Set Squares

The set squares are triangular in shape with one of the angle as right angle and made of wood, tin, celluloid or plastic. Set squares made of transparent celluloid are the most satisfactory ones as the lines underneath them can be seen quite easily. Set squares of different sizes are available in the market. Set squares are used for drawing all straight lines except the horizontal lines which are drawn with T-square or mini drafter. Generally, two types of set squares are in use. They are:

(i) Thirty-Sixty degree (30⁰-60⁰) set square and

(ii) Forty-five degrees (45⁰) set square

The 30⁰-60⁰ set square of 250 mm length has three angles with the measures of 30⁰, 60⁰ and 90⁰ respectively. Similarly, the 45⁰ set square of 200 mm length has three angles with the measures of 45⁰ and 90⁰ respectively. Those made of transparent celluloid or plastic are commonly used as they retain their shape and accuracy for a longer time. Set squares sometimes lose their accuracy due to internal strains. So they should be tested periodically. Sometimes set squares have French curves.

Fig. 1 45⁰ Set Square

Fig. 2 30°-60° Set Square

Uses

i) Set-squares are used for drawing all straight lines except the horizontal lines which are usually drawn with the T-square. Vertical lines can be drawn with the T-square and the set-square.

ii) In combination with the T-square, lines at 30° or 60° angle with vertical or horizontal lines can be drawn with 30°- 60° set-square and 45° angle with 45° set-square. The two set-squares used simultaneously along with the T-square will produce lines making angles of 15°, 75°, 105° etc. as shown in Fig. 3 and 4. In general, set-squares are used to draw angles of 15°, 30°, 45°, 60°, 75°, 90°, i.e, any multiples of 15°.

Fig. 3 Drawing lines at 30°, 60° and 90°

Fig. 4 Drawing lines at 15°, 75° and 105°

iii) Parallel straight lines in any position, not very far apart, as well as lines perpendicular to any line from any given point within or outside it, can also be drawn with the two set-squares.

iv) A circle can be divided in six, eight, twelve and twenty-four equal parts by using set-squares and T-square.

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T- square

 A T-square is made up of hard quality wood such as teak or mahogany, etc. It consists of two parts - the stock and the blade - joined together at right angles to each other by means of screws and pins. T- square is used with its head against the ebony edge of the drawing board to draw horizontal lines, parallel lines and to guide/hold the setsquares, stencils etc. The stock is placed adjoining the working edge of the board and is made to slide on it as and when required. The blade is fitted with an ebony or plastic piece to form working edge of T-square. The blade lies on the surface of the board. Its distant edge which is generally beveled, is used as the working edge and hence, it should be perfectly straight. The nearer edge of the blade is never used. The length of the blade is selected so as to suit the size of the drawing board. Now-a-days T- square is also available of celluloid or plastic with engraved scale.

Fig. 1 T- square

Uses

1) The T-square is used for drawing horizontal lines. The stock of the T-square is held firmly with the left hand against the working edge of the board and the line is drawn from left to right as shown in Fig. 2. The pencil should be held slightly inclined in the direction of the line (i.e. to the right) while the pencil point should be as close as possible to the working edge of the blade. Horizontal parallel fines are drawn by sliding the stock to the desired positions. 

Fig. 2 Drawing using T-square

2) The working edge of the T-square is also used as a base for set-squares to draw vertical, inclined or mutually parallel lines. A pencil must be rotated while drawing lines for uniform wear of lead. The T-square should never be used on edge other than the working edge of the board. It should always be kept on the board even when not in use.

Testing the straightness of the working edge of the T-square

Mark any two points A and B (Fig. 3) spaced wide apart and through them, carefully draw a line with the working edge. Turn the T-square upside down as shown by dashed lines and with the same edge, draw another line passing through the same two points. If the edge is defective the lines will not coincide. The error should be rectified by planning or sand papering the defective edge. 

Fig. 3 Testing the straightness of the working edge of the T-square

T-square should never be used as a hammer or as guide for trimming papers. T-Square is used as a base for drawing various angles with the help of set squares. The standard ‘T’ square are designated as follows with dimensions shown in mm as per IS:1360-1989.

Table 1 Designation of T-square

Sl. No.	Designation of T-square	Blade length (mm)	To be used with Drawing Board
1	T0	1500 ± 10 mm	D0
2	T1	1000 ± 10 mm	D1
3	T2	700 ± 5 mm	D2
4	T3	500 ± 5 mm	D3

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General Types of Soils

Soils which are formed by weathering of rocks may remain in position at the place of region. In that case these are ‘Residual Soils’. These may get transported from the place of origin by various agencies such as wind, water, ice, gravity, etc. In this case these are termed ‘‘Transported soil’’.

1) Residual Soil

Residual soils differ very much from transported soils in their characteristics and engineering behaviour. They are relatively shallow in depth. They are characterized by a gradual transition from soil through partially weathered rocks, fractured and fissured rock, to bedrock. The degree of disintegration may vary greatly throughout a residual soil mass and hence, only a gradual transition into rock is to be expected. An important characteristic of these soils is that the sizes of grains are not definite because of the partially disintegrated condition. The grains may break into smaller grains with the application of a little pressure. Generally, the depth of residual soils varies from 5 to 20 m. Residual soils have not received much attention from geotechnical engineers because these are located primarily in undeveloped areas. In some zones in South India, sedimentary soil deposits range from 8 to 15 m in thickness.

