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Forestsurveying and engineering
 

Forestsurveying and engineering

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Notes on forest survey and engineering for both indian forest service examination and under graduate programme in forestry

Notes on forest survey and engineering for both indian forest service examination and under graduate programme in forestry

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    Forestsurveying and engineering Forestsurveying and engineering Document Transcript

    • FFS 102 FOREST SURVEYING AND ENGINEERING (1+2)Theory Introduction - Principles of surveying - Errors in surveying - Scope of surveying inforestry - Scales - Definition - Construction of Scales: simple, diagonal, vernier andcomparative scales - choice of scales - Measurement of distances - linear measurement -chains - testing and adjusting of chains - arrows, pegs - tapes - ranging rods - rangingout Survey lines - chaining on plain and sloping lands - errors in chaining - chainingaround obstacles - chain surveying - Principles - methods of Surveying - base, tie andcheck lines - Survey with straight and irregular boundaries - offsets - methods ofrecording and plotting. Measurement of angles - objects - triangulation - instruments for measurementof angles - compass - bearings - whole circle and reduced bearings - meridians - true,magnetic and arbitrary meridians, local attraction - correction. Chain and compass surveying - methods of surveying - radiation, intersectionand traversing - closed and open traverse - method of plotting - parallel meridian -forestry field problems - laying out a coupe and its demarcation - finding horizontaldistance to an inaccessible point. Theodolite surveying - Measurement of horizontal, vertical angles - use inforestry - Plane table surveying - Principles - Instruments - centering and orientation -methods of plane table surveying - Applicability in forestry. Leveling - topographical surveying - utility and scope - leveling instruments -dumpy level - temporary and permanent adjustments - difference in levels - benchMarks - reduction of levels - rise and fall method - Height of collimation method. Topographical surveying - methods of contouring - characteristics and use ofcontours - Ghat tracers - principles - use - map and map reading - principles of mapreading - copying, enlargement and reduction of maps - computation of areas - methodsof computation. Land development - material used for construction – brick, cement. Lime –manufacturing – Masonry – brick and stone – its classification – Foundation – types andsuitability for different locations. Roads - profile - types - classification – types of gradient – alignment of roads inplains and hills - Bridges and Culverts – types.Practical Construction of scales - chain survey of an area, field work - plotting - chain andcompass surveying - Methods – Radiation, Intersection and traversing - Plane tablesurveying - Radiation, Intersection and traversing. Leveling - Reduced levels -measurement - contouring – plotting, map reading, enlargement and reduction of maps 1
    • - computation of areas. Theodolite surveying, Ghat tracer Manufacturing of brick, lime inkilns – cement manufacturing – foundation – masonry – brick and stone. Roads -alignment of roads in hills and plains – earthwork estimation in roads – bridges andculverts.Lecture Schedule1. Introduction and principles of surveying.2. Scales - Simple, diagonal and vernier scales3. Measurement of distances - chains, errors in chaining, Ranging4. Chaining on plains, slopes, around obstacles and irregular areas5. Offset - method of plotting6. Measurement of angles, bearings, meridian and local attraction.7. Compass - Prismatic compass – Radiation, intersection and traversing8. Theodolite surveying9. Mid-Semester Examination10. Plane table survey11. Leveling, benchmark, reduction of levels12. Contour - map reading - computation of areas of irregular boundaries13. Study of minor survey instruments - Abney level, Ghat tracer14. Materials for construction - Bricks, lime, cement15. Foundation - types - Factors affecting foundation16. Masonry - Brick and stone, Bonds - types17. Road - classification - WBM and Earthen road - Bridges, culverts - types.Practical Schedule1) Construction of scales2) Chaining on plain areas3) Chaining around obstacles and irregular areas4) Ranging of straight lines5) Cross staff survey6) Compass survey - Radiation7) Compass Survey - Intersection8) Compass Survey - Traversing9) Plane table survey - Radiation method10) Plane table survey - Intersection method11) Plane table survey - Traversing12) Demarcation of a coupe13) Leveling using Dumpy level14) Leveling by rise and fall method15) Leveling by height of collimation method16) Leveling along the forest roads using ghat Tracer17) Profiling of forest streams by leveling18) Contouring - field work19) Plotting20) Interpolation of contours21) Map reading 2
    • 22) Computation of areas23) Theodolite survey - measuring distances24) Measuring angles - Height and elevation25) Application problems on surveying26) Visit to quarrying site27) Study of brick and lime kilns28) Study of different types of brick and stone masonry29) Designing foundation for different locations30) Alignment and setting of roads31) Earthwork estimation of road32) Visit to road laying sites33) Visit to different bridges and culvert sites and recording the construction features34) Final Practical ExaminationAssignment1. Preparation of road map of FC&RI, MTP2. Prepare an estimate for earthwork excavation of trench around the campus3. Preparation of contour map of FC&RI fieldsReference BooksKanetkar,T.P. and Kulkarni, S.V. 1982. Surveying and levelling, Part I, A.V. Sathya Gruga Prakashan, Poona - 4Masani, N.J. 1990. Forest Engineering without Tears, Nataraj Publication, Dehra Dun.Michael, A.M and Ohja, T.P. 1995 Principles of Agricultural Engineering - Vol.II, Jain Brothers, New Delhi.Negi, S.S. 1994. Hand book of Forest Engineering, International Book Distributors, Dehra Dun.Ram Prakash, 1983. Forest Surveying, International Book Distributors, DehraDun.Rangawala, S.C and Rangwala, P.S. 1985. Surveying and Leveling, Character Publishing House, Anand. 3
