Geology and Surveying (Part B - Surveying) Distance Measurement

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

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

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

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.

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

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 division58 Leader Total Distance59.987

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 Even metre84 Leader 1.692

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.

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.

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

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

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.

Reductions and Corrections to be Applied Temperature Correction Tension Correction Sag Correction Slope Correction

Temperature Correction

Temperature Correction - Example

Tension Correction

Tension Correction - Example

Sag Correction

Sag Correction - Example

Slope Correction A B’ B l d’

Combining Corrections - Example

Corrections when Setting Out

Setting Out - Example Answer

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

EDM Signal

EDM Return Signal

EDM Prism

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

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.

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

Questions?