CHAPTER 5 Vertical Control. CE 316 January 2012

Transcription

1 CHAPTER 5 Vertical Control CE 316 January

2 5.1 Introduction Vertical Datums Leveling Techniques and Corrections Bench Mark Design and Construction Bench Mark Data Trigonometric Barometric Leveling Leveling Equipment 138

3 5.1 Introduction 139

4 5.1 Introduction 140

5 5.1 Introduction James Brindley ( ) 141

6 5. Vertical Datums Two. The vertical Datum is not a mathematical surface (i.e. ellipsoid), but referenced to the geoid (equipotential surface of the earth s gravity field closely approximating sea level). Canadian Geodetic vertical datum (CGVD8) [USA (NGVD9)] Since 198, over km of lines have been added to the system Defined in 198, based on only 30,000 km of levelling. There are over 75,000 benchmarks The adjustment of the datum, depended on the tidal stations at Halifax, Yarmouth, and Father Point, on the Atlantic, at Vancouver and Prince Rupert on the Pacific, and on Rouses Point [Quebec]. US National Geodetic Vertical Datum NGVD9 106,75km of levelling constituting 46 closed loops 6 Tidal Stations across North America were used to provide a fixed datum Alaska has own vertical datum 14

7 5. Vertical Datums Map of primary Canadian Vertical Control Network. Consisting of more than 130,000 km of precise leveling to over 75,000 bench marks. Elevations refer to CGVD8 143

8 5. Vertical Datums IGLD 1985 (Canada & U.S.A) Great Lakes Vertical Datum - Completed in 199 This datum was established in 1955 to give more accurate hydrological readings. IGLD was the first common datum for the U.S. and Canada Revised in 1985 and a new reference zero point at Rimouski, Quebec was established. North American Vertical Datum NAVD 88 (Canada & U.S.A) Involved a redefinition and readjustment of the geodetic vertical control networks. In June, 1991 a continental adjustment was carried out This included 77,000 km of levelling in Canada NAVD was referenced to the 1985 IGLD datum 144

9 5. Vertical Datums IMPACT OF VERTICAL ADJUSTMENT NAVD88 minus NAVD9 Approximate shift in vertical datum (in mm) for U.S.A. NOTE: Father s Point, Quebec, only tidal station used today in N.A. for mean sea level determination 145

10 5.3 Levelling Techniques and Corrections Precise elevations are determined relative to the datum by a process known as. Point established are called bench marks (BM) or temporary bench marks Rods are held vertically, A on a point of known elevation and B on a turning point The change in elevation is calculated by subtracting the sum (B.S.) - Sum (F.S.) = D Elevation Accuracy is related to the difference between forward and backward leveling. 146

11 5.3 Levelling Techniques and Corrections Production Varies according to terrain 100 to 00 set-ups per day 3. 8 to 14 km/day Routes Railways, Roads, Rivers, Ice, etc. Special points Balance B.S. s and F.S. s. Line of Sight 0.5 m above grd. Max. length of shots m A B.S. F.S. B D Elev. g D Elev. = D Elev. = + (higher elevation) 147

12 5.3 Levelling Techniques and Corrections Correction for Curvature and Refraction (Cc+r) (Approx.) R R + D + D = ( R = R + C C + C C ) + 0 RC C D RC = C ft. ft. 580 x 580 D mi. mi. C ( ft.) = = C D, for D in miles x 0,890,000 ft. 1 C - R C C 7 C + (ft.) = D, or C + (m) = C R C R 148

13 5.3 Levelling Techniques and Corrections mm Axis of the vial tangent at midpoint R SENSITIVITY ANGLE S = q FOR ARC = mm a a Level rod d Level Line g 149

14 5.3 Levelling Techniques and Corrections d a = ARCSIN a d q = ARC SIN [ where, n = number of mm divisions] a n d p rads q " = [ Note : arc 1" = = ] a ( n) arc 1" 360x60x60 150

15 5.3 Levelling Techniques and Corrections Example For parallel plate micrometer, d = 5 mm when rotated 30 o. Calc. thickness of glass if refractive index =

16 5.3 Levelling Techniques and Corrections t AB = BC = d cosa 1 = sina 1 sin ( 90 + a ) t d = sin ( a1 -a) cosa t d = (sina1 cosa - cosa 1sin a ) cosa d = t (sina 1- cosa - cosa 1sin a ) 1- sin a 1 d = t sina 1 1- n - sin a 1 ( - ) d = t a 1 1 [ in Rads] 15

17 5.3 Levelling Techniques and Corrections Precise Leveling Equipment Parallel plate micrometer 40x magnification /mm sensitivity or better Different Observers Rods Circular levels on rods Foot plates for turning points Sun shade for instrument 153

18 5.3 Levelling Techniques and Corrections Specifications The different orders of vertical control are defined in terms of the allowable discrepancy between independent forward and backward leveling between bench marks as follows: Special First Order First Order ± 4 mm k Second Order ± 8 mm k Third Order ± 4 mm k Fourth Order ± 10 mm k Note: k(kilometers) = One way distance between bench marks along leveling route 154

