# CH3-3LEVEL-METHODS-4-7-04

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CH. 3 LEVELING. 4/15/03. Perused Kavanagh Ch. 3:. 3.1 Know these definitions (not verbatum) 3.2-3.3 Understand the uniqueness between a flat line and a level line, and the proportionality of mistake because of ebb and flow and refraction with separation of the shot.

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﻿CH. 3 LEVELING 4/15/03

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Read Kavanagh Ch. 3: 3.1 Know these definitions (not verbatum) 3.2-3.3 Understand the uniqueness between an even line and a level line, and the proportionality of mistake because of bend and refraction with separation of the shot. 3.4 Skim read, with the exception of read 3.4.2 Level Tube. Comprehend the connection between the optical quality and accuracy of the level, and the sweep of bend of the level tube. 3.5 Skip. 3.6 Know what a compensator does, and theoretically how it works. 3.7-3.8 Skim read. Turned out to be for the most part acquainted with what an advanced level is, and what a bar code is, and how they work. 3.9-3.10 Skim read. 3.11 Know what these terms mean. 3.12 Understand differential leveling technique 3.13 Skim read for Field Exercise. Know how to hold a pole, and "shaking" (waving) the rod. Know how to peruse the shaking bar. Comprehend field notes for leveling 3.14 Skim read. 3.15 Skim read. Comprehend Table A.11 3.16 Differentiate between plan, profile, and cross-segment sees. Comprehend Fig. 3.22. Comprehend profile and cross-segment field note positions. 3.17-3.20 Skip. 3.21 Understand the ideas of permissible blunder and conforming a level circle. 3.22-3.24 Read for Field Exercise.

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3.1 Definitions Leveling = a method used to decide heights of focuses or contrasts in rise between focuses Elevation = vertical separation above or beneath a reference datum. Datums Mean ocean level = a generally utilized reference datum. National Geodetic Vertical Datum (NGVD) of 1929. North American Vertical Datum (NAVD 88). MOST AREAS USE MEAN SEA LEVEL AS THEIR DATUM, either NGVD 29 or NAVD 88

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VERTICAL DATUMS MEAN SEA LEVEL DATUM OF 1929 NATIONAL GEODETIC VERTICAL DATUM OF 1929 ( As of July 2, 1973 ) NORTH AMERICAN VERTICAL DATUM OF 1988 ( As of June 24, 1993 )

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COMPARISON OF VERTICAL DATUM ELEMENTS NGVD 29 NAVD 88 DATUM DEFINITION 26 TIDE Gages FATHER'S POINT/RIMOUSKI IN THE U.S. & CANADA QUEBEC, CANADA BENCH MARKS 100,000 450,000 LEVELING (Km) 102,724 1,001,500 GEOID FITTING Distorted to Fit MSL Gages Best Continental Model

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NGVD 29 and NAVD 88

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4

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Benchmark (BM) = a reference check whose rise is known in respect to a given datum. Backsight = a direct which is toward be utilized to decide the rise and additionally precise introduction of the looking over instrument Foresight = an indicate which an instrument locating is made for measuring or setting up its rise or potentially its even position Turning Point = a brief point whose rise is resolved amid the way toward leveling; used to set up the Height of Instrument Height of Instrument = in leveling, the tallness of the viewable pathway of the leveling instrument over the received datum; in flat edge estimation, the stature of the focal point of the telescope (even pivot) over the ground or station check.

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3.2 Differential Leveling Procedure

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How to Read a Level Rod

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How to Hold A Level Rod

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Notes on How To Perform Differential Leveling Level the instrument by focusing the bullseye level Focus two things: 1) line of sight; 2) question; to keep away from parallax mistake Rodperson begins at backsight (pt. of known elev.), rocks bar or uses level rod bubble Field notes (see illustration). Take note of that entireties of BS and FS ought to break even with. Rodperson: pick defining moments for reproducibility Avoid c ollimation mistake by making backsights and premonitions a similar length

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3.3 Common Methods of Leveling There are 2 basic techniques for leveling: Direct Differential Leveling (Spirit Leveling) = regular strategy for deciding height contrasts. Utilizes a soul level and a pole, or an advanced level and pole. The instrument does not tilt; you set it up so the observable pathway is in the even plane. Trigonometric leveling = flat and vertical separations are measured to register rise contrasts. Useful for difficult to reach focuses e.g. peaks, seaward development, and so forth. (These days when substantial separations are included, GPS is generally utilized rather than trigonometric leveling.)

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3.4 Instruments Commonly Used for Leveling Dumpy Level = in like manner utilize around the most recent couple of decades. A few temporary workers still utilize them. Called "dumpy" on the grounds that optical framework permitted them to be shorter than past levels (for the same amplifying power). Primary segments: telescope, leveling tube, leveling head .