The residual soil profile may be divided into three zones: (i) the upper zone in which there is a high degree of weathering and removal of material; (ii) the intermediate zone in which there is some degree of weathering in the top portion and some deposition in the bottom portion; and (iii) the partially weathered zone where there is the transition from the weathered material to the un-weathered parent rock. Residual soils tend to be more abundant in humid and warm zones where conditions are favourable to chemical weathering of rocks and have sufficient vegetation to keep the products of weathering from being easily transported as sediments. The depth of residual soils depends primarily on climatic conditions and the time of exposure. In some areas, this depth might be considerable. In temperate zones residual soils are commonly stiff and stable. An important characteristic of residual soil is that the sizes of grains are indefinite. For example, when a residual sample is sieved, the amount passing any given sieve size depends greatly on the time and energy expended in shaking, because of the partially disintegrated condition.

2) Transported Soils

Transported soils are soils that are found at locations far removed from their place of formation. The transporting agencies of such soils are glaciers, wind and water. Transported soils may also be referred to as ‘Sedimentary’ soils since the sediments, formed by weathering of rocks, will be transported by agencies such as wind and water to places far away from the place of origin and get deposited when favourable conditions like a decrease of velocity occur. A high degree of alteration of particle shape, size and texture as also sorting of the grains occurs during transportation and deposition. A large range of grain sizes and a high degree of smoothness and fineness of individual grains are the typical characteristics of such soils. Transported soils may be further subdivided, depending upon the transporting agency and the place of deposition, as under:

1) Alluvial Soil

Soils transported by rivers and streams. Alluvial soils are the soils which have been transported and subsequently deposited by flowing water. An alluvial fan is formed when the velocity of a soil laden stream suddenly deceases due to abrupt decrease in gradient. Floodplains are formed on the sides of a stream due to overflowing of flood water. A delta is formed just before a stream reaches the standing water of the sea. Alluvial soil deposits are usually stratified because of fluctuations in velocity of flowing water. The average particle size of alluvial deposits decreases with increasing distance from the source of stream. The delta soils are soil deposits farthest from the source of a stream and usually consist of silt and clay.

Example: Sedimentary clays

2) Aeolian Soil

Soils transported by wind.

Example: loess

3) Glacial Soil

Soils transported by glaciers.

Example: Glacial till

4) Lacustrine Soil

Soils deposited in lake beds.

Example: Lacustrine silts and lacustrine clays

5) Marine Soil

Soils deposited in sea beds.

Example: Marine silts and marine clays

General Types of Soils

The individual size of the constituent parts of even the weathered rock might range from the smallest state (colloidal) to the largest possible size (boulders). This implies that all the weathered constituents of a parent rock cannot be termed soil. According to their grain size, soil particles are classified as cobbles, gravel, sand, silt and clay. Grains having diameters in the range of 4.75 to 76.2 mm are called gravel. If the grains are visible to the naked eye, but are less than about 4.75 mm in size the soil is described as sand. The lower limit of visibility of grains for the naked eyes is about 0.075 mm. Soil grains ranging from 0.075 to 0.002 mm are termed as silt and those that are finer than 0.002 mm as clay. This classification is purely based on size which does not indicate the properties of fine grained materials.

Commonly Used Soil Designations

The following are some commonly used soil designations, their definitions and basic properties.

1) Bentonite

Decomposed volcanic ash containing a high percentage of clay mineral montmorillonite. It exhibits the properties of clay to an extreme degree such as high degree of shrinkage and swelling.

2) Black Cotton Soil

Black soil containing a high percentage of montmorillonite and colloidal material and it exhibits high degree of shrinkage and swelling. The name is derived from the fact that cotton grows well in the black soil.

3) Boulder Clay

Glacial clay containing all sizes of rock fragments from boulders down to finely pulverized clay materials. It is also known as ‘Glacial till’.

4) Caliche

Soil conglomerate of gravel, sand and clay cemented by calcium carbonate.

5) Hard Pan

Densely cemented soil which remains hard when wet. Boulder clays or glacial tills may also be called hard-pan and it is very difficult to penetrate or excavate.

6) Laterite

Deep brown soil of cellular structure, easy to excavate but gets hardened on exposure to air owing to the formation of hydrated iron oxides.

7) Loam

Mixture of sand, silt and clay size particles approximately in equal proportions; sometimes contains organic matter.

8) Loess

Uniform wind-blown yellowish brown silt or silty clay; exhibits cohesion in the dry condition, which is lost on wetting. Loess is a fine-grained, air-borne deposit characterized by a very uniform grain size, and high void ratio. The size of particles ranges between about 0.01 to 0.05 mm. The soil can stand deep vertical cuts because of slight cementation between them. particles It is formed in dry continental regions.

9) Marl

Mixtures of calcareous sands or clays or loam; clay content not more than 75% and lime content not less than 15%.

10) Moorum

Gravel mixed with red clay.

11) Top-soil

Surface material which supports plant life.

