In the world of land surveying, “chain surveying” is a straightforward yet essential method. This introduction explores the basics of chain surveying, a technique where measurements are made using a chain. Whether you’re a landowner or just curious about surveying, understanding chain surveying can provide insights into mapping and measuring land accurately.
What Is Chain Surveying?
Chain surveying is the method of surveying in that horizontal measurement and angle area taken in fieldwork. These types are of surveys mainly suitable for surveying small areas of land. It describes the boundaries of the plot, the area of land, and other distances and angles on the field.
In chain surveying, measurements are noted in a separate book which is called “filed book”. The data of the survey includes – angle measurement, distance measurement, survey station, base details, etc.
The data in the filed book is used to draw the survey work on the paper by taking the proper scale.
Principles Of Chain Surveying
The main principle of surveying is to divide the area of a survey into numbers of small survey areas by using triangles. Measure the length with a tap and angle with a compass. The measurement is used to plot a survey drawing on paper.
Since triangulation forms the principle of chain surveying, the chain survey is similarly sometimes called chain triangulation. If the area to be surveyed is triangular and if the lengths and sequence of its 3 sides are recorded, the plan of the area can be easily drawn.
However, if the area has more than three straight boundaries, for instance as in figure (a) it is no longer enough to measure the lengths of the sides completely.
The field measurements must be so arranged that the area can be plotted by laying down triangles. Various arrangements should be prepared to satisfy this condition but only two are given here as shown in figure (b) and (c).
Equipment Used In Chain Surveying
The several equipment used in chain surveying are as follows.
- Ranging Rods
- Plumb Bob
- Cross Staff
In chain, surveying chains are the considerably essential equipment for the procedure of survey. Chains are utilized to measure horizontal distances. Chains are created of straight links of galvanized mild steel wire named links.
The ends of each link are bent into a looped hand connected using three oval rings which afford flexibility to the chain.
The chain is formulated of mild steel. The ends of the chain are given brass handles for dragging the chain on the ground.
The outside of the handle is the zero points or the endpoint of the chain and the length of the chain is assessed from the outside of one handle to the outside of the additional.
The length of a link is the distance between the centers of the two consecutive intermediate rings. The end links contain the handles.
These are the marking pens made of steel wire and mainly, 10 arrows are given with a chain survey. Length may differ from 25 mm to 50 mm but indicated length as per the IS-Code.
The arrow is made sharp and another end is bent into a loop or circle for the facility of carrying. The usage arrows are injected into the ground after every chain length measured on the ground.
Pegs are utilized to mark the position station or terminal point of a survey line. They are pushed into the ground with the support of the wooden hammer and kept 40 mm above the ground surface.
The dimension of the pegs is mainly 150 mm long and 30 mm square at the top. Pegs are generally available in wooden.
4. Ranging Rods
Ranging rods are 2 m – 3 m high rods of steel or well-seasoned wood utilized for the ranging of points. They are coated in alternate colors of the band either white & black, white & red, or black, white, and red in series.
The band is of length 200 mm, so that can be utilized for the rough measurement of smaller lengths 2 m ranging rod being more popular.
They are octagonal or circular in cross-sections of 30 mm in diameter and are almost invisible at a distance of 200 m. They are given a white or yellow flag 0f 30 – 50 sq. cm area tied near its stop.
5. Plumb Bob
While chaining along the sloping surface of the ground, a plumb bob is required to transfer the points to the ground.
It is similarly utilized for accurate centering of the theodolite compass, plane table, etc over a station mark and for assessing the verticality of ranging poles.
A hammer is used to drive the pegs and wooden pegs into the earth. Because some hard soil surface hammer is a must insert the pegs into the soil
7. Cross Staff
This is the tool utilized for setting out right angles to a chain line. It includes either the frame or box with two pairs of vertical slits and is mounted on a pole shoe for fixing in the ground.
The three types of cross-staff,
- Open cross-staff
- French cross-staff
- Adjustable cross-staff
The offset rod is the same as that of the ranging rod. They are should with a pointed iron shoe at one end and given with a notch or a hook at the different for pushing or pulling the chain through hedges or different obstructions.
