Geological and geotechnical studies around Kaswati dam,Kachchh, India: implications on tectonic stability, rock massproperty and water retention capacity

Niladri Bhattacharjee & Sarada Prasad Mohanty*

Department of Applied Geology, Indian Institute of Technology (Indian School of Mines), Dhanbad 826004, IndiaN.B., 0000-0001-9293-9346; S.P.M., 0000-0003-0397-8744

*Correspondence: mohantysp@yahoo.com

Abstract: The Kachchh region, located in the highest seismicity belt of peninsular India, has undergone continuous tectonismalong regional faults since Mesozoic times. The Kaswati dam, situated between two asymmetrical domes, witnessed a Mw 7.6earthquake in 2001. The present investigation was carried out around the dam site to assess the cause of geotechnical hazards(ground motion amplification, soil liquefaction, landslide and surface ruptures) that occurred during the earthquake. Analysesof the spatial distribution of discontinuities, their relationship with deformed litho-units and different parameters ofdiscontinuities (i.e. spacing, orientation, persistence, aperture, roughness, filling and weathering) were undertaken tocharacterize rock mass properties and seepage over time. Measured joint frequency, joint volume, block volume and blockshape factor provide quantified data on the degree of jointing, shape and size of the block, Rock Quality Designation, RockMass Rating, Geological Strength Index and hydraulic aperture. The coefficient of permeability was determined from rockdiscontinuities to estimate the amount of seepage of water through rock joints. Rock mass characterization and water retentioncapacity were measured via an indirect method, which might be useful during the preliminary study of site characterization andproduce accurate results at very low cost.

Received 1 August 2017; revised 15 November 2017; accepted 17 January 2018

The Kachchh province is a part of the Stable Continental Region(SCR) in India (Fig. 1). The region covers a major seismic domainwith records of historical seismicity of Mw >5 (Malik et al. 1999).Several monuments in the region were destroyed during seismicevents dating back to the ninth century AD (Rajendran et al. 2001).An earthquake of Mw 7.7, the most disastrous in recent history,occurred on 26 January 2001 in the area and damaged buildings innearby areas within a radius of 400 km. The Kachchh province has anumber of highlands (uplifts/domal structures) bordered by regionalfaults. These regional faults are involved in neotectonic activitiesand pose a risk for development activities in engineering structures.Several alluvial fans present along the base of the topographic highsprovide evidence of fault movement and rejuvenation. The semi-arid climate and poor vegetation cover in the region haveencouraged construction of a large number of small dams toovercome water scarcity. However, most of these dams remain dryfor a considerable time of the year. Knowing the potentiality of largemagnitude earthquakes to affect engineering structures, the studywas undertaken around one small dam on the Kaswati River nearLodai, which is located close to the epicentre of the Mw 7.7earthquake of 2001 and incurred severe damage. The objectives ofthe work were to map the regional structures, to study the rock masscharacter of the area and to analyse the effect of rock mass propertiesfor stability as well as the water retention capacity of the dam.

Regional geology

The Kachchh region was developed as a rift basin during Jurassictimes by the separation of the Indian Plate from Gondwanaland(Biswas 1982, 1987). A series of east–west-striking normal faults,such as Nagar Parkar Fault (NPF), Allah Bund Fault (ABF), IslandBelt Fault (IBF), Banni Fault (BF), Kachchh Mainland Fault(KMF) and Katrol Hill Fault (KHF) (Fig. 1), developed in the area

during the initial period of extension (Biswas 1982, 1987). After theinitial extensional stress regime, the collision of the Indian andEurasian plates during the Miocene (c. 20 Ma) gave rise to a north–south to NNE–SSW compressional regime in the Kachchh rift basin(KRB) (Gowd et al. 1992; Gombos et al. 1995). The east–west-trending faults were reactivated from time to time because of thiscompression (Biswas 1982, 1987; Talwani & Gangopadhyay 2001;Biswas & Khattri 2002; Bodin & Horton 2004). In addition to theregional east–west faults, several transverse faults striking north–south, NNE–SSW, ENE–WSW and WNW–ESE were developedduring various neotectonic events (Biswas 1987; Sohoni et al. 1999;Thakkar et al. 1999; Maurya et al. 2003; Sinha & Mohanty 2012).The networks of faults define a series of highlands or uplifts,separated from one another by depressions or basins. The highlandsinclude the Kachchh mainland in the south, the Wagad uplift in thecentre, and the Pachham, Khadir, Bela and Chorar uplifts in thenorth, forming the Island belt. The western and northern part ofKachchh is covered by a marshy land, known as the Great Rann, andthe eastern part is also covered by marshy areas of recent alluvium,known as the Little Rann. The plain area between the Kachchhmainland and the Island belt is referred to as the Banni plain.

