Unit - 1

Introduction to Surveying

• The making plans and layout of all Civil Engineering initiatives inclusive of creation of highways, bridges, tunnels, dams and many others are primarily based totally upon surveying measurements.
• Moreover, for the duration of execution, challenge of any importance is built alongside the strains and factors set up with the aid of using surveying.
• Thus, surveying is a simple requirement for all Civil Engineering initiatives.
• Other major works wherein surveying is frequently utilised are:

1. To repair the countrywide and kingdom boundaries;
2. To chart coastlines, navigable streams and lakes;
3. To set up manage factors;
4. To execute hydrographic and oceanographic charting and mapping; and
5. To put together topographic map of land floor of the earth.

1. The curvature of the earth is not taken into consideration.
2. It is carried out for small area.
3. Plane surveying is conducted by state agencies.
4. It is carried out over an area less than 250 km².

1. The curvature of the earth is taken into consideration.
2. It is carried out for large area.
3. Geodetic surveying conducted by survey of India Department.
4. It is carried out over an area greater than 250 km².

• The relative position of a point to be surveyed is located by measurement from at least two points of reference, the positions of which have already been fixed.
• If P and Q are the two reference points on the ground, any other point, such as R, can be found by any of the direct methods. A single method is sufficient to locate the relative position of ‘R’ with respect to reference points P and Q, it is necessary to adopt at least any two methods to fix the position of point ‘R’.

• Here it is always desirable to carryout survey work from whole to part which means, when an area is to be surveyed then first a system of control points is to be established covering the whole area with very high precision. Then small details are located by less accurate methods.
• The idea of working this way is to prevent the accumulation of errors and to control and localize minor errors which would expand to greater magnitudes if the reverse process is followed, thus making the work uncontrolled at the last.

• The stations taken along the boundary of an area as controlling points are known as ‘main stations. The lines joining the main stations are called ‘main survey lines.

• The stations are on the main survey lines or any other survey lines are known as “subsidiary station”. These stations are taken to run subsidiary lines for dividing the area into triangles, for checking the accuracy of triangles and for locating interior details.

• Tie stations are also subsidiary stations taken on the main survey lines.
• Lines joining the tie stations are called tie lines.
• Tie lines are mainly taken to fix the directions of the adjacent sides of the chain survey map.

• It is a line produced on a cast by a surveyor marking the contour in relation with planned path of placement of a restoration is known as survey line.

• The lines joining the main stations are called main Survey or Chain lines.

• The line on which the framework of survey is formed is known as the ‘base line’. It is most important line of the survey.
• The longest of the main survey lines is considered the base line.
• This line should be taken through fairly level ground, and should be measured very carefully and accurately.

• The line joining the apex points of triangle to some fixed point on its base is known as the ‘check line’. It is taken to check the accuracy of the triangle.

• It is the process of establishing intermediate point on a straight line between two end points.
• There are two methods of ranging.

• Direct method: when intermediate ranging rods are fixed on a straight line by direct observation from end stations, the process is known as direct ranging
• Indirect ranging method: when the end station is not intervisible due to being high ground between them, intermediate ranging rods are fixed on the line in an indirect way this method is known as indirect ranging.

• The reference line with respect to which horizontal angle of survey line is measured, known as meridian.

• The horizontal angle made by a survey line with reference to magnetic north pole in a clockwise direction is called as the bearing of a line.

• Generally, the bearings of survey lines are designated in the following two types:

1. Whole circle bearing (W.C.B.) system
2. Reduced bearing (Quadrantal) system

• When the bearing of a line is measured with respect to magnetic north in clockwise direction, it is called as magnetic bearing or whole circle bearing.
• The value of W.C.B. Varies from 0° to 360°.
• Four quadrants I, II, III and IV are shown in Fig.
• The W.C.B. Of a line OA in the first quadrant is (between 0° to 90°).
• The W.C.B. Of a line OB in the second quadrant with respect to north is (between 90° and 180°) W.C.B. Of a line OC in the third quadrant with respect to north is (between 180° and 270°) and W.C.B. Of a line OD in the fourth quadrant with respect to north is , (between 270° and 360°).

• In reduced bearing, the bearing of survey lines is measured with respect to north and south line either in clockwise or anticlockwise direction towards east or west.
• Fig. Shows quadrantal bearing system.
• Any line in any of the four quadrant is expressed by an angle which is measured from either north or south.
• The directions are essentially written before and after the value of angle.
• This helps to identify in which quadrant the lines lie. The maximum bearing in such case is 90°.

• In this method, the reduced level of collimation plane or height of instrument is determined for each set up of dumpy level and then reduced levels (R.L.) of the other points are found out with respect to the plane of collimation or height of instrument.

• Step 1: To prepare the format of level page before levelling work start:

• Step 2: To find the height of instrument (H.I.) or R.L. Of plane of collimation:

• Step 3: To find R.L. Of intermediate points or change points:

• Step 4: To find new height of instrument or new plane of collimation:

• Step 5: To find reduced levels of the remaining points:

• Step 6: To finish the levelling work:

• Step 7: To find arithmetical check:

• Arithmetical check:

• Note: It is noted that the arithmetical check can be taken at each level page.

