Geology and Surveying

70380

(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 division 58

Leader 1.987

Total Distance 59.987

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 85.692

Even metre 84

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

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

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?