    • FFS102 – Forest Survey and Engineering (1+2) Course Teacher – Dr S.V. Kottiswaran Professor (SWC) I. ScalesGeneral The distances measured on ground are plotted on paper in such a way that a fixedratio is maintained between the distance on ground to the corresponding distance onpaper. This ratio is known as scale and the process of plotting with scale is known asdrawing to scale. Thus, the scale is defined as the ratio of ground distance to the plotteddistance on plan, i.e.,Scale = Ground distance Plan distanceFor instance, if the scale is 1 cm = 5 cm, it means that one cm on paper indicates fivemeters on ground.Scales can be expressed in the following three ways:(1) Engineers scale: In this case, the relation between the distance on plan and the distance on ground is mentioned numerically in the style as 1 cm = 5 m, etc. such an expression grants convenience in reading and plotting.(2) Graphical scale: The scale is drawn on plant itself. Hence, a graphical scale represents a line, which is subdivided into plan distance to the corresponding convenient units of length on the ground. As the plan or map becomes old, the engineers scale may shrink and may not give accurate results. However, such is not the case with graphical scale because if the plan or map shrinks, the scale will also shrink. Hence, graphical scale is drawn on survey maps.(3) Representative fraction: In this case, the ratio is worked out in such a way that numerator is unity and denominator is a fraction in the same unit of measurement as 4
    • the numerator. This fraction is known as representative fraction and it is brieflywritten as R.F. it is desirable to write the scale in R.F. also. For instance, R.F. of ascale 1 cm = 5 m can be worked out as follows: 5
    • Classification of scales:Scales are classified in the following four categories:I. Plain scaleII. Diagonal scaleIII. Vernier scaleI. Plain scale : From this type of scale, it is possible to read only in two dimensions on paper such as metres and decameters, hundreds and tenths, units and tenths, etc.Solution The procedure for construction of this scale will be as follows: (1) Select suitable number of metres divisible by 10 and work out the length of scale (2) Draw a line 8 cm long the divide it into 4 equal parts. Each part then represents 109 m. (3) Divide the first compartment into 10 equal parts, each part representing 1 m. (4) Finish up the scale, and mark on it 37 m as required.II. Diagonal scale: From this type of scale, it is possible to read in three dimensions on paper such asmetres, decameters and centimeters; units, tenths and hundredths; etc.Solution: The procedure for construction of this scale will be as follows: (1) Construct the plain scale as before. (2) Make the construction on subdivision portion. Finish upon the scale and mark on it 26.6 m and 30.3m.III. Vernier scale: To read the fractional part of the smallest division of the main or primary scale, adevice was found out by A.N. Vernier in 1631 and after his name, the device has cometo be known as vernier scale. 6
    • The difference between the smallest division on the main scale and that on thevernier scale indicates the fineness of vernier reading and it is known as the least count ofthe vernier. Vernier scale are of the following five types: (1) Direct vernier (2) Retrograde vernier (3) Extended vernier (4) Double vernier (5) Double-folded vernier(1) Direct vernier: In case of direct vernier, both the scales, namely, vernier and main move in the samedirection and they are graduated in the same direction. As shown in fig. (n-1) parts of themain scale are taken and they are divided into n equal parts on the vernier scale. n Main Scale Vernier Scale 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 (n-1) Let d = value of the smallest division on main scale U = value of the smallest division on vernier scale.Then,or n −1 u= d n 7
    • (n −1)d = nuLeast count of vernier = d -u n −1 =d− d n  n − n +1= d   n  d= nthus, the ratio of the value of the smallest division on main scale to the total number ofdivisions on vernier scale indicates the least count of the vernier scale.(2) Retrograde vernier: In case of retrograde vernier, main scale and vernier scale move in oppositedirections and graduations are also marked in opposite directions. (n+1) parts of the mainscale are taken and they are divided I to n equal parts on the vernier scale. Thus, in caseof retrograde vernier, the divisions of vernier scale will be larger than those of main scaleand it will facilitate in easy reading. However, direct vernier is commonly used as it issimple is operation. Let d = value of the smallest division on main scale u = value of the smallest division on vernier scaleThen, (n + 1)d = nuor n +1 u= d n 8
    • Least count of vernier = u -d= (n + 1)d d n d= n Thus least counts of direct and retrograde verniers are the same.(3) Extended vernier : This type of vernier is just similar to the direct vernier scale except that every second division is omitted. It, the therefore, follows that in case of extended vernier scale, (2n-1) divisions of the main scale are taken and they are divided into n equal parts. Let d = value of the smallest division on main scale u = value of the smallest division on vernier scale Then (2n −1)d = nvorv= (2n − 1)d nLeast count of vernier = 2d -u= 2d − (2n − 1)d n  2n − 2n + 1 = d   n  d= n 9
    • (4) Double vernier: When the main scale is running in both the directions with common zero, itbecomes easier to employ a single vernier scale with common zero, as shown in fig. 2-1.Such cases usually occur when vertical angels are to be measured with a commonhorizontal plane. Extreme care should be exercised to properly read the vernier scale,i.e., the directions of reading of main and vernier scales should be the same.Exercise I1. Draw a plain scale 1cm = 5m and show on it 48m.2. Draw a diagonal scale 1cm = 4m to show m and dm. Show on the scale 23.2m and 37.4m.3. Construct a vernier scale with least count as 1/100. The smallest division on the main scale is 0.10m. Show a reading of 3.46m. 10
