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Petrography of Siwalik sandstones from Kaladungi-Ramnagar area, Nainital district, Uttrakhand and its bearing on engineering

properties

Misra, Sarvesh

School of Sciences, Indira Gandhi National Open University,

Maidan Garhi, New Delhi-110068.

Mishra, Meenal

School of Sciences, Indira Gandhi National Open University,

Maidan Garhi, New Delhi-110068.

Tewari, Ram Chandra

Geology Department, Sri. J. N. P. G. College, Lucknow-22600 (Retired).

E-mail (Corresponding Author):[email protected]

Abstract

The prime focus of this research is to study the petrography of sandstones from Siwalik subgroups of Kaladungi-Ramnagar area, Uttrakhand. These sandstones are fine to medium-grained and moderately sorted. The framework minerals are composed of quartz, rock fragments and feldspar and the accessory minerals include chlorite, zircon, epidote, rutile, illmenite, chromite, sphene, apatite and tourmaline. The groundmass matrix is less than 15% in general and also exceeds to more than 15%. The quartz and rock fragments are angular to sub angular whereas those feldspar grains are sub-rounded. The Siwalik sandstones are classified as sub-lithic arenite and sub-lithic wacke. The relative abundance of mineral grains and textural parameters suggest that the Siwalik sandstones are immature to sub mature texturally as well as compositionally. The physical and mechanical properties are determined viz. Uniaxial Compressive Strength (25-60MPa) on the basis of its mineralogical constituents and textural parameters, with a view to access the suitability of Siwalik sandstone. The results suggest that the sandstones of Siwalik Group are regarded as sufficiently moderate to strong and such sites are appropriate for construction purposes. Moreover, mineralogical and textural properties of Siwalik sandstones are also found to be suitable for construction material.

1. Introduction:

Sandstone composed of sand-sized (0.0625 to 2mm) mineral particles/rock fragments

is the most abundant clastic sedimentary rock in nature. Petrographic studies of sandstone provides useful information about classification, provenance determination and diagenetic modification (Pettijohn et al., 1987). The mechanical and physical characteristics of rocks generally depend upon their composition and texture (Tamrakar et. al., 2007). The relationship between the textural and mechanical parameters of rock mass from the rock mechanic point of view is although complicated (Li Huamin et al. 2018), but quite useful in defining rock strength. According to Spry (1969) texture is defined on the basis of absolute grain size, size distribution (single graded or well graded), shape and spatial orientation of mineral grains. In addition, other petrological parameters like mineral distribution, grain boundary relations, the amount of micro-cracks, mineral deformation and degree of alteration also affect the mechanical strength. A majority of these properties can be quantified with high accuracy mainly through microscopic examination of rocks (Nalsund & Jensen, 2013). All the above mentioned parameters may be present at the same time but with varying magnitude from sample to sample and are difficult to translate into absolute figures in terms of functional properties. Examining different rock samples, all these parameters mentioned above may be present at the same time

Journal of Engineering Geology Volume XLIII, Nos. 1 & 2

A bi-annual Journal of ISEG June-December 2018

176

but with varying magnitude from sample to sample. Thus it becomes difficult to document the degree of correlation between a texture or petrologic parameter on one hand, and mechanical parameter on the other. Thus, many researchers examine one rock at a time to minimize the number of variables. Considering all these aspects, Siwalik sandstone of Kaladungi-Ramnagar area, Nainital district, Uttrakhand is selected for detail petrological study with a view to assess its mechanical suitability for constructing major structures on it. The objectives of this study are to carry out textural and compositional studies of Siwalik sandstone which include grain size, packing density, degree of interlocking, type and length of grain contacts, type and abundance of cement/matrix, sorting and mineralogical composition to characterize its behavior as bed rock. Indeed, Siwalik sandstone is considered as the most important surface and subsurface bed rock for many projects in India, Pakistan and Nepal such as hydropower, road and railway tunnels etc., located in the sub-Himalayan zone. A large number of mega hydroelectric projects including 167m high Bhakra dam, 147m high Mangla dam, 128m high Ramganga/Kalagarh dam, 116m high Lower Subansiri dam were successfully constructed in the Siwalik rocks. The other structures of Lower Subansiri Hydroelectric Project are under construction and 136m high Jamrani dam project is in the line of being constructed. Moreover, it is also worthwhile to mention that railway line between Jammu to Srinagar has also been successfully constructed which include many tunnels and bridges on Siwalik sandstone. Many other railway lines are proposed to be constructed in Sikkim and Arunachal Pradesh which will certainly encounter the Siwalik sandstone and are under investigation. A detail petrographic study is hence, important in geotechnical engineering to understand the mechanical behavior of sandstone for slope or foundation excavation and developing suitable support system in tunneling and underground structures. The petrological investigations have been utilized for the purpose of characterization on the basis of modal mineralogy, grain size, assessing the degree of sorting and extent of textural and mineralogical maturity. The mechanical and physical properties of similar rock composition of Siwalik sandstones determined in different locales elsewhere were utilized to make a relationship with, to evaluate and assess the potential of Siwalik sandstone as suitable sites for construction purposes as well as its suitability as construction material. 2. Geology of the Area:

The term Siwalik was introduced by Cautley and Falconer (1835) to describe the sub-Himalayan hill ranges occurring between the river Ganga and Yamuna near Haridwar region. It represents a continuous series of Tertiary formations stretching from Pakistan in northwest to Irrawaddy River in Myanmar towards northeast (Deoja et al, 1991). Thus, it comprises youngest rocks namely soft, loose and easily erodible sandstone, mudstone and conglomerate measuring between 500-7000m thickness. Structurally Siwaliks have been involved in the later phase of Himalayan orogeny leading to folding and over thrusting (Wadia, 1953). It is bounded by one of the most conspicuous fault Main Boundary Thrust (MBT) in the north and Main Frontal Thrust which is also referred as Himalayan Frontal Thrust towards the south. MFT separates Siwaliks from the Gangetic alluvium plain whereas MBT forms the boundary between Siwaliks and Lesser Himalaya. However the frequent reversal of stratigraphy



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sequences in Siwalik Group is brought by post depositional thrusting (Mainak et al 2018). The Siwalik Group of the Ramanagar-Kaladungi area which is a part of one of the Siwalik basin (Figure 1) is, represented by Lower, Middle and Upper Siwalik sub-groups with distinct lithological characters. These three subdivisions are well demarcated in the geological map of Ramnagar-Kaladungi area (Figure 2). Local gradational contacts observed in upward transitions from the Lower to Middle and Middle to Upper Siwalik. Further subdivisions into Formations are not shown in the available geological map as these are basically based of fossils and the area is devoid of these fossils. Therefore, the Siwalik Group of the study area is analyzed under the three broad divisions of Lower, Middle and Upper. The regional strike of Siwalik rocks is east-west and the dips are steep and highly variable from 30º to 82º direct towards NE. Siwalik sediments about 2950m are exposed in and around Kaladungi-Ramnagar area where Lower, Middle and Upper Subgroups represent about 1600m, 750m and 600m respectively. It is interesting to note that Siwalik sediments of the given area broadly represent coarsening upward sequence from Lower through Middle up to Upper Siwalik Group. The sandstone is the principal and basic rock type distributed in the area especially in Lower and Middle Siwalik Subgroups, however, conglomerate is dominant in Upper Siwalik Subgroup. Hence, petrographic studies of sandstone were taken up in detail and presented hereunder.

