Engineering Geology 135-136 (2012) 1–9

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Technical Note

Relationship between textural, petrophysical and mechanical properties ofquartzites: A case study from northwestern Himalaya

Vikram Gupta ⁎, Ruchika SharmaGeotechnical Laboratory, Wadia Institute of Himalayan Geology, 33 General Mahadeo Singh Road, Dehra Dun - 248 001 (Uttarakhand) - India

⁎ Corresponding author. Tel.: +91 135 2525403; fax:E-mail address: vgupta_wihg@yahoo.com (V. Gupta

0013-7952/$ – see front matter © 2012 Elsevier B.V. Alldoi:10.1016/j.enggeo.2012.02.006

a b s t r a c t

a r t i c l e i n f o

Article history:Received 12 November 2010Received in revised form 13 February 2012Accepted 16 February 2012Available online 5 March 2012

Keywords:Texture coefficientP- and S- wave velocityUnconfined compressive strengthQuartziteHimalaya

The quantification of various textural parameters and petrophysical & mechanical properties of quartzites locatedin the Lesser and Higher Himalayas has been carried out. A dimensionless quantity ‘Texture Coefficient’representing rock texture incorporates various textural parameters like grain shape, orientation, degree of graininterlocking and relative proportion of grain andmatrix (packing density) has beenmeasured, besides shape pre-ferred orientation and grain suturing (fractal dimension). These have been correlated with the seismic propertieslike P- and S- wave velocities and attenuation characteristics and unconfined compressive strength. It has beennoted that seismic velocity in rocks is a function of various textural parameters, like with the increase of aspectratio, grain size and shape preferred orientation, velocity increases and with the increase of suturing (fractal di-mension) the velocity decreases. The Texture Coefficient is noted to be inversely proportion to the velocity andthere exits strong positive relationships (R=0.71) between Texture Coefficient and the unconfined compressivestrength. However the relation between the velocity and the unconfined compressive strength is meaningless.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

Petrophysical, textural andmechanical properties of rocks have beeninvestigated since long (Montoto, 1983; Beavis, 1985) and it has beenclassically disputed that many petrophysical and mechanical propertiesof rocks rely on the geologic or petrographic description, includingtextural characteristics. Petrophysical properties that include density,porosity, permeability, water saturation, seismic wave propagation, at-tenuation characteristics etc. describe the occurrence and behavior ofrocks. Textural characteristics refer to the geometrical features of rockparticles such as grain size, grain shape, grain orientation, degree ofgrain interlocking and grain packing density (Williams et al., 1982). Allthese textural parameters have been expressed by a single dimension-less quantity ‘Texture Coefficient’ (Howarth and Rowlands, 1987).Mechanical properties refer to the strength characteristics of rocks.There are numerous studies exhibiting the qualitative relationshipbetween the various parameters of rock texture and the mechanicalproperties of rocks (Olsson, 1974; Bell, 1978; Irfan and Dearman, 1978;Hugman and Friedman, 1979; Onodera and Asoka, 1980; West, 1986;Jeng et al., 2004). There are also studies expressing the relationship be-tween petrophysical and mechanical properties of rocks (Gupta andRao, 1998; Chatterjee and Mukhopadhyay, 2002; Tamrakar et al.,2007). However, quantitative approach of textural characterization andTexture Coefficient is relatively new and is being adopted in rock

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mechanics study only recently (Brosch et al., 2000; Akensson et al.,2001, 2003; Jeng et al., 2004; Raisanen, 2004). This may probably bedue to laborious and time consuming factors.