    • II. Chain SurveyingPrinciple of chain survey The main principle of chain survey is to prepare a framework or network oftriangles because a triangle is a figure, which can be plotted on paper by measuring itssides only. Great care has to be exercised in the formation of well-proportioned or well-conditioned triangles so that the process of chain surveying becomes smooth. A well-proportioned or well-shaped triangle has no angle greater than 1200 or smaller than 300.As far as possible, the triangles formed should resemble to the shape of an equilateraltriangle. If, however, the conditions are not favorable for forming well-proportionedtriangles, extreme care should be taken in chaining and plotting of the unavoidable ill-proportioned or ill-conditioned triangles.Instruments required in chain survey: Following instruments are required for carrying out a chain surveying: (1) Chain and 10 arrows (2) Tape of 10 m or 20 m length (3) Ranging rods about 10 to 15 in number (4) Offset rod (5) Cross-staff or optical square to set right angles (6) Plumb bob (7) Field book with pencils, rubber, pen-knife, etc. (8) Box sextant, if any angle other than 900 is to be set up or measured. (9) Miscellaneous items such as hammer, axe, nails pegs, bundle of string, chalk, etc.Procedure for carrying out chain survey:Following are the four distinct steps involved in carrying out the chain survey of any plotof land: (1) Reconnaissance survey (2) Marking of stations (3) Preparation of reference sketches (4) Running of survey lines 11
    • (1) Reconnaissance survey; A reconnaissance survey indicates the preliminary inspection of the site of work andhence, first of all, the survey our visits the area to be surveyed. The salient features of thesite are studied with reference to the following aspects: (i) Index plan: The survey our prepares an index plan or sketch in the field book showing roughly the area to e surveyed and important objects such as buildings, roads, streams, etc. are included in this index plan. It also contains the sequence in which the survey lines are to be measured. The stations are indicated by number or letter and the direction in which the work is to proceed is shown by arrows. (ii) Main station: Suitable positions of main stations are decided by the surveyor. The important fact to be kept in mind is the intervisibility of main stations. The lengths of main survey lines are measured roughly by pacing or some such approximate method of measurement. (iii) Study of area: During reconnaissance survey, the surveyor has to carry out intensive study of the site so that he can get a clear picture of the area to be surveyed, probable difficulties to be encountered during the work, time required to finish up the job, etc.(2) Marking of stations: The stations selected during reconnaissance survey should be properly marked onground by using suitable equipment so that they can be readily and easily identified.Depending upon the nature of ground and importance of stations, the marking of stationsis done with ranging rods, wooden pegs, nails, stones, etc.(3) Preparation of reference sketches: After marking of stations, the location or reference sketches of these stations should be neatly drawn in the field book. The reference sketch of a station helps in locating the station at a future date or in cases where its position is not traceable ad it is to be fixed again. Two measurements from permanent structures will be sufficient. But usually three measurements are taken to ensure the check on exact location of the stations. The measurements are taken with reference to the permanent objects that 12
    • may be in the form of corner of a building, electric or telegraph post, compound wall or gate, trees, etc. The measurements are taken to the nearest 5-mm. North line should invariable be drawn on the reference sketch. Thus, the position of a station is resorted with the help of its reference sketch by swinging arcs from the respective permanent structures.(4) Running of survey line: The work of chaining is then started. Base line is first to be measured. The work is carried out as follows: (i) Chain is laid down on the ground after proper ranging. (ii) Offsets of nearby details are taken and recorded in the field book in the usual manner. (iii) Chain is then stretched or taken forward and the process is repeated till the end of line is reached. (iv) Other lines of the framework are then gradually taken and measured.Plotting work The details entered in the field book are ten plotted on paper in the drawing office. The drawing materials required for plotting work include brushes, colours, ink,pencils, pins, rubber, saucers, weights, etc. following are the drawing instrumentsrequired for plotting work. (1) compass box (2) drawing board of suitable dimensions; (3) drawing table; (4) paper; (5) protractor; (6) rolling parallel ruler (7) set of French curves (8) set of scales; (9) set squares; (10) straight edge of steel (11) tee - square etc. 13
    • The plotting work should be carried out carefully so that a decent well-lookingdrawing emerges after the work is completed. The items such as lettering, inking,colouring, etc. should be done in an artistic way. The map must contain the scale withwhich it is drawn and the north line should be exhibited at suitable spot on the map. Theconventional signs which are commonly used must be used.Exercise II1. Calculate the distance of the road around the buildings of the campus by chain surveying2. Find the area of the field by cross staff survey 14
    • II. Compass survey The process of triangulation is not possible when the area is to be surveyed islarge with irregular boundaries and many obstacles. In such cases, traversing is adopted.In the process of traversing, the direction of the survey line is fixed by taking the angularmeasurements with suitable instruments. Thus, a traverse consists of a series of connectedlines whose lengths and direction are known.Compass: The instruments which is used for finding out the magnetic bearings or simplybearings of a line is known s a compass and any compass essentially consists of thefollowing three parts: (1) Circle - with graduations; (2) Line of sight; and (3) Magnetic needle supported loosely.Following are the main five types of compasses: (1) Prismatic compass (2) Surveyors compass (3) Compass over a level (4) Trough compass (5) Tubular compass.Each type of the above compass will be now briefly described.Prismatic compass: The prismatic compass is the most convenient, handy and portable instrument. Itis circular is shape and its diameter varies from 85 mm to 110 mm. it is made up of anon-magnetic metal. It essentially consists of the following parts; (i) A magnetic needle of broad type supported over a centrally situated pivot made of hard steel is provided. (ii) A graduated aluminum ring is attached with the needle and it is divided into degrees and half degrees. The graduations start from zero marked at south end of the needle and they run clockwise so that 900, 1800 and 2700 15
