Survey Model Sheet

 

Model Questions of Surveying:

1.      Define surveying. Explain its importance for Civil Engineers. What are the purpose of surveying?

1. Definition of Surveying

Surveying is the art and science of determining the relative positions of different natural and man-made features on, above, or beneath the surface of the earth. This is achieved by taking direct or indirect measurements of distance, direction, and elevation.

The primary objective of surveying is to prepare plans or maps that represent an area on a horizontal plane.

2. Importance / purpose of Surveying for Civil Engineers

Surveying is considered the "foundation" of civil engineering because no project can start without it. Its importance includes:

  • Map and Plan Preparation: It is the first step in any project to create a blueprint (map) of the existing ground.
  • Project Alignment: It is used to mark the exact path (alignment) for infrastructure like roads, railways, canals, tunnels, and pipelines.
  • Setting Out (Layout): It helps transfer the design from the paper to the actual ground, ensuring buildings and bridges are built in the correct spot.
  • Accurate Estimation: By measuring the ground profile, engineers can calculate earthwork (cutting and filling) quantities, which prevents over-estimation of project costs.
  • Support for Construction: It assists site engineers in placing structural materials precisely according to the design.
  • Safety and Monitoring: Surveying is used to monitor if a structure (like a dam or high-rise) is shifting or settling over time. 

 

2.      Explain the fundamental principles of surveying.

There are two primary fundamental principles of surveying. These are essential for ensuring accuracy and preventing errors in any project.

1. Working from Whole to the Part

This is the most critical principle in surveying.

  • The Process: First, a system of high-precision control points is established covering the entire area. Once these main points are fixed, the smaller details are surveyed using less precise methods within that established framework.
  • The Purpose: Its main idea is to prevent the accumulation of errors.
    • If you work from part to whole, small errors made at the beginning will multiply and become very large by the end.
    • By working from whole to part, any error made in a small area stays localized and does not affect the rest of the survey.

2. Location of a Point by Reference to Two Known Points

To establish the position of any new station or point, it must be measured from at least two previously established reference points (control points).

According to the diagrams on  a new point 'C' can be located from known points 'A' and 'B' using these method

Other Supporting Principles (from your notes):

  • Consistency in Work: Using uniform instruments and methods to maintain the same level of precision throughout.
  • Independent Check: Every measurement should be verified by a separate method to catch mistakes.
  • Economy of Accuracy: Choosing the right tools—don't use expensive high-precision tools for simple, low-accuracy tasks.

 

3.      Explain the classification of surveying on the different basis.

Based on the classifications provided in your notes (Page 2, 3, and 5), surveying is categorized based on the following three main criteria:

A. On the Basis of Earth’s Curvature

  1. Plane Surveying: The earth's surface is considered a flat plane. The curvature is neglected. It is suitable for small areas (up to 260 sq. km).
  2. Geodetic Surveying: The curvature of the earth is taken into account. It is used for very large areas and requires high precision.

B. On the Basis of Field Nature (Place of Work)

  1. Topographic Survey: To determine the natural features (rivers, hills) and man-made features (roads, buildings) of a country.
  2. Cadastral Survey: Conducted on a large scale to determine property boundaries and land ownership.
  3. City Survey: Done for urban planning, such as laying out streets, water supply lines, and sewers.
  4. Hydrographic Survey: Related to large water bodies (oceans, lakes) for navigation and finding the Mean Sea Level (MSL).
  5. Astronomical Survey: Determining the absolute position of a point on earth by observing stars or the sun.

C. On the Basis of Purpose

  1. Engineering Survey: To collect data for designing engineering projects like roads, railways, and dams.
  2. Military Survey: Preparing maps for defense and strategic purposes.
  3. Mine Survey: For exploring mineral wealth and preparing maps for mining operations.
  4. Geological Survey: To study the different layers and composition of the earth’s crust.
  5. Archaeological Survey: To unearth and map ancient relics and civilizations.

D. On the Basis of Instruments Used

AExplain the classification of surveys based on the instruments used.

  1. Chain Survey: The simplest type of survey where only linear measurements are taken using a chain or tape. No angular measurements are made.
  2. Compass Survey: A survey where the directions of lines are determined using a magnetic compass (Prismatic or Surveyor's compass) and lengths are measured with a chain/tape.
  3. Theodolite Survey: A precise survey where a theodolite is used to measure both horizontal and vertical angles. It is much more accurate than a compass survey.
  4. Plane Table Survey: A graphical method where the fieldwork and plotting are done simultaneously. A plane table and an alidade are the primary tools used.
  5. Triangulation Survey: A survey where the area is divided into a network of triangles, and the angles are measured with high precision using a theodolite.
  6. Photographic Survey: A method where maps are prepared from photographs taken from ground stations or from the air.
  7. Tacheometric Survey: A branch of angular surveying where both horizontal and vertical distances are determined by taking telescope readings on a graduated staff, eliminating the need for a chain.
  8. Aerial Survey: A survey conducted using cameras mounted on aircraft or drones to map large areas or inaccessible terrain quickly.

4.      Write about the chain survey and compass surveying.

1. Chain Surveying

Chain surveying is the simplest method of surveying where only linear measurements are taken in the field. No angular measurements are taken.

  • Principle: The fundamental principle is Triangulation. The area is divided into a network of well-conditioned triangles.
  • Suitability: It is best for small, open, and level ground with few details. It is unsuitable for large, crowded, or wooded areas.
  • Process: Distances are measured using a chain or tape. To locate internal details, offsets (perpendicular or oblique) are taken from the main survey lines.
  • Key Terms:
    • Base Line: The longest line that acts as the backbone of the survey.
    • Check Line: Used to verify the accuracy of the framework.
    • Tie Line: Used to take internal details and check the accuracy.
    • Main survey line: chain line use to connect main survey station
    • Main Survey stations: Main survey stations are the primary, fixed control points marking the corners or endpoints of the main survey lines, which define the outer boundary and main framework of a survey are

2. Compass Surveying

Compass surveying is a branch of surveying where the directions of survey lines are determined using a magnetic compass, and their lengths are measured with a chain or tape.

