Test: Surveying- 1

Two theodolite method: In this method, curves are staked out by angular measurements only. Accuracy attained in this method is quite high. Thus, the method is used when higher accuracy is required and when the topography is rough or field condition is difficult. Whenever curve is to be set out over rough ground this method is adopted.

Tacheometric Method: This method is sometimes used when the ground is rough and chaining cannot be done accurately. The usual table of tangential angles can be used to obtain the direction of the respective points on the curve.

As the chain is a metal made, it may undergo many changes due to temperature effect or human error and etc. So for all lengths of chain a tolerance is given:

1. 5 meter chain: + or – 3 mm

2. 10 meter chain: + or – 3 mm

3. 20 meter chain: + or – 5 mm

4. 30 meter chain: + or – 8 mm

The stadia diaphragm essentially consists of one stadia hair above and the other an equal distance below the horizontal crosshair i.e a crosshair with two horizontal

The stadia hair being mounted in the same ring and in the same vertical plane as the horizontal and vertical cross-hair. In stadia systems, staff intercepts, at a pair of stadia hairs present at the diaphragm.

In the stadia system, Targets on the staff are fixed at a known interval and the stadia hairs are adjusted to bisect the upper target at the upper hair and the lower target at the lower hair.

In ordinary transit system, observations are not taken on stadia hairs.

The parallax bar is an instrument designed for use with a mirror stereoscope that has a stereo base of ten inches or less. The bar is used to determine the height difference of natural and man-made features when viewing stereoscopic photographs. It is used to measure Parallax difference.

Latitude = Lcosθ

Departure = Lsinθ

So, for θ lies between 90° to 180°, cos θ is -ve and sin θ is +ve

So, Latitude is -ve and Departure is +ve

True Bearing: It is horizontal distance between the true meridian and the survey line measured in a clockwise direction.

Azimuth: it is the horizontal angle or direction of a compass bearing.

Arbitrary Meridian: Any convenient direction from a survey station to some well defined permanent object is known as arbitrary meridian. This is used for small area survey or to determine the relative directions of small traverse.

Grid Meridian: For survey of country, the true meridian passing through the central place is sometimes taken as a reference meridian for the whole country. Such a meridian is known as Grid meridian.

Temporary Adjustments of Compass are:

1. Fixing the compass to the tripod.

2. Centering the compass: Making the pivot exactly vertically over the ground station mark

3. Levelling the compass

4. Sighting the object: By focusing through prism

5. Observation of bearings

A Geographic Information System (GIS Software) is designed to store, retrieve, manage, display, and analyze all types of geographic and spatial data.

Temporary Adjustment of Theodolite:

Firstly, Instrument is at set-up at concerned station, Then

1. Cantering: To place the vertical axis exactly over the station mark

2. Levelling: Levelling adjustment of the theodolite is done using levelling screws or foot screws. The objective of levelling in surveying is to make the vertical axis of the instrument truly vertical.

3. Elimination of Parallax: Parallax is the condition arising when the image formed by the objective is not in the plane of crosshairs. This one of important steps in the temporary adjustment of theodolite or telescope.

Upon solving,

1/500 = 0.002

1/1000 = 0.001

1/2500 = 0.0004

1/50000 = 0.00002

Largest is 0.002 i.e. 1/500

RL of Bottom of Bridge Deck = 112.565 + 1.320 + 2.835

RL of Bottom of Bridge Deck = 116.720 m.

The smallest value that can be measured by the measuring instrument is called its Least Count. 

Least count of Prismatic Compass = 30 minutes = 30’

Least Count of surveyor’s Compass = 15 minutes = 15’

From (a) and (b)

In a two theodolite method, curves are staked out by angular measurements only. Accuracy attained in this method is quite high. Thus the method is used when higher accuracy is required and when the topography is rough or field condition is difficult.

Telescopic alidade consists of a telescope mounted on a column fixed to the ruler. The line of sight through the telescope is kept parallel to the bevelled edge of the ruler. The telescope is provided with a level tube and vertical graduation arc. If the horizontal sight is required, bubble in the level tube is kept at the centre.

If inclined sights are required, vertical graduation helps in noting the inclination of the line of sight. By providing telescope the range and the accuracy of the line of sight are increased.

Curvature correction is negative and refraction correction is positive. If previous reading is less than the next consecutive reading then it will indicate a falling gradient.

Rise and fall method applies to check on B.S. and F.S., last RL and first RL. Rise and fall method is better than the height of the instrument method.

Deflection angle, 

Length of the vertical curve,