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ENGI NEERI NGGEOLOGY
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IMTS (ISO 9001-2008 Internationally Certified) ENGINEERING GEOLOGY
ENGINEERING GEOLOGY
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CONTENTS ENGINEERING GEOLOGY UNIT I
01-11
IDENTIFICATION OF TYPE OF ROCK – IGNEOUS, SEDIMENTARY AND DISCUSS THEIR PROPERTIES UNIT II
12-16
IDENTIFICATION OF SOIL TEXTURE – CLAY, SAND, LOAMY
UNIT III
17-18
IDENTFICATION OF SOIL TYPES – RED SOIL, BLACK SOIL UNIT IV
19-33
DIAGRAMMATIC REPRESENTATION OF SOLAR, LUNAR ECLIPSES, DAY AND NIGHT UNIT V
34-41
IDENTFICATION OF COAL FIELDS – ECONOMIC ASPECTS, AVAILABILITY OF COAL AND USAGE OF TOPOGRAPHIC MAPS – TO STUDY ABOUT LAND FORMS
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1
UNIT I: IDENTIFICATION OF TYPE OF ROCK – IGNEOUS, SEDIMENTARY AND DISCUSS THEIR PROPERTIES Introduction: Petrology is the study of rocks (from the Greek petra, “rock,” and logos, “discourse or explanation”), therefore occupies a central position among the earth sciences. The observation and study of the rocks of the crust and mantle is the source of information that constrains most of our ideas and models about the history of Earth. Knowledge about igneous, sedimentary, and metamorphic rocks, their origins, their ages, and their distribution, is potentially capable of contributing to the solution of a wide variety of problems that run the gamut of geological interests. Rocks are naturally occurring, mechanically coherent aggregates of minerals or mineraloids (coal, glass, opal), some with interstitial fluids, and most consisting of several different minerals. Rocks are traditionally divided into three major groups: igneous, sedimentary, and metamorphic. In most outcrops and hand specimens it is not difficult to apply these categories to rock identification, and they serve the useful purpose of sorting rocks on the basis of observable characteristics that depend on the conditions of initial formation. The rock types are classified into three major types.
Igneous rock: Rock that solidified from a molten or partly molten material, that is, from magma.
Sedimentary rock: Rock resulting from the consolidation of loose sediment that has accumulated in layers. Examples include clastic rock consisting of mechanically formed fragments of older rock transported from their source and deposited in water or from air or ice; A chemical rock formed by precipitation from solution; An organic rock consisting of the remains or secretions of plants and animals.
Sedimentary rocks are composed either of particles or precipitated crystals and occur in stratified sequences of beds. Laminae are thin layers within beds. Sedimentary rocks are classified in two categories reflecting particulate or crystalline origins. 1. Detrital rocks and 2. Non-detrital rocks.
Detrital Rocks:
Detrital rocks consist of particles of rocks and or minersl derived from the weathering and erosion of any pre- existing rock type. These are classified principally by grain texture based on the sizes, shapes, sphericity, sorting and orientation of the enclosed grains. Some of the detrital rocks are discussed below
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Conglomerate and Breccia
Conglomerate and breccia are coarse grained, with the largest clasts ranging from pebble – size to boulders. Conglomerate consists of various shape, rounded clasts embedded in a matrix of sand, silt and clay, and cementing minerals. Breccia clasts are little abraded and thus, have “Sharp” edges and angular shapes.
Sandstones
Sandstones consist of sand-sized particles (1-16-2 mm) of any composition cemented by minerals or finer grained particles, and are classified by the bulk minerals composition of the particles bound by cement of finer – grained matrix. Arkose is a sandstone composed of ≤25% feldspar grains. The grains are typically coarse (1.5 -2 mm), usually angular, of uniform size and bound by cement. Graywacke is sandstone composed of quartz, feldspar and rock fragments. The clasts are bound by a dark colored, fine grained matrix comprising >20% of the rock and giving it a “dirty” appearance. The sand-sized grains tend to be angular and of mixed sizes in contrast to the more uniformly large and cemented grains of arkose. Subgraywacke consists of abundant quartz and chert, but few feldspar grains, in a mud matrix comprising about 15% of the rock. Quartz sandstone is composed of ≤95% quartz grains. They are usually light in color, ranging from white, yellow and brown to red, and are commonly laminated.
Siltstone
Fifty percent or more of siltstone grains range between 1/256-1/16 mm in diameter. Some grains may be barely visible, but most of the rock resembles hardened mud or clay. The grains are, how ever, coarse enough to make the surface feel slightly rough and gritty to the teeth. Sandstone grains, by contrast, are easily visible and give the rock a sandpaper- like feel. Thin laminations marked by color differences are common in siltstones.
Shales and Claystones
Shale and claystone are composed of the finest mud-sized grains(<1/256 mm) of clay minerals too small to be seen with the unided eye. In contrast to siltstones, these are smoothe to the touch and appear to be hardened mud or clay. Claystones are not laminated, whereas those having thin, easily split laminations resembling the pages of a book are called shales.
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ENGINEERING GEOLOGY Non-Detrital Rocks:
Nondetrital rocks, biologically formed particles and chemically precipitated crystals. These rocks are classified according to their origin and composition. They form from the accumulation of biological particles, from chemical parecipitates, or both. The classification used here 1. carbonate rocks whether of biological or chemical origin, and of clastic or crystalline texture; 2. crystalline rocks formed by precipitation of dissolved slats during evaporation ; 3. a miscellaneous category of biologic origin, including coals and cherts.
Carbonate rocks
Carbonate rocks include limestones, composed largely of calcite (CaCO3 ) or another crystal shape variant of calcium carbonate known as aragonite and, dolostone, largely of composed of dolomite (2CaMg (CO3)2). Dolostone originates from chemical process(es), and limestone from disintegrated shell, skeleton and algae, or from marine or fresh water precipitates.
Limestone is commonly soft and effervesces readily in a 10% solution of HCL. Dolostone may appear identical to limestone, but it will not react with HCL unless scratched or powdered thus, exposing more reactive surface area.
Limestone and dolostone may be composed of 1) mud-sized crystals ;2) Large crystals; 3) Fossils or other clasts bound by a carbonate mud or crystalline matrix; 4) Loosely-cemented microscopic “shells”; 5) chemically precipitated clasts ; 6) fossil fragments bound by calcite cement.
Chert
Chert is a dense microcrystalline quartz having many of the properties of other quartz minerals. Most beded chert probably originates from accumulations of the siliceous “Shells” of single-celled organisms and particles of the skeletons of some sponges.