The study area is located between 23° 21′–23° 23′30′′N latitudesand 69° 52′30′′ E–69° 56′ E longitudes around the Kaswati earthdam near Lodai village, Gujarat (Fig. 2). The earth dam is forirrigation purposes in a semi-arid climate and was completed in1976. The dam has a crest length of 1455 m, a maximum height of16.15 m, gross reservoir storage capacity of 8.88 million m3 and acatchment area of 67 km2, covering part of the northern hill range,which is the last limit of the Kachchh Mainland (NWRWS 2010).The northern hill range is made up of series of domes of Jurassicrocks with a gentler southern flank, and a steeper northern flank,truncated by the KMF (Biswas 1987). The dam is located betweentwo domes (Habo andWanthra), separated by a depression occupied

© 2018 The Author(s). Published by The Geological Society of London. All rights reserved. For permissions: http://www.geolsoc.org.uk/permissions.Publishing disclaimer: www.geolsoc.org.uk/pub_ethics

Research article Quarterly Journal of Engineering Geology and Hydrogeology

Published online April 30, 2018 https://doi.org/10.1144/qjegh2017-091 | Vol. 51 | 2018 | pp. 338–351

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by the Kaswati River basin. At the site the Kaswati River is afifth-order stream, which flows from the northern hill range andpasses through the Kachchh mainland, emptying into the Rann ofKachchh. The bifurcation ratio, circularity ratio, drainage textureratio, asymmetry factor, drainage density and sinuosity indices ofthe Kaswati River basin indicate continuous tectonic activity(Singh 2013).

The lithological units exposed near Lodai are stratigraphicallygrouped under the Habo Formation of Bathonian to Oxfordian age(Kanjilal 1978), which is equivalent to the Jhurio Formation andJumara Formation of Biswas (1991) and Pachcham and ChariFormation of Merh (1995), and the Katrol Formation. The HaboFormation is classified into five members, which include (frombottom to top): black limestone, Dhrang, Jhikadi, Rudramata andLodai (Kanjilal 1978). The study area has exposures of fossiliferousgreen to yellowish gypsiferous shale with flat pebble conglomerate

(the Rudramata Member), overlain by alternating fossiliferouslimestone and shale (the Lodai Member) and stratigraphically upperunits of the Katrol Formation (gypsiferous shale and calcareoussandstone). The Jurassic sediments were deformed and covered bybasaltic flows (Deccan Trap) of Late Cretaceous and EarlyPaleocene age (Biswas 1987). The modification of the rivercourse, development of new lineaments and reactivation of earlierfaults suggest the effects of neotectonic activity in the area(Humphrey & Konrad 2000).

The intraplate seismicity model explains the KRB block as a localzone of weakness sandwiched within the Indian craton comprisingof Precambrian granitic rocks (Talwani & Gangopadhyay 2000).After the 2001 Bhuj earthquake, different ground motion features,such as deep cracks, uplifts, flexures, craters, and lateral spreadingdue to liquefaction, formed in this area (Rastogi 2001; Rajendranet al. 2001). The deformation structures developed in the Kaswati

Fig. 1. Structural map of the Kachchh area,showing major faults and epicentres ofseismic activity (after Biswas & Khattri2002). Inset: location map of the studyarea.

Fig. 2. Structural map of the area aroundKaswati dam, Lodai. The area north of theKachchh Mainland Fault (KMF) is referredto as Sector I, and the area south of KMFis identified as Sector II, which is furtherdivided as IIa (west: Habo dome) and IIb(east: Wanthra dome).

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dam site during the 2001 earthquake include bulging of the groundsurface near the upstream, liquefied alluvium below the upstreamsection, a curved sliding surface below the semi-pervious shell ofthe upstream slope and longitudinal cracks on the crest of the dam(Fig. 3, EERI 2001). Previous analysis of the earthen dams in theKachchh area included total risk analysis, coupling nonlineardynamic analysis (Srivastava & Babu 2010), seismic slope stabilityanalysis (Patel & Sanghvi 2012), and assessment of liquefactionpotential and the sliding block method (Singh et al. 2005).

Different structural units

The geometry and distribution of different planar structures, such asbedding, joints, faults, dykes and folds, control the tectonic stabilityof a site and water retention in the reservoir. We have collected dataconcerning such features in the field and used the data forcalculation and interpretation of geotechnical parameters. Duringthe present investigation, a map was prepared for both the sides ofthe Kaswati dam (Fig. 2). The KMF divides the area into twosectors: Sector I covers the northern part of the KMF and Sector II islocated in the southern part of KMF. The details of structuralfeatures in the different sectors are given here.

Bedding

Sector I is comprised of coarse to fine calcareous sandstone, with anintercalation of glauconitic shale and marl. Primary bedding isidentified by sand, shale and limestone intercalation as well as colourvariations in different litho-units (Fig. 4a). The beds on the easternside of this sector show continuous variation in strike from east–westto NE–SW with a dip of 30° to 50° towards the north to NW. Thecentral part has a NW–SE to NNW–SSW strike and a dip of 20° to45° towards the NE to ENE. In thewestern part, beds strike east–westand have a steep dip of 55° to 85° towards the north (Fig. 2).

