Surveying or survey levelling is practised to recognize the distinctions in key (= upright distances) between various point out in the field, come measure ranges (horizontal distances), to collection out edge lines etc. Major surveying works are done by engineers or default surveyors using sophisticated equipment such as the levelling tool (see Fig. 33). This section will only address elementary equipment. Most equipment can it is in home-made and also be supplied by the farmers themselves after tiny training. Fig. 33 an example of a levelling instrumentThe various types of equipment and their use described in the sections the follow, are:- Boning rods: horizontal lines and also slopes - N-frame level: slopes and also contour lines- flexible tube water level: countour lines and differences in elevation- Hand level: edge lines and differences in elevation.6.1 Boning Rods 6.1.1 description 6.1.2 usage of boning rods6.1.1 Description
Boning rods space T-shaped and also made that wood. Their elevation is normally 100 cm and the cross-lath is 50 centimeter x 10 cm. The bottom part is sometimes reinforced with steel (see Fig. 34).Fig. 34 A boning rod
Boning rods are provided to set out horizontal present or lines with a constant slope. In certain they are used for setting out canal excavation works, but additionally for roads and also dyke construction. To it is in able to collection out horizontal lines or lines through a consistent slope, the elevation (or height) of 2 points ~ above the heat (preferably the beginning and end points) need to be known.126.96.36.199 setup out horizontal linesSuppose a horizontal line has to be collection out in between the Bench marks A and B. Bench point out A and B have actually the exact same elevation. The procedure is:Step 1Set out a straight line in between A and B (see thing 2) and place intermediary pegs at regular intervals (see Fig. 35a; pegs C and also D).Fig. 35a setup out a horizontal line, action 1Step 2Place boning rods on peak of the two Bench Marks and on top of peg C. The observer, looking simply over the height of boning rod A make the efforts to lug the tops of the boning rods A, B and also C in line.As can be checked out from Fig. 35b, boning pole C and also thus peg C is also high; the top of the boning rods are not in line.
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Fig. 35b setting out a horizontal line, action 2Step 3Hammer peg C more into the soil. It may be important to dig deep into some of the soil bordering peg C in stimulate to have the ability to lower peg C sufficiently.The peak of peg C is in ~ the exactly elevation when, looking end the top of boning stick A, the top of the boning rods A, C and B room in heat (see Fig. 35c).Fig. 35c setup out a horizontal line, action 3Step 4Place a boning rod on peg D. As soon as looking end the top of the boning rods A and B the is not feasible to see the optimal of the boning stick on peg D, as peg D is also low (see Fig. 35d).Fig. 35d setting out a horizontal line, action 4Step 5Replace peg D by a much longer peg or pull the end peg D and include some floor in the prompt surroundings that D and also hammer peg D again into the soil. Repeat this process until the correct elevation that peg D is discovered (see Fig. 35e).Fig. 35e setting out a horizontal line, action 5Step 6The 2 Bench point out A and also B and the pegs C and D all have the very same elevation. Line ACDB is horizontal (Fig. 35f).Fig. 35f setting out a horizontal line, step 188.8.131.52 setup out slopesThe use of boning rods when setting out a slope is the exact same as described in 184.108.40.206 only, in this case, the Bench clues A and also B perform not have actually the same elevation. Bench note A is either greater or reduced than B. As soon as the difference in elevation and also the horizontal distance in between A and B space known, the slope can be calculation (see Volume I, thing 3 and also Volume 2 thing 3 and sections 6.3 and also 6.4).6.2 The N-Frame Level 6.2.1 description 6.2.2 testing the N-frame level 6.2.3 usage of the N-frame level
This instrument, provided to set out edge lines or slopes, consists of a wooden framework (a key lath, 2 legs and 2 overcome poles) as displayed in number 36a. ~ above the main lath, a carpenter level is firmly fixed (e.g. With metal strips).6.2.2 trial and error the N-frame levelBefore fixing the carpenter level to the frame, the instrument need to be tested to make certain that the carpenter level is in the correct position.The structure is put on two points which have actually the exact same elevation (for example on a horizontal table or top top a floor that has been checked formerly with the carpenter level). If the bubble of the level tube is not precisely in in between the marks, the carpenter level should be adjusted by placing a spacer (e.g. Thin piece of board) under one end of the level (see Fig. 36a and b).Fig. 36a The N-frame level
The N-frame level is used to collection out contour lines and slopes on the field.220.127.116.11 setting out edge linesStarting native peg (A), a edge line has to be set out. The procedure to follow is:Step 1One leg of the tool is put close come peg (A). By transforming the frame roughly this leg, a place of the structure is discovered such that the 2nd leg is ~ above the ground and the bubble of the carpenter level is in between the marks. This way that the clues thus uncovered by the 2nd leg that the structure is in ~ the exact same elevation as the beginning point. Both clues belong come the same contour line. A brand-new peg (peg B) is propelled in close come the 2nd leg to note the ar (see Fig. 37 a).Fig. 37a setting out a edge line, step 1Step 2The N-frame is moved to the newly-placed peg and the procedure is repeated until the end of the ar is reached. Every the pegs, for this reason driven in the ground, type a contour heat (see Fig. 37b).Fig. 37b setup out a contour line, step 2Step 3When the an initial contour line has been pegged out it can be essential to do minor adjustments by moving some