3. Petrography of Sandstone:

The granulometric analysis including textural attributes and mineralogy of sandstones are important aspects not only for analysis and interpretations of sediment maturity, depositional behavior of sediments, relief, hydrodynamics, and composition of provenance ( Friedman and Sanders, 1978; Dickinson and Suczek, 1879; Blatt, 1982; Pettijohn, 1984; Pettijohn et al., 1987; Johnson, 1994), but also provides some important inputs for its engineering geological characteristics (Tugrul, A. & Zarif, I. H. 1999, Prikryl, R. 2001, Linqvist, J. E. et al. 2007, Johansson, 2011, Li Huamin, 2018).

Figure 1 Sketch map of Himalayan foreland basins showing present area

(after Tewari and Khan, 2015)

Figure 2 Geological map of the area around Ramnagar-Kaladungi, District

Nainital, Uttrakhand



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Study of sandstone's petrology therefore provides insight into its mechanical behavior for constructing any surface of subsurface engineering structures. Based on the granulometric analysis and composition of detrital constituents in the Siwalik Group sandstones, this study provides insight problems and suitability of constructing any civil engineering structure on or within it. Various textural parameters such as graphic mean, standard deviation (sorting), skewness and kurtosis are useful for understanding in grasping rock mass behavior of Siwalik sandstone and hence were undertaken. 4. Methodology:

The Siwalik sandstones are generally hard and compact and render ineffective in all attempts to disaggregate them. Therefore, the textural characteristics of these sandstones are studied in thin sections following the recommendations of several workers (Friedman, 1958, Blatt, 1967, Friedman and Sanders, 1978). Twenty four sandstone samples (10 from Lower Siwalik Subgroup, 10 from Middle Subgroup, and 04 from Upper Siwalik Subgroup) were collected for present study representing all the possible stratigraphical horizons of the area. The less number of Upper Siwalik sandstones were studied because of their limited occurrence and friable nature. The thin sections of sandstones were analyzed using a polarizing microscope. A petrographic study was carried out to determine the textural parameters (grain size, grain roundness and shape of grains), cement, packing density, packing proximity, dry density, saturated density, porosity, contact type and composition of sandstones following standard procedures. The grain diameter was measured down to 0.06mm (4Ø) and all the material less than this limit were treated as clay and silt (matrix).The conversion table of Page (1955) was used to convert millimeter values to equivalent Phi (Ø) values. Cumulative curves were drawn for Lower, Middle and Upper Siwalik sandstones separately on the semi-log graph paper following Friedman (1958) to determine the sieve size equivalents of thin section data. To describe the textural characters of sediments, the statistical parameters such as Mean Size (Mz), Standard Deviation (Sd), Skewness (Ski) and Kurtosis (KG) were calculated following Folk and Ward (1957). The Size frequency data and statistical parameters calculated from the cumulative curves including calculated Mz, Sd, Ski, & KG are listed in Tables 1 and 2. The Waskom method (1958) of assigning roundness to the individual grains to appropriate power’s classes on the basis of the modified version of the criteria originally described by Pettijohn (1957) was followed. The arithmetic mean roundness from each thin section was computed as described by Krumbein and Pettjhon (1938). The results are listed in Table 3. The shape of the detrital grains is described in terms of elongation ratio (long axis/shot axis) by Bokman (1952). The length and breadth of 100 detrital grains are measured in each thin section with the help of micrometer eyepiece to compute the elongation ratio. The data on the elongation ratio of 100 grains in the Lower, Middle and Upper Siwalik sandstones is listed in Table 4.



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Table 1 Size Frequency Data (in percent) of Lower, Middle, and Upper Siwalik Sandstones,

Ramnagar-Kaladungi Area

Sample Number

Class Interval

-1.0Ø to -0.5Ø

-0.5Ø to

0.0Ø

0.0Ø to 0.5Ø

0.5Ø to

1.0Ø

1.0Ø to 1.5Ø

1.5Ø to

2.0Ø

2.0Ø to

2.5Ø

2.5Ø to

3.0Ø

3.0Ø to

3.5Ø

3.5Ø to

4.0Ø

Upper Siwalik

U-1 - - 8.33 16.67 25.67 20.33 12.33 13.67 2 1

U-2 - 2.00 3.33 15.67 21.33 24.67 17.67 9.67 4.67 1

U-3 - 10 5 11.67 15.33 27 12.33 6.33 9.67 2.67

U-4 3 10 4.67 19.67 12.33 7.67 16.67 11.67 7.67 6.67

Middle Siwalik

M-1 - - 3.67 15.33 21.33 26.67 18.67 9.67 4.67 -

M-2 - 0.67 4.33 11.67 17.33 22.33 16.00 10.00 11.33 6.33

M-3 - - 2.67 13.67 23.33 30.00 12.00 7.67 5.00 5.67

M-4 - - 2.33 9.33 16.33 23.33 15.00 13.67 11.00 9.00

M-5 - - - 7.33 22.33 30.00 20.67 6.33 5.33 8.00

M-6 - 2.00 5.00 11.00 30.33 19.00 13.67 5.67 4.00 9.33

M-7 - 10.00 4.33 13.67 18.67 25.00 9.33 5.67 9.00 4.00

M-8 - - - 7.33 22.33 30.00 20.67 6.67 5.00 8.00

M-9 2.00 8.00 4.33 12.67 27.00 15.33 10.33 6.67 10.67 3.00

M-10 - - 2.33 12.67 20.00 29.00 15.00 11.33 3.00 6.67

Lower Siwalik

L-1 - - - - - 1.00 16.67 30.67 27.67 24.00

L-2 - - - - 2.00 11.67 28.33 24.33 22.67 11.00

L-3 - - - - 1.00 6.00 15.00 34.67 20.33 23.00

L-4 - - - - 11.67 7.00 14.67 23.00 26.67 17.00

L-5 - - - - - 6.67 13.00 31.33 31.33 17.67

L-6 - - - 3.33 6.67 14.33 19.67 24.67 15.33 16.00

L-7 - - 1 2 6.67 11.67 28.33 21.33 15.67 13.33

L-8 3.33 7.00 30.00 9.67 6.67 13.67 7.67 6.00 11.67 4.33

L-9 - 0.67 2.00 14.67 29.33 29.00 9.00 4.67 7.67 3.00

L-10 - - 1.00 3.67 10.00 22.33 25.67 15.67 12.00 9.67



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Table 2 Size Frequency Percentile and Parameters of Siwalik Sandstones

Sample

No.