19 5.3 Levelling Techniques and Corrections U.S. Geodetic Survey Leveling Specifications 155

20 5.4 Bench Marks Design and Construction Defined as fixed reference point whose elevation has been determined and whose position is so described that it may be identified in the future (no vertical movement should take place. Value of level line is a function of the number of properly positioned bench marks. Improperly set bench mark(s) provide totally misleading information Bench marks either permanent or temporary 156

21 Bench Marks Design and Construction V CUT 1 16 DEEP MATERIAL: BRONZE 1 8 DRILL 1 4 DIA. SLOT SURVEY TABLET MARKER TYPE

22 5.4 Bench Marks Design and Construction CONVEX CURVATURE ON TOP BRONZE CAP THREADED TO PIPE PIN TO SECURE CAP TO COLUMN 4 to 8 1 GALVANIZED STEEL PIPE 7 DIA. BASE (CAST IRON) THREADED TO PIPE SURVEY IRON PIPE MARKER WITH BASE TYPE 3 158

23 5.4 Bench Marks Design and Construction CAST IRON RIM & COVER TYPE 1 OR MARKER UPPER 6 OF PIPE FILLED WITH NON-SHRINKING GROUT GALV. STEEL PIPE DRIVEN TO DESIRED DEPTH EARTH MARKER MAY BE SET WITH BRONZE TABLET FLUSH WITH GROUND LEVEL. PILE DRIVEN SURVEY PIPE MARKER TYPE 5 159

24 5.4 Bench Marks Design and Construction CYLINDRICAL FORM MINIMUM 10 TYPE 1 or MARKER GROUND LEVEL CONCRETE SUBSURFACE ROCK 4-3 REINFORCING STEEL BARS 4 SURVEY MARKER IN SHALLOW OVERBURDEN TYPE 7 160

25 ABOUT 3 ABOUT 3 COMPRE SIBLE SOIL GALVANIZED IRON RIM AND COVER REFUSAL OR BEDROCK CASING LIFTED 1 GALVANIZED STEEL PIPE CASING (COUPLED IN SECTIONS) GALVANIZED STEEL PIPE 3 8 (COUPLED IN SECTIONS) FOOT (see detail) * N.R.C. TYPE DEEP BENCH MARK TYPE 1 * National Research Council 5 STAINLESS STEEL BALL WELDED TO COUPLING ANNUILAR SPACE BETWEEN PIPES FILLED WITH SAE 80 OIL 10 CONCRETE TILE FILLED WITH CRUSHED STONES a = 1 38 a to 1 1 TO FIT 1 PIPE CASING STD. PIPE THREAD 40 TIP CUT OFF MATERIAL - COLD ROLLED STEEL STEEL FOOT DETAIL CASING LIFTED GALVANIZED IRON RIM AND COVER STAINLESS STEEL BALL WELDED TO COUPLING ANNUILAR SPACE BETWEEN PIPES FILLED WITH SAE 80 OIL 10 CONCRETE TILE FILLED WITH CRUSHED STONES COMPRESSIBLE SOIL 1 GALVANIZED STEEL PIPE CASING (COUPLED IN SECTIONS) 3 8 GALVANIZED STEEL PIPE (COUPLED IN SECTIONS) a a = to 1 1 TO FIT 1 PIPE CASING STD. PIPE THREAD STEEL FOOT DETAIL 40 REFUSAL OR BEDROCK FOOT (see detail) N.R.C. TYPE DEEP BENCH MARK * TYPE 1 * National Research Council TIP CUT OFF MATERIAL - COLD ROLLED STEEL 161

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28 =55 N =53 N

29 3 3 3S Scale 1:500,000 QUAD NO

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31 5.5. WWW OPDS: World Wide Web Online Product Delivery Service WWW OPDS replaced the Canadian Geodetic Bulletin Board Service (CGBBS) early in 1999, to allow Geodetic clients direct access to Geodetic products and services. The following Products are available through CSRS: Primary Vertical and Horizontal Networks Products (survey station data) Direct access to the Canadian Spatial Reference System (CSRS) via the Canadian Active Control System (CACS) Geodetic Software and Related Data Products Publications Coordinates issued by the Division for horizontal networks are based on the North American Datum 1983 (NAD83), which is compatible with the World Geodetic System 1984 (WGS84). 167

32 5.5. WWW OPDS: World Wide Web Online Product Delivery Service Computer listings of horizontal and/or vertical survey stations are available in the following formats: Long: Short: Geographics, UTM's, cartesians, height and undulation, station monumentation, location description and inspection data. Geographics, UTM's, cartesians, height and undulation. Geolist: Geolist-UTM: Geographics, height, marker class and condition. Same as GEOLIST with UTM coordinates. For guest users of the CSRS on-line data only the geolist format is available and the elevations of the stations are rounded off

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34 5.6 Trigonometric Leveling CD = DE tan a DF = (C & R) ED DH = AE + DF + DE tana - BC AB DH = AE + DF + EC sina - BC AB 170

35 5.7 Barometric Levelling 3 methods of survey Single barometer Three barometers (two fixed, one higher & one lower) 171