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Automatic or Self-Leveling Levels = present day sorts most normally utilized these days. Programmed levels have bullseye level to get instrument roughly level. The instrument then sets itself level. It has a swinging crystal or mirror compensator which keeps up an even viewable pathway by permitting just the flat beams coming into the instrument to go through the optical focal point of the instrument. Great instruments to utilize on the grounds that they can keep up level regardless of the possibility that the instrument is shaken around a bit. Alerts when utilizing programmed levels: 1) the compensator is hung by fine wires that effectively break with harsh taking care of; 2) the compensator can every so often get hung up. Tap the finish of the telescope or turn one of the leveling screws somewhat. The line of sight ought to seem to avoid quickly before coming back to its unique bar perusing.

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Electronic Digital Levels

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Tilting Level (Can be utilized for accuracy work, or utilize programmed levels)

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Laser Level = normally utilized by temporary workers for evaluating, setting frames, and so on. Two sorts: 1) settled single laser; 2) turning laser. The turning laser gives a level plane from which specific separations can be measured. Great < 1000 ft.

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Transits and theodolites might be utilized as a part of lieu of a level, however give poor outcomes. Add up to stations give similarly better outcomes, yet are not by and large as precise for leveling as programmed levels, and ought to for the most part not be utilized for vertical control of development activities, or where third request or better exactness is required.

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3.5 The Telescope High-controlled telescope (20x to 45x power) with a soul bubble tube joined.

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Main parts of the telescope: 1) Positive target focal point = shapes a picture of the protest located. The picture would be framed in front of the focus. 2) Negative centering focal point = veers the light beams to bring them into concentrate on the focus. 3) Reticle = glass with the line of sight on it. 4) Eyepiece = really a magnifying lens to expand the picture from the reticle. Centering the eyepiece, e.g. centering the line of sight, changes the separation amongst it and the line of sight (wind the eyepiece to focus). 5) Hanging crystals = swings on wires to keep observable pathway level

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3.6 Level Bubble The exactness of any review instrument is by and large most influenced by the arrangement (or misalignment) of the level air pocket. Affectability % f ( sweep of bend) = edge of tilt/one division of scale on glass But the bigger the span of shape, the more troublesome it is to level!

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Example: If it takes 20" of circular segment to move the rise by 2 mm then the span of ebb and flow is: For first request leveling, the instruments have 2" bubbles (2" of curve to move the bubble 2 mm) with "680 ft sweep. Two sorts of level air pockets: 1) tube; and 2) bullseye. Affectability guideline = same for both.

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3.7 Sighting Through the Telescope Inaccurate sightings happen if the line of sight and the degree are not appropriately engaged. This is because of the issue of parallax. Parallax = the obvious uprooting of the position of the fact of the matter being located happening while moving the eye up or down while looking through the telescope Proper technique to maintain a strategic distance from parallax: 1) Focus the focus on the eyepiece. Hold a paper around six crawls before the focal point with the goal that it seems fluffy, and turn the eyepiece until the line of sight come into center 2) Sight the proposed bar or protest. (Utilize the guiding framework on top of the barrel toward help find the bar or protest). Concentrate on the pole or question. 3) Check for parallax by moving the eye here and there or sideways while viewing the pole. On the off chance that the line of sight seem to move as for the picture located, then either the line of sight or protest are not appropriately engaged.

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3.8 Correction for Inclined Line of Sight ("Collimation Error") If instrument is not exactly level but rather separate D is same for both BS and FS, then the blunders wipe out.

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3.9 Common Leveling Mistakes (Blunders) 1) Misreading bar 2) Moving defining moment 3) Field not botches 4) Rod not completely stretched out 5) Forgot to level the instrument

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3.10 Common Leveling Errors 1) Level pole not vertical 2) Settling of level bar on defining moment 3) Mud, snow or ice development on base of pole 4) Rod harmed 5) Incorrect bar length (same as off base tape length) 6) BS & FS separations not equivalent (collimation blunder) 7) Bubble not focused/compensator not swinging free 8) Settling of level legs (tripod) 9) Instrument out of modification 10) Improper centering of instrument (parallax blunder) 11) Heat waves 12) Wind or vibration bringing on instrument development 13) Bumping into tripod

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3.11 Corrections: Curvature and Refraction Curvature blunder, c = the dissimilarity between a level line and an even line over a predetermined separation c = 0.667K 2 c in ft, K is dist. In miles Rays of light are refracted descending under ordinary P,T conditions. In this way, viewable pathway is twisted dow