Surveying Techniques and Levelling Operations

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is a key factor in ensuring accurate readings when using a levelling rod?

The rod should be laid flat against the ground.

The rod should be extended and left unsecured.

The rod should be held at an angle for better visibility.

The rod should be held plumb for all rod readings. (correct)

What issue may arise if the barcodes on a levelling rod are damaged?

The rod will automatically adjust its length.

Errors will occur in distance reading. (correct)

Barcode rods will no longer be used.

The rod will become too heavy to lift.

Which of the following measurements can a traditional foot rod read most accurately?

0.1 ft

0.01 ft (correct)

0.01 inches

0.001 ft

What is the primary purpose of the Two Peg Test in levelling operations?

To test the accuracy of a level. Signup and view all the answers

What should be done if a rod is held temporarily near, but not on, a required location?

The rod should be turned away from the instrument. Signup and view all the answers

What is the primary purpose of cross section leveling?

To understand the undulation of the ground surface Signup and view all the answers

Under what circumstances is differential leveling most commonly used?

When there are obstacles between the points Signup and view all the answers

Which technique is NOT mentioned for determining elevation?

Water Level Technique Signup and view all the answers

What is a key feature of a digital level?

It operates in electric mode and utilizes barcode graduation Signup and view all the answers

What is the method primarily used in simple leveling?

Measuring the elevation between two close points using a single setup Signup and view all the answers

Which type of leveling instrument uses a compensator to maintain a horizontal line of sight?

Automatic Level Signup and view all the answers

What material can leveling rods be made from?

Wood, metal, or fiberglass Signup and view all the answers

In profile leveling, where is the leveling typically performed?

At the midpoint of the road at regular intervals Signup and view all the answers

What is the formula used to calculate the RL in the Rise & Fall method?

Sum Rise - Sum Fall Signup and view all the answers

In the Height of Collimation method, what is the first step when starting the calculation?

Add the first back sight reading to the first RL Signup and view all the answers

When using the Rise & Fall method, if the sum of the BS readings is 3.6 and the sum of the FS readings is 11.08, what is the difference calculated?

-7.48 Signup and view all the answers

What changes the height of collimation in the Height of Collimation method?

The position of the level instrument Signup and view all the answers

Which of the following statements about the Rise & Fall method is true?

It includes separate columns for rise and fall. Signup and view all the answers

How is the RL for a station found in the Height of Collimation method?

By subtracting the height of collimation from the staff reading. Signup and view all the answers

What does not affect the calculations in the Rise & Fall method?

The total distance measured Signup and view all the answers

If the first back sight reading is 1.27 and the first RL is 356.68, what is the height of collimation?

357.95 Signup and view all the answers

What is the purpose of a datum in leveling?

To serve as a reference surface for measuring elevations. Signup and view all the answers

Which term describes the reading taken after the level has been set up?

Back sight (BS) Signup and view all the answers

What is a Bench Mark (BM) in the context of leveling?

An object with a known elevation above or below a datum. Signup and view all the answers

Which of the following best describes Reduced Level?

The elevation of a point above or below a datum. Signup and view all the answers

What is the primary objective of leveling?

To set the base level of a building. Signup and view all the answers

Which type of sight represents readings taken between the back sight and fore sight?

Intermediate Sight (IS) Signup and view all the answers

In which situation is leveling NOT typically used?

To determine angle of elevation for surveying. Signup and view all the answers

What does the term 'Fore sight (FS)' refer to?

The last reading taken before moving the level. Signup and view all the answers

What error is introduced when the Automatic Prism compensator goes out of alignment?

Collimation Error Signup and view all the answers

Which error becomes significant when leveling over long distances?

Earth Curvature Error Signup and view all the answers

Which of the following methods is used to record the height of water levels continuously?

Tide Gauge Signup and view all the answers

How can parallax error be reduced when using an optical leveling instrument?

By ensuring the cross hairs are focused precisely Signup and view all the answers

In the Rise & Fall leveling method, what does the last RL minus the first RL indicate?

Net height difference Signup and view all the answers

What should the sight lengths be kept under to eliminate curvature error effects?

150 ft Signup and view all the answers

What type of error is related to the movement of one's head while viewing the cross hairs?

Parallax Error Signup and view all the answers

What is the primary concern of errors in leveling for short segments connecting to nearby benchmarks?

Significant potential sources of errors Signup and view all the answers

Study Notes

Leveling Unit 3

Leveling is the process of determining the relative heights of points on or below the Earth's surface. It focuses on measurements in the vertical plane.
Leveling is the overall term for various processes used to determine elevations or differences in elevation.
It involves measuring vertical distances using direct or indirect methods to ascertain elevations.

