International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com June 2015, Volume 3, Issue 6, ISSN 2349-4476

Geotechnical Charaecteraization of Weathered Khondalite Zones, Indrakheeladri Hills, Vijayawada, Andhra Pradesh, India

Dr. T.S. R .Chowdary1 , Dr K.S.R Prasad1, T.S. Ram Babu2 Professor1, Assoc. Professor2 Department of Civil Engineering, VR Siddhartha Engineering College, Vijayawada, A.P India-520007

Abstract The Present study is an attempt on evaluation of geotechnical characterization of the cut slope sections along the Godess Kanakadurga temple, Indrakheeladri Hills, Vijayawada, Andhra Pradesh. These rocks typically show varied weathering characteristics and may contribute to instability of slopes along the road sections. The surface and core rock samples are collected for at different depths and were described into four geotechnical units i.e KH-I to KH-IV .The geotechnical characterization of all these four units were studied by density, porosity and strength properties. Based on the Field, physical and mechanical properties, it is suggested that the KH-IV zone expected to behave like a weak rock and in some cases expected to have a soil characteristics. The stability of these slopes are highly controlled by persistent joint sets. The study also suggested that major failures were caused by the presence of weak cohesive layers , steep cutting angles and unfavorable dip of strata along the slopes

Key words: weathering, khondalites, geotechnical characters, slope stability.

Introduction The influence of rock weathering and evolution of rock slopes is an important part of study in any civil engineering project involves along the slopes .Weathering influences the strength of rock slopesDuncan(1969) defines ‘rock material’ as an aggregate of mineral particles and voids that may be isolated or interconnected, and air or water-filled. It is synonymous with the term ‘intact rock’ which specifically refers to rock containing no discontinuities (Johnson and DeGraff, 1988). It is essential to remember how highly variable rock is compared to synthetic engineered materials normally used in construction, such as concrete or steel (Hudson and Harrison, 1997).The weathered rock material strength is a fundamental quantitative geotechnical property. Intact rock strength by definition is the amount of applied stress at rock failure or rupture(Johnson and DeGraff, 1988). Strength is particularly affected by the nature of the bonds or cement between particles within a specimen and weathering nature . (de Freitas, 1993).Water also substantially influences rock strength and is known to influence the molecular structure of mineral surfaces. Although all rocks appear to lose strength when exposed to moisture, rocks that are weak to begin with are often affected considerably more (de Freitas,1993). Anisotropy, where a material varies in different directions, is also particularly important factor to be considered in the slope stability. Rock slides are the most common feature along the ghat road sections on the way to Godess Kanakadurga temple, Indrakheeladri hills at close proximity with Vijayawada city. Every year lakhs of people pilgrimage the temple. Rock and debris slides are the major failures are reported. Even though, the temple authorities have adopted several remedial measures to stabilize the slopes a series of incidents occur every year leading to damage of civil engineering structures and road blockages. Present study The Main objective of the present study is to: • Evaluate the engineering behavior of the weathered rock material along the cut slopes of the Indrakheeladri Hills.. • Determination of the rock material characteristics by means of relevant laboratory testing and suggest the suitable measures to prevent the rock slides during the monsoon season

199 Dr. T.S. R .Chowdary, Dr K.S.R Prasad, T.S. Ram Babu

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com June 2015, Volume 3, Issue 6, ISSN 2349-4476

Location and Geology of the area Indrakheeladri is a piligramic centre situated with a close proximity to Vijayawada city The area under investigation falls mostly in the Khondalitic-Charnockitic Zone of the eastern ghat group of rocks. Figure1 shows the geology and major tectonic features of the study area. Eastern Ghats, covering parts of Orissa, Andhra Pradesh, Tamil Nadu and a small part of Karnataka, comprises of typical assemblage of charnockite and khondalite groups, migmatitic gneisses, granitoids and pegmatite,all metamorphosed in high-grade granulite facieses. The Eastern Ghats Mobile Belt (EGMB) occupies an area ofover 15,000 sq. kms in the north east and south west and extends from Brahmani River in Orissa to Ongole in Andhra Pradesh for a distance of about 900 kms with a maximum width of 300 kms in the northern parts ofOrissa. It tapers down to less than 10 kms in width to the southern parts of Andhra Pradesh. It is broadly divided infour longitudinal zones as: (1)Western Charnockite Zone(WCZ), (2) Western Khondalite Zone (WKZ), (3)Central Migmatite Zone (CMZ) and (4) EasternKhondalite Zone (EKZ) (Nanda 1995, Ramakrishnanet.al., 1998), (Fig. 1).Zonation in EGMB was visualized by Banerjee et.al.,(1987 and Ramakrishnan et.al., 1998) with reference to WCZ,WKZ,CMZ and EKZ. The nature of the EGMB is marked by metasediments of khondalite group, restricted granulititc formations in conspicuous units, concordant sheets of pyroxene granulites, shear zones, lineaments The area comprises mainly of rock units of the khondalite(garnet silimanite cordirite gneiss associated with minorquartzite) and charnockite groups of the Eastern Ghats Super Group and granite gneisses of Achaean age, Cenozoic late rites and Recent alluvium.

