GE 11 LAB EXERCISE #2 DIFFERENTIAL LEVELING
Submitted to: Mr. Jeark Principe Submitted by: Ace Cantillep Troy Cabalza Gie Cadelina Rex Carranza Fzaira Cerrero Nobee Codamon
Differential Leveling August 18 & 25, 2012 Weather condition: Sunny and humid
I.
Objectives:
Properly execute field procedures for differential leveling operation
Strategically establish turning points to eliminate errors due to earth’s curvature and
II.
atmospheric refraction Check leveling accuracy for third-order vertical con trol establishment Apply arithmetic checks for observations in a leveling survey Establish elevations of control points from a known bench mark Properly document a leveling survey
Group Compositions
• CANTILLEP, Ace – rod man 1, sighter 2 • CERRERO, Fzaira – rod man 2 • CABALZA, Troy – rod man 3 • CARRANZA, Rex – sighter 3, pacer • CODAMON, Nobee – Recorder 2 • CADELIÑA, Gie – Recorder 1, sighter 1 III.
Instruments and Accessories used
IV.
1 NI2 Automatic level 2 leveling rods 1 tripod Station marker: paint, stake, hub, or nails
Procedures
1. Conduct a rough reconnaissance of the area for your leveling survey. Check which route is assigned to your group:
Groups 1,3,5: BM1→NEC→ECON→LAW→ACAD OVAL→BM1 Groups 2,4,6: BM1→ACAD OVAL→LAW→ECON→NEC→BM1
2. Setup and level the instrument at a convenient location between BM1 and your first turning point (TP1). Ensure that the BS and F S distances (max of 50m) are almost equal by estimating these distances through pacing.
3. Sight the rod at BM1 and record the middle reading at the backsight (BS). Refer to table 4.1 for a sample of leveling survey notes. Record also the two othe r thread readings (upper and lower). Quickly compute for the BS distance. 4. Sight the rod at TP1 and record the middle reading as foresight (FS). Record al so the two other thread readings (upper and lower). Quickly compute for the FS distance. 5. Compare the two distances (FS and BS), the difference of which should not exceed 2m. Otherwise, you may adjust your FS point to fulfill this requirement.
Note that the upper and lower readings as well as the computed BS and FS readings are not required in the differential-leveling notes (Table 2.1 ) but must be included in your report as supplementary data.
Levels for Bench Marks in UP Diliman Sta. B.S. H.I. F.S. BM1 0.99 37.206 TP1 2.455 38.611 1.05 TP2 2.00 40.179 0.432 Law 2.01 39.639 2.55 Econ 0.86 39.879 0.62 TP3 0.58 38.264 2.195 TP4 0.28 36.154 2.39 BM1 1.90 BS = FS = 9.175 11.137
Elev. 36.216 36.156 38.179 37.629 39.019 37.684 35.874 34.254
Top Hydrant on the East Wing of Melchor Hall
Elev. In meters above MSL
Control point along the UP Academic Oval Control point along the UP Academic Oval
H.I. = B.S. + Elev BM Elev = H.I. – F.S.
