Surveying With Construction Applications, 7th Edition Chapter 2 Leveling

General Terms Elevation: a vertical distance above or below a reference datum (MSL) Vertical line : a line from surface of the earth to the earth center. Level line : a line in a level surface. A level surface is curved surface parallel to the mean surface of the earth. Horizontal line : a straight line perpendicular to a vertical line Mean sea level: The reference datum that is universally employed. Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Leveling Standards and Specifications Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Leveling Concepts Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Leveling Process Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Effects of Curvature and Refraction Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Effects of Curvature and Refraction In fact , the divergence between a level line and horizontal line is quite small . For example , over a distance 1000 ft , the divergence is 0.024 ft and for 100 m the divergence is 0.0008 m. All sight lines are refracted downward by the earth’s atmosphere. Refraction is generally considered to be about one –seventh of the curvature error. Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

C= KA2 /2R+C c= KA2 /2R c= KA2 /2*6370 =0.0000785 kA2 km= 0.0785 kA2 m (R+c)2= R2+ KA2 R2+2Rc+c2= R2+ KA2 c(2R+c) = KA2 C= KA2 /2R+C c= KA2 /2R c= KA2 /2*6370 =0.0000785 kA2 km= 0.0785 kA2 m If r= 0.14c , then c+ r= 0.0675 K2 Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Types of Surveying Levels Automatic Digital Tilting Dumpy (see Appendix G) Rotary Laser (see Part II) Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Equipment: Level Instrument Automated Levels Easy to use (not power!) Needs experience Digital Levels Push-button technique No reading errors, special staff Readings are stored and analyzed digitally Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Tilting level: very precise leveling can be achieved using the tilting screw; however, needs to be leveled before each important rod reading, which is very time consuming, thus it is rarely used Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Leveling Rods: foot rods can be read to 0.01 ft and metric rods usually only to 0.01 m are made from wood, metal or fiberglass and are graduated in feet or meters most leveling surveys use two- or three-piece rods, which either fold, slide or fit together telescopically for heights of 3, 5, and 7 m, from a stored height of 1.5 m rods are graduated in a wide variety of markings and are plumbed by using a rod level or by waving the rod slightly so that the instrument operator can take the most precise reading Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Leveling Rods Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Equipment: Tripod Wooden design or aluminum From “easy to sit” to “ops, this is high” ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium - 13-24 Nov. 2006

Equipment: Bubble Keep the pole upright Any tilt will disturb your readings ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium - 13-24 Nov. 2006

Survey Markers Gives you a fixed point Should be of good quality Should be long-term Preferable in bedrock, settled buildings, or bridges Do not use fences or walls ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium - 13-24 Nov. 2006

Definitions Bench Mark (BM): is a permanent point of known elevation . BM established by using precise leveling techniques ( GPS),marked by bronze disk and published by federal and municipal agencies Temporary Bench Mark (TBM) : is a semi permanent point of known elevation . TBM can be on fire hydrant, top corner of concrete culvert head wall. TBM are available from various surveying agencies Turning Point (TP): is a point used to transfer an elevation Height of Instrument (HI): is the elevation of the line of sight through the level. Backsight (BS): is the rod reading taken on a point of known elevation to establish the elevation of the instrument line of sight Foresight (FS): is a rod reading taken on TP,BM or TBM to determine its elevation Intermediate Sight (IS): is a rod reading taken at any other point where elevation is required Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Definitions Back sight (BS) Fore sight (FS) Intermediate sight (IS) The first reading from a new instrument stand point (i.e. take the height to the instrument) Fore sight (FS) The last reading from the current instrument station (i.e. give the height to a benchmark) Intermediate sight (IS) Any sighting that is not a back sight or fore sight ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium - 13-24 Nov. 2006

Leveling Procedure – One Setup Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Leveling Procedure – Multiple Setups Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Leveling Field Notes for Slide 11] Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Example of Profile Leveling Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Field Notes for Slide 14 Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Cross Section Surveying Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Cross Section Field Notes Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Peg Test The purpose of peg test is to check that the line of sight through the level is horizontal( i.e., parallel to the axes of bubble tube) Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Peg Test Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Trigonometric Leveling The difference in elevation between A &B in the figure shown in next slide can be determined if the vertical angle (a) and the slope distance (s) are measured. These measurements can be taken with total station or with electronic distance measurements (EDM) /theodolite combinations V =S sin α Elevation at point A+hi +(or – V)- rod reading (RR)= elevation at B Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Trigonometric Leveling Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Level Loop Adjustments Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