Coal Coal is composed of ≥50% plant – derived carbon, and silt and/ or clay. It forms only if abundant plant materials accumulates rapidly or within water lacking oxygen because plant fibres decompose readily under other conditions. Various types of coal result from differing degrees of burial temperature and pressure, and differ also in sulfur and other elemental abundances
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Evaporites
Evaporites rocks form by crystal precipitation during the evaporation of extremely salty water. They are composed of bedded or massive crystals of minerals such as halite (NaC1), gypsum (CaSO4.2H2O), and anhydrite. PROPERTIES OF SEDIMENTARY ROCKS ROCK TYPE
COMPOSITION
Conglomerate
Clasts of quartz, chert, quartzite, rock fragments quartz, chert, quartzite,granite Quartz, common accessory minerals; mica, garnet, magnetite
Breccia Quartz Sandstone
Graywacke
Quartz, feldspar, fragments
Arkose
Feldspar, quartz
Coquina Silt stone
Shell fragments Quartz, mica, clay minerals
Shale
Clay minerals, feldspar, quartz, chlorite, mica, calcite
Claystone Limestones
As above Macroscopic & microscopic fossils or unfossilifereous, ooids, pellets, angular plates of lime mud (intraclasts) Fossil molds & casts, other clasts, above
Dolomite
clay
minerals
rock
Chert
Microcrystalline quartz â&#x20AC;&#x201C; siliceous tests & sponge spicules, altered volcanic ash
Coal
Plant carbon, clay & silt
Halite
NaCl
Gypsum
CaSO4.2 H2O
OTHER COMMON PROPERTIES Poorly bedded to unbedded Unbedded Silica/calcite cement well bedded. Light-reddish commonly Dark silt-clay matrix, matrix angular grains, poor sorting Calcite cement, clay or iron oxide. Often coarse, angular grains Calcite cements Angular grains, laminated, various colors. Laminated & fissible. Gray, black, green, red, blue, etc. colours. Soft-blocky Thin to thick-bedded, often light colored, effervesces in dilute HCL. Often pink, hard, poor fossil preservation, often cherty. Hardness = 7, conchoidal fracture ceramic â&#x20AC;&#x201C; waxy luster, gray,black, red, brown, white. Often occurs as nodules Brown, fibrous, unlithified = peat brown, fibrous, lithified = lignite black, oily luster, blocky fracture = biturninous brown to brown-black. Hard nodular = anthracite. Transparent-translucent. Salty, greasy luster, cubic cleavage Satiny-earthy luster,
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5 fiberous cleavage directional.
two
Igneous Rocks:
Granites
Definition: Granites are defined as plutonic, light coloured are acidic igneous rocks. They are the commonest types of igneous rocks. The word ‘Granite’ is derived from latin word ‘Granum’ meaning a grain and obviously refers to the texture of the common rock.
Composition: The most common mineralogical constituents of Granites are Quartz and Felspars. Among other minerals, the most important are ‘micas’ (both Muscovite and Biotite), amphiboles, commonly Hornblende, and rarely pyroxenes like Augite and Hypersthene. Similarly, accessory minerals like oxides of iron (chiefly magnetite), apatite, garnet and tourmaline may appear in some granite.
Texture: Granites are generally coarse to medium-grained polycrystalline (phaneric) and evengrained rocks).
Types: Many types of granites are distinguished on the basis of relative abundance of some accessory minerals and special textural features. The common types of granites include muscovite –granite, biotite-granite, hornblende-granite ; augite-granite, hypersthene – granite, and tourmaline-granite. Some of varieties based on the textures such are graphic and porphyritic granite.
Occurance: Granites are the most widely distributed types of the igneous rocks. They occur chiefly as deep-seated intrusions like sills, stocks and batholiths.
Identification: Granites can be identified hand specimen by their coarse to medium grained texture; mineralogical constituents, especially the abundance of felspars association with quartz, and light-colored (leucocratic)appearance.
Origin: The origin of the granites is one of the most controversial problems, in petrology. Most minor granitic bodies appear to be of clearly intrusive character and such their formation from a magmatic sorce is easily accepted.
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Definition: It is an intermediate igneous rock of plutonic origin with a silica of 52% and 66%.
Composition: Diorites are typically rich in plagioclase feldspars of sodic group. Besides plagioclase and alkali feslpar, diorites also contain accessory minerals like hornblende, biotite and some pyroxenes. Quartz is also present in some diorites
Textures: In the textures, diorites show quite close resemblance to granites and other plutonic rocks, generally, they are course to medium grained.
Occurrences: Diorites commonly occur in the form of small dykes, sills, stocks and other such intrusive bodies and also as rock formed on the margins of bigger granite masses.
Andesites
Definitions: These are volcanic rocks in which plagioclase felspars sodic and sub-calcic varieties like albite, andesine, labradorite etc. are the predominant constituents making the potash felspars only subordinate members.
Composition: Mainly Plagioclase and potash feldspars and may contain small amounts of quartz as well as biotite, hornblende, augite, olivine and hypersthene from among the dark minerals.
Occurance: Most abundant volcanic rocks, next to basalts and form flows of huge dimentions.
Syenites
Definition: It is defined as igneous, plutonic, even grained rocks in which alkali feldspar.
Composition: Syenites contain chiefly felspars of which many types may occur simultaneously or in different rocks. The most common felspars of the syenite are orthoclase and albite, although microcline, oligoclase and anorthite are also present in many of them and common accessory minerals are apatite, zircon and sphene,
Texture: Syenites show textural types almost similar to that of granites they are also coarse-to medium-grained, holocrystalline in nature exhibiting graphic, inter-growth or porphyritic relation among the constituents.
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Types: Nordmarkites – a syenite with some quartz; Monzonite – in which plagioclase felspars become approximately equal in proportion to alkali felspars; Larvikite –sometimes known as ‘blue-granite’ is actually a syentic rock in which feldspar labradorite (a plagioclase) is prominent constituent; Nepheline Syenites - These are syenite rocks in which nepheline becomes an important component. Quartz is absent.
Gabbro
These are coarse grained, dark- colored plutonic igneous rocks of basic character. Plagioclase felspars of lime-soda composition (eg. labaradorite and anorthite) are the chief constituents; besides these, the mafic minerals like augite, hornblende, olivine, biotite and iron oxides are also common.
Texture: Variable generally medium to coarse-grained; reaction rims are frequently observed).
Types: The chief gabbroic rock are: i)
Norite: Containing orthorhombic pyroxenes like hypersthene, enstatite in addition to labradorite.
ii)
Gabbro (type rock): It contains Monoclinic Pyroxenes (most commonly augite0 as the dominant mafic minerals.
iii)
Anorthosite – is a mono-minerallic rock containing generally, feldspar labradorite.
iv)
Eucrite – in which feldspar bytownite or anorthite dominates; pyroxenes are also abundant in it.
v)
Essexite – is characterized by the presence of some nepheline in addition to felspars and the mafic minerals.
vi)
Troctolite – is that gabboric rock which contains mainly felspars, and olivines, the pyroxenes being absent.
vii)
Dunite – is characterized by the absence of felspars and domination of olivine and pyroxenes.
Dolerites
Definition: These are igneous rocks of typically hypabyssal origin having formed as shallow sills and dikes. They may be regarded as roughly equivalent to gabbros of plutonic origin on the one hand and basalts of volcanic origin on the other.
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Composition: Dolerites are predominated by calcic plagioclases (e.g. anorthite, labradorite) and sufficient quantity of dark minerals like augite, olivine, and iron oxides etc.
Texture:
Dolerites are mostly fine to medium grained rocks; ophitic and prophyritic
textures are typically common in most of them.
Basalts
Basalts are roughly the volcanic equivalents of gabbros. They are most widespread of the volcanic rocks and are characterized by amygdaloidal or compact structures and a variety of textures, (e.g. porpyritic) but are invariably fine-grained.
A few of these are: Spilite showing pillow structure); Tepherite (olivine free type); Basanite (olivine rich type): Tachylyte (a glassy basalt). The olivine-free basalts are often called “Tholeiites”.
Occurrences: Gabbroic rocks occur in sills and dykes and also as plugs, stocks and lopoliths.
Pegmatites
Definition:
These are exceptionally coarse-grained igneous rocks which are generally
characterized by richness in “big” crystals of the component minerals.
