SSC JE Surveying Questions with Detailed Solutions

Indirect Ranging:

When the end stations between which a straight line is to be laid, are not inter-visible, then the indirect method of ranging is adopted. It is being carried out either by reciprocal method or by random line method.

As shown in the above figure station A and station B are not inter-visible, then, first of all, the two intermediate points M₁ and N₁ are located close to the chain line such that from point M₁ both N₁ and B are visible.

Similarly from N₁ both M₁ and A must be visible. Then, two ranging rods are placed at points M₁ and N₁. Then, the surveyor at M₁ signals the surveyor at N₁ to move to the new point N₂. It must be noted that the new point N₂ is in line with the line M₁B.

Similarly, the surveyor at point N₂ signals the surveyor at M₁ to move to a position M₂. It must be noted that the new point M₂ is in line with line N₂A.

Finally, the two surveyors are at points M₂ and N₂. This process is then repeated continuously until the points M and N are in line with the actual survey line AB.

After the final points, M and N are fixed, other successive points are easily fixed by direct ranging.

Hence the minimum number of persons required in indirect ranging is 2.

 Levelling is the process by which elevations of points or differences in elevation are determined.
 Types of levelling instruments used in surveying are:
Auto-level: 
 An automatic level is an optical instrument used to establish or verify points in the same horizontal plane in a process known as levelling.
 Its provides consistent level accuracy more quickly than many other leveling instruments.
 Auto level has internal compensator mechanism to automatically adjust the line of sight.
Tilting level:
 A surveying instrument with sighting telescope so mounted that it can be raised or lowered through a limited arc without impairing accuracy of reading, though axis of rotation is not precisely horizontal.
 Its function is to determine the distance between the point where the line of collimation (line-of-sight) of the level intersects the staff and the next lower staff graduation, and thus eliminates the need for estimation.
Abney level:
 An Abney level is an instrument used in surveying which consists of a fixed sighting tube, a movable spirit level that is connected to a pointing arm, and a protractor scale.
 An internal mirror allows the user to see the bubble in the level while sighting a distant target.
 They are used to measure degrees, percent of grade and topographic elevation.
​
Wye-level:
 An instrument, consisting of a spirit level mounted under and parallel to a telescope, that can be rotated in its Y-shaped supports for adjustment.
 The wye level has an advantage over the dumpy level in the fact that the adjustments can be tested with greater rapidity and ease.

Meridian is defined as a fixed line of reference that can be any line in the survey or an imaginary line. Meridians used in surveying can be
1. Arbitrary Meridian or Assumed Meridian
 A meridian that is arbitrarily chosen is called an arbitrary or assumed meridian. This meridian cannot be re-established if the original points are lost.
 The first line of a traverse is taken as an arbitrary meridian in a general situation. It helps to determine the relative direction of the traverse lines.
2. True Meridian/Astronomic Meridian
 If the meridian is the north-south line passing through the geographical poles of the earth, then it is called a True Meridian/Astronomic Meridian. This meridian is used for astronomical observations.
 The directions measured with respect to the true meridian do not change as the true meridian is a fixed direction.
3. Grid Meridian
 If a meridian lies parallel to the central true meridian for a specified area that is covered by a plane coordinate system, it is called a grid meridian. 
 For example, in order to survey a large area of a state, the true meridian of the central location of the country is taken as the reference meridian. This reference meridian is called as grid meridian.
4. Magnetic Meridian
 If the meridian reference line lies parallel to the magnetic lines of force (magnetic poles) of the earth, i.e. passing through the magnetic north and magnetic south of the earth is called as as magnetic meridian.
 A magnetic meridian can be identified using a freely-suspended magnetic needle that is influenced by the earth's magnetic needle. Hence, for each location, magnetic poles created changes. Hence a magnetic meridian is not a fixed direction.
 All the magnetic meridians will converge to a central point, called the magnetic pole. Used for rough surveys and to check surveys.
 The magnetic meridian and true meridian won't coincide with each other in place. The horizontal angle between these two meridians is known as magnetic declination. 

​$$\text{Given data:} \\[6pt]\text{RL of point} = 120 \, m \\\text{Elevation of the instrument } (h) = 1 \, m \\\text{Elevation of contour line from datum} = 119 \, m \\\text{Reading on the staff (S)} = ? \\[10pt]\text{Height of Instrument (H)} = \text{RL of Instrument Station (Point)} + \text{Elevation of the Instrument (h)} \\[6pt]= \text{RL of Staff Point + Staff Reading} \\[10pt]120 + 1 = 119 + S \\[6pt]121 = 119 + S \\[6pt]S = 2 \, m \\[10pt]\text{Staff reading (S)} = 2 \, m \\[6pt]\text{Reading on staff on a contour line (S)} = 2 \, m$$​​

Depression:
A set of close contours with lower figures inside and higher figures outside indicates depression.

