Chapter 3 Leveling - Philadelphia University leveli… · - Differential leveling is the process...

transcript

PHILADELPHIA UNIVERSITY

Faculty of Engineering. Department of Civil Engineering.

SURVEYING

Chapter 3

Leveling

• Leveling: the operation of determining the difference in elevation between points. • Elevation: (height or altitude ) : the vertical distance above or below a surface, called datum . The most commonly used datum is mean sea level. • A level surface at any specified elevation can be used to serve as a datum .

• the elevation of a point can be considered as its vertical coordination .Ii can be (+) or (-) depending on whether the point above or bellow the datum . •Level line: the line generated at a point in terrain that is parallel to MSE. • Horizontal line: the line tangent to level line.

BS : The first reading from any instrument position is termed backsight. IS : Readings which are neither the first nor the last from the instrument station are termed intermediates. FS: The last reading from an instrument position is termed a Foresight.

BM : By reading a graduated rod held vertically on a point of known elevation (Bench Mark) a difference in elevation can be measured and a height of instrument (H.I.): calculated by adding the rod reading to the elevation of the bench mark.

Kind of Level -Dummy level -Tilting level - hand level -Laser Level -Automatic level Electronic Digital (Bar-code) Level Thedeolite and total station

DUMMY Tilting level

Automatic level

Laser Level

Electronic Digital

total station Thedeolite

Dummy Level :(Engineer's Level ) Telescope with a bubble tube and tripod .

Aluminum tripod Wooden tripod

Staff :measuring rod with cm (or mm) divisions on it

Parallax -When focussing any optical instrument It is vitally important that we eliminate Parallax. - Move the eye up and down (or from left to right) over the eyepiece of the telescope. -If the cross hairs move relative to the object being Observed then Parallax exists and the focussing is not satisfactory.

Elimination of Parallax Focus the crosshairs (using the Eyepiece) Focus the object (using the Focusing screw) Move eye up and down over the eyepiece Images appear to move Parallax exists and must be removed by better focusing Parallax has been removed. Therefore focusing is good

Errors and how to eliminate them Refraction - varies with line of sight, and time. BS = FS -sight to the same staff first - -don’t take reading lower than 0.5m

Instrument errors -Staff errors graduation error - staff not vertical

- adjustment of the circular bubble -

Ec = d²/2R ( earth curvature correction for leveling)

Ea=0.14 Ec. Ea: atmospheric reflection correction.

Closure error: Δc= m √k k: loop distance in km. m: factor depend on survey order Δc( acceptable ) = m √k If error computed > Δc Then reject leveling If error computed < Δc Distribute error Let Δc= 6.57mm Error computed= 5mm < 6.57 so distribute Correction=(error computed) (point distance/total distance)

- Set the tripod - Take out the instrument from its case - Put the instrument on the table of the tripod and fix it using tightening screw. - Center circular level (leveling the instrument roughly) with using three foot screws. - Aim the telescope to the staff (bring the image of the staff in the objective) using clamping screw. - Focus the staff using the focus screw. - Sharpen the image of cross hairs using focusing ring on the eye piece. - Bring the vertical cross hair exactly on the staff using tangent screw. - Center the bubble of spirit level using knob for coincidence setting. - Read the staff in mm precision. - Check the bubble.

Using a level instrument

Direct leveling methods: - Differential leveling is the process used to determine a difference in elevation between two points. •A Level is an instrument with a telescope that can be leveled with a spirit bubble. •The optical line of sight forms a horizontal plane, which is at the same elevation as the telescope crosshair.

The most important methods of leveling are : 1- Reduce level 2- Rise & Fall

• By reading a graduated rod held vertically on a point of known elevation (Bench Mark) a difference in elevation can be measured and a height of instrument (H.I.) calculated by adding the rod reading to the elevation of the bench mark. • Once the height of instrument is established, rod readings can be taken on subsequent points and their elevations calculated by simply subtracting the readings from the height of instrument.

DIRECT OF LEVELING

2ND SITATION OF LEVELING

1- Reduce level method :