BM1 H.I. = 36.216 + 0.99 = 37.206 TP1 Elev = 37.206 – 1.05 = 36.156 HI = 36.156 + 2.455 = 38.611
TP2 Elev = 38.611 – 0.432 = 38.179 HI = 38.179 + 2.00 = 40.179 LAW Elev = 40.179 – 2.55 = 37.629 HI = 37.629 + 2.01 = 39.639
ECON Elev = 39.639 – 0.62 = 39.019 HI = 39.019 + 0.86 = 38.879
TP4 Elev = 38.264 – 2.39 = 35.874 HI = 35.874 + 0.28 = 36.154
TP3 Elev = 39.879 – 2.195 = 37.684 HI = 37.684 + 0.58 = 38.264
BM1 Elev = 36.154 – 1.9 = 34.254
Corrections:
E = Elevobserved - Elevtheoretical = 34.254 – 36.216 = -1.962 L = 21 + 22 + 39 + 39 +30 +30 +24 + 26 + 26 + 27 + 40 + 40 + 47 + 46 = 457 m = 0.457 km Point
Dist. from BM1 (km) 0.000 0.043 0.121 0.181 0.231 0.284 0.364
BM1 TP1 TP2 LAW ECON TP3 TP4 BM1
Obs. Elev. (m)
Correction (m )
Adj. Elev. (m)
36.216 36.516 38.179 37.629 39.019 37.684 35.874 34.254
0.0000 +0.1846 +0.5195 +0.7770 +0.9917 +1.2193 +1.5627 +1.9620
36.341 38.699 38.406 40.011 39.903 37.437 36.214
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6. Transfer the instrument at a convenient location along the leveling route assigned to your group. Setup and level the instrument and backsight TP1. Repeat step 3 for backsight observation. 7. Establish another station (TP2) as your second turning point. Repeat step 4 for foresight observations. 8. Repeat step 5 for a check on BS and FS distances. 9. Repeat steps 2 to 5 until a foresight reading is taken on BM1. 10. Complete your field notes with the value of H.I. per setup and elevations for each station. Use the following equations: H.I. = Elev. + B.S. Elev. = H.I.- F.S. 11. Provide also the necessary arithmetic check on the bottom of your field notebook: ARITHMETIC CHECK:
ElevBM1 + ƩB.S. – ƩF.S. = ElevBMfinal 36.216 + 9.175 – 11.137 = 34.254
12. Check if your level-loop closure ( ) is within third-order accuracy standard for vertical controls: Maximum closure= 12mm√ Where K is the level distance of the route in kilometers
( ) = (9.175 – 11.137) = -1.962 mm√ = ~8.11
V.
Graphical Representation
VI.
Results and Conclusion
Results: The activity aims to determine the elevation of a pre-set route by properly executing field procedures for differential levelling operation using an automatic level. The students must exercise the use of right strategic judgment in placing turning points in order to eliminate errors
due to the earth’s curvature and atmospheric refraction. In order to be consistent, the students only used one person as a pacer to avoid or minimize mistakes. The bench mark used in the levelling exercise is the fire hydrant near the corner of Apacible street and Osmeña Avenue. It has a known elevation of 36.216 meters. The initial data (in meters) for TP 1, TP 2, Law, Econ, TP 3, TP 4, and BM 1 are 36.156, 38.179, 37.629, 39.019, 37.684, 35.874, and 34.254 respectively. Note that the known elevation of BM 1 is not equal to the elevation the students got. The students then adjusted the elevation by computing the needed corrections. The students got that the correction in elevations in TP 1, TP 2, Law, Econ, TP 3, TP 4, and BM 1 are +0.1846, +0.5195, +0.7770, +0.9917, +1.2193, +1.5627, +1.962 respectively, thus making the final adjusted elevations 36.3406, 38.6985, 38.4061, 40.0107, 38.9033, 37.4367, 36.214. The known elevation is now equal to the final adjusted elevation. Conclusion: The elevation of a point can be determined by using an automatic level, a stadia rod and a bench mark. A bench mark is a point where the elevation is known. To get the elevation, first you need to sight the benchmark using the level and a stadia rod on that point. The middle reading is the backsight reading. You then need to add the backsight reading and the elevation of the benchmark to get the height of the instrument. Next, you need to get the foresight reading by sighting the unknown point. The middle reading is the foresight reading. To get the elevation of the unknown, you need to subtract the foresight reading to the height of the instrument you got. After the traverse, you may notice that the kn own benchmark reading is not equal to the benchmark reading you got. This is mainly due to many errors that could have happened in the exercise. The longer the traverse, the larger the error may be. This is because no measurement is perfect. Every measurement is prone to error, especially if you don’t know the right procedures. In the end, no matter how high tech the instrument may be, the precision of the instrument still depends on the skill and knowledge of the person using it.