Sector II has outcrops of fossiliferous limestone, calcareoussandstone and gypsiferous shale sandwiched between sandstoneand polymictic conglomerate. Primary sedimentary structures, suchas cross-bedding (Fig. 4b) and asymmetrical ripple marks (Fig. 4c),are very prominent in this area. Sharp topographic highs and lowsare present in this area. The strike of bedding in the western partvaries from NE–SW to NW–SE and the dip ranges from 10° to 20°towards the SE to NE. This sector is a part of the eastern margin ofthe Habo dome and includes another domal structure to the east, theWanthra dome, in which trends of lithological units changecontinuously from east–west to NW–SE, and NE–SW to againeast–west, with a dip away from the centre (Fig. 2).

Fold

Primary sedimentary bedding shows continuous variation inorientation due to compression and deformation of litho-units bymovement of blocks along the fault present in the area, giving rise to

Fig. 3. Profile section of the KaswatiDam, showing damage zones developedduring the 2001 Mw 7.7 earthquake(modified from EERI 2001).

Fig. 4. Field photographs of (a) bedding 120°/30° NNE, (b) cross-bedding and (c) curved asymmetrical ripple marks.

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monoclinal flexures with intense fractures. The maximum fre-quency of fractures is found in the hinge zone of the fold, and theorientation of fracture changes away from the hinge (Fig. 2). Sector Ishows girdle distribution of bedding, indicating the presence of afold, with the fold axis plunging 10° towards 091° (Fig. 5a). InSector II the fold axis plunges 07° towards 091° in the west and 08°towards 277° in the east (Fig. 5b and c). Between two transversefaults and very near to the KMF, the folds (with steeply dippinglimbs) plunge 55° towards 350° (Fig. 6).

Rock joints

Joint sets and joint orientations

Sector I of the area has four sets of joints with strikes of 005°, 035°,085° and 145° (Fig. 7a). Among these, the first three sets are verydominant. Sector II has four joint sets in the western part, having

average trends of 015°, 115°, 155° and 85° (Fig. 7b), but the easternpart of the sector has three joint sets trending 005°, 105° and 035°(Fig. 7c). These joints have very steep dips of 70°–90°. Columnarblocks of rock are formed by two perpendicular sets of joints(Fig. 8a), and mixed shapes of blocks and wedges are developed bymore sets of joints (Fig. 8b). However, all the joint sets show a veryclosely fractured rock with randomly oriented discontinuities,which are prone to circular failure (Fig. 9). At some places joints areoriented parallel to the strike as well as perpendicular to the strike ofthe lithological units (Fig. 10).

Joint length and spacing

The areal extent of joint sets has low (Fig. 10a, c, e and f) to medium(Fig. 10b, d and g) persistence (ISRM 1978) and joint spacing in theLodai area (Fig. 10a–f ) is very close to close (Fig. 10g) in nature(ISRM 1978).

Joint surface and opening

Inherent surface unevenness and waviness in the area can bedistinguished as smooth (Fig. 10a, c, d and g), slightly rough(Fig. 10e and f) and rough (Fig. 10b). Due to various surfaceroughness and movement along the face, the blocks show mismatchin some places (Fig. 10a, b and f) and some have matched blockfaces (Fig. 10c, d, e and g). The joint aperture in the area is widelyopen (Fig. 10a–d, f and g) to open (Fig. 10e) and the aperture hassoft filling material of high friction sand and crushed rock (Fig. 10).

Faults

The Kachchh Mainland Fault, which strikes east–west and dipstowards the north, is a very prominent regional fault in the area,demarcated by the presence of a fault scarp (Fig. 11a). In addition tothis, several transverse faults, which run across the east–west trend

Fig. 6. Field photograph of a fold plunging towards 350°.

Fig. 5. Equal-area stereographic projection of bedding planes of the Lodai area. (a) Sector I: total data 78; mean principal orientation 138°/14° NE;calculated girdle 181°/80° E; calculated beta axis 10° →091°. (b) Sector IIa (west): total data 59; mean principal orientation 013°/07° ESE; calculated girdle181°/83° E and calculated beta axis 07° →091°. (c) Sector IIb (east): total data 8; mean principal orientation 122°/19° SSW; calculated girdle 187°/82° Eand calculated beta axis 08° →277°.

Fig. 7. Rose diagram for joint strikedirections of the Lodai area. (a) Sector I:total data 102; sector angle 10°; outerlimit 9.8%; mean resultant direction 000°–180°; and c. 95% confidence interval±90.0°. (b) Sector IIa (west): total data96; sector angle 10°; outer limit 12.5%;mean resultant direction 135°–315°; andc. 95% confidence interval ±90.0°.(c) Sector IIb (east): total data 23; sectorangle 10°; outer limit 21.7%; meanresultant direction 006°–186°; and c. 95%confidence interval ±90.0°.

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and laterally displace the KMF at several places, were identified(Fig. 2). Structural mapping brings out the truncated and foldednature of bedding in the area to the north of the KMF (Sector I).Sector II covers two domal structures in the Habo and Wanthraareas. The eastern margin of the Habo dome was developed by theinfluence of F2, F3, F4, F9, F10, F14, F18 and the KMF, and thewestern margin of the Wanthra dome was developed by theinfluence of F13, F15, F16, F18, F23 and the KMF. The area betweenthe two domal structures is occupied by the valley of the KaswatiRiver, which follows the trend of the transverse faults (F18, F10 andF11) and a sharp change in the river course is along the left lateraltransverse faults (F1, F2, F3, F4). In the southeastern portion of thestudy area, the tributaries of all lower-order rivers follow the trendsof the nearest faults. Several faults surround the Kaswati dam. Theseinclude F9, F10, F11, F12, F14 and the KMF, which pass through thedam. Regional transverse faults display dominantly right-lateraloblique-slip movements (Fig. 2). Some oblique-slip faults withmultiple offsets (both sinistral and dextral) are also present in the

area (Fig. 11b and c). Geomorphic features, such as flexure,uplifting and extensional cracks, are associated with these faultsystems.

