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Note for Surveying-1 - s-1 by GARIKAPATI RAMBABU

  • Surveying-1 - s-1
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  • Civil Engineering
  • B.Tech
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Garikapati Rambabu
Garikapati Rambabu
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Sai Tirumala NVR Engineering College SURVEYING JNTUK R13 UNIT 1 & 2 UNIT-1 & 2 Syllabus: Unit 1: Introduction: Definition-uses of surveying-overview of plane surveying (chain, compass and plain table), objectives, principles and classification – errors in survey measurements. Unit 2: Distance and Direction: distance measurement conventions and methods; use of chain and tape, electronic distance measurements (EDM) – principles of electro optical EDM-errors and corrections to linear measurements – compass survey – meridians, azimuths and bearings, declination, computation of angles, Traversing – purpose - type of traversing – traverse computation – traverse adjustment – omitted measurements. Introduction: Surveying is perhaps as old as human civilization. Surveying is one form or the other hand been used for distinguishing one persons land from other since time immemorial. In ancient time Babylonians practiced types of surveying as early as 2500 B.C. Surveying in some form is used in India and Egypt to divide the land for taxation purpose even in 1400 B.C. The surveying in those times used triangular frames fitted with plumb bob to obtained level foundation. Definition: It is the art of determining the relative position of point on, above or below the surface of earth by means of direct or indirect measurement of distance, direction and elevation. The relative positions are determined by measuring horizontal distance, vertical distance(elevation) accurately using various surveying instruments i.e. It also indicates the art of establishing points by pre determined angular and linear measurements from the plan or map on to the ground. Objectives of surveying: The aim of surveying is to prepare a map to show the relative position of the object on the surface of the earth. The map is drawn to some suitable scale. It shows the natural features of a country such as towns, villages, roads, railways, rivers, etc. map may also include details of different engineering works such as roads railways, irrigation canal, etc. Uses of surveying: Surveying may be used for the following various applications. 1. To prepare a topography map which shows the hills, valleys, rivers, village, towns, forest, etc. of a country. 2. To prepare a cadastral map showing the boundaries of fields, houses and other properties. 3. To prepare an engineering map which shows the details of engineering works such as roads, railways, reservoirs, irrigation canals, etc. Department Of Civil Engineering Page 1

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Sai Tirumala NVR Engineering College SURVEYING JNTUK R13 UNIT 1 & 2 4. To prepare a military map showing the road and railway communications with different parts of a country. Such a map also shows the different strategic point important for the defense of a country. 5. To prepare a contour map to determine the capacity of a reservoir and to find the best possible route for roads, railway, etc. 6. To prepare a geological map showing areas including underground resources. 7. To prepare an archeological map including places where ancient relics exist. CLASSIFICATION: Primary classification of Surveying: Primary divisions of Surveying are made on the basis whether the curvature of the earth is considered or whether the earth is assumed to be a flat plain. The actual shape of the earth is oblate1 spheroid of revolution, flattened at the poles and bulging2 at the equator. The length of the polar axis is about 12713.168 km and that of the equatorial axis is about 12756.602 km thus the polar axis is shorter than the equatorial axis by 42.95 km. Relatively the diameter of the earth, the difference in lengths of the two axes is a very small quantity, about 0.34%. If we neglect the irregularities of the earth the surface of the imaginary spheroid3 is a curved surface, every element of which is normal to the plumb line4. Surveying is primary divided into two types: 1. Plane surveying 2. Geodetic surveying (1) Plane Surveying: It is the type of surveying in which the curvature5 of the earth is neglected and it is assumed to be flat surface. All distance and horizontal angles are assumed to be projected onto horizontal plane. A horizontal plane at a point is the plane which is perpendicular to the vertical line at that point. The vertical line is indicated by freely suspended plumb bob. A single horizontal plane of reference is selected for the entire survey of the small area. Thus the plumb bob lines at all points of the area are assumed to be parallel. In everyday life we are concerned with small portion of earth’s surface and the above assumptions seem to be reasonable in light of the fact that the length of an arc 12 kilometers long lying in the earth’s surface is only 1cm greater than extended cord and further that the difference between the sum of the angle in a plane triangle and the sum of those in a spherical triangle is only one second for a triangle at the earth’s surface having an area of 195 sq. km. (2) Geodetic surveying: It is a type of surveying in which the curvature of the earth is taken into consideration and a very high standard of accuracy is maintained. The main objective of the surveying is to determine the precise location of a system of widely spaced point on the surface of the earth. In geodetic surveying the earth major and minor axis is computed accurately and a spheroid of a reference is visualized. Department Of Civil Engineering Page 2

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Sai Tirumala NVR Engineering College SURVEYING JNTUK R13 UNIT 1 & 2 Spheroid & Geoids: The spheroid is a mathematical surface obtained by revolving an ellipse about the earth’s polar axis. The earth’s mean sea level surface which is perpendicular to the direction of gravity at every point is called geoids. Because of variation in the earth’s mass distribution, the surface of the geoids is irregular. However if the irregularities of the surface are neglected the geoids can be very closely approximated as the spheroid. Secondary classification of surveying: 1. Based on instruments: (a) Chain surveying, (b) Compass surveying, (c) Plane table surveying, (d) Theodolite surveying, (e) Tacheometric surveying, and (f) Photogrammetric surveying. 2. Based on methods: (a) Triangulation surveying, and (b) Traverse surveying. 3. Based on object: (a) Geological surveying, (b) Mine surveying, (c) Archeological surveying, and (d) Military surveying. 4. Based on nature of field: (a) Land surveying, (b) Marine surveying, and (c) Astronomical surveying. 1. Based on instruments: (a) Chain surveying: This is the simplest type of surveying in which only linear measurements are taken with a chain or a tape. Angular measurements are not taken. “Chain survey is generally used when high accuracy is not required.” (b) Compass surveying: In compass surveying, the horizontal angles are measured with the help of a magnetic compass, in addition to the linear measurements with chain or a tape. As a magnetic compass is not a precise angle-measuring instrument, the compass survey is not very accurate. However, it is more accurate than a chain survey. (c) Plane table surveying: In plain table surveying, a map is prepared in the field while viewing the terrain after determining the directions of various lines and taking the linear measurements with a chain or a tape. The accuracy of the plain table surveying is low. Its main advantage is that the measurements and plotting are done simultaneously in the field. (d) Theodolite surveying: A Theodolite is a very precise instrument for measuring horizontal and vertical angles. Theodolite survey is quite accurate. Department Of Civil Engineering Page 3

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