Percentile size in phi units Mz Sd Ski KG

Ø5 Ø16 Ø25 Ø50 Ø75 Ø84 Ø95

Upper Siwalik

U-1 0.25 0.90 1.23 1.76 2.33 2.85 3.56 1.83 0.99 0.06 1.23

U-2 0.02 0.65 1.00 1.63 2.72 3.15 3.68 1.81 1.18 0.11 0.87

U-3 0.96 1.40 1.61 2.10 2.90 3.30 3.85 2.26 0.90 0.13 0.92

U-4 0.80 1.20 1.50 1.91 2.10 2.60 3.20 1.90 0.72 0.01 1.64

Middle Siwalik

M-1 0.05 0.50 0.65 1.30 2.60 3.13 3.58 1.64 1.19 0.20 0.74

M-2 0.95 1.27 1.45 1.76 2.19 2.62 3.49 1.88 0.72 0.14 1.41

M-3 1.25 1.75 1.95 1.38 2.95 3.27 3.79 2.47 0.72 0.74 1.04

M-4 0.35 1.00 1.28 1.70 2.23 2.40 2.87 1.70 0.73 0.00 1.09

M-5 1.45 2.03 2.27 2.68 3.25 3.50 3.87 2.74 0.73 0.06 1.01

M-6 0.85 1.29 1.54 2.03 2.73 3.20 3.70 2.17 0.91 0.11 0.98

M-7 0.93 1.28 1.46 1.89 2.40 2.85 3.60 2.01 0.79 0.11 1.16

M-8 0.97 1.42 1.65 2.15 2.94 3.35 3.84 2.30 0.92 0.12 0.91

M-9 1.22 1.49 1.67 2.03 2.54 2.90 3.79 2.14 0.14 0.12 1.21

M-10 0.65 1.25 1.43 1.77 2.12 2.85 3.79 1.96 0.88 0.18 1.87

Lower Siwalik

L-1 2.30 2.60 2.77 3.13 3.55 3.75 3.96 3.16 0.54 0.04 0.87

L-2 1.85 2.02 2.40 2.77 3.27 3.46 3.80 2.75 0.66 0.02 0.92

L-3 2.05 2.50 2.70 3.05 3.53 3.70 3.95 3.08 0.55 0.04 0.94

L-4 1.43 2.00 2.38 2.98 3.43 3.60 3.86 2.86 0.77 0.11 0.95

L-5 1.96 2.54 2.75 3.13 3.47 3.54 3.90 3.10 0.57 0.09 1.10

L-6 1.23 1.98 2.40 2.78 3.26 3.58 3.86 2.78 0.79 0.00 1.25

L-7 0.9 1.75 1.48 1.9 2.17 2.65 3.20 1.93 0.70 0.33 1.37

L-8 1.05 1.37 1.55 1.86 2.29 2.72 3.59 1.98 0.72 0.14 1.41

L-9 1.26 1.55 1.85 2.25 2.50 3.06 3.76 2.28 0.74 0.04 1.58

L-10 1.10 1.48 1.66 2.09 2.60 3.05 3.80 2.20 0.79 0.11 1.18



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Table 3 Roundness data of detrital quartz grain in Lower, Middle and Upper Siwalik

sandstones

Sample No.

Very Angular Angular Sub-angular Sub-rounded Rounded Well-rounded Mean roundness

Ma-pxn/100

Roundness Class

p n pxn p n pxn p n pxn p n pxn p n pxn p n pxn

Upper Siwalik

U-1 0.14 6 0.84 0.21 23 4.83 0.30 45 13.50 0.41 20 20 0.59 5 2.95 - - - 0.30 Sub-angular

U-2 - - - 0.21 25 5.25 0.30 53 15.90 0.41 18 18 0.59 4 2.36 - - - 0.31 Sub-angular

U-3 0.14 13 1.82 0.21 28 5.88 0.30 41 12.30 0.41 18 18 - - - - - - 0.27 Sub-angular

U-4 0.14 12 1.68 0.21 48 10.08 0.30 32 9.60 0.41 10 10 0.59 2 1.18 - - - 0.27 Sub-angular

Middle Siwalik

M-1 0.14 2 0.28 0.21 43 9.03 0.30 29 8.70 0.41 18 7.38 0.59 8 4.72 - - - 0.30 Sub-angular

M-2 - - - 0.21 33 6.93 0.30 38 11.40 0.41 20 8.20 0.59 9 5.31 - - - 0.32 Sub-angular

M-3 0.14 2 0.28 0.21 17 3.57 0.30 54 16.20 0.41 24 9.84 0.59 3 1.77 - - - 0.32 Sub-angular

M-4 - - 0.00 0.21 16 3.36 0.30 40 12.00 0.41 27 11.07 0.59 17 10.03 - - - 0.36 Sub-rounded

M-5 0.14 9 1.26 0.21 36 7.56 0.30 43 12.90 0.41 19 7.79 0.59 2 1.18 - - - 0.31 Sub-angular

M-6 0.14 12 1.68 0.21 42 8.82 0.30 30 9.00 0.41 10 4.10 0.59 6 3.54 0.27 Sub-angular

M-7 0.14 8 1.12 0.21 26 5.46 0.30 27 8.10 0.41 23 9.43 0.59 16 9.44 0.84 2 1.68 0.35 Sub-rounded

M-8 0.14 5 0.70 0.21 35 7.35 0.30 35 10.50 0.41 10 4.10 0.59 13 7.67 - - - 0.30 Sub-angular

M-9 0.14 7 0.98 0.21 35 7.35 0.30 46 13.80 0.41 12 4.92 - - 0.00 - - - 0.27 Sub-angular

M-10 0.14 2 0.28 0.21 20 4.20 0.30 47 14.10 0.41 21 8.61 0.59 10 5.90 - - - 0.33 Sub-angular

