Surveying Levelling: Types, Advantages & Disadvantages

The height of the ground surface, buildings, and other structures is determined through levelling in surveying.

Levelling is one of the most important components of surveying before building roads, dams or any other type of structure. Finding a point’s elevation in reference to a datum level above or below the ground is the focus of this area of surveying. In this post, we will define levelling, discuss the many kinds of levelling that are used in surveys, as well as their advantages and disadvantages.

What does the term levelling mean?

Identifying the relative heights or elevations of distinct locations on the surface of the earth allows for their representation on a plan or map. The levelling process mostly involves measurements in the vertical plane. A levelling technique entails measuring the vertical ground level.

The reason for levelling

The goal of levelling is to establish the elevation or height of a point, or group of points, in relation to a benchmark or reference datum. To measure the vertical distances between locations, a levelling instrument and a levelling staff are commonly employed. In many different industries, including building, engineering, architecture, and land surveying, levelling is a crucial surveying method.

• In architecture, levelling determines the proper height and alignment of structures like roads and buildings.

• Additionally, it is employed to guarantee that the ground is level even before a building’s foundation is laid.

• To guarantee that a pipeline or drainage system operates properly, levelling is used in engineering to calculate the slope of the system.

• Levelling in architecture makes ensuring that walls, floors, and ceilings are all even and level.

• The contours of the land are measured and mapped during land surveying, which is essential for planning and development purposes.

Levelling: Types

Barometric averaging

The phrase “barometric levelling” refers to levelling that makes use of the relationship between elevation differences between two sites in dissimilar places and variations in air pressure at these locations.

Using a barometer to calculate the difference in elevation between two locations on Earth’s surface is an ancient and well-known art.

A barometer may be used to gauge atmospheric pressure at any altitude. This form of levelling is rarely used in surveying work. Barometric levelling is typically employed in surveillance or exploratory surveys.

Levelling using trigonometry

Trigonometric levelling, in which the elevation of the points is determined from their vertical angles and measured horizontal distances, is one of the simplest levelling techniques.

Trigonometric levelling is also known as indirect levelling. The length of any side of a triangle may be calculated in the same way using basic trigonometric relations.

Direct levelling

It is the levelling method that is most frequently employed. This method involves taking measurements directly from the levelling apparatus. According on observation points and instrument positions, direct levelling can take several different forms, which are as follows:

Simple levelling

In basic levelling, determining the elevation difference between two locations is a straightforward task. The instrument is placed so that both dots may be seen in the space between them.

The distance between the two locations shouldn’t be too great because doing so makes it more difficult to get readings from both locations. Only when the points are near to one another and there are no obstructions in their route is the basic levelling procedure acceptable.

The following are the stages for the straightforward levelling:

• Let’s imagine that the earth’s surface has two locations. Call them A and B for now.

• The instrument can be placed anywhere, but to minimise instrument errors, it should be placed midway between the two points.

• Focus the telescope on the staff being held vertically at point A after carefully levelling the apparatus.

• Take the readings where the staff is being cut by the horizontal hair. Now, vertically hold the staff at point B.

• The staff is held vertically at the spot, and the telescope is properly focused on it. Take readings at point B, making sure the bubble is centred in the circle.

Differing the levelling

• Differential levelling is used in surveying when it’s required to determine the elevation difference between two locations that are too far away and have a sizable height difference.

• When levelling obstacles make it impossible for the points to be observed from one instrument configuration, differential levelling is used. It is crucial to set up the instrument in several locations and work in stages as a consequence.

• When there is a longer distance between the two locations, the differential levelling approach is acceptable.

Mutual levelling

• Reciprocal levelling is used to detect the precise level difference between locations that are far apart from one another.

• When a river, pond, or other impediment prevents the level from being put up between the two locations, the reciprocal levelling procedure is used.

• Reciprocal levelling gets rid of mistakes caused by curvature and collimation. Additionally, the error caused by the collimation line is removed.

• In this case, the instrument is positioned on each side of the riverbank or valley bank, and the staff is held stationary on both banks to obtain two staff readings.

Fly levelling

When levelling a fly, only the rear and foresight values are recorded; intermediate sight readings are not collected at any point throughout this operation.

Fly levelling is used to create the benchmarks, connecting them to the starting point of the project. When the project site is far from the benchmark, fly levelling is used. The surveyor in this case starts the operation by setting up the instrument in the proper location and getting a backsight reading on the benchmark.

Profile levelling

Profile levelling is the process of measuring the height of the points along a fixed line, such as the centre of a railway, road, canal or sewer.

The fixed line might be made up of several straight lines or just one straightforward line. It is also known as longitudinal sectioning.

Benefits of levelling

The height of the ground surface, the height of buildings or other structures, and the elevation of features like rivers, lakes, and other bodies of water are all commonly measured using this method.

The construction of a road’s centerline is a crucial use of levelling. Surveyors use levelling techniques to measure the height of the ground at several spots along the road to make sure it is level and safe for cars. It enables them to design a road that takes elevation variations into account and guarantees that the road surface will be level and smooth.

Understanding the topography of the soil is another significant use of levelling. Surveyors can produce a contour map that depicts the form of the terrain by measuring the height of the ground at various locations. Planning land uses, managing the environment, and undertaking engineering projects all require this knowledge.

Levelling is a very helpful building technique for creating structures. For the safety and durability of the project, builders utilise levelling to make sure that the foundations are level and sturdy. In order to design drainage and stop erosion, they also utilise levelling to assess the slope and grade of the ground.

Levelling: Limitations

There are a number of advantages to levelling, but there are also some possible disadvantages. Here are a few of the most significant:

Levelling is a time taking process

Levelling might take a while, especially when there are big regions or complicated topographies. It’s because it requires utilising specialised equipment, like a level or total station, to measure the height of the ground at various spots. To guarantee accuracy, the procedure might need to be carried out more than once, which would add to the time needed.

Expensive

If the area to be levelled is extensive or the topography is complicated, the cost may be high. It frequently calls for expensive specialised equipment and highly trained workers. Levelling costs may also differ based on the project’s complexity, location, and other elements, such as the requirement for permits or other governmental clearances.

Levelling demands the expertise of competent professionals.

Levelling is a skilled job that calls for knowledge of engineering and surveying. The procedure normally calls for skilled personnel with expertise with surveying tools, a working knowledge of levelling concepts, and the ability to evaluate data. The levelling procedure must be carried out precisely and effectively, and this requires skilled staff.

Plotting strata on a map or sheet needs several calculations and takes time.

The data received from levelling must next be processed and examined to produce a contour map or other output. It can take a lot of time and include multiple calculations, especially if the region being surveyed is complicated or huge. It takes meticulous attention to detail and a full comprehension of surveying and levelling concepts to produce an accurate map or sheet.

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