|written 4.6 years ago by||• modified 3.4 years ago|
|written 4.6 years ago by|
The various methods of levelling are as follows:
- Simple levelling
- Differential levelling
- Profile levelling
- Fly levelling
- Check levelling
- Reciprocal levelling
- Trigonometrical levelling
- Precise levelling
1. Simple levelling- when we want to find the difference in elevation between the point which is visible from the same position of the instrument station such levelling called as simple levelling.
2. Differential levelling- differential levelling is used when it is required to find the difference in elevation between the two-point having considerable distance between them.
This method is adopted for the following two cases:
when the difference in elevation between the two point is much more.
when there is some obstacle such as heel, tree, heap, crest and trough in a ground or any object come in the way of levelling work.
3. Profile levelling- Profile levelling is the process of determining the elevation of the point at measure interval along a fixed line such as the centre line of a railway, railway, highway, canal or sewer it is also known as longitudinal sectioning.
4. Fly levelling- fly levelling is the process of determines the elevations of the point which are a certain distance apart. A series of a level is taken from one B.M to the other. it is used to establish benchmark it is also known as differential levelling or compound levelling.
5. Reciprocal levelling- reciprocal levelling is adapted to determine the difference of level between two point accurately when points are at a considerable distance apart, it is also used when it is not possible to set up a level in between the point due to river or ponds etc.
6. Precise levelling- precise levelling is used for establishing a benchmark with great accuracy at widely distribute points.
precise levelling differs from the ordinary levelling in the following point:
high-grade level and stadia rod are used in precise levelling
length of sight is limited to 100m in length.
rod reading is taken against the three horizontal hair of a diaphragm.
7. Trigonometric levelling- It is the process of determining the differences of elevations of stations from observed vertical angles and known distances.
8. Precise levelling- It is particularly an accurate method of differential levelling which uses highly accurate levels and with a more rigorous observing procedure than general engineering levelling. It aims to achieve high orders of accuracy such as 1 mm per 1 km traverse.