  • Principle: The fundamental principle is Traversing. A traverse consists of a series of connected lines where the magnetic bearing (angle) of each line is measured. Where end point is known as traverse stations and every simple line called traverse leg.
  • Instrument: It uses a Prismatic Compass or a Surveyor's Compass.
    • Magnetic Bearing: The horizontal angle a line makes with the magnetic meridian (North-South line).
  • Suitability: It is used for surveying large areas, long narrow strips (like roads or rivers), and crowded places where triangulation (chain surveying) is difficult.
  • Types of Traverses:
    • Closed Traverse: Starts and ends at the same point (e.g., surveying a pond or a building site).
    • Open Traverse: Starts at one point and ends at a different point (e.g., surveying a road or a canal).

Summary Comparison:

  • Chain Survey uses only distances (Triangles).
  • Compass Survey uses both distances and angles (Traverse).

Field Book

A field book in surveying is a specialized, durable notebook used by surveyors to record measurements, sketches, observations, and calculations made during field work.

Field books are categorized based on the ruling on their pages, specifically how the chain line is represented: 

1. Single Line Field Book

·        Structure: A single red line is ruled through the center of each page.

·        Usage: The central line represents the chain line or traverse line. Chainages (measurements along the line) are recorded on the line, while offsets (lateral measurements to objects) are sketched and written to the left or right of it.

·        Application: Generally used for detailed surveys where less space is needed in the center. 

 

2. Double Line Field Book

·        Structure: Two parallel red or blue lines, spaced about 1.5 cm to 2 cm apart, are ruled down the center of each page.

·        Usage: The entire space between the two lines represents the chain line. Chainage figures are written inside this space, while offsets and sketches are drawn in the margins on either side.

·        Application: This is commonly used for general surveying, such as chain surveying or road construction, as it provides better separation between the chainage data and the sketches. 

 

 

 

5.      List out the different between plane and geodetic surveying.

Feature

Plane Surveying

Geodetic Surveying

Curvature

Curvature of the Earth is neglected.

Curvature of the Earth is included.

Surface Shape

Surface is considered a flat plane.

Surface is considered spherical/arc.

Area Size

Suitable for small areas (up to 260 sq. km).

Suitable for very large areas.

Accuracy

Lower accuracy.

Higher accuracy (accounts for atmospheric refraction).

Line joining points

Considered a Straight line.

Considered an Arc of a circle.

 

6.      Write the types of scale and map.

Based on the details in your notes (Page 6 and Page 3), here are the types of scales and maps explained in simple engineering terms:

1. Scale (माननाप)

A scale is the ratio between the distance of two points on a map (or plan/photo) and the actual horizontal distance between those same two points on the ground.

  • Formula: $\text{Scale} = \frac{\text{Map distance}}{\text{Ground distance}}$

Types of Scales (by usage in Engineering):

  • Large Scale: Used for Plans. It shows a small area in great detail (e.g., 1 cm = 10 m).
  • Small Scale: Used for Maps. It covers a very large area with less detail (e.g., 1cm = 10km}$).

2. Types of Maps (नक्सा)

A map is a graphical representation of the Earth's features on a small scale, projected onto a horizontal plane. According to your notes, maps are categorized based on their nature and purpose:

A. Based on Field Nature (Page 3):

  1. Topographic Map: Shows natural features (mountains, rivers, forests) and physical objects on the Earth's surface.
  2. Cadastral Map: Drawn to a large scale to show property lines and land ownership boundaries.
  3. City Map: Used for urban development, showing roads, water supply lines, and sewer systems.
  4. Hydrographic Map: Shows large water bodies, shorelines, and navigation routes.

B. Based on Purpose (Page 3):

  1. Engineering Map: Prepared to show details and quantities for projects like roads, reservoirs, and dams.
  2. Military Map: Prepared specifically for defense and military strategies.
  3. Geological Map: Shows the layers of rocks and minerals beneath the Earth's surface.
  4. Archaeological Map: Shows details of ancient civilizations and cultural sites.

Key Difference (From Page 6):

  • Plan: Large scale, 2D (Easting & Northing), no height info, used for construction.
  • Map: Small scale, 3D (Easting, Northing & Height), shows true geographical position on the globe.

 

7.      Define ranging and its types.

Ranging is a fundamental process in surveying, particularly in chain surveying. Here is the definition and its types explained in simple engineering terms:

Definition of Ranging

Ranging is the process of establishing intermediate points on a straight line between two fixed end stations.

In surveying, if the distance between two points is greater than the length of the chain or tape, you cannot measure it in one go. You must establish intermediate points so that the measurements are taken along a perfectly straight line. If the line is not straight, the measured distance will be longer than the actual distance, leading to an error.

Types of Ranging

There are two main types of ranging used in the field:

1. Direct Ranging

Direct ranging is possible when the two end stations are inter-visible (you can see the ranging rod at the far end from the starting point).

  • Process: A surveyor stands at one end station and directs an assistant (holding a ranging rod) to move left or right until the assistant's rod is perfectly aligned with the far end rod.
  • Methods: It can be done by eye (naked eye) or by using an optical instrument like a line ranger or a theodolite for better accuracy.

2. Indirect Ranging (Reciprocal Ranging)

Indirect ranging is used when the two end stations are not inter-visible due to high ground, a hill, or a long distance.

  • Process: Since you cannot see from Point A to Point B, two intermediate points (say $M_1$ and $N_1$) are selected such that from $M_1$, both $N_1$ and $B$ are visible, and from $N_1$, both $M_1$ and $A$ are visible.
  • Mechanism: The two surveyors at the intermediate points signal each other to move until all four points ($A, M, N, B$) lie on a single straight line. This is a repetitive process until perfect alignment is achieved.

