15-10-2012, 01:51 PM
Civil Engineering Surveying
Civil Engineering.ppt (Size: 220 KB / Downloads: 229)
Planning A Survey
Planning requires a well rounded understanding of surveying practices
Process:
Choice of accuracy required (depends on use to be made)
Basic Control
Topographic
Photogrammetry
Existing Control
Search records for existing control in area
Illinois Geological Survey – Urbana, IL
National Geodetic Survey – Rolla, MO or Rockville, Maryland
Reconnaissance:
Search Procedure:
Description often dated
Can use GPS receiver (Lat. And Long)
Probe, detectors – often problems - brass
Accuracy and Errors
Accuracy depends on:
Precise instruments
Precise Methods
Good Planning
Example: Angle turned with theodolite, pointed with care; readings checked thus good precision. Angle’s of 2-3” expected, real results angle’s 15” = accuracy
Errors
3 Types
Blunders
Systematic Error
Accidental Error
Blunder is a mistake, to help eliminate:
Every value to be recorded must be checked by some independent field observation
Systematic Error – an error that under the same conditions will always be of same size and sign.
Basic Rules to Eliminate:
All surveying equipment must be designed and used so that whenever possible systematic errors will be eliminated automatically
Systematic error which can not be eliminated must be evaluated and their relationship to conditions that cause them must be determined.
Example: Temperature Corrections
Hydrographic Surveys
Surveys and mapping of bodies of water and shorelines
Rivers and Lakes – Process different
Rivers
Normal process is to establish 2 parallel lines of control points on opposite sides
River Portion: 2 processes
EDM similar to radial
Dual instrument with position by angle and intersection
Lakes
Normal process same as river but generally do not have current problems
Overall Process:
Establish control points both horizontal and vertical
Preplan where sections are to be taken (this is basis for control points on shore)
Cross sections taken
If EDM, radials taken from control points due to difficulty in obtaining shots under 300’
May have to combine cross sections and radial location to pick up anomalies not covered by cross sections
Gauging Stations
Purpose is to install either manually read or automatic gauges to determine stream, river, lake, or ocean elevations
Process:
Establish system of BM’s throughout area gauges will be installed
Establish elevation mark at site for installation
After gauges are installed, check elevation of each