Composition: Broadly speaking, pegmatites exhibit great variation in their mineralogical composition. These consist of felspars (mainly alkali felspars like Orthoclase, microcline and albite) and Quartz as the dominant constituents besides a variety of minerals like muscovite, tourmaline, topaz, fluorite, lithium mica, spodumene, beryl, cassiterite, wolframite, columbite and tantalite etc. Granite pegmatites are especially rich in white mica (muscovite) and commonly form the source rock of this industrial mineral.
Occurrence:
As in their mineralogical composition, pegmatites show a good deal of variation
in their mode of occurrence also. They have been recorded forming veins, dykes and patches of irregular outlines and variable dimensions.
Structures and Textures:
Pegmatites do not show any typical texture or structure in
general, except that they are invariably coarse grained and mostly inequigranular. In many pegmatite bodies, a zonal structure (i.e. different minerals occurring in definite zones starting from the periphery of the body and proceeding towards its centre) is often distinctly developed.
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Varieties:
Many varieties of pegmatites are recognized on a number of bases. Thus,
petrologically, pegmatites may be differentiated into granite-, diorite-, and syenite-pegmatitie, etc.
Origin: (i)
most pegmatites give no indication of movement of magma in molten condition from their structures and textures.
(ii)
In many cases, the pegmatites are situated in places devoid of large plutons or rocks that could be considered their source.
At present, two modes are commonly suggested and each may be applicable in different cases:
(a) Pegmatites are believed to have formed from magmatic melts most probably towards the end of the process of crystallization of granitic magma. The residual solutions from which pegmatites were formed were rich in volatile components of the rare minerals. (b) Other view holds pegmatite masses having originated from pre-existing rocks under the influence of chemically active fluids-vapours, gases and liquids-, the process involved being replacement of original components by new ones.
Aplites
These are igneous rocks of plutonic origin but characterized by a fine-grained, essentially equi-granular, allotriomorphic texture. Essential minerals of aplites are generally the same as that of granites, i.e. felspars and quartz.
Lamprophyres
These form a group of igneous rocks which occur typically as dykes or sills. Their important characters are:
(i) Texture:
panidiomorphic (in which most of crystals show perfect outlines); fine-grained
and holocrystalline.
(ii) Composition:
Lamprophyres show a great variation in their mineralogical composition.
Mostly they are rich in ferromagnesian silicates. Important minerals are: biotite, pyroxenes (augite), amphiboles (hornblende), felspars, and olivine.
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(iii) Types: Many types of lamprophyres are distinguished on the basis of feldspar and dark minerals present in them. Minette, a lamprophyre with feldspar orthoclase and biotite; Vogesite when augite or hornblende is present. Instead of biotite.
Peridotites
Definition:
The term peridotite is commonly used to express the ultra-mafic igneous rocks
that are highly rich in a ferromagnesian mineral Olivine (Mg, Fe), Sio4. Their chief characters are:
(i)
low silica index; such rocks invariably contain less than 45 percent silica,
(ii)
high colour index; rich as they are in dark minerals, the colour index is invariably above 70, but generally in the range of 90-100.
Texture:
Peridotites are generally massive and coarse grained in texture.
Varieties:
A number of peridotites are distinguished on the basis of accessory minerals,
e.g. hornblende peridotite, pyroxene peridotite etc. “Kimberlites” are peridotites in which olivine is altered to serpentine. Other rocks related to peridotites include such monomineralic varieties as Dunite – composed wholly of olivine; Pyroxenite – containing only pyroxenes and Serpentinites, and bronzitites, etc.
Occurrence:
Peridotites generally form sills, sheets and dykes of moderate size.
Origin: A number of modes of origin have been suggested for the peridotites.
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TABLE: General characteristics of igneous and sedimentary rocks IGNEOUS ROCKS 1. Volcanoes and related lava flows
SEDIMENTARY ROCKS 1. Stratification and sorting
2. Cross-cutting relations to surrounding rocks, as in dykes, veins, stocks, and batholiths
2. Structures such as ripple marks, crossbedding, or mud cracks
3. Thermal effects on adjacent rocks, such as recrystallization, color changes, reaction zones
3. Often widespread and inter-bedded with known sediments
4. Chilled (finer-grained) borders against adjacent rocks
4. The shape of the body may be characteristic of a sedimentary form, such as a delta, bar, river drainage system, and so on
5. Lack of fossils and stratification (except for pyroclastic deposits)
5. The rocks may be unconsolidated or not
6. Generally structureless interlocking grains
rocks
composed
of
7. Typically located in Precambrian or orogenic terranes 8. Characteristic shapes and sizes, as in laccoliths, lopoliths, sills, stocks, batholiths, and lava flows.
Textures Porphyritic, glassy, vesicular, amygdaloidal, graphic, pyroclastic, or interlocking aggregate Characteristic minerals Amphihole Feldspar abundant Leucite Micas Nepheline Olivine Pyroxene Quartz Glass
Fragmental, fossiliferous, oolitic, stratified, interlocking aggregate
pisolitic,
Abundant quartz, carbonates (especially calcite and dolomite), or clays Anhydrite Chert (microcrystalline quartz) Gypsum Halite
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UNIT II IDENTIFICATION OF SOIL TEXTURE â&#x20AC;&#x201C; CLAY, SAND, LOAMY Introduction: Natural soils are comprised of soil particles of varying sizes. The soil particle-size groups, called soil separates, are sands (the coarsest), silts, and clays (the smallest). The relative proportions of soil separates in a particular soil determine its soil texture.
Texture is an important soil characteristic because it will, in part, determine water intake rates (infiltration), water storage in the soil, the ease of tilling the soil, the amount of aeration (vital to root growth), and will influence soil fertility. For instance, a coarse sandy soil is easy to till, has plenty of aeration for good root growth, and is easily wetted, but it also dries rapidly and easily loses plant nutrients, which are drained away in the rapidly lost water. High-clay soils (over 30 percent clay) have very small particles that fit tightly together, leaving little open pore space, which means there is little room for water to flow into the soil. This makes high-clay soils difficult to wet, difficult to drain, and difficult to till.
Soil Separate Sizes:
This has established limits of variation for the soil separates and has assigned a name to each size class (Refer Table). This system has been approved by the Soil Science Society of America. Other particle-size classification systems are used in the United States and throughout the world. Table: Soil Separates and Their Diameter Ranges Soil Separate Name
Diameter Range (mm)
Very coarse sand Coarse sand Medium sand Fine sand Very fine sand Silt Clay
2.0-1.0 1.0-0.5 0.5-0.25 0.25-0.10 0.10-0.05 0.05-0.002 Less than 0.002
Visual Size Comparison of Maximum size House key thickness Small pinhead Sugar or Salt Crystals Thickness of book page Invisible to the eye Visible under microscope Most are not visible even with a microscope
Soil Textural Classes: Textural names are given to soils based on the relative proportions of each of the three soil separates-sand, silt, and clay. Soils that are preponderantly clay are called clay (textural
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class); those with high silt content are silt (textural class); those with a high sand percentage are sand (textural class). A soil that does not exhibit the dominant physical properties of any of these three groups (such as a soil with 40% sand, 40% silt, and 20% clay) is called Loam. Note that loam does not contain equal percentages of sand, silt, and clay. It does, however, exhibit approximately equal properties of sand, silt, and clay.
The textural triangle (See Figure) is used to determine the soil textural name after the percentages of sand, silt, and clay are determined from a laboratory analysis. Since the soilâ&#x20AC;&#x2122;s textural classification includes only mineral particles and those of less than 2mm diameter, the sand plus silt plus clay percentages equal 100%. (Note that organic matter is not included). Knowing the amount of any two fractions automatically fixes the percentage of the third one. In reading the textural triangle, any two particle fractions will locate the textural class at the point where those two intersect.