• In this method, instead of H.I. Column in the format of level page, two columns of rise and fall are introduced for calculation of R.L's. Difference of levels between consecutive points is found by comparing the staff readings on the two points for the same setting the instrument.

• Step 1: Prepare the format of level page before levelling work start, as shown below:

• Step 2: The difference in staff readings between the consecutive points is found out.
• Step 3:

1. If the staff reading of second point in level page is higher than the first, then it indicates fall which is then to be subtracted from R.L. Of previous point.
2. If the staff reading of second point in level page is lower than the first one, then it indicates rise which is further to be added to the R.L. Of previous point.

• Step 4: Repeat the same procedure till the levelling work is over.
• Step 5: After completion of levelling work, the arithmetical check is found out, which shows accuracy and cross check of the field work in levelling. Note that, the check can be taken at each level page and on R.L., of every intermediate points.
• Arithmetical check:

• Note: It is noted that arithmetical check can be taken on R.L. Of intermediate points.
• In this method calculation work is more, therefore it is tedious but there is check on every point; hence it is accurate method rather than H.I. Method.

1. Let PQR be the given line of section.

1. The chainage of the staff points is continuous from the beginning to the end of the section line.
2. To eliminate the instrumental errors, the back sight and fore-sight distance should be approximately equal.
3. Bubble must be in the centre of its run when the B.S and F.S readings are taken.
4. The features such as Road, Foot path, nalla, river etc crossed by the line should be fully located by taking bearing of their centre lines, their width or by offsets.

• When the heights of all the points along the section have been calculated, a profile can be drawn.
• The horizontal distance is plotted along the horizontal axis to some convenient scale and the distances are also marked. The vertical lines are drawn at these points representing the elevations above the reference level. Each ground point is thus plotted by two coordinates i.e., chainage and elevation. The line joining the top points of these ordinates then represents the ground sections.
• Since the horizontal distances involved are in general very much greater than the variations in level. Thus, y axis scale is larger than the x axis. In this way irregularities of the ground are made more apparent. The ratio of exaggeration adopted runs from 5 to 15 times.

• The lines of cross-sections are in general perpendicular to the longitudinal section line.
• The purpose of cross sectioning is to furnish the engineer with sufficient information regarding the levels of the ground on either side of the longitudinal section to enable him to design the intended work. Cross-sections are taken at every 20 m or 30 m distance along the centre line. The length of cross-section may be run at closer intervals to outline the features of road, nala, etc. Electro refining
• The cross sections are numbered consecutively from the commencement of the centre line and are set out at right angles to the main line of section with the chain and tape, the cross-staff or the optical square and the distances are measured left and right from the centre peg. The length of cross-section depends upon nature of work Refer Fig.

• The plotting of cross sections observed as above is similar to that of profiles, except that, in this case vertical and horizontal measurements plotted to the same scale.
• The point along the longitudinal section is plotted at the centre of the horizontal axis.
• The points to the left of center are plotted to the left and those to the right are plotted to right. The points so obtained are joined by straight lines.

1. Instrumental Errors
2. Collimation Error
3. Error due to Curvature & Refraction
4. Other Errors

1. Collimation error
   1. Correction: Check before use and equalise sights.
2. Under sensitive bubble.
3. Errors in staff graduation
   1. Correction: Check 
4. Loose tripod head.
5. Telescope not parallel to bubble tube
   1. Correction: Permanent adjustment.
6. Telescope not at right angles to the vertical axis
   1. Correction: Permanent adjustment

• Rod reading is too high
• Error increases exponentially with distance

• Select an instrument station C from which all the points to be surveyed are visible.
• Set up and level the board and clamp it.
• Select a point C, on the sheet to represent the instrument station.
• Draw the direction of the magnetic meridian with the help of trough or circular compass in the top corner of sheet.
• With alidade touching C, sight various points P.QR.S.T etc. to be located, draw rays towards them
• Measure the distance CP, CQ, CR, CS, CT etc. and plot them to scale and join the points pqrst so obtained.

• This method is used for small area which can be commanded from a single
• This method is employed in combination with some other method.

• In intersection method the point is fixed on plan by the intersection of the rays drawn from the two instrument stations.

• Select two points L and M in a commanding position.
• The line joining the station L and M is known as base line.
• Measure the base line LM.
• Set up the table at the start L and mark point I on sheet over L.
• Orient the board by placing alidade along Im and turn the board until the ranging rod at B is bisected. Clamp the board.
• With alidade touching point I draw rays 1, 2, 3 of indefinite length as shown in Fig.
• The table is then shifted to station M, orient it by back sighting method on L.
• Through m draw rays towards the point previously sighted i.e., 4, 5 are drawn determine the points on intersection a and b.

1. Locating details of area.
2. For locating distant and inaccessible points, broken boundaries, bank of river etc.
3. For plotting position of points to be used subsequently as the instrument stations.
4. It is suitable when it is difficult or impossible to measure distance as in the case of the survey of mountainous country.

