FACULTY OF CIVIL ENGINEERING & EARTH RESOURCES ENGINEERING SURVEY FIELDWORK. LEVELING (Standard Of Procedure)

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1 FACULTY OF CIVIL ENGINEERING & EARTH RESOURCES ENGINEERING SURVEY FIELDWORK LEVELING (Standard Of Procedure) Subject Code Date Group Number Student Name & ID Number Group Member Name & ID Number 1 2 Lecturer Marks Remarks Endorsement

2 Objective: 1. To make close fly-leveling survey (vertical control) from TBM to site location. 2. To determine reduce level for Sation1 of group planimetric control. Scope of works: 1. Each group shall be carried out on a vertical control within the allocated area employ all normal survey practice to control the accuracy of the survey works. 2. The accuracy of the survey shall be (±0.02(K) meter, where K is in kilometers. 3. Each group shall be prepared a report of had been done (Appendix III). The report shall be submitted one week after completed the fieldwork. List of Devices: 1. 1 set of Leveling Instrument completed with accessories set of Staff completed with accessories. 3. Fieldbook. Procedure of works: 1. Conducting a survey (Appendix I & II). Distance from leveling instrument to backsight staff and to foresight staff shall be same as possible. 2. Recording the survey (Appendix I). Staff reading must be recorded in permanent ink in the appropriate columns of the observation pages immediately after they are made.

3 Appendix I FLY LEVELING Introduction: Linear surveying such as traverse survey, representing the earth s features in two dimensions on plan. To be practical value, however, the third dimension, namely the height of the feature, must be shown by some means on the plan. The heights (Reduced level or elevation) of the points are referred to some horizontal plane of reference called the datum (universally employed Mean sea level). In surveying, these heights are found by leveling. Leveling is the procedure used when one is determining differences in elevation between points that are remote from each other. Leveling Terminology: Elevation (Reduce level): the vertical distance from a vertical datum Vertical datum: any level surface to which elevations are referred (i.e. mean sea level) Mean Sea Level (MSL): the average height of the sea s surface for all stages of the tide over a 19-year period. Temporary Bench Mark (TBM) : is a semipermanent point of known elevation. Bench Mark (BM) : is a permanent point of known elevation. The elevation determine by JUPEM Backsight (BS) : is a rod reading taken on a point of known. Intermediate sight (IS) : is a rod reading taken at any other point where the elevation is required. Foresight (FS) : is a rod reading taken on a turning point, bench mark or TBM in order to determine its elevation. Differential Leveling: The above figure shows a peg A situated beside a manhole cover at the bottom of a fairly steep slope. The height of the peg A is known to be m above datum (MSL), having already been surveyed from a nearby BM. The known height of peg A is called the reduced level (RL) of A; i.e. RL A = m AOD The peg A need not have a known height relative to datum (MSL), in which case it

4 would be assigned an arbitrary level of, say, m 0r m above an assumed datum. The reduced level of A would therefore be written as RL A = m AD The reduced level of peg B, at the top of the slope, is required. The level is set up approximately midway between the points, accurately leveled, a first reading is taken to a staff held vertically on A. Let the reading be 2.500m. The staff is then transferred to B, held vertically on the station and then and a second reading taken. Let this reading be 0.500m. From the sketch it is obvious that point B is higher than A by = m. In other words, the ground rises from A to B by m. In this example, if the height of the ground at A is m above datum, the height of the ground at B above datum can be readily deduced. Since the ground rises by 2.000m from A to B, point B must lie = m above datum. BS IS FS Rise Fall RL Remarks A. Peg level B. Peg level Fly Leveling: In figure, some of difficulties are present, so a set-up position has to be chosen from which the BM mark is visible. The instrument is set-up at (1) and BS is taken to the BM (RL 35.27m), followed by sights to as many other points as possible or desirable. In this case only the points A, B, C and D are visible from the instrument. IS are taken to points A, B and C, and FS taken to the final point D. The readings are entered in the field book and point D is noted as change point (CP). It is now possible, though not usual in practice, to reduce the levels in exactly the same manner as before. The fieldwork and associated calculations finished on point D, which is a change point. The second series of readings must therefore begin on point D which in effect has become a temporary bench mark. The instrument is removed to instrument set-up point 2 and a BS taken to the point D. It is entered in the field book, in the BS column on line D. Thus there are two field readings on the same line since they were taken to the same station, i.e. point D. The levelling is continued with another series of readings taken to any further accessible points. These are IS to E and F and FS to G, which becomes the second CP. These results are calculated and entered in the field book. The RL E, F and G are calculated from CP D. The instrument is removed to set up point 3 and the third series of levels is taken. From this position only the points G and H can be seen. Point G is a BS. The reading is entered in the field book in the BS column, on line G. Point H is a FS and is the next CP. The relevant calculations to obtain the RL of H, shown in table.

5 From instrument position 4, the fourth series of levels is observed, beginning with BS to H and finishing with FS to the BM. The observations and relevant results are shown in table. BS IS FS Rise Fall Reduced Level Remarks BM A. Manhole B. Fence C. Corner of building D. Corner of building [Change Point 1] E. Fence F. Fence G. Corner of building [Change Point 2] H. Corner of building [Change Point 3] I. Fence J. Fence K. Corner of building BM =0.01 =0.01 =0.01 Check The arithmetical check shows that the levels have been correctly calculated and also shows that an error of 10mm has been made in the field work. The normal acceptable limit of error is ±20mm for this levelling. It was stated earlier that it is unusual to calculate the results in parallel with the field work for the simple reason that if any observation is wrongly read the calculated results must also be wrong. It is therefore wise to complete the field work and verify that levelling closes before calculating any results. The logical order in any levelling calculation is therefore: 1. Complete the fieldwork 2. Check that the sum BS column = sum FS column within the acceptable limit of error. If the error exceeds these limits there is no point in continuing the calculation. 3. Calculate rises and falls 4. Check that (sum rise column sum fall column) = (sum BS column sum FS column). 5. Calculate reduced levels. 6. Check that (last RL first RL) = (sum rise column sum fall column)

6 Appendix II Procedure 1. Setting up the level Setting the tripod The tripod legs are spread out and rested lightly on the ground around the survey point. Judging by eye, the legs are moved to bring the tripod head over the point, keeping the tripod head as level as possible. Mounting the instrument The level is carefully removed from the box and screwed to the tripod. Levelling Levelling is accompolished by raising or lowering the legs of the tripod, using the sliding leg arrangement, until the circular spirit level is centred. Refinements to the centring and leveling of the instrument must now be made; (a) Set the plate spirit level over two screws and centralize the bubble, (b) Turn the instrument through 90 o and recentralize the bubble (c) Repeat operations (a) and (b) until the bubble remains central for both positions. Parallax elimination A piece of paper is held in front of the telescope and the observer, sighting the paper through the telescope, turns the eyepiece carefully until the cross-wires of the reticule are sharply defined. 2. Obtained Staff Reading Released Horizontal plate. Rotate the level horizontally, collimate the staff Appendix III Report: Each group shall submit the report one week after completed the fieldwork. The report shall be consisted hereundera) Introduction b) Objective c) Devices d) Procedure e) Product Fieldbook. f) Analysis g) Conclusion