Particle-size (Mechanical) Analysis:
The procedure used to separate a soil into various size groups from the coarsest sand, through silt, to the finest clay, is particle-size analysis (mechanical analysis). For this purpose, the mineral matter less than 2mm in diameter is considered separately from the larger particles. All rocks, pebbles, roots, and other rubble are removed (and measured) by screening the finer soil parts through a 2mm sieve before analysis. Humus is removed from the soil sample by destroying it with an oxidizing chemical (such as hydrogen peroxide) before particle-size separation is done. An example of determining soil textural class is given in Note 1. The basis of particle-size separations, stokesâ&#x20AC;&#x2122; law, is given in Note 2.
Note 1: Determining Textural Class Names
Problem: A sample of soil was screened and had the size separates in material smaller than 2mm determined by particle-size (mechanical) analysis, with the following results:
Sand content (2-0.05mm diameter)
140g
Silt content (0.05-0.002mm diameter)
38g
Clay content (less than 0.002mm diameter)
22g
Total dry soil weight: 200g
Determine the textural class name.
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Solution: Textural names consider only the less than 2mm portion;
140g/200g x 100 = 70 percent sand
38g/200g x 100 = 19 percent silt
22g/200g x 100 = 11 percent clay
1. Using the textural triangle (Fig-1), place the triangle with 100 percent clay at the top and read across parallel with the base along the 11 percent line. Keeping this line in mind, turn the triangle so 100% silt is now at the top and read across parallel to the new base of the triangle along the 19% line. The 11% clay and 19% silt lines intersect in the Sandy loam. The percentage of sand value could have been used as easily as either clay or silt values, because the lines for all the three size fractions intersect at the same point. The content of organic matter is ignored. If the soil contains more than 15% (by volume) of particles larger than sand, a “coarse fragment” adjective is added to the textural name (i.e., gravelly sandy loam).
2. The correct complete name above is sandy loam. Note 2: Stokes’ Law of Settling Velocities
To separate particles or to measure densities at a certain depth in a suspension of soil in water requires knowledge of settling rates for different-sized particles. Stokes’ law simply balances the downward force due to gravity with the resisting force due to buoyancy (surface friction and solution movement). Stokes’ law assumes that smooth rigid spheres are settling in a quiescent (non-turbulent) viscous fluid of known density and viscosity (resistance to flow). The equation for Stokes’ law is 2
V = D (ρp-ρw)g/18η Where V = velocity of fall (cm/s) 2
g = acceleration of gravity (cm/s ), usually 980 cm/s 2
2
2
D = “equivalent” diameter of particle (cm) (D = 4r ) 3
ρp = density of particle (g/cm ), about 2.6g/cm
3
ρw = density of the solution (g/cm-s), about 1.0g/cm
3
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Ρ = viscosity of the solution (g/cm-s), about 0.010 poise at 20c and about 0.008 poise at 30c (one poise = 1g/cm-s)
The densities, gravity, and viscosity can be expressed by a constant (k), so 2
V = kD = 8711D
2
The speed with which particles fall is proportional to the square of their diameters. Any calculation using this law is only approximately correct for soils because the particles are not spherical, are not smooth, and vary in mineral density. 2
Example Calculations: Using the value of 8711D (above) for mineral fall in water at 20c, the following rates of fall were calculated: Medium sand of 0.5mm diameter = 0.05cm diameter. Then V = 8711D2 = 8711 (0.05cm)2 = 21.8cm/s fall Medium sand (0.05mm diameter) = 22cm/s fall rate Find sand (0.20mm diameter) = 3.5cm/s fall Medium silt (0.01mm diameter) = 0.0087cm/s = 0.52cm/min Coarse clay (0.002mm diameter) = 0.00035cm/s = 0.021cm/min = 1.26cm/h Fine clay (0.0002mm diameter) = 0.0000035 cm/s = 0.30cm/day.
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UNIT III IDENTFICATION OF SOIL TYPES – RED SOIL, BLACK SOIL Introduction: The characteristics of each of the soil types are primarily manifestations of the prevailing climatic conditions. The term ‘pedalfer’ gives a clue to the basic characteristic of this soil type. The word is derived from the Greek pedon, meaning ‘soil’, and the chemical symbols ‘Al’ (aluminum) and ‘Fe’ (iron). Pedalfers are characterized by an accumulation of iron oxides and aluminium – rich clays. The areas annual rainfall exceeds 63cm (25 inches) most of the soluble materials, such as calcium carbonate, are leached from the soil and carried away by underground water. The less soluble iron oxides and clays are carried from the A horizon and deposited in the B horizon, giving it a brown to red-brown color. These soils are best developed under forest vegetation where large quantities of decomposing organic matter provide the acid conditions necessary for leaching. Pedocal is derived from the Greek pedon, meaning ‘soil’, and the first three letters of calcite (calcium carbonate). As the name implies, pedocals are characterized by an accumulation of calcium carbonate. The chemical weathering is less intense in dry areas, pedocals generally contain a smaller percentage of clay minerals than pedalfers.
In the hot, wet climates of the tropics, soils called laterites may develop. Since chemical weathering is intense under such climatic conditions, these soils are usually deeper than soils developing over a similar period of time in the mid-latitudes. Not only does leaching remove the soluble materials such as calcite, but the great quantities of percolating water also remove much of the silica, with the result that oxides of iron and aluminum become concentrated in the soil. Iron gives soil a distinctive red color. When dried, laterites are very hard. In fact, some people use this soil for making bricks. If the parent rock contained little iron, the product of weathering is an aluminum-rich accumulation called bauxite.
Since bacterial activity is very high in the tropics, laterites contain practically no humus. This fact, coupled with the highly leached and bricklike nature of these soils, make laterites poor for growing crops. The infertility of these soils has been borne out repeatedly in tropical countries where cultivation has been expanded into such areas.
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In cold or dry climates soils are generally very thin and poorly developed. The reasons for this are fairly obvious. Chemical weathering progresses very slowly in such climates, and the scanty plant life yields very little organic matter.
Based on the general characteristics of the area, the soil types can be identified and tabulated below. Table: Summary of Soil Types: Climate
Temperate
Temperate
humid
(<63cm rainfall)
rainfall)
desert
Grass and brush
Grass and trees
Almost none, so
(>63cm
dry
Tropical
(heavy
Extreme arctic or
rainfall) Vegetation
Forest
no
humus
develops Soil Type
Pedalfer
Top soil
Sandy,
light
colored; acid
Pedocal
Laterite
Commonly
Enriched in iron
No real soil forms
(and aluminum);
because there is
brick red color
no
All
material.
enriched calcite;
in whitish
color Subsoil
Enriched
in
aluminum,
iron
and clay; brown
Enriched calcite;
in
elements
whitish
removed
other
organic
Chemical by
color
leaching
Caliche is name
Apparently
applied
bacteria destroy
weathering very slow
color Remarks
Extreme development conifer
in
forests,
because
accumulation calcite
abundant humus
to
the of
humus,
so
no
acid is available to remove iron.
makes groundwater very acid. light
Produces gray
soil
because
of
removal of iron
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is
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UNIT IV DIAGRAMMATIC REPRESENTATION OF SOLAR, LUNAR ECLIPSES, DAY AND NIGHT Introduction: A solar eclipse occurs when the Moon passes in front of the Sun and obscures it totally or partially. This configuration can only exist at New Moon, when Sun, Moon and Earth are on a single line with the Moon in the middle. Near the beginning and end of total solar eclipse, the thin slice of the Sun visible appears broken up into beads of light. These lights are called 'Baily's Beads' after the British astronomer Francis Baily, who discovered them. They occur because the edge of the Moon is not smooth but jagged with mountain peaks.