Leveling Terminologies

Datum: An imaginary level surface to which all elevations are referenced (often sea level).
Elevation: The vertical distance from a datum to a point or object.
Bench Mark (BM): A permanent, natural or artificial object with a marked point whose elevation relative to a datum is known or assumed.
Back Sight (BS): The initial reading taken after setting up the level.
Fore Sight (FS): The last reading taken before moving the level; it's also a reading to a point whose height is needed.
Intermediate Sight (IS): Staff readings taken between BS and FS (medium readings).
Change Point (CP) or Turning Point (TP): Staff position where FS and then BS readings are taken.
Reduced Level: Calculated elevation of a point above or below sea level; also called reduced height.

Primary Objective of Leveling

Determine the elevations of given points relative to a datum.
Establish points with a specified height above or below a datum line.

Uses of Leveling

Setting the base level for buildings.
Creating contour maps to determine sites for reservoirs, catchment areas, and alignments of roads, railways, canals, or sewage lines.
Determining altitudes of points on a hill or finding reduced levels of points above or below the Earth's surface.
Calculating the capacity of a reservoir.

Create Profile View Maps (Profile Leveling)

Used to understand the shape of the ground surface.
Measurements are taken along the center of the road, at regular intervals (e.g., 20m, 30m).

Create Cross Section Maps (Cross Section Leveling)

Used to determine the undulations of the ground surface across the road.
Measurements are perpendicular to the center line of the alignment, at regular intervals (e.g., 20m, 40m).

Types of Leveling

Simple Leveling: A method for measuring elevation differences between two points that are close together and have no obstacles. The level instrument is set up at the midpoint allowing direct vision of both points.
Differential Leveling: Used when points are far apart, the difference in elevation is large, or there are obstacles. An instrument is moved from station to station to determine elevations.

Theory of Differential Leveling

Techniques for finding elevations: Leveling, Total Station Technique, GPS Vertical Position Technique, Remote Sensing (Lidar or Aerial photography).

Types of Level Instrument

Dumpy Level
Tilting Level
Automatic Level
Digital Level

Digital Level

An automatic level with normal optical leveling capabilities and a graduated rod.
Operates using electrical measurements; rod graduations use barcodes.
Can get distance and elevation readings with a button press.
Data is stored and transferable.

Automatic Level

Uses a compensator to maintain a horizontal line of sight, even when the telescope is tilted.
Bubble-based system centers itself (or nearly so), so the compensator maintains the horizontal line of sight.

Accessories

Traditional Levelling Rod (Leveling Staff): Made of wood, metal, or fiberglass. The surveyor should study unfamiliar rods prior to use. Graduated in feet or meters,
Foot Rod: Can be read to 0.01 ft.
Metric Rod: Can be read to 0.01 meter with estimations for millimeters
Levelling Rod (Barcode Rod): Rod with barcode graduated scale. Used with digital levels for distances up to 100m
The rod should be plumb and held in the correct upright position for accurate measurement.
Turning Level Plate: Part to help maintain a horizontal plane.
Rod Bubble: Used to help maintain horizontal plane.

Suggestions for Rod Work

Extend and clamp the rod properly and hold on firm ground.
Hold the rod plumb for all readings.
Use the same rod position for backsight and foresight at change points.
If the rod is held nearby but not on the location, turn the face away from the instrument to avoid mistakes.

Two Peg Test

Used to check accuracy of a level (optical or digital).
Set up three points (A, C, B) in a straight line (A to C = C to B = 30m).
Position the level at C and measure staff readings at A and B.
The true difference in level is obtained, even if the instrument is slightly out of adjustment.

Two Peg Test 2

Move the level to the higher end (B) and position it on a line with A, extending slightly beyond B.
Read the staff readings at A and B again.
If the instrument is adjusted, the B reading should equal the A reading plus the elevation difference measured in the first test.

Booking for Two Peg Test

A table is used to record the data (eg. BS, IS, FS, Horizontal distance, reduced levels, etc.) with comments for each measurement.
The difference between two measurements of the same point is used as checks to verify accuracy.

Rise and Fall Method

Used for calculating RL's along a line by recording BS & FS and rise & fall.
A table is used to record the data (eg. BS, IS, FS and others).
Arithmetic checks help identify accuracy.

Height of Collimation Method

Another approach for leveling calculations.
Height of collimation is used to calculate the RL of a station by subtracting the staff reading from the current height of collimation.
The height of collimation is updated when the level is repositioned.

Theory of Differential Leveling (Tide Gauge)

A modern water level monitoring station with sensors to continuously record surrounding water levels.

Errors in Leveling

Collimation Error: Level alignment issue.
Parallax Error: Cross-hairs or image issue if not precisely focused.
Error Due to Earth's Curvature: The line of sight deviates from horizontal as the distance increases.
Error Due to Refraction: Light bending affects readings.
Sight Length: 300 ft (1mm effect), keep sights under 150ft and equal lengths for backsights/foresights eliminate effects.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on key concepts and techniques in surveying, specifically focusing on levelling operations and the use of levelling rods. This quiz covers important factors that affect accuracy, various leveling methods, and the purpose of specific tests within the field. Perfect for students and professionals in surveying engineering.