Brief overview of rise and fall table in land surveying

This construction video tutorial is very useful for land surveyor. The tutorial sheds light on the rise and fall table in land surveying. Get some useful tricks to resolve the rise and fall table.

Rise and fall method is applied to resolve the levelling to detect the variation in elevation and elevation of points..


By resolving this table, it is possible to work out the reduced level of each point captured at staff rod with leveling machine. In order to work out the reduced level of an individual point, it is necessary to compute the rise and fall of points. After that, for reduced level, the following formula is applied :-

new R.L = old R.L – Fall
new R.L = old R.L + Rise

The table contains various heads like number, B.S (back sight), I.S (inter sight), F.S (fore sight), Rise, Fall, R.L (reduced level) and remarks.

B.S - Back sight (BS) is the abbreviation for "back sight reading". It means the first staff reading captured by the surveyor as soon as the levelling instrument is arranged and levelled. B.S is normally captured on the point of known reduced level as on the benchmark or a change point. The normally applied datum is mean sea level.

Fore sight (FS) is the abbreviation for "fore sight reading". It means the last staff reading captured prior to modify the instrument to the other position. It refers to the staff reading captured on point whose RL is to be ascertained. This sight is treated as negative and assumed from Height of Instrument to find out RL of the point.

Reduced Level (RL) in surveying stands for equating elevations of survey points relating to a common assumed datum. It refers to a vertical distance among survey point and selected datum plane. Therefore, it is taken as the base elevation that is applied as reference to consider heights or depths of other important places.

To get more detailed information, watch the following video tutorial.

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Published By

Rajib Dey

www.constructioncost.co

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Details of chain surveying - Benefits and Drawbacks

Chain surveying is the sort of surveying in which only linear measurements are selected in the jobsite.

This type of surveying is undertaken for surveys of small span to specify the boundaries of plot of land to detect the existing features on them.

Chain surveying is the simplest form of survey in which surveying area is segregated into a number of triangles and the sides of different triangles are calculated directly in the field through a chain or a tape and no angular measurements are chosen. Chain is most recommended for initial survey process.

Chains stands for the measuring devices which are applied in surveying. These are produced with the 100 links of 4mm galvanized mild steel wire. These links are attached with 3 circular or oval wire rings. These rings make the chains flexible.

The chain comprised of several small segments to manage or study the measurements.

At the ends chain contains brass handle with swivel joint to simplify the process for rolling or unrolling the chain devoid of twisting and knots.

At each 10th link is arranged with a total of one teeth, 20th link with a total of two teeth and so on till 40th link. With these arrangements, the reading of measurements can be taken efficiently.

At the center of the chain, there is a circular talley used for easy reading.

Chain surveying devices: 1. Chain, 2. Tape, 3. Arrows, 4. Ranging Rods, 5. Offset Staff, 6. Optical Square

Types of Chains utilized in Surveying - The chains are categorized as follow depending on the length of the chain:

Metric chains, Steel band or Band chain, Gunter’s chain or surveyor’s chain, Engineer’s chain, Revenue chain

Benefits of chains :-

a. The chains can be read easily and instantly
b. They can resist wear and tear
c. They can be repaired in the jobsite without any difficulty
d. There is no requirement to adjust measuring tape
e. This type of survey work is very effective for a small plain ground.
f. It needs simple instruments.
g. Plotting of maps is very simple and trouble-free.

Drawbacks of chain:

a. They are heavy and take long time to open or fold.
b. They turn to be longer or shorter because of repeated use.
c. If measurement is done in suspension the chain sags greatly.
d. Error in measurement may occur because of temperature, sagging and marking.
e. Requires more manpower to complete the layout.

This type of surveying is recommended for undulation land where chaining operation is tiresome and prone to errors. This method should not be undertaken for a crowded city containing a huge numbers of buildings and obstacles since it cannot be separated into well-conditioned triangles. As for instance route surveying.

For conducting the survey work of a road, irrigation canal, railways, water and sewer lines, tunneling etc., this method is not suitable at all.



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Published By
Rajib Dey
www.constructioncost.co
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