Among all the textural characteristics, grain size is noted to be thedominant intrinsic rock property that reflects ultimate strength(Olsson, 1974; Bell, 1978; Hugman and Friedman, 1979). It has alsobeen reported that greater grain contact and packing density enablegreater strength (Bell, 1978; Dobereiner and De Freitas, 1986; Bell andCulshaw, 1998). Ulusay et al. (1994) reported that textural characteris-tics appear to be more important than mineral composition to the me-chanical behavior of rocks. Turgul and Zarif (1999) also reported thatthe type of contacts and the grain shape and size significantly influencethe engineering properties of granitic rocks. Limited study available onthe quantification of rock textural properties (Howarth and Rowlands,1987; Ersoy andWaller, 1995; Prikryl, 2006) establishes the relation be-tween Texture Coefficient and the mechanical properties of rocks(Howarth and Rowlands, 1987; Azzoni et al., 1996; Alber andKahraman, 2009). Texture Coefficient returns statistically highly signif-icant correlation with the rock strength and drillability data emphasiz-ing that igneous rocks had high Texture Coefficient, high strength andlow drillability, whereas, sandstone had low Texture Coefficient, lowstrength and high drillability (Howarth and Rowlands, 1987). However,so far the effect of Texture Coefficient on the seismic wave velocity inrocks, particularly from the Himalaya, has not been investigated. Thepresent study emphasizes the quantification of Texture Coefficient, var-ious petrophysical and mechanical properties of quartzites from theLesser and Higher Himalayas, and establishes the inter-relationshipamong them as these rocks are widely used in the construction of

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dams, roads, bridges, tunnels etc. The result of this study could be usedas a guideline to understand the strength characteristics of quartzitebased on the petrographic characteristics.

2. Study area

The study area is located along Alaknanda river and its tributaryDauliganga river in the Garhwal Himalaya. It lies between longitudes78°55'E and 79°35'E and latitudes 30°15'N and 30°42'N and forms apart of the Lesser and the Higher Himalaya (Figure 1). The lesserand higher Himalayan rocks are separated from each other by amajor ‘Main Central Thrust’ (MCT) zone. The zone located near villageHelang separates the medium to high grade metamorphic rocks of theHigher Himalaya from underlying low grade metamorphics and sed-imentary rocks of the Lesser Himalaya. It is characterized by therocks of Munsiari Group dominantly exhibiting quartzites and micaschist with bands of amphibolite (Tapovan Formation). The HigherHimalayan rocks located in the north of the MCT zone are character-ized by the Vaikrita Group of rocks. The dominant lithologies in theVaikrita Group are gneisses and leucogranite (Badrinath Formation),quartzite (Pandukeshwar Formation) and porphyroblastic gneisses(Joshimath Formation). The general trend of these rocks is towardseast-west having northerly dip with an angle varying between 20°and 40°. The rocks belonging to the Lesser Himalayan sequence arecharacterized by the Garhwal Group dominantly exhibiting limestone(Deoban Formation) and quartzite (Berinag Formation). The BerinagFormation is traversed by the Alaknanda Thrust striking NNW–SSE.

Fig. 1. Location map of the area depicting g

The attitude of the Lesser Himalayan rocks is highly variable. In addi-tion, Lesser Himalayan crystalline rocks are also exposed in the formof Klippe (Munsiari Group) around Nandprayag. The detailed geolog-ical set up of the area and its surrounding has been described bySrivastava and Ahmad (1979).

3. Materials and methodology

Five samples of quartzite from Pandukeshwar Formation (P1-5),five from Tapovan Formation (T1-5) and eight samples of quartzitesfrom Berinag Formation (B1-8) were analyzed for the present study.The sampling locations are marked in Fig. 1.

About 30 cm×20 cm×15 cm block of each sample was collectedin the field. In order to remove the effect of anisotropy, all the blocksamples were drilled, parallel to visible linear aligned structure (bed-ding, minerals etc.), to obtain 2.54 cm diameter and about 4–5 cmlength cylindrical cores. Also the thin sections were cut along thelength of the cylindrical cores by intersecting the visible linear struc-ture at an angle of 90º. This helped to carry out the seismic velocitymeasurement and the micro-fabric analysis in one direction only.Physical (dry density and porosity), mineralogical (major mineralconstituents), textural (quantification of textural parameters viz as-pect ratio, grain size, shape preferred orientation, fractal dimensionanalysis, indicating smoothness of the grain boundaries and finallyTexture Coefficient), seismic (P- and S- waves velocity and attenua-tion characteristics) and mechanical (unconfined compressivestrength) properties of each sample were determined. Physical and

eological set up and the sampling sites.

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mechanical properties of each sample were determined as per thestandard testing procedures (I.S.R.M., 1981). Themineral compositionand textural characteristics were studied by means of optical micros-copy, X-ray diffractometry and image analysis software.