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When just one bead is visible, the effect is often likened to a diamond ring.
There are four types of solar eclipses:
A partial solar eclipse occurs when the Sun is only partially overlapped by the Moon.
A total solar eclipse occurs when the Moon completely obscures the Sun. This happens when the Moon is near perigee and its angular diameter as seen from Earth is identical to or slightly larger than that of the Sun. A total solar eclipse is the only opportunity to observe the Sun's corona without specialised equipment.
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ENGINEERING GEOLOGY ď&#x201A;ˇ
An annular (ring-formed) eclipse occurs when the Moon's center passes in front of Sun's center while the Moon is near apogee. The Moon's angular diameter is then smaller than that of the Sun so that a ring of the Sun can still be seen around the Moon. This is similar to a penumbral eclipse.
ď&#x201A;ˇ
A hybrid eclipse occurs when the curvature of Earth's surface causes a single solar eclipse to be observed as annular from some locations but total from other locations. A total eclipse is seen from places on the Earth's surface that lie along the path of the eclipse and are physically closer to the Moon, and so intersect the Moon's umbra; other locations, further from the Moon, fall in the Moon's antumbra and the eclipse is annular.
The term "solar eclipse" is a misnomer: the phenomenon is actually an occultation. An "eclipse" occurs when one celestial object passes into the shadow cast by another (as with an eclipse of the Moon). An "occultation' occurs when one body passes in front of another. When at its new phase the Moon passes in front of, or occults, the Sun, as seen from Earth, the Moon also casts a small shadow on Earth. An "occultation" of the Sun is therefore also a partial "eclipse" of Earth. Observing a solar eclipse: Looking at the Sun is dangerous at any time when any part of the brilliant visible disk of the Sun (its photosphere) is visible; to do so can cause permanent eye damage. This is true at any time, including during solar eclipses; since an eclipse offers an unusually high temptation to look at the Sun, there is a high incidence of eye damage caused during solar eclipses. Viewing the Sun through any kind of optical aid, binoculars, a telescope, or even a camera's viewfinder- is extremely dangerous. Solar Viewing: The Sun can be viewed using appropriate filtration to block the harmful part of the Sun's radiation. Note that sunglasses are of little use, since they don't block the harmful and invisible infra-red radiation which causes retinal damage; other improvised methods, such as using a reflection in water, or looking through a compact disk, are equally dangerous. Only properly designed and certified solar filters should ever be used for direct viewing of the Sun; and these must be in perfect condition, as even a small defect could cause damage. The safest way to view the Sun is by indirect projection. This can be done by projecting an image of the sun onto a white piece of paper or card using a pair of binoculars (with one of the
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ENGINEERING GEOLOGY lenses covered), a telescope, or another piece of cardboard with a small hole in it (about 1 mm diameter), often called a pinhole camera. The projected image of the sun can then be safely viewed; this technique can be used to observe sunspots, as well as eclipses. However, care must be taken to ensure that no-one looks through the projector (telescope, pinhole, etc.) directly, as this will cause severe eye damage; particular care should be taken if children are present.It is safe to directly observe the total phase of a total solar eclipse, when the Sun's photosphere is completely covered by the Moon; indeed, this is a very beautiful sight. The Sun's faint corona will be visible, and even the chromosphere, solar prominences, and possibly even a solar flare may be visible. The danger here is of being caught out by the end of the total phase, and the return of the "exposed" Sun; because all parts of the Sun's disk are of similar intensity, even a tiny sliver of the Sun could cause permanent eye damage. For this reason, viewing the total phase of a solar eclipse through binoculars or a telescope should not be recommended.
Diagram of solar eclipse Total and annular eclipses both occur when the Moon lines up with the Sun exactly, but since the Moon's orbit is not perfectly circular it is sometimes farther away from Earth and doesn't always cover the entire solar disc from an Earthly vantage point. It is one of the most remarkable coincidences of nature that the Sun lies approximately 400 times as far away from Earth as does the Moon, and the Sun is also approximately 400 times as large in diameter as the Moon. As a result, as seen from Earth, the Sun and the Moon appear to be nearly the same apparent size. The Moon orbits Earth in an elliptical, or elongated orbit, however, and not in a circular orbit. Thus during about 55-60% of its orbit the Moon is far enough from Earth ("apogee") that it is too small to cover the Sun's surface completely. During the remaining portion of its orbit, it is closer to Earth ("perigee") and large enough in apparent size to cover the Sun completely.
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ENGINEERING GEOLOGY When a solar eclipse occurs near apogee, there is therefore a small ring or annulus of Sun that remains uncovered even at the moment of maximum eclipse. This produces an "annular" eclipse, during which the brilliant and blinding uncovered ring of the Sun makes the solar corona invisible. When a solar eclipse occurs near perigee, however, the Moon is close enough to Earth and large enough in the sky that it can cover the entire bright surface (the photosphere) of the Sun completely, and the observer sees a total eclipse, at which time the ghostly white solar corona appears. A solar eclipse can only be seen in a band across Earth as the Moon's shadow moves across its surface, while a total or annular eclipse is actually total or ring-formed in only a small band within this band (the eclipse path), and partial elsewhere (total eclipse takes place where the umbra of the Moon's shadow falls, whereas a partial eclipse is visible where the penumbra falls). The full band is generally around 100 km in width. The eclipse path will be widest if the Moon happens to be at perigee, in which case the eclipse path alone can reach 270 km in width. Total solar eclipses are rare events. Although they occur somewhere on Earth approximately every 18 months, it has been estimated that they recur at any given spot only every 300 to 400 years. And after waiting so long, the total solar eclipse only lasts for a few minutes, as the Moon's umbra moves eastward at over 1700 km/h. Totality can never last more than 7 min 40 s, and is usually a good deal shorter. During each millennium there are typically fewer than 10 total solar eclipses exceeding 7 minutes. The last time this happened was June 30, 1973. Those alive today probably won't live to see it happen again, on June 25, 2150. The longest total solar eclipse during the 8,000-year period from 3000 BC to 5000 AD will occur on July 16, 2186, when totality will last 7 min 29 s. (eclipse predictions by Fred Espenak, NASA/GSFC.) For astronomers, a total solar eclipse forms a rare opportunity to observe the corona (the outer layer of the Sun's atmosphere). Normally this is not visible because the photosphere is much brighter than the corona. Calculating the date of a solar eclipse: If you know the date and time of a solar eclipse, you can predict other eclipses using eclipse cycles. Two well-known eclipse cycles are the Saros cycle and the Inex cycle. The Saros cycle is probably the most well known, and one of the best, eclipse cycles. The Inex cycle is itself a poor cycle, but it is very convenient in the classification of eclipse cycles. After a Saros cycle finishes, a new Saros cycle begins 1 Inex later (hence its name: in-ex).
