Civil Engineering/Surveying/leveling/types of leveling /Profile levelling

Summary

The script explains the process of profile leveling, a surveying technique used in engineering to determine the amount of earth to be cut or filled for leveled construction. It involves setting up a level instrument, taking readings at regular intervals along a central line, and recording these in a level notebook. The method includes marking points, taking foresights and backsights, and using either the height of instrument or rise and fall method for level reduction. The final step is plotting a profile, which graphically represents the ground points on a longitudinal section, with a larger vertical scale to highlight elevation differences.

Takeaways

• 📏 Profile leveling is a surveying technique used to determine earthwork quantities for construction projects.
• 📍 It is conducted along the central line of a track of land where linear engineering work is planned.
• 🔍 The process involves setting up a level instrument at various locations and taking readings at regular intervals.
• 📋 A benchmark is used as a reference point for taking back sights and foresights with a leveling staff.
• 📏 Turning points (TP) and salient points are marked and observed to capture changes in the gradient.
• 📊 The readings are recorded in a level notebook, detailing each observation's station and elevation.
• ✂️ The reduction of levels can be calculated using either the height of the instrument method or the rise and fall method.
• 📊 Plotting the profile leveling provides a graphical representation of the ground points on a longitudinal section.
• 📐 The vertical scale of the profile is typically larger than the horizontal scale to emphasize elevation differences.
• 📈 Segmented straight lines connecting the reduced level points represent the ground's longitudinal profile.

Q & A

What is profile leveling?

Profile leveling is a method of surveying carried out along the central line of a track of land where a linear engineering work is to be constructed. It is also known as longitudinal sectioning.

Why is profile leveling important in engineering?

Profile leveling is important as it helps determine how much earth needs to be cut or filled to make a leveled construction, which is essential for the planning and execution of linear engineering projects like roads, railways, and canals.

What are the steps involved in carrying out profile leveling?

The steps include setting up the level on a convenient location, taking a backsight on a benchmark, marking points at regular intervals, taking observations at these points using a leveling staff, repositioning the instrument, and recording the readings in a level notebook.

How are the readings from profile leveling recorded?

The readings are recorded in a level notebook with columns for backsight, intermediate sides, and foresight. The reduced levels of various stations are computed and plotted to create a profile.

What is the purpose of marking points at regular intervals during profile leveling?

Marking points at regular intervals allows for systematic data collection along the alignment, which is necessary for accurately determining the depth of cutting or filling required at each point.

What is the significance of the benchmark in profile leveling?

The benchmark serves as a reference point for the leveling process. A backsight is taken on this marked benchmark to establish a known starting elevation for the leveling work.

How are the reduced levels of various stations computed?

The reduced levels can be computed using either the height of instrument method or the rise and fall method, which involve calculations based on the readings taken at different points along the profile.

What is the purpose of plotting a profile after leveling?

Plotting a profile provides a graphical representation of the ground points on a longitudinal section, which helps visualize the elevation changes and plan the construction work more effectively.

Why is the vertical scale of a profile plot generally larger than the horizontal scale?

The vertical scale is drawn larger than the horizontal scale to accentuate the differences in elevations, making it easier to identify and plan for the necessary earthwork.

How are salient points, such as changes in slope, recorded in profile leveling?

Salient points like changes in slope are recorded by taking foresights at these points during the leveling process and noting down the readings in the level notebook.

Outlines

00:00

🏗️ Profile Leveling in Engineering Surveying

This paragraph introduces the concept of profile leveling, a surveying technique used by engineers to determine the amount of earth to be cut or filled for leveled construction. It explains that profile leveling is conducted along the central line of a track of land where linear engineering work is planned. The process involves marking the line on the ground, setting up a level at convenient locations, and taking observations at regular intervals using a leveling staff. The readings are recorded in a level notebook, and the reduction of levels can be done using either the height of the instrument method or the rise and fall method. The paragraph concludes with a brief mention of plotting a profile, which provides a graphical representation of the ground points on a longitudinal section.

05:02

📊 Plotting the Longitudinal Profile

The second paragraph delves into the plotting of profile leveling, which is essential for visually representing the ground points on a longitudinal section. It describes how to plot a profile by drawing a datum line and marking the distance of points, then plotting the reduced levels along vertical lines drawn on these marked points. The segmented straight lines joining the reduced levels represent the longitudinal profile of the ground surface. The paragraph mentions that the vertical scale of the profile is typically larger than the horizontal scale to emphasize the difference in elevations. The paragraph concludes with a reference to a figure that would show the complete profile of the longitudinal section of the profile leveling.

Keywords

💡Profile Leveling

Profile leveling is a surveying method used to determine the amount of earth that needs to be cut or filled to create a leveled construction. It is crucial for linear engineering works such as roads, railways, and canals. In the script, profile leveling is described as being carried out along the central line of a track of land, which helps in determining the depth of cutting or filling on the proposed gradient.

💡Longitudinal Sectioning

Longitudinal sectioning is another term for profile leveling. It involves creating a vertical cross-section of the ground along the proposed alignment of a construction project. This technique is essential for planning the earthwork required for the project. The script mentions that the line along which a profile runs is marked on the ground before taking any observations, indicating the preparatory step in longitudinal sectioning.

💡Level Instrument

A level instrument, often referred to as a theodolite or level, is a tool used in surveying to measure angles and elevations. In the context of the script, the level instrument is set up at convenient locations to take readings for profile leveling. It is used to ensure accurate measurements of the ground's elevation at various points along the construction line.

💡Benchmark

A benchmark is a known reference point used in surveying to establish elevations. In the script, a benchmark is marked and used as a starting point for taking back sights with the level instrument. This ensures that all subsequent measurements are relative to a consistent and known elevation.

