Unit 10 Surveying in Construction LINEAR MEASUREMENT Angelo

Unit 10 -Surveying in Construction LINEAR MEASUREMENT Angelo Filomeno HEPS Higher Education & Access Studies angelo. filomeno@cnwl. ac. uk

Linear Measurement • In these lectures we will cover : – The role of linear measurement – Equipment – Procedures and rules – Errors – Applications of linear measurement

What is linear measurement? • Simply the measurement of distance : New building site how big is it? 50. 5 metres 27. 9 metres 50. 5 metres

Distance measuring equipment and typical accuracies • • • Pacing (1: 100) Optical range finder (1: 300) Trundle wheel (1: 500) Stadia tacheometry (1: 1000) Taping or chaining (1: 10, 000) Electronic distance measurement (1: 50, 000)

Some things to note… • • Equipment is fairly cheap (except EDM) Equipment is easy to maintain and adjust (!) Distances are easy to measure Very accurate results can be achieved (with care) • Measurement line needs to be unobstructed • Errors occur and need to be managed or minimised

Taping procedures • • Tape must always be straight Tape must not be twisted Use chaining arrows for intermediate points Tape horizontally if possible Tape on the ground if possible Slope taping needs to be reduced Catenary taping requires correction Step taping suits some applications

Tape must be straight… e c n ta obstruction dis st i d e c n a ed r i u req ed r u s measured distance required distance

Use chaining arrows… di sta nc dis e e c n ta ed r su ed a e uir m req measured distance required distance

Slope correction… s = ce n a st i d ) e p lo s ( d e r asu e m q horizontal distance = h H To calculate the horizontal distance : h = s cosq or h = (s 2 - DH 2)1/2 For example : Or…. = 30. 589 s =s 30. 589 mm 2. 5 o m Hq==1. 334 H = 1. 334 m then h = (30. 5892 - 1. 3342)1/2 = 30. 589 h =h 30. 560 m cos(2. 5) h = 30. 560 m

Step taping… required (horizontal) distance

Catenary taping… mea sure e c n a t s i d d required distance measured distance required distance

Types of errors • Blunders – mistakes and gross errors • Systematic errors – repeated size and sign – affect accuracy These error types apply to any measurement technique used in surveying… • Random errors – small and usually undetectable (noise) – affect precision

Accuracy and precision

Sources of error in taping • Temperature correction L = L +L. c. T where : L is the corrected distance L is the measured distance c= 1. 15 x 10 -5 m/o. C (for a steel band) T = Tactual - Tstandard

Sources of error in taping • Standardisation – The tape is not of “true” length

Sources of error in taping • Catenary (sag) – A suspended tape will measure too long where : M is the mass per unit length (0. 011 kg/metre) g is gravity (9. 8 metre/sec 2) T is the tension (50 Newton) is the slope angle

Sources of error in taping • Tension – Tape length will depend on applied tension • Slope – Distances must always be reduced to horizontal

Applications • • • Dimensions of building features Block dimensions Location and size of site features Setting out for construction Clearances and tolerances

An example road width side boundary clearances building setbacks block dimensions building dimensions underground services

Further Details on measuring for obstructed vision See word documents