UNIT 4
INTRODUCTION TO SURVEYING AND LEVELLING
Q 1: - Explain Approximate method of Linear Measurement?
Ans: -
Approximates Methods of Linear Measurements:
These methods are used in reconnaissance survey or to detect major mistakes committed while measuring with better methods. On smooth roads they can give results within 1 per cent error. These approximate measurements may be by:
(i) Pacing
(ii) Passometer
(iii) Pedometer
(iv) Odometer
(v) Speedometer.
Q 2: - Classify the tape, used in linear measurement?
Ans: -Depending upon the materials used, tapes are classified as:
(i) cloth or linen tape
(ii) metallic tape
(iii) steel tape
(iv) invar tape.
Q 3: - What are the instruments used in chain survey?
Ans: - The following instruments are required for measurements with chain and tape:
(i) Arrows
(ii) Pegs
(iii) Ranging rods and ranging poles
(iv) Offset rods
(v) Laths
(vi) Whites
(vii) Plumb bobs and
(viii) Line ranger.
Q 4: -What are the points consider during selection of station point?
Ans: -
Station is a point of importance at the beginning or at the end of a survey line. The following points should be considered in selecting station points:
(i) It should be visible from at least two or more stations.
(ii) As far as possible main lines should run on level ground.
(iii) All triangles should be well conditioned (No angle less than 30º).
(iv) Main network should have as few lines as possible.
(v) Each main triangle should have at least one check line.
(vi) Obstacles to ranging and chaining should be avoided.
(vii) Sides of the larger triangles should pass as close to boundary lines as possible.
(viii) Trespassing and frequent crossing of the roads should be avoided.
Q 5: - What are the Contour lines?
Ans: -A contour line is an imaginary line which connects points of equal elevation. Such lines are drawn on the plan of an area after establishing reduced levels of several points in the area. The contour lines in an area are drawn keeping difference in elevation of between two consecutive lines constant.
Characteristics of Contours:
The contours have the following characteristics:
1. Contour lines must close, not necessarily in the limits of the plan.
2. Widely spaced contour indicates flat surface.
3. Closely spaced contour indicates steep ground.
4. Equally spaced contour indicates uniform slope.
5. Irregular contours indicate uneven surface.
Q 6: - Give the applications of Remote Sensing?
Ans: - Application of Remote Sensing:
Various applications of remote sensing may be grouped into the following:
1. Resource exploration 2. Environmental study
3. Land use 4. Site investigation
5. Archaeological investigation and 6. Natural hazards study.
Q 7: - What is Bearing?
Ans: - Bearing of a line is the angle made by the line with respect to a reference direction, the reference direction being known as meridian. The direction shown by a freely suspended and properly balanced magnetic needle is called magnetic meridian and the horizontal angle made by a line with this meridian is known as magnetic bearing. The points of intersection of earth’s axis with surface of the earth are known as geographic north and south pole. The line passing through geographic north, south and the point on earth is called true meridian at that point and the angle made by a line passing through that point is called true bearing.
While traversing along lines A, B, C, D ..., the bearing of lime AB is called for bearing of AB and the bearing of BA is called back bearing. Fore bearing and back bearing differ by 180°.
Q 8: - Define WCB and RB system?
Ans: -
WHOLE CIRCLE BEARING:
In whole circle bearing (WCB) the bearing of a line at any point is measured with respect to a meridian. Its value varies from zero to 360°.
REDUCED BEARING:
In reduced bearing (RB) system, bearings are measured from north or south direction towards east or west. Hence, angles are from 0 to 90°.
Q 9: The following fore bearings were observed for lines, AB, BC, CD, DE, EF and FG respectively. Determine their back bearings:
(i) 148°. (ii) 65°
(iii) 285°. (iv) 215°
(v) N 36° W. (vi) S 40° E
Solution: The difference between fore bearing and the back bearing of a line must be 180°. Noting that
in WCB angle is from 0° to 360°, we find back bearing = fore bearing ± 180°
+ 180° is used if θ is less than 180° and
– 180° is used when θ is more than 180°.