Summary Table for Exam

Feature

Direct Ranging

Indirect (Reciprocal) Ranging

Visibility

End stations are inter-visible.

End stations are NOT inter-visible.

Obstacle

Clear, flat ground.

A hill or high ground in between.

Accuracy

Higher for short distances.

Requires multiple steps to ensure a straight line.

 

8.      What are the different types of levels used in levelling with sketches?

10. Different Types of Levels Used in Levelling

In civil engineering, various types of levels are used depending on the required accuracy and the nature of the terrain. Here are the most common types:

1. Dumpy Level

The Dumpy Level is the most commonly used instrument in simple levelling.

  • Description: The telescope is rigidly fixed to its supports and cannot be rotated about its horizontal axis or removed from its supports. It is simple, compact, and stable.
  • Sketch Note: When drawing, show a long telescope tube fixed onto a vertical spindle with three leveling foot screws at the bottom.

2. Tilting Level

  • Description: Unlike the Dumpy level, the telescope can be tilted slightly (about $4^\circ$) in the vertical plane using a fine-pitch tilting screw. This allows you to bring the bubble to the center accurately for each reading without releveling the whole base.
  • Sketch Note: Draw a telescope with a small circular hinge at one end and a micrometer/tilting screw at the eyepiece end.

3. Automatic Level (Self-Aligning Level)

This is the modern standard for site work.

  • Description: It contains a compensator mechanism (a system of prisms suspended by fine wires). Once the base is approximately levelled using the circular bubble, the compensator automatically makes the line of sight perfectly horizontal.
  • Sketch Note: Draw a shorter, boxier instrument with a small circular "bullseye" bubble on the side.

4. Wye (Y) Level

  • Description: The telescope is held in two Y-shaped supports. It can be rotated or even removed and reversed. It is mostly used for checking the internal adjustments of the instrument itself.
  • Sketch Note: Draw two distinct "Y" brackets holding the telescope tube.

5. Digital Level

  • Description: This is an electronic instrument that reads a special barcoded levelling staff. It eliminates human reading errors and automatically calculates and stores the Reduced Levels (R.L.).

Comparison Table for Quick Reference

Level Type

Portability

Accuracy

Main Feature

Dumpy

High

Medium

Rigid and robust construction.

Tilting

Medium

High

Ideal for precise work; telescope tilts.

Automatic

High

Very High

Fastest to set up; has a compensator.

Digital

Medium

Highest

No manual reading; electronic data storage.

Pro-Tip for Loksewa Exam:

If this question carries 8 marks, always include a labeled diagram of the Dumpy Level or Automatic Level. Label parts like the Objective Lens, Eyepiece, Cross-hairs, Focusing Screw, and Foot Screws.

 

9.      Define the following: Level line, Level surface, Horizontal line, Horizontal surface, Line of collimation, Axis of telescope, Foresight, Back sight, Intermediate sight, Bench mark, Mean sea level, Height of instrument and Reduced level.

Key Definitions in Levelling

  1. Level Surface: A curved surface that is at every point perpendicular to the direction of gravity (plumb line). The surface of a still lake is the best example.
  2. Level Line: A line lying on a level surface. It is therefore a curved line, not a straight line.
  3. Horizontal Surface: A plane surface tangent to the level surface at a specific point. It is perpendicular to the plumb line at that point.
  4. Horizontal Line: A straight line tangential to a level line at a particular point. It is the line along which we take our survey measurements.
  5. Line of Collimation: The imaginary line passing through the intersection of the cross-hairs and the optical center of the objective lens. It is also known as the Line of Sight.
  6. Axis of Telescope: An imaginary line passing through the optical centers of the objective lens and the eyepiece.
  7. Back Sight (B.S.): The first staff reading taken after the instrument is set up. It is always taken on a point of known elevation (like a Bench Mark).
  8. Fore Sight (F.S.): The last staff reading taken before shifting the instrument or finishing the work. It is used to determine the elevation of a new point.
  9. Intermediate Sight (I.S.): Any staff reading taken between a Back Sight and a Fore Sight from the same instrument setup.
  10. Bench Mark (B.M.): A relatively permanent point of known elevation used as a reference for levelling.
  11. Mean Sea Level (M.S.L.): The average height of the sea for all stages of the tide. In Nepal, the M.S.L. used as a reference is taken from Karachi, Pakistan (or sometimes via Indian Railway points).
  12. Height of Instrument (H.I.): The elevation (R.L.) of the Line of Collimation above the datum when the instrument is correctly levelled.
    • Formula: $H.I. = R.L. \text{ of B.M.} + B.S.$
  13. Reduced Level (R.L.): The vertical distance (elevation) of a point above or below a chosen datum (usually M.S.L.).

 

 

10.   Describe the temporary adjustments of a level.

 Temporary adjustments are the steps performed at every instrument station before taking any observations.

For a level (like a Dumpy Level), the process involves these three main steps:

1. Setting up the Level

This step involves placing the instrument over the station and making it ready for work.

  • Fixing: The level is fixed onto the tripod stand. The tripod legs are spread wide apart and firmly pressed into the ground to ensure stability.
  • Leg Adjustment: The legs are adjusted so that the telescope is at a convenient height for the surveyor and the tripod head is approximately level by eye.

2. Levelling (Centering the Bubble)

This is the most critical step to ensure the Line of Collimation is truly horizontal.

  • Using Foot Screws: Most levels use a three-screw system. The telescope is placed parallel to any two foot-screws and turned until the bubble is in the center.
  • 90-Degree Turn: The telescope is then turned 90 degrees (over the third screw), and that screw is adjusted to bring the bubble back to the center.
  • Verification: This is repeated until the bubble stays in the center regardless of which direction the telescope is pointed.

