Levelling report

INTRODUCTION

The traditional methods of conducting laboratory activities (assigned as Level 0) will not be able to provide the avenue for students to enhance independent learning activities and inculcate creativity and innovation. The traditional method is fully prescriptive where the three elements namely problem, ways & means and answers are guided/fully given to the students. However, it is still necessary to be implemented as part of the whole laboratory course activity especially to first and second year students. In these laboratory activities, reduced level will be obtained at every specific point to produce ground profile. The ground profile can be used to provide information for the purpose of construction design, cut and fill, landscape and site investigation.

OBJECTTIVE The objective of this laboratory is obtain and determining level profile for an existing site location by levelling.

THEORITICAL BACKGROUND Concept of Levelling Instruments Main parts of levelling instruments: 1. Binocular 2. Bubbles (alidade) 3. Base (tribrachs) 1. Binocular. Every level is equipped with astronomic binocular with Huygen’s or Ramsden’s eye piece with the very high luminance lens. The usual magnification is 1

50x, newer versions are constructed with an inside optical focus which secures the focus on the backside. Crosshairs are placed into binoculars are usually engraved into glass plate and they come in many various shapes. Parallax of crosshair (movement of crosshair in regards to picture due to the eye movement) happens when the sight of crosshair is not the same as the sight of the binocular. This can be eliminated by focusing the level rod and focusing of the crosshair. 2. Bubbles (alidade) For the rough level of the instrument, circular bubbles are usually used. For more precise instruments or applications, pipe bubbles are used (usually with the 1-2 mm precision). More precise instrument, the pipe bubbles are connected with binocular. For the very precise levelling, the split bubble is used. Ends of the bubble are shown in the sight of the binocular through prism system. Sensibility of bubbles: (a) Centre angle alpha equals one part d=1 or d=2 mm which is indicated on the bubble itself. (b) By radius of the cut of bubble 3. Base (tribrachs) Most common is the tribrach with a set of three levelling screws. This tribrach can be connected with tripod. The horizontal movement is done by horizontal circle which can be fine-tuned via fine screw. Flying Level Vertical distances of various points are measured with respect to the given datum and relative differences in elevation between the points determined. A horizontal line of sight of any point is measured using a vertical staff as shown in Figure 1. From the measurement of vertical heights, therefore the reduced level of the points can be obtained using; Rise and Fall Method or Height of Collimation Method (HOC). Profile Levelling Profile levelling is also known as longitudinal levelling and the objective of this levelling is to determine the profile of the ground surface of the predetermined 2

line, which may be single straight line or may consists of a series of straight lines changing a direction or connected to a curve. The point established on the predetermined line at measured intervals is obtained from the staff readings shown in Figure 2(a) and 2(b). From the measurement of vertical heights, therefore the reduced level of the points can be obtained by using Rise and Fall Method or Height of Collimation Method (HOC).

Rise and Fall Method Second Reading less than the first = RISE

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Second reading greater than the first = FALL

Height of Collimation Method (HOC)

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PROBLEM STATEMENT An existing road alignment is to be scraped and levelled to a proposed reduced level. The chainage interval for the existing road alignment is at every 25 m interval and the existing level have to be determined by using profile levelling method by assuming assumed Benchmark (BM) level given at UiTM Pasir Gudang having RL 100.00 m. The road alignment and CP must be sketched to show the alignment of the road.

APPARATUS 1. Auto Level 2. Tripod 3. Levelling Staff 4. Bubble level 5. Measurement tape

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PROCEDURE 1. First staff is sited on the Benchmark (BM) having RL 100.00 m. The level points are then sited at intervals of 25 m each. 2. The instrument is then positioned and temporarily at a point where every levelling point can be observed. For first staff, the reading is recorded as back-sight and then the readings of other staff positioned are noted as intermediate-sight until the last point where the instrument is then shifted to another point. This point is known as change point (CP). Within the 25 m interval, the distance between intermediate points given is 5 m. 3. The instrument is then shifted to the next point and temporarily adjusted but staff noted as fore sight from the previous reading is not shifted and the reading is recorded as back sight. Step (2) is the repeated. 4. Steps (2) and (3) are repeated until the chainage point is at 200.00 m from the BM.

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DATA ACQUISITION RISE AND FALL

BS

IS

FS

RISE

FALL

1.292 1.777 1.363

0.485 0.777 0.697 0.593

2.554 2.060

2.459

2.653 1.778 1.102

∑=6.55

0.368 1.001 ∑=6.57

0.681 0.676 0.734 0.437 ∑=2.52

∑=2.55

2

6

8

2

1.438

RL (m) 100.000 99.515 98.738 98.041 97.448 98.129 98.805 99.539 99.976

Distanc e (m) 0 25 50 75 100 125 150 175 200

Arithmetic ˇ; ∑ BS−∑ FS=∑ RISE−∑ FALL=RL n−RL 1 ST 6.552 m−6.576 m=2.528 m−2.552 m=99.976 m−100.000 m −0.024 m=−0.024 m=−0.024 m

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Remarks BM1 100.000 CP1 CP2 CP3 BM1 100.000

HEIGHT OF COLLIMATION (HOC)

BS

IS

FS

1.292

HOC

RL (m)

