Geology and Surveying 70380 (Part B - Surveying) Distance Measurement

1. Geology and Surveying 70380 (Part B - Surveying) Distance Measurement

2. Objectives • Select suitable distance measuring equipment for a particular task. • Take Chaining measurements. • Reduce and correct field chaining measurements. • Understand fundamental principles of EDM.

3. General • Direct • “Chaining” • EDM • Indirect • Triangulation • Optical distance measurements • Approximate • Pacing • Measuring wheel • Optical range finders

4. Chaining Equipment • Plumb Bob • Spring Balance • Thermometer • Steel Band / Tape / Chain • Clinometer (or theodolite)

5. Standardisation of Survey Tapes • To provide legal traceability of measurements to a known standard. • Accounts for • Expansion and contraction with change in temperature • Elasticity of steel tape with variations in length and tension applied. • Hence subsidiary standard tapes note a standard temperature and tension at which indicated distance is true.

6. Field Procedures - Chaining • Fully supported • Level • Slope • In Catenary • Level • Slope • In all cases ensure the tape follows a straight line

7. Measuring Between Stations • Hold even metre mark on one peg. • Pull required tension while plumbing over marks. • Read leader. • Record readings. • Add distances: • 2 m division 58 Leader 1.987 Total Distance 59.987

8. Setting out a Station • Hold desired even metre mark. • Calculate required leader reading. • Pull required tension while plumbing. • Place peg under leader at required reading. • Add distances: • Set out 85.692 Even metre 84 Leader 1.692

9. Fully Supported M’mt • Should only be done when surface is even and free of obstacles. • Ensure tape is aligned with terminal points. • Measure slope if necessary. • Avoids necessity for making a sag correction.

10. Measurement in Catenary • Should only be done when necessary. • Ensure full catenary where possible. • Ensure tape is aligned with terminal points. • Measure and record tension applied. • Measure slope if necessary. • Must use at least one plumb bob.

11. Step Chaining • Avoids the need to make repeated slope corrections Plumb bob line Level Chain Level Chain Surface

12. Measuring Long Distances • Ensure a straight line is maintained. • Use accurate temporary intermediate marks. • Keep a running record (chainage) in field notes.

13. Care of the Steel Band • Do not pull the chain tight if there are any “kinks” in it - IT WILL BREAK! • Do not form any “loops” when unrolling of rolling up. • Do not “double back” - keep band straight. • Do not allow vehicles to drive over the band. • Apply light oil when necessary.

14. Reductions and Corrections to be Applied • Temperature Correction • Tension Correction • Sag Correction • Slope Correction

15. Temperature Correction

16. Temperature Correction - Example

17. Tension Correction

18. Tension Correction - Example

19. Sag Correction

20. Sag Correction - Example

21. Slope Correction B d’ l B’ A

22. Combining Corrections - Example

23. Combining Corrections - Example

24. Corrections when Setting Out

25. Setting Out - Example Answer

26. Electromagnetic Distance Measuring Equipment (EDME) • In common use from around 1960s. • Work on: • Light waves • Microwaves • Pulse laser (no reflector required) • Common accuracy today 3mm ± 3ppm • Equates to 6mm over 1 Km • Must be corrected for atmospheric and many other effects including standardisation

27. EDM Signal

28. EDM Return Signal

29. EDM Prism

30. Total Stations Measure H and V distances Measure Distances Use COGO functions Use other in-built functions

31. Summary • Understanding of accuracy means you are able to select suitable distance measuring equipment for a particular task at hand. • We investigated different Chaining measurements and saw how to carry out reduction and correction of field chaining measurements. • We looked at the fundamental principles of EDM.

32. Self Study • Read Module 18 • Do self assessment Questions • Access edm.exe

33. Questions?