3. Elimination of Parallax

Parallax occurs when the image of the object does not fall exactly on the plane of the cross-hairs, causing the image to shift when the observer's eye moves.

  • Focusing the Eye-piece: A white paper is held in front of the objective lens, and the eye-piece is turned in or out until the cross-hairs appear sharp and distinct.
  • Focusing the Objective: The telescope is directed at the levelling staff. The focusing screw is turned until the image of the staff is clear and sharp.
  • Final Check: The surveyor moves their eye slightly; if the staff image doesn't move relative to the cross-hairs, parallax is eliminated.

 

11.   Describe fully the methods of reduction of levels and discuss their merits and demerits.

Based on your notes, the reduction of levels is the process of calculating the Reduced Level (R.L.) of various points from the readings taken in the field. There are two primary methods used for this.

1. Line of Collimation Method (Height of Instrument Method)

In this method, the elevation of the horizontal line of sight (Height of Instrument or H.I.) is calculated for each setup of the level. The R.L. of subsequent points is then found by subtracting the staff readings from this H.I.

  • Formula:

Merits (Advantages):

  • Speed: It is very fast and involves fewer calculations.
  • Efficiency: It is highly efficient when a large number of Intermediate Sights (I.S.) are taken from a single instrument station.
  • Simplicity: The process is straightforward to understand and execute in the field book.

Demerits (Disadvantages):

  • Limited Check: There is no arithmetic check on the R.L.s of intermediate points. If an error is made in calculating an I.S., it will not be detected by the final check.
  • Accuracy Risk: Because intermediate points aren't fully checked, it is considered less reliable for high-precision work.

2. Rise and Fall Method

This method involves comparing the staff reading of a point with the reading of the point immediately preceding it. If the reading is smaller than the previous one, it indicates a Rise; if it is larger, it indicates a Fall.

  • Formula:

Merits (Advantages):

  • Complete Check: It provides a full arithmetic check on all points, including Intermediate Sights. Every calculation is verified.
  • High Accuracy: Due to the rigorous checking of every point, errors are caught immediately. It is the preferred method for precise engineering work.

Demerits (Disadvantages):

  • Time-Consuming: It is much slower because every point requires a calculation for rise or fall before finding the R.L.
  • Complex Calculations: The number of steps is significantly higher, which can lead to fatigue or manual errors in large datasets.

Arithmetical Checks Summary

Method

Check Formula

Collimation


Rise & Fall


 

12.   Compare ‘line of collimation’ method with the ‘rise and fall’ method for reducing levels.

Here is the comparison between the Line of Collimation (Height of Instrument) method and the Rise and Fall method in simple engineering terms:

Comparison of Methods for Reducing Levels

Feature

Line of Collimation (H.I.) Method

Rise and Fall Method

Basic Concept

It focuses on finding the elevation of the horizontal line of sight (Height of Instrument) first.

It focuses on the difference in height between two consecutive points (Rise or Fall).

Speed

Faster and simpler, especially when there are many Intermediate Sights (I.S.).

Slower and more tedious as it requires more calculation steps.

Calculations

Less calculation is required.

More calculation is required for every single point.

Check on I.S.

It does not provide a check on the accuracy of Intermediate Sights (I.S.) calculations.

It provides a complete check on all readings, including Intermediate Sights (I.S.).

Accuracy

Generally considered less reliable because calculation errors in I.S. can go unnoticed.

Highly reliable and accurate as every calculation is verified.

Suitability

Best for Profile Levelling or contouring where many readings are taken from one setup.

Best for precise levelling and Bench Mark establishment where accuracy is the priority.

Arithmetic Check



 

Summary: Use the Line of Collimation method when you want to save time on projects with many side shots (like road profiles). Use the Rise and Fall method when you need to ensure that every single reduced level is mathematically correct and error-free.

13.   Explain (i) reciprocal levelling (ii) fly levelling (iii) differential levelling (iv) simple levelling and state where each is used.

Based on the provided notes, here is the explanation for the various types of levelling and their specific uses:

(i) Reciprocal Levelling

  • Explanation: This is a method used to find the exact difference in elevation between two points when it is impossible to set up the level midway between them. It involves taking two sets of observations (one from each side) to eliminate errors caused by the earth's curvature, atmospheric refraction, and instrument defects.
  • Where it is used: Used when crossing wide obstacles like rivers, deep valleys, or ravines where a bridge abutment or deck slab level needs to be determined.

(ii) Fly Levelling

  • Explanation: Fly levelling is a quick method used to determine approximate elevations. It is generally done at the end of a day's work to connect the last point reached back to the original starting Bench Mark (BM). Only Back Sights (BS) and Fore Sights (FS) are taken.
  • Where it is used: Used to check the accuracy of a series of levels or to "fly" a level from a known Bench Mark to the starting point of a new survey site.

(iii) Differential Levelling

  • Explanation: This method is used when the distance between two points is very large, the difference in elevation is great, or there are obstacles in between. It requires shifting the instrument multiple times.
  • Where it is used: Used for establishing Bench Marks (BM) at various locations and for long-distance projects like highway or railway surveys.

(iv) Simple Levelling

  • Explanation: This is the most basic form of levelling where the instrument is set up in a single position, and readings are taken on two points that are relatively close to each other.
  • Where it is used: Used for small, simple tasks where the two points are clearly visible from a single instrument station and the distance between them is short.

Here are the questions copied from the image you provided: next part

  1. The following readings were successively taken with an instrument in levelling work:
    0.32, 0.53, 0.62, 1.78, 1.91, 2.35, 1.75, 0.35, 0.69, 1.24 and 0.98 m
    The position of the instrument was changed after 3rd, 7th and 9th readings. Draw out the form of a level book and enter the above readings properly. Assume the R.L. of the 1st point as 81.53m. Calculate R.L. of all points and apply usual checks.