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ENGINEERING GEOLOGY Indian Astronomy: Indian astronomy is largely wrapped up in the Vedic religious treatises, but one individual, Aryabhata of Kusumapura, born in AD 476 is noteworthy. He is the first known astronomer on that continent to have used a continuous system of counting solar days. His book, The Aryabhatiya, published in 498 AD described numerical and geometric rules for eclipse calculations. Indian astronomy at that time was taking much of its lead from cyclic Hindu cosmology in which nature operated in cycles, setting the stage for searching for numerical patterns in the expected time frames for eclipses, click link above for more.
Explanation of Solar Eclipse Maps: Each eclipse is represented on an orthographic projection map of Earth that shows the path of the Moon's penumbral (partial) and umbral / antumbral (total, hybrid, or annular) shadows with respect to the continental coastlines, political boundaries (circa 2000 CE) and the Equator. North is to the top and the daylight terminator is drawn for the instant of greatest eclipse. An "x" symbol marks the sub-solar point or geographic location where the Sun appears directly overhead (zenith) at that time. All salient features of the eclipse maps are identified in Figure 1-1 which serves as a key.
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ENGINEERING GEOLOGY The limits of the Moon's penumbral shadow delineate the region of visibility of a partial solar eclipse. This irregular or saddle shaped region often covers more than half the daylight hemisphere of Earth and consists of several distinct zones or limits. At the northern and/or southern boundaries lie the limits of the penumbra's path. Partial eclipses have only one of these limits, as do central eclipses when the Moon's shadow axis falls no closer than about 0.45 radii from Earth's center. Great loops at the western and eastern extremes of the penumbra's path identify the areas where the eclipse begins/ends at sunrise and sunset, respectively. If the penumbra has both a northern and southern limit, the rising and setting curves form two separate, closed loops (e.g., 2017 Aug 21). Otherwise, the curves are connected in a distorted figure eight (e.g., 2019 Jul 02). Bisecting the "eclipse begins/ends at sunrise and sunset" loops is the curve of maximum eclipse at sunrise (western loop) and sunset (eastern loop). The eclipse magnitude is defined as the fraction of the Sun's diameter occulted by the Moon. The curves of eclipse magnitude 0.5 delineate the locus of all points where the local magnitude at maximum eclipse is equal to 0.5. These curves run exclusively between the curves of maximum eclipse at sunrise and sunset. They are approximately parallel to the northern/southern penumbral limits and the umbral/antumbral paths of central eclipses. The northern and southern limits of the penumbra may be thought of as curves of eclipse magnitude of 0.0. For total eclipses, the northern and southern limits of the umbra are curves of eclipse magnitude of 1.0. Greatest eclipse is the instant when the axis of the Moon's shadow cone passes closest to Earth's center. Although greatest eclipse differs slightly from the instants of greatest magnitude and greatest duration (for total eclipses), the differences are negligible. The point on Earth's surface intersected by the axis of the Moon's shadow cone at greatest eclipse is marked by an asterisk symbol "*". For partial eclipses, the shadow axis misses Earth entirely, so the point of greatest eclipse lies on the day/night terminator and the Sun appears on the horizon.
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ENGINEERING GEOLOGY LUNAR ECLIPSE
Schematic diagram of the shadow cast by the Earth. Within the central umbra shadow, the Moon is totally shielded from direct illumination by the Sun. In contrast, within the penumbra shadow, only a portion of sunlight is blocked.
As seen by an observer on Earth on the imaginary celestial sphere, the Moon crosses the ecliptic every orbit at positions called nodes twice every month. When the full moon occurs in the same position at the node, a lunar eclipse can occur. These two nodes allow two to five eclipses per year, parted by approximately six months. (Note: Not drawn to scale. The Sun is much larger and farther away than the Moon.)
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A total penumbral lunar eclipse dims the moon in direct proportion to the area of the sun's disk blocked by the earth. This comparison shows the southern shadow penumbral lunar eclipse of January 1999 (left) to the same moon outside of the shadow (right) demonstrates this subtle dimming.
As viewed from Earth, the Earth's shadow can be imagined as two concentric circles. As the diagram illustrates, the type of lunar eclipse is defined by the path taken by the Moon as it passes through Earth's shadow. If the Moon passes through the outer circle but does not reach the inner circle, it is a penumbral eclipse; if only a portion of the Moon passes through the inner circle, it is a partial eclipse; and if entire Moon passes through the inner circle at some point, it is a total eclipse. A lunar eclipse is an eclipse which occurs whenever the moon passes behind the earth such that the earth blocks the suns rays from striking the moon. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, there is always a full moon the night of a lunar eclipse. The type and length of an eclipse depend upon the Moon's location relative to its orbital nodes. The next total lunar eclipse occurs on December 21, 2010. The next eclipse of the Moon is a penumbral eclipse on July 7, 2009.
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ENGINEERING GEOLOGY Types of lunar eclipses The shadow of the Earth can be divided into two distinctive parts: the umbra and penumbra. Within the umbra, there is no direct solar radiation. However, as a result of the Sun's large angular size, solar illumination is only partially blocked in the outer portion of the Earth's shadow, which is given the name penumbra. A penumbral eclipse occurs when the Moon passes through the Earth's penumbra. The penumbra causes a subtle darkening of the Moon's surface. A special type of penumbral eclipse is a total penumbral eclipse, during which the Moon lies exclusively within the Earth's penumbra. Total penumbral eclipses are rare, and when these occur, that portion of the Moon which is closest to the umbra can appear somewhat darker than the rest of the Moon. A partial lunar eclipse occurs when only a portion of the Moon enters the umbra. When the Moon travels completely into the Earth's umbra, one observes a total lunar eclipse. The Moon's speed through the shadow is about one kilometer per second (2,300 mph), and totality may last up to nearly 107 minutes. Nevertheless, the total time between the Moon's first and last contact with the shadow is much longer, and could last up to 3.8 hours. The relative distance of the Moon from the Earth at the time of an eclipse can affect the eclipse's duration. In particular, when the Moon is near its apogee, the farthest point from the Earth in its orbit, its orbital speed is the slowest. The diameter of the umbra does not decrease much with distance. Thus, a totallyeclipsed Moon occurring near apogee will lengthen the duration of totality. A selenelion or selenehelion occurs when both the Sun and the eclipsed Moon can be observed at the same time. This can only happen just before sunset or just after sunrise, and both bodies will appear just above the horizon at nearly opposite points in the sky. This arrangement has led to the phenomenon being referred to as a horizontal eclipse. It happens during every lunar eclipse at all those places on the Earth where it is sunrise or sunset at the time. Indeed, the reddened light that reaches the Moon comes from all the simultaneous sunrises and sunsets on the Earth. Although the Moon is in the Earth's geometrical shadow, the Sun and the eclipsed Moon can appear in the sky at the same time because the refraction of light through the Earth's atmosphere causes objects near the horizon to appear higher in the sky than their true geometric position. The Moon does not completely disappear as it passes through the umbra because of the refraction of sunlight by the Earth's atmosphere into the shadow cone; if the Earth had no atmosphere, the Moon would be completely dark during an eclipse. The red colouring arises because sunlight reaching the Moon must pass through a long and dense layer of the Earth's
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ENGINEERING GEOLOGY atmosphere, where it is scattered. Shorter wavelengths are more likely to be scattered by the small particles, and so by the time the light has passed through the atmosphere, the longer wavelengths dominate. This resulting light we perceive as red. This is the same effect that causes sunsets and sunrises to turn the sky a reddish colour; an alternative way of considering the problem is to realise that, as viewed from the Moon, the Sun would appear to be setting (or rising) behind the Earth. The amount of refracted light depends on the amount of dust or clouds in the atmosphere; this also controls how much light is scattered. In general, the dustier the atmosphere, the more that other wavelengths of light will be removed (compared to red light), leaving the resulting light a deeper red colour. This causes the resulting coppery-red hue of the Moon to vary from one eclipse to the next. Volcanoes are notable for expelling large quantities of dust into the atmosphere, and a large eruption shortly before an eclipse can have a large effect on the resulting colour. Danjon scale: The following scale (the Danjon scale) was devised by AndrĂŠ Danjon for rating the overall darkness of lunar eclipses: L=0: Very dark eclipse. Moon almost invisible, especially at mid-totality. L=1: Dark Eclipse, gray or brownish in colouration. Details distinguishable only with difficulty. L=2: Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright. L=3: Brick-red eclipse. Umbral shadow usually has a bright or yellow rim. L=4: Very bright copper-red or orange eclipse. Umbral shadow is bluish and has a very bright rim. Eclipse cycles: Every year there are usually at least two partial lunar eclipses, although total eclipses are significantly less common. If one knows the date and time of an eclipse, it is possible to predict the occurrence of other eclipses using an eclipse cycle like the Saros cycle. Unlike a solar eclipse, which can only be viewed from a certain relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of the Earth. Recent and upcoming lunar eclipse events:
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March 3, 2007, lunar eclipse - The first total lunar eclipse of 2007 occurred on March 03, 2007, and was partially visible from the Americas, Asia and Australia. The complete event was visible throughout Africa and Europe. The event lasted 01h:15m, began at 20:16 UTC, and reached totality at 22:43 UTC.