Lower Siwalik

L-1 - - - 0.21 18 3.78 0.30 41 12.30 0.41 40 16.40 0.59 1 0.59 - - - 0.33 Sub-angular

L-2 0.14 2 0.28 0.21 20 4.20 0.30 37 11.10 0.41 32 13.12 0.59 7 4.13 2 2 1.68 0.35 Sub-rounded

L-3 0.14 12 1.68 0.21 31 6.51 0.30 22 6.60 0.41 20 8.20 0.59 11 6.49 4 4 3.36 0.33 Sub-angular

L-4 0.14 19 2.66 0.21 40 8.40 0.30 20 6.00 0.41 18 7.38 0.59 3 1.77 - - - 0.26 Sub-angular

L-5 - - 0.00 0.21 29 6.09 0.30 23 6.90 0.41 39 15.99 0.59 8 4.72 1 1 0.84 0.35 Sub-rounded

L-6 0.14 10 1.40 0.21 43 9.03 0.30 37 11.10 0.41 10 4.10 - - - - - - 0.26 Sub-angular

L-7 - - - 0.21 9 1.89 0.30 45 13.50 0.41 39 15.99 0.59 7 4.13 - - - 0.36 Sub-rounded

L-8 - - - 0.21 15 3.15 0.30 30 9.00 0.41 49 20.09 0.59 6 3.54 - - - 0.36 Sub-rounded

L-9 0.14 4 0.56 0.21 20 4.20 0.30 40 12.00 0.41 25 10.25 0.59 11 6.49 - - - 0.34 Sub-angular

L-10 0.14 7 0.98 0.21 21 4.41 0.30 38 11.40 0.41 34 13.94 0.59 10 5.90 - - - 0.37 Sub-angular



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Table 4 Grouped Data of Elongation Ratio (length/breadth) of Detrital Quartz Grains of

Lower, Middle and Upper Siwalik Sandstones

Sample No.

1.0-1.2 1.2-1.4 1.4-1.6 1.6-1.8 1.8-2.0 2.0-2.2 2.2-2.4 2.4-2.6 2.6-2.8 2.8-3.0 3.0-3.2 3.2-3.4 3.4-3.6 3.6-3.8

Upper Siwalik

U-1 13 26 18 8 11 9 6 4 2 3 - - - -

U-2 8 13 24 16 8 7 8 5 3 4 3 1 8 -

U-3 17 16 15 12 11 10 6 5 5 1 - - 1 1

U-4 11 23 20 12 14 7 4 3 4 1 - - 1 -

49 78 77 48 44 33 24 17 14 9 3 1 10 1

Middle Siwalik

M-1 6 14 20 29 11 6 7 0 4 -- 2 1 - -

M-2 13 13 22 19 8 4 8 2 5 3 1 2 - -

M-3 10 9 18 26 13 2 7 3 7 1 2 3 - -

M-4 6 8 15 33 13 8 12 1 3 1 2 - - -

M-5 8 6 10 13 18 4 36 1 2 1 1 3 - -

M-6 4 10 23 23 17 11 4 3 4 - - - - -

M-7 7 15 25 19 15 11 2 4 1 1 - - - -

M-8 2 20 31 17 10 14 1 2 2 1 1 - - -

M-9 9 13 25 16 8 7 8 5 3 4 3 1 - -

M-10 11 18 26 21 7 8 5 4 2 - - - - -

75 126 215 216 120 75 90 25 33 12 12 9 0 0

Lower Siwalik

L-1 14 27 16 9 12 8 5 2 3 2 1 2 - -

L-2 11 18 26 21 7 8 5 4 2 - - - - -

L-3 10 16 28 20 9 6 5 2 2 2 1 - - -

L-4 11 12 24 14 9 12 8 5 2 2 2 1 2 -

L-5 12 22 20 12 14 10 4 3 4 - - - 1 -

L-6 13 6 17 23 11 8 7 6 5 1 3 1 1 1

L-7 14 10 12 22 14 18 5 4 1 1 0 - - -

L-8 15 18 23 26 8 6 4 3 2 1 3 - - -

L-9 16 4 28 19 9 15 6 4 1 1 0 - 2 -

L-10 17 12 20 18 12 8 4 5 2 2 0 - - -

133 145 214 184 105 99 53 38 24 12 10 4 6 1



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The mineralogical composition of sandstones was determined by modal analyses of about 500 points counted for each thin section using Gazzi-Dickinson method (Dickinson, 1970; Ingersoll et. al., 1984) and presented in subsequent sub-section of this paper. 5. Frequency and Cumulative Curves:

Frequency curves are drawn on the semi-log graph paper following Friedman (1958), which show distribution of particle size and indicate frequency distribution of the sediment populations. Most of the samples (12 samples) are fine grained sand and some are very fine (3 samples) to medium grained (9 samples) sand (Table 2). The analyzed sandstone samples show unimodal (10 samples), bimodal (4 samples) and polymodal nature (6 samples). Therefore the results show that most of the samples are fine-grained and unimodal. Cumulative curves are plotted on the semi-log graph paper following Friedman (1958) with the combination of cumulative weight percentage at the Y- axes and phi values at the X-axes (Figure 3). These curves provide grain size information values of phi, which were used in mathematical calculations of statistical parameters (graphic mean, graphic standard deviation, graphic skewness and graphic kurtosis) following Folk and Ward (1957). The size distribution of Siwalik sandstones were also shown graphically as histograms in Figure 4.

Figure 3 Cumulative curves of Lower, Middle and Upper Siwalik Sandstones



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Figure 4 Histogram Showing Size Distributions in Siwalik Sandstones

6. Textural Parameters:

Different textural parameters are determined graphically through cumulative curves by reading the values of phi of ø1, ø5, ø16, ø25, ø50, ø75, ø84, and ø95. A number of formulae have been proposed by different workers to calculate four main statistical parameters viz. graphic mean (Mz), graphic standard deviation (Sd), graphic skewness

(Ski) and graphic kurtosis (KG) (Wentworth 1929, Krumbein and Pettijohn 1938;

Friedman 1961, 1962, 1967: Sahu 1964). However, the formulae given by Folk and Ward (1957) including 90% of the curve are most suitable and used in the present work to calculate following statistical parameters. These parameters are effective tools for the interpretation of textural maturity. 7. Graphic Mean (Mz):

The graphic mean is the average particle size of the sediment and is calculated by the formula ( ø16+ø50+ø84)/3. Out of analyzed samples, about 50% samples are fine grained (2.01-2.86ø), 37.5% medium grained (1.81-1.98ø) and 12.5% samples (M-10, L-2 & L-4) very fine grained (3.10-3.16ø). Thus, the majority of the studied sandstones are fine grained with average value of 2.29ø (Table 2).