  1. The following consecutive readings were taken with a level and a 4 m staff on a continuously sloping ground at a common interval of 20 metres:
    0.855 (on Q), 1.545, 2.335, 3.115, 3.825, 0.455, 1.380, 2.055, 2.855, 3.455, 0.585, 1.015, 1.850, 1.850, 2.755, and 3.845 (on R).
    Enter the readings as on a field book page, reduce the levels, apply the checks and determine the gradient of line QR.

Station

Chainage (m)

B.S.

I.S.

F.S.

Rise (+)

Fall (-)

R.L. (m)

Remarks

1

0

0.855



100.000

Point Q

2

20

1.545

0.690

99.310

3

40

2.335

0.790

98.520

4

60

3.115

0.780

97.740

5

80

0.455

3.825

0.710

97.030

CP 1

6

100

1.380

0.925

96.105

7

120

2.055

0.675

95.430

8

140

2.855

0.800

94.630

9

160

0.585

3.455

0.600

94.030

CP 2

10

180

1.015

0.430

93.600

11

200

1.850

0.835

92.765

12

220

1.850

0.000

92.765

13

240

2.755

0.905

91.860

14

260

3.845

1.090

90.770

Point R

Total

1.895

11.125

0.000

9.230

Result: The gradient is approximately 1 in 28.17 (Falling).

  1. Reciprocal levels were taken with a dumpy level and following observations were recorded:

Inst. near Station

Staff reading at station A

Staff reading at station B

A

1.225

1.375

B

0.850

0.500

R.L. of station A is known to be 626.155. Calculate the R.L. of station B.



 

  1. Enumerate the instruments used in plane tabling.

Based on standard engineering practices for Plane Table Surveying, here is the list of essential instruments and their functions:

1. Plane Table and Tripod

The main drawing board (usually 60cm x 75cm) made of well-seasoned wood, mounted on a sturdy tripod. It provides a stable horizontal surface for drawing in the field.

2. Alidade

A straight-edge ruler used for sighting objects and drawing lines.

  • Plain Alidade: Has two vertical slits (eye vane and object vane).
  • Telescopic Alidade: Includes a telescope for better accuracy and for sighting distant or high objects.

3. Plumbing Fork (U-Fork) and Plumb Bob

Used for Centering. It ensures that the point on the drawing paper is exactly above the corresponding station point on the ground.

4. Spirit Level

A small tube containing a bubble used to ensure the plane table is perfectly Level (horizontal) in all directions.

5. Trough Compass

A long, narrow compass used to mark the Magnetic North on the drawing sheet. It is also used for rough orientation of the table.

6. Drawing Materials

  • Drawing Sheet: High-quality paper that does not expand or contract much with moisture.
  • Pencils, Erasers, and Pins: For plotting and securing the paper.
  • Scale: For converting ground distances to map distances.

7. Waterproof Cover

A plastic or cloth cover used to protect the drawing sheet from rain, dust, or moisture.

 

  1. Describe the method of plane table surveying.

In plane table surveying, there are four specific methods used to locate points and details. Each method is chosen based on the terrain and the distance of the objects from the station.

1. Radiation Method

This is the simplest method, used when the points to be located are nearby and easily accessible from a single station.

  • Process: The plane table is set up at a central station (P). The alidade is pivoted at point 'p' on the paper, and sightings are taken to various objects (A, B, C). Distances are measured with a tape and plotted to scale along the radial lines.
  • Suitability: Best for small areas and locating nearby details from one central point.

2. Intersection Method (Graphic Triangulation)

This method is used when the points are inaccessible (e.g., a point across a river or a mountain peak) or when distances are too long to measure with a tape.

  • Process: The object is sighted from two different stations (A and B). The intersection of the two lines of sight on the paper gives the exact position of the object.
  • Suitability: Best for distant objects, broken ground, or crossing obstacles like rivers.

3. Traversing Method

Similar to compass traversing, this method is used to connect a series of survey stations to form a framework.

  • Process: The table is moved from station to station. At each new station, the table is oriented by back-sighting to the previous station, and the next station is then sighted and plotted.
  • Suitability: Best for surveying long, narrow strips like roads, rivers, or boundaries.

4. Resection Method

This is used to locate the position of the plane table itself on the map using already plotted control points.

  • Process: New stations are established by sighting towards known points whose positions are already on the map.
  • Key Techniques: The most famous resection problems are the Two-Point Problem and the Three-Point Problem.
  • Suitability: Used when the surveyor needs to set up the table at a convenient location that has not been previously plotted.

Summary Table for Exam

Method

Main Feature

Primary Use

Radiation

Single station setup.

Locating nearby, accessible details.

Intersection

Two station sightings.

Inaccessible points (rivers/hills).

Traversing

Multiple station sequence.

Road, railway, or river surveys.

Resection

Locating the table's position.

Establishing new stations from known points.

 

  1. Discuss the advantages and disadvantages of plane table surveying over other methods of surveying.

Plane table surveying is a unique graphical method where field observations and plotting are done simultaneously. Here are its advantages and disadvantages compared to other methods like chain or theodolite surveying:

Advantages

  • Real-time Plotting: Since plotting is done in the field, there is no risk of omitting (forgetting) important details.
  • No Field Book Required: Measurements are plotted directly on paper, eliminating the need for a separate field book and reducing transcription errors.
  • Visual Verification: The surveyor can compare the plotted map with the actual ground features immediately, allowing for instant correction of errors.
  • Speed: For small-scale mapping of open areas, it is much faster than theodolite surveying as no complex calculations are needed.
  • Ease of Use: It does not require high-level mathematical skills compared to compass or theodolite traversing.

Disadvantages

  • Weather Dependent: It is unsuitable for work in rainy, windy, or very humid weather, as the drawing paper can get wet or expand.
  • Bulkiness: The equipment (table, tripod, alidade) is heavy and difficult to carry in hilly or dense forest areas.
  • Daylight Only: Work can only be done during daylight hours with good visibility.
  • Lower Precision: It is not suitable for high-precision work or large-scale engineering projects because the accuracy is limited by the scale of the drawing.
  • No Permanent Record: Unlike a field book, if the drawing sheet is lost or damaged, all field data is lost since no numerical records are kept.
  1. Describe the working operation of plane table surveying.