of the pegs to the left or come the ideal to find a smooth line. Most of the pegs will stay in the very same place. The smooth line thus developed by the pegs represents the first contour line.Step 4The next step is to recognize the second contour line. A an option has to it is in made top top how many centimetres reduced (or higher) the next contour line must be. This selection should be based on the forced accuracy (a little difference in height method it is more accurate), the general slope the the area and also the regularity of the general slope of the area. In practice, the height distinction will vary between 10 and 50 cm.In this example, a height difference of 20 centimeter was chosen. This way that the soil level close to peg A should be 20 cm higher than the ground level near peg A (see Fig. 38). The position of peg A. Is discovered by trial and also error, utilizing e.g. The method described in ar 3.4 to measure up the vertical distance between the floor levels near A and A1. Peg (A1) to represent the beginning point that the second contour line. Now follow the procedure described over to identify the 2nd contour line (see Fig. 38).Fig. 38 setting out the second contour line18.104.22.168 setting out slopesIn addition to the determination of edge lines the N-frame level deserve to be supplied to collection out lines through a uniform slope, which is useful, e.g. For setup out furrows or ditches.ExampleSuppose the the steep of a ditch come be collection out on the ar is 1% (one percent). In bespeak to usage the N-frame level to collection out slopes, it needs a modification; one leg needs to be shortened. In this example, one leg needs to be shortened by 2 cm, together the size of the main lath is 2 m and the compelled slope is 1%. (Note 1% the 2 m = 2 cm). SeeFig. 39 modified N-frame levelA slope of 1.5% would require one foot to be 3 cm (1.5% the 2 m) shorter; a steep of 2% would need a 4 cm (2% the 2 m) shorter leg.Step 1The shortest foot of the N-frame is inserted close come the starting peg (A). By turning the N-frame about this leg, a position is uncovered such that the second leg is ~ above the ground and also the balloon of the carpenter level is in in between the marks. The clues thus uncovered is 2 cm lower than the starting point and also is significant with a new peg (peg B)(see Fig. 40a).Fig. 40a setup out a slope, step 1Step 2The N-frame is moved and also the quick leg is placed near peg (B). The procedure is recurring until the finish of the field is reached. The sequence of pegs thus placed kind a line through a steep of 1% (see Fig. 40b). This line would be, after correction, the centre heat of a ditch with a steep of 1%.Fig. 40b setup out a slope, action 26.3 The versatile Tube Water Level 6.3.1 description 6.3.2 usage of the flexible tube water level6.3.1 Description
The flexible tube water level, used for contour lines and measuring differences in elevation, is composed of 2 staffs through a size of around 2 m and a transparent flexible tube of about 14 m long. The ends of the tube room firmly resolved to the staffs (see Fig. 41).Sometimes, a 10 m lengthy rope is resolved to the staffs to limit the distance in between the staffs. The rope hence helps to prevent damages to the tube.6.3.2 usage of the flexible tube water level 22.214.171.124 setting out edge lines 126.96.36.199 Measuring differences in elevation
The tube is filled v muddy water so that the water level is about 1 m high in each of the pipe ends. The is crucial Chat no air bubbles room trapped in the tube. Wait bubbles have the right to be removed by tapping the tube through the finger. Where the two staffs are set, the free water surface in the tube ends have actually the very same level (see Fig. 42). This is dubbed the "communicating vessel" principle.Fig. 41 functional tube water level
The hand level is composed of a 10-12 cm long tube through an eye piece at one end and two hair present (one horizontal and the other vertical) at the other end. Attached come the pipe is a little carpenter level (see Fig. 47).Fig. 47 A hand level
The hand level have the right to be offered to set out edge lines and also to measure the difference in elevation in between two points.188.8.131.52 setting out contour linesStep 1The forked pole is set on the starting point. The hand level is put on the crotch that the forked pole and also tilted slowly until the bubble is viewed at the horizontal hair heat (see Fig. 49a).Fig. 49a setup out a edge line, action 1
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Fig. 51 measure the difference in elevation between two remote points A and also BStep 2The observer takes increase a position between A and also C and measures the distinction in elevation between suggest A (near peg A) and point C (near suggest C) as described in the ahead section.Step 3The observer takes up a place between allude C and suggest D. The assistant turns the staff at allude C in the direction of suggest D. The staff must stay in the very same position and also not be lifted.Step 4Measure the distinction in elevation in between points C and also D as defined in the vault section. Continue until the distinction in elevation between the last intermediate allude and B has actually been determined.Step 5The difference in key between suggest A and point B is the sum of the differences in key between suggest A, all intermediate points and suggest B.Note: The difference in elevation between suggest A and suggest B have the right to be uncovered with the formula:Difference in elevation between A and B = sum of ago readings - amount of prior readingsEXAMPLE (see Fig. 51):Between points:Back analysis (m)Front analysis (m)Difference in key (m)A and also C0.651.40- 0.75C and also D0.201.25- 1.05D and also E1.800.50+ 1.30E and also F1.750.95+ 0.80F and also B1.371.24+ 0.13Total5.775.34+ 0.43Difference in elevation between A and B = sum of back readings - sum of prior readings = 5.77 - 5.34 = + 0.43 mThe distinction in elevation is positive, which means that allude B is over point A.