12) Varved Clay

Consist of alternating layers of clay and silt of glacial origin, essentially a lacustrine deposit; varve is a term of Swedish origin meaning thin layer. They possess the undesirable properties of both silt and clay.

13) Kaolin, China Clay

They are very pure forms of white clay used in the ceramic industry.

14) Calcareous Soil

It is a soil containing calcium carbonate.

15) Peat

It is a fibrous aggregate of finer fragments of decayed vegetable matter. Peat is very compressible and one should be cautious when using it for supporting foundations of structures.

16) Shale

It is a material in the state of transition from clay to slate. Shale itself is sometimes considered a rock but, when it is exposed to the air or has a chance to take in water it may rapidly decompose.

Organic and Inorganic Soils

Soils in general are further classified as organic or inorganic. Soils of organic origin are chiefly formed either by growth and subsequent decay of plants such as peat or by the accumulation of fragments of the inorganic skeletons or shells of organisms. Hence a soil of organic origin can be either organic or inorganic. The term organic soil ordinarily refers to a transported soil consisting of the products of rock weathering with a more or less conspicuous admixture of decayed vegetable matter. Organic soil contains carbon-based material that is living or was once living. Soil contains many different things that have been deposited over time. Many places around the world do not have adequate soil or soil that needs amendments to become organic and rich. Organic soil also benefits the environment. Non-organic soil media consists of materials that have been manufactured and are free of nutrients and contaminants.

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Stones

A building stone is a piece of rock quarried and worked into a required size and shape for a particular purpose. A building stone may be defined as a sound rock that can be safely used in some situation in the construction as a massive dressed or undressed unit. Granites and marbles used in the form of finely dressed blocks or slabs or columns in monumental and costly buildings, are good building stones. Similarly, sandstones and limestone used in forts, retaining walls and boundary walls and also as blocks in stone houses and bungalows are typical building stones. Slates used in many areas as roofing material for ordinary constructions and in pavements also fall in the category of building stones. The stones are used in the construction of buildings from the ancient times and most of the ancient temples, forts and mosques were built with stones as the major material. At present, they are largely used as the basic material for the manufacturing of the other construction materials like concrete, bricks etc.

Stone masonry is an engineering art that is preserved in many historical buildings in all parts of the world. This skill is still used, though on a lesser scale (because of the advent of concrete) in the construction of common residential houses and palatial buildings in many places. The Taj Mahal at Agra, the Red Fort in Delhi and temples of Lord Jagannath puri are some of the best known stone marvels of India. Following are the various uses to which stones are employed.

1) Structural elements: The stones are used for foundations, walls, columns, lintels, roofs, floor, damp proof courses etc.

2) Facing: The stones are adopted to give massive appearance to the structure. The walls are of bricks and facing is done in stones of desired shades. This is known as the composite masonry.

3) Paving: The stones are used to cover floor of buildings of various types such as residential, commercial, industrial etc. They are also adopted to form paving of roads, footpaths etc.

4) Basic Material: The stones are disintegrated and converted to form a basic material for cement concrete, moorum/murrum of roads, calcareous cements, artificial stones, hollow blocks etc.

5) Miscellaneous uses: In addition to the above uses the stones are also used as:

i) Ballast for railways
ii) Blocks in construction of bridges, piers, abutments, retaining walls, light houses, dams etc.

iii) Flux in blast furnaces

Type of Stones

1) Granite

It is a deep seated igneous rock, which is hard, durable and available in various colours. It has a high value of crushing strength and is capable of bearing high weathering. Granite is used for bridge components, retaining walls, stone columns, road metal and ballast for railways, foundation, stone work and for coarse aggregates in concrete. These stones can also be cut into slabs and polished to be used as floor slabs and stone facing slabs. Granite is found in the states of India like Maharashtra, Rajasthan, Uttar Pradesh, Madhya Pradesh, Punjab, Assam, Tamil Nadu, Karnataka and Kerala.

The minerals of granite are quartz, feldspar and mica. It has a specific gravity 2.63 to 2.75. They also have light or dark grey, pink or reddish colour. They have a crushing strength of 1000 to 1400 kg/m². It is very strong heavy, hard durable. It contains silica of about 60 to 80%.

2) Sandstone

This stone is form of sedimentary rock formed by the action of mechanical sediments. It has a sandy structure which is low in strength and easy to dress. They are used for ornamental works, paving and as road metal. It is available in the states of India like Madhya Pradesh, Rajasthan, Uttar Pradesh, Himachal Pradesh and Tamil Nadu. Sandstone is composed of sand grains, cemented together by calcium or magnesium carbonate or silicic acid, alumina and also oxide of iron. It also has a specific gravity 2.25. They have white, grey, brown or red in colour. It has a crushing strength of 400 to 800 kg/m². These are strong under pressure, but it is flaky when it contains mica. They are easily workable and also resists the weathering in a better way.

3) Limestone

It is a sedimentary rock formed by remnants of seaweeds and living organisms consolidated and cemented together. It contains a high percentage of calcium carbonate. Limestone is used for flooring, roofing, pavements and as a base material for cement. It is found in the states of India like Maharashtra, Andhra Pradesh, Punjab, Himachal Pradesh and Tamil Nadu. These are carbonate of lime intermixed with other minerals and impurities such as silica, magnesium carbonate, aluminium and iron. It has yellow, brown, grey or violet colour. It has a specific gravity 2.56. They have crushing strength 300 to 500 kg/m². These are soft and absorbent and so they do not resist the weathering action properly.