3.1. Rock microfabric and its quantification

Rock fabric describes the three-dimensional arrangement of rockforming minerals (Sander, 1966). It includes texture, mainly the geo-metrical aspects of minerals like their shape, size and preferred orien-tation of grains. The quantification of the rock fabric was done in thinsections, prepared along the length of the cylindrical cores, usingimage processing software ImageJ v1.37 developed by Wayne Ras-band of National Institute of Health, USA (http://rsb.info.nih.gov/ij/).The procedure consists of image acquisition, digitization, measure-ment, data analysis and output. During image acquisition, the imagewas captured using a digital camera attached to the microscope. Theboundary of an individual quartz crystal was traced. About 120-150quartz grains in each slide were traced. Data on the area (number ofpixels present within grain boundary), perimeter (number of pixelspresent along grain boundary margin), major axis (number of pixelsadjoining two points defining the major axis) and minor axis (num-ber of pixels adjoining two points defining the minor axis) and theangle between the long axis of each grain and a reference axis i.e. hor-izontal line of the slide were generated. The measured data serve forthe computation of additional fabric parameters, such as grain shape,compactness, shape factor, aspect ratio, grain boundary smoothnessand finally the Texture Coefficient.

Texture Coefficient for all the samples was calculated using thefollowing formula.

TC ¼ AW � N0

N0 þ N1� 1FF0

� �þ N1

N0 þ N1� AR1 � AF1

� �� �

where AW is grain packing weighting, which is the ratio of total grainareawithin reference area boundary and total area enclosed by referenceboundary (includingmatrix), which is 1 in the present case as there is nomatrix, N0 is numbers of grains whose aspect ratio is below pre-set dis-crimination level ‘2’, in the present study, N1 is numbers of grainswhose aspect ratio is above a pre-set discrimination level ‘2’, in the pre-sent study, FF0 is the arithmeticmean of discriminated foamor shape fac-

tor of all N0 grains calculated using4:π:Area

Perimeter2, AR1 is arithmeticmean of

aspect ratio of N1 grains calculated usingMajorAxisMinorAxis

, AF1 is the angle fac-

tor orientation of all N1 grains calculated using15

X9i¼1

XiN N−1ð Þ=2, where N

is the total number of elongated particles, Xi is the number of angulardifferences in each class and i is the weighing factor and class number.Generally, higher Texture Coefficient represents increased roughnessof the grain boundaries, higher elongation and higher grain packingdensity. Detailed description for the calculation of the Texture Coeffi-cient is presented by Howarth and Rowlands (1987) and Ersoy andWaller (1995).

3.2. Quantification of shape preferred orientation

Shape preferred orientation (SPO) defines the strength of linearalignment in a given rock. The intensity of SPOwas quantified by calcu-lating the strength ofmineral lineation defined by the quartz grains. Theangle between the longest axis of each quartz grain and the E–Worien-tation of the microscope stage was determined. The intensity of SPOwas determined by calculating the concentration parameters for quartzusing the excel worksheet of Piazolo and Passchier (2002). The

statistical details about the concentration parameter (k-) have beengiven by Masuda et al. (1999).

3.3. Fractal dimension analysis

The Fractal dimension defining the degree of grain boundary su-turing (smoothness of the grain boundary) was calculated usingarea – perimeter method (Mandelbrot, 1977) using the formula: D ¼logpd where D is fractal dimension, p is the perimeter of the quartzgrain, d is diameter of the equivalent circle having the same area asthat of the quartz grain. It is=2 (a/π) 1/2, where a=area of the quartzgrain. It can be explained as the deviation from the circular grainboundary. For smoother circular grain, ‘D’ is one, the higher the ‘D’,the higher is the suturing of the grain.

3.4. Measurement of seismic wave velocity

Seismic (both P- and S-) wave velocities of the rock cylindrical coreswere measured using ‘time-of-flight ultrasonic pulse transmission tech-nique’ as described by Birch (1960). The velocity measurements weredone at room temperature at ambient conditions. The values of traveltime (tp and ts) and the pulse width (Δtp and Δts) were calculatedusing the time cursor of the oscilloscope as discussed by Rao et al.(2006). The velocities were calculated from the core length and the trav-el time measurement using the formula, velocity=core length / traveltime.

