Surveying-levelling
August 29, 2020
Saturday, August 29, 2020
Saturday, August 22, 2020
Surveying-levelling
August 22, 2020
Accessories of linear measurement
Accessories of linear measurement
A. Chain
B. Tape
C. Peg
D. Arrow
E. Ranging rod
F. Offset rod
G. Plumb bob
A. Chain
It is a type of linear measurement. It is formed by several links having a fixed length provided with circular ring with handles at both ends with swivel joints.
chain in surveyingSo that, the chain may be turned without twisting. The chain is available in several in numerous different lengths. Generally it's in 5 m,10 m,20 m,and 30 m.
There are following types of chain are as follows :-
- Metric chain
- Guntor'S chain
- Engineer's chain
- Revenue chain
- Steel band chain
1. Metric chain
The chain in which a reading is taken in metric system is called metric chain. It is generally available in 5 m, 10 m, 20 m,and 30 m. In 5 m and 10 m chain, tally are provided at each one meter length.
- It is made up of galvanized mild steel wire.
- Handle is made up of brass.
- In 20 m, and 30 m chain, tally are provided at each 5 m length and every 1m length ring is provided.
2. Guntor's chain
In this chain, 100 links are attached to form a length of 66 feet and each link length is 0.66 foot. This chain is used in convenience land measure due to following advantages.
10 square chains = 1 Acre
10 chains = 1 Furlong
80 chains = 1 Mile
8 furlong = 1 mile
3. Engineer's chain
The length of this chain is 100 feet. They consist of 100 links. Any link length is 1 foot. Tally are provided at every 10 links (10 feet) and central tally can be round.
4. Revenue chain
The length of this chain is 33 feet and consist of 16 links. Hence, each link will be two and one sixteenth feet. It is mainly used in codastral survey.
5. Steel band chain( Band chain)
It is consist of a steel having width 12 mm to 16 mm and thickness 0.32 mm to 0.66 mm. It is available in length of 20 m,and 30 m.
It has a brass handle at each ends. The readings are marking in meter, decimeter, or centimeter one side.
The steel band is used in projected area where more accuracy is required.
Advantages of chain
- They can be ready easily & quickly.
- They can with stand wear and tear.
- They can be easily repaired in the field.
Disadvantages of chain
- They are heavy and take an excessive amount of time to open or fold.
- They become longer or shorter because of continuos use.
- When the measurement is taken in suspension the chain sag excessively.
B. Tape
It is also linear measuring instrument by which a distance can be measured more accurately than a chain.
Generally it is available in 2 m, 5 m, 10 m, 20 m, 25 m, 50 m, 100 m,and also in feet such as 33 feet, 50 feet, 66 feet, and 100 feet available in market.
There are following types of chain are as follows :-
- Cloth or linen tape
- Metallic tape
- Steel tape
- Inver tape
C. Peg
It is used to mark the position of the station or terminal point of a survey line. It is made up of seasoned timber.
Generally upper surface of peg is 2.5 cm square or 3 cm square and 15 cm length tapered at the end. They are driven into the ground with the help of wooden hammer.
D. Arrow
It is made up of steel wire of 4 mm diameter. One end of the arrow is bent into a ring of 50 mm diameter and other end is inserted in the ground. It is used for the counting number of chains.
E. Ranging rod
It is made up of well seasoned straight timber which is used ranging rod and offset rod ranging rods are used forranging rod in surveyingfor ranging the intermediate points in the survey line. Generally it is available in 2 m & 3 m length.
It can be easily inserted in the ground. It is painted in alternative colour/ band of either black or white. Each bands being 20 cm or 0.2 m depend upon ranging rod.
F. Offset rod
It is similar to ranging rod which is used for drawing offset on survey line. It is available in 3 m and alternatively coloured in black & white.
It is painted with iron shoe at one end and provided with notch or hook on the other end.
G. Plumb bob
It is an instrument which is used for transferring the height to the ground. It is also used in centring the theodolite, compass and plane table in survey.
plumb bob in civil engineering
Saturday, August 15, 2020
Surveying-levelling
August 15, 2020
Principle of surveying and scale & its types
Principle of surveying
There are following types of principle of surveying are as follows
- Working from whole to part
- Location of a point by measurement from two points reference
1. Working from whole to part
According to this principle , the surveying is to work from whole to part either in plane or geodetic surveying.
First, the whole area is enclosed by main stations, and main station line. The area is divided into a number of parts by forming well condition triangles (30°< α >120°).
The main station lines are measured very accurately with standard chain or tape, then the side of the triangle are measured. The aim of this process is to be prevent accumulation of errors.
During this procedure if there's any error within the measurement of any side of triangle then it will not be affect the whole work. The error will be always detected & eliminated .
2. Location of a point by measurement from two points reference
According to this principle relative position of a point should always be fixed by measurement (linear or angular) from two points of reference through the help of chain, tape, compass, or theodolite.
Let A & B be the two reference points on the ground. The distance of AB can be measured accurately and its relative position C can be plotted on the sheet paper with a suitable scale.
- Distance AC and BC can be measured and point C can be plotted by using the chain or tape.
- A perpendicular CD can be measured on the reference line AB and length AD and BD are measured. The point C can be plotted with the help of Set Square or cross staff.
- The distance AC and BC are not measured but angle BAC & angle ABC are measured with a theodolite or compass survey
What is scale :-
The drawing of objects are not possible to represents the actual length of an object on a drawing sheet paper.
Scale is that the fixed ratio that any distance on the plan with a corresponding distance on the surface. Scale is the generally necessary to draw then to a convenient scale.
There are following types of scales:-
- Plane scale
- Diagonal scale
- Vernier scale
- Comparative scale
1. Plane scale
It is used to read only two dimensions successively of such as meter and decimeter.
2. Diagonal scale
It is used to read only three dimensions successively of such as meter, decimeter, and centimeter.
3. Vernier scale
It is used for the measuring fractional part of the smallest division of the main scale.
4. Comparative scale
A scale which is used for common representative fraction (R. F) but read in measure is called comparative scale.
Note:-
Representative fraction (R. F)
It is the ratio of the corresponding distance of a map to the corresponding distance on the ground is known as representative fraction.
Terms used in vernier scale
* Direct vernier
The smallest division of a vernier is shorter than a smallest division of the primary scale.
* Retrograde
The smallest division of a vernier is longer than the smallest division of the primary scale.
* Least count
The ratio of the smallest division on the main scale to the quantity of division on the vernier is known as least count.
Mathematically,
Least count = x/n
Where, x = smallest division on main scale.
n = No. of division on the vernier.