Figure 1. Location of EGMB and the study area along with geology, major tectonic elements and epicenters of earthquakes of the studyarea. Epicenter data (after Krishna Brahmam,1989)

Investigation Methodology Several stages of investigation were necessary to determine the geotechnical issues facing a proposed extension of slopes in the Indrakheeladri.. Initial field work involved checking litho logical boundaries from existing geological maps. Drilled core samples were collected during exploratory drill holes from proposed construction activities .Both physical and mechanical properties of the khondalites and over burden material were assessed by means of laboratory testing of drill cores. The samples were divided into four litho logical units and compared in terms of rock material behavior. The physical tests chosen were porosity, density which give indications of strength and weathering properties of the materials 200 Dr. T.S. R .Chowdary, Dr K.S.R Prasad, T.S. Ram Babu

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com June 2015, Volume 3, Issue 6, ISSN 2349-4476

The mechanical tests included unconfined compressive strength,. For determination of the uniaxial compressive strength of rock materials as published in Brown (1981) was followed for sample preparation and testing. The core samples with the length to diameter ratio of 2.5:1 suggested. However the grinding process to produce flat and parallel ends caused several samples to lose some length when they broke along bedding planes. Hawkes and Mellor (1970) reviewed the effect of varying the specimen length and they concluded that minimum acceptable L:D ratio was 2.0:1. The minimum length tested by this author was 140 mm (2.3:1) which is well above this. The diameter of each sample was measured at the top, middle and bottom of the sample and averaged. The diameter and length were both measured using a digital calliper to 0.01mm. All samples were tested as collected and saturation was assumed as natural moisture content. Rock Mass Properties Detailed study was made on structural discontinuities along the ghat road section (Fig.2).They were under taken along walls with different orientations, which reduces sampling bias, and on both sides of the valley to include any large scale structural deformation. The properties recorded include defect type, defect orientation, spacing, hardness, strength, persistence, aperture, infilling and roughness. Drill core records were assessed to give an indication of rock quality and were analyzed by graphical methods. From this, the rock slope stability was determined to provide a prediction of what might be expected to occur along the ghat road.. Kinematic feasibility checks on proposed orientations for the ghat road cut section, were performed for planar, wedge and toppling type failures. An optimum orientation is suggested and any likely failures are discussed as well as other slope stability considerations.

Physical Description of Rock Formations KH-I. Slightly weathered, moderately weak to moderately strong, light brownish grey or dark brownish grey, massive or finely layered, khondalite with Micaceous flakes. (Figure 3) KH-II. Moderately weathered, weak to very weak, dark greyish brown, massive or finely layered, KH-III. Slightly weathered, moderately weak to very weak, light brownish or yellowish grey, fine layers (0.5- 5mm) and coarse layers (80-100mm), khondalite interbedded with pegmatite veins. KH-IV. Completely weathered, very weak, light brownish grey, massive, loose Khondalite. (Figure.4)

Figure 2: Location Showing the details of the cut slope road section along the weathered khondalitic zones (KH-I to KH-IV) 201 Dr. T.S. R .Chowdary, Dr K.S.R Prasad, T.S. Ram Babu

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com June 2015, Volume 3, Issue 6, ISSN 2349-4476

Figure 3: KH –III Zone of Partially weathered Rocks

Figure 4: KH-IV- Zone of Completely Weathered rocks

Geotechnical Properties of weathered Formations Porosity-Density The porosity of a sample of rock material is defined by Duncan (1969) as the ratio of the volume of voids to the total volume. It therefore depends on the shape of the grains within the sample, their size distribution, orientation and the amount of compaction and cementation that has occurred. When pores are present the strength decreases in the fabric of the rock material and the deformability or elastic modulus increases (Hawkes & Mellor, 1970). Correlations with mechanical properties such as unconfined compressive strength however usually involve significant scatter (Goodman, 1980). Most rocks show a correlation between porosity and dry density when they have similar grain densities.