• In this method the instrument is shifted from one station to another.

• Set up the instrument at station P. Select the point 'p' on the sheet. Center and level the table when the board is clamped.
• Mark direction of magnetic meridian on sheet by trough or circular compass.
• Touching the alidade on 'p' sight the ranging rod at Q and draw a ray.
• Measure the distance PQ with chain or tap and lay it off to scale on the ray drawn towards Q Thus fixing the position of q on the sheet.
• Shift the instrument and set up at Q, orient it by any method on P with the alidade along qp and then clamp the table.
• With the alidade touching q, sight the station R and draw a ray.
• Measure the distance QR and lay it off to scale on the ray drawn towards R to fix the point r on the sheet.
• The nearby details are also located as usual.
• Proceed the traverse until all the stations are plotted.
• At any station the work can be checked by taking sights to two or more proceeding stations visible from the station occupied.

1. For running survey lines between the stations previously fixed by any method.
2. To locate the topographical details.
3. For survey of roads, rivers etc.

• Only the instrumentation stations established by this method.
• After fixing the stations, details are located either by radiation or intersection.

• As in the intersection method select a base line AB on the ground.
• With the help of tape, measure it accurately and plot it to scale on the sheet as 'ab' in a suitable position.
• Set up the table at A. Centre it so that A is exactly over A and then level it accurately.
• Place the alidade along AB, then orient the table until ranging road at B is bisected and then clamp it.
• With the alidade touching A, sight the station C which is to be located by resection and draw a ray along the ruling edge of the alidade. Mark the point 'c' along the rays by estimation.
• Shift the table to point C such that 'e' is over C. Orient the table by back sight at point A and clamp it.
• Place the alidade against b and sight B where the edge of alidade cuts (resects) draw a ray. The point of intersection of this ray and that preciously drawn from A gives the required point c.
• Continue the process to establish the other station points.
• The above explained method is also called as back ray method as it necessary to draw a ray from the preceding station to the station to be occupied by the plane table.
• Errors in centering though inevitable, it will not affect the accuracy of the work as it is only used for small work.
• Details are best located by radiation or intersection.

• The contour lines have the following characteristics
• All points on a contour line have the same elevation or R.L's. Fig. Shows the contour lines of equal elevation.

• Two contour lines of different elevations cannot cross each other. However, in case of overhanging cliff two contour lines of different elevations can intersect. For such case, refer the Fig.

• Steeps slope:

• Hill: Closed contour lines with higher values inside indicate hill. See Fig.

• Ridge line:

1. Direct method
2. Indirect method

• In the direct method, the contour to be plotted is actually traced on the ground.
• These points are plotted on ground and contours are marked through them. This method is followed where great accuracy is required.

• Consider an area as shown in Fig. Which is to be surveyed for contouring.

• In this method spot levels are taken at regular interval along predetermined lines on the ground. The work is then plotted on plan and then the required contour lines are drawn by the process of interpolation.
• The indirect method is less tedious and speedy as compared to direct method.
• The methods followed in indirect method of contouring are:

• This method is suitable for roads, railways and canal survey. Consider X, Y, Z as the centre line of the road or railway or canal route as shown in Fig. Cross sections are set at every 10 m on the centre line whereas the other dimension to complete a rectangle may be 5 m.

• The spacing of the cross-section depends upon the nature of terrain. The cross-sections are more closely spaced where the contours curve abruptly. Staff readings of all the nodal points are determined and the R.L's are calculated. The same cross-section is plotted on the sheet to a suitable scale. The respective R.L's are written on the nodal point as shown in Fig. And then the required contours are interpolated between the R.L's.

• In this method the area to be surveyed is divided into a number of squares of size 5 to 20 m depending upon the nature of the ground and contour interval required. The elevations of the corners of the squares (called nodal points here) is determine by means of process of levelling. The calculated reduced level of these nodal points are then written on the respective nodal and contours are interpolated between them.
• This method is used when the area to be surveyed is small and the ground is not mush undulating because on undulating ground it would be practically impossible to form squares.

• In the case of hilly areas, tacheometric contouring method is used. Here instrument known as tacheometer which is a theodolite, is utilized which determines horizontal distances and elevation of points.
• As shown in Fig. The tacheometer is set at a point approximately at the centre of the area. Radial lines are set making angles with either the magnetic meridian or with the first radial line. On each radial line staff readings are observed at different points. When the readings along all the radial lines have been observed, it is then plotted on a sheet to a suitable scale. The required contour lines are then interpolated as usual.

• A contour map can be used to determine the intervisibility of two points knowing the elevations of two stations at a farther distance. If a contour line passes in between them of more elevation then the stations will not be intervisible.

• The contour plan used to calculate the storage capacity of reservoirs. The areas between the contours are found by planimeter and multiplied by contours interval, will give the total volume of water that can be stored in a reservoir.

• If a contours plan is given and a section is drawn along any direction, the general shape of the ground can be known.
• Fig.  shows section of line PQ

• A contour plan is very much useful in locating the route of a highway, railway, canal or any other communication line Fig. Show route P to Q at an upward gradient.