Mafic igneous intrusions

Mafic igneous rocks are present in the northeastern and south-western part of the Lodai dam in the form of long narrow dykes.These dykes follow the trend of the regional transverse faults,possibly along the pathway of the least tensile strength of the hostrock (Fig. 2). These are considered to be the feeder dykes forvolcanic flows forming the Deccan Trap. The interfaces between thedykes and the country rocks show zones of alteration (Fig. 10d). Thedykes have three sets of joint planes (Fig. 10d).

Methodology and numerical analysis

Calculation of joint parameters

Intersecting joints in a rock mass divide the rock into blocks withsizes ranging from cubic centimetres in fragmented or crushed rockto several cubic metres in massive rocks. These sizes depend on thefrequency of joints, joint spacing, number of joint sets andpersistence of the joints. Further, the features of discontinuitiesare the key to reliable measurements of the properties of rock blocks.These parameters were measured in the field and were analysed todetermine the three-dimensional block volume (Vb) and thevolumetric joint count (Jv), which are important inputs to the rockengineering calculations. The most appropriate method of variousmeasurements of the block size or degree of jointing (i.e. averagejoint spacing, joint frequency, joint volume, block shape and size,block volume) are described below.

Joint frequency (Table 1), defined as the number of joints permetre length, was calculated using the formula (Palmstrom 2000):

l ¼ 1

S(1)

where λ represents joint frequency and S represents the jointspacing.

Average spacings (Table 1) of multiple joint sets are calculated as(after Palmstrom 2000, 2002),

1

Sa¼ 1

S1þ 1

S2þ 1

S3� � � þ 1

Sn(2)

where 1/Sa is the average spacing and S1, S2, S3… Sn are jointspacing.

Fig. 8. Field photograph showing joints: (a) cross joints 060°/90° and 325/90° developing columns; (b) three sets, 175°/90°, 090°/90° and 140°/75° NE,developing wedges.

Fig. 9. Stereographic projection of pole of joint planes in and around theKaswati dam site. The faces of upstream and downstream aprons aremarked by red and blue colours, respectively.

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Fig. 10. Field photographs showing different joint sets in the upstream side of the Kaswati River in one square metre grid (except Fig. 10 c, e & f; as thedimension of those exposures are less than the required grid). (a) Three sets (064°/84° NW, 110°/15° SSW, 190°/65° E) in profile view; (b) three sets(035°/58° SE, 132°/35° SSW, and followed by younger joint set 105°/70°–90°) in profile view; (c) bedding 050°/22° SE and two sets of joints 103°/80°NNE, 040°/70° NW in surface view; (d) three sets of joints 020°/78° ESE, 100°/78° N, 044°/18° NW (profile view).

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The volumetric joint count (Table 2), a measure of the number ofjoints per unit volume of the rock, can be calculated using theformula of Palmstrom (1982, 1986) and Sen & Eissa (1991, 1992).

Jv ¼ 1

S1þ 1

S2þ 1

S3� � � þ 1

Sn(3)

where Jv is the volumetric joint count and S1, S2, S3… Sn are jointspacing.

The block volume (Table 3) is measured from the equation (afterPalmstrom 2000),

Vb ¼ S1 � S2 � S3 � (sin a� sin b� sin g) (4)

where Vb is the block volume, S1, S2, S3 are joint spacing for eachjoint set and α, β, γ are the angle between the joint sets.

Block shape factor (B) is estimated (Table 4) from the relationbetween the block volume (Vb) and the volumetric joint count (Jv)

(after Palmstrom 2002, 2005), i.e.

Vb ¼ B� J�3v � [1 4 (sin a� sin b� sin g)] (5)

where α, β, γ are the angle between the joint sets.

Calculation of Rock Quality Designation

The Rock Quality Designation (RQD), a quantitative estimate ofrock mass quality from drill core logs, was developed by Deere(1963) and was further modified by Deere et al. (1967) and Deere &Deere (1989). The RQD is used as a rock quality index forevaluating the engineering properties (mainly deformation modulusand unconfined compressive strength) of rock masses. Based on theRQD, other different indices of rock mass classification such asRock Mass Rating (RMR), Q and Geological Strength Index (GSI)are obtained. When cores are not available, RQD may be estimatedfrom different empirical relations (Zhang 2016). Palmstrom (2005)proposed a method of calculation of RQD from number of joints per

Fig. 10. Continued. (e) bedding 105°/15° NNE and three sets of joints 085°/75° S, 095°/80° N and 175°/80° W (profile view); (f ) bedding 100°/10° NNEand two sets of joints 100°/80° S, 010°/85° E; (g) bedding 125°/55° SW and two sets of joints 125°/42° NE, 045°/82° SE (profile view).