202 Dr. T.S. R .Chowdary, Dr K.S.R Prasad, T.S. Ram Babu

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com June 2015, Volume 3, Issue 6, ISSN 2349-4476

Density is defined as the weight of the solid mineral matter per unit volume (Duncan, 1969). Table .1 provides a summary of the properties obtained from the density testes recommended by IS codes. Unit KH-I KH-II KH-III KH-IV (1) (2) (3) (4) (5) light brownish brownish red, brownish and highly weathered Unit Description grey, slightly Moderately yellowish reddish yellow weathered weathered rock highly with mica rock rock weathered rock Number of 10 09 08 06 samples *Porosity(%) 5.56 4.69 7.52 11.44

*Void ratio(e) 0.1 0.14 0.13 0.19

*Dry Density 2337 1988 1781 1262 ( Kg /m3)

*Saturated 2567 2679 2321 1867 Density ( Kg /m3) *Compressive strength (Kg/cm2) 1242 1145 956 546

*average values Table 1: Showing summary of Porosity – Density Parameters with physical appearance of samples.

In the present study the porosity values ( Table 1) show considerable variations within the rock units . However there is a small variation noticed between KH-I and KH-II units due to presence of structural lineation and foliation of rock. The results can be further assessed using Lucas’s rock classification Table,2 as follows:

Classification Porosity(%) Density (kg/m3) (1) (2) (3) Very High >30 >2500

High 10-30 2300-2500

Medium 5-10 2100-2300 Low 2.5-5 1900-2100

Very Low <2.5 <1900

Table 2: Showing classification of porosity-density on weathered rocks (after Lucas ,2002) The average dry and saturated densities show considerable scatter between the units tested due to non uniformity of weathering of the rocks. Slightly and moderately weathered rock units suggest higher values than the completely weathered rocks. The relationship between dry density and porosity for all the units is shown in Fig.5 and the dry density does indeed decrease with increasing porosity There is a clear overlap between values for all zones,

203 Dr. T.S. R .Chowdary, Dr K.S.R Prasad, T.S. Ram Babu

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com June 2015, Volume 3, Issue 6, ISSN 2349-4476

Figure 5: Showing the density Vs porosity values of weathered zones

Strength Uniaxial compressive strength (UCS) is one of the most significant geotechnical properties of rock, being of importance in slope stability analyses and other mining projects. The UCS is useful approximate parameter when considering a variety of issues encountered during blasting, excavation and supporting engineering works(Hock,1977).UCS values are also employed in geo mechanical classification of rock mass ( Barton et al..1974) UCS tests are performed using NX-size (54mm) core samples of weathered khondalitic rocks. A considerable change in the UCS values in all the four zones. The average UCS values in different khondalitic zones are given in Table.1. The rate of weathering proceeds measurable decrease in the UCS values is observed and it will also serve as aid to classify the rocks into four distinct zones.

RQD The RQD for each interval of every drill core was calculated. The results from the 8 drill holes show that 20% of core was within the excellent class (RQD =90-100%), while 73% was at the other end of the scale, in the very poor quality rock (RQD = 0-25%). This suggests that the rate of weathering is not uniform and also controlled by persistent joint sets. The RQD values were also established according to the four units KH-I to KH-IV e. Histogram and frequency of values within a range of RQD (%).of rock quality are calculated using Barton et al., (1974) for all the bore hole samples( Figure 7and Figure 8 and Table 3 and Table 4).

Drilled *0-24 25-49 50-74 75-89 90-100 Total core samples (1) (2) (3) (4) (5) (6) (7) KS1 8 4 1 1 0 12 KS2 9 3 0 0 0 12 KS3 6 2 2 1 3 14 KS4 5 4 3 2 1 15 KS5 11 5 2 1 1 20 KS6 12 2 1 0 0 15 KS7 16 3 3 1 1 24 KS8 21 3 2 1 1 28 *(frequency interval after Barton etal.,(1974) Table 3: Showing frequency of values within a range of RQD (%). 204 Dr. T.S. R .Chowdary, Dr K.S.R Prasad, T.S. Ram Babu

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com June 2015, Volume 3, Issue 6, ISSN 2349-4476

UNIT KH-I KH-II KH-III KH-IV (1) (2) (3) (4) (5) Interval *0-24 6 14 19 0 25-49 1 4 6 0 50-74 1 8 4 3 75-89 7 6 3 2 90-100 13 9 14 4 *(frequency interval after Barton etal.,(1974) Table 4: Showing frequency of RQD (%) values for each unit.

