AGM 2210 Surveying Earthwork and Land Area Measurements

Rod Reading

We are used to feet and inches - Maybe meters and cm • Surveyors use "decimal feet" - Foot made up of tenths and hundredths - Our measuring rod (and later

What is Surveying?

"Surveying is the science of determining relative positions of points or objects on or near the earth's surface. "

Leveling definition

Backsight (BS): A rod reading (also called a "shot") taken on a point of known elevation - Establishes the elevation of the instrument (level) line of sight • Height of Instrument (HI): Elevation of the line of sight of the instrument (level) HI = BM + BS • Foresight (FS): Rod reading (shot) taken on a TP, BM, or TBM to determine its elevation Elevation of TP, BM, or TBM = HI - FS • Intermediate Sight (IS): Rod reading taken on any other point where an elevation is required. HI - IS = elevation of point

Field Book Layout

Cotton-based waterproof paper • Lefthand page features large grid squares • Suitable for tabulations • Righthand page features small grid squares • Suitable for sketches • Place tabulations, calculations, and descriptions on left page • Make relevant sketches on right page • Include North arrow on all drawings • Label all buildings, features, roadways, survey points, other landmarks • Include dimensions where applicable • Utilize straight edge or protractor

Leveling Definitions

• Benchmark (BM): A permanent point with known elevation. Typically published by Federal, State, or Local Agency • Temporary Benchmark (TBM): Semi-permanent point with defined elevation • Turning Point (TP): Temporary point used "pivot" between points and transfer elevations

Some EXAMPLES

- Boundary Survey • Establish property corners - Property Survey • Structures, boundaries, waterways, etc. located on a parcel - Construction Survey • Locate existing buildings • Future building placement - Highway Survey • Establish right-of-way • Locations of bridges, on-ramps - As-Built • Documents improvements to structures / land - Topographical Survey • Record elevation data • Prep for grading, water retention

Two methods: slope taping and horizontal taping In slope taping, the slope distance is measured and the horizontal distance is calculated. h = s cos(Ɵ)

Example: Measured length of s = 309.23 ft angle Ɵ = 8° h = 309.23 x cos(8) 309.23 x 0.9902 306.20 ft

What do surveyors do? Measurements of what?

In short, surveyors take measurements.Distances, angles, positions, areas, and boundaries

Leveling

Leveling: The process of measuring the difference in elevation between points that are some distance apart • Mean Sea Level (MSL): Vertical reference datum - "What we measure from" - Value of 0.000 ft • Above Ground Level (AGL) - Altitude - How far above something are we Think of drones

Differential Leveling

Measuring vertical distances from a known elevation point to determine elevations of unknown points - Utilizes surveyor's level and graduated measuring rod

Methods of Measuring

Pacing • Odometer readings • Stadia • Taping & Chaining • Electronic distance measuring (EDM) equipment

Recording Field Notes

Recording Field Notes • Data Collectors - Interface with Total Station or GPS - Allow for image capture, location recording, note entering • Field Books - Traditional recording method - Still utilized for many applications

Allowable Misclosure

Some amount of misclosure is allowed - The amount allowable depends on the number of Height of Instrument (HI) measurements - If your error is within the allowable, we must correct the elevations - If the amount of error is outside of the allowable, your survey is "no good" - Allowable misclosure depends on the job, an informal standard is: C = Allowable Error N = Number of HI measurements C = 0.02√N

Measuring With Gunter's Chain

Why a chain length of 66ft? 66' 660' 1 chain x 10 chains 66' x 660' = 43,560 ft² = 1 acre • 1785 - Public Land Survey Ordinance • Established measurements to be done with chain • Chain used to lay out grids across United States

Requirements of Good Field Notes

• Accuracy - If distances and angles are not accurately recorded, your work has no value • Legibility - Yourself and others will refer to your surveying notes in the future • Integrity - Purposefully reducing error will cause problems in the long run • Clarity - Too many abbreviations, page crowding, and omissions will make interpretation difficult • Arrangement - Use of notation and recording appropriate to the particular job will aid in interpretation

Branches of Surveying

• Geodetic - Accounts for Earth's curvature - Usually over very long distances • Planar: - Does not account for curvature - Assume the area of interest is flat We will utilize Planar surveying & leveling in this course

Making field notes

• Making quality field notes is equally as important as taking quality measurements - Recordings from field books • Field notes are the only permanent record of work completed at a job site - Any recordings made later are copies • Field books are legal documents used in litigation - Responsibility of good quality notes is with you, the surveyor

Differential Leveling - Misclosure

• Sources of Misclosure: - Improper instrument adjustment - Bubble not centered (instrument not level) - Incorrect rod readings - Rod not plumb - Rod not fully extended - Inconsistent or poor turning points • Good Practices - Proper instrument adjustment - Keep rod plumb - Keep bubbles centered - Clearly mark turning point locations

Types of Field Notes

• Tabulations - Numbers, measurements, and calculations pertaining to the survey • Sketches - Clarify field notes with graphics - May be drawn to scale, or exaggerated certain features • Descriptions - "Verbal sketches" - Used to provide details for later reference - Clarify measurements

Leveling

• The end of a leveling process must end on a point of known elevation • This point can be original starting point or a BM of known elevation. This ensures that the accuracy of the survey can be determined. Arithmetic check: When the sum of the BS are added to the starting elevation and the sum of the FS is then subtracted from that value, the remainder should equal the final elevation. During the survey, we are calculating elevations. When closing out the survey on a benchmark point, the foresight value we get is a calculated point. We then compare it to the known value, which is not a calculated point. We want the two to be the same, if they are not, we have error (topic for next class)