Characteristics of contour lines:
All the points of the contour line have the same elevation.
Two contour lines do not intersect each other except in the case of an overhanging cliff or a cave penetrating a hillside.
Equally spaced contour represents a uniform slope and contours that well apart represent a gentle slope.
Contour line is a closed curve, they may close either on the map or outside the map it depending on the topography.
A set of close contours with higher figures inside and lower figures outside indicates a hillock, whereas in the case of depressions lakes, etc., the lower figures are inside and higher figures are outside.
Contour lines of a V shape with convexity towards higher ground represent the valley.
Contour lines of a U shape with convexity towards the lower ground (or with concavity towards the higher ground) represent the ridge line.

The fundamental principles of plane surveying are:
1. Location of a point by measurement from two points of reference:
Two control points are selected in an area and the distance between them is measured accurately.
2. Working from whole to the part:
Major control points are selected and measured first with a high degree of precision, minor details can be collected later on even with less degree of precision. In this manner, errors involved in minor detailing will be compensating and will not affect the major dimensions.

Chain Survey:
The principle of chain surveying is triangulation.
This means that the area to be surveyed is divided into a number of small triangles because the triangle is a simple figure that can be plotted from the length of its sides.
In chain surveying, the sides of the triangles are measured directly on the field by chain or tape, and no angular measurements are taken.

Theodolite has two types of adjustments:  
(1) Temporary (2) Permanent.
​Permanent Adjustment of Theodolite are
Adjustment of Horizontal Plate Levels: 
​The axis of the plate levels must be perpendicular to the vertical axis.
Collimation Adjustment: 
The line of collimation should coincide with the axis of the telescope and the axis of the objective slide and should be at right angles to the horizontal axis.
Horizontal axis adjustment: 
The horizontal axis must be perpendicular to the vertical axis.
Adjustment of Telescope Level or the Altitude Level Plate Levels:  
The axis of the telescope levels or the altitude level must be parallel to the line of collimation.
Temporary Adjustment: 
There are three temporary adjustments of a theodolite: 1.Centering; 2. Levelling; 3. Focussing.

True bearing of line T.B = Magnetic beating + Magnetic declination (+ve due to eastward declination)
∴ True Bearing = 180° + 60° = 240°

A theodolite is an instrument which is used to measure both horizontal and vertical Angles.
It is also used for many other subsidiary work during surveying such as setting up of intermediate points between inter visible points, establishment of inter visible points, prolonging a line, laying out traverse etc.
​Electronic Digital Theodolite: 
It is a precision instrument for measuring angles in the horizontal and vertical planes.
Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like meteorology and rocket launch technology.

Contour Line: A contour line is an imaginary outline of the terrain obtained by joining its points of equal elevation.
Characteristics of Contour: The following point are consider which are as follows:
All points in a contour line have the same elevation;
Flat ground is indicated where the contours are widely separated and steep-slope where they run close together.
A uniform slope is indicated when the contour lines are uniform spaced (i.e. tends to parallel each other).
A plane surface when they are straight parallel and equally spaced.
A series of closed contour lines on the map represent a hill, if the higher values are inside.

The minimum number of persons required in indirect ranging is 2.

Total Station : A total station is a surveying instrument which is used to measure angles in the horizontal and vertical planes with an electronic distance meter to measure distances and angles simultaneously.
Use of total station :
i) Land surveying for area computation
ii) Construction of building
iii) Mining survey
iv) Archaeology

Theodolite : Theodolite is an instrument which is used for measuring horizontal and vertical angle.
Measurement of horizontal angle :
a) Repetition Method :
→ This method is used for very accurate work.
→ In this method same angle is added several times mechanically and the correct value of the angle is obtained by dividing the accumulated reading by the no. of repetitions.
→ The angle should be measured clockwise in the face left to face right position with three repetitions at each face.
→ The final reading of the first observation will be the initial reading of the second observation and so on.
b) Reiteration method :
→ This method is another precise and comparatively less tedious method of measuring horizontal angles.
→ It is generally preferred when several angles are to be measured at a particular station.
→ This method consist of measuring several angles successively and finally closing the horizon at the starting point.
Elimination of different error present during the measurement of horizontal angle :
→ Error due to adjustment of line of collimation and the grunion axis are eliminated by taking both face readings.
→ Error due to eccentricity of Vernier’s and Centre get eliminated as readings from both the Vernier’s are taken.