Reciprocal Leveling To cancel instrumental and natural errors it is advised to keep BS & FS distances roughly equal In some situation such as river crossing ,it is not always possible to balance BS & FS distances Reciprocal leveling technique is used Surveying With Construction Applications, 7th Edition Barry F. Kavanagh

CONTOURING FROM GRID (OR SPOT) ELEVATIONS

Definition A contour line is an imaginary line that passes through points having the same elevation.*

Uses of Contour Map Preparation of approximate ground profiles along suggested axes of projects. Determining the capacity of a reservoir or a dam. Calculation of earthworks volume. Studying possible routes in highway and railway engineering. Determining watershed lines for hydrological studies….etc.

characteristics of contour lines Contour lines are continuous. Contour lines are relatively parallel Evenly spaced lines indicate an area of uniform slope. A series of closed contours with increasing elevation indicates a hill and a series of closed contours with decreasing elevation indicates a depression Closed contours may be identified with a +, hill, or -, depression The height between successive contours is called the vertical interval or the contour interval, the contour interval is kept constant for a map. The horizontal distance between the same two contours is called the horizontal equivalent. 8. Closely spaced lines indicates a steep gradient. Widely spaced lines indicate a flatter gradient

. Contours are Continuous Some contour lines may close within the map, but others will not. In this case, they will start at a boundary line and end at a boundary line. Contours must either close or extend from boundary to boundary.

Contour Spacing Evenly spaced contours indicate an area of uniform slope. Unevenly spaced contours indicates an area with variable slope.

Hills and Depressions A series of closed contours with increasing elevation indicates a hill. Hills may be identified with a “+” with the elevations

Hills and Depressions--cont. A series of closed contours with decreasing elevation indicates a depression. Depressions may be identified with a “-”.

Contour Spacing Contours spaced close together indicate a higher % slope. Contours spaced wider apart indicate lower % slope.

The Gradient between A and B = Vertical Interval / Horizontal Equivalent . 5 10 15 20 25 A 25 B 20 10 15 5

Data Collection

Two Issues On Data Collection When collecting data there are two important issues: Ensuring sufficient data is collected to define the object. Ensuring two types of information is gathered for each station: Location Elevation

Interpolation

Interpolation Drawing contour lines to produce a topographic map requires the ability to interpolated between points. Interpolation is required because contour lines are lines of constant elevation and the station elevations that are measured in the field seldom fall on the desired contour elevation. Interpolating is finding the proportional distance from the grid points to the contour line elevation.

Interpolation Interpolating can be done by estimation for low precision maps. It should be done by calculation and measurement for higher precision maps. A combination of methods can also be used, depending on the use of the map.

Interpolating by Estimation Study the illustration. Logic or intuitive reasoning would conclude that when the grid points are at 102 feet elevation and 98 feet elevation, then a contour line of 100 feet elevation would be half way in between. Note: that a dashed line has been drawn between the two points. In topographic surveying it is assumed that the area between two measured stations is a plane.

Interpolating by Calculation Proportional distance is calculated using an equation. For the previous example this would result in: The 100 foot contour line would be located 0.5 or half of the distance between the two stations.

Interpolation by Calculation &Estimation The same equation is used for all grid distances and all contour lines. Example: Determine the location of the 96 foot contour line for the illustration.

Interpolation by Calculation and Measurement Start by selecting an contour interval and two grid points. This example starts with the 110 foot interval. The first step is to calculate the position of the 110 foot contour between stations A1 and A2.

Interpolation by Calculation and measurement--cont. The next step is to measure and mark the position of 0.6. Next, determine which direction the contour goes between the diagonal and the other three sides of the grid. Mark the next points.

Interpolation by Calculation and measurement--cont. The 110 foot contour line passes between B1 and B2, therefore the next station is the diagonal. These steps are followed one grid line at a time until the contour closes, or reaches the edge of the map.

Interpolation by Calculation and measurement--cont. Determining the proportion for line B1:B2.

Interpolation by Calculation and measurement--cont. The grid lines and diagonals for each square are considered and the contour is extended.

Interpolation by Calculation and measurement--cont. The next grid line is between B2 and C2.

Interpolation by Calculation and measurement--cont. Each grid line and diagonal is considered and the contour line is extend between the appropriate points.

Interpolation by Calculation and measurement--cont. When the contour points form a closed shape or have extended from one edge of the map to another, a smooth line is drawn connecting the points. The contour lines must be labeled.