Chain surveying is an old method of surveying that involves measuring distances and angles between points on the ground with a chain or tape measure, often using trigonometry to calculate the distance between two points in space.
This article will provide an overview of chain surveying, including its definition, detailed information on how it works, and the aspects that make it more accurate than other methods.
Definition of chain surveying
A type of surveying in which measurements are only taken in a linear manner in the field is known as chain surveying. One of the soil measurement techniques, chain surveying only includes linear measurements and not angular measurements.
Importance of chain surveying
It is apt for survey of small areas that are simple and basic and do not have complicated features to consider. Chain surveying is named after the equipment it uses for measuring- the chain.
Basic principles of chain surveying
Triangulation is the cornerstone of the chain surveying methodology. To account for this, the whole survey region is split up into numerous appropriate triangles. In this way, a system of interconnected triangles is created. The triangles should be constructed such that their interior angles range from 30 degrees to 120 degrees, with no interior angle being under 30 degrees or larger than 120 degrees. Equilateral triangles are preferred but not required. Thus, the design is mapped out and made ready by counting and estimating the vertices of the triangle.
Basic chain surveying terminology
The following is a concise explanation of a number of terms that are frequently used in chain surveying:
Main stations
As the name implies, the main stations are the terminals of the primary survey lines that make up the framework.
Tie or subsidiary stations
For the purpose of calculating the interior details, these are the transitional stations that are included in the major survey lines. Some examples of these kinds of interior elements include things like fences, hedges, and so on.
Base line
The baseline is the primary survey line as well as the longest one. It is the line in relation to which all other metrics for the purpose of describing the activity are obtained. In most cases, it begins in the exact middle of the level field (i.e. diagonally).
Chain lines
Main survey lines are another name for chain lines, which are also extensively used. These connect any two of the primary stations.
Tie lines
The term “tie line” may sometimes be used interchangeably with the term “subsidiary line.” These lines connect the various subsidiary stations with one another. These lines are useful for ensuring that the interior details are accurate.
Check lines
These are often referred to as the proof lines. They serve the purpose of ensuring that the framework is accurate. The span of the check line, as determined on the ground, has to be the same as the extent of the check line, as shown on the plan.
Offsets
Offsets are lateral measures that are measured from the baseline. Offsets may be positive or negative. The primary objective of using offsets is to find the location of various objects in relation to the baseline. Offsets may be either perpendicular or oblique, and these two orientations are the most common ones in practice.
Types of instruments used for chain surveying
The following is a list of the many kinds of equipment that are used in the process of chain surveying:
Chains
When doing a chain survey, chains are an extremely important piece of equipment to have on hand for the actual surveying process. Chains are often deployed to get accurate measurements of horizontal distances.
Arrows
The marking pens are often made of steel wire, and a chain survey typically includes ten arrows for use. The length might be anything between 25 and 50 millimetres. However, the specified length will be based on the IS-Code. A circle or loop is twisted into the arrow’s opposite end for portability.
Pegs
Putting in a peg at the end of a survey line or at a position station indicates the end of the line. With the aid of the wooden hammer, they are driven into the ground and retained at a height of 40 mm. Pegs typically measure 150 millimetres in length and have a square top that is 30 millimetres in size. Pegs are typically made of wood and are widely accessible.
Ranging Rods
Two to three-metre-long rods made of steel or dry, seasoned wood are used for the range of points. White and black, white and red, or white, black and red coatings alternate to provide the band’s signature look.
Since the band is 200 mm in length, it may be used for a rough measurement with the shorter 2 m ranging rod, which is more often used. At 200 metres, you won’t be able to see their octagonal or circular cross-sections.
ALL ABOUT: Ranging Rods
Plumb Bob
When chaining along a slope, a plumb bob is used to accurately transfer marks to the surface. It’s also used to evaluate the verticality of range poles and to precisely centre the theodolite compasses, plane tables, etc., over a station mark.
Cross Staff
This instrument is used to mark the starting and ending points of a chain line at right angles. Pole shoes are used to secure the unit to the ground, and it consists of a framework or container with two sets of vertical slots.
Offset Rod
The function of the range rod and the offset rod are equivalent. They have a hooked iron shoe on one end and a groove or a hook on the other to help you push or drag the chain over obstacles like hedges.
Surveying chain types
The following is a list of the several kinds of chains that are often used in surveying:
Metric Chain
The most common lengths of metric chains are five metres, ten metres, twenty metres, and thirty metres. To facilitate fraction readings along a surveying chain, tallies are installed every metre along a 5- and 10-metre chain, and every 5 metres along a 20- and 30-metre chain. Apart from where the tallies are fastened, there is a little brass ring at each metre.
Surveyor’s Chain
A Gunter’s chain, also known as a Surveyor’s chain, has a total length of 66 feet and is made up of 100 connections, each of which is 0.66 feet (7.92 inches) in length. The standard length of a chain used in surveying is 66 feet, which was chosen for its practicality in calculating land areas.
