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 InstrumentsMain parts of levelling instruments:1. Binocular2. Bubbles (alidade)3. Base (tribrachs)

1. Binocular.Every level is equipped with astronomic binocular with Huygens or Ramsdens eye piece with the very high luminance lens. The usual magnification is 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 LevelVertical 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 LevellingProfile 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 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 MethodSecond Reading less than the first = RISE

Second reading greater than the first = FALL

Height of Collimation Method (HOC)

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 Level2. Tripod3. Levelling Staff4. Bubble level5. Measurement tape

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.

DATA ACQUISITION

RISE AND FALL

BSISFSRISEFALLRL (m)Distance (m)Remarks

1.292100.0000BM1 100.000

1.7770.48599.51525

1.3632.5540.77798.73850CP1

2.0600.69798.04175

2.4592.6530.59397.448100CP2

1.7780.68198.129125

1.1020.67698.805150

1.4380.3680.73499.539175CP3

1.0010.43799.976200BM1 100.000

=6.552=6.576=2.528=2.552

HEIGHT OF COLLIMATION (HOC)

BSISFSHOCRL (m)Distance (m)Remarks

1.292101.292100.0000BM1 100.000

1.77799.51525

1.3632.554100.10198.73850CP1

2.06098.04175

2.4592.65399.90797.448100CP2

1.77898.129125

1.10298.805150

1.4380.368100.97799.539175CP3

1.00199.976200BM1 100.000

=6.552=6.576

ANALYSIS

RISE AND FALL

RISEFALLRL (m)CORRECTIONFRL (m)Distance (m)Remarks

100.0000100.0000BM1 100.000

0.48599.5150.00699.52125

0.77798.7380.00698.74450CP1

0.69798.0410.01298.05375

0.59397.4480.01297.460100CP2

0.68198.1290.01898.147125

0.67698.8050.01898.823150

0.73499.5390.01899.557175CP3

0.43799.9760.024100.000200BM1 100.000

HEIGHT OF COLLIMATION (HOC)

RISEFALLRL (m)CORRECTIONFRL (m)Distance (m)Remarks

100.0000100.0000BM1 100.000

0.44599.5150.00699.52125

0.77798.7380.00698.74450CP1

0.69798.0410.01298.05375

0.59397.4480.01297.460100CP2

0.68198.1290.01898.147125

0.67698.8050.01898.823150

0.73499.5390.01899.557175CP3

0.43799.9760.024100.000200BM1 100.000

DISCUSSION

At first there was aslight difference between the final RL and theinitial RL, this is due tosome errors like parallax error or the unevenground which the equipment is set up on. After that, in order toright the wrong, first we had todo the checking by finding the difference between the total value ofbacksight and the total value of foresight, difference between the total value of riseand fall and the difference between the final RL and theinitial RL. If the checking is allthe same, then we hadto find the misclosure by deducting the actual RL and themeasured RL. The next step is todistribute the error by the number of setups.

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 oni.The magnification and image clarity afforded by the telescopeii.The manner in which staff is markediii.The length of sight

b.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 engineers 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 MethodThe 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 RLVisualization 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.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 RLUsed 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.Anchor tripod legs firmlyb.Check the bubble level before and after readingc.Take as little time as possible between BS and FS equald.Try to keep distance to BS and FS equale.Provide the rod person with a level for the rod

CONCLUSION

Leveling is to determine the difference in height between twopoints in an area. The main purpose of leveling is todesign the highways, railroad, sewers, water supply system and provides grade lineson theexisting topography. Besides, leveling can also layout 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 inconstruction sites. Leveling is an inexpensive, simple and accurate methodfor 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 thats one of the factors to achieve the objective of these experiments.

APPENDIX

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