How do you do chain surveying in a field?

 Comprehensive Guide to Chain Surveying: Techniques, Tools, and Procedures

Main Headings

1. Historical Background of Chain Surveying ("Overview of Chain Surveying")
2. Advantages and Limitations ( "Definition and Purpose of Chain Surveying")
3. Essential Surveying Tools ("Tools and Equipment Used")
4. Main Stations vs. Tie Stations ( "Types of Survey Stations")
5. Classification of Survey Lines ("Types of Lines in Chain Surveying")
6. Perpendicular vs. Oblique Offsets ( "Offsets in Chain Surveying")
7. Step-by-Step Surveying Process ("Procedures for Conducting Chain") 

1.Overview of Chain Surveying

Chain surveying is one of the oldest and simplest methods of surveying, primarily focused on linear measurements. Historically, this technique was predominant in the field until it fell out of favor in the late 1800s, primarily due to the challenges posed by manually pulling long chains, such as 100-foot steel chains. As technology progressed, practical applications evolved with the introduction of modern tools, including digital measuring devices, which greatly enhance the efficiency and accuracy of surveying tasks.

2.Definition and Purpose of Chain Surveying

Chain surveying is defined as a method of taking linear measurements directly in the field using a chain or tape. In addition to these direct measurements, the calculations and plotting of the data are typically conducted in an office setting. This method is characterized by its emphasis on linear measurements, which means that angular measurements are not taken into account. Chain surveying is especially advantageous for small areas with minimal terrain variation and few details.

3.Tools and Equipment Used

The essential tools required for chain surveying include:

·         Chain or Tape: Used for measuring the distances between points.

·         Ranging Rods: These are long, straight sticks used to mark survey stations and help in aligning the chain.

·         Arrows: Used to indicate the endpoints of measurements or to indicate directions.

·         Cross Staff: Sometimes employed to set right angles while aligning the chain or tape.

·         Pegs: Used to mark various positions in the survey area.

4.Types of Survey Stations

In chain surveying, the selection of survey stations is vital to ensuring accuracy. There are two major types of survey stations:

1. Main Stations: These are the critical points at either end of the survey chain that define the boundaries of the surveyed area.
2. Tie (Subsidiary) Stations: These are additional points along the main chain line that help to identify and plot interior details of the area, like the location of buildings or fences.

Considerations for Station Selection

When establishing survey stations, several factors are essential:

·         Visibility: Each station should be visible from at least two other stations to ensure accurate alignment.

·         Ground Level: Where possible, main lines should run along level ground to ensure measurements are consistent.

·         Triangle Formation: The formed triangles should avoid angles less than 30 degrees to maintain accuracy.

·         Check Lines: At least one check line should be defined for each triangle to verify precision.

5.Types of Lines in Chain Surveying

Chain surveying utilizes several types of lines:

1. Base Lines: The longest line in the survey, functioning as the foundational reference from which all other measurements are derived.
2. Chain Lines (Main Survey Lines): Lines connecting the main survey stations that define the overall layout of the area.
3. Tie Lines: These lines connect fixed points on the main chain line and are essential for verifying interior details.
4. Check (Proof) Lines: Lines used to validate the accuracy of the survey framework by comparing the actual measured length against its recorded length on the plan.

6.Offsets in Chain Surveying

Offsets are lateral measurements taken from the base line to locate additional features within the surveyed area. Typically, offsets are established at right angles to the baseline. The two primary types of offsets are:

·         Perpendicular Offsets: Measured at a right angle to the baseline, these are used for direct placements of objects.

·         Oblique Offsets: Taken at angles other than 90 degrees, these assist in documenting irregular shapes or features.

7.Procedures for Conducting Chain Surveying

1. Reconnaissance: Inspect the area and prepare a key plan outlining the survey's scope.
2. Station Marking: Use ranging poles, pegs, or stones to mark the positions of the survey stations.
3. Determining Main Line Path: Establish a main line that runs through the center of the field to streamline measurements.
4. Aligning Ranging Rods: Fix ranging rods at each station to aid in visibility and alignment during the survey.
5. Conducting Measurements: Begin the chaining process, taking necessary measurements, and making offsets as required. Carefully record all data gathered for later analysis.

In summary, chain surveying remains a fundamental surveying technique suitable for uncomplicated and small areas. Although contemporary technology has provided more efficient options, the basic principles of chain surveying provide a solid foundation for understanding more advanced surveying methods.