The attenuation (α) of P- and S-waves have also been computed using

α ¼ 8:686πfVQ

where

f is frequency of pulser which is 1 MHz in the present study,V is velocity in cm/s andQ is Quality Factor (dimensionless quantity) obtained by the

following formula

Q ¼ LVΔt

where

L is length (cm) of the core sample,V is velocity in cm/s andΔt is the change in pulse width in microseconds

4. Petrography

The petrographic study of Pandukeshwar, Tapovan and Berinagquartzites reveal that these are essentially composed dominantly ofquartz grain with minor amount of sillimanite, muscovite, garnet andopaques as accessory minerals. The petrographic characteristics of eachare as follows:-

4.1. Pandukeshwar quartzite

Pandukeshwar quartzites are medium grained consisting mainlyof quartz grains showing undulatory as well as straight extinctionwith heterogranular texture (Figure 2a). The boundaries of the quartzgrains in all the samples are highly serrated and irregular. Minoramount of sillimanite and muscovite is also present which is alignedin one particular direction (Figure 2a). P4 is weathered with smallbroken pieces of garnet visible in thin section (Figure 2b). P3 containsappreciable amount (~20%) of micaceous minerals (15% biotite and

Fig. 2. Photomicrographs of the quartzite studied (a) Pandukeshwar quartzite (P1): quartz grains with preferred orientation exhibiting irregular and serrated grain boundariesshowing undulose extinction (b) Pandukeshwar quartzite (P4): Garnet exhibiting high relief and quartz grains are seen (c) Pandukeshwar quartzite (P5): quartz grains exhibitingirregular and serrated grain boundaries. Muscovite and opaque minerals are also visible (d) Tapovan quartzite (T5): large amount of preferentially orientated muscovite separatedby quartz rich layers (e) Tapovan quartzite (T2): quartz and muscovite grains exhibiting strong preferred orientation of grain. The grain boundaries are generally straight and su-tured. (f) Berinag quartzite (B4): Inequigranular quartz grains exhibiting straight grain boundaries. Very fine siliceous material is present between two grain boundaries exhibitingfoam texture (g) Berinag quartzite (B5): Elongated, undulose quartz surrounded by fine grained recrystallised quartz. The grain boundaries of quartz exhibiting preferred orienta-tion are highly serrated (h) Berinag quartzite (B8): Poorly sorted, rounded to sub-rounded highly cracked quartz grains embedded in silicious cementing material.

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5% muscovite) and opaques as accessory minerals, whilst P5 containsabout 1–2% of opaque minerals (Figure 2c).

4.2. Tapovan quartzite

Tapovan quartzites are medium to coarse grained. These mainlycomprise ~93%–95% quartz and ~5%–7% micaceous minerals, except

T5 which contains about 10% micaceous minerals that are aligned toform lineation (Figure 2d). The quartz grains are mainly equigranularand exhibit interlocking texture showing straight extinction. Thequartz grain boundaries in most of the samples are straight meetingat triple junction (Figure 2e), whereas quartz grain boundaries in T3and T5 are slightly serrated. T5 is foliated quartzite defined by themica rich and the quartz rich layers (Figure 2d).

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4.3. Berinag quartzite

The size of the quartz grains in the Berinag quartzites varies fromvery fine to coarse grained. The contacts between the individual quartzgrains in B1-4 are straight exhibiting foam texture (Figure 2f). Smallamount of micaceous minerals are present in B2. B5-6 exhibit preferredorientation of quartz grains (Figure 2g). Many smaller recrystallisedquartz grains are also visible surrounding the larger quartz grains(Figure 2g). These larger quartz grains exhibit undulose extinction(Figure 2g). B7 exhibits sub-rounded to rounded quartz grains showingstraight and undulose extinction. B8 exhibits rounded to sub-roundedwell sorted fractured grains of quartz (Figure 2h).

5. Results

The results of the fabric analysis, petrophysical and mechanicalproperties are presented in Table 1 and are described hereunder:-

5.1. Grain morphometry

5.1.1. Aspect ratio (AR)Aspect ratio, indicating the elongation of an individual grain is de-

fined as the ratio of length and width of the grain. For the circulargrain, aspect ratio is 1, and it increases as the grains become elongat-ed. It has been observed that in Pandukeshwar, Tapovan and Berinagquartzites, the aspect ratio varies between 1.48–1.98, 1.51–1.71 and1.41–1.94 with an average value of 1.66, 1.61 and 1.61, respectively.Further B1 exhibits the lowest (1.42) aspect ratio, whereas P1 thehighest (1.98) (Table 1).