    • are marked respectively at west, north and east. The figures are written inverted. (iii) Eye vane and object vane are fixed diametrically opposite to each other. The reflecting prism is provided near eye vane. The line joining eye vane and object vane passes through the centre of compass. (iv) Focussing stud is provided to adjust the eyesights of the different persons. (v) A break pin is provided to stop the oscillations of the ring. (vi) A glass cover is provided at the top so that dust particles cannot enter the compass box. (vii) Sunglasses are provided to facilitate the sighting of objects in sunlight. (viii) A hinged mirror with sighting or object vane is provided. The mirror can be inclined at any angle so that it becomes possible to sight the objects which are too low or too high.Method of using the prismatic compass: Suppose it is required to observe the bearing of line AB. The procedure will be asfollows. (i) The temporary adjustments of the compass are carried out. it involves two operation, namely, centering and leveling. The process of obtaining centre of compass over the centre of the peg is known as centering. The can be done either by a plumb bob or by allowing a small pebble to fall from the centre of the compass and hit the peg. The compass can be held in hand, but it is generally mounted on a light tripod. The process of making the needle horizontal is known as leveling and it is achieved h means of a ball and socket joint. When the compass is leveled, the need swings freely. It should be clamped, when perfectly leveled. (ii) After centering and leveling of the compass is done over the station A, the sighting vane and prism of the compass are raised. The prism is adjusted so that readings can be clearly seen. 16
    • (iii) The compass box is rotated until the ranging rod at station B, hair of object vane and slit of eye vane are in the same line. (iv) The needle is brought to rest by pressing the knob, if necessary and then, the reading is taken. The readings are usually taken upto an accuracy of 15 minutes. The reading will indicate the angle, which the line AB makes with the north line.Exercise III a1. Estimate the area of the field by compass survey by radiation and traversing.2. Find the included angles of the marked points in the field. 17
    • Measurements of angles and bearingsDefinitions:Bearings: A bearing of a line is defined as the angle made by the line with some referencedirection or meridian.Meridians: Following are the three meridians that are commonly used in survey work: (1) Arbitrary meridian (2) Magnetic meridian (3) True meridian.Methods of designation: Following are the two systems of designation of bearings; (1) Quadrantal bearing system (2) Whole circle bearing system(1) Quadrantal bearing system: In this system, the angle is measured from north or south to east or west. Thus, there are four quadrants, namely, NE, SE, SW and NW, as shown in fig. 7-10. Thus, 9in this system, the numerical value of the angle does not exceed 900 and it also helps in trigonometrical calculations. The quadrantal bearings are also referred to as reduced bearings or R.B(2) Whole circle bearing system: In this system, the angle is measured from the magnetic north in clockwise direction and its value will therefore vary from 00 to 3600. The bearing is known as whole circle bearing or W.C.B.Every line has two bearings, namely, fore bearing (F.B) and back bearing (B.B.). Thereading of line AB taken from point a is the F.B. of line AB and the reading of line ABtaken from point B is its B.B. 18
    • Let us consider the W.C.B. system for finding out the relation between F.B. andB.B. of a given line AB.In case I, B.B. = F.B. + 1800In case II , B.B. = F.B. - 1800.Thus, a general expression can be framed as follows: B.B. = F.B. ± 1800.Use + sign if F.B. is less than 1800 andUse - sign if F.B. is greater than 1800. In the quadrantal system, there will not be any changes in the value of F.B. andB.B. except that their respective quadrants will be interchanged. Thus if F.B. is in NEquadrant, B.B. will be in SW quadrant. Thus N is to be substituted for S and E is to besubstituted for W and so on.Exercise III b1. Convert the Q.B. to W.C.B.a. N120 280 E. b. N 680 270 W c. S 430 380 E d. S 370 520 W2. Convert W.C.B. to Q.B. a. 3050 170 b. 650 40 c. 1710 37 d. 2080 19 19
    • IV Plane Table SurveyGeneral In case of plane table survey, the measurements of survey lines of the traverse andtheir plotting to a suitable scale are done simultaneously on the field. Following are thecases in which the plane table survey is found to be useful. (1) Compass survey cannot be carried out with success in industrial areas of the town. Plane table survey will be the best alternative in such cases. (2) For preparing plans on a small scale, plane table survey proves to be speedy, easy and accurate. (3) The city or town has expanded within two or three decades and it is required to plot the developed area on the previously plotted plan of the existing area.Instruments required for plane table survey: (1) Alidade (2) Drawing board.Accessories required for plane table survey: (1) Plumbing fork (2) Spirit level (3) Trough compass (4) Miscellaneous.Miscellaneous: In addition to the above-mentioned accessories, the miscellaneous items requiredwill be the drawing paper of the best quality, pencil, rubber, scale, pins, water-proofcover to protect the board, etc. 20
    • Temporary adjustments of plane table: Following three distinct operations at each survey station are carried out for thetemporary adjustments of a plane table; (1) Centering (2) Levelling (3) Orientation.Methods of plane table survey Following re the four methods by which an object might be located on paper byplane table: (1) Radiation (2) Intersection (3) Traversing (4) Resection.(1) Radiation: This is the simplest method and it is useful only when the whole traverse can be commanded from a single station. The procedure is as follows:(2) Intersection: This method is useful where it is not possible to measure the distances on ground as in case of a mountainous country. Hence, this method is employed for locating inaccessible points, the broken boundaries, rivers, fixing survey stations, etc. 21