Hence
(i) BB of AB = 145° + 180° = 325°
(ii) BB of BC = 65° + 180° = 245°
(iii) BB of CD = 285° – 180° = 105°
(iv) BB of DE = 215° – 180° = 35°
In case of RB, back bearing of a line can be obtained by interchanging N and S at the same time E and W. Thus
(v) BB of EF = S 36° E
(vi) BB of FG = N 40° W.
Q 10: - Explain various method of Levelling?
Ans: -The following methods are used to determine the difference in elevation of various points:
(i) Barometric levelling (ii) Hypsometric levelling (iii) Direct levelling and (iv) Indirect levelling.
1 Barometric Levelling:
This method depends on the principle that atmospheric pressure depends upon the elevation of place. Barometer is used to measure the atmospheric pressure and hence elevation is computed. However, it is not accurate method since the atmospheric pressure depends upon season and temperature also. It may be used in exploratory surveys.
2 Hypsometric Levelling
This is based on the principle that boiling point of water decreases with the elevation of the place. Hence the elevation difference between two points may be found by noting the difference in boiling point of water in the two places. This method is also useful only for exploratory survey.
3 Direct Levelling
It is common form of levelling in all engineering projects. In this method horizontal sight is taken on a graduated staff and the difference in the elevation of line of sight and ground at which staff is held are found. Knowing the height of line of sight from the instrument station the difference in the elevations of instrument station and the ground on which staff is held can be found. This method is thoroughly explained in next article.
4 Indirect Methods
In this method instruments are used to measure the vertical angles. Distance between the instrument and staff is measured by various methods. Then using trigonometric relations, the difference in elevation can be computed. This is considered beyond the scope of this book. One can find details of such methods in books on surveying and levelling.
TYPES OF DIRECT LEVELLING
The following are the different types of direct levelling:
(i) Simple levelling (ii) Differential levelling
(iii) Fly levelling (iv) Profile levelling
(v) Cross sectioning (vi) Reciprocal levelling.
UNIT 4
INTRODUCTION TO SURVEYING AND LEVELLING
Q 1: - Explain Approximate method of Linear Measurement?
Ans: -
Approximates Methods of Linear Measurements:
These methods are used in reconnaissance survey or to detect major mistakes committed while measuring with better methods. On smooth roads they can give results within 1 per cent error. These approximate measurements may be by:
(i) Pacing
(ii) Passometer
(iii) Pedometer
(iv) Odometer
(v) Speedometer.
Q 2: - Classify the tape, used in linear measurement?
Ans: -Depending upon the materials used, tapes are classified as:
(i) cloth or linen tape
(ii) metallic tape
(iii) steel tape
(iv) invar tape.
Q 3: - What are the instruments used in chain survey?
Ans: - The following instruments are required for measurements with chain and tape:
(i) Arrows
(ii) Pegs
(iii) Ranging rods and ranging poles
(iv) Offset rods
(v) Laths
(vi) Whites
(vii) Plumb bobs and
(viii) Line ranger.
Q 4: -What are the points consider during selection of station point?
Ans: -
Station is a point of importance at the beginning or at the end of a survey line. The following points should be considered in selecting station points:
(i) It should be visible from at least two or more stations.
(ii) As far as possible main lines should run on level ground.
(iii) All triangles should be well conditioned (No angle less than 30º).
(iv) Main network should have as few lines as possible.
(v) Each main triangle should have at least one check line.
(vi) Obstacles to ranging and chaining should be avoided.
(vii) Sides of the larger triangles should pass as close to boundary lines as possible.
(viii) Trespassing and frequent crossing of the roads should be avoided.
Q 5: - What are the Contour lines?
Ans: -A contour line is an imaginary line which connects points of equal elevation. Such lines are drawn on the plan of an area after establishing reduced levels of several points in the area. The contour lines in an area are drawn keeping difference in elevation of between two consecutive lines constant.