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unit volume (Jv) in the absence of core data as

RQD ¼ 110� 2:5Jv (6)

Hudson & Priest (1979) have proposed a RQD calculation fromjoint frequency (λ) as:

RQD ¼ 100� e�0:1l � (1þ 0:1l) (7)

The calculated RQD value of the study area using these formulae(equations 6 and 7) is given in Table 5.

Calculation of the Rock Mass Rating system

RMR (Bieniawski 1973, 1989), and Q (Barton et al. 1974) are twowidely used rock mass classification scheme of multiparametriccomponents, but RMR uses compressive strength directly, while Qconsiders strength related to the in situ stress in competent rocks.Here we consider only compressive strength.

RMR is calculated as:

RMR ¼ R1 þ R2 þ R3 þ R4 þ R5 (8)

where R1 denotes the Uniaxial Compressive Strength (UCS; Hoek& Brown 1997) of rock, R2 the Rock Quality Designation (RQD),R3 the spacing of discontinuity, R4 the condition of discontinuityand R5 the groundwater condition. The results of RMR for the studyarea are given in Tables 6 and 7.

Estimation of the Geological Strength Index in terms ofRQD and joint condition

The Geological Strength Index (GSI) was introduced by Hoek(1994) and was further elaborated by Hoek et al. (1995), Hoek &Brown (1997) and Marinos & Hoek (2001). Later it was modifiedby Sonmez & Ulusay, (1999) and Osgoui et al. (2010). In the chartprepared for GSI (Fig. 12), the vertical scale represents discontinu-ity surface conditions and the horizontal scale represents theblockiness of the rock mass. The value of GSI is given by the sum ofthese scales (Table 8) i.e.

GSI ¼ 1:5� JCond89 þ RQD

2(9)

where JCond89 is the joint condition rating defined by Bieniawski(1989) and RQD is the Rock Quality Designation calculated fromequations (6) and (7) (Hudson & Priest 1979; Palmstrom 2005).

Calculation of the coefficient of permeability of rock joints

Assuming parallel plate theory or cubic flow law (i.e. two smoothparallel plates and the flow to be steady, single phase, laminar andincompressible), the hydraulic conductivity/coefficient of perme-ability through rock joints (Table 9) is estimated (after Zhao &Brown 1992; Scesi &Gattinoni 2007; Dardashti &Ajalloeian 2015)from the equation

K ¼ (g � d2e )

12n(10)

Fig. 11. Field photographs of faults:(a) fault scarp of Kachchh Mainland Fault;(b) oblique-slip faults showing bothsinistral and dextral offset; (c) multipleoffsets (dextral and sinistral) on plan view.

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where K is the coefficient of permeability, g the acceleration due togravity (9.81 m s−2), de the equivalent hydraulic aperture of therough joint and ν the kinematic viscosity of the fluid (1.01 ×10−6 m2 s−1 for pure water at 20°C).

On the basis of experimental data for increasing sheardisplacement (δs) and peak shear displacement (δsp) with δs≤0.75 δsp, Barton et al. (1985) proposed the relationship betweenequivalent hydraulic aperture and real joint aperture based on theJoint Roughness Coefficient (JRC) as

de ¼ JRC2:5

(d 4 de)2 (11)

where d is the aperture of smooth plates and de the equivalenthydraulic aperture of the rough joint.

Olsson & Barton (2001) proposed an improved model for δs≥δsp, when the geometry of the wall changes with increasing sheardisplacement. The hydraulic aperture (de) can be calculated by theequation

de ¼ d

de

� �� JRC2

mob (12)

where d is the aperture of smooth plates, de the equivalent hydraulicaperture of the rough joint and JRCmob themobilized value of the JRC.

Discussion

Artificial structures, such as buildings, bridges, earth dams andports, close to the epicenter, as well as areas up to c. 350 km fromBhuj, were damaged during the 26 January 2001 earthquake.Unmapped lineaments on the surface were considered to beimportant for this research to assess possible earthquake occurrenceand consequent damage potential. The impact of lineaments aroundthe Kaswati dam of the Lodai area were effectively analysed byintegrated structural geology and a geotechnical approach looking ataspects of the structural feature, rock mass property and fluid flowthrough rock discontinuities.

Structural features

This area comes under seismological active zone V. During the2001 earthquake, ground stress was released through the discon-tinuities, influencing engineering design and historical constructionof the area. Structural mapping (Fig. 2) portrayed different structuralelements of the site by characterization of the orientation andinterface type of the discontinuities. Tilting and rotation of litho-units along the discontinuities developed flexures and folds near tothe surface. These processes resulted in the formation of thetectonically controlled landscape of uplifts and residual depres-sions. Based on the spatial distribution of these features, differentsets of discontinuities are identified. Basic igneous intrusions alsogive a clue as to the least tensile pathway or discontinuity (Fig. 10d).It was noted that the study area is a highly fractured terrain with threeto four sets of joints (Fig. 7). Among different joints, longitudinal,transverse, cross, strike and dip joints are very common features onthe folded surface. Apart from the regular joints, non-systematicdiscontinuous random fractures are very common in this area(Fig. 9). A large number of closely placed joints very near toupstream and downstream aprons of the dam developed fragmentedrock bodies which have the potential to develop circular failures.Therefore, the inverse relationship between the strength of the rockand the number of joints has possibly affected the mechanicalproperties of the rockmass of the area. In this area, the main regionalfault trending east–west is known as the Kachchh Mainland Faultand it dips towards the north. Due to the compressional regionalsetting, stress is continuously building up in the study area overtime. This accumulated stress is released along the existing planes ofT

able1.

