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
- 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).
- 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)
- Topographic
Survey: To
determine the natural features (rivers, hills) and man-made features
(roads, buildings) of a country.
- Cadastral
Survey: Conducted
on a large scale to determine property boundaries and land
ownership.
- City
Survey: Done for
urban planning, such as laying out streets, water supply lines, and
sewers.
- Hydrographic
Survey: Related
to large water bodies (oceans, lakes) for navigation and finding the Mean
Sea Level (MSL).
- Astronomical
Survey: Determining
the absolute position of a point on earth by observing stars or the sun.
C. On the Basis of Purpose
- Engineering Survey: To collect data for designing engineering projects
like roads, railways, and dams.
- Military Survey: Preparing maps for defense and strategic purposes.
- Mine Survey: For exploring mineral wealth and preparing maps for
mining operations.
- Geological Survey: To study the different layers and composition of
the earth’s crust.
- 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.
- Chain
Survey: The
simplest type of survey where only linear measurements are taken using a chain
or tape. No angular measurements are made.
- 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.
- 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.
- 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.
- 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.
- Photographic
Survey: A method
where maps are prepared from photographs taken from ground stations
or from the air.
- 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.
- 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):
- Topographic
Map: Shows
natural features (mountains, rivers, forests) and physical objects on the
Earth's surface.
- Cadastral
Map: Drawn to
a large scale to show property lines and land ownership boundaries.
- City Map: Used for urban development, showing roads, water
supply lines, and sewer systems.
- Hydrographic
Map: Shows
large water bodies, shorelines, and navigation routes.
B. Based on Purpose (Page 3):
- Engineering
Map: Prepared
to show details and quantities for projects like roads, reservoirs, and
dams.
- Military
Map: Prepared
specifically for defense and military strategies.
- Geological
Map: Shows the
layers of rocks and minerals beneath the Earth's surface.
- 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
- 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.
- Level Line: A line lying on a level surface.
It is therefore a curved line, not a straight line.
- Horizontal Surface: A plane surface tangent to
the level surface at a specific point. It is perpendicular to the plumb
line at that point.
- 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.
- 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.
- Axis of Telescope: An imaginary line passing
through the optical centers of the objective lens and the eyepiece.
- 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).
- 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.
- Intermediate Sight (I.S.): Any staff reading
taken between a Back Sight and a Fore Sight from the same instrument
setup.
- Bench Mark (B.M.): A relatively permanent
point of known elevation used as a reference for levelling.
- 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).
- Height of Instrument (H.I.): The elevation
(R.L.) of the Line of Collimation above the datum when the instrument is
correctly levelled.
- Formula:
$H.I. = R.L. \text{ of B.M.} + B.S.$
- 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.
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.
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
- 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.
- 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).
- 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.
|
|
|
- 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.
- 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.
|
- 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.
- 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.
- 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.
|
- 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.
- 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:
- Vertical Axis: The axis about which the instrument rotates in a
horizontal plane.
- Horizontal Axis (Trunnion Axis): The axis about which the telescope rotates in a
vertical plane.
- 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.
- Axis of Telescope Level (Bubble Tube Axis): The line tangential to the longitudinal curve of
the bubble tube at its midpoint.
- 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.
- 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.
- 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:
- 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.
- 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.
- 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.
- 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.
- Determining Catchment Areas: Contour maps help identify the watershed or
catchment area of a river, which is crucial for designing bridges and
drainage systems.
- 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.
- Identification of Landforms: They help in identifying features like hills,
valleys, ridges, and cliffs at a glance.
- 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.
- 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:
- Tangent Length ($T$):
$$T = R \tan \left( \frac{\Delta}{2} \right)$$ - Length of Curve ($l$):
$$l = \frac{\pi R \Delta}{180^\circ}$$ - Length of Long Chord ($L$):
$$L = 2R \sin \left( \frac{\Delta}{2} \right)$$ - Apex Distance ($E$):
$$E = R \left( \sec \frac{\Delta}{2} - 1 \right)$$ - Mid-Ordinate ($M$):
$$M = R \left( 1 - \cos \frac{\Delta}{2} \right)$$ - Degree of Curve ($D$): For a 30m chain length:
$$D = \frac{1719}{R} \quad (\text{approximately})$$
- 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.
- 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]