4) Slate

These are also composed of silica and alumina. These are usually grey-black or dark blue in colour. It has a specific gravity of 2.8. It has crushing strength 700 to 2100 kg/m². It is a metamorphic rock which can be split easily. It is used for damp-proofing, flooring and roofing.

5) Basalt and Trap

They are originated from igneous rocks in the absence of pressure by the rapid cooling of the magma. They have the same uses as granite. Deccan trap is a popular stone of this group in South India.

6) Gneiss

It can be recognized by its elongated platy minerals usually mixed with mica and used in the same way as granite. They can be used for flooring, pavement and not for major purposes because of its weakness. It is found in the states of India like Karnataka, Andhra Pradesh, Tamil Nadu and Gujarat.

7) Marble

It is a metamorphic rock which can be easily cut and carved into different shapes. It is used for ornamental purposes, stone facing slabs, flooring, facing works etc. It is found in the states of India like Rajasthan, Gujarat and Andhra Pradesh.

8) Quartzite

It is a metamorphic rock which is hard, brittle, crystalline and durable. It is difficult to work with and used in the same way as granite but not recommended for ornamental works as it is brittle.

9) Laterite

It is decomposed from igneous rocks; occur in soft and hard varieties. It contains a high percentage of iron oxide and can be easily cut into blocks. The soft variety is used for walls after curing while the hard blocks are used for paving the pathways.

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Rock and Classification of Rocks

Rock can be defined as a compact, semi-hard to hard mass of natural material composed of one or more minerals. The rocks that are encountered at the surface of the earth or beneath are commonly classified into three groups according to their modes of origin. They are igneous, sedimentary and metamorphic rocks. The mineral grains that form the solid phase of a soil aggregate are the product of rock weathering. The size of the individual grains varies over a wide range. Many of the physical properties of soil are dictated by the size, shape and chemical composition of the grains. Fig.1 shows a diagram of the formation cycle of different types of rock and the processes associated with them. This is called the rock cycle.

Fig. 1 Rock Cycle

Classification of Rocks

Rocks used for engineering works may be classified in the following three ways.

1) Geological

2) Physical

3) Chemical

Fig. 2 Classification of Rocks

I) Geological Classification of Rocks

Based on their origin of formation rocks are classified into three main groups - Igneous, sedimentary and metamorphic rocks.

1) Igneous Rock

Igneous rocks are considered to be the primary rocks formed by the cooling of molten magma or by the recrystallization of older rocks under heat and pressure great enough to render them fluid. Igneous rocks are formed by the solidification of molten magma ejected from deep within the earth’s mantle. After ejection by either fissure eruption or volcanic eruption, some of the molten magma cools on the surface of the earth. They have been formed on or at various depths below the earth surface. There are two main classes of igneous rocks. They are

1. Extrusive (poured out at the surface), and

2. Intrusive (large rock masses which have not been formed in contact with the atmosphere).

Intrusive rocks formed in the past may be exposed at the surface as a result of the continuous process of erosion of the materials that once covered them.

Initially both classes of rocks were in a molten state. Their present state results directly from the way in which they solidified. Due to violent volcanic eruptions in the past, some of the molten materials were emitted into the atmosphere with gaseous extrusions. These cooled quickly and eventually fell on the earth's surface as volcanic ash and dust. Extrusive rocks are distinguished by their glass like structure. Intrusive rocks, cooling and solidifying at great depths and under pressure containing entrapped gases, are wholly crystalline in texture. Such rocks occur in masses of great extent, often going to unknown depths. Table 1 shows the mineral composition of igneous rocks.

Table 1 Mineral Composition of Igneous Rocks

Mineral	Percentage
Quartz	12-20
Feldspar	50-60
Ca, Fe and Mg, Silicates	14-17
Micas	4-8
Others	7-8

Feldspars are the most common rock minerals, which account for the abundance of clays derived from the feldspars on the earth's surface. Quartz comes next in order of frequency. Most sands are composed of quartz.

Some of the important rocks that belong to the igneous group are granite and basalt. Granite is primarily composed of feldspar, quartz and mica and possesses a massive structure. Basalt is a dark coloured fine grained rock. It is characterized by the predominance of plagioclase, the presence of considerable amounts of pyroxene and some olivine and the absence of quartz. The colour varies from dark grey to black. Both granite and basalt are used as building stones. Generally igneous rocks are strong and durable.

Example: Basalt, Trap, Andesite, Rhyolite, Diorite, Granite

2) Sedimentary Rock

When the products of the disintegration and decomposition of any rock type are transported, redeposited and partly or fully consolidated or cemented into a new rock type, the resulting material is classified as a sedimentary rock. Due to weathering action of water, wind and frost; existing rocks disintegrates. The disintegrated material is carried by wind and water. Flowing water deposits its suspended materials at some points of obstacles to its flow. These deposited layers of materials get consolidated under pressure and by heat. Chemical agents also contribute to the cementing of the deposits. The rocks thus formed are more uniform, fine grained and compact in their nature.