Determinationof

average(Avg)spacing(S

a)andaveragejointfrequency(λ)*

Serialno.

Jointspacing

Anglebetween

joint(α,β

,γ)(°)

Average

joint

frequency(λ)

Average

spacing

(Sa)(m

)Descriptio

n(ISRM

1978)

Set1

Set2

Set3

Min

(m)

Max

(m)

Avg

(m)

Min

(m)

Max

(m)

Avg

(m)

Min

(m)

Max

(m)

Avg

(m)

a0.03

0.07

0.05

0.11

0.15

0.13

0.15

†0.35

†0.25

85,4

0,60

31.69

0.031

Veryclosespacing

b0.03

0.10

0.065

0.25

0.45

0.35

0.33

0.34

0.335

70,8

0,30

21.23

0.047

Veryclosespacing

c0.04

0.16

0.10

0.04

0.23

0.135

0.20

†0.80

†0.50

80,4

0,50

19.41

0.051

Veryclosespacing

d0.03

0.20

0.115

0.05

0.17

0.11

0.15

†1.00

†0.575

85,2

0,65

19.52

0.051

Veryclosespacing

e0.04

0.10

0.07

0.03

0.05

0.04

0.20

†0.50

†0.35

80,6

5,35

42.14

0.020

Veryclosespacing

f0.05

0.11

0.08

0.06

0.16

0.11

0.25

†0.55

†0.40

90,6

5,25

24.10

0.041

Veryclosespacing

g0.07

0.17

0.12

0.10

0.23

0.165

0.35

†0.85

†0.60

90,7

0,20

16.06

0.062

Close

spacing

*The

averagevaluewas

calculated

from

theminim

umandmaxim

umvalue,as

thenumberof

datawas

limited.

†Spacing

oftherandom

joints,i.e.5

times

thespacingof

themainjointset(Palmstrom

2000

).

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weakness, causing reactivation of earlier discontinuities anddevelopment of new faults oblique to the KMF. Study of strainvariations in the Kachchh region (Sinha & Mohanty 2012) hasshown that the direction of maximum deformation is through theNNW–SSE to NNE–SSW transverse faults of the area, in additionto the east–west faults. Trends of a few transverse faults,accompanied by fractures, run parallel to the Kaswati dam axis(Fig. 2). Therefore, during ground shake, lateral spreading of soilbeneath the dam possibly amplified the ground motion and severelyaffected the stability of the dam by developing different longitudinalcracks (Fig. 3) in the form of surface ruptures.

Rock mass properties

Discontinuities of small to intermediate scales have significanteffects on the rock masses. The characteristic features ofdiscontinuities were determined for the study area (Table 6). Theareal extent of joints show low to medium persistence, and the joint

spacing ranges from very close to close (Table 1). These two factorsindicate the potential for sliding in the dam foundation. At someplaces in the study area, discontinuity surfaces matched, but someplaces have mismatched fracture planes. The roughness index variesfrom smooth to slightly rough and rough. The initiation and amountof shear displacements are controlled by the roughness of thefracture surface. The aperture index in the area is widely open, and isparticularly important where permeability is concerned. Adjacentwalls have a soft of crushed rock. The finer soft filling materialshows swelling characteritics, which reduces the shear strength ofthe rock mass. In the study area, the characterization of block sizewas done on the basis of joint spacing to calculate the block volume(Vb) and the volumetric joint count (Jv). The determined Jv roughlyvaries from 19.27 to 53.43 in 1 m3 (Table 2), suggesting a stronglyto very strongly jointed rock mass. The block volume (Vb) rangesfrom 0.7 to 7.2 dm3 (Table 3), which matches with small to verysmall block size. The block shape factor shows a wide range ofvariation, i.e. equidimensional, slightly long (prismatic), slightlyflat (tabular), moderately long, moderately flat, long and flat blocks(Table 4). All these properties indicate rock masses behave asdiscontinuous materials, influenced by the geometry of joints andtheir properties. Here, accounted RQD is very poor to fair (Table 5).The RMR, based on five parameters, varies from poor to fair(Table 7). The combination of two parameters, i.e. RQD (Table 5)and joint condition (Table 6) of the rock mass in the GSI chart(Fig. 12), describes a wide range of rock structure, such aslaminated, disintegrated, disturbed, very blocky, blocky, with thequality of the discontinuity surface recorded as very poor to fair. TheGSI and RMR of the area show a positive correlation (Fig. 13). Weknow that the deformation modulus (Em/Er) and unconfinedcompressive strength (δcm/δc) decrease with decreasing RQD,RMR and GSI. Hence, both single parametric and multiparamericrock mass classification systems indicate the quality of the rockmass is poor in the study area mainly due to the high degree ofjointing and poor joint conditions, arising out of multipleneotectonic events in the area.