Characteristics of Contours:
The contours have the following characteristics:
1. Contour lines must close, not necessarily in the limits of the plan.
2. Widely spaced contour indicates flat surface.
3. Closely spaced contour indicates steep ground.
4. Equally spaced contour indicates uniform slope.
5. Irregular contours indicate uneven surface.
Q 6: - Give the applications of Remote Sensing?
Ans: - Application of Remote Sensing:
Various applications of remote sensing may be grouped into the following:
1. Resource exploration 2. Environmental study
3. Land use 4. Site investigation
5. Archaeological investigation and 6. Natural hazards study.
Q 7: - What is Bearing?
Ans: - Bearing of a line is the angle made by the line with respect to a reference direction, the reference direction being known as meridian. The direction shown by a freely suspended and properly balanced magnetic needle is called magnetic meridian and the horizontal angle made by a line with this meridian is known as magnetic bearing. The points of intersection of earth’s axis with surface of the earth are known as geographic north and south pole. The line passing through geographic north, south and the point on earth is called true meridian at that point and the angle made by a line passing through that point is called true bearing.
While traversing along lines A, B, C, D ..., the bearing of lime AB is called for bearing of AB and the bearing of BA is called back bearing. Fore bearing and back bearing differ by 180°.
Q 8: - Define WCB and RB system?
Ans: -
WHOLE CIRCLE BEARING:
In whole circle bearing (WCB) the bearing of a line at any point is measured with respect to a meridian. Its value varies from zero to 360°.
REDUCED BEARING:
In reduced bearing (RB) system, bearings are measured from north or south direction towards east or west. Hence, angles are from 0 to 90°.
Q 9: The following fore bearings were observed for lines, AB, BC, CD, DE, EF and FG respectively. Determine their back bearings:
(i) 148°. (ii) 65°
(iii) 285°. (iv) 215°
(v) N 36° W. (vi) S 40° E
Solution: The difference between fore bearing and the back bearing of a line must be 180°. Noting that
in WCB angle is from 0° to 360°, we find back bearing = fore bearing ± 180°
+ 180° is used if θ is less than 180° and
– 180° is used when θ is more than 180°.
Hence
(i) BB of AB = 145° + 180° = 325°
(ii) BB of BC = 65° + 180° = 245°
(iii) BB of CD = 285° – 180° = 105°
(iv) BB of DE = 215° – 180° = 35°
In case of RB, back bearing of a line can be obtained by interchanging N and S at the same time E and W. Thus
(v) BB of EF = S 36° E
(vi) BB of FG = N 40° W.
Q 10: - Explain various method of Levelling?
Ans: -The following methods are used to determine the difference in elevation of various points:
(i) Barometric levelling (ii) Hypsometric levelling (iii) Direct levelling and (iv) Indirect levelling.
1 Barometric Levelling:
This method depends on the principle that atmospheric pressure depends upon the elevation of place. Barometer is used to measure the atmospheric pressure and hence elevation is computed. However, it is not accurate method since the atmospheric pressure depends upon season and temperature also. It may be used in exploratory surveys.
2 Hypsometric Levelling
This is based on the principle that boiling point of water decreases with the elevation of the place. Hence the elevation difference between two points may be found by noting the difference in boiling point of water in the two places. This method is also useful only for exploratory survey.
3 Direct Levelling
It is common form of levelling in all engineering projects. In this method horizontal sight is taken on a graduated staff and the difference in the elevation of line of sight and ground at which staff is held are found. Knowing the height of line of sight from the instrument station the difference in the elevations of instrument station and the ground on which staff is held can be found. This method is thoroughly explained in next article.
4 Indirect Methods
In this method instruments are used to measure the vertical angles. Distance between the instrument and staff is measured by various methods. Then using trigonometric relations, the difference in elevation can be computed. This is considered beyond the scope of this book. One can find details of such methods in books on surveying and levelling.
TYPES OF DIRECT LEVELLING
The following are the different types of direct levelling:
(i) Simple levelling (ii) Differential levelling
(iii) Fly levelling (iv) Profile levelling
(v) Cross sectioning (vi) Reciprocal levelling.