5.1.2. Grain sizeIt has been observed that the grain size of the quartz grains in the

Pandukeshwar, Tapovan and Berinag quartzites varies between 4.70–15.34 mm2, 4.58–20.11 mm2, and 6.06–26.60 mm2 with an averagevalue of 9.00 mm2, 13.24 mm2 and 11.95 mm2, respectively. Generally,all the quartzites are medium to coarse grained, however, P1 belongingto Pandukeshwar quartzite, T1, T2 and T4 belonging to Tapovan quartz-ite and B6 and B7 belonging to Berinag quartzite are more coarser(>14 mm2) than P3-5 belonging to Pandukeshwar quartzite, T3 and T5belonging to Tapovan quartzite and B1-5 and B8 belonging to Berinagquartzite (b14 mm2) (Table 1). Our petrographic studies on these

Table 1Textural characteristics (aspect ratio, grain size, shape preferred orientation, fractal dimensteristics, mechanical properties (unconfined compressive strength) and physical properties

SampleNo

TexturalProperties

AspectRatio

Area(mm2)

Shape PreferredOrientation

FractalDimension

TexturCoeffic

PandukeshwarQuartzite

P1 1.98 15.34 2.05 1.292 2.01P2 1.48 5.73 0.38 1.293 3.22P3 1.56 13.86 0.70 1.262 2.79P4 1.48 5.37 0.35 1.285 2.60P5 1.81 4.70 1.59 1.330 2.74

Tapovan Quartzite T1 1.66 14.71 1.66 1.258 2.16T2 1.71 17.48 2.23 1.247 1.77T3 1.51 9.31 1.19 1.269 2.77T4 1.52 20.11 0.88 1.250 2.33T5 1.64 4.58 1.33 1.275 2.41

Berinag Quartzite B1 1.42 8.46 0.21 1.245 3.31B2 1.66 8.12 2.46 1.300 1.69B3 1.59 6.15 1.88 1.260 1.97B4 1.45 6.06 0.73 1.255 2.58B5 1.94 8.40 2.05 1.262 1.49B6 1.79 26.60 1.50 1.251 2.20B7 1.53 21.17 0.57 1.252 2.70B8 1.49 10.65 0.51 1.236 2.60

quartzites also reveal P1 belonging to Pandukeshwar quartzite(Figure 2a), T1-2 and T4 belonging to Tapovan quartzite and B6-7 belong-ing to Berinag quartzite are coarser grained and the rest are mediumgrained.

5.1.3. Shape preferred orientationThe shape preferred orientation of quartz grains for Pandukeshwar,

Tapovan and Berinag quartzites are presented in Table 1. It has beennoted that among all the quartzites studied, P1 (Pandukeshwarquartzite), T2 (Tapovan quartzite) and B2 and B5 (Berinag quartzite) in-dicate strong preferred orientation of quartz grains with k-value >2.0,whereas P5, T1, T3, T5, B3 and B6 indicatemoderate preferred orientationof quartz grains with k- value between 1.0 and 2.0, and the rest ofthe quartzites indicate no preferred orientation of quartz grains withk-value b1.0 (Table 1).

5.1.4. Grain boundary suturing (D)The fractal dimension ‘D’ of Pandukeshwar, Tapovan and Berinag

quartzites are presented in Table 1. It has been noted that all thequartzites are sutured with P5 and B2 indicating more suturing(‘D’>1.3) than the rest of the quartzites (‘D’ between 1.2 and 1.3).