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8. Graphic Standard Deviation:

Graphic standard deviation (Sd) is calculated by the formula ((φ84– φ16)/4 + (φ95–

φ5))/6.6 and it measures the sorting or uniformity of the grains and indicates the state of the energy conditions prevailing during transport and in the basin of deposition. Among 24 samples, 66.67% samples are moderately sorted (Sd = 0.72 - 0.99), about 20.83% are moderately well sorted (Sd = 0.54 - 0.79), 8.33% are poorly sorted (Sd = 1.18 - 1.19), and 4.17% (sample, M-23) are very well sorted (Sd = 0.14) (Table 2). 9. Graphic Skewness:

Skewness (Ski) measures the degree of asymmetry in the frequency curves in terms of domination of fine or coarse-grained fractions. It has been calculated by the formula

φ84+ φ16– 2 φ50/2(φ84–φ16)+φ5+φ95–2φ50/2(φ95– φ5). The analyzed 24 samples of sandstones show that 45.83% samples are positively skewed (Ski = 0.11 to 0.18), 41.67% samples near symmetrically skewed (Ski = - 0.09 to 0.06), 8.33% strongly positively skewed (Ski = 0.33 to 0.74) and 4.17% negatively skewed (Ski = -0.11). Data shows that maximum samples are positively skewed ranging in Skewness values from -0.11 to 0.33 denoting domination of finer material in the tail (Table 2). Though, only one sample (L-5) is negatively skewed with Sk

i value - 0.11 indicating domination of coarser material in the tail. 10. Graphic Kurtosis:

According to Cadigan (1961), Kurtosis (KG) is the measure of peakedness of the

frequency curve. It is calculated by formula (φ95– φ5/2.44 (φ75– φ25). Kurtosis is a quantitative measure of shape of the frequency curve, and ratio between the sorting in the tail and central portion of the curve. Accordingly, if central portion is better sorted than the tail, the curve is said to be leptokurtic (excessively peaked), but if tail is better sorted than the central portion, it is called platy kurtic (flat peaked) and when both the portions tail and centre are equal, the curve is called meso kurtic. The analyzed 24 samples of sandstones show that 50% falls in leptocurtic (KG = 1.1 to 1.41) or very lepto kurtic category (KG = 1.58 to 1.87), 33.33% in meso kurtic (KG = 0.91 to 1.09) and 16.67% in platy kuritic (KG = 0.74 to 0.92). 11. Roundness of Grains: About 100 detrital quartz grains from each thin section were taken to determine roundness of Siwalik sandstone (Chayes, 1949). The data are then grouped into Power (1953) roundness classes. The arithmetic mean roundness for each thin section was computed as described by Krumbein and Pettijhon (1938). Out of the 24 samples analyzed, 75% samples show sub-angular nature and the mode falls in the sub-angular class. The remaining 25% exhibit sub-rounded nature and the mode falls in sub-rounded class. The arithmetic mean roundness varies from 0.26 to 0.37 (Table 3).



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12. Shape of Grains:

The shape of detrital grains is described in terms of elongation ratio (long axis/short axis) by Bokman (1952). The length and breadth of 100 detrital quartz grains were measured in each thin section with the help of micrometer eye piece and the ratio were grouped into classes with interval of 0.2 (Table-4). The quartz grains exhibit a wide scattering of the elongation ratio. The principal modal class lies in the 1.2-1.4 and 1.4-1.6 elongation class and contains 35.63% of the total number of the grains. 13. Mineralogical Composition:

The main detrital constituents of Siwalik sandstone are quartz (metamorphic, Igneous and sedimentary), rock fragments, feldspar, accessory minerals and matrix/cement (Table 5).Quartz grains of igneous, metamorphic and sedimentary origin are classified on the criteria such as degree of extinction, elongation ratio, and presence of inclusions (Blatt, 1982). The mineral composition of Siwalik sandstone is dominated by quartz (41.40% to 55.68% in the three Subgroups), both monocrystalline and polycrstalline quartz grains are noted, the latter are more abundant. A few quartz grains also have inclusions of zircon, tourmaline, apatite and mica which are arranged regularly and irregularly. The quartz grains embedded in carbonate matrix/cement are slightly corroded at places. Rock fragments constitute another dominant constituent of Siwalik sandstone ranging from 15.96 to 29.60% in different Subgroups. The rock fragments are composed of different types of phyllite, gneiss and schist, quartzite, limestone, chert basalt, dolerite and sandstone. Among these the rock fragments of phyllite and schist are dominant. Feldspar (6.62% to 7.25%), mica (2.9% to 6.05%), accessory minerals (2.1% to 3.2%) and matrix/cement (7.46% to 16.94%) are other components of Siwalik sandstone. The accessory minerals are tourmaline, rutile, garnet, staurolite, kyanite, epidote, zircon, apatite and few opaques. The cementing material is mostly calcareous; however, ferruginous and argillaceous cement is also present. The matrix is unequally distributed in different thin sections and is generally seems to be post depositional in origin. Much of the matrix identified is sericite and chlorite which occur in finely divided flakes. The other constituents of the matrix are fine quartz, silt and clay, fine mica flakes. It is noteworthy that in Siwalik sandstone matrix dominant over cementing material in most places. The abundance of rock fragments besides detrital quartz together with more matrix than mineral cement, evidently suggest that the Siwalik sandstones are lithic-wacke and lithic-arenite following sandstone classification of Dott (1972). Further, the compositional and textural attributes deduced here are suggestive of immature nature of Siwalik sandstones texturally as well as compositionally following Pettihohn (1975) and Blatt (1982).



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Table 5 Mineral Composition (Percent by volume) of Lower, Middle Siwalik Sandstones

Sample No.