The sedimentary rocks generally formed in quite definitely arranged beds or strata, which can be seen to have been horizontal at one time although sometimes displaced through angles up to 90 degrees. Sedimentary rocks are generally classified on the basis of grain size, texture and structure. From an engineering point of view, the most important rocks that belong to the group are sandstones, limestones and shales.

The deposits of gravel, sand, silt and clay formed by weathering may become compacted by overburden pressure and cemented by agents like iron oxide, calcite, dolomite and quartz. Cementing agents are generally carried in solution by groundwater. They fill the spaces between particles and form sedimentary rock. Rocks formed in this way are called detrital sedimentary rocks. All detrital rocks have a clastic texture. Sedimentary rock also can be formed by chemical processes. Rocks of this type are classified as chemical sedimentary rock. These rocks can have clastic or non-clastic texture. Table 2 shows some examples of chemical sedimentary rock.

Table 2 Chemical Composition of Sedimentary Rock

Composition	Rock
Calcite (CaCO3)	Limestone
Halite (NaCl)	Rock salt
Dolomite [CaMg(CO3)]	Dolomite
Gypsum (CaSO4 - 2H2O)	Gypsum

Limestone is formed mostly of calcium carbonate deposited either by organisms or by an inorganic process. Most limestone has a clastic texture; however, non-clastic textures also are found commonly. Chalk is a sedimentary rock made in part from biochemically derived calcite, which are skeletal fragments of microscopic plants and animals. Dolomite is formed either by chemical deposition of mixed carbonates or by the reaction of magnesium in water with limestone. Gypsum and anhydrite result from the precipitation of soluble CaSO₄ due to evaporation of ocean water. They belong to a class of rocks generally referred to as evaporites. Rock salt (NaCl) is another example of an evaporite that originates from the salt deposits of seawater. Sedimentary rock may undergo weathering to form sediments or may be subjected to the process of metamorphism to become metamorphic rock.

Example: Limestone, Sandstone, Dolomite and Slate

3) Metamorphic Rock

Metamorphism is the process of changing the composition and texture of rocks (without melting) by heat and pressure. During metamorphism, new minerals are formed and mineral grains are sheared to give a foliated texture to metamorphic rock. Rocks formed by the complete or incomplete recrystallization of igneous or sedimentary rocks by high temperatures, high pressures and/or high shearing stresses are metamorphic rocks. The rocks so produced may display features varying from complete and distinct foliation of a crystalline structure to a fine fragmentary partially crystalline state caused by direct compressive stress, including also the cementation of sediment particles by siliceous matter. Metamorphic rocks formed without intense shear action have a massive structure. Some of the important rocks that belong to this group are gneiss, schist, slate and marble.

Gneiss is a metamorphic rock derived from high grade regional metamorphism of igneous rocks, such as granite, gabbro and diorite. Low grade metamorphism of shales and mudstones results in slate. Slate is a dark coloured, platy rock with extremely fine texture and easy cleavage. Because of this easy cleavage, slate is split into very thin sheets and used as a roofing material. The clay minerals in the shale become chlorite and mica by heat; hence, slate is composed primarily of mica flakes and chlorite. Phyllite is a metamorphic rock, which is derived from slate with further metamorphism being subjected to heat greater than 250 to 300°C. Schist is a type of metamorphic rock derived from several igneous, sedimentary and low grade metamorphic rocks with a well foliated texture and visible flakes of platy and micaceous minerals.

Metamorphic rock generally contains large quantities of quartz and feldspar as well. Marble is formed from calcite and dolomite by recrystallization. The mineral grains in marble are larger than those present in the original rock. Green marbles are coloured by hornblends, serpentine, or talc. Black marbles contain bituminous material and brown marbles contain iron oxide and limonite. Quartzite is a metamorphic rock formed from quartz rich sandstones. Silica enters into the void spaces between the quartz and sand grains and acts as a cementing agent. Quartzite is one of the hardest rocks. Under extreme heat and pressure, metamorphic rocks may melt to form magma and the cycle is repeated.

Example : Due to metamorphic action granite becomes gneiss, trap and basalt change to schist and laterite, lime stone changes to marble, sand stone becomes quartzite and mud stone becomes slate.

II) Physical Classification of Rocks

Based on the structure, the rocks may be classified as:

1) Stratified Rocks

These rocks are having layered structure. They possess planes of stratification or cleavage. They can be easily split along these planes.

Example : Sand stones, lime stones, slate etc.

Fig. 3 Stratified Rock

2) Unstratified Rocks

These rocks are not stratified. They possess crystalline and compact grains. They cannot be split in to thin slab.

Example : Granite, trap, marble etc.

Fig. 4 Unstratified Rock

3) Foliated Rocks

These rocks have a tendency to split along a definite direction only. The direction need not be parallel to each other as in case of stratified rocks. This type of structure is very common in case of metamorphic rocks.

Fig. 5 Foliated Rock

III) Chemical Classification of Rocks

On the basis of their chemical composition rocks are classified as:

1) Silicious Rocks

The main content of these rocks is silica. They are hard and durable.

Example : Granite, trap, sand stones etc.

