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Survey Levelling: Importance and Types in the Field of Construction
In the field of construction, survey levelling refers to the process of determining the elevations of various points on a construction site relative to a common reference level or benchmark. This is typically done using surveying instruments such as a level, which measures the difference in height between two points by using a levelling staff or rod.
The purpose of survey levelling is to establish a level and flat surface on which to build, ensuring that the finished construction is stable and safe. By determining the elevations of various points on the site, the surveyor can create a detailed topographic map of the site, which can then be used by engineers and architects to design and plan the construction project.
Survey levelling can also be used during the construction process to ensure that the building is being constructed according to the plans and specifications. By periodically measuring the elevations of key points during construction, surveyors can detect any deviations from the design and make adjustments as necessary to ensure the final product meets the required standards.
What are some important terms related to survey levelling in construction?
Here are some important terms related to survey levelling in construction that you need to know:
- Sight line: The line of sight through a levelling instrument from the observer's eye to the staff.
- Intermediate sight: A sight taken on a levelling staff between the backsight and foresight.
- Trigonometric levelling: A method of survey levelling that involves using trigonometric formulas to calculate elevations, rather than physically measuring with a levelling instrument.
- Check levelling: The process of repeating survey levelling measurements to ensure accuracy and identify any errors.
- Contour line: A line connecting points of equal elevation on a topographic map.
- Cross section: A drawing or diagram that shows a view of the terrain or ground surface along a vertical plane.
- Spot elevation: The elevation of a single point on a construction site.
- Vertical control: The process of establishing accurate elevations at multiple points on a construction site to ensure that the finished product is level and stable.
- Differential levelling: A method of survey levelling that involves taking readings at two or more points to determine the difference in elevation between them.
- Global Positioning System (GPS): A satellite-based navigation system that can be used to determine the exact location and elevation of points on a construction site.
- Benchmark: A fixed point of known elevation used as a reference point for survey levelling.
- Levelling staff or rod: A graduated staff or rod is used to measure the height difference between two points during levelling.
- Levelling instrument: A device used to measure the difference in height between two points, such as a spirit level or a laser level.
- Datum: A horizontal reference plane used as a basis for measuring elevations.
- Backsight: The first reading taken on a levelling staff at a point of known elevation.
- Foresight: The reading taken on a levelling staff at a point of unknown elevation.
- Reduced level: The elevation of a point on the site relative to a specified datum.
- Line of collimation: An imaginary line connecting the center of the objective lens of a levelling instrument to the center of the eyepiece.
- Instrument height: The height of the levelling instrument above the benchmark or reference point.
- Rise and fall method: A method of survey levelling that involves adding up the rises and subtracting the falls to determine the net change in elevation between two points.
What are the different types of Survey Levelling in the field of Construction?
The process of survey levelling, which includes figuring out the relative heights or elevations of various places on a site, is crucial in the building industry. There are several survey levelling methods employed in building, such as:
- Differential levelling: This is the most common type of levelling technique used in construction. It involves using a levelling instrument, such as a dumpy level or a digital level, to measure the difference in height between two points. The instrument is set up on a tripod, and the height of the instrument is determined by measuring the distance between the instrument and a benchmark point.
- Trigonometric levelling: This technique involves using trigonometric functions to calculate the height difference between two points. It is often used when there are obstacles, such as buildings or trees that make it difficult to measure the height difference directly.
- Barometric levelling: This technique involves using a barometer to measure the atmospheric pressure at different points on the site. By comparing the atmospheric pressure at different points, it is possible to determine the relative heights of those points.
- GPS levelling: This technique involves using GPS technology to determine the height of different points on a site. GPS levelling is often used in large-scale construction projects where the site is spread over a large area.
- Total station levelling: This technique involves using a total station, which is a combination of a theodolite and an electronic distance meter, to measure the height difference between two points. The total station can also be used to measure angles and distances, making it a versatile tool for surveying in construction.
Survey levelling techniques each have advantages and disadvantages, and the selection depends on the construction project's specific requirements.
What are some errors that can occur in Survey Levelling in Construction?
In order to create elevations or contours, survey levelling is a crucial construction activity and measures the height differences between various sites on the ground. Even with the precision of current surveying technology, mistakes can still happen when doing a survey. Here are some typical survey levelling mistakes that might happen in construction:
- Instrumental errors: These errors result from problems with the surveying equipment, such as a damaged level vial or a misaligned telescope. They can also occur if the equipment is not calibrated correctly.
- Human errors: These errors result from mistakes made by the surveyor or surveying team, such as reading the levelling staff incorrectly or failing to level the instrument properly.
- Environmental errors: These errors are caused by changes in the environment, such as temperature or air pressure fluctuations, that can affect the accuracy of the measurements.
- Refraction errors: These errors occur when light rays bend as they pass through different layers of the atmosphere, causing the surveyor to misread the staff.
- Benchmark errors: These errors occur when the surveyor uses an incorrect or poorly established benchmark, resulting in inaccurate elevations.
- Mistakes in record keeping: These errors occur when survey data is recorded incorrectly or incompletely, leading to errors in calculations or interpretations of the data.
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Lecturer: OTENBuildingCourses
To guarantee that the building project is built to the right elevations and contours, as well as to prevent expensive rework or safety concerns, it is imperative to minimise these survey levelling mistakes. Survey levelling mistakes may be reduced with adequate training, careful preparation, and attention to detail.
