Survey project report b. Nalei 18300164 PDF

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leveling to determine reduce level with respect to a datum ...

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The P Papua apua New Guinea Univ Univer er ersity sity of Tec echnology hnology Depar Department tment of Sur Surv veying & Land Studies Second Y Year ear Civil Engineering Semester Semester;; 1, 2019

1. Introduction. Levelling is a branch of surveying that deals with the determination of relative height with respect to the height of different points above the surface of the earth. In leveling all the measurements are taken with respect to a base point known as benchmark (the civil engineers’ magazine). The main purpose of levelling in surveying are to find the elevations of given points with respect to a given datum and to establish points at given elevations or different elevations with respect to the given or assumed datum. Before commencing any construction work, it is important that the land is made flat and that there is not much difference in its gradient. For this reason, leveling is carried out. The various methods of leveling include barometric leveling, trigonometric heighting, tachometry, photogrammetry, satellite geodesy and spirit leveling and the common levelling instruments include the spirit level, the dumpy level, the digital level, and the laser level. This report will describe levelling process which was carried out from a known bench mark (BM9X) at the fire hydrant near the security office to a new temporary bench mark (TBM) at Amphitheatre and back to BM9X to ensure the levelling applications are correctly done.

2. Aim: To perform right engineering Levelling Process in the field environment, office computations and report presentation.

3. Equipment     

1 x Automatic Level instrument 1 x staff 1 x stuff bubble 1 x 30m tape measure Cap nails



Field Book

4. Description of work:

The task of this survey project was to level from a known benchmark BM9X located at the top of the fire hydrant near the Unitech security post, to a new temporary bench mark (TBMX) located at the Unitech amphitheater and then back to the TBM9X. The project site if from the road at the security office to the amphitheater. The project involved 9 change points and three intermediate sights, two of which involved determining the slope of a drainage and the third involved an inverted reading to determine the height of a roof (bus stop like structure near the security post). Before commencing the actual project run, a two peg test was done to determine the collimation error of the levelling instruments so that there are no miscalculations when working on the actual project. All leveling operations have to be checked on completion of the project. the major checks in accuracy include arithmetic checks, checks on accuracy and the two peg test.

4.1 The arithmetic check At any set up the Rise or Fall is equal to the difference in successive staff readings taken at that setup. Hence for a run of levels between two points the algebraic sum of each should be equal. This is the bases of all the arithmetic checks possible (Mr. Popeu, 2019) Checks on accuracy

4.2 Check on accuracy Maximum permissible error = 0.005m√n where; n = number of instrument set ups = 0.005m√11 = 0.017m This check is done basically to determine the level misclose of the data obtained and to compare it with the expected level misclose to see if there are any errors.

4.3 Two Peg Test: All instruments are subjected to error. The checking of the levelling instrument is therefore important. The main error is where the line of sight is not parallel to the horizontal line of collimation. In this case your level would not be correct. A test for checking the level is known as

the two peg test. This test determines the amount of error and if an error occurs notify the technician. How we checked the level? On the ground, two points point A and B were marked approximately 60m apart with two pegs. The level was set up half way between the two points and carefully levelled. The staff was placed on peg B and a staff reading (S1) was taken then the staff was placed on A and a reading (S2) was taken. The staff reading at B was 1.269m and at A was 1.561m. The difference between the readings is 0.292 Then the level was moved 6m behind peg A and two staff readings were taken at A and B again. Reading at A is 1.761m and at B is 1.466m. STAGE 1 Backsight

Foresight 1.269m (S1)

Remarks Peg B Peg A

Foresight 1.466m (S3) 1.761m (S4)

Remarks Peg B Peg A

1.561m (S2)

STAGE 2 Backsight

(S1-S2) - (S3-S4) = (1.269-1.561) – (1.466-1.761) = -0.292 – (-0.295) = 0.003m

Collimation Error = 0.003 m per 60 m

4.4 level line Our level run involved 9 change points which were set out at 60 m apart and two intermediate sights, one taken at the first instrument setup. The other intermediate sight was taken at the fourth instrument setup. The first change point (CP1) was set out 60m away from BM9X towards the direction of the road leading to the amphitheater. The leveling machine was set up halfway between CP1 and BM9X then the staff was held vertically on top of the fire hydrant and a back sight reading was manually taken and recorded. This allowed the computation of the height of the instrument (HI) above the datum level. Then the staff was placed at an unknown point (CP1) and a reading was taken in the same manner allowing the elevation of the new (foresight) point to be computed. This process was repeated throughout the 9 change points until the end point of the project (temporary bench mark) was reached. Then a reverse run back to the starting point was done to minimize the error. In the reverse run, the back sights became the foresights and the foresights became the back sights. The same procedure was then repeated until the starting point (BM9X) was reached.

