Visayas State University College of Engineering
Department of Geodetic Engineering Visca, Baybay City, 6521-A, Leyte, Philippines -----------------------------------------------------------------------------------------------------------------------------------------------------------------Vision: The premier university of science and technology in the Visayas. Mission: Provide excellent instruction, conduct relevant research and foster community engagement that produce highly competent graduates necessary for the development of the country. ------------------------------------------------------------------------------------------------------------------------------------------------------------------
GEng 111c General Surveying I
TAPING OVER UNEVEN AND SLOPING GROUND Exercise No. 6
Name: Kharla C. de Leon Laboratory Schedule: MW 7-10 Group No. : 5 I.
Date Performed: Sept. 5, 2016 Date Submitted: Sept. 14, 2016
Introduction Taping is the process of directly measuring distances with the use of graduated tape. The usual procedure of taping will involve the process of aligning the tape, stretching it, plumbing selected tape marks, marking and recording tape lengths. It is standard to practice to hold the tape horizontally above ground and to plumb at one or both ends when taping on sloping and uneven terrain surfaces. This requires the measurement of shorter distances which are accumulated to total a full tape length. The procedure is referred to as “breaking tape”.
II.
Objectives: 1. To measure the horizontal length of a line using a measuring tape over an uneven and sloping ground by the method of breaking tape; and 2. To acquire an acceptable relative precision of the measured horizontal length of a line in surveying operations.
III.
Instruments and Accessories:
30 meters or 50 meters steel tape/measuring tape, chaining pins, range poles, pegs or hubs, chalk or marking crayons and plumb bob IV.
Procedure:
A. Measuring Uphill. 1. The professor/instructor will designate two points A (downhill) and B (uphill) approximately 150 to 300 meters apart in an uneven and sloping ground to be measured using the breaking the tape method. 2. Set or hold range poles behind points A and B and along intermediate points to aid the students to travel in a straight path along the course AB. 3. The head tapeman unreels and spreads out the tape and pulls the zero mark uphill along the line from point A. The rear tapeman raises the 30-m or 50-m end of the tape breast high while the head tapeman moves back to a place on the line near a full meter (or foot) mark where the ground surface is as high as the other raised end of the tape. The head tapeman stays by the side of the line measured and holds a chaining pin on the ground. 4. The rear tapeman temporarily releases end of tape and signals head tapeman to either move to the right or to the left in order to align him. When the pin of the head tapeman is in line with the range pole held over point B, the head tapeman is then signalled to stick the pin vertically into the ground. 5. The rear tapeman plumbs from point A to the terminal mark of the tape with a plumb bob and maintains this plumb bob steadily over A while head tapeman pulls the tape taut, and making sure that the tape is on line by bringing one of its edges in contact with the previously aligned pin. The head tapeman then moves the pin opposite the nearest full meter or foot mark of the tape and he sticks it firmly into the ground. 6. The rear tapeman leaves his end of the tape, moves up the slope and gets hold of the tape at the point previously held by the head tapeman. The next measurement is made horizontally from the pin stuck in the ground by the head tapeman as done at point A. 7. The process is repeated until the whole tape length is used up thus finishing the measurement of one tape length of horizontal distance. 8. From the pin marking the end of one tape length measurement, the horizontal measurement is continued until point B is reached. The last partial tape length is measured with the rear tapeman holding the tape until he has a full meter (or foot) mark at his end while the head tapeman pulls the tape taut and takes note of the fractional measurement. Then the number of tape lengths and the last partial measurement are totalled to determine the horizontal length of the line measured.
Figure 1. An illustration of the breaking tape method in downhill measurement B. Measuring Downhill. 1. In measuring down the slope, the tape is reversed to bring its zero end forward in the direction of point A along the line. Horizontal measurement starts from B with the rear tapeman holding his terminal meter (or foot) mark of tape in level with B. 2. After the plumb bob of the head tapeman has been aligned with the range pole held at A, the head tapeman drops the plumb bob causing it to leave a mark on the ground. He then sticks a pin at the ground mark left by the plumb bob. 3. The next horizontal measurement starts from the pin until one whole tape length is measured. As in measuring up the slope, the number of tape lengths plus the partial tape length at the end of the line determines the total horizontal length of the line. 4. Tabulate observed and computed values accordingly. Refer to the accompanying sample format for the tabulation of data.