💡Back Sight

A back sight is a measurement taken with a level instrument towards a benchmark or a previously established point of known elevation. In the script, back sights are taken at benchmarks and turning points to establish a consistent elevation reference for the leveling process.

💡Foresight

Foresight refers to the measurement taken with a level instrument towards an unknown point whose elevation is to be determined. In the script, foresights are taken at turning points and salient points to record their elevations relative to the benchmark, which is essential for determining the earthwork needed.

💡Turning Point

Turning points are specific locations along the construction line where the direction of the alignment changes, such as at corners or curves. In the script, observations are taken at turning points using a leveling staff to record their elevations, which are critical for understanding how the ground slopes and how it will affect construction.

💡Leveling Staff

A leveling staff is a graduated rod used in conjunction with a level instrument to measure the vertical distance from the instrument to the point being observed. In the script, a leveling staff is used to take foresights and backsights at regular intervals, helping to determine the elevation changes along the construction line.

💡Salient Point

Salient points are specific locations where there are changes in the slope or gradient of the ground. These points are important for understanding the terrain's profile. The script mentions taking readings at salient points to capture these changes, which are crucial for the accurate planning of earthworks.

💡Reduction of Levels

Reduction of levels is the process of calculating the true elevations of points based on the observed readings and known elevations. The script describes two methods for this: the height of instrument method and the rise and fall method. This step is essential for converting the raw leveling data into a usable format for construction planning.

💡Plotting Profile

Plotting a profile involves graphically representing the ground points on a longitudinal section along the alignment. The script explains that the vertical scale is typically larger than the horizontal scale to emphasize elevation differences. By plotting the reduced levels on a datum line, engineers can visualize the terrain's profile and plan the necessary earthworks.

Highlights

Profile leveling is a surveying method used to determine the amount of earth to be cut or filled for leveled construction.

It is also known as longitudinal sectioning, used for linear engineering works like tracks or roads.

The process involves marking the central line of the land where the construction will take place.

A level instrument is set up at a convenient location to take observations.

Back sight is taken on a benchmark to establish a reference point.

Points are marked at regular intervals, such as every 10 meters, along the central line.

Observations are taken at these points using a leveling staff to measure the elevation.

The level instrument is repositioned to take further observations at different locations.

Readings are recorded in a level notebook, including back sights, foresights, and salient points.

The reduction of levels can be done using either the height of instrument method or the rise and fall method.

The reduced levels of various stations are computed and recorded.

Plotting of profile leveling provides a graphical representation of the ground points on a longitudinal section.

The vertical scale of the profile is typically larger than the horizontal scale to emphasize elevation differences.

A datum line is drawn for plotting, with distance of points marked along it.

Reduced levels are plotted along vertical lines drawn on marked points.

Segmented straight lines joining the reduced level points represent the longitudinal profile of the ground surface.

The final figure shows the complete profile of the longitudinal section of the profile leveling.

Transcripts

profile leveling

do you know how engineers come to decide

as to how much earth is to be cut or

filled to make a leveled construction

have you ever wondered how to determine

the depth of cutting

or filling on the proposed gradient

well it is determined by plotting a

profile leveling

and now we will learn in detail how it

is done

profile leveling is a method of

surveying

that has been carried out along the

central line

of a track of land on which a linear

engineering work is to be constructed

profile

leveling is also known as longitudinal

sectioning the line along which a

profile runs

is to be marked on the ground before

taking

any observation to carry out profile

leveling

firstly set up the level on a convenient

location

say l1 level the instrument

and take a back sight on a marked

as the benchmark now

mark points at regular intervals say 10

meters

on the lineup to the turning point dp1

take the observations at these regular

intervals

using leveling staff take a foresight on

turning point tp1

and note down all the readings now let

us

reposition the instrument to some other

convenient

location l2 set up the instrument

and level it on the location l2

now take a backsight on tp1 and take

readings at regular intervals using a

leveling staff

now take a foresight on the final

station c

and also take the readings at salient

point

say x where changes in slope occur

as soon as readings are taken the notes

of the profile

are recorded in a level notebook

the readings are filled in the notebook

as

follows for instrument position at

l1 the back side is taken at benchmark

and the reading of 3.005

meters is placed in its column in the

row of station a

the readings for intermediate sides for

one is 2.285 meters

2 is 1.56 meters

3 is 1.785 meters

and for 4 is 2.105

meters are placed in the corresponding

row

the foresight taken at the station tp1

3.105 meters is placed

in its row after changing the instrument

location

the back side at tp1 is entered in its

row

in the back side column the readings

intermediate sides for 5 is 3.465 meters

6 is 3.12 meters

7 is 3.015 meters

8 is 2.58 meters

and 9 is 1.955 meters

are placed in the corresponding row

the readings of the salient point x

is 3.955 meters

is placed between the intermediate sides

at its place

the foresight 1.465 meters

taken at station c is placed in its row

the reduction of levels can be done

either

by height of instrument method or rise

and fall method

the following table indicates the

computations done by both

height of the instrument and rise and

fall methods

now that the reduced levels of various

stations are known

let us learn how to plot a profile

plotting of profile leveling provides a

graphical representation

of the ground points on a longitudinal

section

along the alignment the vertical scale

of the profile is

generally drawn much larger than the

horizontal scale

in order to accentuate the difference of

elevations

to plot a profile a datum line is drawn

along which distance of points are

marked

the reduced levels are plotted along

vertical

lines drawn on marked points

segmented straight lines joining the

reduced

level points represent the longitudinal

profile

of the ground surface the following

figure

shows the complete profile of

longitudinal section

of the profile leveling