Quartz Rock Fragment

Feldspar Mica Accessory Minerals

Cement/ matrix

Metamorphic Igneous Sedimentary Total

Upper Siwalik

U-1 20.8 16.6 - 37.4 35.0 8.0 7.0 3.2 9.4

U-2 21.8 19.2 2.2 43.2 32.8 7.0 4.0 2.0 11.0

U-3 30.2 19.6 - 49.6 23.8 6.0 8.4 3.2 8.8

U-4 19.2 14.8 1.4 35.4 26.8 8.0 4.8 4.2 10.8

Average 41.40 29.60 7.25 6.05 3.15 10.00

Middle Siwalik M-1 27.0 16.4 1.6 47.0 21.8 16.4 2.6 3.2 9.0

M-2 20.4 15.6 8.0 44.0 26.2 11.2 8.8 4.2 5.6

M-3 28.0 16.0 2.0 46.0 38.2 5.8 3.0 1.2 5.8

M-4 34.6 20.0 - 54.6 26.0 8.6 4.0 1.0 5.8

M-5 26.2 9.0 1.0 36.2 36.6 7.4 6.2 1.8 11.8

M-6 39.4 10.6 - 41.0 31.4 8.0 4.8 1.8 13.0

M-7 26.8 18.6 - 45.4 27.6 7.2 8.2 1.8 9.8

M-8 28.0 21.4 - 49.4 30.8 10.6 2.4 2.4 4.4

M-9 30.4 26.2 - 56.6 25.6 8.0 5.6 1.2 3.0

M-10 24.4 20.4 - 44.8 31.4 8.6 6.0 2.8 6.4

Average 46.50 29.56 9.18 5.16 2.14 7.46

Lower Siwalik L-1 47.4 10.6 3.0 61.0 7.0 4.4 5.0 5.6 17.0

L-2 28.6 13.0 4.2 45.8 20.6 9.4 3.6 2.4 18.2

L-3 32.6 11.4 8.6 52.6 18.2 6.2 2.2 1.8 19.0

L-4 40.2 15.2 4.8 60.2 13.8 4.0 2.8 1.4 17.8

L-5 53.0 8.6 8.4 70.0 7.0 3.0 2.0 1.0 17.8

L-6 32.8 9.4 - 42.2 31.0 8.8 1.8 2.2 16.0

L-7 34.4 10.4 10.0 54.8 19.2 9.4 4.6 2.0 10.0

L-8 54.0 6.6 3.4 64.0 10.8 6.0 1.2 1.0 17.0

L-9 48.2 11.8 - 60.0 13.2 6.4 2.2 1.6 15.8

L-10 37.8 8.4 - 46.2 18.8 8.6 3.6 2.0 20.8

Average 55.68 15.96 6.62 2.9 2.1 16.94

14. Packing density and Packing Proximity:

Packing density and packing proximity are two important petrographic parameters which affects the strength of rock. They are quantified according to Kahn’s method (1956). Packing density (Pd) is defined as the ratio of the sum of the grain length encountered along the traverse across the thin section to the total length of traverse (Kahn,1956) and is calculated using formula Pd = ∑gi/t X 100 where gi is ith intercept of grain length in the traverse and t is the total traverse length. It gives a relative percentage of the length of the sandstone occupied by the grains. In other words, it represents the closeness or spreading of the particles.

Higher packing density means the particles are closed and tightly packed (Ulusay et al. 1994). It can also be said that higher packing density sample have less matrix content. Computed packing densities of Siwalik sandstone (in percent) are listed in Table 6.



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Table 6 Packing Density of Lower, Middle and Upper Siwalik Sandstones

Sample No. Packing Density (in %) Sample No. Packing Density (in %)

Upper Siwalik

U-1 24 U-3 38

U-2 40 U-4 46

Middle Siwalik Lower Siwalik

M-1 58 L-1 54

M-2 46 L-2 77

M-3 45 L-3 68

M-4 51 L-4 80

M-5 58 L-5 65

M-6 46 L-6 62

M-7 60 L-7 76

M-8 56 L-8 69

M-9 59 L-9 58

M-10 62 L-10 79

The Lower Siwalik sandstones possess higher packing density as compared to the Middle Siwalik sandstones implying differences in the depth of burial, greater in the Lower than the Middle Siwalik. Most of the grain contacts are floating to tangential in the Middle Siwalik sandstones and tangential to suture type in the Lower Siwalik sandstones evidently justify higher degree of compaction and interlocking in Lower as compared to the younger sandstones. Packing proximity is defined as the ratio of the number of grain contacts to total number of contacts along a given traverse (Kahn, 1956). Packing proximity represents whether the particles are properly interlocked or not. Higher packing proximity with less cement or matrix represents the grains are tightly packed (Ulusay et al. 1994) if the particles are properly interlocked with smaller grain sizes then the packing proximity increases. 15. Dry Density, Saturated Density and Porosity:

The dry density is the ratio of mass to volume when it is totally dried. In this study the dry density have found to be varying from 1.85g/cc to 2.45g/cc. The dry density has been found to be less (1.85 to 2.16) for coarse grained sandstones. However, higher values of density have been found for fine grained sandstones. Saturated density is the ratio of the mass and volume of the specimen when it is totally saturated. Generally it is measured by placing the whole specimen inside water and measuring the mass after 48 hours assuming that all the pore spaces are occupied by water. If the rocks are having same dry mass and same volume and among them one has more amount of pore spaces then saturated density has been found to be increased. In this study the saturated density has been found to be varied from 2.02g/cc to 2.61g/cc. The increase in density after immersion in water have been found to be more for coarse grained sandstone as compared to fine grained sandstones. Porosity is defined as the ratio of porous volume of (Vp) the rock to that of the total volume (Vt) of the rock. While determining porosity first the sample is oven dried so that proper estimation of the water which occupies the pore spaces can be made.



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Table-7 Porosity of Lower, Middle and Upper Siwalik Sandstones

Sample

No. Dry Density

(g/cc) Saturated Density (g/cc)

Porosity (In %)

Sample No.

Dry Density (g/cc)

Saturated Density (g/cc)

Porosity (In %)

Upper Siwalik

U-1 1.97 2.152 17.45 U-3 2.01 2.18 17.35

U-2 1.85 2.03 17.69 U-4 1.91 2.1 18.1

Middle Siwalik Lower Siwalik

M-1 2.28 2.45 15.79 L-1 2.25 2.45 11.83

M-2 2.4 2.5 10.1 L-2 2.32 2.43 11.45

M-3 2.47 2.61 14.6 L-3 2.1 2.38 11.64

M-4 2.28 2.43 15.02 L-4 1.87 2.00 12.62

M-5 1.89 2.02 17.24 L-5 1.95 2.01 14.7

M-6 1.85 2.07 18.34 L-6 2.16 2.28 12.21

M-7 2.17 2.35 15.1 L-7 2.47 2.61 14.6

M-8 2.16 2.28 12.21 L-8 2.23 2.35 11.72

M-9 1.86 2.03 17.2 L-9 2.342 2.45 10.8

M-10 1.85 2.04 17.42 L-10 2.35 2.46 11.8

16. Engineering Properties of Siwalik Sandstone:

Construction engineers especially the design engineers request the "Uniaxial Compressive Strength" more often than any other rock engineering property (Bieniawski, 1974). The Uniaxial Compressive Strength is solicited nearly nine times more frequently (Cargil and Shakoor, 1990). Accordingly emphasizing the UCS, the studies carried out on similar type of Siwalik sandstones having almost similar textural and mineralogical composition were compiled and presented in Table-8.