5.1.5. Texture coefficientThe Texture Coefficient (TC) in the Pandukeshwar, Tapovan and

Berinag quartzites varies between 2.01–3.22, 1.77–2.77 and 1.49–3.31 with an average value of 2.67, 2.29 and 2.32, respectively(Table 1). It has been noted that B1 exhibits the highest Texture Coef-ficient (3.31) followed by P2 (3.22). The lowest TC is exhibited by B5(1.49). T2, B2 and B3 exhibit TC between 1.5 and 2.0, whereas rest ofthe quartzites exhibit TC between 2.0 and 3.0. (Table 1)

5.2. Physical characteristics of quartzite

The physical properties of Pandukeshwar, Tapovan and Berinagquartzites are almost same. The average density of Pandukeshwar,Tapovan and Berinag quartzites is 2.71 g/cm3, 2.66 g/cm3 and2.69 g/cm3, respectively. Quartzites containing heavy minerals likegarnet and opaques show slightly higher density like P4 (Figure 2b)and P5 (Figure 2c) than the quartzites containing quartz only. Howeverthe porosity of all the quartzites studied is b1% (Table 1).

ion and texture coefficient), Seismic (P- and S-) wave velocity and attenuation charac-(density and porosity) of the Pandukeshwar, Tapovan and Berinag quartzites.

Physical Properties SeismicProperties

MechanicalProperties

eient

Density(g/cm3)

Porosity(%)

Vp(m/s)

Vs(m/s)

AttenuationVp (db/cm)

AttenuationVs (db/cm)

UCS (MPa)

2.6 0.6 4324 3223 0.72 5.90 632.65 0.3 3244 2334 1.93 6.00 982.67 0.5 2302 1424 1.53 6.90 902.82 0.9 1476 990 1.32 13.09 1012.81 0.8 4120 2053 3.00 8.55 1412.63 0.4 3554 2927 0.90 5.27 882.63 0.6 5531 3955 0.52 3.20 522.64 0.7 5288 3330 1.50 3.96 1112.69 0.7 4944 3678 1.08 5.40 792.69 0.9 3300 2423 1.66 4.74 552.63 0.5 2812 2246 2.07 7.88 1222.74 0.6 3966 2621 0.39 5.85 462.76 0.5 2375 2466 0.71 6.77 862.74 0.5 2509 1651 1.33 4.94 922.71 0.7 4432 2910 0.94 4.99 502.63 0.6 5418 3449 0.95 3.90 1252.61 0.5 5010 3445 1.45 3.00 1092.73 1.5 4533 2964 1.36 3.00 87

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5.3. Seismic (P- and S-) wave velocities and attenuation characteristicsof quartzite

Tapovan quartzites exhibit the highest average Vp (4523 m/s) andVs (3263 m/s) followed by Berinag (Vp 3882 m/s, Vs 2719 m/s) andPandukeshwar (Vp 3093 m/s, Vs 2005 m/s) quartzites (Table 1).Within the Pandukeshwar quartzites, P1 exhibits the highest Vp and Vs(4324 m/s and 3223 m/s) and P4 the lowest (1476 m/s and 990 m/s),within Tapovan quartzites, T2 exhibits the highest Vp and Vs (5531 m/sand 3955 m/s) and T5 the lowest (3300 m/s and 2423 m/s) and withinBerinag quartzites, B6 exhibits the highest Vp and Vs (5418 m/s and3449 m/s) and B3 the lowest (2375 m/s and 2466 m/s). Large variationin Vp andVs in each group of quartzitemay be related to varying texturalcharacteristics.

As expected, it has also been noted that the attenuation of S-wavesis higher than P-waves. Among all the quartzites, Pandukeshwarquartzites exhibit the highest P- and S- wave attenuation characteris-tics of 1.70 db/cm and 8.09 db/cm, followed by Berinag and Tapovanquartzites exhibiting average attenuation characteristics of 1.15 db/cm and 5.04 db/cm and 1.13 db/cm and 4.51 db/cm, respectively.

5.4. Mechanical characteristics of quartzite

The unconfined compressive strength (UCS) for the Pandukeshwar,Tapovan and Berinag quartzites varies between 63 MPa–141 Mpa,52 MPa–111 MPa and 46 MPa–125 MPa with an average value of99 MPa, 79 MPa and 90 MPa (Table 1). Within the Pandukeshwarquartzites, P5 exhibits the highest (141 MPa) UCS and P1 the lowest(63 MPa), within Tapovan quartzites, T3 exhibits the highest(111 MPa) UCS and T2 the lowest (52 MPa) and within Berinag

Fig. 3. Relationship between various texture parameters (a) Aspect ratio (b) grain size (c) shwave (P- and S- waves) velocity in Pandukeshwar, Tapovan and Berinag quartzites. (Blacvelocity).

quartzites, B6 exhibits the highest (125 MPa) UCS and B2 the lowest(46 MPa). All these quartzites were classified as strong to very strong(Bieniawski, 1979). It has also been noted that failure of the all thequartzites were like an explosion with no visible failure plane.