Figure 6: Histogram showing the frequency of RQD for each unit as a percentage

Figure 7: Histogram showing the frequency of RQD for Drilled core samples 205 Dr. T.S. R .Chowdary, Dr K.S.R Prasad, T.S. Ram Babu

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com June 2015, Volume 3, Issue 6, ISSN 2349-4476

Summary and Conclusion Based on the Field, physical and mechanical properties , it is suggested that the KH-III and KH-IV zone expected to behave like a weak rock and in some cases expected to have a soil characteristics. The slope stability of these zones is highly controlled by persistent joint sets. Establishment of these joint sets is further aid to short and long term stability of the hill slopes along the ghat road. The study showed that major cut slope failures were caused by the presence of weak cohesive layers consist of soft pegmatitic clay material. In addition to the steep cutting angles and unfavorable dip of strata are the alarmingly high level of instability in cut slopes with more than 60 percent of the entire length was found to have high level of instability.

References  Barton, M.E., Mockett, .D.,and Palmer, S.N., 1993. An engineering geological classification of the soil/rock borderline materials between sands and sandstones, in Cripps, J.C.,  Coulthard,J.M., Culshaw, M.G., Forster, A., Hencher, S.R., and Moon, C.F., eds., The engineering geology of weak rock: Engineering Geology Special Publication, vol.8, p. 125-138.  Barton, N., and Choubey, V. 1977. The shear strength of rock joints in theory and practice: RockMechanics, v. 10, p. 1-54.  Barton, N., Lien, R., and Lunde, J., 1974. Engineering classification of rock masses for design oftunnel support: Rock Mechanics, v. 6, p. 189-236.  Barton, N.R., 1973. Review of a new shear strength criterion for rock joints: Engineering Geology,v. 7, p. 287- 322.  Bell, D.H, and Pettinga, J.R., 1983: Rock Material Description System, University of Canterbury  Benerji, P. K., On the geology of the Eastern Ghats of Orissa and Andhra Pradesh, India. In Precambrian Continental Crust and its Mineral Resources (ed. Naqui, S. M.), Elsevier, 1990, pp. 391–407  Brown, E.T. (Editor), 1981. Rock Characterisation, Testing and Monitoring, ISRM SuggestedMethods: England, Pergamon Press, 211 p.  de Freitas, M.H., 1993. Introduction to Session 1.2; Weak arenaceous materials, in Cripps, J.C.,Coulthard, J.M., Culshaw, M.G., Forster, A., Hencher, S.R., and Moon, C.F., eds., The  Engineering geology of weak rock: Engineering Geology Special Publication, vol.8, p. 115-123.  Duncan, N., 1969. Engineering Geology and Rock Mechanics: London, Leonard Hill, 267 p.  Goodman, R.E., 1976. Methods of geological engineering in discontinuous rocks: St Paul, Minnesota, West Publishing Co., 472 p.  Hawkes, I., and Mellor, M., 1970. Uniaxial testing in rock mechanics laboratories: Engineering Geology, v. 4, p. 177-285.—, 1980. Introduction to Rock Mechanics: New York, John Wiley & Sons, 478 p.  Hudson, J.A., and Harrison, J.P., 1997. Engineering Rock Mechanics: An Introduction to the  Principles: Oxford, Pergamon, 444 Fetter, C.W., 2001. Applied Hydrogeology: New Jersey, Prentice-Hall, 598 p.  Johnson, R.B., and DeGraff, J.V., 1988. Principles of Engineering Geology: New York, John Wiley& Sons, 497 p.  Krishna Brahmam, N., Gravity and seismicity of the Cuddapah basin and surrounding places. J. Geol. Soc. India, 1989, 34, 373–384.  Ramakrishnan, M.,Tectonic evolution of the Archean high grade terrains of South India. J. Geol. Soc. India, 1988, 13, 118–120.

206 Dr. T.S. R .Chowdary, Dr K.S.R Prasad, T.S. Ram Babu