Table 2. Determination of average joint volume (Jv)*

Serial no.

Joint volume calculation (m3)Average jointvolume (m3)

Nature of Jv(ISRM 1978)

Block size (ISRM1978)

Degree of jointing(ISRM suggested)For min. spacing For max. spacing

a 49.09 23.80 36.44 Very high Very small block Very strongly jointedb 40.36 15.16 27.76 High Small block Strongly jointedc 55.00 11.85 33.42 Very high Very small block Very strongly jointedd 60.00 11.9 35.95 Very high Very small block Very strongly jointede 63.33 32.00 53.43 Very high Very small block Very strongly jointedf 40.70 17.16 28.93 High Small block Strongly jointedg 27.14 11.41 19.27 High Small block Strongly jointed

*The average value was calculated from the minimum and maximum value, as the number of data was limited.

Table 3. Determination of block volume (Vb)*

Serialno.

Block volume calculationfrom joint spacing (m3)

Average blockvolume (m3)

Description (afterPalmstrom 1985)

For min.spacing

For max.spacing

a 0.000274 0.002037 0.001155 Small blockb 0.001145 0.007079 0.004112 Small blockc 0.000155 0.014276 0.007215 Small blockd 0.000069 0.010499 0.005284 Small blocke 0.000122 0.001279 0.000700 Very small blockf 0.000287 0.003707 0.001997 Small blockg 0.000787 0.010681 0.005734 Small block

*The average value was calculated from the minimum and maximum value, as thenumber of data was limited.

Table 5. Determination of RQD from joint volume and joint frequency forthe Lodai area

Serialno.

RQD fromjoint volume

RQD fromjoint frequency

Approximatevalue of RQD

Rock quality(Deere et al.

1967)

a 18.88 17.52 18 Very poorb 40.60 37.37 39 Poorc 26.45 42.22 34 Poord 20.20 41.91 31 Poore −9.16 7.71 00 Very poorf 37.67 30.63 34 Poorg 61.82 52.30 57 Fair

Table 4. Determination of block shape factor (B)

Serialno.

Block shapefactor (B) Description (after Palmstrom 1985)

a 30.99 slightly long (prismatic) and for slightly flat(tabular) blocks

b 40.70 for moderately long and for moderately flat blocksc 130.59 for long and for flat blocksd 75.81 for long and for flat blockse 54.66 for moderately long and for moderately flat blocksf 18.52 for equidimensional (cubical or compact) blocksg 13.18 for equidimensional (cubical or compact) blocks

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Table 6. Determination of joint condition for the Lodai area

Serial no.

Persistence Aperture Roughness Filling Weathering

Total ratingNature (m) Rating Nature (mm) Rating Nature Rating Nature Rating Nature Rating

a 1–3 4 1–5 1 Smooth 1 Soft filling <5 mm 2 Highly weathered 1 9b 3–10 2 1–5 1 Rough 5 Soft filling <5 mm 2 Highly weathered 1 11c 1–3 4 >5 0 Smooth 1 Soft filling >5 mm 0 Slightly weathered 5 10d 3–10 2 >5 0 Smooth 1 Soft filling >5 mm 0 Moderately weathered 3 6e 1–3 4 0.1–1 4 Slightly rough 3 Soft filling <5 mm 2 Highly weathered 1 14f 1–3 4 1–5 1 Slightly rough 3 Soft filling <5 mm 2 Moderately weathered 3 13g 3–10 2 1–5 1 Smooth 1 Soft filling <5 mm 2 Slightly weathered 5 11

After Bieniawski (1989).

Table 7. Determination of RMR for the Lodai area

Serial no.

UCS (R1) RQD (R2) Joint spacing (R3)Joint condition (R4)

Water condition (R5)

RMR (R1 + R2 + R3 + R4 + R5) RemarksMPa Rating % Rating m Rating Rating Nature Rating

a 25–50 4 18 3 0.031 5 9 Completely dry 15 36 Poor rockb 5–25 2 39 8 0.047 5 11 Completely dry 15 41 Fairc 50–100 7 34 8 0.051 5 10 Completely dry 15 45 Faird 25–50 4 31 8 0.051 5 6 Completely dry 15 38 Poor rocke 5–25 2 0 3 0.020 5 14 Completely dry 15 39 Poor rockf 25–50 4 34 8 0.041 5 13 Completely dry 15 45 Fairg 50–100 7 57 13 0.062 8 11 Completely dry 15 54 Fair

After Bieniawski (1989).

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Fluid flow

TheKaswati dam is situated between two asymmetrical domes, i.e. theHabo dome and Wanthra dome. Here the thickness of the alluviumbelow the basement of the dam is very low and the permeability of thefoundation depends mostly on bedrock. Fluid flow through a jointnetwork depends on aperture, filling material, the variable surfaceroughness of joints, the discrete point of contact in place to place, thestiffness of joints, etc. Analyses of different joint parameters were used

to determine the hydraulic aperture and coefficient of permeability,which controls fluid flow through the rockmasses. Thismethod shouldbe very useful during the preliminary study of any artificial structure atlow cost. One can apply the in situ permeability test later.