August 2007 lunar eclipse - August 28, 2007, saw the second total lunar eclipse of the year. The initial stage began at 07:52 UTC, and reached totality at 09:52 UTC. This eclipse was viewable form Eastern Asia, Australia and New Zealand the Pacific, and the Americas.
February 2008 lunar eclipse - The only total lunar eclipse of 2008 occurred on February 21, 2008, beginning at 01:43 UTC, visible from Europe, the Americas, and Africa.
The next partial eclipse of the Moon will occur on December 31, 2009.
The next total eclipse of the Moon will occur on December 21, 2010.
Day and Night
We all live on Earth. It is like a big, round ball. And it is spinning. This is hard to believe because we do not feel any motion. Everything stays in place because the Earth pulls everything to itself. This pull is called gravity. The Earth always spins at the same speed (about 1000 miles per hour!). The Earth spins around one time, or makes one full rotation, in 24 hours.
Light from the sun falls on one half of the spinning Earth. This half has day. The other, darker half has night. As the Earth spins, we move through the light, into the darkness, and back again. This makes day and night. Half of the Earth is always in the light and half of the Earth is always in the dark. The Earth is always spinning and that is why it is always changing. Look at the pictures below to see how the Earth rotates and where the sun is at each time of day.
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People at point A can see the sun rise.
As the Earth turns, the people move to point B. It is the middle of the day for them. The sun is straight up in the sky. This means it is noontime.
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When the people are at C, the sun is going down. This means it is sunset.
At D it is midnight. Now it is very dark. Twenty-four hours, or one day, will have gone by once they get back to A. The sun will rise again and a new day will be starting. This is what we see everyday from Earth as it rotates and the sun moves across the sky. In the morning you can see the sunrise. Around noontime, the sun is straight up in the sky. At night, you can see the sunset.
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Try this experiment to see how the Earth moves from day to night. The turning Earth gives us about twelve hours of daylight and twelve hours of darkness. This gives us enough time to go to school, go to work, and play during the day and enough time to sleep at night.
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UNIT V IDENTFICATION OF COAL FIELDS – ECONOMIC ASPECTS, AVAILABILITY OF COAL AND USAGE OF TOPOGRAPHIC MAPS – TO STUDY ABOUT LAND FORMS IDENTFICATION OF COAL FIELDS – ECONOMIC ASPECTS AND AVAILABILITY OF COAL Introduction:
Coal is one of the principal mineral fuels. Many scientist defined, coal is a combustible rock which had its origin in the accumulation and partial decomposition of vegetation. Palaeobotanists have shown conclusively that coal had been formed usually from land plants.
Composition:
Chemically coals are composed of organic and mineral matter. Their organic mass consists of carbon (60 to 90%), hydrogen (1 to 12%), oxygen (2 to 20%), nitrogen (1 to 3%) and slight amounts of sulphur and phosphorus. The proportion of these elements progressively varies with the advance of coalification process starting from plant material.
Origin: It has been established that ‘coal had its origin in the accumulation of vegetal matter, which has been subjected to a variety of geological processes bringing about marked changes in the physical and chemical composition. The changes are revealed by the gradual darkening of colour, increase in compactness, hardness and carbon content and decrease in moisture and volatiles.
Formation of Coal:
The process of formation of coal is complex and involves both bacteriological and physical agencies. According to A.M. Bateman, the following things are essential for the formation of coal:
(a) Source materials: plants and trees are the chief source material. (b) Places and conditions of accumulation: The extensive distribution of individual coal seams implies swamp-accumulation, on broad delta and coastal plain areas, on broad interior basin low lands that have been base leveled etc. Thus the coal bearing horizon should be a basin like structure where the area should be swampy naturally. (c) Climatic condition: The favourable climatic conditions are
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ENGINEERING GEOLOGY (i)
mild-temperate to sub-tropical climate,
(ii)
with moderate to heavy rain-fall, well distributed throughout the year.
Mode of occurrence:
Coal occurs as a sedimentary rock in association with sandstone, carbonaceous shale and occationally fireclay in a regular succession and with repetitions. Tertiary coal, in certain cases, found to occur as in-situ deposits. But Gondwana coal occurs as drifted deposits. Igneous intrusions in the form of dykes and sills are present in the coal seams. Generally the intrusives are of mica-peridotite, lamprophyre and basic dolerites.
Distribution of Indian Coal:
The Coals of India belong to two principal geological periods, such are
(i)
The Lower â&#x20AC;&#x201C; Gondwana coals of Permian age, and
(ii)
Tertiary coals of Eocene to Miocene age.
The greatest period of coal-formation, in India, is the Permian. The important coal-bearing formations are collectively known as Damudas and belong to the Lower-Gondwana System. The Lower â&#x20AC;&#x201C; Gondwana coals account for more than 98% of the annual production of coal, which are generally of Bituminous-rank; whereas in Tertiary coal-fields lignite predominates.
i) Gondwana coals:
The Gondwana coals are largely confined to the river valleys like the Damodar, Mahanadi, Godavari, etc. The workable coal seams are confined to the Damuda group of the Lower Gondwana, wherein they occur in two main horizons, (a) the Barakar measures of the lowerpermian age and (b) the Raniganj measures of the Upper Permian age. The coal seams of the Barakar measures are more important because they are of better quality and occur in all the fields, whereas coal seams of Raniganj measures occur principally in the Raniganj coalfield only.
Barakar coals (of the Jharia coal-field) possess low moisture, low volatile, high fixed carbon, high ash, low sulphur and low phosphorous content. In comparison to this the Raniganj coals contain high moisture (3 to 10%), high volatiles, medium fixed carbon, medium ash, low
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ENGINEERING GEOLOGY suphur and low phosphorus contents. While the Barakar coals are good coking and steam coals, the Raniganj coals are poorly coking but excellent steam coals.
