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What is the principle and procedure of chain surveying
Principle of Chain Survey
WELL CONDITIONED TRIANGLE
The Principle of chain survey is TRIANGULATION. The triangles are the simple plane figure which can be easily drawn by his lengths. The angles are used in chain surveying is approximately nearly about 60 degrees or nearly equilateral triangles. In the chain surveying, the triangles used named as well-conditioned. The well-conditioned triangle consists of no angle smaller than 30º and no angle greater than 120º
There are the following abbreviations used in chain surveying.
Survey stations:- Survey station is a point of importance at the beginning and end of a chain line. The survey stations are two types of Main station and subsidiary or tie station. It is expressed in a small circle with a number of numerical or alphabetical numbers.
Survey line:- The line joining between survey stations is called Survey lines. It is in two types. The lines joining between main survey stations is called the main survey line or chain lines. Subsidiary or tie stations is the point on the main lines to locate the interior detail such as fences, hedges, building, etc.
It is expressed in AB, BC, or ab, bc, etc.
Baseline:- In surveying the longest of the chain line is used as a baseline. It is a build-up of the framework of the survey. It should be laid off on as level ground as possible through the centre and the length of the area. It should be correctly measured horizontally.
Check Line: -A check line is a line joining the apex of a triangle to some fixed points on any two sides of the triangle.
Tie Line:- Tie line used to tie some fixed point on the main survey lines. It is also used for dual purposes one is to check the accuracy of the survey framework and the other is to locate the interior details.
Offsets:- To locate the surface features on the map. It is measured left or right on the survey line. There are two kinds of offsets. One is perpendicular offsets and the other is oblique offsets.
Selection of Station
1. Main stations should be intervisible
2. The main principle of surveying is to work whole to the part.
3. If possible, a long line should be run roughly through the centre and the whole length of the area.
4. All triangles should be well-conditioned.
5. Each triangle should be as few as practicable.
6. Tie lines used for filling details of the interior.
7. The survey lines should be so arranged as to avoid obstacle to ranging and chaining.
8. The survey lines should lie over as level ground as possible.
The Equipment Required For a Chain Survey
i. A Chain:-This is an accurate and common method of measuring distance in this method the distance are measured in the field by chain or tape. A metric chain divided into 100 links is made of galvanized mild steel wire 4 mm in diameter. The ends of each link are bent into loops and connected together by means of three oval rings. Which afford flexibility.
ii. A Metallic Tape:- When linen tape is reinforced on brass or copper wires is called metallic tape, it is available the length of 15mt,20mt, and 30mt. It is covered in a leather box.
iii. Ranging Rod:- Rods which is used for ranging for making a line is called ranging rod. It is available in wooden and metal made, its circular diameter is 25 mm and 2 MT height.
iv. An optical square:-Optical square is used for finding the foot of the perpendicular from a given point to a line and it is also used for setting out a right angle at a given point on a line.
v. A plumb Bob
vi. An offset rod
vii. A survey field book
ix. Chalk, Stout string, hammer,axe, nails,tar,etc
The Procedure of Chain Survey
Reconnaissance:- Before start, the chain survey field works the surveyor walk over the whole area which is to be surveyed and examine the ground for the arrangement of the framework. During the exam the surveyor to find the possibility for all areas covers the main survey lines, The triangle made well-conditioned, the shortest offset distance, intervisible all the stations. The baseline possible centre of the area. During the reconnaissance, the surveyor should prepare a neat hand sketch called a key plan. The plan showing boundaries, the principal features such as building, roads, nallas, etc. The positions of the stations and chain lines which should be lettered or numbered, and the directions in which the chain lines are to be measured by the arrowheads. The sketch is drawn in the field book.
Marking The Stations On The Ground
After complete, the reconnaissance and preparation of the key plan mark the station on the ground. On the ground-driven wooden pegs, pegs are normally 15 cm long, and width 2.5 cm square and pointed ends.pegs are driven on the ground and height 2.5 cm above the ground.
A reference sketch is made of all stations, if the pegs are removed from their own position then use the reference sketch to find the stations.
Running Survey Lines
After complete priliminary work starts the chaining work. First, start the chaining of the baseline, and carried all the lines of the framework. A survey line consists of chaining the line and locating from it the nearby detail. For chaining the chain is stretched in true alignment and the arrow inserted in the ground, offsets are taken their position and booked in the field book.