POINT BS IS FS RL PL

A (BM) 1.64 22.22

B 2.01

C 2.46

D 2.77

E(TP) 1.56 3.04

F 1.91

G 1.82

Difference

A (BM) 1.64 23.86 22.22

B 2.01

C 2.46

D 2.77

E(TP) 1.56 3.04

F 1.91

G 1.82

Difference

A (BM) 1.64 23.86 22.22

B 2.01 21.85

C 2.46

D 2.77

E(TP) 1.56 3.04

F 1.91

G 1.82

Difference

A (BM) 1.64 23.86 22.22

B 2.01 21.85

C 2.46 21.40

D 2.77

E(TP) 1.56 3.04

F 1.91

G 1.82

Difference

A (BM) 1.64 23.86 22.22

B 2.01 21.85

C 2.46 21.40

D 2.77 21.09

E(TP) 1.56 3.04

F 1.91

G 1.82

Difference

A (BM) 1.64 23.86 22.22

B 2.01 21.85

C 2.46 21.40

D 2.77 21.09

E(TP) 1.56 3.04 20.82

F 1.91

G 1.82

Difference

A (BM) 1.64 23.86 22.22

B 2.01 21.85

C 2.46 21.40

D 2.77 21.09

E(TP) 1.56 3.04 22.38 20.82

F 1.91

G 1.82

Difference

A (BM) 1.64 23.86 22.22

B 2.01 21.85

C 2.46 21.40

D 2.77 21.09

E(TP) 1.56 3.04 22.38 20.82

F 1.91 20.47

G 1.82

Difference

A (BM) 1.64 23.86 22.22

B 2.01 21.85

C 2.46 21.40

D 2.77 21.09

E(TP) 1.56 3.04 22.38 20.82

F 1.91 20.47

G 1.82 20.56

Difference

A (BM) 1.64 23.86 22.22

B 2.01 21.85

C 2.46 21.40

D 2.77 21.09

E(TP) 1.56 3.04 22.38 20.82

F 1.91 20.47

G 1.82 20.56

TOTAL 3.20 4.86

Difference -1.66

A (BM) 1.64 23.86 22.22

B 2.01 21.85

C 2.46 21.40

D 2.77 21.09

E(TP) 1.56 3.04 22.38 20.82

F 1.91 20.47

G 1.82 20.56

TOTAL 3.20 4.86

Difference -1.66 -1.66

Check O.K

2- Rize & Fall Method

POINT BS IS FS RISE(+) FALL(-) PL

A (BM) 1.64 22.22

B 2.01 0.37

C 2.46

D 2.77

E(TP) 1.56 3.04

F 1.91

G 1.82

Difference

A (BM) 1.64 22.22

B 2.01 0.37

C 2.46 0.45

D 2.77

E(TP) 1.56 3.04

F 1.91

G 1.82

Difference

A (BM) 1.64 22.22

B 2.01 0.37

C 2.46 0.45

D 2.77 0.31

E(TP) 1.56 3.04

F 1.91

G 1.82

Difference

A (BM) 1.64 22.22

B 2.01 0.37

C 2.46 0.45

D 2.77 0.31

E(TP) 1.56 3.04 0.27

F 1.91

G 1.82

Difference

A (BM) 1.64 22.22

B 2.01 0.37

C 2.46 0.45

D 2.77 0.31

E(TP) 1.56 3.04 0.27

F 1.91 0.35

G 1.82

Difference

A (BM) 1.64 22.22

B 2.01 0.37

C 2.46 0.45

D 2.77 0.31

E(TP) 1.56 3.04 0.27

F 1.91 0.35

G 1.82 0.09

Difference

A (BM) 1.64 22.22

B 2.01 0.37 21.85

C 2.46 0.45 21.40

D 2.77 0.31 21.09

E(TP) 1.56 3.04 0.27 20.82

F 1.91 0.35 20.47

G 1.82 0.09 20.56

Difference

A (BM) 1.64 22.22

B 2.01 0.37 21.85

C 2.46 0.45 21.40

D 2.77 0.31 21.09

E(TP) 1.56 3.04 0.27 20.82

F 1.91 0.35 20.47

G 1.82 0.09 20.56

TOTAL 3.20 4.86 -1.66

Difference

A (BM) 1.64 22.22

B 2.01 0.37 21.85

C 2.46 0.45 21.40

D 2.77 0.31 21.09

E(TP) 1.56 3.04 0.27 20.82

F 1.91 0.35 20.47

G 1.82 0.09 20.56

TOTAL 3.20 4.86

Difference -1.66 -1.66

Check O .K

Indirecte leveling methods -Barometric leveling: the existence of an inverse relationship between the height and the value of atmospheric pressure . -It Is determined by finding the differences in elevations between the measured air pressure at each Point.

-Trigonometric leveling : In this method is to measure the horizontal distances and vertical angles by using theodolites to calculate differences in Elevations (heights).. -It is Considered is the only method to measure elevations and elevations in mountainous areas . -This method is used in case of finding teams elevations of the objectives can not be accessed -(Such as the top of a minaret , a tall building -and the side of the waterway

-Hydrostatic leveling:

-Profile leveling : -Is the operation of determining the elevation of the points at regular intervals along a fixed line

Chapter 3 Leveling - Philadelphia University leveli… · - Differential leveling is the process...

Documents