Surveying is the science and art of determining the relative positions of the points on, above (or) beneath the earth surface.
Primary divisions of surveying: Surveying may primarily be divided into two divisions
1. Plane surveying
2. Geodetic surveying
Plane surveying: The surveys in which earth surface is assumed as plane and the curvature of the earth is ignored, are known as Plane surveys.
Geodetic surveying: The surveys in which curvature of the- earth is taken into account and higher degree of accuracy in linear and angular observations, is achieved, are known as Geodetic surveys.
Liner measurements and equipment's:
In engineering survey, the linear horizontal distance is to be measured to complete a survey. The measurement of this linear horizontal distance between two points on the earth surface is known as linear measurement. Linear measurement can be achieved by various instruments.
The following instruments are used while chaining:
1. Chains
2. Tapes
3. Arrows
4. Ranging rods and offset rods
5. Pegs
6. Plumb-bob
Chain
The chain is composed of 100 or 150 pieces of galvanized mild steel wire called links, joined together with oval rings and handles at both ends. The end of each link are bent into a loop and connected together by means of three oval rings. The ends of the chain are provided with brass handles for easy handling. The length of chain is measured from one handle to other handle.
Tapes
Tapes are used for more accurate measurements. The tapes are classifiedbased on the materials of which they are made of such as:
1. Cloth or linen tape
2. Fibre tape
3. Metallic tape
4. Steel tape
5. Invar tape
Arrows or chain pins
They are also called as marking or chaining pins and are used to mark the end of chain during the process of chaining. They are made up of good quality hardened and tempered steel wire of 4mm in diameter. The arrows are made400 mm in length. The one pointed part of an arrow is inserted into ground and the other is attached with ring.
Ranging rods or offset rods or ranging poles
Ranging rods or offset rods are round poles made up of wood or metal. These rods are used to range intermediate points of a survey and to set out straight lines on the field when the surveying length is long. The only difference between ranging rods and poles is the length. Ranging rods and offset rods are commonly occurs in 3m length but the ranging poles are available up to 8mlength. The rods possess a metal point at its bottom and the rod or pole is painted with red & white or black & white successive combination. When the survey lines are too lengthy a flag with red/white/yellow colour will be attached to the top of the pole for easy identification.
Pegs
The pegs are made up with wood and they used to mark the survey positions or terminals. The size of the pegs (40 to 60 cm) depends on the type of survey work they are used for and the type of soil they have to be driven in. Although the pegs are driven into the ground 1/5 of its part should be visible on the ground surface.
Plumb-bob
A string suspended with a weight at the bottom will be both vertical and perpendicular to any level plane through which it passes. The plumb consists of a specially designed weight and coarse string or special threads. At one end of the string the weight is affixed. Precisely machined and balanced bobs have pointed tips, and can be made of brass, steel, or other materials, including plastic.
FIELD BOOK
All observations and measurements taken during chain surveying are to be recorded in a standard field book. It is a oblong book of size 200 mm × 120mm, which can be carried in the pocket. There are two forms of the book (i)single line and (ii) double line. The pages of a single book are having a red line along the length of the paper in the middle of the width. It indicates the chain line. All chain-ages are written across it. The space on either side of the line is used for sketching the object and for noting offset distances. In double line book there are two blue lines with a space of 15 to 20 mm is the middle of each book. The space between the two lines is utilized for noting the chain-ages.
Figure shows typical pages of a field books.
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