Fig. 12. The GSI values of different rock masses of the Lodai area (afterHoek & Marinos 2000).

Table 8. Determination of GSI for the Lodai area

Serial no. RQD Joint condition GSI

a 18 9 22.5b 39 11 38.75c 34 10 34d 31 6 25e 00 14 21f 34 13 39g 57 11 48.5

Table 9. Determination of the coefficient of permeability (K) at the Lodai area

Serial no.Average

aperture (m)Equivalent hydraulic

aperture (m)Joint Roughness Coefficient

(mobilized value)Coefficient of

permeability (K ) (m s−1) Relative permeability

a 0.0030 0.000438 6–8 0.1552 Perviousb 0.0039 0.000499 6–8 0.2015c 0.0067 0.000818 8–10 0.5415d 0.0051 0.000428 4–6 0.1482e 0.0010 0.000189 4–6 0.0289f 0.0045 0.000670 8–10 0.3633g 0.0017 0.000329 6–8 0.0876

Fig. 13. (a) Graphical representation of both Rock Mass Rating (RMR)and Geological Strength Index (GSI) at different points of observation;(b) correlation between GSI and RMR of rock masses.

Fig. 14. Photograph of the Lodai dam in the post monsoon period,January 2013.

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A parallel plate model can explain fluid flow through the rockjoint. It deviates (overestimates) from the real model due to aperturechanges from point to point because of variations in jointparameters. Fluid flow through the dam foundation (i.e. homoge-neous and isotropic) depends on the hydraulic conductivity of theground. The calculated hydraulic conductivity of the area variesbetween 0.0289 and 0.5415 m s−1 (Table 9). However, in asedimentary terrain, where the basement of the dam is composedof fine sandstone, shale hydraulic conductivity should be restrictedto between 10−5 and 10−8 m s−1. The high hydraulic conductivitycan be explained by an increase in the effective porosity through anetwork of intersecting joints, which acted as conduits forcontinuous water movement. Therefore, the basement beneath thefoundation is considered here as a pervious layer. During the post-monsoon period much smaller amounts of water than expected areretained in the reservoir because of continuous seepage through thebasement fractures (Fig. 14).

Conclusions

During the 2001 Bhuj earthquake, ground deformations, in theform of lateral spreading, uplift, deep and wide fractures,developed in the area between the regional faults. Detailedmapping in the area around the dam site shows the presence offour sets of joints, regional faults (the Kachchh Mainland fault andtransverse faults), tilting of beds along the discontinuities, andemplacement of igneous intrusions along the pre-existingdiscontinuities. Distribution of such lineaments, i.e. rock unitattitudes, faults and joint systems, folding, and intrusive bodies,indicates that the site is neotectonically active. A rock masscharacterization study indicates the geotechnical condition of theground in terms of strength and quality is mostly affected bycontinuous tectonism. The basement of this embankment dam iscomposed of loose sediments of Jurassic sandstone and shale,which exhibit characteristics for potential liquefaction duringground shaking and damage at the upstream and downstream faceof the dam. The network of joints, the nature of the aperture,roughness and joint-filling material develop zones of weakness inthe foundation substrate and provide the multiple flow paths thatconduct water through the rock mass. Hence the site is not freefrom continuous seepage due to the high hydraulic conductivity ofjointed rocks. The earth dam near Lodai does not fulfil thepurpose of providing facilities in water supply for domestic andirrigation of agriculture land in this semi-arid region because thereservoir retains a small quantity of water during the post-monsoon period. From a seismic stability point of view, the damhas to withstand excessive settlement, cracks and the stability ofslopes. On the basis of rock mass classification, sufficientremedial measures in redesign and construction of some parts ofthe dam to prevent failure during future earthquakes arerecommended. Special care must be given to the construction ofthe upper part of the dam and of the abutment contacts. Thestrength of the upper part of the dam can be increased either by theprovision of rock mass reinforcement or widening the crest ofthe dam. The slope of upstream and downstream aprons should begentler for creating a wider base to spread the additional loadduring seismic instability. Sealing of foundations should beimproved by taking some treatment, such as grouting and seamtreatment, to enhance the water retention capacity. The controlagainst the longitudinal cracks can be overcome by introducing afull height upstream filter consisting of cohesionless material and awide transition/filter zone using a sand/gravel mixture in thedownstream slope.

Acknowledgements The authors are thankful to Peter Arnold forconstructive comments on the manuscript.

Funding Wewould like to acknowledge IIT (ISM), Dhanbad for sponsoringthe research work of NB and the Department of Science and Technology,Government of India for sponsoring the work of SPM (Grant No. SR/S4/ES-639/2012 dated 17 June 2013).

Scientific editing by Nick Koor; Jim Griffiths

Correction notice: The authors’ names are now in full and the link in thereference NWRWS 2010, has been corrected.

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