In plane table surveying, "Working Operation" refers to the initial steps performed at each station to prepare the table for drawing. Based on standard engineering practice, there are four essential operations performed in this specific order:

1. Fixing

The plane table is securely attached to the tripod stand. The tripod legs are spread wide and firmly pressed into the ground so that the table is at a convenient height (usually waist height) for the surveyor to work.

2. Leveling

This ensures that the board is perfectly horizontal.

  • For small-scale surveys, a circular spirit level is used.
  • For precise work, a trough spirit level is placed in two perpendicular directions on the board. The tripod legs are adjusted until the bubble stays in the center in all directions.

3. Centering

This ensures that the point on the drawing paper is exactly above the corresponding point on the ground.

  • A U-fork (Plumbing fork) with a plumb bob is used.
  • One end of the fork is placed on the point on the paper, and the table is moved until the plumb bob at the other end hangs exactly over the ground peg.

4. Orientation

This is the most important operation. Orientation is the process of keeping the table parallel to the position it occupied at the previous station. This ensures that all lines on the paper are parallel to their corresponding lines on the ground.
There are two methods:

  • Orientation by Magnetic Needle: Using a Trough Compass to align the table with the Magnetic North. (Less accurate due to local attraction).
  • Orientation by Back Sighting: Aligning the table by sighting back to the previous station. (Most accurate method).

Summary for Exam:

In a Loksewa exam, remember the sequence: Fixing - Leveling - Centering -Orientation.

 

 

  1. Explain the different types of theodolite.

Theodolites are precision instruments used to measure both horizontal and vertical angles. They are classified based on their construction and operation as follows:

1. Based on the Movement of the Telescope

  • Transit Theodolite: A theodolite is called "transit" when its telescope can be rotated through a complete circle ($180^{\circ}$) in the vertical plane about its horizontal axis. This is the most common type used in modern engineering.
  • Non-Transit Theodolite: In this type, the telescope cannot be rotated in a full vertical circle. These are now mostly obsolete.

2. Based on the Measurement System

  • Vernier Theodolite: This instrument uses Vernier scales to read the angles. It is a traditional manual instrument commonly used for educational and basic construction purposes. It can typically read up to an accuracy of 20 seconds ($20"$).
  • Microptic (Optical) Theodolite: Instead of a metal scale, it uses glass circles. The readings are taken through a small internal microscope. It is much more accurate than a Vernier theodolite, often reading up to 1 second ($1"$).
  • Digital (Electronic) Theodolite: This is the modern version. It features a digital display that shows angles automatically, eliminating manual reading errors. It is fast and easy to use on construction sites.

3. Based on Precision

  • Precise Theodolite: Used for high-level geodetic surveys where accuracy is the top priority.
  • General Purpose Theodolite: Used for everyday engineering tasks like road layout or building construction.

Summary Table for Exam

Type

Main Feature

Best Use

Transit

Full vertical rotation.

Most common field work.

Vernier

Manual scale reading.

Education/Simple tasks.

Digital

Electronic display.

Fast construction layout.

Microptic

Glass scale/Microscope.

High-precision surveys.

 

  1. Describe temporary adjustments of a theodolite.

Based on standard engineering practices for a transit theodolite, temporary adjustments are the steps performed at every instrument station before starting observations.

The process involves the following three main steps:

1. Setting Up the Theodolite

This includes the initial placement of the instrument over the station.

  • Fixing: The theodolite is securely attached to the tripod head.
  • Centering: The instrument is placed exactly over the station mark (peg). This is done using a plumb bob or an optical plummet.
  • Leveling by Tripod: The tripod legs are adjusted so that the instrument is at a comfortable height and the plate level is approximately centered.

2. Leveling Up

This is done to make the vertical axis truly vertical. It uses the plate level and the tripod foot screws.

  • Parallel Position: The plate level is placed parallel to any two foot screws. Both screws are turned (either both inward or both outward) until the bubble is in the center.
  • 90-Degree Turn: The telescope is rotated $90^{\circ}$ so it is over the third foot screw. This screw is then turned to bring the bubble back to the center.
  • Verification: This process is repeated until the bubble remains centered in every position of the telescope’s rotation.

3. Elimination of Parallax

Parallax is the apparent movement of the image relative to the cross-hairs. It is removed in two stages:

  • Focusing the Eyepiece: The telescope is pointed at the sky or a white paper. The eyepiece is turned until the cross-hairs appear sharp and dark.
  • Focusing the Objective: The telescope is directed at the target (ranging rod or staff). The focusing screw is turned until the image of the object is perfectly sharp and coincides exactly with the cross-hairs.

Key Difference from a Level:

Unlike a dumpy level, a theodolite requires Centering as its first priority because it is used to measure horizontal angles between specific ground points.

  1. Name the fundamental axes of a theodolite. State the relationship that must exist between them when the instrument is in adjustment.

The fundamental axes of a theodolite and their relationships are essential for its precision. Here is the explanation based on standard engineering survey principles:

1. Fundamental Axes of a Theodolite

A theodolite has five main axes:

  1. Vertical Axis: The axis about which the instrument rotates in a horizontal plane.
  2. Horizontal Axis (Trunnion Axis): The axis about which the telescope rotates in a vertical plane.
  3. Line of Collimation (Line of Sight): The imaginary line passing through the intersection of the cross-hairs and the optical center of the objective lens.
  4. Axis of Telescope Level (Bubble Tube Axis): The line tangential to the longitudinal curve of the bubble tube at its midpoint.
  5. Axis of Plate Level: The line tangential to the longitudinal curve of the plate level bubble.