    • (3) Traversing: This method resembles the work of a compass survey and it is useful for the survey work of roads, rivers, etc. the traverse is run as usual and the details on the line are taken by radiation or offsets.(4) Resection: The process of resection is used for establishing the instrument stations only and it thus helps in ascertaining the fact that the point plotted on plan is the station occupied by the plane table.Exercise IV1. By plane table survey using radiation method and intersection method plot the field boundaries.2. Find the area of the field by triangulation. 22
    • V LevellingGeneral Levelling is defined as a method of determining the relative elevations of pointson the surface of earth or an operation for finding out the difference in heights. Thus, thedata obtained from the process of Levelling will be useful in the following two respects; (1) To establish points for various engineering purposes at desired elevations with respect to a given datum. (2) To work out the elevations of given points relative to each other or with respect to a given datum.Definitions of some common terms in levellings: (1) Backsight and foresight and intermediate sight: Backsight or B.S. is the first reading from any set up of the instrument and foresight or F.S. is the last reading taken before disturbing the instrument from its set up. All sights taken between B.S. and F.S. are known as intermediate sights or I.S. (2) Bench mark: A fixed point of known elevation is called the bench mark or B.M. (3) Change point or turning point: The point indicating the shifting of level is known as a change point (C.P.) or a turning point (T.P.) (4) Datum: A datum surface or line is any arbitrarily assumed level surface or line from which the vertical distance are measured. (5) Elevation: The vertical distance of a point with respect to a given datum, either positive or negative, is known as the elevation of that point. (6) Height of instrument: The elevation or R.L. of the line of collimation, when the instrument is correctly levelled, is known as the height of instrument. 23
    • (7) Horizontal line: The line in a horizontal plane is known as a horizontal line. A horizontal plane at any point is a plane tangential to the level surface at that point(8) Level line: The line drawn on a level surface is known as a level line.(9) Level surface: This is a surface on which all the points are equidistant from the centre of earth. As earth is sphere, a level surface will be a curved surface. Examples of a level surface are liquid surface or a sea water, liquid surface of lake, etc.(10) Line of collimation: The line joining the intersection of cross-hairs and optical centre of the object glass and its continuation is known as line of collimation.(11) Mean sea level: The average height of the sea for all states of the tides is known as mean sea level or M.S.L.(12) Reduced level: The elevation of a point or its vertical distance above or below the datum is known as its reduced level or R.L.(13) Station: The point which is to be set up at a given elevation or whose elevation is to be found out is known as the station and it thus indicates the point at which the staff is held and not the point at which the level is set up.(14) Vertical angle: The angle formed by the intersection of two lines in a vertical plane is known as the vertical angle.(15) Vertical line or plumb line: The line normal to a level surface is known as a vertical line or a plumb line and the plane which contains a vertical line is called a vertical plane. 24
    • Principles of levelling Some of the important principles that are to be observed in simple direct levellingare as follows. (1) Change point: The intermediate staff should be carefully selected and it should be in the form of firm point which can be easily located. The elevation of change point should be carefully determined as a slight error in it will be reflected in the subsequent readings. If convenient, a bench mark can be used as a change point. (2) Lengths of B.S. and F.S.: For accurate work, the lengths of B.S. and F.S. should be maintained nearly equal. If this condition is satisfied, the error due to non-parallelism of the line of collimation and the bubble line will be reduced to a great extent. This fact can be proved by considering the line of collimation downwards and upwards.Entering the staff readings: The staff readings are to be noted immediately after they are observed. For thispurpose, a level book with specially ruled out columns is used. Following points shouldbe observed at the time of entering staff readings in a field book: (1) The staff readings should be entered in proper columns and in order of their observations. (2) The first entry and the last entry on any page are respectively B.S. and F.S. Hence, if I.S. is to be carried over to the next page, it is to be entered as I.S. and F.S. on the carried forward page and B.S. and I.S. on the brought forward page. (3) For each staff reading, a horizontal row is reserved except for staff reading of a C.P. In case of staff reading for a C.P., F.S. of C.P. are written in the same 25
    • horizontal line with the note of C.P. in the remarks column in the same horizontal line. (4) The R.L. of plane of collimation should be written in line with B.S. (5) The description of B.M. should be briefly and accurately written in the remarks column. If required, the description of other important, features and change points may be entered in the remarks column and the sketches may be drawn on the left hand side of the page.Reduction of levels: Following are the two methods of working out the reduced levels of points fromthe observed staff readings: (1) Collimation system (2) Rise and fall system(1) Collimation system; In this system, the level of line of collimation is found out by adding the B.S. takenon B.M. of known R.L. the readings of various other points, when subtracted from thislevel, will give the R.L. of the respective points. At every point, a new level of line ofcollimation is obtained and the process is repeated till the last point is reached. The arithmetical check of this system is carried out by applying the following rule: ∑ F.S. - ∑ B.S. = First R.L. - Last R.L. It should, however, be noted that the above rule does not provide the check on thereduced levels of the intermediate points. However, this system proves to be easy,simple and rapid. 26