101.292

100.000 99.515 98.738 98.041 97.448 98.129 98.805 99.539 99.976

1.777 1.363

2.554

100.101

2.653

99.907

0.368 1.001 ∑=6.576

100.977

2.060 2.459 1.778 1.102 1.438 ∑=6.552

Distance

Arithmetic ˇ; ∑ BS−∑ FS=RL n−RL1 ST 6.552 m−6.576 m=99.976 m−100.000 m

−0.024 m=−0.024 m

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(m) 0 25 50 75 100 125 150 175 200

Remarks BM1 100.000 CP1 CP2 CP3 BM1 100.000

ANALYSIS RISE AND FALL

RISE

FALL

Distance

RL (m)

CORRECTION

FRL (m)

100.000

0

100.000

0

0.485

99.515

0.006

99.521

25

0.777

98.738

0.006

98.744

50

0.697

98.041

0.012

98.053

75

0.593

97.448

0.012

97.460

100

0.681

98.129

0.018

98.147

125

0.676

98.805

0.018

98.823

150

0.734

99.539

0.018

99.557

175

CP3

0.437

99.976

0.024

100.000

200

BM1 100.000

Different of BM 1 100.000−99.976= ¿ 0.006

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(m)

0.024 4

Remarks

BM1 100.000

CP1

CP2

HEIGHT OF COLLIMATION (HOC)

RISE

FALL

Distance

RL (m)

CORRECTION

FRL (m)

100.000

0

100.000

0

0.445

99.515

0.006

99.521

25

0.777

98.738

0.006

98.744

50

0.697

98.041

0.012

98.053

75

0.593

97.448

0.012

97.460

100

0.681

98.129

0.018

98.147

125

0.676

98.805

0.018

98.823

150

0.734

99.539

0.018

99.557

175

CP3

0.437

99.976

0.024

100.000

200

BM1 100.000

Different of BM 1 100.000−99.976= ¿ 0.006

10

(m)

0.024 4

Remarks

BM1 100.000

CP1

CP2

DISCUSSION At first there was a slight difference between the final RL and the initial RL, this is due to some errors like parallax error or the uneven ground which the equipment is set up on. After that, in order to right the wrong, first we had to do the checking by finding the difference between the total value of backsight and the total value of foresight, difference between the total value of rise and fall and the difference between the final RL and the initial RL. If the checking is all the same, then we had to find the misclosure by deducting the actual RL and the measured RL. The next step is to distribute the error by the number of set ups. The observation data that we got from this experiment has shown in the data sheet above. The errors was been checked and after that there was no single error was suspected during the fieldwork. Factors affecting the accuracy in levelling are: a.

Reading of staff.

These errors depends on i. ii. iii. b.

The magnification and image clarity afforded by the telescope The manner in which staff is marked The length of sight

Bubble displacement.

The bubble centring accuracy depends on the method used to view the bubble. The uncertainty caused by bubble mislevelment in tilting level is comfortable to the uncertainty due to mislevelment of the compensator in automatic instruments. The accuracy of the engineer’s level is in range of ±1.5’’ to ±0.5’’ with more precise instrument capable of being set horizontal to ±0.2’’ In this experiment, we have used 2 methods (rise & fall and HPC) Rise and Fall Method • The levels are recorded in the level book and arithmetic check involved in the reduced level are as follows; ∑BS-∑FS=∑(rise)-∑(fall)=last RL-first RL • Visualization is necessary regarding the nature of the ground. • Reduction of levels takes more time. • Preferable for check levelling where number of change points are more.

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• By following the step above, we have ensure that there are no error in calculation in rise & fall method Height of Collimation Method (HOC) • The arithmetical checks applied are as follows; ∑BS-∑FS=last RL-first RL • Used where more number of readings can be taken with less number of change points for constructional work and profile levelling. • It also no error in calculation this method because it is easier compared to rise & fall method. To make sure the levelling is good and accurate; a. b. c. d. e.

Anchor tripod legs firmly Check the bubble level before and after reading Take as little time as possible between BS and FS equal Try to keep distance to BS and FS equal Provide the rod person with a level for the rod

CONCLUSION Leveling is to determine the difference in height between two points in an area. The main purpose of leveling is to design the highways, railroad, sewers, water supply system and provides grade lines on the existing topography. Besides, leveling can also lay out the construction projects according to the planned elevations and enables to calculate the volume of earthworks. Leveling requires equipment such as leveling staff, tripod, auto level meter, staff bubble and measuring tape. Leveling method is now widely used in construction sites. Leveling is an inexpensive, simple and accurate method for measuring height. Besides construction site, leveling are also used for measurements of rivers or lake. From the experiment, we can conclude that the test been done successfully. The result obtained is acceptable. We have done two different methods in order to finish up our experiment which is ‘Rise & Fall Method’ and ‘Height of Collimation Method’. In ‘Rise & Fall Method’, once we do the arithmetic checking, we get the same value which is –0.024 while in ‘Height of Collimation Method’, we get an arithmetic checking value which is -0.024 the checking is to ensure that the reduced level is true and there is no error in reading. Furthermore, great teamwork was occurred during running this experiments and that’s one of the factors to achieve the objective of these experiments. 12

APPENDIX

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