2. Relationships for a Perfectly Adjusted Instrument

When the theodolite is in permanent adjustment, the following relationships must exist:

  • Axis of Plate Level: The axis of the plate level must be perpendicular to the Vertical Axis. (This ensures the vertical axis is truly vertical when the bubble is centered).
  • Line of Collimation: The line of collimation must be perpendicular to the Horizontal Axis. (This ensures that the telescope traces a vertical plane when rotated).
  • Horizontal Axis: The horizontal axis must be perpendicular to the Vertical Axis.
  • Bubble Tube Axis: The axis of the telescope level must be parallel to the Line of Collimation.
  • Vertical Circle Index: The vertical circle should read zero ($0^\circ$) when the line of collimation is perfectly horizontal.

Summary for Exam:

In the Loksewa exam, these relationships are often asked as multiple-choice questions or short-answer definitions. Remembering that the Horizontal, Vertical, and Collimation axes are all mutually perpendicular to each other is a great way to memorize the main points.

 

  1. Define contours and give characteristics of contours.

Here are the definitions and characteristics of contours explained in simple engineering terms, as required for your exam preparation:

1. Definition of Contours

A Contour is an imaginary line on the ground surface connecting points of equal elevation (Reduced Level) above a datum (usually Mean Sea Level). A map showing these lines is called a Contour Map, and it represents the 3D topography of the land on a 2D surface.

2. Characteristics of Contours

Understanding these characteristics is essential for interpreting the nature of the terrain:

  • Equal Elevation: All points on a single contour line have the same elevation.
  • Closed Loops: Every contour line must eventually close upon itself, either within the map or outside its boundaries.
  • Non-Intersecting: Contour lines of different elevations never cross each other.
    • Exception: They only appear to cross in the case of an Overhanging Cliff.
  • Non-Merging: Contour lines of different elevations never unite into one line.
    • Exception: They appear to merge into a single line in the case of a Vertical Cliff.
  • Slope Indication:
    • Steep Slope: Indicated when contour lines are close together.
    • Gentle Slope: Indicated when contour lines are far apart.
    • Uniform Slope: Indicated when contour lines are equally spaced.
  • Hills and Depressions:
    • Hill: A series of closed contours where values increase toward the center.
    • Depression/Pond: A series of closed contours where values decrease toward the center.
  • Ridge and Valley Lines:
    • Ridge Line: Contour lines form a 'U' or 'V' shape pointing away from the higher ground.
    • Valley Line: Contour lines form a 'U' or 'V' shape pointing toward the higher ground. (A valley line is crossed by contours at right angles).

Key Term: Contour Interval

The vertical distance between any two consecutive contour lines is called the Contour Interval. It is usually kept constant for a single map to maintain consistency.

  1. What are the uses of a contour map?

A contour map is a topographical map that uses contour lines (lines connecting points of equal elevation) to represent the three-dimensional shape of the earth's surface on a two-dimensional paper.

In civil engineering, specifically for projects in hilly regions like Nepal, contour maps are used for the following purposes:

  1. Selection of Suitable Sites: They help engineers find the best locations for projects like dams, reservoirs, or buildings by identifying flat areas or natural depressions.
  2. Alignment of Roads and Railways: Contour maps are used to plan the easiest and most economical path for roads, railways, or canals, ensuring the gradient (slope) is within safe limits.
  3. Calculation of Reservoir Capacity: By measuring the area enclosed by contour lines at a dam site, engineers can calculate the total volume of water a reservoir can hold.
  4. Earthwork Estimation: They allow for the calculation of the volume of soil to be cut or filled for construction, which is essential for cost estimation.
  5. Determining Catchment Areas: Contour maps help identify the watershed or catchment area of a river, which is crucial for designing bridges and drainage systems.
  6. Inter-visibility between Points: Engineers can determine if two points are visible to each other (important for surveying and communication towers) without visiting the site.
  7. Identification of Landforms: They help in identifying features like hills, valleys, ridges, and cliffs at a glance.
  8. Tracing Grade Contours: They are used to mark a line on the ground that maintains a constant slope, which is the first step in hill road design.
  1. What are the elements of a simple circular curve? Give their relationships.

 

A simple circular curve is used in road and railway engineering to connect two straight lines (tangents) to allow for a smooth change in direction.

1. Key Elements of a Simple Circular Curve

Referencing standard engineering terms, here are the main parts:

  • Back Tangent (T1): The straight line before the curve starts.
  • Forward Tangent ($T_2V$): The straight line after the curve ends.
  • Point of Curve (P.C. or $T_1$): The point where the curve begins.
  • Point of Tangency (P.T. or $T_2$): The point where the curve ends.
  • Point of Intersection (P.I. or $V$): The point where the two tangents meet.
  • Deflection Angle ($\Delta$ or $\phi$): The angle by which the forward tangent deflects from the back tangent.
  • Intersection Angle ($I$): The interior angle between the tangents ($I = 180^\circ - \Delta$).
  • Radius ($R$): The radius of the circle of which the curve is a part.
  • Tangent Length ($T$): The distance from $T_1$ or $T_2$ to the point of intersection $V$.
  • Long Chord ($L$): The straight line joining $T_1$ and $T_2$.
  • Length of Curve ($l$): The length of the arc from $T_1$ to $T_2$.
  • Apex Distance (External Distance, $E$): The distance from the Point of Intersection $V$ to the midpoint of the curve.
  • Mid-Ordinate ($M$): The distance from the midpoint of the curve to the midpoint of the long chord.