    • (2) Rise and fall system: This system consists of finding out the difference in levels between two consecutivepoints by comparing each point with the preceding point. Rise is indicated, if the staffreading is smaller and fall is indicated, if the staff reading is greater. By adding rise orsubtracting the fall, R.L. of each point can be obtained This system provides arithmetical checks in three ways as follows: ∑ F.S. - ∑ B.S. = Σ Falls - ∑ Rises = First R.L. - Last R.L. It is thus seen that this system provides a complete check on intermediate calculationsalso. Hence, this system, though laborious and tedious, is adopted for accurate work.Exercise V1. Find the reduced levels of the points of the given points by height of collimationmethod and rise and fall method and check arithmetically 27
    • VI ContouringGeneral: A contour is an imaginary line, which joins the points of equal elevation on theground. Thus, it represents a line in which the surface of the ground is intersected by alevel surface. The plan showing the elevations and depressions of the surface of theground is known as the contour plan or contour map.Contour interval: The vertical distance between any two consecutive contours in known as contourinterval and it is kept constant for a contour plane, once it is adopted. The horizontaldistance between two points on two consecutive contours is known as the horizontalequivalent and it will naturally depend on the steepness of the groundInterpolation of contours: The process of placing or spacing the contour lines proportionally between theplotted ground points is known as the interpolation of contours and it is based on theassumption that the slope of ground between the two point is uniforms. Following are thethree methods of interpolation of contours: (1) Estimation (2) Arithmetical calculations (3) Graphical.(1) Estimation; In this method, the position of contour point is judged by estimation only. The method is rapid. But as it give approximate results, it is useful for small scale maps only. 28
    • (2) arithmetical calculations; In this method, the position of contour point is worked out by exact mathematical calculation. Let us take a simple case to illustrate this method. IF two-ground points P and Q are situated at a distance of 25 m with respective elevations as 80.50 m and 70.50 m. Assuming, the contour intervals as 2 m, the contour points for 72 m, 74 m, 76 m, 78 m and 80 m will have to be established on line PQ by applying the rule of three. Now, difference in levels between P and Q = 80.50-70.50 = 10 m. Distance between P and Q = 25 m.  25 x0.5 =  = 1.25m  10  Similarly, distance of 78 m contour point from P  25 x 2.5  =  = 6.25m  10  distance of 76 m contour point from P  25 x 4.5  =  = 11.25m  10 Exercise VI1. Find the reduced levels of the points in the field for a given grid interval and plot thecontour map of the area. 29
    • VII. Computation of AreasMethods for computation of areas Following are three methods adopted for the purpose of computing the areas: I. Geometrical figures II. Ordinates III. PlanimeterII. Ordinates The above method becomes tedious especially when the plot is in the form of along narrow strip and hence, in such cases, the area of the plot is computed by drawing abase line and ordinates are put up along this base line at regular intervals. The height ofeach ordinate is measured. By knowing the length of constant interval between theordinates and height of each ordinate, the area of the plot can be computed by adoptingany one of the following rules: 1. Mid-ordinate rule 2. Average ordinate rule 3. Trapezoidal or average end area rule 4. Simpson or parabolic rule(1) Mid –ordinate ruleLet n = Number of equal parts d= Length of each equal part L= Length of base line = nd or d= L/n 30
    • h1, h2 etc = Ordinates at mid-points of each division.Then, Area = dh1+dh2+dh3+ . . .. dhn = d(h1+h2+h3+ . . . . hn ) = L/n (h1+h2+h3+ . . .. hn)(2) Average ordinate rule In this case, the length of average ordinate is obtained by dividing the sum of allordinates with the total number of ordinates measured.Let O1, O2, etc. = Ordinates at each of the points of division n,d and L as above.ThenNumber of ordinates = n+1 O0 + O1 + O2 .... + On Area = n +1(3) Trapezoidal or average end area rule: In this case, the area of each trapezium formed between successive divisions iscalculated independently and then added together to obtain the total area of the plot. Thismethod of more accurate than the previous two methods.  O + O1 O + O2 O + On = 0 d+ 1 d + ....... n −1 d  2 2 2  31
    • = d 2[O0 + 2O1 + 2O2 + 2O3 + ....... + On ]  O + On = d 0 + O1 + O2 + O3 + ........ + On −1   2 (4) Simpson or parabolic rule In this case, the boundary of the plot is not assumed straight. But it is consideredas a curve in the form of a parabola.Area of figure ABGDE = area of trapezium ABGE + area under curve EDG  O + O2 = 0 x 2d  + 2 × Area of parallelogram CFGE  2  3  O + O2  = 0 x 2d  + 2 × 2d × DH  2  3 O0 + O2 Now DH = O1 − 2  O + O2  O + O2 = 0 x 2d  + 2 × 2d × O1 − 0  2  3 2 = d/3 [3Oo+3O2+4O1 - 2O0 - 2O2] = d/3 [ Oo+4O1+O2]Similarly, area between ordinates O2 and O4 will be given by the equation. 32
    • = d/3 [ O2+4O3+O4] and so on.Hence, total area between ordinates Oo and O4= d/3 [ Oo+4O1+2O2 + 4O3 + O4]The above rule can be summarized as follows: d/3 [ Oo+4O1+2O2 + 4O3 +. . . . . . 2On-2+4On-1 + On]It is thus seen that there should be even number of divisions of the area or in other words,the total number of ordinates must be odd. If this is not the case, the area of the lastdivision is worked out separately and then, added together to obtain the final area. Thearea of plot, if worked out by this rule, gives better results as compared o abovementioned all the rules.Exercise VII1. Following perpendicular offsets were taken from a chain line to a curved boundary lineat intervals of 10m:0,7.38, 5.26, 6.45, 7.33, 7.87, 8.23, 0. Compute the area between the chain line, the curved boundary line and the endoffsets by applying (1) average ordinate rule, (2) trapezoidal rule, and (3) simpsonrule.2. Following table gives the perpendicular offsets taken from the center-line of road to ahedge: Offset no. Oo O1 O2 O3 O4 O5 O6 O7 O8 Offset in m 4 6 5 7 5 4 3 4 6 Distance in m 0 15 30 45 60 80 100 110 120Compute he area between the center-line of road and hedge by applying (1) trapezoidalrule and (2) Simpson rule. 33
