1

II. INTRODUCTION

Leveling in which a continuous check is maintained on the accuracy of the leveling

procedure. It is called double rodding because it can be done most conveniently by two

rodmen. However, it is possible to carry out the procedure using only one rodman. In

double rodding, you determine the HI at each setup point by backlights taken on two

different TPs. If no mistake or large error has been made, the result will be two HIs that differ

slightly from each other. Elevations computed this way will also differ slightly. In each case,

the average is taken as the elevation.

2

III. OBJECTIVES AND INSTRUMENTS

OBJECTIVES

1. To develop skills in determining the difference in elevation between two points

without the need of returning the circuit to the original point of reference by using

two observation points every time BS and FS are taken.

2. To master the art of using the precise level during fieldwork.

3. To acquire the confidence of working with one’s party or group and to be fully

responsible in the performance of the assigned task.

INSTRUMENTS

1. Precise level 2. Chalk

- An instrument similar to an ordinary - A soft compact calcite with

surveyor's level but capable of finer varying amounts of silica, quartz,

readings and including a prism arrangement feldspar, or other mineral impurities,

that permits simultaneous observation generally gray-white or yellow-white

of the rod and the leveling bubble. and derived chiefly from fossil

3. Leveling Rod 4. Plumb bobs

- used with a levelling instrument to - is a weight, usually with a pointed tip

determine the difference in height on the bottom, which is suspended

between points or heights of points above from a string and used as a vertical

a datum surface. reference line

3

IV. PROCEDURE & COMPUTATIONS

A. Determination of the difference in elevation between two points, which are at a

considerable distance from each other

1. The professor designates the locations of two benchmarks BM-1 and BM-2, which is

about 300m to 500m away from each other and of considerable difference in elevation.

2. Setup the level on a suitable location and take the BS of BM-1 (point of known elevation)

while the rod man is holding the level exactly at BM-1. Compute the height of the

instrument by using the formula: HI = Elevation of the point + BS.

3. The rod man now transfers to another location, preferably the same distance of the BM-1

to the instrument as the distance of the first turning points (namely TP1L and TP1H) to the

instrument.

4. The rod man must mark two points on this location and call them TP1L and TP1H with a

chalk or marking pins. Preferably, these two points must be of considerable difference in

elevation but quite near each other.

5. The instrument must take two FS’s one on each TP1L and TP1H and record the readings

on the computation sheet provided for in this fieldwork.

6. Compute the elevations of these TP1L and TP1H using the formula: Elevation of TP1L =

HI – FS of TP1L and Elevation of TP1H = HI – FS of TP1H. Record the results in the

computation sheet.

7. The instrument man must now transfer the level pass of the two TP1 and along the route

to BM-2.

8. After leveling the instrument firmly, two BS’s must be taken one on each TP1L and

TP2H. Record these readings.

9. Compute the new height of the instrument on its current location by basing it from the

two turning points. Use these formulas: HI = Elevation of the TP1L + BS of TP1L and HI

= Elevation of the TP1H + BS of TP1H. These two computed values of HI must be very

near each other.

10. Again the rod man transfers to another location, along the same route preferably the same

distance of the instrument from TP1’s, and should now call them TP2’s.

11. The instrument man gets two FS’s one on each TP2L and TP2H and record these rod

readings on the computation sheet.

4

12. Compute the elevations of these TP2L and TP2H using the same previous formulas.

13. These steps must be followed closely until the leveling work will reach BM-2. Two

foresights will be recorded for BM-2 and two independent elevations of BM-2 will be

computed. However, these elevations of BM-2 must be very near each other. The mean

of the two elevations will be considered the most probable elevation of BM-2.

COMPUTATION:

The computation of sample field notes is done in accordance with the steps listed hereunder:

A. Computation of the height of the instrument

The height of the instrument is always equal to the elevation of the point where the back

sight is being observed plus the elevation of the point itself.

B. Computation of the height of the instrument

The elevation of the turning point is always equal to the height of the instrument minus the

foresight of the TP being observed.

C. Computation of the most probable elevation of BM2

The most probable elevation of BM-2 is the mean elevation of BM-2 between the computed

values from the last turning points low and high.

