# Surveying in civil engineering Essay Example

Surveying

1. 1. Briefly clarify the terms below:

1. Angles: Is the quantity that gives angularity

This is the type of bearing which is given in terms of 90 degrees in the west or east direction of the north or South.

1. Whole Circle Bearing

This is where the horizontal angle is measured from the North limb of the meridian with

the angle variation being between 0 to 360 degrees

1. Magnetic Bearing

This is direction is given using the reference point as magnetic north.

This is the number of degrees either from north or any other direction that a line runs and is usually measured in clockwise direction. (10 marks)

2. In relation to leveling clarify the terms below:

1. Spirit Leveling: This is the process in determining the differences in elevation between points that are remote from each other by use of horizontal leveling equipment like a dumpy level.

1. Bench Mark: This is a point whose location and elevation is known and it is used as the reference point when surveying.

1. Datum Surface :

This is a point that acts as a reference level to all other points when surveying.

1. Dynamic Heights:

It is a height which is based on geopotential number for a certain point where the potential number denotes the geopotential surface at the point.

1. Reduced Level: this is the height of a point with respect to another point whose height is taken to be zero

(10 marks)

3. In the leveling process you have to understand the terms below. Explain briefly:

1. Closed leveling

This is where surveying starts at a point and ends up at the same point resulting in an enclosed area.

1. Back Sight this is the sight where the first reading is taken after setting a survey at a point.

1. Mean Sea Level

This is the point between the low tide and high tide which is used as the zero reference point when measuring heights above sea level.

1. Intermediate

This is a point which lies between the back sight and fore sight and is also referred to as inter sight

1. Change Point

These are points which are selected and are used in transferring elevations between benchmarks. At any change points there is one back sight reading and one fore sight reading.

(10 marks)

4. Height Information are needed for various reasons. Among the importance is the need for scientific studies. List down four (4) other uses of height information:

1. Helps in calculating the gradient of a slope

2. Is important in establishing the volume of earth work to be involved in construction work

3. Height in formation helps in establishing the cost involved in a construction project

4. In hydraulics height information helps in establishing the energy requirements in pumping.

(8 marks)

5. Stadia Tacheometry for distance measurement makes use of the formula :

Describe the term D , K , s , C above and explain why finally the formula becomes

D is the distance from the instrument to the staff

s is the object height

D = K s + C finally becomes D=100s because in most instruments which is a

constant always 100 and C always tends to 0.

(10 marks)

5. Answer all the questions below by filling in the spaces provided:

a) Name 3 planimetric control framework in surveying (i) Control network

ii) Survey grid (iii) Permanent ground markers

b) Errors are inevitable and are found in surveying. Name two errors that you know (i) blunders (ii) systematic errors

1. Magnetic variation is the difference between the direction of magnetic north and

True north

1. Lines of equal magnetic variation are called equal flux lines .

2. In the measurement of distances using EDM two types of modulation are used.

They are frequency modulation and amplitude modulation

1. Total station is actually an instrument combining an …………..theodolite, a

microprocessor , data collector and a distance meter instrument

(12 marks)

6. A levelling exercise to determine the height of point C is as shown below. Fill up the Height of Collimation Line column and obtain the Reduced Level of point C using the Height of Collimation Method

Height of collimation (HC) = Reduced level + Back sight

Also Reduced level (RL) = Height of collimation – Fore sight

Sample calculation

HC (1) = 21.550 +2.52 = 24.07

RL (2) = 24.135-2.620 =21.515

RL (3) = 24.135-2.510 = 21.635

 Back sight Ht of Collm Line 24.07 (1) 21.515(2) 21.635(3)

(10 marks)

7. A levelling exercise was done to determine the Reduced Levels of two Lampost. The survey started at BM A and closed at BM E . What is the misclose at BM E ? If the misclose is allowable what would be the Final Reduced Levels of the lampost 1 and 2

Rise (+) [or Fall(-)] = BS – FS

Reduced level = Previous Elev + Rise (or Fall)

HX= HBM + (BS – FS)

Sample calculations

Rise (1) = 2.520 – 1.675 = 0.845

Fall (2) = 1.74-2.62 = -0.88

Reduced level (3) = 21.550+0.845 = 22.395

Reduced level (4) = 22.395-0.88 = 21.515

 Back sight Correctn 0.845(1) 22.395(3) 21.515(4) Lampost 1 Lampost 2

(20 marks)

Closure error = 21.645-21.637 = -0.0085

8. A levelling project as in the diagram below started from TBM A and ended at TBM B. The route encountered an overhead structure X, Y, Z which had to be reported and its Reduced Levels determined. .The Reduced Level of TBM B is given as in the table.

1. Obtain the Reduced level of point Z

2. Obtain the Reduced Level of TBM and deduce whether there is any misclose

Rise (+) [or Fall (-)] = BS – FS

Reduced level = Previous Elev + Rise (or Fall)

HX= HBM + (BS – FS)

Sample calculations

Rise = 1.317 – (-3.018) = 1.317+3.018 = 4.335

RL (2) = 25.125 – 5.912 =19.213 Back sight Correctn 4.335(1) 19.213 (2)

(10 marks)

The reduced level of Z= 24.242

Value of misclose = Reduced levels at TBM B – Final Reduced level at TBM B

= 19.142-19.140 = 0.002m