    • VIII. Theodolite SurveyingGeneral The Theodolite is an extraordinary accurate instrument used in surveying formeasuring horizontal and vertical angles. It has also very wide applications in varioussurveying operations such as establishing grades, setting out curves, extending surveylines, etc. Thus, a Theodolite is an instrument for angular measurements and it givenangles of required precision.Definitions and terms used for Theodolite work It is necessary to clearly understand the meanings of the following terms that areused during the manipulation process of a Theodolite: (1) Axis of level tube: It is a straight line tangential to the longitudinal curve of the level tube at its center. It is also known as the bubble line and it is horizontal, when the bubble is central. (2) Axis of telescope: It is the line joining the optical center of the object glass to the center of the eyepiece. (3) Centering: It is the operation carried out to ascertain the fact that the vertical axis of the instrument passes through the center of the peg fixed at the required station point. It is carried out by suspending a plumb bob from the underside of the instrument. (4) Changing face: The operation of changing the position of vertical circle either from left to right or from right to left of the observer is known as changing face. For a transit Theodolite, it is done by revolving the telescope through 180o in the vertical plane and through 180o in a horizontal plane. For a non-transit Theodolite, releasing and then do it, reversing the telescope for end to end. (5) Face left: When the vertical circle of the instrument is on the left of the observer taking reading, the position is known as face left position and in such position, 34
    • the telescope is said to be in normal or direct or in bubble up position. The observation of an angle (horizontal or vertical) made with face left position is known as face left (F.L) observation.(6) Face right: When the vertical circle of the instrument is on the right of the observer taking reading, the position is known as face right position and in such position, the telescope is said to be in inverted or reversed or in bubble down position. The observation of an angle (horizontal or vertical) made with face right position is known as face right (F.R) observation.(7) Horizontal axis: It is the axis about which the telescope and the vertical circle rotate in a vertical plane. It is also known as trunnion axis or transverse axis.(8) Line of sight: The term line of sight or line of collimation is used to indicate an imaginary line joining the optical center of the object glass and intersection of the crosshairs of the diaphragm and its continuation.(9) Swinging the telescope: It is the operation of turning the instrument in a horizontal plane about its vertical axis. Swinging is said to be right swing if the instrument is moved in clockwise direction and it is said to be left swing, if the instrument is moved in anti-clockwise direction.(10) Transitting: It is the operation of revolving the telescope in a vertical plane by 180o about the horizontal or trunnion axis. It is also referred to as plunging or reversing.(11)Vertical axis: It is the axis about which the telescope can be rotated in a horizontal plane. The lower and upper plates of the instrument rotate about this axis.Temporary adjustments of Theodolite At every set up of the instrument, certain temporary operations are carried outbefore the observations are made. These operations are known as temporaryadjustments or station adjustments and they are made to achieve the following twoconditions. 35
    • 1. The plane of collimation is horizontal2. The vertical axis passes through the center of the peg.Following are the three temporary adjustments of a Theodolite:1. Levelling up2. Elimination of parallax.Measurement of horizontal angles The general procedure for measuring horizontal angle by theodolite will be asfollows. (1) The instrument is set up at station O and the temporary adjustments are performed to level it accurately. (2) Let the verniers on upper plate be named as A and B. Adjust the vernier A to the zero (usually marked 360o) of the horizontal circle. If there is no instrumental error, the reading on vernier B will be 180o. Also see that the vertical circle is to the left. Now both plates are clamped and thus the instrument will revolve about its outer axis. (3) The lower clamp is loosened and it is pointed towards the left hand side object P. The lower clamp is tightened and the object is bisected accurately by using the lower tangent screw. The readings of verniers A and B should be checked and as such, there should be not change in the previous readings. It may also be noted that the left hand side object is bisected first because of the fact that the graduations on the scale plate run in clockwise direction. 36
    • (4) The upper clamp is loosened and the instrument is rotated clockwise about the inner axis to bisect the object Q. The upper clamp is then clamped and the object Q is bisected accurately by using upper tangent screw. (5) The readings of both the verniers are taken. The reading of vernier A gives directly the angle POQ while the value of angle POQ on vernier B can be obtained by deducting 180o from the reading. (6) The man value of two readings gives the angle POQ with one face. (7) The face is changed by transiting the telescope and the whole process is repeated. Thus, mean value of angle POQ is obtained with other face. (8) The average horizontal angle is thus obtained by taking the mean of the two values obtained with two faces. During the above process, care should be taken to manipulate the proper clamps andto record the readings properly. It is also not necessary to set vernier A to zero initially.It may be set at any desired reading. But in that case, the difference between the initialand final readings on vernier A should be worked out to get the angle POQ. For measuring horizontal angles with high precision without increasing the size of thescale plate, the following two methods have been found out: (1) Repetition method (2) Reiteration method(1) Repetition method In this method, the same angle is repeatedly measured two times or more byallowing the vernier to remain clamped each time at the end of each measurement andthus, the angle is added several times mechanically. However, care should be taken toadd 360o for every complete evolution to the final reading. The average horizontal angle 37