Table 8

Engineering Properties of Siwalik Sandstone of Similar Textural and Mineralogical Composition of Different Constructed Projects

Project specific names

Equivalent to

UCS (dry) (in MPa)

UCS (wet) (in MPa)

Important geological and engineering/mechanical properties noted if any

Katra Sandstone

Middle Siwalik

8-25 Mpa 2-8 Mpa • Sandstone contain matrix and fractured quartz in between grains

• The feldspar + mica contain is >25%

• Post failure behavior of rock depicts increase in strength and failure strain with increase in strain rate.

• Exhibits axial splitting failure which changes to single and conjugate shear failure under triaxial compression.

• Triaxial stress-strain curves demonstrate increase in strength with confining pressure.

• Volumetric strain is characterized by initial phase of compaction dominated behavior followed by dilency.

Subansiri Sandstone

Middle Siwalik

15-20 Mpa 4-7 Mpa • Sandstone contains 3-5% quartz, 5-8% feldspar, 3-5% mica and 15-25% matrix.

• Sandstone is fine to medium grained mostly massive and at places bedded too.

• Sandstone exhibits concretions as well at places.

Mangla Sandstone (Pakistan)

Lower and Middle Siwalik

10-50 MPa 39-395 KN/m²

• Sandstone contains 15-45% quartz, 3-12% feldspar, 3-15% mica and 3-10% cement.

• Sandstone is fine to medium grained interbedded with siltstone and shale. At places massive too.

• Permeability ranges between 9.5 × 10-5 to 10-8 cm/sec.

(Compiled from the published work of Malik M. H., 1986, Garg, A. et al., 2008, and Mainak G. R. et al. 2018)



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Zorulu et al. (2008) has compiled a database of 138 sandstones (Table 9) for developing a model to predict Uniaxial Compressive Strength of sandstones using petrographic properties. The method applied by Zorulu et al. (2008) for estimation of UCS value were also used for the present study and included in Table-9 with predicted value of Uniaxial Compressive Strength of Siwalik sandstone. For calculating the values for Siwalik sandstone, the average of all samples analyzed (Tables-1, 2, 3, 4, 5 and 7) were taken for each petrological and mineralogical parameters separately and presented in the table 9. As the predicted value of Uniaxial Compressive Strength are calculated from the thin section study where saturated conditions cannot be developed, hence all estimated values are under unsaturated condition i.e. UCS (dry).

Table 9

Statistical summary of general database (aggregated data) including data of Bell (1978), Shakoor and Bonelli (1991), Ulusay et al. (1994), Bell and Lindsay (1999), Zorulu et al. (2008) and separately for this study (the unit of Uniaxial Compressive

Strength(UCS in MPa) and that of others in percentage) (Modified table of Zorulu et al., 2008)

Min. Max. Mean Median Mode Standard

Deviation Variance Skewness Kurtosis Siwalik

Sst. (this study)

Angular N/A N/A N/A N/A N/A N/A N/A N/A N/A 75

Rounded N/A N/A N/A N/A N/A N/A N/A N/A N/A 25

Spherecity N/A N/A N/A N/A N/A N/A N/A N/A N/A 34.98

Packing density

17.00

97.80 66.05 71.85 83.00 21.33 454.83 -0.70 -0.53 57.38

Packing proximity

0.00 87.00 46.30 52.90 0.00 25.68 659.27 -0.32 -1.21 N/A

Concavity-convexity

0.00 61.11 22.61 21.36 0.00 12.43 154.61 0.45 0.55 N/A

Straight 0.00 69.10 38.82 42.60 0.00 15.54 241.53 -1.00 0.72 N/A

Point 0.00 57.44 14.46 9.00 0.00 14.87 221.14 1.13 0.26 N/A

Sutured 0.00 31.19 7.42 5.40 0.00 7.60 57.78 0.88 -0.05 N/A

Quartz 2.60 93.30 45.86 36.75 18.60 27.58 760.71 o.37 -1,29 47.86

Feldspar 0.00 31.50 12.05 10.85 20.00 8.20 67.22 0.36 -1.04 7.68

Rock fragments

N/A N/A N/A N/A N/A N/A N/A N/A N/A 25.04

Accessary/Heavy mineral

N/A N/A N/A N/A N/A N/A N/A N/A N/A 2.46

Mica N/A N/A N/A N/A N/A N/A N/A N/A N/A 4.70

Matrix/Cement

0.00 66.00 10.60 7.05 0.00 11.26 126.88 1.72 3.78 11.47

UCS 17.5 214.0 78.97 74.60 141.0 39.76 1581.03 0.93 0.67 25.00 to 60.00

Note: 1. The mean, median, mode, standard deviation, variance skewness and kurtosis values of Siwalik

sandstone as per the present study briefed later in this write up. 2. The spherecity was calculated for the grains which fall in dominant elongation class. 3. The estimated UCS is calculated conservatively after taking all the considerations of present study.

17. Discussion and Conclusion:

Several researchers, attempted to establish a correlation between textural parameters of sandstone with special reference to the nature of mineral cement/matrix present in