C. Computations: 1. The first discrepancy for the measurement is the difference between the first measurement and the second measurement.
Discrepancy=Measured Length AB−Measured Length BA 2. The mean length of the measured line is determined by adding the two measurements and dividing the sum by two. This is also known as the most probable value of the length of the line.
Mean Length=MVP=
Measured Length AB+ Measured Length BA 2
3. The relative precision (RP) of the measurement is determined by dividing the discrepancy by the mean length, where the numerator is reduced to unity or 1. Relative precision is expressed in fractional form and the denominator is rounded to the nearest hundredth. The acceptable precision should be at least 1/1,000. If this is not attained the measurement should be repeated.
RP=
Discrepancy Mean Length
Guide Questions: 1. What are the common sources of errors in taping using the breaking tape method and how would you lessen if not eliminate these errors? The common sources of errors in taping using the breaking tape method are incorrect tape length and sag. These errors can be lessen by detecting the corrections and applying it to the observed length. 2. How would you eliminate the effect of sag in taping a sloping ground? Sag shortens the horizontal distance between end graduations since the tape length remains the same. Thus, when a stretched tape sags, the actual distance between the points is something less than the reading on the tape. The correction due to sag is difference in length between the arc formed by the tape and the subtending chord. V.
Results and Discussion: table 1. Relative precision of a sloping and uneven ground. Trial Line Length Difference Mean 1 2
AB BA
131.61 m 131.58 m
0.03 m
131.595 m
Relative Precision 1/4387
Table 1 shows that the gathered data for line AB is précised because of its high precision value which is 1/4387. The most probable value or the most probable distance of line AB is 131.595 m, computed as what the computations stated. As the group who conducted this exercise follows the procedure, they realized into good and acceptable data. VI.
Conclusion and Recommendations:
VII.
Thus, following the respective procedures correctly and setting up the instruments properly to come up with an acceptable data. References: La Putt, J.P. (1985). Elementary Surveying Lab Manual. Baguio Research and Publishing Center. Baguio City, Philippines.
La Putt, J.P. (1987). Elementary Surveying. 3rd Edition. National Book Store. Philippines.
Remarks, Hints and Precautions 1. The procedure of breaking tape involves the measurement of short horizontal distances and accumulating these distances to total full tape length. This is done when a 30-m (or 100-ft) tape cannot be held horizontal without plumbing from above shoulder length.
2. Except for the use of a plumb bob, the process of taping over uneven and sloping ground is similar to taping over smooth and level ground. 3. It is important to determine if the tape is held nearly horizontal since it is the usual tendency to hold the downhill end of the tape too low. 4. A hand level should be used to check if the tape ends are held correctly so as to have a good horizontal measurement. 5. A firm stance is important during taping. The tapeman should position the plane of his body parallel to the tape, with his legs well apart. His forearm should be in line with the tape, and he should snub it against his body comfortably. 6. If a hand level is not available, the tape maybe estimated to be horizontal by eye. It is usually sufficient to compare the tape with some level line or have the two ends in line with the horizon. 7. The tape sags between supports when taking horizontal measurements over uneven and sloping ground thus making the tape shorter. To eliminate the effect of sag, the tape should be standardized, corrected for sag, or normal tension is used. 8. As a variation to breaking tape, the line may also be measured by short and segmented individual distances and these distances are added up to determine the total length. This practice, however, requires continuous recording of each partial length measured and may also lead to mistakes in addition. 9. The designated line should be measured in two trials, once uphill and once downhill. The ratio of discrepancy to length should be determined. The acceptable precision should be at least 1/1,000. If this is not attain the measurement should be repeated.