    • is then obtained by dividing the final reading by the number of repetitions. The face isthen changed and the whole process is repeated. Thus, the average horizontal angle isobtained by taking the mean of the two value obtained by taking the mean of the twovalues obtained with two faces. The procedure is the same as described above. But is is more exhaustive andlaborious. However, there is no advantage by increasing the number of repetitionsindefinitely. Usually the angle is accumulated three times with each face and it givesfairly accurate result. When this method is adopted, the following errors are eliminated: (1) Error due to eccentricity of verniers; (2) Error due to inaccurate bisection of the object; (3) Error due to inaccurate graduations and (4) Error due to line of collimation and trunnion axis not being perpendicular to each other.The repetition method of measuring horizontal angle does not eliminate errors due to slip,displacement of station signals, dislevelment of the bubble, etc. because these errors arecumulative in nature.(2) Reiteration method This method is also known as method of series or direction method. It isgenerally preferred when several angles are to be measured at a station. The procedureconsists in measuring successively several angles in clockwise direction and finally thehorizon is closed. The term closing the horizon is used to mean the process of measuringthe angle between the last station and the initial station. Thus, it gives a check on theangle measured because of the fact that sum of angles around a point is 360o. Thismethod is less tedious than the repetition method and it gives equally preciseobservations in short time. 38
    • Measurement of vertical angles: The angle made between the inclined line of sight and the horizontal line ofcollimation is known as the vertical angle. If the point is above the horizontal plane, it iscalled the angle of depression and is treated as negative.Following is the procedure for measuring vertical angle, as shown in (1) The instrument is set up at station O and it is leveled accurately with reference to the altitude bubble. (2) The zero of vertical vernier is exactly set to zero of the vertical circle with the help of the vertical circle with the help of the vertical circle clamp and tangent screw. (3) The bubble of the altitude level is brought at the center by means of the clip screws. Thus, the line of collimation becomes horizontal with respect to the zero reading on the vernier. (4) The vertical circle clamp is loosened and the telescope is sighted in vertical plane to P. The accurate bisection is obtained with the help of vertical circle tangent screw. (5) The readings on both the verniers of vertical circle are taken, the mean of which gives the required vertical angle. (6) The face is changed and another value of angle is obtained by repeating the process. (7) The average vertical angle is thus obtained by taking the mean of the two values obtained with two faces. It is easy to understand that the above procedure can also be adopted to measure the vertical angle between two points subtended at the instrument station. It will be equal to the sum or difference of the two readings depending on the relative positions of the points with reference to the horizontal line of collimation.Exercise VIII1. Determine the horizontal angles by theodolite survey2. Using the theodolite find the vertical angle and horizontal distances 39
    • IX. Ghat tracerGhat tracer is an useful instrument for finding gradients, setting out grade contours,preliminary survey of hill route for road alignment and also for contouring andleveling.Construction: It consists of a triangular frame with a hollow metal sighting tube fittedwith an eyepiece at one end and with cross wires at the other. It is hung by a pivot atapex, on an upright staff, by means of a clamping pin and nut. About 2 to 3 cm belowthe sighting tube and parallel to it there is a racked horizontal bar, attached to the tuberigidly by 2 small vertical bars, one at other end. A weight suspended on the bar canbe moved along the racked bar by means of a screw, fixed on the supporting bracket,operating the pinion on the rack. Upper part of the weight has a knife edge, whichforms an index, by which readings can be taken on the scale of the gradients of 1 in 6or 1 in 120. The line of sight is the line joining the centre of the eyehole and theintersection of cross wires. The tube and consequently the line of sight can be set toany desired gradient by moving the weight of the racked bar.Method of use:The T shaped sight vane or target, on which readings are taken, has its cross line atthe same height as the height of the axis of the sighting tube. To find the gradient ofslope an assistant is sent ahead with the sight vane and the weight is moved along thebar till the cross wires are aligned on the sight vane and the gradient read on thescale. When the sight is taken uphill weight is moved backward from zero mark andvice versa. If it is desired to layout on the ground an alignment at a fixed gradient theindex is set to the required gradient and the weight screwed down. An assistant issent with the sight vane, who moves up and down till he is on the required gradient.To establish a line of sight, set the index exactly in the centre of the sighting tube atzero gradients.Exercise IX1. Using the ghat tracer mark the contours of the alignment 40
    • CONTENTSEx. No. Title Page No.I. Scales 1II. Chain Surveying 7III. Compass Surveying 11IV. Plane Table surveying 16V. Levelling 19VI. Contouring 24VII. Computation of areas 26VIII. Theodolite surveying 30IX. Ghat tracer 36 41