Data Collected from the Survey using Rise and Fall Method. Table 1.4.1 Data for both Forward and Reverse Run of the Survey

File No. S.S. ……….. Bearin g

Vert. Angl e

Survey of: levelling from BM9X to TBMX

Lower

Mean

Upper

B.S. 1.380

I.S.

F.S.

-1.130 1.332 1.149

Vert. Difference in distance height Rise

Survey by: BECV 2A Group____ Date: 25/03/19 Horiz. Reduce cod Distance d Level e

Fall 59.26 61.77 0.248 0.228 0.491

59.012 58.784 58.293

BM 9X Roof underside CP1 CP2 CP3

0.501

57.792 57.864

Crate CP4

0.581 0.317

57.238 56.966 57.021

CP5 BM45 CP6

2.51 1.628 1.560 1.690

Chain of Remarks

1.154 1.655 1.583 1.074 1.289 1.481 1.250

1.655 1.606 1.426

0.072

0.055

1.523 2.001 1.939 1.189 0.749 0.311 1.676 1.506

1.614 0.369 0.768 1.189 1.939 1.983 1.461 1.309 1.561

0.364 1.154 1.233 0.75 0.75 1.234 1.15 0.367 0.055

56.657 57.811 59.044 59.794 59.044 57.81 56.66 57.027 56.972

CP7 CP8 CP9 TBM CP9 CP8 CP7 CP6 BM45

57.292

CP5

57.869 57.817 57.301

CP4 Crate CP3 CP2

1.622 1.759 1.760

1.302

0.32

1.182

0.577

1.812 1.741 1.481

0.025 1.328 1.250

1.669

0.484 0.491

1.259

58.792 59.014 61.775

0.222 2.761

-1.092 1.442

ΣB . S 31.085

2.534

ΣF . S

Σ RISE

31.10 4

10.996

31.104 -0.019 Level Miss close = -0.019 m

Σ FALL 11.015

-59.26

-0.019

-0.019

∑BS - ∑FS = ∑Rise - ∑Fall = RL final point – RL initial point. 31.085 - 31.104 = 10.996 - 11.015 = 59.241 - 59.26 = - 0.019m

Gradient of the drain =

rise run

0.005 √11 = ± 0.017

=

R Lf − R 59.241

-11.015

Arithmetic checks for both Forward and Reverse Run

Expected level miss-close =

59.241

1.655 60

= 0.0276m

CP1 Roof underside BM 9X

Roof height = 1.628 – (-1.130) = 2.758m Reduced level of temporary bench mark (TBM) = 59.794m Description of the tabulated data The difference in staff readings of two points from the same instrument station represents the difference in RL’s between two consecutive points. Hence, the difference in elevation = back sight – foresight. A positive answer indicates a Rise, while a negative answer indicates a Fall For example, the back sight to BM9X is 1.390m, which means that the horizontal line of sight defined by the level is 1.390m below the instrument height. Similarly, a foresight to CP1 = 1.628m meaning that CP1 is 1.628m below the instrument height. Hence, the difference in elevation between BM9X and CP1 is 1.390 – 1.628 = - 0.248m which indicates a fall. Basically the difference in RL's between two consecutive points is computed directly as the difference in staff readings to those points from the same instrument stationing in which height of instrument is not computed. Therefore, the same procedure is repeated until a reduced level for the final point (TBM) is derived.

5. DISCUSSION: The purpose of this project was to accurately define the boundaries above and below the ground. Leveling is done to make the field even so that the field area being surveyed is perfectly horizontal to the bare eye. For the actual survey (the forward and reverse run) the calculated miss – close was about 0.019 which is a bit over the expected level miss-close. As can be seen in the recorded bookings of the reduced level, the level line seems to decrease from CP1 to BM45 then it increases from there to the temporary bench mark (TBM). The reduced level for the temporary bench mark was determined to be 0.534m below BM9X where the project began. The gradient of the drain was determined to be 0.028m above ground level. The errors encountered in the project were mainly from the project readings and bookkeeping, including transposing of digits, forgetting a book entry, entering in the wrong column and parallax reading

error. These errors may have caused the calculated level miss-close to be slightly above the expected level miss-close.

6. CONCLUSION: To conclude we have successfully completed our objective of determining the height difference between the temporary bench mark (TBM) at the amphitheater and bench mark 9 (BM9X) located at the top of the fire hydrant near the security office. Having done the project, we are now quite confident that we can handle surveying equipment’s out in the field and take accurate readings to measure difference in elevations between two points.

REFERENCE: - Popeu. M. (2018). Surveying for Engineers I; Level and Levelling Lecture Notes, Department of Surveying and Land Studies, Papua New Guinea University of Technology, PNG. - http: //readcivil.com/leveling-objectives-and-methods/...