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Chain Surveying Faculty of Applied Engineering and Urban Planning Civil Engineering Department 2 nd Semester 2007/2008 Surveying

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Contents Types of Distance Measurement Measurement Methods Direct (tapes) Indirect: (EDM, Stadia) Errors and Corrections for Tape Measurement EDM

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3 Introduction One of the fundamentals of surveying is the need to measure distance. Distances are not necessarily linear, especially if they occur on the spherical earth. In the present subject we will deal with distances in Euclidean (geometric) space, which we can consider a straight line from one point or feature to another.

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Common Methods for Measuring Distances Pacing Taping Tachometry (required theodolite, and graduated rod) EDM (Electronic Distance Measurement)

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Equipment Used in Chain Surveying Measurement of Lines Chain Tapes Invar Tapes (more accurate, 65% steel, 35 Nicke) Making Right Angles Optical Prism Others Ranging Rods Arrows Pegs Plumb bobs

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6 Types of Distance Measurement

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9 Examples: When use which 1. If you are intending to draw a map or area, horizontal distance and height difference (vertical distance) should be used to enable plan and height information to be drawn. 2. If you are to locate points such as a corner of a building or centre line of a road, slope distance and vertical distance are required to enable pigs be located at correct points on site (Layinging Out).

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10 Methods of Measurement Pacing Accuracy 1 : 100 Taping Accuracy 1 : 10,000 Electronic Distance Measurement (EDM) Accuracy 1 : 10,000 to 1:100,000

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11 Pacing Practical measure of distance. Don't try to pace out one meter with every step. Walk casually over 100 m counting the number of steps. Work out the length of a casual step and use this instead. Varies with uphill, downhill, and your age. Low accuracy No equipment needed

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12 Taping (or chaining) Chaining is applied to measurement with a steel tape or synthetic tape (plastic or fiberglass). All standard in lengths 100 m, 50m, 30 m, 20 m. It is fairly quick, easy and cheap, and hence is the most common form of distance measurement. Unfortunately, Chaining is prone to errors and mistakes. For high accuracy, steel tape should be used which is graduated in mm and calibrated under standard temp (20 degree) and tension (5kg). Be careful, easily break. Synthetic tape is more flexible graduated in 10mm

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Equipment Used in Chain Surveying

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15 Measuring wheels Tapes in lengths up to 100 ft Some Taping Instruments

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16 Taping Procedures ranging rods set up between points A and B from A to B, set zero of tape at A tape unwound towards B A third range rod is “ranged” in at C Tape straightened, held tight and read at rod C C marked with a pin for next bay, tape moved from A and zero set at C and so on

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17 Accessories

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Processes in Chain Surveying Ranging and Measurement of Lines Level Ground Uniformly Sloping Ground Uneven Ground

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Level Ground ABA1A1 A2A2 A3A3 A4A4 Rod

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Stationing Along Baseline: stations At right angle: offset dist

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22 Length AB = 4 x Full tape distance + 1 Short section REMEMBER ! It works only on smooth ground or uniform slope surfaces

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23 Example

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24 Example How about this very uneven case or high accuracy is required?

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25 Example Sag curve Sag curve measurement is not common nowadays and is restricted to steel tape only.

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Processes in Chain Surveying

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Uniformly Sloping Ground

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Uneven Ground

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In Previous Ranging and Measurement of Lines Level Ground Uniformly Sloping Ground Clinometers Abney Level Uneven Ground

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Homework Solve Problems: 1.5, 1.6, , 2.2, 2.5

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Lecture 5

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Setting Out Right Angles Method 1 Extend tape horizontally, swing it left and right, observe min. Reading This method is primarily used on smooth ground where a free swing of tape is possible. C AB

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Setting Out Right Angles Method 2 With free end of tape, strike an arc to cross the line AB at points D & E. bisect DE at F. Then angle CFE=90 A D E C B F

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Setting Out Right Angles Method 3 Run tape from C to D, bisect CD, with E as center and radius equal to ED, strike an arc to cross line AB at F, then DFC=90 C A D E F B

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Setting Out Right Angles Method 4 Using optical square with double prism Prove Method 4 provided in the text book

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Method 1 Setting Out a Line at Right Angles

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Method 2

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Setting Out a Line at Right Angles Method 3 3 m 4 m 5 m

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Mapping Details Methods of Locating Ground Details Method of Ties: a point is located by measuring two reasonable distance called ties between this point and two points on the chain line (a) Method of Offsets : a point is projected on he chain line and then the distance between the points and its projection (called offset) as well as the distance from the beginning point of the line to the projected point are measured. (b)

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Choice of Chain Lines Well conditioned triangles (Angles 30 – 120)

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As close as possible to the buildings Choice of Chain Lines

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At least two stations can be seen Choice of Chain Lines

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Minimum Number of Lines Choice of Chain Lines

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Provide check line possibility Choice of Chain Lines

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Avoid obstacles Choice of Chain Lines

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Booking Details

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Begin with fresh page All measurement should be recorded Proceed with booking from the bottom of the page to the top, the records should be recorded in the direction of chaining All details must be sketched neatly and roughly to scale All other chain lines which meet the chain line being measured should be recorded in appropriate place

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Plotting the details

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Booking the Measurements

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