Friday, September 13, 2013

Surveying one liners- part 3 - GATE 2014 preparation

1. If W is the weight of the chain, L is the span and P is the tension or pull, then sag correction for chain line will be (W^2L)/(24.P^2).

2. Normal tension is that pull which neutralizes the effect due to pull and sag in chain/tape.

3. If O is the angle of slope, L is the length of the slope and H is the difference in elevation between two ends of the line, then slope correction will be 2.L.sin^2(O/2).

4. Limiting length of offset depends upon the accuracy desired, scale of plotting and nature of the ground.

5. Sag correction for chain or tape is always negative.

6. Plane tabling is a graphical method of surveying.

7. Chaining or tape is the best method for the linear measurements.

8. Curves are necessary to change the direction and vertical alignments of the routes.

Tuesday, September 10, 2013

Part-2 Surveying one liners - GATE 2014 exam preparation

1. Incorrect holding of a chain at arrow is compensating error.
2. French cross staff is used to set out 45 degrees offset with a chain.
3. A discrepancy is the difference between two measured values of the same quantity.
4.  A revenue chain is 33 feet long and consist of 16 links.
5. Every 20 m chain must be accurate to within +-5 mm.
6. For chaining on the slopping ground one can use the stepping method and hypotenuse allowance method etc.
7. Compensating errors in chain are proportional to the square root of the length of the line.
8. Error due to bad ranging is cumulative positive.
9. Negative errors in the chain are caused in chain, when its length is more than the standard length.
10. An error under the same condition always of the same size and sign is called, systematic and cumulative error.

To be continued in part 3...

Saturday, September 7, 2013

Surveying - one line statements useful for GATE, PSUs examination preparations -Part 2

1. Theory of probability is applied to accidental errors.
2. Most probable value of an observed quantity available from a given set of observation is the one for which the sum of the square of errors is a minimum. This statement is called principle of least square.
3. For a measured distance L along a slope, the required slope correction is 2L.[sin(A/2)]^2.
4. A 30 m chain was found to be 20 cm too long after chaining 1500 m. Correct length of the total distance chained will be 1510 m.
5. If n observations are taken then the accidental errors are proportional to n^(1/2).
6. If a chain is found too short on testing then it can be adjusted by straightening the links, inserting additional circular links and flattening the circular rings.
7. Permissible limits of error in chaining for measurement on rough or hilly ground is 1:250
8. Position of point can be fixed more accurately by perpendicular offset.
9.  Positive error is caused if  length of chain is shorter than standard, slope and sag corrections in not applied and measurements are made along the incorrectly aligned line.
10. If during a chain survey along a straight line, leader of the survey party has three arrows and while follower has five arrows, then distance of the follower from the starting point is Five chains.

Reference: GK publishers

Friday, September 6, 2013

Inter-visibility of Triangulation stations

There is formula given by G.T. McCaw
where, h1= elevation of station !
            h2 = elevation of station B
             h= elevation between intervening station C
             2S = distance between stations A and B
           s+d = distance of C from A
          s-d = distance of C from B
        z = zenith distance from A and B

Sunday, September 1, 2013

Minor Surveying Instruments


There are some instruments used for the rough surveys, they are not used for the precise surveys.

 These are following.
  •  Hand Level:
It is compact instrument used for locating contours, taking cross sections in reconnaissance surveys.
  • Clinometer:
It is a light compact instrument used for measuring vertical angles, finding out slope of the ground and for locating points on a given grade. There are three commonly used forms of clinometers:
 (i) Abney's level
(ii) Tangent Clinometer
 (iii) Ceylon Ghat Tracer

  • Box Sextant: 
It is a reflecting instrument capable of measuring up to 120 degrees with an accuracy of one minute. It is one of the most precise hand instrument.

  • Pantagraph: It is used to reduce or enlarge the given figure.

  • Planimeter: It is used to measure the area of the given figure.


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