Most Probable Elevation of BM – 2 = Mean Elev. Of BM – 2

Mean.elev.BM – 2 = ELEV.BL−2.fr.TPlastLow+Elev.BL−2 .fr.TPlastHigh

2

HI = Elevation of the point + BS

Elevation TP1 = HI - FS

5

VIII. RESEARCH AND DISCUSSION

This fieldwork is all about differential leveling, the same as the previous fieldwork. But

the difference between these two fieldworks is the measurement of backsight and foresight. In the

previous fieldwork, we measured the backsight and proceed to the other point to measure the

foresight.

Double rodded leveling is a method of determining the differences in elevation between

points by employing two level routes simultaneously. Two turning points are established such that

at each set up of the leveling instrument, two sets of independent back sights and foresights are

taken.

But in this fieldwork, we measured the backsight and its left and right location with the

same distance of the actual backsight. We did the same thing for the foresight. But when it comes

to computation, we did the same thing as of the previous fieldwork. We computed for the height

of the instrument as the sum of the elevation and the backsight after we measured for the backsight.

Then we computed for the elevation by finding the difference of height of the instrument and the

foresight after we measured for the foresight. For us to find the backsight and foresight, we should

compute for the average of two backsights and two foresights, each in left and right. This is the

illustration of what we did for the double-rodded differential leveling.

6

IX. CONCLUSION

In this fieldwork, we had a differential leveling with turning points. But this time, it is

double rodded. This means that we find the backsight and foresight not directly in their actual

point, but to their left and right. The distance is 2 meters each from the actual point of backsight

and foresight. So, the average of the left and right backsight will be the measurement for our

backsight, and the same for foresight. But the rest of the procedure is almost the same as of the

previous fieldwork.

Base on the result of our fieldwork, the elevation is close to each other, even though they

are different to each other. It is normal that they are different because the land that we measured

for the elevation is not that straight, which means that the elevation is not constant. This means

that we come up for a good result in this fieldwork.

The possible source of error is the inaccuracy of the measurement of the user. The setup of

the points in the field can be another source of error. The points must be followed closely until the

leveling work will reach BM-2. In the process error due to measurement are made.

For this fieldwork, I recommend to learn the value of patience because there are multiple

measurements that you will do in this fieldwork. You should be accurate in measurements by using

the equipment in the correct way and be careful on what you measure. I recommend to strictly

follow the procedures and accurately check the measurement in the leveling rod. Always make

sure that the bubble is in the center. Because if not, it can lead to an error in results. This is one of

the common human error that we commit. And most of all, you should have a teamwork with your

groupmates by assigning different tasks in every members of the group so that you can easily finish

the fieldwork in a few possible time and for you to come up with a good result.

Application:

The field work can be applied for running long lines of levels on routes where no

established benchmarks are available for checking. In the industry when there is no established

benchmarks and there is an urgent need to undertake differential leveling in a short period of time.

7

FINAL DATA SHEET

FIELD WORK 3 TAPING ON SLOPING GROUND

DATE: 10/27/15 GROUP NO.: 4

TIME: 8:00-10:00AM LOCATION: Intramuros Walls

WEATHER: Cloudy PROFESSOR: Engr. Balmoris

A. PROFILE LEVELING

B. COMPUTATION

HI = ELEV + BS ELEV = HI − FS

= 100 + 0.73 = 100.73 − 0.8125

= 100.73 𝑚 = 99.905 𝑚

BENCHMARK

NO.

BS

(m)

HI

(m)

FS

(m)

ELEVATION

(m) REMARKS

BM 1 0.73 100.73 100

TP1L 1.425 101.43 0.8125 99.905

TP1H 0.706 101.026 1.526 100.32

TP2L 1.425 101.33 1.435 99.905

TP2H 0.40 101.016 0.41 100.616

TP3L 1.4325 101.3465 1.416 99.914

TP3H 0.74 101.031 0.725 100.291

TP4L 1.425 101.334 1.4375 99.909

TP4H 0.4125 101.031 0.4125 100.6185

TP5L 1.45 101.3465 1.4075 99.8965

TP5H 0.68 100.956 0.755 100.276

BM − 2L 1.35 99.9965

BM − 2H 1.35 99.606

8

Sketch:

Determination of the backsight and foresight of the Turning Points, TP1H and TP1L

Determining the backsight of BM1

9