Different Chains Used In Surveying
Depending upon the length of the chain, these are divided into the following types,
1. Metric Chains
Metric chains are the most commonly utilized chain in India. These types of chains come in various lengths such as 5 m, 10 m, 20 m, and 30 m. The most commonly utilized is a 20 m chain.
Tallies are given at every 2 m of the chain for quick reading. Every link of this type of chain is 0.2 m. The total length of the chain is noted on the brass handle at the ends.
2. Steel Band Or Band Chain
These types of chains come up the steel small band strip of the same width of 12 mm-16 mm and 0.3 mm-0.6 mm thickness. This chain is divided by brass studs at every 20 cm or instead of brass studs, the band chain may have graduated carving as a centimeter.
For easy usage and workability, band chains are wound on steel crosses or metal reels from which they can be handily unrolled. This steel band is accessible in 20 m-30 m in length and a width of about 12 mm-16 mm.
3. Gunther’s Chain
A Gunter’s chain is 66 feet lengthy and contains 100 links, each link 0.66 feet lengthy (7.92 inches). It was originally obtained for comfort in land measurement since 10 square chains are equal to 1 acre, also while measuring linear measurement.
- 10 Gunter’s chain = 201.17 meter
- 80 Gunter’s chain = 1609.36 meter
4. Engineer’s Chain
Being 100 feet long and contains 100 links, each link being 1 foot. At every 10 links brass tags are clamped with notches specifying 10 links segments.
The usages of the engineer’s chain are mainly measured to Feet.
5. Revenue Type of Chain
The Revenue chain is 33 feet lengthy and contains 10 links each link is 2 feet 0.75 inches long, the chain in surveying is utilized for measuring fields in cadastral surveys.
Procedure Of Chain Surveying
The procedure of chain surveying is as follows,
- Reconnaissance: The preliminary inspection of the to be surveyed is named the reconnaissance. The surveyor evaluates the area to be surveyed, surveys, or prepares an index drawing or key plan. He should also evaluate the problems of plotting the survey line and supplementary work.
2. Marking Station: The survey fixed up the required no. of stations at the spot from where the maximum possible station can be plotted
- Fixing of ranging rod or poles.
- Driving pegs.
- Making a cross (X) if the surface is hard.
- Digging & fixing a stone.
3. Choose a way for passing the mainline. Which should be as horizontal and clean as feasible and should be passed almost through the center of work.
4. The ranging rods are fixed on the station.
5. After fixing the stations, a chain-in could be initiated.
6. Make ranging where ever essential.
8. Measure the chain edge and offsets.
9. Enter the observation and measurement in the field book.
Errors In Chain Surveying
Errors in chaining may be classified as,
- Personal Errors
- Compensating Errors
- Cumulating Errors
1. Personal Errors
Personal errors include incorrect recording, reading from the incorrect end of the chain, etc., which are personal errors.
These errors are serious and cannot be inspected easily. Care should be taken to prevent such kinds of errors.
2. Compensating Errors
This type of error may be sometimes positive and sometimes negative. Thus they are likely to get compensated when a large number of readings are obtained.
The magnitude of such errors can be assessed by the theory of probability. The following are the examples of the errors,
- Wrong marking of the end of a chain.
- A fractional part of the chain may not be accurate though the total length is corrected.
- Graduations in the tape may not be similar throughout.
- In the method of stepping while assessing the sloping ground, plumbing may be crude.
3. Cumulating Errors
The errors that arise often in a similar direction are called cumulative errors. In each reading, the error may be small, but when a large number of measurements are given rise to they may be considered since the error is often on one side. Some examples of such errors are:
- Bad ranging
- Bad straightening
- Erroneous length of chain
- Temperature deviation
- Variation in applied pull Non-horizontality
- A sag in the chain, if discontinued for measuring horizontal distance on sloping ground.
Advantages Of Chain Surveying
The advantages of the chain surveying method are as follows,
- A chain survey is an easiest and commonest method utilized in surveying exercises.
- The equipment utilized to conduct a chain survey is simple to utilize.