Engineer’s Chain
The engineer’s chain has a total length of one hundred feet and is made up of one hundred links, each of which is one foot in length. When using this kind of chain for surveying, a brass label is affixed once every ten links. The tags have notches on them, which indicate the number of ten-link segments that are present between the tags and the ends of the chain.
Revenue Chain
The length of this type of chain is 33 feet, and it comprises 16 links. In the field of surveying, this particular type of chain is used for the purpose of measuring fields during cadastral surveys.
Steel Band
These chains are made from one continuous, thin steel link anywhere from 12 mm to 16mm in width and 0.3 mm to 0.6 mm in thickness. Band chains may also include graded etching in centimetre increments as an alternative to the brass studs that divide this chain every 20 centimetres. Band chains in surveying are coiled on steel crossovers or metal lurches, making them easy to use and manage.
Consecutive stages in a survey chain
Reconnaissance
Reconnaissance refers to the first exploration of the region subject to a chain survey. The surveyor will go over the location to be mapped out and make any necessary adjustments before beginning the survey, including inspecting the land on foot, making a note of the location of borders, roads, rivers, and other obstacles to chain lines, as well as the locations of potential stations.
Marking stations
Marking a station may be done with a range rod or a wooden peg, by putting a spike or nails into a hard surface, or by embedding a stone with a cross-shaped mark.
Reference sketches
After the station has been marked, it has to be referenced or localised, using a method of measurement known as ties, which is taken from three fixed places that are simple to identify, such as the building’s corner.
Running survey line
Following the completion of the preparatory work, the chaining procedure begins at the baseline and is carried out constantly along each line of the framework. Therefore, the chain is put down and held in place while offset measurements are recorded to pinpoint the neighbouring features. Wherever it is essential, perform ranging. Take a reading of the change as well as the offset, then record it in the record sheet.
Errors in chain surveying
Chain surveying is prone to making three significant errors. They are as follows:
Personal Errors
Personal errors are defined as mistakes that are made by the surveyor as a result of their own carelessness or poor judgement. These flaws are significant and cannot be discovered with relative ease. To reduce the likelihood of these types of mistakes occurring, the appropriate safeguards need to be followed. Some personal mistakes are:
- Wrong recording
- Poor ranging
- Inadequate plumbing
- Wrong reading
- Reading from the incorrect ends of the chain
Compensating Errors
This kind of error might have both beneficial and harmful effects. This means that compensation is more likely to occur when a substantial number of measurements are taken. The probability theory may be used to evaluate the severity of such mistakes. Several common mistakes are as follows:
- Even if the overall length of the chain has been adjusted, there is a possibility that a portion of it is inaccurate.
- It is possible that not all of the graduations on the tape are the same.
- There may be some rough plumbing involved in the procedure of stepping when gauging the slope of the ground.
Cumulating Errors
Mistakes that tend to crop up again along the same general path are referred to as cumulative errors. It is possible that the mistake is negligible for each individual reading, but when a significant number of observations are taken, it is necessary to take this into account since the inaccuracy is often focused on one side. The following are some instances of such errors.
- Bad repositioning
- Inaccurate chain length
- Temperature variation
- Changes in applied pull
- A sag in the chain if the measurement of horizontal distance on hilly terrain is halted
Merits of chain surveying
The following is a list of some of the benefits that may be achieved by chain surveying:
- The chain surveying technique is the most straightforward approach to surveying. It is not very difficult to carry out.
- It does not need any expensive equipment or instruments to be used.
- A reasonable degree of precision in the preparation of the design for small areas is the desired quality.
- The computations and charting are also quite easy to understand.
see also: Plane Table Surveying: Precision Mapping Method
Negative aspects of chain surveying
The following is a list of some of the downsides that are associated with chain surveying:
- The use of chain surveying is not recommended for vast regions. As the chaining together of huge regions becomes more laborious.
- It is rather challenging to be performed in places that are densely populated or overgrown.
- It is not appropriate for use on terrain that has undulations since chaining in such places is complex and prone to mistakes.
- It is possible that the findings that were acquired would not always produce correct outcomes.
see also: City surveying: Everything you need to know about it
FAQs
Which line in a chain survey is the longest?
The term Base line refers to the line that is the longest from the origin and will split the whole area into two equal pieces. This line serves as the primary reference line, and it is used to determine the location of a variety of stations as well as the path that other lines should take.
Which tool is used to fix direction in a chain survey?
In chain surveying, the instruments that are used for determining and fixing directions are called ranging rods.
What are the objectives of doing a chain survey?
Chain surveying is the surveying subdiscipline for recording linear measurements. This is appropriate for the assessment of small regions with minimal features and generally straight terrain.
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