2) Argillaceous Rocks

The main constituent of these rocks is argil i.e., clay. These stones are hard and durable but they are brittle. They cannot withstand shock.

Example : Slate and laterite

3) Calcareous Rocks

The main constituent of these rocks is calcium carbonate. Limestone is a calcareous rock of sedimentary origin while marble is a calcareous rock of metamorphic origin.

Example : Limestone, marble, kankar, dolomite and gravel

Rock Minerals

It is essential to examine the properties of the rock forming minerals since all soils are derived through the disintegration or decomposition of some parent rock. A 'mineral' is a natural inorganic substance of a definite structure and chemical composition. Some of the very important physical properties of minerals are crystal form, colour, hardness, cleavage, luster, fracture and specific gravity. Out of these only two, specific gravity and hardness are of foundation engineering interest. The specific gravity of the minerals affects the specific gravity of soils derived from them. The specific gravity of most rock and soil forming minerals varies from 2.50 (some feldspars) and 2.65 (quartz) to 3.5 (augite or olivine). Gypsum has a smaller value of 2.3 and salt (NaCl) has 2.1. Some iron minerals may have higher values, for instance, magnetite has 5.2. It is reported that about 95 percent of the known part of the lithosphere consists of igneous rocks and only 5 percent of sedimentary rocks. Soil formation is mostly due to the disintegration of igneous rock which may be termed as a parent rock.

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Stages of Highway Development

Highway design is only one element in the overall highway development process. Historically, detailed design occurs in the middle of the process, linking the preceding phases of planning and project development with the subsequent phases of right-of-way acquisition, construction and maintenance. Now, it is during the first three stages planning, project development and design. The designers and communities, working together can have the greatest impact on the final design features of the project. In fact, the flexibility available for highway design during the detailed design phase is limited a great deal by the decisions made at the earlier stages of planning and project development.

Objectives of Highway Planning

Planning is considered as a pre requisite before attempting any development programme in the present era. This is particularly true for any engineering project, as planning is the basic requirement for any new project or an expansion programme. Thus there is a need for planned development of the road network and the links. Highway planning is of great importance when the funds available are limited whereas the total requirement is much higher. In developing countries like India it is important to utilize the available funds in the best possible manner by resorting to best planning principles. The objects of highway planning are briefly given below.

• To plan overall road network for efficient and safe traffic operation, but at minimum cost. Here the costs of construction, maintenance and resurfacing or strengthening of pavement layers and the vehicle operation cost are to be given due consideration.
• To arrive at the road system and the lengths of different categories of roads which could provide maximum utility and could be constructed within the available resources during the plan period under consideration.
• To divide the overall plan into phases and to decide priorities.
• To fix date-wise priorities for development of each road link based on utility as the main criterion for phasing the road development programme.
• To plan for future requirements and improvements of roads in view of anticipated developments.
• To work out suitable financing system phases of highway planning.

Highway planning includes the following phases.

1. Assessment of road length requirement for an area (it may be a district, state or the whole country)
2. Preparation of master plan showing the phasing of plan in five year plans or annual plans. (In order to plan the road system in the selected region, state or country, different studies and surveys are to be carried out to collect the data required. The data collected are to be processed and analyzed to arrive at the best possible road network and to arrive at the optimum length of the road system.)

Stages of Highway Development

Although the names may vary by State, the five basic stages in the highway development process are: planning, project development (preliminary design), final design, right of way and construction. After construction is completed, ongoing operation and maintenance activities continue throughout the life of the facility.

1) Planning

The initial definition of the need for any highway or bridge improvement project takes place during the planning stage. This problem definition occurs at the State, regional or local level, depending on the scale of the proposed improvement. This is the key time to get the public involved and provide input into the decision making process. The problems identified usually fall into one or more of the following four categories.

1. The existing physical structure needs major repair/replacement (structure repair).
2. Existing or projected future travel demands exceed available capacity and access to transportation and mobility need to be increased (capacity).
3. The route is experiencing an inordinate number of safety and accident problems that can only be resolved through physical and geometric changes (safety).
4. Developmental pressures along the route make a re-examination of the number, location and physical design of access points necessary (access).

Factors to Consider During Planning

It is important to look ahead during the planning stage and consider the potential impact that a proposed facility or improvement may have while the project is still in the conceptual phase. During planning, key decisions are made that will affect and limit the design options in subsequent phases. The important factors to be considered in planning include the following.

• Physical character
• Cost
• Safety
• Capacity
• Environmental quality
• Historic and scenic characteristics
• Multimodal consideration
• Other factors

2) Project Development

After a project has been planned and programmed for implementation, it moves into the project development phase. At this stage, the environmental analysis intensifies. The level of environmental review varies widely, depending on the scale and impact of the project. It can range from a multiyear effort to prepare an Environmental Impact Statement (a comprehensive document that analyses the potential impact of proposed alternatives) to a modest environmental review completed in a matter of weeks. Regardless of the level of detail or duration, the product of the project development process generally includes a description of the location and major design features of the recommended project that is to be further designed and constructed, while continually trying to avoid, minimize and mitigate environmental impact.