2. Important Relationships (Formulas)

These formulas are critical for Loksewa exams and field calculations:

  1. Tangent Length ($T$):
    $$T = R \tan \left( \frac{\Delta}{2} \right)$$
  2. Length of Curve ($l$):
    $$l = \frac{\pi R \Delta}{180^\circ}$$
  3. Length of Long Chord ($L$):
    $$L = 2R \sin \left( \frac{\Delta}{2} \right)$$
  4. Apex Distance ($E$):
    $$E = R \left( \sec \frac{\Delta}{2} - 1 \right)$$
  5. Mid-Ordinate ($M$):
    $$M = R \left( 1 - \cos \frac{\Delta}{2} \right)$$
  6. Degree of Curve ($D$): For a 30m chain length:
    $$D = \frac{1719}{R} \quad (\text{approximately})$$

 

  1. Describe a method of setting out of small building.

Setting out is the process of transferring the design from the drawing paper onto the actual ground. For a small building, the most common method used in Nepal is the Center-Line Method (also known as the Batter Board or Pegging method).

Here is the step-by-step procedure:

1. Preparation and Cleaning

  • The site is cleared of bushes, loose soil, and debris.
  • The surveyor studies the Foundation Plan to identify the outer boundary and the center lines of all walls.

2. Establishing the Baseline

  • A Baseline is established parallel to a known boundary (like a road or a neighbor's wall) using a tape or a Total Station.
  • The front corners of the building are marked on this baseline using wooden pegs.

3. Marking the Corners (The 3-4-5 Rule)

  • To ensure the corners are perfectly square ($90^{\circ}$), the 3-4-5 triangle rule (Pythagoras theorem) is used.
  • One side is measured as 3m, the adjacent as 4m; if the diagonal is exactly 5m, the corner is a perfect right angle.

4. Fixing the Batter Boards (Profiles)

  • Since pegs at the actual corners will be removed during excavation, Batter Boards (horizontal wooden planks on posts) are fixed 1 to 2 meters outside the building area.
  • Nails are driven into these boards exactly on the center lines of the walls.

5. Stretching the Strings

  • Thin strings or wires are stretched tightly between the nails on opposite batter boards.
  • The intersection of these strings represents the Center Point of the columns or walls.

6. Marking for Excavation

  • A Plumb Bob is dropped from the string intersections to the ground to mark the center.
  • Using the width of the foundation from the drawing, the excavation limits are marked on the ground using white lime powder.

7. Checking Diagonals

  • Before digging, the diagonals of each room or the whole building are measured. If the diagonals are equal, the building is perfectly rectangular and "square."

Summary for Exam:
In the Loksewa exam, mention that the Batter Board method is permanent during construction, while simple pegging is temporary. Always mention the 3-4-5 rule and the Diagonal check as these are key engineering steps.

  1. Write about total station and GPS.

Based on current engineering standards here is an explanation of Total Station and GPS in simple terms:

1. Total Station

A Total Station is a modern, electronic version of a theodolite. It is an "all-in-one" instrument used to measure both distances and angles simultaneously.

  • How it Works: It combines an Electronic Theodolite (for angles) and an Electronic Distance Meter (EDM) (for distances) with a built-in computer to process data.
  • Main Features:
    • Distance: It uses infrared or laser pulses to measure distance without a tape.
    • Coordinates: It automatically calculates the X (Easting), Y (Northing), and Z (Elevation) of points.
    • Data Storage: It records measurements electronically, which can be downloaded directly to a computer for mapping (AutoCAD).
  • Importance: It is much faster and more accurate than traditional chain or compass surveying. It is used for complex projects like bridge construction, tunnels, and large-scale highway layouts.

2. Global Positioning System (GPS)

GPS is a satellite-based navigation system used to find the exact location of a point on Earth. In surveying, we specifically use GNSS (Global Navigation Satellite System) for high precision.

  • How it Works: A GPS receiver on the ground picks up signals from at least four satellites orbiting the Earth. By calculating the time the signals take to arrive, the receiver determines its exact latitude, longitude, and altitude.
  • Surveying Types:
    • Handheld GPS: Used for general mapping or reconnaissance (approximate accuracy).
    • Differential GPS (DGPS) / RTK: Highly accurate (up to a few centimeters). It uses a "Base Station" at a known point and a "Rover" at the new point to correct errors.
  • Importance: GPS allows surveyors to establish control points over very large distances (even across mountains or cities) where traditional "line-of-sight" instruments cannot work.

Summary Comparison

Feature

Total Station

GPS (GNSS)

Visibility

Requires a clear line of sight between instrument and staff.

Requires a clear view of the sky (satellites).

Range

Limited to a few kilometers.

Can cover global distances.

Accuracy

Extremely high for short/medium distances.

High precision (if using DGPS/RTK).

Application

Construction, building layout, small detail surveys.

Large-scale mapping, establishing national control points.

 

Types of compass

The primary difference between a Prismatic Compass and a Surveyor Compass lies in how they measure angles and how the observer reads them. A prismatic compass allows you to sight an object and read the measurement at the same time using a prism, whereas a surveyor compass requires you to sight the object first and then look down at the needle to take a reading. [1, 2, 3, 4, 5]

Key Differences at a Glance

Feature [1, 2, 4, 6, 7, 8, 9, 10]

Prismatic Compass

Surveyor Compass

Reading System

Whole Circle Bearing (WCB): 0° to 360°

Quadrantal Bearing (QB): 0° to 90° in four quadrants

Sighting & Reading

Simultaneous (via prism)

Done separately (no prism)

Needle Type

Broad needle: Attached to the graduated ring

Edge bar needle: Free-moving (ring is fixed to the box)

Tripod Usage

Optional; can be held by hand

Essential; cannot be used accurately without one

Graduations

Marked inverted (read through the prism)

Marked erect/directly

Least Count

Typically 30 minutes ($30'$)

Typically 15 minutes ($15'$)

Practical Applications

  • Prismatic Compass: Best for quick, preliminary surveys, military navigation, or rough traverses where speed and portability are prioritized.
  • Surveyor Compass: Historically used for more formal land surveying and mine surveying where higher precision was needed. It is sometimes called a circumferentor. [1, 6, 10, 11, 12, 13]

 

 

 

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