Principle of Chain Surveying, Instruments Used in Chain Surveying, and Types of Chain Surveying

Chain surveying is one of the simplest and most widely used methods of land surveying. It is mainly used when the area is relatively small, the ground is fairly level, and the details of the site can be measured using linear measurements. Unlike advanced surveying methods that use electronic instruments, chain surveying primarily depends on measuring distances and creating a network of triangles.

In this article, we will explain the principle of chain surveying, the instruments used in chain surveying, and the types of chain surveying in simple language.

What Is Chain Surveying?

Chain surveying is a method of surveying in which measurements are taken mainly using a chain or measuring tape. The positions of different points on the ground are determined by measuring distances between selected points.

The method is particularly useful for small plots, fields, roads, simple construction sites, and preliminary surveys. Since it does not normally require angular measurements, it is considered one of the simplest methods of surveying.

Principle of Chain Surveying

The basic principle of chain surveying is triangulation.

In this method, the survey area is divided into a series of interconnected triangles. The lengths of the sides of these triangles are measured directly on the ground. By using suitable measurements and well-selected survey stations, the relative positions of important points can be plotted on a drawing.

A good chain survey should preferably contain well-conditioned triangles. A triangle is considered well-conditioned when its angles are not too small or too close to 180°. Generally, triangles with angles between approximately 30° and 120° are considered suitable for surveying purposes.

Main Principles

The important principles include:

• The area is divided into a network of triangles.

• Distances between survey stations are measured directly.

• Main survey lines are established first.

• Important details are located using suitable measurements from survey lines.

• Check lines are used to verify the accuracy of the survey.

• The measurements are recorded in a field book and later plotted to prepare the survey plan.

Main Survey Line

The main survey line is an important line connecting two principal stations. It is selected so that it passes through or near the center of the survey area and provides a convenient reference for locating other details.

Check Line

A check line, also called a proof line, is measured to check the accuracy of the framework. If the measured and calculated results agree within acceptable limits, it provides confidence in the survey.

Instruments Used in Chain Surveying

Several simple instruments are commonly used for chain surveying. Each instrument has a specific purpose.

1. Chain

The chain is the main measuring instrument. Different types of surveying chains are available, including metric chains and engineer's chains.

A chain consists of a series of connected metal links with handles at the ends. It is used to measure horizontal distances on the ground.

2. Measuring Tape

A measuring tape can also be used for measuring distances, especially when greater convenience or accuracy is required. Steel tapes are commonly used for surveying and construction measurements.

3. Ranging Rod

A ranging rod is used to mark survey stations and to establish straight lines between points.

It is generally painted with alternating bands so that it can be easily seen from a distance.

4. Arrows

Arrows, also called chain pins, are used to mark the end of each chain length during measurement.

They help the surveyor keep track of the number of chain lengths measured.

5. Wooden or Iron Pegs

Pegs are driven into the ground to permanently or temporarily mark important survey stations.

6. Cross-Staff

A cross-staff is used for setting out right angles from a survey line. It helps the surveyor locate points that are offset from the main chain line.

7. Optical Square

An optical square is another instrument used for setting out right angles. It generally provides better accuracy than a simple cross-staff.

8. Plumb Bob

A plumb bob is used for transferring points vertically and for ensuring that measurements or points are properly positioned when required.

9. Field Book

A field book is used to record measurements, chainages, offsets, sketches, and other observations made during the survey.

Accurate field notes are extremely important because they are later used to prepare the final survey plan.

Types of Chain Surveying

The types of chain surveying can be discussed according to the arrangement and purpose of the survey lines.

1. Simple Chain Survey

In a simple chain survey, the area is relatively small and uncomplicated. The surveyor establishes a suitable chain line and measures the required distances to locate important details.

This method is suitable for small and fairly open areas.

2. Chain Survey with Tie Lines

Tie lines are additional lines introduced into the survey framework to locate interior details and provide additional checks.

They can make the survey more reliable and help in locating features that are away from the main survey lines.

3. Chain Survey with Check Lines

Check lines are included to verify the accuracy of the survey framework. Their measured lengths are compared with the corresponding plotted or calculated lengths.

This is particularly useful for detecting errors in measurements or plotting.

Important Terms in Chain Surveying

Understanding common terminology makes chain surveying easier to learn.

Survey Station

A survey station is a fixed point on the ground from which measurements are taken or to which measurements are referred.

Chain Line

A chain line is a line joining two survey stations along which measurements are made.

Base Line

The base line is an important and usually the longest main survey line. It provides a fundamental reference for the survey framework.

Tie Line

A tie line connects two points on the main survey lines and is mainly used to locate interior details.

Check Line

A check line is used to check the accuracy of the triangular framework.

Offset

An offset is a lateral measurement taken from a chain line to locate an object or detail such as a building, road, boundary, or tree.

Offsets may be perpendicular or oblique, depending on the surveying requirement.

Advantages of Chain Surveying

Chain surveying has several advantages:

• It is simple to understand and perform.

• The equipment is relatively inexpensive.

• It is suitable for small areas.

• It requires comparatively simple calculations.

• Field measurements can be performed quickly under suitable conditions.

• It is useful for basic engineering and land-surveying work.

Limitations of Chain Surveying

Despite its simplicity, chain surveying has some limitations:

• It is not suitable for very large areas.

• It becomes difficult in rough or heavily obstructed terrain.

• It is less suitable for areas with complicated details.

• Errors can occur due to incorrect distance measurements.

• Accurate ranging is important for obtaining reliable results.

• It is not ideal when precise angular measurements are required.

Applications of Chain Surveying

Chain surveying can be used for:

• Small land plots

• Agricultural fields

• Road surveys

• Building sites

• Property boundary surveys

• Preliminary engineering surveys

• Preparing simple site plans

• Locating existing physical features

Conclusion

Chain surveying is a fundamental surveying technique based mainly on linear measurement and triangulation. The principle of chain surveying involves dividing an area into suitable triangles and measuring their sides to establish the relative positions of points.

The main instruments used in chain surveying include chains, measuring tapes, ranging rods, arrows, pegs, cross-staffs, optical squares, plumb bobs, and field books. Different arrangements, including simple chain surveys, surveys using tie lines, and surveys using check lines, can be used depending on the site and surveying requirements.

For civil engineering students, understanding chain surveying provides an important foundation for learning more advanced surveying techniques and modern instruments.