SURVEYING - 1 Short Answets-II

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Primary adjustments of transit theodolite: (1) setting up (2) centring (3) leveling (4) focusing of the eye piece (5) focusing the objective. Plunging the telescope: it is the process of rotating the telescope over the horizontal axis through 1800 in the vertical plane. Swinging the telescope: it is the process of turning the telescope about the vertical axis in a horizontal plane. Swing left: the swing is called left swing when the telescope is turned counter clockwise. Swing right: when the telescope is turned clockwise from the previous position. Face left observation: if the vertical circle is on the left side of the observer the theodolite is in the face left condition. Face right condition: if the vertical circle is on the right side of the observer, the theodolite is in the face right condition. Latitude: the latitude of a line is its orthographic projection on the N-S axis representing the meridian. Departure: the departure of a line is its orthographic projection on the axis perpendicular to the meridian. This perpendicular axis is also known as the E-W axis. Open traverse: an open traverse starts from one station and closes at another station whose location is neither known nor established. Closed traverse: a closed traverse starts from one traverse station and closed either on the same station or another traverse station whose location is already known. Bowditchs rule: according to this rule, the ratio of the error in latitude or departure of a traverse line to the total error in latitude or departure is equal to the ratio of the length of that line to the total length (perimeter) of the traverse. Transit rule: transit rule is used to balance a traverse in which the angular measurements aremore precise than the linear measurements. According to transit rule, the ratio of the error in the latitude or departure of a line to the total error in latitudes is equal to the ratio of the latitude of that side to the arithmetic sum of all the latitudes or departures. Traversing: a traverse is a series of connected lines whose lengths and directions are measured in the field. Gales traverse table: traverse computations are usually done in a tabular form known as gales traverse table. It provides a systematic method of recording the computations of the traverse. Open traverse: an open traverse starts from one station and closes at another station whose location is neither known nor established.Closed traverse: a closed traverse starts from one traverse station and closed either on the same station or another traverse station whose location is already known. Bowditchs rule: according to this rule, the ratio of the error in latitude or departure of a traverse line to the total error in latitude or departure is equal to the ratio of the length of that line to the total length (perimeter) of the traverse. Transit rule: transit rule is used to balance a traverse in which the angular measurements aremore precise than the linear measurements. According to transit rule, the ratio of the error in the latitude or departure of a line to the total error in latitudes is equal to the ratio of the latitude of that side to the arithmetic sum of all the latitudes or departures. Gales traverse table: traverse computations are usually done in a tabular form known as gales traverse table. It provides a systematic method of recording the computations of the traverse. Criteria for selection of traverse stations: (1) As far as possible try to work from the whole to part. (2) Keep the number of stations to a minimum. (3) An attempt should be made to keep the lengths of the traverse lines as long as possible to reduce the effect of any centring error. (4) The traverse stations should be selected according to the requirement of the work. (5) Stations should be clearly intervisible. When a theodolite is set up at one station it should be possible to see the pegs at two adjacent stations. Omitted measurements: some measurements which should have been taken were not taken and were thus omitted. Such measurements are called omitted measurements. These are made calculated by the algebraic sum of latitudes or departures which the summation is equal to zero. Fundamental lines of theodolite: vertical axis, horizontal axis, line of collimation, altitude level axis, plate level axis.LEVELLING PRINCIPLES: Vertical line: The vertical line is the basic line of reference in leveling. It is the line indicated by a freely suspended plumb bob. It is the line along the direction of gravity. Level surface: the level surface is a surface that is perpendicular to the direction of gravity at every point. Mean sea level: The mean sea level at a location is obtained by averaging the height of the water surface of the sea for all stages of the tides for a long period (Usually 19 years). Basic definitions: Level line: the level line is a line in a level surface. As the level surface is a curved surface, the level line is also curved. Datum surface or datum: it is a level surface which is taken as a reference surface for determination of elevations of various points. Elevation: it is the vertical distance of the point above or below the datum surface. Some times the term height is also used for elevation. Altitude: it is the vertical distance of the point above mean sea level. Therefore if the datum surface is the mean sea level, the elevation is the same as the altitude. Difference of elevations: it is the vertical distance between the level surfaces passing through the two points. Reduced level: the reduced level of a point is its height relative to the datum. It is the calculated reduced height of the point above or below the datum. Horizontal plane: it is a plane perpendicular to the direction of gravity. It is therefore tangential to the level surface at that point. Horizontal line: it is a line in a horizontal plane. The horizontal line is therefore, perpendicular to the vertical line at that plane. Vertical plane: it is a plane which contains the vertical line at that point it may be noted that infinite number of vertical planes can contain a vertical plane. Bench marks: there are four types of bench marks namely:- G.T.S Bench marks, Permanent bench marks, Temporary bench marks, arbitrary bench marks. (* for detail note refer text book surveying vol:I by Dr.K.R.arora page: 262).Different method of leveling: The following methods are used to determine the difference of elevations of various points: 1. direct leveling 2. trigonometric leveling 3. barometric leveling 4. hypsometric leveling (* for detail note refer text book surveying vol:I by Dr.K.R.arora page: 263). Classification of direct leveling: 1. simple leveling 2. differential leveling 3. check leveling 4. fly leveling 5. profile leveling 6. cross section leveling 7. reciprocal leveling 8. precise leveling (* for detail note refer text book surveying vol:I by Dr.K.R.arora page: 264). Sensitivity of level tube: the sensitivity of the level tube is expressed in terms of the angle in seconds subtended at the centre by an arc of the level tube equal to one division of the tube. Terms used in leveling: Backsight reading (BS):- this is the first staff reading taken in any set up of the instrument after the leveling has been perfectly done. Foresight reading (FS):- it is the last staff reading in any set up of the instrument and indicates the shifting of the latter. Intermediate sight (IS):- it is any other staff reading between the BS and FS in the same set up of the instrument. Change point (CP):- This point indicates the shifting of the instrument. At this point, an FS is taken from one setting and a BS from the next setting. Height of instrument (HI):- when the leveling instrument is properly leveled, the RL of the line of collimation is known as the height of the instrument.Difficulties of leveling:The following difficulties are sometimes encountered in the field while doing leveling. 1. Staff station above the line of sight. 2. Staff station much below the line of sight. 3. Staff too near the instrument. 4. Leveling across a hill. 5. Leveling across a hallow. 6. Leveling on a steep slopes. 7. Leveling across a pond or a lake. 8. Leveling across a river. 9. Leveling across a high wall. 10. Leveling across a low boundary wall. (* for detail note refer text book surveying vol:I by Dr.K.R.arora page: 298 to 302). Contouring: Contour: an imaginary line which joins the points of same level on the surface of the earth. (Or) The line of intersection of a level surface with the ground surface is known as the contour line or simply contour. Contour interval: the vertical distance between any two consecutive contours is known as a contour interval. Contour gradient: a contour gradient is a line on the surface of the ground having a constant inclination to the horizontal. Uses of the contour maps: 1. Determination of character of the terrain. 2. selection of a suitable site. 3. determination of sections. 4. intervisibility between two points. 5. location of a route. 6. determination of the catchments area. 7. estimation of reservoir capacity. (* for detail note refer text book surveying vol:I by Dr.K.R.arora page: 330 to 333) .