3) Final Design

After a preferred alternative has been selected and the project description agreed upon as stated in the environmental document, a project can move into the final design stage. The product of this stage is a complete set of plans, specifications and estimates of required quantities of materials ready for the solicitation of construction bids and subsequent construction. Depending on the scale and complexity of the project, the final design process may take from a few months to several years. The following concepts are important considerations of design and it includes the following.

a) Developing a Concept

A design concept gives the project a focus and helps to move it toward a specific direction. There are many elements in a highway and each involves a number of separate but interrelated design decisions. Integrating all these elements to achieve a common goal or concept helps the designer in making design decisions. Some of the many elements of highway design are

• Number and width of travel lanes, median type and width and shoulders
• Traffic barriers
• Overpasses/bridges
• Horizontal and vertical alignment and affiliated landscape

b) Considering Scale

People driving in a car see the world at a much different scale than people walking on the street. This large discrepancy in the design scale for a car versus the design scale for people has changed the overall planning of our communities. The design element with the greatest effect on the scale of the roadway is its width or cross section. The cross section can include a clear zone, shoulder, parking lanes, travel lanes and/or median. The wider the overall roadway, the larger its scale; however, there are some design techniques that can help to reduce the perceived width and thus, the perceived scale of the roadway. Limiting the width of pavement or breaking up the pavement is one option. In some instances, four lane roadways may look less imposing by designing a grass or planted median in the centre.

c) Detailing the Design

Particularly during the final design phase, it is the details associated with the project are important. Employing a multidisciplinary design team ensures that important design details are considered and those they are compatible with community values. Often it is the details of the project that are most recognizable to the public. A multidisciplinary design team can produce an aesthetic and functional product when the members work together and are flexible in applying guidelines.

4) Right-of-way

Once the final designs have been prepared and needed right-of-way is purchased, construction bid packages are made available, a contractor is selected and construction is initiated. During the right-of-way acquisition and construction stages, minor adjustments in the design may be necessary; therefore, there should be continuous involvement of the design team throughout these stages.

5) Construction and Maintenance

Construction may be simple or complex and may require a few months to several years. Once construction has been completed, the facility is ready to begin its normal sequence of operations and maintenance. Even after the completion of construction, the character of a road can be changed by inappropriate maintenance actions. For example, the replacement of sections of guardrail damaged or destroyed in crashes commonly utilizes whatever spare guardrail sections may be available to the local highway maintenance personnel at the time.

Highway Route Surveys and Location

To determine the geometric features of road design, the following surveys must be conducted after the necessity of the road is decided. A variety of survey and investigations have to be carried out by Road engineers and multidiscipline persons.

1) Transport Planning Surveys

• Traffic Surveys
• Highway inventories
• Pavement Deterioration Study
• Accident study

2) Alignment and Route location surveys Desk study Reconnaissance Preliminary Survey Final location survey

3) Drainage Studies

4) Soil Survey

• Surface run-off - Hydrologic and hydraulic
• Subsurface drainage - Ground water & Seepage
• Cross–drainage - Location and waterway area required for the cross-drainage structures.

5) Pavement Design investigation, Soil property and strength, Material Survey

6) Desk study

7) Site Reconnaissance

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Horizontal Distance Measurement

The task of determining the horizontal distances between two existing points and of setting a new point at a specified distance from some other fixed position are fundamental surveying operations. The surveyor must select the appropriate equipment and apply suitable field procedures in order to determine or set and mark distances with the required degree of accuracy. Depending on the specific application and the required accuracy, one of several methods may be used to determine horizontal distance. The most common methods include pacing, taping, and EDM (Electronic Distance Measurement). Taping has been the traditional surveying method for horizontal distance measurement for many years. It is a direct and relatively slow procedure, which requires manual skill on the part of the surveyors.

One of the basic measurements in surveying is the determination of the distance between two points on the earth’s surface for use in fixing position, set out and in scaling. Usually spatial distance is measured. In plane surveying, the distances measured are reduced to their equivalent horizontal distance either by the procedures used to make the measurement or by applying numerical corrections for the slope distance (spatial distance). The method to be employed in measuring distance depends on the required accuracy of the measurement and this in turn depends on purpose for which the measurement is intended. Horizontal distances may be determined by many methods.

Rough Distance Measurement

In certain surveying applications, only a rough approximation of distance is necessary; a method called pacing or the use of a simple measuring wheels, may be sufficient in these instances. 

Example - Locating topographic features during the preliminary reconnaissance of a building site, searching for the property corners etc.

1) Pacing

Pacing consists of counting the number of steps or paces in a required distance. This is used to provide distance estimates when no measuring device is available or precision is not required. Distances obtained by pacing are sufficiently accurate for many purposes in surveying. Pacing is also used to validate survey work and eliminate any taping blunders. Measuring your pace length requires a measured 100 feet distance. You then walk this distance and count the number of steps. It is best to repeat the process four times and average the results. In this method, distances can be measured with an accuracy of about 1:100 by pacing.

Distance = Unit Pace × Number of Paces

Fig. 1 Distance Measurement by Pacing

It is possible to adjust your pace to an even three feet, but this should usually be avoided. It is very difficult to maintain an unnatural pace length over a long distance. Accurate pacing is done by using your natural pace, even if it is an uneven length such as 2.6 feet. It is difficult to maintain an even pace when going uphill or downhill. Using your natural pace will make this easier.

