Chain Survey- Procedure, Applicability, Survey Stations and Their Selection,

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Chain surveying considered to be the simplest method of surveying in which measurements are taken in the field and other works like plotting calculations are carried out in office. The measurement in chain surveying are linear; angle measurements are not considered.

Moreover, it provides fairly accurate result provided that the work is conducted carefully. Chain surveying is suitable for small areas with few details. Tools and equipment required include chain, tape, ranging rod, arrows and sometime cross staff.

In this type of
surveying, survey stations (main stations, tie or subsidiary stations) shall be
specified carefully otherwise the outcome of the surveying process may not be
accurate.

Applicability of Chain Survey

Obviously,
chain surveying cannot be used in all cases. It can be used if the area under
consideration meet the following conditions:

  1. The
    area shall be fairly small
  2. The
    ground is moderately level
  3. The
    area needs to be open
  4. The
    ground has few and simple details
Chain Surveying
Fig. 1: Chain Surveying

Chain Survey Tools

  1. Chain
  2. Tape
  3. Ranging-Rod
  4. Arrows
  5. Cross staff
Ranging Rod
Fig. 2: Ranging Rod
Pegs in Chain Surveying
Fig. 3: Pegs in Chain Surveying

Chain Survey Stations

Survey stations
are points of importance at the beginning and end of a chain line. There are
two major types of stations in chain surveying:

1. Main stations

Main stations
are the end of lines that determine the boundary of the surveying.

2. Tie (Subsidiary) Stations

Tie stations
are points which are specified on the chain line (main survey lines) where it
is required to identify interior details like buildings and fences.

Factors Affecting Survey Station Selection

  1. Stations
    should be visible from at least two or more stations.
  2. As
    far as possible main lines should run on level ground.
  3. All triangle
    shall be defined properly (No angle less than 30º).
  4. Each
    triangle should have at least one check line.
  5. Survey
    lines should be as few as possible.
  6. Obstacles
    to ranging and chaining should be avoided.
  7. Sides
    of the larger triangles should pass as close to boundary lines as possible.
  8. Trespassing
    and frequent crossing of the roads should be avoided.

Line Types in Chain Survey

1. Base Lines

It is the main
and longest line from which all measurements to demonstrate details of the work
are taken. The base line passes through the center of the field. 

2. Chain Line (Main Survey) Lines

The lines that
join main stations are termed as chain line or main survey lines.

3. Tie (Subsidiary) Lines

It joins two fixed
points on the chain line. The advantage of tie line is checking surveying
accuracy locating interior details such as buildings and paths.

4. Check (Proof) Lines

It joins
triangle apex to some fixed points on any two sides of a triangle. It is used
to examine the accuracy of the framework. The length of check line measured on
ground shall be consistent with its length on the plan.

Types of Lines in Chain Surveying
Fig. 4: Types of Lines in Chain Surveying

Offsets in Chain Survey

Lateral
measurements from the baseline are termed as offsets. They are used to fix
locations of various objects with respect to the baseline. Commonly, offsets
are established at right angle. There are two major type of offsets namely:
perpendicular offsets and oblique offsets.

Perpendicular and Oblique Offset
Fig. 5: Perpendicular and Oblique Offset

Chain Survey
Procedures

  1. Firstly,
    inspect the area to be surveyed and prepare key plan. This stage is termed as
    reconnaissance phase.
  2. Then,
    mark stations using suitable means such as fixing ranging poles, driving pegs, and
    digging and fixing a stone.
  3. After
    that, specify the way for passing the main line which should go through the
    center of the field.
  4. Fix
    ranging road on stations
  5. Then,
    chaining can be begun.
  6. Make
    ranging wherever necessary.
  7. Measure
    the change and offset and record them.  
Chain Surveying- Procedure
Fig. 6: Chain Surveying- Procedure



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