Amongst the important lower-Gondwana coal-fields of India, mentioned may be made of
(1) Raniganj coal-fields of West-Bengal. (2) The Jharia, Giridh and Bokaro coal-fields of Bihar. (3) The Talchir coal-field of Orissa. (4) The Umaria, Sohagpur, Mohapani, Korba and Pench-valley coal-fields of Madhya Pradesh. (5) The Singreni coal fields of Hyderabad.
ii) Tertiary coals:
They principally occur in Assam, in the Himalayan foot-hills of Kashmir and in Rajasthan (Palna in Bikaner) in Eocene strata. Besides, lignite deposits are found to occur in South Arcot district of Tamil Nadu, in Kutch of Gujarat and also in the State of Kerala. The Neyveli lignite field of Tamil Nadu (which is of Miocene age), is the largest lignite deposit of South India.
In India, coals of Super-bituminous to anthracite variety occur in the Eocene formation of Kashmir along the Himalayan foot hills, as well as in the Lower Gondwana strata in the Eastern, Himalayan region.
Uses:
1. Coal is a primary source of heat and power (thermal power). 2. It is also used in the production of water gas. 3. In metallurgical operations, for the purpose of extraction of metals like iron, zinc etc. 4. Gasification of coal which leads to the production of coal, gas, tar, coke etc. 5. Different types of varnish and germicides are also produced from coals.
Identification of Coal:
1. Name : Anthracite Colour: Black Form: Massive and Compact
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ENGINEERING GEOLOGY Lustre: Vitreous Cleavage: Streak: Black Fracture: Uneven Hardness: 2-3 Specific Gravity: Low Composition: Carbon Occurrence: Coal seams/beds in continental sedimentary rocks deposited in a swampy or Deltailc or lacustrine environment in which dead material are reduced to coal. Associated Rocks: Clay, Shales and Sandstone Distribution: Rare
2. Name : Bituminous Colour: Black Form: Massive and Compact Lustre: Vitreous Cleavage: Streak: Black Fracture: Uneven Hardness: Low Specific Gravity: Low Composition: Carbon Occurrence: Coal seams/beds in continental sedimentary rocks derived from a swampy or Deltailc or lacustrine environment in which dead material are reduced to coal. Associated Rocks: Clay, Shales and Sandstone Distribution: Jharia coal field Giridish coal field Bokaro coal field
3. Name : Peat Colour: Brown Form: Fissile Lustre: Dull Cleavage: Streak: Brown Fracture: Uneven Hardness: Low
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ENGINEERING GEOLOGY Specific Gravity: Low Composition: Carbon Mode of Occurrence and Origin: Coal seams/beds in continental sedimentary rocks deposited in a swampy or Deltailc or lacustrine environment in which dead material are reduced to coal. Associated Rocks: Clay, Shales and Sandstone Distribution: Palani, Nilgiri Hills, Kanyakumari district of Tamil Nadu
4. Name : Lignite Colour: Brown Form: Massive and Compact Lustre: Dull Cleavage: Streak: Brown Fracture: Uneven Hardness: Low Specific Gravity: Low Composition: Carbon Orign: Coal seams/beds in continental sedimentary rocks deposited in a swampy or Deltailc or lacustrine environment in which dead material are reduced to coal. Associated Rocks: Clay, Shales and Sandstone Distribution: Neyveli, Tamil Nadu USAGE OF TOPOGRAPHIC MAPS â&#x20AC;&#x201C; TO STUDY ABOUT LAND FORMS Introduction: A map is a representation on a flat surface of all or a part of the earthâ&#x20AC;&#x2122;s surface drawn to a specific scale. Maps are often the most effective means for showing the locations of both natural and manmade features, their sizes, and their relationships to one another. Like photographs, maps readily display information that would be impractical to express in words.
While most maps show only the two horizontal dimensions, geologists, as well as other map users, often require that the third dimension, elevation, be shown on maps. Maps that show the shape of the land are called topographic maps. Although various techniques may be used to depict elevations, the most accurate method involves the use of contour lines.
Contour Lines:
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ENGINEERING GEOLOGY A contour line is a line on a map representing a corresponding imaginary line on the ground that has the same elevation above sea level along its entire length. While many map symbols are pictographs, resembling the objects they represent, a contour line is an abstraction that has not counterpart in nature. It is, however, an accurate and effective device for representing the third dimension on paper.
Some useful facts and rules concerning contour lines are listed as follows. 1. Contour lines bend upstream or upvalley. The contours form Vâ&#x20AC;&#x2122;s that point upstream, and in the upstream direction the successive contours represent higher elevations. For example, if you were standing on a stream bank and wished to get to the point at the same elevation directly opposite you on the other bank, without stepping up or down, you would need to walk upstream along the contour at that elevation to where it crosses the stream bed, cross the stream, and then walk back downstream along the same contour. 2. Contours near the upper parts of hills from closures. The top of a hill is higher than the highest closed contour. 3. Hollows (depressions) without outlets are shown by closed, hatched contours. Hatched contours are contours with short lines on the inside pointing downslope. 4. Contours are widely spaced on gentle slopes. 5. Contours are closely spaced on steep slopes. 6. Evenly spaced contours indicate a uniform slope. 7. Contours usually do not cross or intersect each other, except in the rare case of an overhanging cliff. 8. All contours eventually close, either on a map or beyond its margins. 9. A single high contour never occurs between two lower ones, and vice versa. In other words, a change in slope direction is always determined by the repetition of the same elevation either as two different contours of the same value or as the same contour crossed twice. 10. Spot elevations between contours are given at many places, such as road intersections, hill summits, and lake surfaces. Spot elevations differ from control elevation stations, such as bench marks, in not being permanently established by permanent markers.
Relief:
Relief refers to the difference in elevation between any two points. Maximum relief refers to the difference in elevation between the highest and lowest points in the area being considered. Relief determines the contour interval, which is the difference in elevation between succeeding
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ENGINEERING GEOLOGY contour lines that is used on topographic maps. Where relief is low, a small contour interval, such as 10 or 20 feet, may be used. In flat areas, such as wide river valleys or broad, flat uplands, a contour interval of 5 feet is often used. In rugged mountainous terrain, where relief is many hundreds of feet, contour intervals as large as 50 or 100 feet are used.
Scale:
Map scale expresses the relationship between distance or area on the map to the true distance or area on the earth’s surface. This is generally expressed as a ratio or fraction, such as 1:24,000 or 1/24,000. The numerator, usually 1, represents map distance, and the denominator, a large number, represents ground distance. Thus, 1:24,000 means that a distance of 1 unit on the map represents a distance of 24,000 such units on the surface of the earth. It does not matter what the units are.
Often, the graphic or bar scale is more useful than the fractional scale, because it is easier to use for measuring distances between points. The graphic scale in Fig. consists of a bar divided into equal segments, which represent equal distances on the map. One segment on the left side of the bar is usually divided into smaller units to permit more accurate estimates of fractional units.
Topographic maps, which are also referred to as quadrangles, are generally classified according to publication scale. Each series is intended to fulfill a specific type of map need. To select a map with the proper scale for a particular use, remember that large-scale maps show more detail and small-scale maps show less detail.
Color and Symbol:
Each color and symbol used on a U.S. Geological Survey topographic map has significance. Common topographic map symbols are shown in Figure. The meaning of each color is as follows: Blue – water features Black – works of man, such as homes, schools, churches, roads, and so forth Brown – contour lines Green – woodlands, orchards, and so-forth Red – urban areas, important roads, public land subdivision lines.
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ENGINEERING GEOLOGY
Sample Topographic Map with Scale:
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ENGI NEERI NGGEOLOGY
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