Another error can occur if you are not consistent in starting with either the heel or toe of your shoe. If you place your toe at the start point, then also measure the end point with your toe. Starting with the heel and ending with the toe is a common mistake. Some surveyors prefer to count strides. A stride is two steps or paces. This reduces the counting but often requires using part of a stride to determine the total distance. Pacing is a valuable skill for surveyors. It requires some practice and concentration.

2) Odometer

Vehicle odometers are helpful in determining long distances such as for layout or checking vision at intersections. Precision of 1/20 is reasonable. Based on diameter of tires (no of revolutions x wheel diameter), this method gives a fairly reliable result provided a check is done periodically on a known length. During each measurement a constant tyre pressure has to be maintained.

3) Measuring Wheel

A simple measuring wheel mounted on a rod can be used to determine distances, by pushing the rod and rolling the wheel along the line to be measured. An attached device called an odometer serves to count the number of turns of the wheels. From the known circumference of the wheel and the number of revolutions, distances for reconnaissance can be determined with relative accuracy of about 1:200. This device is particularly useful for rough measurement of distance along curved lines. It is commonly used to record distances such as curb length or paving quantities and can also be helpful for determining distances along a curve.

Distance = Odometer Reading x Circumference of the Wheel (𝜋D)

Where D is the diameter of the measuring wheel

Fig. 2 Measuring Wheel

4) Tape

This method involves direct measurement of distances with a tape or chain. Steel tapes are most commonly used. It is available in lengths varying from 15m to 100m. Measuring horizontal distances with a tape is simple in theory, but in actual practice, it is not as easy as it appears at first glance. It takes skill and experience for a surveyor to be able to tape a distance with a relative accuracy between 1:3000 and 1:5000, which is generally acceptable range for most preliminary surveys.

5) Tachometry

Distance can be measured indirectly by optical surveying instruments like theodolite. The method is quite rapid and sufficiently accurate for many types of surveying operations.

6) Electronic Distance Measurement (EDM)

These are indirect distance measuring instruments that work using the invariant velocity of light or electromagnetic waves in vacuum. They have high degree of accuracy and are effectively used for long distances for modern surveying operations. This quickly provides very precise measurements but requires experienced personnel and relatively expensive equipment.

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K-Slump Tester

The new apparatus called “K-Slump Tester” can be used to measure the slump directly in one minute after the tester is inserted in the fresh concrete to the level of the floater disc. This tester can also be used to measure the relative workability. The apparatus comprises of the following four principal parts.

1) A chrome plated steel tube with external and internal diameters of 1.9 and 1.6 cm respectively. The tube is 25 cm long and its lower part is used to make the test. The length of this part is 15.5 cm which includes the solid cone that facilitates inserting the tube into the concrete. Two types of openings are provided in this part. Four rectangular slots 5.1 cm long and 0.8 cm wide and 22 round holes 0.64 cm in diameter; all these openings are distributed uniformly in the lower part as shown in Fig 2.

2) A disc floater 6 cm in diameter and 0.24 cm in thickness which divides the tube into two parts; the upper part serves as a handle and the lower one is for testing. The disc serves also to prevent the tester from sinking into the concrete beyond the preselected level.

3) A hollow plastic rod 1.3 cm in diameter and 25 cm long which contains a graduated scale in centimeters. This rod can move freely inside the tube and can be used to measure the height of mortar that flows into the tube and stays there. The rod is plugged at each end with a plastic cap to prevent concrete or any other material from seeping inside.

4) An aluminium cap 3 cm diameter and 2.25 cm long which has a little hole and a screw that can be used to set and adjust the reference zero of the apparatus. There is also in the upper part of the tube, a small pin which is used to support the measuring rod at the beginning of the test. The total weight of the apparatus is 226 g.

Fig. 1 K Slump Test

Test Procedure

• Wet the tester with water and shake off the excess.
• Raise the measuring rod, tilt slightly and let it rest on the pin located inside the tester.
• Insert the tester on the levelled surface of concrete vertically down until the disc floater rests at the surface of the concrete. Do not rotate while inserting or removing the tester.
• After 60 seconds, lower the measuring rod slowly until it rests on the surface of the concrete that has entered the tube and read the K-Slump directly on the scale of the measuring rod.
• Raise the measuring rod again and let it rest on its pin.
• Remove the tester from the concrete vertically up and again lower the measuring rod slowly till it touches the surface of the concrete retained in the tube and read workability (W) directly on the scale of the measuring rod.

Fig. 2 K Slump Tester

In the concrete industry, the slump test is still the most widely used test to control the consistency of concrete mixtures, even though there are some questions about its significance and its effectiveness. Several apparatuses have been proposed to replace or supplement the slump cone, but in general they have proved to be rich in theory and poor in practice. Their use is still limited mainly to research work in laboratories. The K-slump apparatus is very simple, practical and economical to use, both in the field and the laboratory. It has proven that it has a good correlation with the slump cone. The K-slump tester can be used to measure slump in one minute in cylinders, pails, buckets, wheel-barrows, slabs or any other desired location where the fresh concrete is placed.

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