slopeface strike. The approximate relationship to obtain thevalue of F1 is:

F1 = (1- sinA)2

Where, A denotes the angle between the strikes of theslope face and that of the joints.

F2 refers to the angle of dip of the joint considered, andvalue ranges from 0.15 to 1.F3 is the relationship between the slope face and jointdip angle.F4 is related to the method of excavation.Romana (1985) used planar and toppling failures for the

analysis using SMR. Anbalagan 1992 considered the plane andwedge failures as different cases and presented a modified SMRapproach for slope stability analysis, which is used for thepresent study. In this approach, the plunge and direction of dipof the line of intersection of unstable wedge were used.

Five different slope faces of the tunnel portals, namelySeti Outlet portal, Seti Inlet portal, Poku Outlet portal, PokuInlet portal and Main Outlet portal, and one in surge shaft area

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Ujjwal Acharya et al.

Fig.

1: G

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l map

of t

he a

rea,

show

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obse

rvat

ion

loca

tions

for m

odifi

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MR

Study of stability of slopes of tunnel portals using modified SMR approach: A Case Study of Lower Likhu Hydropoer Project

279

of the Lower Likhu Hydropower Project (28.1 Mw) were studiedfor the slope analysis and the support were suggested for therock classes according to the obtained value of SMR.

RESULTSSix rock slopes were chosen and RMRbasic for different

slopes were calculated (Table 1). The graphical analysis isperformed for the joints to deduce the mode of failure usingDips (Fig. 2).

Fig. 2: Stereo-plot for identification of wedge

Table 1: RMR calculation at different locations

Surge ShaftMain Outlet

Poku InletPoku Outlet

Seti InletSeti Outlet

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Ujjwal Acharya et al.

Fig.

1: G

eolo

gica

l map

of t

he a

rea,

show

ing

obse

rvat

ion

loca

tions

for m

odifi

ed S

MR

Study of stability of slopes of tunnel portals using modified SMR approach: A Case Study of Lower Likhu Hydropoer Project

279

of the Lower Likhu Hydropower Project (28.1 Mw) were studiedfor the slope analysis and the support were suggested for therock classes according to the obtained value of SMR.

RESULTSSix rock slopes were chosen and RMRbasic for different

slopes were calculated (Table 1). The graphical analysis isperformed for the joints to deduce the mode of failure usingDips (Fig. 2).

Fig. 2: Stereo-plot for identification of wedge

Table 1: RMR calculation at different locations

Surge ShaftMain Outlet

Poku InletPoku Outlet

Seti InletSeti Outlet

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Ujjwal Acharya et al.

formed at different locations were found to be partially stable(Table 3). Spot bolting is recommended for the completelystable slopes, spot or systematic bolting is recommended forstable slopes, and systematic bolting with systematic shotcreteis recommended for the partially stable slope to contain thepossible slope failure.

ACKNOWLEDGEMENT

Authors are thankful to Lower Likhu Hydropower Projectfor giving us permission to publish the data.

The orientatation of intersection of the joint planes fordifferent locations were found as shown in Table 2.

The analysis of discontinuities using the software Dipsproduced eight different wedges probable to failure. The slopestability of wedges was analysed using the modified SMRapproach, and the results are tabulated (Table 3).

CONCLUSIONModified SMR approach was applied on six different

slopes containing different rock types. Among eight wedgeswith potential wedge failure formed, three wedges were foundto be stable and partially stable and the remaining five wedges

REFERENCE

Anbalagan, R., Sharma, Sanjeev and Raghuvanshi, T.K.1992. RockMass Stability Evaluation Using Modified SMR Approach,Proceedings of 6th National Symposium on Rock Mechanics.Bangalore, India. pp. 258–268.

Bieniawski, Z.T. 1989. Engineering rock mass classifications. 251p.New York: John Wiley & Sons.

DMG 1984. Geological Map of Eastern Nepal.Romana, M. 1985. New Adjustment Ratings for Application of

Bieniawski Classification to slopes, International Symposiumon the Role of Rock Mechanics,Zacatecas, pp. 49–53.

Table 3: Slope Mass Rating results

Table 2: Attitude of slope face (Strike/Dip amount/Dipdirection) and (Trend/Plunge) of wedge formed byintersection of joint planes

Bulletin of Nepal Geological Society, 2019, vol. 36

281

*Madan Bhattarai and Ujjwal Acharya

Sanima Hydropower Limited, Kathmandu, Nepal

*Corresponding author: bhattaraimadan97@gmail.com

ISSN 2676-1386 (Print); ISSN 2676-1394 (Online)

Estimation of Achievable Rate of Tunneling: A Case Study of Lower LikhuHydropower Project

INTRODUCTION

The Lower Likhu Hydropower Project (28.1 Mw) is run-off river (RoR) type project located at Ramechhap andOkhaldhunga Districts. The total length of the headrace tunnelis 4797 m, and the excavation of tunnel is done by traditionaldrilling and blasting process from six portals. The total of 1046.7m has been excavated till 13.04.2019.

There are numerous uncertainties encountered duringthe excavation of tunnels. The probable time of completion oftunneling is grossly underestimated due to varying geology,management complications, and different types of breakdownor hold-ups. This paper includes the prediction of achievableprogress rate in the tunnel of the Lower Likhu HydropowerProject using classification system developed by Chauhan(1982).

METHODOLOGY

The assessment of rate of tunneling is done accordingto the classification system (Table 1) proposed by Chauhan(1982). The classification system comprises of classification oftwo conditions: ground conditions and management conditions.

Classification of Ground Conditions

The rate of tunneling is seriously affected by the groundconditions. The factors are:

a) Geology (RQD, dip/strike of strata, presence of majorfaults, rock mass properties)b) Method of excavation including blast pattern anddrilling arrangementc) Type of support system and its capacityd) Inflow of watere) Presence of inflammable gas

ABSTRACTThe process of tunneling is very challenging process in case of Nepal due to complex geology and managerial complications. Properprediction of monthly progress rate under a definite set of ground and management condition is important in tunneling project forachieving the milestone within the projected timeframe. This paper predicts achievable progress rate in the tunnel of the Lower LikhuHydropower Project.

Key words: Lower Likhu Hydropower Project, Achievable rate of tunneling, Run-off river type project, Tunnel

f) Size and shape of the tunnelg) Construction aditsh) High temperature in very deep tunnels.These geologic conditions are classified in the tunnelinto good, fair and poor conditions.

Classification of Management ConditionsThe rate of tunneling varies in the same ground condition

depending upon management quality. The management factorsaffecting the tunneling quality are:

a) Overall job planning, including selection of equipmentand decision making process,b) Training of personnel,c) Equipment availability including parts and preventivemaintenance,d) Operating supervision,e) Incentives to workmen,f) Co-ordination,g) Punctuality of staff,h) Environmental conditions, andi) Rapport and communication at all levels.These factors are assigned to weighted rating and the

rating of all factors is added to obtain a collective classificationrating for management condition. Using this rating, themanagement condition is classified into good, fair and poor.

Table 1: Ground and management factors (Chauhan 1982)