The Survey Camp provided us an opportunity to gain and update theoretical and practical
knowledge of surveying in actual field work. This report consists of the major part of survey
camp working day. The plotting of detailed topographic map of surveyed area, and then
those of road alignment and the bridge site survey.survey camp is completed in complete 11 days
|S.N||DAY||Survey Field Work|
|1||DAY 1||Reconnaissance AND Major Traverse Survey|
|2||DAY 2||Major Traverse Survey|
|3||DAY3||Major & Minor Traverse Survey|
|4||DAY4||Major & Minor Traverse Computation|
|5||DAY5||Two Peg Test, Fly levelling & Rl Transfer of Major &minor Station|
|6||DAY6||Tacheometry /Detailing /Field Verification|
|9||DAY9||Road survey/RL Transfer|
|11||DAY11||Bridge Survey /Rl Transfer|
DAY 1-DAY 3
Reconnaissance (Recce) means the preliminary inspection of the area before commencing the actual detail survey, for the purpose of fixing the survey stations and forming a general plan for the network of the chain lines. For this purpose the detailed inspection of the given area of Tribhuvan University was carried out by reconnaissance survey.
During reconnaissance the major and minor traverse control points to form a closed traverse around the perimeter of the area was found out. While selecting the major and minor control points following points should be considered:
- The adjacent stations should be clearly inter-visible and cover the whole area with least number of stations as far as possible. The traverse station should maintain the ratio of maximum traverse leg to minimum traverse leg less than 2:1.
- The steep slopes and badly broken ground should be avoided as for as possible, which may cause inaccuracy in tapping.
- The stations should provide minimum level surface required to set up the tripod of the instrument.The traverse line of sight should not be near the ground level to avoid the refraction.
- If possible well-conditioned triangles should be formed to give good graphical intersection during plotting
FOR MAJOR TRAVERSE
The leg ratio of maximum traverse leg to minimum traverse leg was maintained within 2:1. The precision in length between the forward measurements and the backward measurements of all the traverse legs was within 1:5000 when measured through total station. The difference between the mean angles of two sets of readings was within a minute for all the angles whereas for two face reading was within 20’’ for all the measured angles.
FOR MINOR TRAVERSE
For the detailed topographical survey, the detail points may not be sufficiently obtained from the control stations of the major traverse. For this minor traverse need to be laid. Minor traverse is that one which runs through the area to make detailing easy. Minor Traverse covers only small area. Less precise work than that of major traverse is acceptable so that single set reading is sufficient
The leg ratio of maximum traverse leg to minimum traverse leg was maintained within 3:1. The precision in length between the forward measurements and the backward measurements of all the traverse legs was within 1:3000.
general procedure for topographic survey:
- Conduct reconnaissance survey of the given area. Form a close traverse (major and minor) around the perimeter of the area by making traverse stations. In the selection of the traverse station, make sure that the stations are inter-visible and maintain the ratio of maximum traverse leg to minimum traverse leg 3:1 for minor traverse and 1:2 in the case of major traverse.
- Measure the traverse legs in the forward and reverse directions by means of a tape calibrated against the standard length provided in the field, note that discrepancy between forward and backward measurements should be better than 1:2000.
- In case of distance measurement by total station in both forward and backward direction the precision of 1:5000 in case of major traverse and 1:3000 in case of minor traverse should be maintained.
- Measure traverse angle on two sets of reading by total station. Note the difference between the mean angles of two sets reading should be within 20 seconds.
- Determine the R.L. of traverse stations by fly leveling from the given arbitrary T.B.M.3 (near bridge site) to T.B.M. 4 (near library building) Perform two-peg test before the start of fly leveling. Note that collimation error should be less than 1:10000. Maintain equal fore sight and back sight distances to eliminate collimation error. Permissible error for fly leveling is ±25√k mm, where k is the distance in kilometer.
- Balance the traverse. The permissible angular error for the sum of interior angles of the traverse should be less than ±30√n seconds and ±1√n minutes for major and minor traverse respectively. The sum of interior/exterior angles in a closed traverse should be equal to (2N±4)*90o where, N is the total number of stations. For major and minor traverse, the relative closing error should be less than 1:5000 and 1:3000 respectively
- Plot the major and minor traverse stations by coordinate method in appropriate scale (1:1000 and 1:500 respectively).
- Carry out the detail survey of the given sub area by total station and tachometric surveying with reference to the major and minor traverse, which have been already plotted. Use conventional symbols for plotting.