5.5. Inter-relationship among textural, petrophysical and mechanicalproperties of quartzite

5.5.1. Textural versus seismic propertiesIt has been observed that seismic (both P- and S-) waves velocity

increases with the increase in AR, grain size and the preferred orien-tation of grains (Figure 3a, b, c). The correlation coefficient (R) be-tween AR, grain size, and SPO is 0.39, 0.65 and 0.37 for the P- wavevelocity and 0.33, 0.67 and 0.41 for the S- wave velocity. Generally,seismic wave velocity should increase with increase in AR and SPO,as the increase in both the parameters indicate the elongation ofgrains. The grain elongation reduces the contact area of any two indi-vidual grains, thereby reducing the attenuation and hence increasesthe seismic wave velocity. The moderately positive strength of rela-tion exists between seismic wave velocity and grain size, whereasweak positive relation exists between seismic wave velocity andother textural parameters like aspect ratio and SPO. These pointtowards the fact that there are other factors like density of cracks,lattice / crystallographic preferred orientation etc. that offset theseismic wave velocity.

It has also been noted that the suturing of the grain boundary doesnot control the seismic wave velocity (Figure 3d), as the strength ofrelationship between fractal dimension and P- wave velocity is poor(R=0.18) and between fractal dimension and S- wave velocity, it isweak (R=0.36). Further the increase in Texture Coefficient also

ape preferred orientation (d) fractal dimension and (e) texture coefficient with seismick soild circles demarcate P- wave velocity and red solid triangles demarcate S- wave

Fig. 4. Relationship between various texture parameters (a) Aspect ratio (b) grain size (c) shape preferred orientation (d) fractal dimension and (e) texture coefficient with uncon-fined compressive strength in Pandukeshwar, Tapovan and Berinag quartzites.

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decreases the seismic wave velocity (Figure 3e) with the correlationcoefficient of 0.31 for P-wave and 0.40 for S-wave.

5.5.2. Textural versus mechanical propertiesFig. 4 plots the relationship between various textural parameters

and unconfined compressive strength (UCS) of all the quartzite stud-ied. It has been noted that UCS decreases with the increase in AR andSPOwith the correlation coefficient of 0.32 and 0.54 (Figure 4a and c).There seems no relationship between grain size and fractal dimensionwith the UCS (Figure 4b and d). However, the relationship betweenTexture Coefficient and the UCS is strong with a correlation coeffi-cient of 0.71 (Figure 4e).

5.5.3. Mechanical versus seismic propertiesFig. 5 plots the relationship between UCS and the seismic wave ve-

locity. In the present case for all the quartzites studied, there is no re-lation between the UCS and the seismic wave velocity.

Fig. 5. Relationship between unconfined compressive strength and seismic wave veloc-ity (P- and S- waves) in all the quartzites. (Black soild circles demarcate P- wave veloc-ity and red solid triangles demarcate S- wave velocity).

6. Discussions

The quantification of textural, petrophysical and mechanical prop-erties of quartzites from Lesser and Higher Himalaya has helped us toestablish the inter-relationship among them. The control of varioustextural parameters is demonstrated on the seismic and mechanicalproperties of quartzite. The samples taken for the present study hassimilar porosity (b1%) and density (2.60–2.82 g/cm3) as these aredominantly made up of quartz and muscovite having an average den-sity of 2.65 g/cm3 and 2.67 g/cm3, respectively. However, two sam-ples P4 and P5 belonging to the Pandukeshwar quartzite has higherdensity of 2.80 g/cm3 and 2.81 g/cm3. The higher density in thesesamples may be attributed to the presence of small quantity (b0.5%)of magnetite. It has been noted in our earlier study on granites thatthe minor quantity of magnetite minerals in rocks significantly in-creases the density, as the density of the single crystal of magnetiteis 5.08 g/cm3, not necessarily affecting the seismic and mechanicalproperties of rocks (Sharma et al., 2011).