- The equipment utilized in the chain survey can easily be replaced. For instance, measuring rods can be replaced with measuring tape.
- This method does not involve complicated mathematical computations. This is a relief for those who are afraid of mathematics.
- In a chain survey, a limited number of people are required to perform the survey. Generally, the chain survey team has three people Booker, the leader, and the follower.
Disadvantages Of Chains In Surveying
Chain surveying has the following disadvantages,
- A simple chain survey cannot be performed in built-up areas and huge areas.
- A simple chain survey is subject to various changes of errors of accumulation which may cause by the difficulty of the chain.
- The chain linkage may fail to stretch up appropriately and result in wrong data. Similarly clogging of the chain may read to an error in reading.
- It is time-consuming.
- It may not be performed in areas with steep slopes or waterlogged areas. Chain survey is generally performed in dry areas with gentle slopes.
- It becomes more difficult when the survey is performed in areas that are in between areas to be surveyed.
Line Types In Chain Surveying
There are four lines for chain surveying,
- Base Lines
- Chain Line
- Tie (Subsidiary) Lines
- Check (Proof) Lines
1. Base Lines
In the chain survey maps, there is three chain line and one extra line is measured with high precision and is called the baseline. The accuracy of survey work in the chain surveying method depends on how precisely the baseline is measured.
To increase the accuracy of survey work, the baseline is selected such it is the longest line among all the other lines and passes to a major area of the survey area. For better results baseline must be lain on a flat ground surface.
2. Chain Line (Major Survey) Lines
The lines that join the main stations are termed chain lines or major survey lines.
3. Tie (Subsidiary) Lines
Tie lines join two fixed points on the chain line. The benefit of a tie-line appears while checking surveying exactness in locating interior details such as buildings and ways.
4. Check (Proof) Lines
It joins the triangle apex to some fixed points on any two triangle sides. It is utilized to evaluate the accuracy of the framework. The length of the check line measured on the ground surface shall be consistent with its length on the plan.
Obstacles In Chain Surveying
There are three obstacles in chain surveying,
- Obstacles To Ranging
- Obstacles To Chaining
- Obstacles To Both Ranging And Chaining
1. Obstacles To Ranging
This type of obstacle in which the ends are not intervisible is relatively common except in a flat region. These may be two cases.
- Both ends of the line may be visible from the middle points on the line.
- Both ends of the line may not be visible from the middle points on the line.
2. Obstacles To Chaining
The obstacle to chaining prevents the chain from measuring immediately between two points and rises to a set of difficulties in which distances are found by indirect measurement.
3. Obstacles To Both Ranging And Chaining
The obstacle to ranging and chaining may be in the two cases,
- When it is likely to chain around the obstacle. For example, a pond, etc.
- When it is not likely to chain around the obstacle. For example, a river.
Offset In Chain Surveying
The offsets are the lateral measurement from the surveying lines to fix the position of various objects concerning the survey lines. The types of offset,
- Perpendicular Offsets
- Oblique Offsets
1. Perpendicular Offsets
When the angle of the offsets is 90° degrees. It is named perpendicular offsets.
Perpendicular offsets are also categorized into two types,
- Pythagoras theorem
- Swing method
This method is utilized to draw perpendicular offsets and it depends on the principle of the Pythagoras theorem.
This method is similarly utilized to draw perpendicular offsets in chains in surveying and another survey. It depends on the principle that the shortest distance of any two-point is nothing but the perpendicular distance.
2. Oblique Offsets
When the angle of offsets is any different angle but not 90°. It is named oblique offsets. Oblique offsets are extremely used in chain surveying.
How to Record Survey Data In Field Book
The chain survey reading is taken with tape and chain measurements are noted down in a separate book, which is called a Field Book.
In the field, there are two lines are drawn by hand in halfway through the page. These two-line represent the chain lines on the field.
1. Single Line Book
Single-line books are used for a bigger larger area for more descriptive measurement work. In such field books, the chain line starts lower side of the page and respectively works upward direction.
2. Double Line Filed Book
The double-line field book shown below in the drawing is the most commonly used for performing ordinary survey works. The observed distance is along the chain which is entered between the two lines of the page.
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