Topic 5: Leveling, Profiles, And Cross Sections

Question 0

Traditional methods to leveling are:

Answer 0

Differential leveling
Trigonometric leveling
Taping
Barometric

Question 1

Leveling

Answer 1

Refers to techniques for determining differences in elevations.
results are used for; design highways, sewers, water supply systems. Layout construction projects according to planned elevations. Calculate volumes of earthwork. Investigate drainage characteristics of an area. Develop maps showing general ground configurations.

Question 2

Vertical Line Definition

Answer 2

A line parallel to the direction of gravity. Determined by plumb bob.

Question 3

Level Surface Definition

Answer 3

A surface of constant elevation and is perpendicular to the plumb line at every point.

Question 4

Elevation Definition

Answer 4

The vertical distance above or below a reference level surface. Normally at sea level.

Question 5

Level Line

Answer 5

A curved line in a level surface, all points of which are of equal elevation.

Question 6

Horizontal line

Answer 6

A straight line tangent to a level line at one point.

Question 7

Differential Leveling

Answer 7

Done by using a “level”, which consist of a high-powered telescope and level bubble.

Types of levels: automatic levels, dumpy levels, tilting levels, digital levels, others (theodolites, total stations).

Question 8

Trigonometric Leveling

Answer 8

Measure horizontal distance and vertical angles to compute elevations. Good for inaccessible points such as mountain peaks, offshore construction.

Question 9

Barometric Leveling

Answer 9

Measuring elevation by measuring change in air pressure. Surveying altimeters can determine elevations within about 2 feet.

Question 10

Automatic Level

Answer 10

Standard instrument’s in today’s surveying.
Has a small circular spirit level called bull’s eye and three leveling screws.
Penned to bring bubble in the circle and instrument does fine tuning automatically.
Good in windy conditions or soft grounds since it can re level itself.

Question 11

Electronic digital level

Answer 11

Automatic instrument.
After the bull’s eye is roughly level, the compensator finishes the leveling.
It displays numerically the rod reading and the distance to the rod.

Question 12

Theodolites

Answer 12

Primary used for angle measurement, however they can be used for leveling.

Question 13

Leveling Equipment

Answer 13

The level is setup on a tripod stand and is leveled. Readings are taken from a level rods. A rod may be used to make sure it is vertical.

Question 14

Bench Mark (BM)

Answer 14

Permanent point of known elevation.

Question 15

Backsight (BS)

Answer 15

Sight taken to the level rod held at a point of known elevation.

Question 16

Height of Instrument (HI)

Answer 16

The elevation of the line of sight of the telescope.

Question 17

Foresight (FS)

Answer 17

A sight taken at any point to determine its elevation.

Question 18

Turning point (TP)

Answer 18

A temporary point established between requires points.

Question 19

Leveling procedure

Answer 19

HI = existing elevation + BS

New Elevation = HI - FS

Question 20

Common Leveling Mistakes

Answer 20

Misreading Rod
Moving turning points: not placing rod back to the same point as before during BS & FS in a TP.
Mistakes with extending the rod
Field notes mistakes

Question 21

Leveling Errors

Answer 21

Level rod not vertical
Settling of rod
Mud, snow, or ice accumulation on base of rod.
Incorrect rod length
BS & FS distance not equal
Bubble not center
Settling of level
Heat waves 
Wind
Instrument out of adjustment
Improper focusing of telescope

Question 22

Suggestions for Good Leveling

Answer 22

Anchor tripod legs firmly
Use straight leg tripods
In sloping ground, two legs of the tripod should be placed on the down hill side.
Check to be sure that the bubble tube is centered before and after.
Take as little time as possible between BS & FS
Use BS and FS distance that are approximately the equal.
Make sure rod is level.

Question 23

Why keep BS and FS distance approximately equal?

Answer 23

When the horizontal lengths of BS(+) & FS (-) are the same, the systematic error of adjustment of the level is canceled.

Question 24

Level Loop Adjustments

Answer 24

When we start with a BM and shoot elevations, we have to close by shooting the same BM.
There will always be some errors
Adjustments to the level loop are based on the relevant distance, or on the number of instrument setups, which is a factor directly related to the distance surveyed.

Question 25

Profile and Cross section leveling

Answer 25

In engineering surveying, a route is considered from three distinct perspectives:
Plane View: looking straight down
Profile: side view or elevation view
Cross section: end view of a section

Question 26

Cross section leveling

Answer 26

Are lines of levels or short profiles perpendicular to center line of a project.
The provide information necessary for estimating quantities of earthwork.
Route cross sections are normally taken in regular intervals 50 or 100 ft stations and at sudden changes in the center line.