There is variation in the aspect ratio of all the quartzite studiedfrom 1.42 to 1.98. Generally, the increase in aspect ratio points to-wards the increase in elongation, thereby aligning the grains in oneparticular direction. This resulted in the reduction in contact areaboundary of two grains and hence lowers the attenuation characteris-tics. Therefore as expected, the attenuation decreases with the in-crease in aspect ratio (Figure 6a) and shape preferred orientation(Figure 6b). Among Pandukeshwar, Tapovan and Berinag quartzites,Tapovan quartzites exhibit the highest average P- and S- wave veloc-ity (Table 1). This may be because of the combined effect of coarsegrained nature, higher aspect ratio and higher preferred orientation.Still within the Tapovan quartzites, T2-4 exhibit an average velocityof 5254 m/s and T1 and T5 exhibit an average velocity of 3427 m/s.The highest velocity in T2 (5531 m/s for P- wave and 3955 m/s forS-wave) may be attributed to the higher SPO (2.23) and higher aspectratio (1.71). The lowest velocity in T5 may be attributed to the smallergrain size of quartz, thus exhibiting higher number of grain

Fig. 6. Relationship between (a) attenuation–aspect ratio and (b) between attenua-tion–shape preferred orientation of all the quartzites . (Black soild circles demarcateP- wave velocity and red solid triangles demarcate S- wave velocity).

8 V. Gupta, R. Sharma / Engineering Geology 135-136 (2012) 1–9

boundaries contact, and higher attenuation. It may be noted that seis-mic velocities find the shortest path to travel from one point to anoth-er. Attenuation of P- and S- waves has also been noted to decreasewith the increase of aspect ratio (Figure 6a) and SPO (Figure 6b).

Velocity is weakly (R=0.2–0.5) to moderately strongly (R=0. 5–0.7) correlated to various textural parameters. It increases with theincrease of aspect ratio (Figure 3a), grain size (Figure 3b) and SPO(Figure 3c) and decreases with the increase in fractal dimension /suturing (Figure 3d). The decrease in velocity with the increase ofTexture Coefficient (Figure 3e) indicates that the offset produced bythe decrease in velocity by fractal dimension is more pronounced thanthe collective increase of velocity by aspect ratio, grain size and SPO.

UCS is also strongly related to Texture Coefficient with a correla-tion coefficient of 0.71. The similar trend of UCS with TC has alsobeen reported by Howarth and Rowlands (1987). However, none ofthe individual textural parameter except aspect ratio and SPO proveda close correlation to the UCS. Aspect ratio and SPO has correlation co-efficient of 0.32 and 0.54 with the UCS. Prikryl (2006) while workingon granites reported that rock mechanical property is a function ofgrain size with fine grained rocks exhibiting more strength than thecoarse grained rocks. However, in the present study strength isnoted to be the function of Texture Coefficient. (Figure 4e)

7. Conclusions

In the present study, the quantification of textural, petrophysicaland mechanical properties of the Lesser and Higher Himalayanquartzites were studied. Our study draws the following conclusions.

• Among Pandukeshwar, Tapovan and Berinag quartzites, Tapovanquartzites exhibit the highest average P- and S- wave velocity(4523 m/s for P- wave and 3263 m/s for S-wave), lowest fractal di-mension (1.260), lowest attenuation (1.13 db/cm for P-wave and

4.51 db/cm for S-wave), and lowest unconfined compressivestrength (77 MPa).

• Various textural parameters like aspect ratio, grain size, and shapepreferred orientation is directly related to the seismic (P- and S-)wave velocity as with the increase of these parameters the velocityincreases (Figure 3a, b & c), whereas the fractal dimension is in-versely related to the seismic wave velocity (Figure 3d).

• The combination of all the textural parameters is reflected in theTexture Coefficient of rocks and it has been noted that seismicwave velocity decreases with the increase of Texture Coefficient(Figure 3e).

• Unconfined compressive strength (UCS) of rocks is strongly related(R=0.71) to Texture Coefficient.

• There exists no relation between velocity and the UCS.• The attenuation characteristic of P- and S- wave is inversely propor-tional to the aspect ratio and SPO.

Acknowledgement

Authors thank the Director, Wadia Institute of Himalayan Geology,Dehra Dun for his kind permission to publish the paper.

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