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the rock to define its mechanical strength. Vutukuri et al. (1974) suggested that rocks with silica cement are the strongest, followed by those with calcite cement, ferruginous material and, at last, the clayey binder. With calcite as the binding material, the sandstone is the second most durable after silica-cemented sandstone. Fahy and Guccione (1979) and, Shakoor and Bonelli (1991) also expressed positive correlation between engineering properties and amount of cement/matrix. Contrarily, Ulusay et al. (1994) and Zorlu et al. (2004) found inverse relationship between these two parameters. A study of the Sherwood Sandstone in England has led Yates (1992) to suggest that strength depends upon the extent of cementation and compaction. With respect to grain roundness, a fairly positive correlation between mechanical properties and percentage of angular grains was observed by Shakoor and Bonelli (1991), while a strong positive relation between engineering properties and the ratio of angular grains to rounded grains, i.e. strength increases with increasing angularity of the frameworks was found by Ulusay et al. (1994). However, neither of these studies could find any linkage between strength and sphericity. Negative correlation between strength and percentage of rounded grains can be reasonably predicted, and the strength and percent angular grains should be positive (Zorlu et al., 2008). Accordingly, Fahy and Guccione (1979) reported a negative relationship between strength and roundness, but found an extremely strong positive relationship between strength and sphericity. Tamrakar et al., (2007) have noticed that the composition/type, shape (sphericity) and degrees of roundness and sorting have a little influence, if at all, on the mechanical and physical properties of the sandstone. Alternatively, the nature of cementing material seems to have been significant in determining strength of the Siwalik Sandstone (Tamrakar et al., 2007). As for packing density/packing proximity is concern, Shakoor and Bonelli (1991) and Bell and Culshaw (1998) did not find a significant relation between the strength and packing properties. However, a slightly positive relationship between strength and both packing density and packing proximity was observed by Ulusay et al. (2004) and Zorlu et al. (2004). The Siwalik sandstones exhibits an increase of strength (unconfined compressive strength) with increase in packing density on plotting average value of packing density against unconfined compressive strength (Ghosh et al. 2012). It is generally believed that strength of clastic rocks is controlled by the strength of constituent minerals, their grain size, shape, packing and nature or extent of bonding and cementation. As far as mineralogical constituents of sandstone are concerned it does not represent an equilibrium assemblage as compared to crystalline rock. Any mineral or mineral assemblage may occur in these rocks where each grain is an independent variable held together by matrix/cement as in the case of Siwalik sandstones. The varied mineral assemblage may reveal definite information about the source rocks but tells very little about their mechanical behavior. Because of the fact that the effect of mineralogy on strength need be very pronounced, the studies carried out in this field are limited. As a rule a positive correlation between strength and percentage of quartz in sandstones as observed by several workers (Merriam et al., 1970, Blatt, 1980, Price, 1960, Price 1966, Bell and Lindsay 1999; Zorlu et al., 2004, 2008). In contrast, Bell (1978), Fahy and Guccione (1979), Shakoor and Bonelli (1991) and Ulusay et al. (1994) did not find any meaningful correlation between engineering properties and percentage of quartz. Morgenstern and Phukan (1966)



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emphasize on the significance of variation in porosity, rather than mineralogy, and its effect on the Uniaxial Compressive Strength of sandstones and Jeremic (1981) considers the presence of clay minerals as a cause for decrease in strength. The clay minerals in sandstones are mainly montmorillonite, kaolinite and illite. The strength of sandstones, therefore may be affected by the amount and type of clay minerals both in cement and detritus; the strength being high when kaolinite is the main clay. The presence of montmorillonite in appreciable amounts, on the other hand, decreases the strength of sandstones. The quartz grains held in clay matrix may be stronger than sandstone with carbonate matrix (Price 1966). The effect of rock composition on rock mechanics properties expressed mainly in terms of the type and amount of major composition and cementing materials, it can be seen that quartz and feldspar have positive effect on rock mechanics properties, however, it is not linearly proportional to unconfined compressive strength (UCS); the unconfined compressive strength and Young Modulus of rocks are not only affected by quartz and feldspar, but also decidedly by the type and amount of cementing materials (Li Huamin et al. 2018). The bonding of cementing materials, grain size and pore size all have effect on rock mechanics properties. The stronger the bonding materials, the larger are the unconfined compressive strength. There is no clear relationship between Young's Modulus and cement. Thus, the smaller the grain size, the larger is the unconfined compressive strength and less pores suggest larger unconfined compressive strength. The unconfined compressive strength increases with decreasing porosity. In light of all these discussion, grain assemblage (distribution of voids, grain contact surfaces and packing density) and mineral constituents (percentage of matrix, percentage of quartz & rock fragments and percentage of other combinations) of the Siwalik sandstones exhibits the changes in voids and their fabric like pore filling by detritus and authigenic clays, fracture filling with clay/calcite, grain connecting with grain, grain connecting with authigenic clay, pore lining, grain adjustment or alignment, bending of mica around grains etc. (Fig-5). Various types of grain contacts are also noticeable like floating grains, tangential contact, long contacts, concavo-convex contact and sutured contact. Tangential inter-granular contacts occur in loosely packed sediments whereas concavo-convex and sutured contacts occur in rocks that have undergone considerable compaction during burial (Blatt, 1982). Hence high strength is expected from rocks with sutured or concavo-convex inter-grain contacts (Zorlu et al., 2008). Correspondingly, Shakoor and Bonelli (1991) and Ulusay et al. (1994) have reported a strong positive correlation between the strength and concavo-convex and sutured type contacts. The Siwalik sandstones, however, shows dominantly grain to grain long contact and concavo-convex contact (Fig. 5). The discussion in rear lines clearly reveals that the strength of sandstone depends on its overall textural and mineralogical composition instead of any single observation as pointed out by a number of researcher referred to above.



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Figure 5 Photomicrographs of Thin Sections Showing Textural Parameters

Detailed petrographic studies of indicate that the Siwalik sandstones are composed of fine to medium size, sub-angular to sub-rounded sand particles consisting of dominantly of quartz minerals and rock cemented with fine grained clayey matrix/ calcareous cement. The relative abundance of mineral grains and textural parameters apparently suggest that the Siwalik sandstones are immature to submature texturally as well as compositionally. It is suggested that all the textural attributes and mineralogical constituents of the Siwalik sandstone with estimated uniaxial compressive strength of 25-60 MPa studied area have considerable impact on its engineering/mechanical properties. Thus, the Siwalik sandstones may sustain engineering projects with suitable treatment.

The conclusions obtained from the present study can be summarized as follows:

1. The textural and mineralogical composition of Siwalik sandstone as noted in this study are generally same as found in other areas and any construction on it or within it can be adequately constructed with due engineering applications.

2. One the basis of textural and mineralogical composition, one can estimate the probable mechanical properties of these rocks like UCS and initiate the work without carrying out rock mechanics testing which are a costly affair and can be conducted subsequently during the different stages of project construction stage. The rock mechanics tests are certainly not avoidable as it can be deferent on surface and underground (in depth).



194

3. The Uniaxial Compressive Strength of Siwalik sandstone can be taken between 25MPa to 60MPaindicating that these sandstones are moderately strong to strong enough.

4. These sandstones have high porosity and comparatively less permeable due to clayey matrix/cement between the grains, hence, it will not take all the grouting easily.

5. In the lower Siwalik alternating bands of shales need to be taken care off for deciding foundation of structure and deciding support system. Middle or Upper Siwalik sandstone are generally massive and need not be causing such problems.

6. The friable Siwalik sandstone of Upper Siwalik or upper portion of Middle Siwalik can be disintegrated easily, therefore, can be crushed into sand and used as a gradient in concrete mixture.

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